JP7005121B2 - Copper paste for non-pressurized bonding, bonded bodies, and semiconductor devices - Google Patents

Description

The present invention relates to a copper paste for non-pressurized bonding, a bonded body using the copper paste, and a semiconductor device.

When manufacturing a semiconductor device, various bonding materials are used to bond the semiconductor element to a lead frame or the like (support member). Among semiconductor devices, high melting point lead solder has been used as a bonding material for bonding power semiconductors, LSIs, etc. that operate at a high temperature of 150 ° C. or higher. In recent years, the operating temperature has risen to near the melting point of high melting point lead solder due to the increase in capacity and space saving of semiconductor elements, and it has become difficult to secure connection reliability. On the other hand, with the tightening of RoHS regulations, lead-free bonding materials are required.

So far, joining of semiconductor devices using materials other than lead solder has been studied. For example, Patent Document 1 below proposes a technique for forming a sintered silver layer by sintering silver nanoparticles. It is known that such sintered silver has high connection reliability with respect to the power cycle (Non-Patent Document 1).

As yet another material, a technique of sintering copper particles to form a sintered copper layer has also been proposed. For example, Patent Document 2 below discloses copper nanoparticles and a bonding material containing copper nanoparticles, copper submicroparticles, or both, and also describes that the bonding material can bond members without pressure. Has been done.

Patent No. 4247800 Japanese Unexamined Patent Publication No. 2014-167145

R. Khazaka, L. et al. Mendizabal, D.M. Henry: J.M. Electron. Mater, 43 (7), 2014, 2459-2466

Since the method described in Patent Document 1 requires densification of the sintered silver layer in order to obtain high connection reliability, a thermocompression bonding process accompanied by pressurization is required. When the thermocompression bonding process accompanied by pressurization is performed, there are problems such as a decrease in production efficiency and a decrease in yield. Further, when silver nanoparticles are used, there is a problem that the material cost due to silver is significantly increased.

Although the method described in Patent Document 2 performs sintering without pressurization, it is not yet sufficient for practical use in the following points. That is, it is necessary to modify the surface of copper nanoparticles with a protective agent in order to suppress oxidation and improve dispersibility, but since copper nanoparticles have a large specific surface area, in a bonding material containing copper nanoparticles as a main component, The amount of surface protective agent compounded tends to increase. In addition, the amount of the dispersion medium to be blended tends to increase in order to ensure dispersibility. Therefore, the bonding material described in Patent Document 2 has a large proportion of a surface protective agent or a dispersion medium for supply stability such as storage or coating, and volume shrinkage during sintering tends to be large. In addition, it is difficult to secure the strength of the sintered body because the density after sintering tends to decrease.

In addition, unpressurized joining using a joining material is performed well when the materials of the members to be joined are the same or close to each other, but when the materials of the members to be joined are different, the joining force is high. It tends to drop significantly. According to the studies by the present inventors, for example, a case where a copper plate having copper on the adherend surface and a copper block having nickel on the adherend surface are bonded, a copper plate having copper on the adherend surface, and an adherend surface. It has been found that the bonding strength of the latter may be significantly reduced depending on the composition of the copper paste for bonding under non-pressurized sintering conditions in the case of bonding with a silicon chip having nickel. That is, when members having different thermal expansion rates, such as a copper block and a silicon chip, are joined together at a neutral pressure, a joining defect may occur.

An object of the present invention is to provide a copper paste for non-pressurization bonding, which can obtain sufficient bonding strength even when members having different thermal expansion rates are bonded to each other without pressure. It is also an object of the present invention to provide a bonded body and a semiconductor device using a copper paste for non-pressurized bonding, and a method for manufacturing these.

In order to solve the above problems, the present inventors conducted the following studies. First, in the bonding with the copper paste for bonding, a deposit of dried copper-based particles is left after the dispersion medium volatilizes during the drying step at the time of bonding or the temperature rise in the sintering step. The dried copper-based particle deposits are in a very fragile state because there is no binding force such as cohesive force of the dispersion medium between the particles. At this time, if the materials of the members to be joined are different, the shearing force due to the difference in thermal expansion rate between the members to be joined due to the temperature difference between the room temperature and the drying process temperature or the temperature difference between the room temperature and the sintering process temperature. It is considered that the deposit layer of copper-based particles is easily peeled off. If the member is positively pressurized in the sintering process, the peeling is crushed and the sintered body of the copper-based particle deposit and the member are joined. May remain exfoliated. From the viewpoint of suppressing such peeling, as a result of studies to control the state of the deposit at the time of temperature rise, by using a specific solvent as a dispersion medium at a specific ratio, members having different thermal expansion rates are eliminated. We have found that sufficient bonding strength can be obtained even when bonding under pressure, and have completed the present invention.

The present invention is a copper paste for non-pressurizing bonding containing metal particles and a dispersion medium, wherein the metal particles are sub-micro copper particles having a volume average particle size of 0.01 μm or more and 0.8 μm or less, and volume average. Copper paste for non-pressurizing bonding contains micro copper particles having a particle size of 2.0 μm or more and 50 μm or less, a dispersion medium containing a solvent having a boiling point of 300 ° C. or higher, and a solvent having a boiling point of 300 ° C. or higher. Provided is a copper paste for non-pressurizing bonding, which is 2% by mass or more based on the total mass of the above.

In the present specification, "no pressurization" means a state in which the weight of the members to be joined or the pressure of 0.01 MPa or less is applied in addition to the weight thereof.

The present invention is also a copper paste for non-pressurizing bonding containing metal particles and a dispersion medium, wherein the metal particles are sub-micro copper particles having a volume average particle size of 0.01 μm or more and 0.8 μm or less. The content of the solvent containing microcopper particles having an average particle size of 2.0 μm or more and 50 μm or less, the dispersion medium containing a solvent having a boiling point of 300 ° C. or higher, and the solvent having a boiling point of 300 ° C. or higher is copper for non-pressurizing bonding. Provided is a copper paste for non-pressurizing bonding, which is 8% by volume or more based on the total volume of the paste.

According to the copper paste for non-pressurization bonding of the present invention, sufficient bonding strength can be obtained even when members having different thermal expansion rates are bonded to each other with neutral pressure. The present inventors infer the reason why such an effect is obtained as follows. That is, when the dispersion medium contains a specific amount of a solvent having a boiling point of 300 ° C. or higher, a predetermined amount of the solvent having a boiling point of 300 ° C. or higher remains in the copper paste between the members during the heating process at the time of joining. It is thought that it can be done. By giving the copper paste flexibility and adhesion due to this residual solvent, the copper paste between the members can be deformed and followed even when the shearing force due to the difference in thermal expansion rate acts, and each member can be deformed and followed. It is probable that they could be joined without peeling.

In the present invention, the solvent having a boiling point of 300 ° C. or higher may have at least one group selected from the group consisting of a hydroxy group, an ether group, and an ester group. When the copper paste for non-pressure bonding contains such a solvent, a surface treatment agent having a similar Hansen solubility parameter, such as an organic acid, an organic amine, a hydroxyl group-containing polymer, or polyvinylpyrrolidone, can be used.

In the copper paste for non-pressure bonding of the present invention, micro copper particles and sub-micro copper particles are sintered when the copper paste for non-pressure bonding existing between two members is heated at a temperature of 250 ° C. or higher and lower than 350 ° C. The two members may be bonded to each other with a die shear strength of 10 MPa or more and a thermal conductivity of 100 W / (m · K) or more to form a metal bond. With such a copper paste for non-pressure bonding, sufficient bonding strength can be easily obtained when bonding members having different thermal expansion rates.

The copper paste for non-pressurized bonding of the present invention has a non-pressurized contact when the content of the solvent having a boiling point of 300 ° C. or higher remaining when the temperature is raised from 25 ° C to 300 ° C is raised to 300 ° C. It may be 1% by mass or more based on the mass of the mixed copper paste. In this case, it is easy to maintain the flexibility of the copper paste composition for non-pressure bonding, and when members having different thermal expansion rates are bonded to each other, the copper paste for non-pressure bonding easily deforms and follows the members. Therefore, it tends to be easy to improve the bonding strength.

The present invention also relates to the copper paste for non-pressurizing bonding, which joins the first member, the second member having a thermal expansion coefficient different from that of the first member, and the first member and the second member. Provided is a bonded body comprising a sintered body.

According to the bonded body of the present invention, since the members are bonded by the sintered body of the copper paste for non-pressure bonding, the members are bonded to each other with sufficient bonding strength even if the members have different thermal expansion rates. Can be a bonded body.

The present invention also comprises the first member, the copper paste for non-pressurizing bonding on the side in which the weight of the first member acts, and the second member having a coefficient of thermal expansion different from that of the first member. A step of preparing laminated bodies in order and sintering a copper paste for non-pressure bonding under the weight of the first member or the weight of the first member and a pressure of 0.01 MPa or less. Provided is a method for manufacturing a bonded body comprising the above.

According to the method for producing a bonded body of the present invention, by using the copper paste for non-pressurizing bonding of the present invention, the members are bonded to each other with sufficient bonding force even if the members have different thermal expansion rates. , It is possible to manufacture a bonded body having excellent connection reliability.

The present invention also relates to the copper paste for non-pressurizing bonding, which joins a first member, a second member having a thermal expansion rate different from that of the first member, and the first member and the second member. Provided is a semiconductor device comprising a sintered body, wherein at least one of a first member and a second member is a semiconductor element.

According to the method for manufacturing a semiconductor device of the present invention, by using the copper paste for non-pressurizing bonding of the present invention, even when the members constituting the semiconductor device have different thermal expansion rates, the members are sufficiently connected to each other. It is possible to manufacture a semiconductor device that is bonded with a flexible bonding force and has excellent connection reliability.

INDUSTRIAL APPLICABILITY The present invention can provide a copper paste for non-pressure bonding capable of obtaining sufficient bonding strength even when members having different thermal expansion rates are bonded to each other without pressure. The present invention can further provide a bonded body and a semiconductor device using a copper paste for non-pressurized bonding, and a method for manufacturing these.

It is a schematic cross-sectional view which shows an example of the bonded body manufactured by using the copper paste for non-pressure bonding of this embodiment. It is a schematic cross-sectional view which shows an example of the semiconductor device manufactured by using the copper paste for non-pressure bonding of this embodiment. It is a figure which shows the SEM image of the cross section of the junction sample of Example 1. FIG. It is a figure which shows the SEM image of the cross section of the junction sample of the comparative example 1. FIG. It is a figure which shows the relationship between the ratio of the solvent having a boiling point of 300 degreeC or more in the copper paste for non-pressure bonding and the die shear strength. It is a figure which shows the relationship between the boiling point of a dispersion medium, and the die shear strength.

Hereinafter, embodiments for carrying out the present invention (hereinafter referred to as “the present embodiment”) will be described in detail. The present invention is not limited to the following embodiments.

<Copper paste for non-pressure bonding>
The copper paste for non-pressure bonding of the present embodiment is a copper paste for non-pressure bonding containing metal particles and a dispersion medium, and the metal particles include sub-micro copper particles and micro copper particles.

(Metal particles)
Examples of the metal particles according to the present embodiment include submicro copper particles, micro copper particles, and other metal particles other than these copper particles.

(Sub-micro copper particles)
The submicro copper particles may be copper particles having sinterability in a temperature range of 250 ° C. or higher and 350 ° C. or lower. Examples of the sub-micro copper particles include copper particles having a particle size of 0.01 μm or more and 0.8 μm or less. For example, copper particles having a volume average particle size of 0.01 μm or more and 0.8 μm or less can be used. Can be used. When the volume average particle size of the sub-micro copper particles is 0.01 μm or more, the effects of suppressing the synthesis cost of the sub-micro copper particles, good dispersibility, and suppressing the amount of the surface treatment agent used can be easily obtained. When the volume average particle size of the sub-micro copper particles is 0.8 μm or less, the effect of excellent sinterability of the sub-micro copper particles can be easily obtained. From the viewpoint of further exerting the above effect, the upper limit of the volume average particle size of the submicro copper particles may be 0.6 μm or less, 0.5 μm or less, or 0.4 μm or less. May be good. Further, the lower limit of the volume average particle size of the submicro copper particles may be 0.02 μm or more, 0.05 μm or more, or 0.1 μm or more. The volume average particle size of the submicro copper particles may be, for example, 0.01 μm or more and 0.5 μm or less, 0.12 μm or more and 0.8 μm or less, and 0.15 μm or more and 0.8 μm or less. It may be 0.15 μm or more and 0.6 μm or less, 0.2 μm or more and 0.5 μm or less, or 0.3 μm or more and 0.45 μm or less.

In the specification of the present application, the volume average particle diameter means a 50% volume average particle diameter. When determining the volume average particle size of copper particles, light scattering is obtained by dispersing dried copper particles obtained by removing volatile components from raw material copper particles or non-pressurized bonding copper paste in a dispersion medium using a dispersant. It can be obtained by a method of measuring with a legal particle size distribution measuring device (for example, Shimadzu nanoparticle size distribution measuring device (SALD-7500 nano, manufactured by Shimadzu Corporation)). When a light scattering method particle size distribution measuring device is used, hexane, toluene, α-terpineol, 4-methyl-1,3-dioxolane-2-one and the like can be used as the dispersion medium.

The content of the sub-micro copper particles may be 20% by mass or more and 90% by mass or less, 30% by mass or more and 90% by mass or less, and 35% by mass or more, based on the total mass of the metal particles. It may be 85% by mass or less, and may be 40% by mass or more and 80% by mass or less. When the content of the sub-micro copper particles is within the above range, it becomes easy to secure the bonding strength of the bonded body manufactured by sintering the copper paste for non-pressure bonding, and the copper paste for non-pressure bonding is a semiconductor. When used for bonding elements, semiconductor devices tend to show good die shear strength and connection reliability.

The content of the sub-micro copper particles is preferably 20% by mass or more and 90% by mass or less based on the total of the mass of the sub-micro copper particles and the mass of the micro copper particles. When the content of the sub-micro copper particles is 20% by mass or more, the space between the micro copper particles can be sufficiently filled, and the bonding strength of the bonded body produced by sintering the copper paste for non-pressurized bonding is sufficient. When a copper paste for non-pressurized bonding is used for bonding a semiconductor element, the semiconductor device tends to show good die shear strength and connection reliability. When the content of the sub-micro copper particles is 90% by mass or less, the volume shrinkage when the copper paste for non-pressure bonding is sintered can be sufficiently suppressed, so that the copper paste for non-pressure bonding is sintered and manufactured. It becomes easy to secure the bonding strength of the bonded body, and when the copper paste for non-pressurized bonding is used for bonding a semiconductor element, the semiconductor device tends to show good die shear strength and connection reliability. From the viewpoint of further exerting the above effect, the content of the sub-micro copper particles may be 30% by mass or more and 85% by mass or less based on the total of the mass of the sub-micro copper particles and the mass of the micro copper particles. , 35% by mass or more and 85% by mass or less, or 40% by mass or more and 80% by mass or less.

The shape of the submicro copper particles is not particularly limited. Examples of the shape of the submicro copper particles include spherical, lumpy, needle-like, flake-like, substantially spherical, and aggregates thereof. From the viewpoint of dispersibility and filling property, the shape of the sub-micro copper particles may be spherical, substantially spherical, or flake-shaped, and from the viewpoint of flammability, dispersibility, mixing with flake-shaped microparticles, and the like, the shape of the submicro copper particles may be spherical. Alternatively, it may be substantially spherical. As used herein, the term "flake-like" includes a flat plate-like shape such as a plate-like shape or a scale-like shape.

The sub-micro copper particles may have an aspect ratio of 5 or less or 3 or less from the viewpoint of dispersibility, filling property, and mixing property with flake-shaped micro particles. As used herein, the "aspect ratio" refers to the long side / thickness of the particles. The measurement of the long side and the thickness of the particle can be obtained, for example, from the SEM image of the particle.

The submicro copper particles may be treated with a specific surface treatment agent. Specific surface treatment agents include, for example, organic acids having 2 to 18 carbon atoms. Examples of the organic acid having 2 to 18 carbon atoms include acetic acid, propanoic acid, butanoic acid, pentanoic acid, hexanoic acid, hepanoic acid, capric acid, methylheptanic acid, ethylhexanoic acid, propylpentanoic acid, pelargonic acid and methyloctane. Acid, ethyl heptanic acid, propylhexanoic acid, capric acid, methylnonanoic acid, ethyloctanoic acid, propylheptanic acid, butylhexanoic acid, undecanoic acid, methyldecanoic acid, ethylnonanoic acid, propyloctanoic acid, butylheptanic acid, lauric acid, methylundecane Acids, ethyldecanoic acid, propylnonanoic acid, butyloctanoic acid, pentylheptanic acid, tridecanoic acid, methyldodecanoic acid, ethylundecanoic acid, propyldecanoic acid, butylnonanoic acid, pentyloctanoic acid, myristic acid, methyltridecanoic acid, ethyldodecanoic acid , Proccundecanoic acid, butyldecanoic acid, pentylnonanoic acid, hexyloctanoic acid, pentadecanoic acid, methyltetradecanoic acid, ethyltridecanoic acid, propyldodecanoic acid, butylundecanoic acid, pentyldecanoic acid, hexylnonanoic acid, palmitic acid, methylpentadecanoic acid, ethyl Tetradecanoic acid, propyltridecanoic acid, butyldodecanoic acid, pentylundecanoic acid, hexyldecanoic acid, heptylnonanoic acid, heptadecanoic acid, octadecanoic acid, methylcyclohexanecarboxylic acid, ethylcyclohexanecarboxylic acid, propylcyclohexanecarboxylic acid, butylcyclohexanecarboxylic acid, pentylcyclohexane Saturated fatty acids such as carboxylic acid, hexylcyclohexanecarboxylic acid, heptylcyclohexanecarboxylic acid, octylcyclohexanecarboxylic acid, nonylcyclohexanecarboxylic acid; octenoic acid, nonenic acid, methylnonenic acid, decenoic acid, undecenoic acid, dodecenoic acid, tridecenoic acid, tetradecenoic acid , Myristoleic acid, pentadecenoic acid, hexadecenoic acid, palmitoleic acid, savienic acid, oleic acid, buxenoic acid, linoleic acid, linoleic acid, linolenic acid and other unsaturated fatty acids; terephthalic acid, pyromellitic acid, o-phenoxybenzoic acid, Examples thereof include aromatic carboxylic acids such as methyl benzoic acid, ethyl benzoic acid, propyl benzoic acid, butyl benzoic acid, pentyl benzoic acid, hexyl benzoic acid, heptyl benzoic acid, octyl benzoic acid and nonyl benzoic acid. As the organic acid, one kind may be used alone, or two or more kinds may be used in combination. By combining such an organic acid with the above-mentioned sub-micro copper particles, there is a tendency that both the dispersibility of the sub-micro copper particles and the desorption property of the organic acid at the time of sintering can be achieved at the same time.

The treatment amount of the surface treatment agent may be an amount that adheres to the surface of the submicro copper particles in a single-layer to a triple-layer. This amount is the number of molecular layers (n) attached to the surface of the sub-micro copper particles, the specific surface area (A _p ) (unit: m ² / g) of the sub-micro copper particles, and the molecular weight (M _s ) of the surface treatment agent. It can be calculated from the unit g / mol), the minimum coating area of the surface treatment agent ( _SS ) (unit m ² / piece), and the Avogadro's number ( _NA ) (6.02 × 10 ²³ pieces). Specifically, the treatment amount of the surface treatment agent is the treatment amount of the surface treatment agent (mass%) = {(n · A _p · M _s ) / ( _SS · NA + n · _{A p} · M _s )}. It is calculated according to the formula of × 100%.

The specific surface area of the sub-micro copper particles can be calculated by measuring the dried sub-micro copper particles by the BET specific surface area measuring method. The minimum coverage area of the surface treatment agent is 2.05 × 10 ^-19 m ^2/1 molecule when the surface treatment agent is a linear saturated fatty acid. In the case of other surface treatment agents, for example, calculation from a molecular model or "Chemistry and Education" (Ashihiro Ueda, Sumio Inafuku, Iwao Mori, 40 (2), 1992, p114-117). It can be measured by the method described. An example of a method for quantifying a surface treatment agent is shown. The surface treatment agent can be identified by a heat desorption gas / gas chromatograph mass spectrometer of a dry powder obtained by removing a dispersion medium from a copper paste for non-pressurization bonding, whereby the carbon number and molecular weight of the surface treatment agent can be determined. The carbon content ratio of the surface treatment agent can be analyzed by carbon content analysis. Examples of the carbon content analysis method include a high frequency induction heating furnace combustion / infrared absorption method. The amount of the surface treatment agent can be calculated from the carbon number, molecular weight and carbon content ratio of the identified surface treatment agent by the above formula.

The treatment amount of the surface treatment agent may be 0.07% by mass or more and 2.1% by mass or less, 0.10% by mass or more and 1.6% by mass or less, or 0.2% by mass. It may be 1.1% by mass or less.

Since the sub-micro copper particles have good sinterability, there are problems such as expensive synthesis cost, poor dispersibility, and reduction of volume shrinkage after sintering, which are found in bonding materials mainly using copper nanoparticles. Can be reduced.

As the sub-micro copper particles according to the present embodiment, commercially available ones can be used. Examples of commercially available sub-microparticles include CH-0200 (manufactured by Mitsui Mining & Smelting Co., Ltd., volume average particle size 0.36 μm) and HT-14 (manufactured by Mitsui Mining & Smelting Co., Ltd., volume average particle size 0.41 μm). ), CT-500 (manufactured by Mitsui Mining & Smelting Co., Ltd., volume average particle size 0.72 μm), Tn-Cu100 (manufactured by Taiyo Nissan Co., Ltd., volume average particle size 0.12 μm).

(Micro copper particles)
As the micro copper particles, copper particles having a particle size of 2.0 μm or more and 50 μm or less can be used. For example, copper particles having a volume average particle size of 2.0 μm or more and 50 μm or less can be used. When the volume average particle size of the micro copper particles is within the above range, volume shrinkage, generation of voids, etc. when sintering the copper paste for non-pressurized bonding can be sufficiently reduced, and the copper paste for non-pressurized bonding is sintered. It becomes easy to secure the bonding strength of the bonded body manufactured by the semiconductor device, and when the copper paste for non-pressurizing bonding is used for bonding a semiconductor element, the semiconductor device tends to show good die shear strength and connection reliability. From the viewpoint of further exerting the above effect, the volume average particle size of the micro copper particles may be 2 μm or more and 20 μm or less, 2 μm or more and 10 μm or less, or 3 μm or more and 20 μm or less. It may be 3 μm or more and 10 μm or less.

The content of the micro copper particles may be 10% by mass or more and 90% by mass or less, 15% by mass or more and 65% by mass or less, and 20% by mass or more and 60% by mass, based on the total mass of the metal particles. It may be mass% or less. When the content of the micro copper particles is within the above range, it becomes easy to secure the bonding strength of the bonded body manufactured by sintering the copper paste for non-pressure bonding, and the copper paste for non-pressure bonding is used as a semiconductor. When used for bonding elements, semiconductor devices tend to show good die shear strength and connection reliability.

The total content of the sub-micro copper particles and the content of the micro copper particles can be 80% by mass or more based on the total mass of the metal particles. When the total content of the sub-micro copper particles and the micro copper particles is within the above range, the volume shrinkage when the copper paste for non-pressurized bonding is sintered can be sufficiently reduced, and the copper paste for non-pressurized bonding can be sufficiently reduced. It becomes easy to secure the bonding strength of the bonded body manufactured by sintering the copper. When a copper paste for non-pressurized bonding is used for bonding a semiconductor element, the semiconductor device tends to show good die shear strength and connection reliability. From the viewpoint of further exerting the above effect, the total content of the sub-micro copper particles and the content of the micro copper particles may be 90% by mass or more, or 95% by mass, based on the total mass of the metal particles. It may be the above, or it may be 100% by mass.

The shape of the micro copper particles is not particularly limited. Examples of the shape of the micro copper particles include spherical, lumpy, needle-like, flake-like, substantially spherical, and aggregates thereof. The shape of the micro copper particles is preferably flake-shaped. By using flake-shaped micro copper particles, the micro copper particles in the copper paste for non-pressurized bonding are oriented substantially parallel to the bonding surface, so that the copper paste for non-pressurized bonding is sintered. Volume shrinkage can be suppressed, and it becomes easy to secure the bonding strength of the bonded body produced by sintering the copper paste for non-pressurized bonding. When a copper paste for non-pressurized bonding is used for bonding a semiconductor element, the semiconductor device tends to show good die shear strength and connection reliability. From the viewpoint of further exerting the above effect, the flake-shaped microcopper particles may have an aspect ratio of 4 or more, or 6 or more.

The presence or absence of treatment with the surface treatment agent is not particularly limited for the micro copper particles. From the viewpoint of dispersion stability and oxidation resistance, the microcopper particles may be treated with a surface treatment agent. The surface treatment agent may be one that is removed at the time of joining. Examples of such a surface treatment agent include aliphatic carboxylic acids such as dodecanoic acid, palmitic acid, heptadecanoic acid, stearic acid, arachidic acid, linoleic acid, linoleic acid, and oleic acid; terephthalic acid, pyromellitic acid, o-. Aromatic carboxylic acids such as phenoxybenzoic acid; fatty alcohols such as cetyl alcohol, stearyl alcohol, isobornylcyclohexanol, tetraethylene glycol; aromatic alcohols such as p-phenylphenol; octylamine, dodecylamine, stearylamine, etc. Alkylamine; aliphatic nitriles such as stearonitrile and decanitrile; silane coupling agents such as alkylalkoxysilane; polymer-treated materials such as polyethylene glycol, polyvinyl alcohol, polyvinylpyrrolidone and silicone oligomers. As the surface treatment agent, one type may be used alone, or two or more types may be used in combination.

The treatment amount of the surface treatment agent may be an amount of one molecular layer or more on the particle surface. The treatment amount of such a surface treatment agent varies depending on the specific surface area of the micro copper particles, the molecular weight of the surface treatment agent, and the minimum coating area of the surface treatment agent. The treatment amount of the surface treatment agent is usually 0.001% by mass or more. The specific surface area of the microcopper particles, the molecular weight of the surface treatment agent, and the minimum coating area of the surface treatment agent can be calculated by the above-mentioned method.

When the copper paste for non-pressurization bonding is prepared only from the above sub-micro copper particles, the volume shrinkage and the sintering shrinkage due to the drying of the dispersion medium are large, so that the copper paste for bonding is easily peeled off from the adherend surface at the time of sintering. , It is difficult to obtain sufficient die-share strength and connection reliability in bonding semiconductor elements and the like. When preparing a copper paste for non-pressurizing bonding only from the above micro copper particles, the sintering temperature tends to be high, and a sintering step of 400 ° C. or higher tends to be required. By using the sub-micro copper particles and the micro copper particles in combination, the volume shrinkage when the copper paste for non-pressure bonding is sintered is suppressed, and the bonded body can have sufficient bonding strength. When the copper paste for non-pressurized bonding is used for bonding a semiconductor element, the effect that the semiconductor device exhibits good die shear strength and connection reliability can be obtained.

As the micro copper particles according to the present embodiment, commercially available ones can be used. Examples of commercially available microparticles include MA-C025KFD (manufactured by Mitsui Metal Mining Co., Ltd., volume average particle size 7.5 μm), 3L3 (manufactured by Fukuda Metal Foil Powder Industry Co., Ltd., volume average particle size 8.0 μm). , 1110F (manufactured by Mitsui Metal Mining Co., Ltd., volume average particle size 3.8 μm), HWQ 3.0 μm (manufactured by Fukuda Metal Foil Powder Industry Co., Ltd., volume average particle size 3.0 μm).

(Other metal particles other than the above copper particles)
The metal particles may include submicro copper particles and other metal particles other than the micro copper particles, and may include, for example, copper nanoparticles, particles such as nickel, silver, gold, palladium, and platinum. .. The volume average particle diameter of the metal particles other than the copper particles may be 0.01 μm or more and 10 μm or less, 0.01 μm or more and 5 μm or less, or 0.05 μm or more and 3 μm or less. .. When other metal particles are contained, the content thereof may be less than 20% by mass and 10% by mass or less based on the total mass of the metal particles from the viewpoint of obtaining sufficient bondability. You may. Other metal particles may not be included. The shape of the other metal particles is not particularly limited.

When metal particles other than copper particles are contained, a sintered body in which a plurality of types of metals are solid-dissolved or dispersed can be obtained, so that mechanical properties such as yield stress and fatigue strength of the sintered body are improved and connection is performed. Reliability is likely to improve. Further, by adding a plurality of types of metal particles, the sintered body of the copper paste for non-pressure bonding can have sufficient bonding strength with respect to a specific adherend. When the copper paste for non-pressurized bonding is used for bonding a semiconductor element, the die share strength and connection reliability of the semiconductor device are likely to be improved.

(Dispersion medium)
The dispersion medium contains a solvent having a boiling point of 300 ° C. or higher. As the boiling point of a solvent having a boiling point of 300 ° C. or higher, from the viewpoint that it does not interfere with sintering and densification during sintering of copper paste for non-pressure bonding and is quickly evaporated and removed when the bonding temperature is reached. May be 300 ° C. or higher and 450 ° C. or lower, 305 ° C. or higher and 400 ° C. or lower, or 310 ° C. or higher and 380 ° C. or higher.

For a solvent having a boiling point of 300 ° C. or higher, it is preferable to select a structure having a high affinity with the surface of the metal particles in order to improve the dispersibility of the contained metal particles. When the metal particles are surface-treated with a surface treatment agent containing an alkyl group, it is preferable to select a solvent having an alkyl group. Examples of the solvent having a boiling point of 300 ° C. or higher include isobornylcyclohexanol (MTPH, manufactured by Nippon Terpen), butyl stearate, exepearl BS (manufactured by Kao), stearyl stearate, and exepearl SS (manufactured by Kao). ), 2-Ethylhexyl stearate, Exepearl EH-S (manufactured by Kao), Isotridecyl stearate, Exepearl TD-S (manufactured by Kao), Isooctadecanol, Fineoxocol 180 (manufactured by Nissan Chemical Co., Ltd.), Fineoxo Cole 180T (manufactured by Nissan Chemical Co., Ltd.), 2-hexyldecanol, Fineoxocol 1600 (manufactured by Nissan Chemical Co., Ltd.), tributylin, tetraethylene glycol, heptadecane, octadecane, nonadecan, eikosan, heneikosan, docosan, methylheptadecane, tridecylcyclohexane, Tetradecylcyclohexane, pentadecylcyclohexane, hexadecylcyclohexane, undecylbenzene, dodecylbenzene, tetradecylbenzene, tridecylbenzene, pentadecylbenzene, hexadecylbenzene, heptadecylbenzene, nonylnaphthalene, diphenylpropane, octyl octanate, myristin Methyl acid, ethyl myristate, methyl linoleate, methyl stearate, triethylene glycol bis (2-ethylhexanoic acid), tributyl citrate, pentylphenol, dibutyl sevacinate, oleyl alcohol, cetyl alcohol, methoxyphenetyl alcohol, benzylphenol , Hexadecanitrile, heptadecanitrile, benzyl benzoate, symmethyrine and the like.

As the solvent having a boiling point of 300 ° C. or higher, it is preferable to select a solvent having a Hansen solubility parameter close to that of the surface treatment agent from the viewpoint of improving dispersibility. Since organic acids, organic amines, hydroxyl group-containing polymers, polyvinylpyrrolidone and the like are easy to handle as surface treatment agents, the solvent having a boiling point of 300 ° C. or higher is at least one from the group consisting of hydroxy groups, ether groups and ester groups. It is preferable to have a seed group. The Hansen solubility parameter can be searched, for example, from the database at the end of the following publication, or searched / calculated by the database and the simulation integrated software HSPiP.
Published document: "HANSEN SOLUBILITY PARAMETERS: A USER'S HANDBOOK" (CRC Press, 1999)

The content of the solvent having a boiling point of 300 ° C. or higher can be 2% by mass or more based on the total mass of the copper paste for non-pressure bonding. The content of the solvent having a boiling point of 300 ° C. or higher may be 2.2% by mass or more or 2.4% by mass or more based on the total mass of the copper paste for non-pressure bonding. When the content of the solvent having a boiling point of 300 ° C. or higher is within the above range, a certain amount of solvent remains in the copper paste for non-pressure bonding when the copper paste for non-pressure bonding of the present embodiment is sintered. The flexibility and adhesiveness of the copper paste between the members can be easily maintained, and even when the members used for joining have different thermal expansion rates, they tend to be joined without peeling. The upper limit of the content of the solvent having a boiling point of 300 ° C. or higher is not particularly limited. From the viewpoint that the time until the dispersion medium is removed at the sintering temperature can be suppressed and the sintering time can be shortened, even if it is 9% by mass or less based on the total mass of the copper paste for non-pressure bonding. good.

Further, in the copper paste for non-pressurized bonding of the present embodiment, the content of the solvent having a boiling point of 300 ° C. or higher may be 8% by volume or more based on the total volume of the copper paste for non-pressurized bonding. It may be 17% by volume or more, or 23% by volume or more. When the content of the solvent having a boiling point of 300 ° C. or higher is within the above range, a certain amount of solvent remains in the copper paste for non-pressure bonding when the copper paste for non-pressure bonding of the present embodiment is sintered. The flexibility and adhesiveness of the copper paste between the members can be easily maintained, and even when the members used for joining have different thermal expansion rates, they tend to be joined without peeling. The upper limit of the content of the solvent having a boiling point of 300 ° C. or higher is not particularly limited. From the viewpoint that the time until the dispersion medium is removed at the sintering temperature can be suppressed and the sintering time can be shortened, even if it is 60% by volume or less based on the total volume of the copper paste for non-pressure bonding. good.

The dispersion medium may contain a solvent having a boiling point of less than 300 ° C. Examples of the solvent having a boiling point of less than 300 ° C. include α-terpineol, diethylene glycol monobutyl ether, diethylene glycol monobutyl ether acetate, 4-methyl-1,3-dioxolan-2-one, diethylene glycol monobutyl ether and the like. Solvents having a boiling point of less than 300 ° C. can be easily removed in the drying step or the heating step prior to the sintering step. As the dispersion medium, one type may be used alone or two or more types may be used in combination from a solvent having a boiling point of 300 ° C. or higher and a solvent having a boiling point of less than 300 ° C.

The content of the dispersion medium may be 5 to 50 parts by mass, with the total mass of the metal particles being 100 parts by mass. When the content of the dispersion medium is within the above range, the copper paste for non-pressure bonding can be adjusted to a more appropriate viscosity, and the sintering of copper particles is less likely to be hindered.

The content of the solvent having a boiling point of 300 ° C. or higher in the dispersion medium may be 20% by mass or more and 100% by mass or less based on the total mass of the dispersion medium. When the content of the solvent having a boiling point of 300 ° C. or higher in the dispersion medium is within the above range, it is easy to secure the content of the solvent having a boiling point of 300 ° C. or higher with respect to the total mass of the copper paste for non-pressurizing bonding.

The type of dispersion medium contained in the copper paste composition for non-pressurization bonding can be analyzed by, for example, a gas chromatograph-mass spectrometry of high-temperature desorbed gas and TOF-SIMS. As another analysis method, the supernatant obtained by separating the particle components by centrifugation may be identified by ordinary organic analysis, for example, FT-IR, NMR, liquid chromatograph, or a combination thereof. The ratio of the types of the dispersion medium can be quantified by a liquid chromatograph, NMR or the like.

(Additive)
For the copper paste for non-pressure bonding, if necessary, a wetting improver such as a nonionic surfactant or a fluorine-based surfactant; a defoaming agent such as silicone oil; an ion trapping agent such as an inorganic ion exchanger, etc. It may be added as appropriate.

In the copper paste for non-pressure bonding of the present embodiment, when the content of the solvent having a boiling point of 300 ° C. or higher that remains when the temperature of the paste is raised from 25 ° C. to 300 ° C. is raised to 300 ° C. It is preferably 1% by mass or more based on the mass of the copper paste for non-pressure bonding. The rate of temperature rise can be 9.2 (° C./min). In this case, it becomes easy to maintain the flexibility of the copper paste between the members, and even when the shearing force due to the difference in the thermal expansion rate acts when joining the members having different thermal expansion rates, the copper paste Can deform and follow the member, so it tends to be able to be firmly joined. The upper limit of the content of the solvent having a boiling point of 300 ° C. or higher that remains when the paste is heated from 25 ° C. to 300 ° C. is not particularly limited, and is until the dispersion medium is removed at the sintering temperature. From the viewpoint of reducing the time and shortening the sintering time, the content may be 9% by mass or less.

Since the copper paste for non-pressure bonding of the present embodiment can have sufficient flexibility at the time of bonding, the copper paste for non-pressure bonding existing between the two members is heated at a temperature of 250 ° C. or higher and lower than 350 ° C. At that time, the micro copper particles and the sub-micro copper particles are sintered to form a metal bond, and the two members can be bonded with a die shear strength of 10 MPa or more and a thermal conductivity of 100 W / (m · K) or more. ..

As one aspect of the copper paste for non-pressure bonding of the present embodiment, the metal particles are submicro copper particles having a volume average particle size of 0.01 μm or more and 0.8 μm or less, and a volume average particle size of 2.0 μm. The content of the solvent containing micro copper particles of 50 μm or more, the dispersion medium having a boiling point of 300 ° C. or higher, and the boiling point of 300 ° C. or higher is based on the total mass of the copper paste for non-pressurizing bonding. , 2% by volume or more, copper paste for non-pressurizing bonding can be mentioned.

The copper paste for non-pressure bonding includes submicro copper particles having a volume average particle diameter of 0.01 μm or more and 0.8 μm or less, micro copper particles having a volume average particle diameter of 2.0 μm or more and 50 μm or less, and 300. A dispersion medium containing a solvent having a boiling point of ℃ or higher and other above-mentioned components as required are blended, and the blending amount of the solvent having a boiling point of 300 ° C. or higher is the total mass of the copper paste for non-pressurizing bonding. As a standard, those having 2% by volume or more can be mentioned.

Even in a paste-like composition in which sub-micro copper particles having a sinterable property and micro-copper particles having a reinforcing effect are mixed with a dispersion medium having a boiling point of less than 300 ° C., a remarkable thermal expansion rate is obtained between the members to be joined. If there is no difference between the two, high-strength bonding can be performed (see, for example, the die-share strength with respect to the Ni-plated Cu plate of Comparative Example 1 in Table 1). However, when such a paste-like composition is used for bonding members having different thermal expansion rates, the bonding force tends to be significantly reduced (for example, the die share strength with respect to the Ni-plated Si chip of Comparative Example 1 in Table 1). See). If the boiling point of the dispersion medium is lower than the bonding temperature, the dispersion medium evaporates during the temperature rise process, and the paste-like composition becomes a brittle composition that dries before reaching the bonding temperature. It is possible that it will end up. When thermal stress is applied to each member having a different thermal expansion rate in this state, the dried and brittle composition cannot follow the member and peels or cracks, and it is considered that the bonding force is lowered as a result.

By containing a solvent having a boiling point of 300 ° C. or higher at which the dispersion medium can remain at the bonding temperature, a solvent having a boiling point of 300 ° C. or higher, preferably 1% by mass or more, is preferably contained in the copper paste for non-pressurizing bonding in the heating process. Since it can remain, it can give flexibility and adherence to the non-pressurized bonding copper paste. Therefore, even when thermal stress is applied to each member having a different thermal expansion rate at the time of joining, the copper paste for non-pressurizing joining deforms and follows, and the members can be joined without peeling.

(Preparation of copper paste for non-pressure bonding)
The copper paste for non-pressure bonding can be prepared by mixing the above-mentioned submicro copper particles, micro copper particles, other metal particles and any additive with a solvent having a boiling point of 300 ° C. or higher, which is a dispersion medium. can. After mixing each component, stirring treatment may be performed. For the copper paste for non-pressure bonding, the maximum particle size of the dispersion may be adjusted by a classification operation. At this time, the maximum particle size of the dispersion liquid can be 20 μm or less, and can also be 10 μm or less.

For the copper paste for non-pressure bonding, sub-micro copper particles, a surface treatment agent, and a dispersion medium, a solvent having a boiling point of 300 ° C. or higher, are mixed in advance and subjected to dispersion treatment to prepare a dispersion liquid of sub-micro copper particles. , Further, microcopper particles, other metal particles and any additive may be mixed and prepared. By performing such a procedure, the dispersibility of the sub-micro copper particles is improved, the mixing property with the micro copper particles is improved, and the performance of the copper paste for non-pressure bonding can be further improved. Aggregates may be removed by classifying the dispersion of submicro copper particles.

The stirring process can be performed using a stirrer. Examples of the stirrer include Ishikawa stirrer, Silberson stirrer, cavitation stirrer, rotating revolution type stirrer, ultra-thin high-speed rotary disperser, ultrasonic disperser, Raikai machine, twin-screw kneader, bead mill, ball mill, and three. This roll mill, homo mixer, planetary mixer, ultra-high pressure type disperser, thin layer shear disperser can be mentioned.

The classification operation can be performed using, for example, filtration, natural sedimentation, and centrifugation. Examples of the filter for filtration include a water comb, a metal mesh, a metal filter, and a nylon mesh.

Examples of the dispersion treatment include a thin layer shear disperser, a bead mill, an ultrasonic homogenizer, a high shear mixer, a narrow gap three-roll mill, a wet ultramicronizing device, a supersonic jet mill, and an ultrahigh pressure homogenizer.

When molding, the copper paste for non-pressure bonding may be adjusted to a viscosity suitable for each printing / coating method. As the viscosity of the copper paste for non-pressure bonding, for example, the Casson viscosity at 25 ° C. may be 0.05 Pa · s or more and 2.0 Pa · s or less, and 0.06 Pa · s or more and 1.0 Pa · s or less. There may be.

<Joints and semiconductor devices>
Hereinafter, preferred embodiments will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are designated by the same reference numerals, and duplicate description will be omitted. Further, the dimensional ratios in the drawings are not limited to the ratios shown in the drawings.

FIG. 1 is a schematic cross-sectional view showing an example of a bonded body manufactured by using the copper paste for non-pressurized bonding of the present embodiment. In the bonded body 100 of the present embodiment, the first member 2, the second member 3 having a thermal expansion coefficient different from that of the first member, and the first member and the second member are bonded to each other. A sintered body 1 of a copper paste for pressure bonding is provided.

Examples of the first member 2 and the second member 3 include semiconductor elements such as IGBTs, diodes, shotkey barrier diodes, MOS-FETs, thyristors, logics, sensors, analog integrated circuits, LEDs, semiconductor lasers, and transmitters. Examples thereof include a lead frame, a ceramic substrate with a metal plate attached (for example, DBC), a base material for mounting a semiconductor element such as an LED package, a copper ribbon, a metal block, a power supply member such as a terminal, a heat dissipation plate, and a water cooling plate.

The first member 2 and the second member 3 may contain metal on the surfaces 4a and 4b in contact with the sintered body of the copper paste for non-pressure bonding. Examples of the metal include copper, nickel, silver, gold, palladium, platinum, lead, tin, cobalt and the like. As the metal, one kind may be used alone, or two or more kinds may be used in combination. Further, the surface in contact with the sintered body may be an alloy containing the above metal. Examples of the metal used for the alloy include zinc, manganese, aluminum, beryllium, titanium, chromium, iron, molybdenum and the like in addition to the above metals. Examples of the member containing metal on the surface in contact with the sintered body include a member having various metal plating, a wire, a chip having metal plating, a heat spreader, a ceramic substrate to which a metal plate is attached, and a lead frame having various metal plating. Alternatively, a lead frame made of various metals, a copper plate, and a copper foil can be mentioned.

The die shear strength of the bonded body may be 10 MPa or more, 15 MPa or more, 20 MPa or more, or 30 MPa from the viewpoint of sufficiently joining the first member and the second member. It may be the above. The die share strength can be measured using a universal bond tester (4000 series, manufactured by DAGE) or the like.

The thermal conductivity of the sintered body of the copper paste for non-pressure bonding may be 100 W / (m · K) or more from the viewpoint of heat dissipation and connection reliability at high temperatures, and is 120 W / (m · K). ) Or more, or 150 W / (m · K) or more. The thermal conductivity can be calculated from the thermal diffusivity, the specific heat capacity, and the density of the sintered body of the copper paste for non-pressure bonding.

The difference in the thermal expansion coefficient between the first member and the second member may be 2 ppm to 30 ppm, 3 ppm to 23 ppm, or 5 ppm to 15 ppm.

Next, a method for manufacturing a bonded body using the copper paste for non-pressurized bonding of the present embodiment will be described.

In the method for manufacturing a bonded body using the copper paste for non-pressurized bonding of the present embodiment, the first member, the copper paste for non-pressurized bonding and the first copper paste on the side in the direction in which the weight of the first member acts. A laminated body in which the second member having a coefficient of thermal expansion different from that of the member is laminated in this order is prepared, and the copper paste for non-pressure bonding is applied to the weight of the first member or the weight of the first member and 0. A step of sintering is provided in a state of receiving a pressure of 01 MPa or less. The direction in which the weight of the first member works can also be said to be the direction in which gravity works.

The laminate is prepared, for example, by providing the copper paste for non-pressure bonding of the present embodiment in a necessary portion of the second member and then arranging the first member on the copper paste for non-pressure bonding. Can be done.

As a method of providing the copper paste for non-pressure bonding of the present embodiment to a necessary portion of the second member, any method may be used as long as the copper paste for non-pressure bonding can be deposited. Examples of such a method include screen printing, transfer printing, offset printing, jet printing method, dispenser, jet dispenser, needle dispenser, comma coater, slit coater, die coater, gravure coater, slit coat, letterpress printing, ingot printing, and gravure. Printing, stencil printing, soft lithograph, bar coat, applicator, particle deposition method, spray coater, spin coater, dip coater, electrodeposition coating and the like can be used. The thickness of the copper paste for non-pressurizing bonding may be 1 μm or more and 1000 μm or less, 10 μm or more and 500 μm or less, 50 μm or more and 200 μm or less, or 10 μm or more and 3000 μm or less. It may be 15 μm or more and 500 μm or less, 20 μm or more and 300 μm or less, 5 μm or more and 500 μm or less, 10 μm or more and 250 μm or less, or 15 μm or more and 150 μm or less.

The copper paste for non-pressurizing bonding provided on the second member may be appropriately dried from the viewpoint of suppressing flow and generation of voids during sintering. The gas atmosphere at the time of drying may be in the atmosphere, in an oxygen-free atmosphere such as nitrogen or noble gas, or in a reducing atmosphere such as hydrogen or formic acid. The drying method may be drying by leaving at room temperature, heating drying, or vacuum drying. For heat drying or vacuum drying, for example, a hot plate, a hot air dryer, a hot air heating furnace, a nitrogen dryer, an infrared dryer, an infrared heating furnace, a far infrared heating furnace, a microwave heating device, a laser heating device, and an electromagnetic wave are used. A heating device, a heater heating device, a steam heating furnace, a hot plate pressing device, or the like can be used. The drying temperature and time may be appropriately adjusted according to the type and amount of the dispersion medium used. As the drying temperature and time, for example, it may be dried at 50 ° C. or higher and 180 ° C. or lower for 1 minute or more and 120 minutes or less.

Examples of the method of arranging the first member on the copper paste for non-pressure bonding include a chip mounter, a flip chip bonder, and a positioning jig made of carbon or ceramics.

By heat-treating the laminate, the copper paste for non-pressure bonding is sintered. For heat treatment, for example, a hot plate, a hot air dryer, a hot air heating furnace, a nitrogen dryer, an infrared dryer, an infrared heating furnace, a far infrared heating furnace, a microwave heating device, a laser heating device, an electromagnetic heating device, etc. A heater heating device, a steam heating furnace, or the like can be used.

The gas atmosphere at the time of sintering may be an oxygen-free atmosphere from the viewpoint of suppressing oxidation of the sintered body, the first member and the second member. The gas atmosphere at the time of sintering may be a reducing atmosphere from the viewpoint of removing surface oxides of copper particles of the copper paste for non-pressurizing bonding. Examples of the oxygen-free atmosphere include introduction of oxygen-free gas such as nitrogen and noble gas, or under vacuum. Examples of the reducing atmosphere include pure hydrogen gas, a mixed gas of hydrogen and nitrogen typified by forming gas, nitrogen containing formic acid gas, a mixed gas of hydrogen and rare gas, and a rare gas containing formic acid gas. Can be mentioned.

The maximum temperature reached during the heat treatment may be 250 ° C. or higher and 450 ° C. or lower, and 250 ° C. or higher and 400 ° C. from the viewpoint of reducing heat damage to the first member and the second member and improving the yield. The temperature may be 250 ° C. or higher and 350 ° C. or lower. When the maximum ultimate temperature is 200 ° C. or higher, sintering tends to proceed sufficiently when the maximum ultimate temperature retention time is 60 minutes or less.

The maximum temperature retention time may be 1 minute or more and 60 minutes or less, or 1 minute or more and less than 40 minutes, from the viewpoint of sufficiently volatilizing the dispersion medium and improving the yield. It may be more than a minute and less than 30 minutes.

By using the copper paste for non-pressure bonding of the present embodiment, the bonded body can have sufficient bonding strength even when bonding without pressure when sintering the laminated body. That is, it is sufficient to receive a pressure of 0.01 MPa or less, preferably 0.005 MPa or less in addition to the own weight of the first member laminated on the copper paste for non-pressure bonding or the own weight of the first member. Bond strength can be obtained. When the pressure received during sintering is within the above range, a special pressurizing device is not required, so that the yield can be reduced, the die shear strength and the connection reliability can be further improved without impairing the yield. Examples of the method in which the copper paste for non-pressure bonding receives a pressure of 0.01 MPa or less include a method of placing a weight on the first member.

In the above-mentioned joint, at least one of the first member and the second member may be a semiconductor element. Examples of the semiconductor element include a power module including a diode, a rectifier, a thyristor, a MOS gate driver, a power switch, a power MOSFET, an IGBT, a shot key diode, a fast recovery diode and the like, a transmitter, an amplifier, an LED module and the like. In such a case, the bonded body becomes a semiconductor device. The obtained semiconductor device can have sufficient die share strength and connection reliability.

In the semiconductor device, the difference in the thermal expansion coefficient between the first member and the second member may be 2 ppm to 30 ppm, and the difference in the thermal expansion coefficient between the first member and the second member may be 3 ppm to 23 ppm. It may be 5 ppm to 15 ppm.

FIG. 2 is a schematic cross-sectional view showing an example of a semiconductor device manufactured by using the copper paste for non-pressurizing bonding of the present embodiment. The semiconductor device 110 shown in FIG. 2 includes a semiconductor element 8 connected to the lead frame 5a via a sintered body 1 of the copper paste for non-pressurizing bonding according to the present embodiment, and a mold resin 7 for molding the semiconductor elements 8. Consists of. The semiconductor element 8 is connected to the lead frame 5b via the wire 6.

Examples of the semiconductor device manufactured by using the non-pressurized bonding copper paste of the present embodiment include diodes, rectifiers, thyristors, MOS gate drivers, power switches, power MOSFETs, IGBTs, shotkey diodes, fast recovery diodes, and the like. Power modules, transmitters, amplifiers, high-brightness LED modules, semiconductor laser modules, logics, sensors, and the like can be mentioned.

The semiconductor device can be manufactured in the same manner as the method for manufacturing a bonded body described above. That is, in the method for manufacturing a semiconductor device, a semiconductor element is used for at least one of a first member and a second member, and the first member and the first member are placed on the side in the direction in which the weight of the first member works for the above-mentioned non-pressure bonding. A copper paste and a laminate in which the second member is laminated in this order are prepared, and the copper paste for non-pressurization bonding is subjected to the own weight of the first member or the own weight of the first member and a pressure of 0.01 MPa or less. It is provided with a process of sintering in the received state. For example, a step of providing a copper paste for non-pressurizing bonding on the lead frame 5a, arranging the semiconductor element 8 and heating the lead frame 5a can be mentioned. The obtained semiconductor device can have sufficient die shear strength and connection reliability even when bonding is performed without pressure. The semiconductor device of the present embodiment has sufficient bonding strength and is provided with a copper sintered body having high thermal conductivity and melting point, so that it has sufficient die shear strength, excellent connection reliability, and a power cycle. It can also be excellent in resistance.

[Example 1]
(Preparation of copper paste for non-pressure bonding)
CH-0200 (50% volume average particle size 0.36 μm, manufactured by Mitsui Mining & Smelting Co., Ltd.) as sub-micro copper particles is 15.84 g (52.8% by mass), and isobornylcyclohexanol as a solvent having a boiling point of 300 ° C. or higher. (Boiling point 308 ° C., hereinafter abbreviated as MTPH) was weighed in 3.6 g (12% by mass) and mixed in an automatic dairy pot for 5 minutes. Further, this mixture was dispersed with an ultrasonic homogenizer (US-600, manufactured by Nippon Seiki Co., Ltd.) at 19.6 kHz and 600 W for 10 minutes.

After transferring the dispersed mixture to a plastic bottle, 10.56 g (35.2% by mass) of MA-C025KFD (50% volume average particle size 5 μm, manufactured by Mitsui Mining & Smelting Co., Ltd.) was weighed and added as microcopper particles, and 2000 rpm. A copper paste for non-pressurizing bonding was obtained by subjecting it to a stirrer manufactured by Shinky Co., Ltd. (Awatori Rentaro ARE-310) under reduced pressure conditions for 2 minutes.

(Measurement of solid content)
A copper paste for non-pressure bonding was taken in a magnetic crucible, and the weight of the copper paste for non-pressure bonding was obtained from the difference between the tare weight of the magnetic crucible and the weight of the magnetic crucible containing the copper paste for non-pressure bonding. A magnetic crucible containing a copper paste for non-pressurizing bonding was placed in a muffle furnace heated to 600 ° C. and treated for 1 hour. From the difference between the weight of the crucible after the treatment and the weight of the tare of the magnetic crucible, the weight of the non-volatile component of the copper paste for non-pressure bonding was obtained. The solid content (mass%) of the copper paste for non-pressure bonding was calculated from the following formula.
Solid content (mass%) of copper paste for non-pressurized bonding = {(weight of non-volatile content of copper paste for non-pressurized bonding) / (weight of copper paste for non-pressurized bonding before heating)} x 100

(Measurement of residual solvent ratio)
The ratio of the dispersion medium remaining in the copper paste for non-pressure bonding (residual solvent ratio) when the temperature was raised from room temperature (25 ° C.) to 300 ° C. was measured. After measuring the mass of the copper plate and the chip, a copper paste for non-pressure bonding was printed on the copper plate, and the chip was mounted on the copper plate to obtain a laminate. At this stage, the mass of the laminate was measured. The laminate was heated in an oven under nitrogen from 25 ° C. to 300 ° C. in 30 minutes, then the laminate was taken out and rapidly cooled on a brass block. The mass of the laminated body after cooling was measured and used as the mass when the temperature reached 300 ° C. The residual solvent ratio when reaching 300 ° C. was calculated from the following formula.

(Preparation of bonded sample for die shear strength test)
(Joined sample using Si chip)
Using a 75 μm thick stainless steel mask and squeegee with a 3 × 3 mm ² square opening, a copper paste for non-pressurized bonding was stencil printed on a copper plate measuring 25 × 20 × 3 mm thick. Si chips (nickel on the adherend surface) in which titanium / nickel is sputtered in this order on the entire surface of the bonding surface with a thickness of 400 μm and a size of 3 × 3 mm on the printed matter of copper paste for non-pressure bonding, and the nickel surface is for non-pressure bonding. The copper paste composition was placed in contact with the composition, and the tip was lightly pressed with a tweezers to bring the nickel surface into close contact with the copper paste for non-pressure bonding. This was placed in a tube furnace, the inside was replaced with argon gas, hydrogen was introduced, and the temperature was raised to 30 minutes, 300 ° C., and 10 minutes for sintering. Then, hydrogen was stopped, the mixture was cooled to 50 ° C. or lower under an argon air flow, and the bonded sample was taken out into the air.

(Joined sample using Cu plate)
A bonded sample was prepared in the same manner as above except that a Cu plate (nickel on the adherend surface) having a thickness of 250 μm and a size of 2 × 2 mm plated with nickel on the entire surface was used.

(Die share strength test)
The bonding strength of the die shear strength sample was evaluated by the die shear strength. Using a universal bond tester (4000 series, manufactured by Daiji Japan Co., Ltd.) equipped with a DS-100 load cell, the bonded sample is pressed horizontally with a Si chip or Cu plate at a measurement speed of 5 mm / min and a measurement height of 50 μm. , The die share strength was measured. A die share strength of 20 MPa or more was considered good for joining.

[Comparative Example 1]
A copper paste for non-pressurizing bonding was obtained in the same manner as in Example 1 except that 9.0 parts by mass of α-terpineol (boiling point 220 ° C.) was used without using isobornylcyclohexanol. The die shear strength was measured in the same manner as in Example 1 except that the copper paste for non-pressure bonding was used. The results are shown in Table 1.

In the sample of Example 1 in which a part of the dispersion medium was MTPH having a boiling point of 308 ° C., a good die shear strength of 31 MPa was shown with respect to the Si chip. On the other hand, in the sample of Comparative Example 1 using the copper paste for non-pressurizing bonding containing no solvent having a boiling point of 300 ° C. or higher, the die shear strength with respect to the Si chip was 9 MPa, resulting in poor bonding.

When the residual solvent ratio was measured, in Example 1, 1.2% by mass of the solvent remained even when the temperature reached 300 ° C. This is 10% by volume by volume, and the residual solvent is not flexible and has sufficient adhesion to sufficiently absorb the displacement applied to the copper paste for non-pressurized bonding due to the difference in thermal expansion rate between the copper plate and the Si chip. It is considered that it was given to the copper paste for pressure bonding. On the other hand, in Comparative Example 1, the residual solvent at the time of reaching 300 ° C. was 0.3% by mass, and the volume was 3% by volume. Therefore, in the copper paste for non-pressurized bonding of Comparative Example 1, there was not enough solvent between the particles, and the copper paste for non-pressurized bonding peeled off from the chip due to the displacement due to the difference in thermal expansion rate, and the die shear strength decreased. Conceivable.

A cross-sectional SEM image of the Si chip / die bond layer interface of the die bond portion where the copper substrate and the Si chip were joined was observed. As the test sample used for observing the SEM image, the one prepared in (Preparation of the bonded sample for the die shear strength test) was used. The cross-sectional SEM image of Example 1 is shown in FIG. 3, and the cross-sectional SEM image of Comparative Example 1 is shown in FIG. In the sample of Example 1, the silicon chip 9 having the Ti / Ni plating layer 10 and the sintered body 11 of the copper paste for non-pressure bonding were well bonded. On the other hand, in the sample of Comparative Example 1, a peeling portion (crack) 12 was generated between the silicon chip 9 having the Ti / Ni plating layer 10 and the sintered body 11 of the copper paste for non-pressurizing bonding, so that the bonding was poor. It was. This is a displacement due to the difference in the coefficient of thermal expansion between the copper substrate and the Si chip, and it is considered that the copper substrate and the Si chip were separated at the Si chip / die bond layer interface before joining.

[Examples 2 to 5, Comparative Example 2]
(Preparation of copper paste composition)
Isobornylcyclohexanol (boiling point 308 ° C., hereinafter abbreviated as MTPH) was mixed as a solvent having a boiling point of 300 ° C. or higher, and α-terpineol (boiling point 220 ° C.) was mixed as another solvent according to the ratio shown in Table 2. There, 10.56 g (35.2% by mass) of MA-C025KFD (50% volume average particle size, manufactured by Mitsui Kinzoku Co., Ltd.) as micro copper particles, and CH-0200 (50% volume average particles) as sub-micro copper particles. 15.84 g (52.8% by mass) of a diameter of 0.36 μm (manufactured by Mitsui Kinzoku Co., Ltd.) was weighed and mixed in an automatic dairy pot for 5 minutes. After transferring the mixture to a plastic bottle, a copper paste composition for non-pressurizing bonding was obtained by subjecting it to a stirrer manufactured by Shinky Co., Ltd. (Awatori Rentaro ARE-310) under the conditions of reduced pressure at 2000 rpm for 2 minutes.

(Die share test sample preparation)
In the same manner as in Example 1, a bonded sample (Si) was prepared using a Si chip in which titanium / nickel was sputtered in this order on the entire surface of the bonded surface having a size of 3 × 3 mm. Further, using a copper plate having a size of 2 × 2 mm and having nickel plated on the entire surface, a bonded sample (copper plate) bonded in the same manner as in Example 1 was prepared. For each bonded sample, the die shear strength was measured in the same manner as in Example 1. The results are shown in Table 2 and FIG.

[Example 6]
A copper paste for non-pressure bonding was prepared in the same manner as in Example 1 except that tributyrin (boiling point 310 ° C.) was used as a solvent having a boiling point of 300 ° C. or higher. A bonding sample (Si) using a Si chip in which titanium / nickel is sputtered in this order on the entire surface of a bonding surface having a size of 3 × 3 mm in the same manner as in Example 1 except that this copper paste for non-pressurized bonding is used. Was prepared and the die shear strength was measured. As a result, the die shear strength showed a good value of 20 MPa.

[Example 7]
A copper paste for non-pressurizing bonding was prepared in the same manner as in Example 1 except that Fineoxocol 180 (isooctadecanol, boiling point 302 ° C., manufactured by Nissan Chemical Industries, Ltd.) was used as a solvent having a boiling point of 300 ° C. or higher. Prepared. A bonding sample (Si) using a Si chip in which titanium / nickel is sputtered in this order on the entire surface of a bonding surface having a size of 3 × 3 mm in the same manner as in Example 1 except that this copper paste for non-pressurized bonding is used. Was prepared and the die shear strength was measured. As a result, the die shear strength showed a good value of 23 MPa.

[Example 8]
A copper paste for non-pressure bonding was prepared in the same manner as in Example 1 except that butyl stearate (boiling point 343 ° C.) was used as a solvent having a boiling point of 300 ° C. or higher. A bonding sample (Si) using a Si chip in which titanium / nickel is sputtered in this order on the entire surface of a bonding surface having a size of 3 × 3 mm in the same manner as in Example 1 except that this copper paste for non-pressurized bonding is used. Was prepared and the die shear strength was measured. As a result, the die shear strength showed a good value of 25 MPa.

[Example 9]
A copper paste for non-pressurizing bonding was prepared in the same manner as in Example 1 except that octyl octanate (boiling point 311 ° C.) was used as the solvent composition having a boiling point of 300 ° C. or higher. A bonding sample (Si) using a Si chip in which titanium / nickel is sputtered in this order on the entire surface of a bonding surface having a size of 3 × 3 mm in the same manner as in Example 1 except that this copper paste for non-pressurized bonding is used. Was prepared and the die shear strength was measured. As a result, the die shear strength showed a good value of 26 MPa.

[Comparative Example 3]
A copper paste for non-pressurizing bonding was prepared in the same manner as in Example 1 except that diethylene glycol monobutyl ether (boiling point 230 ° C., hereinafter abbreviated as DEGBE) was used as the dispersion medium. A bonding sample (Si) using a Si chip in which titanium / nickel is sputtered in this order on the entire surface of a bonding surface having a size of 3 × 3 mm in the same manner as in Example 1 except that this copper paste for non-pressurized bonding is used. Was prepared and the die shear strength was measured. As a result, the die share strength was 6 MPa, and it was judged that the connection was poor.

[Comparative Example 4]
A copper paste for non-pressurizing bonding was prepared in the same manner as in Example 1 except that diethylene glycol monobutyl ether acetate (boiling point 247 ° C., hereinafter abbreviated as BDGAC) was used as the dispersion medium. A bonding sample (Si) using a Si chip in which titanium / nickel is sputtered in this order on the entire surface of a bonding surface having a size of 3 × 3 mm in the same manner as in Example 1 except that this copper paste for non-pressurized bonding is used. Was prepared and the die shear strength was measured. As a result, the die share strength was 5 MPa, and it was judged that the connection was poor.

Table 3 shows the results of Examples 6 to 9 and Comparative Examples 3 and 4. FIG. 6 plots the die shear strength of the bonding sample (Si) using the non-pressurized bonding copper pastes of Examples 1, 6, 7, 8 and 9 and Comparative Examples 1, 3 and 4 with respect to the boiling point of the solvent. did. In the examples using a solvent having a boiling point of 300 ° C. or higher, good die shear strength of 20 MPa or higher was obtained in each case. On the other hand, in the comparative examples using the solvent having a boiling point lower than 300 ° C., the die shear strength was as low as 9 MPa or less, and the bonding was poor.

1 ... Sintered body of copper paste for non-pressure bonding, 2 ... First member, 3 ... Second member, 5a, 5b ... Lead frame, 6 ... Wire, 7 ... Mold resin, 8 ... Semiconductor element, 9 ... Silicon chip, 10 ... Ti / Ni plating layer, 11 ... Sintered body of copper paste for non-pressure bonding, 12 ... Peeling part.

Claims (11)

A copper paste for non-pressurizing bonding containing metal particles and a dispersion medium.
The metal particles include submicrocopper particles having a volume average particle size of 0.12 μm or more and 0.8 μm or less , and flake-shaped microcopper particles having a volume average particle size of 2.0 μm or more and 50 μm or less .
The dispersion medium contains a solvent having a boiling point of 300 ° C. or higher, and the content of the solvent having a boiling point of 300 ° C. or higher is 2% by mass or more based on the total mass of the copper paste for non-pressurizing bonding. , Copper paste for non-pressurized bonding. A copper paste for non-pressurizing bonding containing metal particles and a dispersion medium.
The metal particles include submicrocopper particles having a volume average particle size of 0.12 μm or more and 0.8 μm or less , and flake-shaped microcopper particles having a volume average particle size of 2.0 μm or more and 50 μm or less .
The dispersion medium contains a solvent having a boiling point of 300 ° C. or higher, and the content of the solvent having a boiling point of 300 ° C. or higher is 8% by volume or more based on the total volume of the copper paste for non-pressurizing bonding. , Copper paste for non-pressurized bonding. The absence according to claim 1 or 2, wherein the content of the sub-micro copper particles is 30% by mass or more and 85% by mass or less based on the total of the mass of the sub-micro copper particles and the mass of the micro copper particles. Copper paste for pressure bonding. The copper paste for non-pressurizing bonding according to any one of claims 1 to 3, wherein the volume average particle diameter of the sub-micro copper particles is 0.2 μm or more and 0.5 μm or less. The non-pressurized contact according to any one of claims 1 to 4, wherein the solvent having a boiling point of 300 ° C. or higher has at least one group selected from the group consisting of a hydroxy group, an ether group, and an ester group. Combined copper paste. The copper paste for non-pressurizing bonding according to claim 5, wherein the solvent having a boiling point of 300 ° C. or higher is isobornylcyclohexanol. When the copper paste for non-pressurizing bonding existing between the two members is heated at a temperature of 250 ° C. or higher and lower than 350 ° C., the micro copper particles and the sub micro copper particles are sintered to form a metal bond, and the metal bond is formed. The copper paste for non-pressurizing bonding according to any one of claims 1 to 6, wherein the two members are bonded with a die shear strength of 10 MPa or more and a thermal conductivity of 100 W / (m · K) or more. The content of the solvent having a boiling point of 300 ° C. or higher remaining when the temperature is raised from 25 ° C. to 300 ° C. is 1 based on the mass of the copper paste for non-pressurizing bonding when the temperature is raised to 300 ° C. The copper paste for non-pressurizing bonding according to any one of claims 1 to 7, which is by mass or more. One of claims 1 to 8, wherein the first member, the second member having a thermal expansion rate different from that of the first member, and the first member and the second member are joined to each other. A bonded body comprising the sintered body of the copper paste for non-pressurized bonding according to the above. The copper paste for non-pressure bonding according to any one of claims 1 to 8 and the thermal expansion coefficient different from those of the first member on the side in the direction in which the weight of the first member works. Prepare a laminated body in which the second member having A method for manufacturing a bonded body, which comprises a step of sintering under pressure. One of claims 1 to 8, wherein the first member, the second member having a thermal expansion coefficient different from that of the first member, and the first member and the second member are joined to each other. The sintered body of the copper paste for non-pressurizing bonding described in the above.
A semiconductor device in which at least one of the first member and the second member is a semiconductor element.

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