JP2005254254A - Lead-free solder, its manufacturing method and electronic component - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide lead-free solder capable of maintaining joining strength under high temperature, and also to provide its manufacturing method and an electronic component that is hierarchically connected at high temperature using this lead-free solder. <P>SOLUTION: Using the lead-free solder containing, in a first alloy phase composed of an Sn base alloy, a second alloy phase composed of Sb alloy having a melting point higher than that of the first alloy phase, joining strength can be maintained at a high temperature, enabling high temperature hierarchical connection. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a lead-free solder, a lead-free solder manufacturing method, and an electronic component that are effective for solder joining in a temperature hierarchy performed when a module of an electronic device is mounted.

  In recent years, with increasing interest in environmental issues from the viewpoint of protecting the global environment, an increase in the amount of industrial waste disposed of has become a serious problem. Solder is used in, for example, power control computer boards, home appliances, personal computers, and the like included in industrial waste, and harmful heavy metals such as lead may flow out from the solder. For example, when lead flows out, it may act on acid rain to produce an aqueous solution containing lead, and the aqueous solution may invade groundwater.

  In Japan, the Home Appliance Recycling Law was enacted in 1998, and in 2001 it was obliged to collect used products for home appliances. In Europe, electrical and electronic product waste EU directives have banned the use of certain substances including lead since 2004. In this way, legal regulations regarding the use of lead have been strengthened, and development of lead-free solder has been urgently performed (see, for example, Non-Patent Document 1). Further, high melting point solder having a melting point of around 300 ° C. is also subject to regulation, and development of high melting point lead-free solder is urgently required (for example, see Non-Patent Document 2).

  Conventional Sn-Pb solders have high melting points such as Sn-95 wt% Pb (melting point: 310-314 ° C.), Sn-90 wt% Pb (melting point: 275-302 ° C.), and the like. However, no lead-free solder has been developed. In addition, in conventional Sn-Pb solder, for example, Sn-95 wt% Pb, Sn-90 wt% Pb, etc., which are high melting point solders, are soldered at a temperature of 330 to 350 ° C. Temperature hierarchy connection has been performed using Sn-37 wt% Pb (eutectic temperature 183 ° C.), which is a low melting point solder that can be joined at a temperature that does not melt the part.

Such a temperature hierarchy connection is applied to a semiconductor device of a type in which a chip is die-bonded or a semiconductor device such as a flip-chip connection. Further, in the conventional module mounting, after the components are primarily reflowed with a high melting point solder, the module terminals are further subjected to secondary reflow with a low melting point solder to a printed circuit board.
(Proposal for a Directive of the European Parliament and of the Council on Waste Electrical and Electronic Equipment, Commission of the European Communities, Brussels, 13.6.2000) (Sendless solder mounting technology trends, Sharp technique, No. 79, April 2001, p33-36)

  In the above-described module mounting, for example, when using conventional lead-free solder for temperature hierarchy connection, primary reflow is performed at a temperature that does not exceed the heat resistance of the component (for example, a temperature of 290 ° C. or less), and the chip component is increased. It is connected to the module substrate with a melting point solder and sealed with a cap or resin. Thereafter, secondary reflow is required with lead-free solder of Sn-0.7 wt% Cu (melting point: 227 ° C.). When secondary reflow is performed with this lead-free solder, the solder joint temperature is 240 to 250 ° C. To reach. Therefore, even if Sn-5 wt% Sb (melting point: 232 ° C.), which is the highest melting point solder among the existing lead-free solders, is used for primary reflow, the solder joints of chip components in the module are subjected to secondary reflow. There was a problem that remelting was inevitable.

  Furthermore, when the solder joint of the chip component in the module is remelted by secondary reflow, there is a problem that the position of the chip component is shifted.

  Therefore, the present invention has been made to solve the above problems, and provides a lead-free solder capable of maintaining the bonding strength at high temperatures and a method for producing the lead-free solder. An object is to provide a hierarchically connected electronic component.

  In order to achieve the above object, the lead-free solder of the present invention contains a second alloy phase made of an Sb alloy having a melting point higher than the melting point of the first alloy phase in the first alloy phase made of an Sn-based alloy. It is characterized by becoming.

  Here, the first alloy phase includes, for example, at least one of Ag, Al, Au, Bi, Co, Cr, Cu, Fe, Ge, In, Mg, Mn, Pd, Si, Sr, Te, and Zn. An Sn-based alloy containing seeds, the balance being Sn and inevitable impurities, and having a melting point of 117 to 350 ° C. is used.

  For example, as an Sn-based alloy, In: 52% by weight, balance: Sn alloy consisting of Sn and inevitable impurities (melting point: 117 ° C.), Bi: 57% by weight, balance: Sn alloy consisting of Sn and inevitable impurities (melting point: 139 ° C.) Zn: 9 wt%, balance: Sn alloy consisting of Sn and unavoidable impurities (melting point 198 ° C.), Cu: 4.5 wt%, balance: Sn alloy consisting of Sn and unavoidable impurities (solidus 227 ° C., liquid phase Line 350 ° C.).

  The second alloy phase contains at least one of Ag, Al, Au, Bi, Co, Cr, Cu, Fe, Ge, In, Mg, Mn, Pd, Si, Sr, Te, and Zn. In addition, an Sb alloy whose balance is made of Sb and inevitable impurities and whose melting point is in the range of 155 to 625 ° C. is used.

  For example, as an Sb alloy, In: 99.3% by weight, balance: Sb alloy consisting of Sb and inevitable impurities (melting point 155 ° C.), Te: 89.5 wt%, balance: Sb alloy consisting of Sb and inevitable impurities (melting point) 424 ° C.), Bi: 55 wt%, balance: Sb and Sb alloy consisting of Sb and inevitable impurities (solid phase line 350 ° C., liquidus 500 ° C.), Cu: 23.5 wt%, balance: Sb and inevitable impurities Sb alloy (melting point 526 ° C.), Ge: 11 wt%, balance: Sb alloy consisting of Sb and inevitable impurities (melting point 590 ° C.), Co: 1.5 wt%, balance: Sb alloy consisting of Sb and inevitable impurities (melting point) 618 ° C.).

  According to this lead-free solder, the lead-free solder is constituted by including the second alloy phase made of the Sb alloy having a melting point higher than the melting point of the first alloy phase in the first alloy phase made of the Sn-based alloy, Soldering can be performed while maintaining the second alloy powder in a solid phase at a temperature at which the first alloy phase is in a molten state. Thereby, the solder joint portion can contain the second alloy powder uniformly dispersed in the first alloy phase while maintaining the characteristics such as the wettability of the first alloy phase.

  Further, by containing the second alloy powder having a melting point higher than the melting point of the first alloy phase, for example, when performing the secondary reflow, even if the first alloy phase is in a molten state, the second alloy powder is The solid phase can be maintained and the melted first alloy phase can be prevented from flowing out due to the surface tension of the second alloy powder. Moreover, when performing secondary reflow, the center part of the second alloy powder may maintain a solid phase and the surface may be in a molten state.

  This lead-free solder is not limited in its application, but it can be used as a high-melting-point solder during primary reflow, for example, bonding of electronic components and boards that are connected in a high-temperature hierarchy, bonding of electronic components, etc. Is preferred.

  The lead-free solder manufacturing method of the present invention includes at least one of Ag, Al, Au, Bi, Co, Cr, Cu, Fe, Ge, In, Mg, Mn, Pd, Si, Sr, Te, and Zn. A first alloy powder containing Sn and inevitable impurities, the melting point being in the range of 117 to 350 ° C., and Ag, Al, Au, Bi, Co, Cr, Cu, Fe, Ge, In, Mg A powder of the second alloy containing at least one of Mn, Pd, Si, Sr, Te, Zn, the balance being Sb and inevitable impurities, and having a melting point in the range of 155 to 625 ° C. A mixture preparation step of preparing a mixture by uniformly mixing at a predetermined ratio, and a paste-like mixture preparation step of preparing a paste-like mixture by mixing the flux with the mixture at a predetermined ratio and stirring the mixture. Have The features.

  The lead-free solder manufacturing method of the present invention includes at least one of Ag, Al, Au, Bi, Co, Cr, Cu, Fe, Ge, In, Mg, Mn, Pd, Si, Sr, Te, and Zn. A first alloy powder containing seeds, the balance being Sn and inevitable impurities, and having a melting point in the range of 117 to 350 ° C .; Ag, Al, Au, Bi, Co, Cr, Cu, Fe, Ge, In , Mg, Mn, Pd, Si, Sr, Te, Zn, the second alloy powder containing at least one selected from the group consisting of Sb and inevitable impurities and having a melting point in the range of 155 to 625 ° C. Are uniformly mixed at a predetermined ratio to produce a mixture, a compounding step in which the mixture is pressed or cold-molded to form a composite, and the composite mixture is formed into a film. Or wire Characterized by comprising a formation step of the form.

Furthermore, the method for producing a lead-free solder according to the present invention includes at least one of Ag, Al, Au, Bi, Co, Cr, Cu, Fe, Ge, In, Mg, Mn, Pd, Si, Sr, Te, and Zn. A forming step of forming a first alloy in the form of a film or a wire containing seeds, the balance being Sn and inevitable impurities, and having a melting point in the range of 117 to 350 ° C., Ag, Al, Au, Bi, Co, It contains at least one of Cr, Cu, Fe, Ge, In, Mg, Mn, Pd, Si, Sr, Te, and Zn, the balance is made of Sb and inevitable impurities, and the melting point is in the range of 155 to 625 ° C. A laminating step of laminating a powder of the second alloy, which is, on the surface of the first alloy formed into a film or wire, and a first alloy on which the powder of the second alloy is laminated Or hot Molding or rolling to characterized by comprising a composite step of compounding.

  The electronic component of the present invention is characterized in that the component is bonded to a base material using any of the lead-free solders of the present invention described above.

  According to this invention, any one of the above-described lead-free solders of the present invention is used, for example, by joining a component to a substrate under a high temperature condition such as primary reflow, thereby enabling high-temperature hierarchical connection such as secondary reflow. Can be possible. Here, examples of components include an intelligent power module for motor variable speed driving, a power integrated module, a converter module, and the like. The ceramic substrate of these power modules is mounted on a Cu base with solder, and the power device chip is integrated on a ceramic substrate.

  According to the lead-free solder, the lead-free solder manufacturing method, and the electronic component of the present invention, the bonding strength can be maintained at a high temperature, and an electronic component that is connected at a high temperature using lead-free solder can be provided.

  Hereinafter, an embodiment of the present invention will be described.

  The lead-free solder of the present invention comprises a second alloy phase made of an Sb alloy having a melting point higher than the melting point of the first alloy phase in the first alloy phase made of an Sn-based alloy constituting the parent phase. Has been.

  The Sn-based alloy forming the first alloy phase is, for example, one of Ag, Al, Au, Bi, Co, Cr, Cu, Fe, Ge, In, Mg, Mn, Pd, Si, Sr, Te, Zn It contains at least one kind, and the balance is composed of Sn and inevitable impurities. The kind and content of the substance contained in Sn are set so that the melting point of this Sn-based alloy is 117 to 350 ° C.

Here, the reason why the melting point of the Sn-based alloy is 117 to 350 ° C. is that the Sn—In alloy has the lowest melting point among the general-purpose alloys, and the eutectic temperature of Sn-52 wt% In is 117 ° C.
Also, Sn-4.5 wt% Cu solid phase line is 227 ° C, liquidus line is 350 ° C, and if it is higher than 350 ° C, it will exceed the heat resistance temperature of the part to be soldered and there is a risk of damage to the part. is there. A more preferable range of the melting point of the Sn-based alloy is 180 to 260 ° C.

  The first alloy phase may be composed of powder, for example. In this case, the average particle diameter of the first alloy powder is preferably in the range of 1 to 100 μm. This is because if the average particle size of the first alloy powder is less than 1 μm, the surface area is large so that it is easily oxidized and the fine powder is expensive. If it exceeds 100 μm, it becomes difficult to control the solder thickness. The particle diameter of the first alloy powder is not particularly limited, but a more preferable average particle diameter is 10 to 50 μm from the viewpoint of ease of handling and economics.

  The Sb alloy forming the second alloy phase is, for example, at least one of Ag, Al, Au, Bi, Co, Cr, Cu, Fe, Ge, In, Mg, Mn, Pd, Si, Sr, Te, Zn 1 type is contained and the remainder is comprised from Sb and an unavoidable impurity. The kind and content of the substance contained in Sb are set so that the melting point of this Sb alloy is 155 to 625 ° C.

  Here, the melting point of the Sb alloy is set to 155 to 625 ° C. The Sb—In alloy has the lowest melting point among the general-purpose alloys, and the eutectic temperature of Sb-99.3 wt% In is 155 ° C. When the liquidus temperature is higher than 625 ° C., the time required for the melting reaction between the first alloy phase and the surface layer portion is long, and the content of the alloy element increases, so that the material characteristics may be deteriorated. This is because the material becomes expensive. A more preferable range of the melting point of the Sb alloy is 250 ° C to 550 ° C.

  Further, the second alloy phase may be composed of powder, for example. In this case, the average particle size of the second alloy powder is preferably in the range of 0.1 to 25 μm. If the average particle size of the second alloy powder is less than 0.1 μm, handling becomes difficult and the cost becomes higher. If the average particle size exceeds 25 μm, it is difficult to disperse uniformly in the first alloy phase, and the maximum effect is achieved with a low content. It becomes difficult to obtain.

  The second alloy phase is contained in the first alloy phase at a content of 1 to 50% by volume. Here, the content rate of the second alloy phase in the first alloy phase is set to 1 to 50% by volume because the effect is small when the content rate of the second alloy phase is less than 1% by volume and exceeds 50% by volume. This is because the melting point becomes high and it becomes difficult to control the temperature.

  The lead-free solder of the present invention can take a paste-like shape in which the first alloy powder, the second alloy powder, a flux, and the like are mixed. The lead-free solder is a mixture of the first alloy powder and the second alloy powder, formed by pressing in cold or hot to form a composite, such as a film or wire. There may be. Moreover, in the lead-free solder formed in a predetermined shape such as a film shape or a wire shape, the second alloy powder may be compounded while being biased to the surface, for example.

  Next, a lead-free solder having a paste shape, a film shape, and a wire shape will be described with reference to FIGS.

  FIG. 1 shows a cross-sectional view of a lead-free solder formed in a paste form. 2 shows a perspective view of the lead-free solder formed in a film shape, and FIG. 3 shows a perspective view of the lead-free solder formed in a wire shape.

First, the paste-like lead-free solder 20 formed in the paste shape shown in FIG. 1 will be described.
The paste-like lead-free solder 20 contains at least one of Ag, Al, Au, Bi, Co, Cr, Cu, Fe, Ge, In, Mg, Mn, Pd, Si, Sr, Te, Zn, A first alloy powder 21 formed of Sn-based alloy powder, the balance of which is Sn and inevitable impurities, and the melting point is in the range of 117 to 350 ° C., and Ag, Al, Au, Bi, Co, Cr, Cu, Fe , Ge, In, Mg, Mn, Pd, Si, Sr, Te, Zn containing at least one of the balance, the balance is made of Sb and inevitable impurities, and the melting point is in the range of 155 to 625 ° C. It is comprised from the 2nd alloy powder 22 formed with a powder, and the flux 23 containing solid content.

  The flux 23 mixed in the mixture of the first alloy powder 21 and the second alloy powder 22 removes the oxide film between the solder and the member joined by the solder, and prevents re-oxidation during heating. To do. As the flux 23, a commonly used activator such as an amine halogen salt or an organic acid is used. The binder contained in the flux 23 is composed of a polymer material and alcohol.

  The content rate of the flux 23 in this paste-like lead-free solder 20 can be appropriately set within a range of 10 to 15% by weight. If the content of the flux 23 is less than 10% by weight, the effect of removing the oxide film between the lead-free solder and the member joined by the lead-free solder and preventing oxidation again during heating is small, 15% by weight. If it exceeds the range, improvement of the effect cannot be expected.

  Moreover, the solid content in the flux 23 can be appropriately set within a range of 30 to 60% by weight. When the solid content is less than 30% by weight, the adhesion state of the solder applied or printed on the surface of the component part becomes insufficient. This is because void defects are likely to occur in the portion.

This paste-like lead-free solder 20 is manufactured as follows.
First, the second alloy powder 22 is uniformly mixed with the first alloy powder 21 at a mixing ratio of 1 to 50% by volume with respect to the first alloy powder 21 to constitute a mixture. This mixing ratio is appropriately set within this range depending on setting conditions and the like. Subsequently, a predetermined amount of a flux 23 containing a binder is mixed into this mixture, and the mixture is stirred uniformly to obtain a paste-like lead-free solder 20.

  Thus, by making the lead-free solder into a paste, it is possible to easily perform joining of joints where it is difficult to place solid lead-free solder, joining of members having complicated shapes, and the like using the paste-like lead-free solder 20. be able to. Further, since the paste-like lead-free solder 20 can be accurately injected into the joint portion having a complicated shape, the reliability of soldering can be improved.

Next, the film-like lead-free solder 30 formed in the film shape shown in FIG. 2 will be described.
The film-like lead-free solder 30 contains at least one of Ag, Al, Au, Bi, Co, Cr, Cu, Fe, Ge, In, Mg, Mn, Pd, Si, Sr, Te, Zn, The remainder is composed of Sn and unavoidable impurities, the first alloy phase 31 formed of an Sn-based alloy having a melting point in the range of 117 to 350 ° C., and uniformly dispersed in the first alloy phase 31, Ag, Contains at least one of Al, Au, Bi, Co, Cr, Cu, Fe, Ge, In, Mg, Mn, Pd, Si, Sr, Te, Zn, and the balance consists of Sb and inevitable impurities, It is comprised from the 2nd alloy powder 32 formed with the powder of Sb alloy whose melting | fusing point is the range of 155-625 degreeC.

  The film-like lead-free solder 30 preferably has a thickness in the range of 20 to 200 μm. This is because when the thickness is smaller than 20 μm, it is difficult to obtain sufficient bonding strength, and when the thickness is larger than 200 μm, the thermal conductivity and electric conductivity are decreased by 200 μm.

This film-like lead-free solder 30 is manufactured as follows.
First, the second alloy powder 32 is uniformly mixed with the first alloy powder at a mixing ratio of 1 to 50% by volume with respect to the first alloy powder forming the first alloy phase 31 to constitute a mixture. This mixing ratio is appropriately set within this range depending on setting conditions and the like. Subsequently, the mixture is filled in a mold, and pressurized and heated to fuse the first alloy powder and the second alloy powder 32 together to obtain a composite material. Subsequently, the composite material is rolled, for example, and the film-like lead-free solder 30 is obtained.

  Here, as another example of the film-like lead-free solder 30, a method for producing a film-like lead-free material in which the second alloy powder is biased to the surface and combined will be described.

  The first alloy powder forming the first alloy phase 31 is filled in a mold, and pressurized and heated to fuse the first alloy powder to obtain a composite material. Subsequently, the second alloy powder 32 is laminated on the surface of the composited first alloy and rolled to obtain a film-like lead-free solder in which the second alloy powder is biased and composited on the surface. .

Next, the wire-shaped lead-free solder 40 formed in the wire shape shown in FIG. 3 will be described.
The wire-shaped lead-free solder 40 contains at least one of Ag, Al, Au, Bi, Co, Cr, Cu, Fe, Ge, In, Mg, Mn, Pd, Si, Sr, Te, Zn, The remainder is composed of Sn and inevitable impurities, the first alloy phase 41 is formed of an Sn-based alloy having a melting point in the range of 117 to 350 ° C., and is uniformly dispersed and contained in the first alloy phase 41, Ag, Contains at least one of Al, Au, Bi, Co, Cr, Cu, Fe, Ge, In, Mg, Mn, Pd, Si, Sr, Te, Zn, and the balance consists of Sb and inevitable impurities, It is comprised from the 2nd alloy powder 42 formed with the powder of Sb alloy whose melting | fusing point is the range of 155-625 degreeC.

The wire-shaped lead-free solder 40 is manufactured as follows.
First, the second alloy powder 42 is uniformly mixed with the first alloy powder at a mixing ratio of 1 to 50% by volume with respect to the first alloy powder forming the first alloy phase 41 to constitute a mixture. This mixing ratio is appropriately set within this range depending on setting conditions and the like. Subsequently, the mixture is filled in a mold, and pressurized and heated to fuse the first alloy powder and the second alloy powder 42 together to obtain a composite material. Subsequently, the composite material is drawn, for example, to obtain a wire-like lead-free solder 40.

  Here, the manufacturing method of the wire-shaped lead-free solder 40 is not limited to the above-described method. For example, a mixture of the first alloy powder and the second alloy powder 42 is packed in a mold having a predetermined shape, and then added. It can also be formed by pressure and heating.

  Further, the lead-free solder wire 40 melts the first alloy powder and uniformly disperses it by mixing the second alloy powder 42 therein, and then pours it into a mold having a predetermined shape, and then cools it. It can also be formed. In addition, when the wire-shaped lead-free solder 40 is manufactured by mixing the second alloy powder 42 with the molten first alloy powder, the temperature of the molten first alloy powder is higher than the melting point of the second alloy powder 42. The temperature is set to a low temperature, and the second alloy powder 42 is not melted but dispersed while maintaining a solid state.

  As another example of the wire-shaped lead-free solder 40, for example, a wire-shaped lead-free solder in which the second alloy powder is biased to the surface and combined can be manufactured by the following method.

  The mold is filled with the first alloy powder forming the first alloy phase 41, and the first alloy powder is fused by pressing and heating to obtain a composite material. Subsequently, the second alloy powder 42 is laminated on the surface of the composited first alloy and press-molded to obtain a wire-like lead-free solder in which the second alloy powder is biased and composited on the surface. it can.

  As described above, the lead-free solder is not limited to the paste form, but can take a film form, a wire form, or the like, and an optimum form of the lead-free solder can be used depending on the use for which the lead-free solder is used. In addition, the shape of the lead-free solder is not limited to the above-described shape, and can be formed by appropriately changing the shape according to the application.

  Here, an example of a method for forming a lead-free alloy such as the first alloy powder 21 and the second alloy powder 22, 32, 42 into a spherical or indefinite shape powder will be described.

First, a lead-free alloy is heated and melted, and the melted mixture is atomized by, for example, an atomizing method using an inert gas such as N ₂ gas, He gas, Ar gas, N ₂ / Ar mixed gas, and solidified. To do. In this atomizing method, a molten mixture is jetted together with an inert gas from a nozzle at a subsonic speed or supersonic speed, and the molten mixture is atomized by a jet stream of the inert gas. Then, from the atomized lead-free alloy powder, a powder having an average particle diameter in a predetermined range is selected using, for example, a sieve.

  The lead-free alloy powder that has been atomized and solidified has a smaller average particle diameter when the velocity of the jet flow of the inert gas injected from the nozzle is larger. In particular, when the jet flow reaches, for example, a supersonic state of about 2 to 3 times the speed of sound, the effect of atomization by a shock wave is added, and the average particle diameter of the powder can be further reduced. Further, since the inert gas is used as the jet flow, oxidation on the surface of the powder can be suppressed. Air or water can be used in place of the inert gas. However, when air or water is used, the effect of suppressing the oxidation of the powder surface is small. It is preferable to use an inert gas for the jet stream because the shape is unlikely to be spherical.

  Next, the joint part joined using the lead-free solder mentioned above is demonstrated with reference to FIG. 4 and 5. FIG. Here, the case where the paste-like lead-free solder 20 described above is used for lead-free solder will be described.

  FIG. 4 shows a cross-sectional view of a state in which the paste-like lead-free solder 20 is installed between the first element member 50 and the second element member 51. Further, FIG. 5 shows a cross section of the solder joint portion 60 after the laminated joint member 52 shown in FIG. 4 is soldered.

  As shown in FIG. 4, the paste-like lead-free solder 20 is disposed between the first element member 50 and the second element member 51. And this lamination | stacking joining member 52 is heated to the temperature more than melting | fusing point of the 1st alloy powder 21 which comprises the paste-form lead-free solder 20, for example in air | atmosphere or inert gas atmosphere. And after melt | dissolving the 1st alloy powder 21, through the cooling process, the solder joint part 60 of a cross-sectional shape as shown in FIG. 5 is obtained.

  Here, in the state in which the first alloy powder 21 is melted, the second alloy powder 22 has a melting point higher than that of the first alloy powder 21, so that it does not enter a molten state but maintains a solid phase. Therefore, after solidifying through the cooling step, as shown in FIG. 5, the second alloy powder 22 is almost uniformly dispersed in the first alloy phase 61 in which the first alloy powder 21 is melted and solidified. It is in a state. In addition, an intermetallic compound phase 63 formed by an alloying reaction between the Sb alloy constituting the second alloy powder 22 and the Sn-based alloy constituting the first alloy phase 61 is formed on the surface of the second alloy powder 22. It is formed.

  The first element member 50 and the second element member 51 soldered using the paste-like lead-free solder 20 are subjected to secondary reflow for wire bonding, for example, and the first alloy phase 61 is in a molten state. However, it is possible to prevent the liquid first alloy phase 61 from flowing out due to the surface tension with the second alloy powder 22 that maintains the solid phase.

  In this case, in order to prevent the first alloy phase 61 from flowing out by the surface tension with the second alloy powder 22, the second alloy powder 22 is uniformly dispersed in the first alloy phase 61. Is preferred. Furthermore, it is preferable to use the second alloy powder 22 having a small particle size in a state where the number density of the second alloy powder 22 is increased.

  Here, an example in which the paste-like lead-free solder 20 is used as the lead-free solder is shown, but the same solder joint is formed when the film-like lead-free solder 30 and the wire-like lead-free solder 40 are used.

  Moreover, the 1st element member 50 can be comprised by Cu heat sink etc. of a power module, for example, and the 2nd element member 51 can be comprised by electronic members, such as a ceramic substrate, for example.

  As described above, the lead-free solder of the present invention containing the second alloy phase made of Sb alloy having a melting point higher than the melting point of the first alloy phase in the first alloy phase made of Sn-based alloy is used. Thus, soldering can be performed while maintaining the solid state of the second alloy powder at a temperature at which the first alloy phase is in a molten state. Thereby, the solder joint portion can contain the second alloy powder uniformly dispersed in the first alloy phase while maintaining the characteristics such as the wettability of the first alloy phase.

  Further, by containing the second alloy powder having a melting point higher than the melting point of the first alloy phase, for example, when performing the secondary reflow, even if the first alloy phase is in a molten state, the second alloy powder is The solid phase can be maintained and the melted first alloy phase can be prevented from flowing out due to the surface tension of the second alloy powder.

  As a result, even when lead-free solder is used, high-temperature hierarchical connection is possible, soldering can be performed while maintaining bonding strength at high temperatures, and the reliability of soldering using lead-free solder can be improved.

  Next, specific examples of the present invention will be described.

(Example 1)
First alloy powder made of Sn-0.7 wt% Cu powder having an average particle size of 25-45 μm, and second alloy powder made of Sb-2.5 wt% Co powder having an average particle size of 0.1-10 μm Were mixed uniformly at a volume ratio of 10: 1 to the first alloy powder and the second alloy powder to prepare a mixture. Subsequently, a flux containing a binder was mixed with this mixture to prepare a paste-like lead-free solder. In addition, the content rate of the flux in a paste-form lead-free solder was 12 weight%.

  Next, the prepared paste-like lead-free solder is poured into a crucible, a melting test is performed at a temperature rising rate of 80 ° C./min in a nitrogen gas atmosphere, and the first alloy powder and The temperature of the two alloy powders was measured. Moreover, after cooling the paste-form lead-free solder in a predetermined temperature stage, the cross section was observed, and the state of the first alloy powder and the second alloy powder was confirmed.

  When the heating temperature rose and reached 227 ° C., the first alloy powder was melted, and the second alloy powder having a melting point of 623 ° C. maintained a solid phase. Furthermore, when the heating temperature is increased to reach 300 ° C., the liquid phase of the first alloy powder is alloyed with the surface portion of the second alloy powder and fused, but the central portion of the second alloy powder maintains a solid phase. Was.

  Thus, at a high temperature of 300 ° C., the first alloy powder is melted into a liquid phase, and the second alloy powder is maintained in a solid phase, in which the liquid phase and the solid phase coexist. I understood.

  Furthermore, the paste which uniformly mixed the 1st alloy powder which consists of the powder of Sn-0.7 weight% Cu of this example, the 2nd alloy powder which consists of the powder of Sb-2.5 weight% Co, and the flux After the chip and the substrate were subjected to primary reflow connection using a lead-free solder, the chip was die-bonded using Sn-0.7 wt% Cu solder.

  Although the die bond temperature has reached 300 ° C., the paste-like lead-free solder used for the primary reflow maintains the state where the liquid phase and the solid phase coexist as described above, and the molten first alloy powder flows out. The connection between the chip and the substrate could be maintained.

(Example 2)
A first alloy powder made of Sn-0.7 wt% Cu powder having an average particle size of 25 μm or less, and a second alloy powder made of Sb-2.5 wt% Co powder having an average particle size of 3 μm or less, The volume ratio of 1 alloy powder and 2nd alloy powder was uniformly mixed in the ratio of 5 to 1, and the mixture was produced. Subsequently, flux was mixed with this mixture to produce a paste-like lead-free solder. In addition, the content rate of the flux in a paste-form lead-free solder was 12 weight%.

  Next, the prepared paste-like lead-free solder is poured into a crucible, a melting test is performed at a temperature rising rate of 80 ° C./min in a nitrogen gas atmosphere, and the first alloy powder and The temperature of the two alloy powders was measured. Moreover, after cooling the paste-form lead-free solder in a predetermined temperature stage, the cross section was observed, and the state of the first alloy powder and the second alloy powder was confirmed.

  When the heating temperature rose and reached 227 ° C., the first alloy powder was melted, and the second alloy powder having a melting point of 623 ° C. maintained a solid phase. Further, when the heating temperature is increased and reaches 350 ° C., the liquid phase of the first alloy powder is alloyed with the surface portion of the second alloy powder, and the central portion of the second alloy powder maintains a solid phase. Was.

  Thus, at a high temperature of 350 ° C., the first alloy powder is melted into a liquid phase, and the second alloy powder is maintained in a solid phase, in which the liquid phase and the solid phase coexist. I understood.

  Furthermore, the paste which uniformly mixed the 1st alloy powder which consists of the powder of Sn-0.7 weight% Cu of this example, the 2nd alloy powder which consists of the powder of Sb-2.5 weight% Co, and the flux After the chip and the substrate were subjected to primary reflow connection using a lead-free solder, the chip was die-bonded using Sn-0.7 wt% Cu solder.

  Although the die bond temperature has reached 350 ° C., the paste-like lead-free solder used for the primary reflow maintains the state where the liquid phase and the solid phase coexist as described above, and the molten first alloy powder flows out. The connection between the chip and the substrate could be maintained.

(Example 3)
A first alloy powder made of Sn-0.7 wt% Cu powder having an average particle diameter of 5 μm or less and a second alloy powder made of Sb-2.5 wt% Co powder having an average particle diameter of 1 μm or less, The volume ratio of 1 alloy powder and 2nd alloy powder was uniformly mixed in the ratio of 10: 1, and the mixture was produced. Subsequently, a flux containing a binder was mixed with this mixture to prepare a paste-like lead-free solder. In addition, the content rate of the flux in a paste-form lead-free solder was 12 weight%.

  Next, the prepared paste-like lead-free solder is poured into a crucible, a melting test is performed at a temperature rising rate of 80 ° C./min in a nitrogen gas atmosphere, and the first alloy powder and The temperature of the two alloy powders was measured. Moreover, after cooling the paste-form lead-free solder in a predetermined temperature stage, the cross section was observed, and the state of the first alloy powder and the second alloy powder was confirmed.

  When the heating temperature rose and reached 227 ° C., the first alloy powder was melted, and the second alloy powder having a melting point of 623 ° C. maintained a solid phase. Further, when the heating temperature is increased and reaches 275 ° C., the liquid phase of the first alloy powder is alloyed with the surface portion of the second alloy powder and fused, but the central portion of the second alloy powder maintains a solid phase. Was.

  Thus, at a high temperature of 275 ° C., the first alloy powder melts into a liquid phase, and the second alloy powder maintains a solid phase, and a state in which the liquid phase and the solid phase coexist is maintained. I understood.

  Furthermore, the paste which uniformly mixed the 1st alloy powder which consists of the powder of Sn-0.7 weight% Cu of this example, the 2nd alloy powder which consists of the powder of Sb-2.5 weight% Co, and the flux After the chip and the substrate were subjected to primary reflow connection using a lead-free solder, the chip was die-bonded using Sn-0.7 wt% Cu solder.

  Although the die bond temperature has reached 300 ° C., the paste-like lead-free solder used for the primary reflow maintains the state where the liquid phase and the solid phase coexist as described above, and the molten first alloy powder flows out. The connection between the chip and the substrate could be maintained.

(Comparative Example 1)
A flux was mixed with an alloy powder of Sn-5 wt% Sb (melting point: 232 ° C.) having an average particle diameter of 25 to 45 μm to prepare a paste-like lead-free solder. In addition, the content rate of the flux in a paste-form lead-free solder was 12 weight%. Next, this paste-like lead-free solder was used to perform primary reflow connection between the chip and the substrate, and then the chip was die-bonded using Sn-0.7 wt% Cu solder.

  As the die bond temperature rose to 300 ° C., the melted Sn-5 wt% Sb solder flowed out, and the connection state between the chip and the substrate could not be maintained.

  Comparing this result with the results in Examples 1 to 3, the first alloy powder forming the parent phase contains the second alloy powder having a melting point higher than that of the first alloy powder. It has become clear that even when the melting point is reached, the molten first alloy powder can be prevented from flowing out. As a result, it has been found that, in soldering using the lead-free solder of the present invention, high-temperature hierarchical connection is possible, and soldering can be performed while maintaining joint strength at high temperatures.

Sectional drawing of the lead-free solder formed in the paste form. The perspective view of the lead-free solder formed in the film form. The perspective view of the lead-free solder formed in the wire form. Sectional drawing of the state which installed the paste-form lead-free solder between the 1st element member and the 2nd element member. Sectional drawing of the solder joint part after soldering the lamination | stacking joining member shown in FIG.

Explanation of symbols

  20 ... Paste-free lead-free solder, 21 ... 1st alloy powder, 22 ... 2nd alloy powder, 23 ... Flux.

Claims (10)

  A lead-free solder comprising a first alloy phase made of an Sn-based alloy and a second alloy phase made of an Sb alloy having a melting point higher than that of the first alloy phase.   The first alloy phase contains at least one of Ag, Al, Au, Bi, Co, Cr, Cu, Fe, Ge, In, Mg, Mn, Pd, Si, Sr, Te, Zn; The lead-free solder according to claim 1, wherein the balance is made of Sn and inevitable impurities.   The second alloy phase contains at least one of Ag, Al, Au, Bi, Co, Cr, Cu, Fe, Ge, In, Mg, Mn, Pd, Si, Sr, Te, Zn; The lead-free solder according to claim 1, wherein the balance is made of Sb and inevitable impurities.   The lead-free solder according to claim 1 or 3, wherein the second alloy phase is contained in an amount of 1 to 50% by volume in the first alloy phase.   The lead-free lead according to any one of claims 1, 3 and 4, wherein the second alloy phase is made of powder, and the average particle size of the powder of the second alloy phase is 0.1 to 25 µm. Solder.   5. The lead-free solder according to claim 1, wherein the first alloy phase is made of powder, and the average particle size of the powder of the first alloy phase is 1 to 100 μm. Contains at least one of Ag, Al, Au, Bi, Co, Cr, Cu, Fe, Ge, In, Mg, Mn, Pd, Si, Sr, Te, Zn, and the remainder from Sn and inevitable impurities A powder of the first alloy, and at least one of Ag, Al, Au, Bi, Co, Cr, Cu, Fe, Ge, In, Mg, Mn, Pd, Si, Sr, Te, Zn. A mixture preparation step of uniformly mixing the second alloy powder consisting of Sb and inevitable impurities at a predetermined ratio, and producing a mixture;
A paste-like mixture producing step of producing a paste-like mixture by mixing a flux with the mixture at a predetermined ratio and stirring the mixture. Contains at least one of Ag, Al, Au, Bi, Co, Cr, Cu, Fe, Ge, In, Mg, Mn, Pd, Si, Sr, Te, Zn, and the remainder from Sn and inevitable impurities A powder of the first alloy, and at least one of Ag, Al, Au, Bi, Co, Cr, Cu, Fe, Ge, In, Mg, Mn, Pd, Si, Sr, Te, Zn. A mixture preparation step of uniformly mixing the second alloy powder consisting of Sb and inevitable impurities at a predetermined ratio, and producing a mixture;
A compounding step of compressing and molding the mixture cold or hot;
And a forming step of forming the composite mixture into a film form or a wire form. Contains at least one of Ag, Al, Au, Bi, Co, Cr, Cu, Fe, Ge, In, Mg, Mn, Pd, Si, Sr, Te, Zn, and the remainder from Sn and inevitable impurities Forming a first alloy formed into a film or wire;
Contains at least one of Ag, Al, Au, Bi, Co, Cr, Cu, Fe, Ge, In, Mg, Mn, Pd, Si, Sr, Te, Zn, and the remainder from Sb and inevitable impurities A laminating step of laminating the second alloy powder formed on the surface of the first alloy formed into the film shape or the wire shape;
And a compounding step of compounding the first alloy on which the powder of the second alloy is laminated by cold forming or rolling in a cold or hot manner.   An electronic component comprising the component joined to a base material using the lead-free solder according to any one of claims 1 to 6.

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