JP2016087641A - Pb-FREE Al-Cu-BASED SOLDER ALLOY - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a Pb-free solder alloy for high temperature use, excellent in bondability, processability and reliability, and significantly inexpensive compared to conventional Au-based solder.SOLUTION: A Pb-free Al-Cu-based solder alloy contains, by mass%, Cu: 24.0 to 42.0, with the balance being Al and unavoidable impurities. The Al-Cu-based solder alloy may contain, in addition to Cu as an essential component, at least one kind of Ag, Sn, Zn, In, Ni, Ge, Mg, Sb and P.SELECTED DRAWING: None

Description

  The present invention relates to a so-called Pb-free solder alloy containing no Pb, and more particularly to a Pb-free Al—Cu solder alloy suitable for high temperature use.

  In soldering in the assembly process of various electronic components including die bonding of power transistor elements, a solder alloy having a relatively high melting point of about 300 to 400 ° C. so as to withstand a reflow temperature of about 300 ° C. High temperature soldering using “high temperature solder alloy” is also performed. Moreover, when melting a solder alloy by a laser heating method or the like, soldering is performed at a temperature of about 500 to 550 ° C. As such a high-temperature solder alloy, a Pb-based solder alloy represented by a Pb-5 mass% Sn alloy has been mainly used conventionally.

  However, in recent years, there has been a strong movement to limit the use of Pb due to consideration for environmental pollution. For example, Pb has become a regulated substance under the RoHS directive. Corresponding to such a movement, in the field of assembling electronic parts and the like, a Pb-free (lead-free) solder alloy, that is, a Pb-free solder alloy is required.

  In the case of solder alloys for medium and low temperatures (about 140 to 230 ° C.), Pb-free solder alloys mainly composed of Sn have already been put into practical use. For example, in Patent Document 1, Sn is the main component, Ag is 1.0 to 4.0% by weight, Cu is 2.0% by weight or less, Ni is 0.5% by weight or less, and P is 0.2% by weight. % Pb-free solder alloy is described. Patent Document 2 describes a Pb-free solder alloy containing 0.5 to 3.5% by weight of Ag, 0.5 to 2.0% by weight of Cu, and the balance being Sn.

  On the other hand, examples of high temperature Pb-free solder alloys include Au—Sn solder alloys and Au—Ge solder alloys. However, these solder alloys are very expensive because they contain Au as a main component, and are limited to limited applications such as optical device-related elements that require high reliability, and are used for general electronic components and the like. There is hardly anything. Therefore, in order to realize Pb-free in relatively inexpensive high-temperature solder alloys used for general electronic parts and the like, researches on Bi-based solder alloys and Zn-based solder alloys have been advanced.

  For example, for Bi-based solder alloys, it is possible to adjust the liquidus temperature and reduce variation by adding a binary eutectic alloy to a eutectic alloy containing Bi and further adding additional elements to Patent Document 3. A method for producing a solder alloy is disclosed. As for the Zn-based solder alloy, for example, Patent Document 4 describes a high-temperature Zn-based solder alloy based on a Zn—Al alloy in which Al is added to lower the melting point of Zn, and Ge or Mg is added thereto. Has been. Patent Document 4 also describes that the addition of Sn or In has an effect of further lowering the melting point.

  Specifically, Patent Document 4 includes 1 to 9% by mass of Al, 0.05 to 1% by mass of Ge, the remaining Zn alloy consisting of Zn and inevitable impurities, and 5 to 9% by mass of Al. %, Mg is contained in an amount of 0.01 to 0.5% by mass, and the balance is a second Zn alloy composed of Zn and inevitable impurities. A third Zn alloy containing 0.01 to 0.5% by mass, the balance being Zn and inevitable impurities, Al 1 to 9% by mass, Ge 0.05 to 1% by mass, Sn and / or In 0.5%. A fourth Zn alloy containing 1 to 25% by mass, the balance being Zn and inevitable impurities, Al 1 to 9% by mass, Mg 0.01 to 0.5% by mass, Sn and / or In 0.1% A fifth Zn alloy containing ~ 25% by mass, the balance being Zn and inevitable impurities, and 1-9% by mass of Al, and 0.5% of Ge. A sixth Zn alloy containing 5 to 1% by mass, Mg of 0.01 to 0.5% by mass, Sn and / or In of 0.1 to 25% by mass, the balance being Zn and inevitable impurities is described. Yes.

  Further, a technique using Al or Cu as a bonding material for brazing material has been proposed. For example, Patent Document 5 discloses a low temperature material mainly composed of Ag, Al, and Cu that can be used in a wide range of application without adversely affecting other constituent members and that can improve bonding characteristics. A method for producing a brazing material is disclosed. Specifically, an alloy powder is produced from a raw material in which Ag is mixed at a blending ratio of 25 to 80% by weight, Al is 14 to 75% by weight, and Cu is 1 to 30% by weight. It describes a method for producing a brazing material characterized by compression molding into a shape.

  Patent Document 6 describes a brazing material containing Al as a main component, Cu containing 11 to 17 atomic%, and Si containing 6.5 atomic% or less. It is described that it is possible to lower the melting point of a brazing material used for joining alloys or joining Al or Al alloy and ceramic, and to obtain a good joined body.

Japanese Patent Laid-Open No. 1999-077366 JP-A-8-215880 JP 2006-167790 A Patent No. 3850135 JP 7-214379 A JP 7-290272 A

  As described above, Pb-5 mass% Sn alloy can be substituted for soldering performed at relatively high temperatures such as die bonding of power transistor elements and soldering for sealing crystal resonators by laser heating. As the solder alloy, for example, Au-based solders such as Au-20 mass% Sn and Au-12.5 mass% Ge have been put into practical use, but all contain about 80 to 90 mass% of expensive Au. It is used only in special cases such as applications that require extremely high reliability. Even in an expensive solder alloy that does not use Au, the Bi-based solder alloy disclosed in Patent Document 3 described above becomes a quaternary or higher multi-component solder alloy only by adjusting the temperature of the liquidus line. Effective improvements have not been made for fragile mechanical properties.

  The Zn-based solder alloy disclosed in Patent Literature 4 often has insufficient wettability within the composition range. That is, it is considered that Zn, which is the main component, is highly oxidizable because of its strong reducibility, and the wettability is extremely deteriorated due to its influence. Moreover, since Al is more reducible than Zn, for example, even when added in an amount of 1% by mass or more, wettability is greatly reduced. These oxidized Zn and Al cannot be reduced even if Ge or Sn is added, and the wettability cannot be improved.

  As described above, the Zn—Al-based alloy is an alloy that has a melting point of about 300 to 400 ° C. (Zn—Al eutectic temperature: 381 ° C.), but is not preferable from the viewpoint of wettability. Furthermore, when Mg or the like is added to a Zn—Al-based alloy, an intermetallic compound is generated and becomes extremely hard, which may cause a problem that good workability cannot be obtained. For example, a Zn—Al-based alloy containing 5% by mass or more of Mg cannot be processed into a wire shape or a sheet shape that is difficult to process.

  Further, the brazing material disclosed in Patent Document 5 has too much Ag content for bonding Si chips, and the liquidus temperature becomes too high. With such a high Ag content, the bonding temperature is too high, so that it cannot be used even for a SiC chip that can operate at a high temperature. The brazing material disclosed in Patent Document 6 is very hard and brittle because the Al—Si alloy is made of a eutectic alloy but Si, which is a nonmetal, is used as the second component. Further, when Cu is added to Al—Si, the brittleness becomes more prominent, and it becomes difficult to process the solder alloy into a shape such as a wire, a ribbon, and a pull foam material.

  As described above, for a high-temperature Pb-free solder alloy, it has been a big challenge to balance the desired melting point and having various properties such as workability and wettability. This problem has not been solved yet except for expensive Au-based solder alloys typified by Au-Sn alloys and Au-Ge alloys. That is, although an inexpensive high-temperature Pb-free solder alloy that can replace the conventional Pb-5 mass% Sn alloy is eagerly desired, it has not been put into practical use.

  The present invention has been made in view of such circumstances, and in assembling a semiconductor device or an electronic component, for example, when a semiconductor element is bonded to a substrate or a crystal resonator is sealed in a casing by a laser heating method or the like. In particular, a high-temperature Pb-free solder alloy having a solidus temperature of about 550 ° C. or lower, excellent in bondability, workability and reliability, and much less expensive than Au solder is provided. With the goal.

  In order to achieve the above object, the Pb-free Al—Cu solder alloy provided by the present invention has a Cu content of 24.0% by mass or more and 42.0% by mass or less, and the balance is Al and inevitable impurities. It is characterized by that.

  According to the present invention, it has a solidus temperature of about 550 ° C. or lower, which is particularly suitable for bonding by, for example, a laser heating method in the assembly of electronic components, etc., and has excellent bondability, workability and reliability, A Pb-free high-temperature solder alloy that is much cheaper than Au-based solder can be obtained.

It is a phase diagram of an Al-Cu type alloy. It is sectional drawing which shows the state which soldered the solder alloy on the Cu board | substrate which has Ni layer for wettability evaluation. FIG. 3 is a side view showing a height Y used for calculating an aspect ratio of the solder alloy of FIG. 2. It is a top view which shows the wetting spread length X1 and X2 used for calculation of the aspect ratio of the solder alloy of FIG.

  The Pb-free Al—Cu-based solder alloy according to the embodiment of the present invention is characterized in that it contains Cu as an essential component, and the balance is composed of elements (inevitable impurities) that are inevitably included in production and Al. By alloying Al and Cu in this way, the solidus temperature can be lowered to 550 ° C. or lower, and the reflow temperature of about 300 ° C. can be sufficiently tolerated. Further, this Pb-free Al—Cu solder alloy is excellent in bondability, workability and reliability, and does not contain expensive Au, so it is much cheaper than Au solder.

  Since this Pb-free Al—Cu solder alloy has a relatively high melting point, it is suitable not only for general solder bonding but also for bonding and sealing by a laser heating method or the like. Especially suitable for high temperature soldering in the assembly process of various electronic parts such as bonding of semiconductor elements featuring high temperature operation such as Si semiconductor elements, SiC semiconductor elements, GaN semiconductor elements, and die bonding of power transistor elements. ing. It is also excellent for sealing a crystal resonator used in the assembly process of the crystal resonator sealing element.

  The Pb-free Al—Cu solder alloy of the embodiment of the present invention may contain one or more of Ag, Sn, and Zn in addition to the above-described essential components Cu and Al, and / or In may be included and / or Ni may be included, and / or one or more of Ge, Mg, and Sb may be included and / or P may be included. Good. In this way, various properties required for solder materials by adding further elements in addition to the essential elements Cu and Al, such as bondability, workability, reliability, and wettability, are appropriately adjusted according to usage requirements. Can be adjusted. Hereinafter, each element contained in the above-described Pb-free Al—Cu solder alloy of the present invention will be described in detail.

<Al-Cu>
Al and Cu are elements that are both essential components in the Pb-free Al—Cu solder alloy of the present invention. By alloying Al and Cu, the solidus temperature can be lowered to 548 ° C. However, it still has a melting point of 500 ° C. or higher and is higher than, for example, Pb-5 mass% Sn, which is a typical high-temperature solder. Therefore, it is not possible to replace all the high-temperature solder currently used. However, in the case of solder that is used for bonding or sealing by, for example, laser bonding, unlike the reflow method in which the entire substrate is heated, Since it is only necessary to raise the temperature partially, it can be suitably used. Further, it can be used for bonding for SiC, which is characterized by high temperature operation.

  The Al—Cu alloy has a composition of eutectic point when the Al content is 67% by mass and the Cu content is about 33% by mass, and produces a eutectic alloy composed of an Al solid solution and a θ phase. 548 ° C. Since Al is a very soft metal, Al—Cu in the vicinity of this composition exhibits flexible properties. Al and Cu are suitable for releasing heat generated from the semiconductor chip because of their excellent thermal conductivity, and are also very suitable as a bonding material because of their excellent electrical conductivity.

  The Cu content necessary for obtaining the excellent effect of such an Al—Cu solder alloy is 24.0% by mass or more and 42.0% by mass or less. If the Cu content is less than 24.0% by mass, the solidus temperature becomes too high, and it does not melt sufficiently at the time of bonding, causing problems such as poor bonding. On the other hand, if it exceeds 42.0% by mass, the proportion of intermetallic compounds will increase too much, the strength of the solder mother phase will become too high and the chip will be destroyed, or there will be coarse intermetallic compounds at the time of joining Will cause problems such as tilting. The Cu content is preferably 30.0% by mass or more and 36% by mass or less. If the composition is within this range, the above-described effects appear more remarkably.

<Ag, Sn, Zn>
Ag, Sn, and Zn are elements that are appropriately contained in the present invention in order to improve or adjust various properties, and the main effects of containing these elements are almost the same, and the bondability is improved. Ag is a solid solution of several mass% in Al. And in Cu, the eutectic alloy which consists of Cu solid solution and Ag solid solution is produced | generated, The eutectic temperature is 779 degreeC. As described above, Ag forms a solid solution in Al or Cu or produces a eutectic alloy composed of a solid solution. Therefore, even if contained in a solder alloy, characteristics such as workability are not deteriorated. In addition, Ag generally contributes to improving the bondability because it is highly reactive with materials such as Cu and Ni constituting the uppermost surface of the substrate.

  The content of Ag necessary for obtaining such an effect of addition of Ag is 0.01% by mass or more and 8.0% by mass or less. If the Ag content is less than 0.01% by mass, the effect of inclusion does not appear substantially. If the Ag content exceeds 8.0% by mass, the liquidus temperature becomes too high. However, it does not melt sufficiently, leading to tip tilt and extreme reduction in bonding strength. It is preferable that the Ag content is 0.3% by mass or more and 4.0% by mass or less because the effect of containing Ag described above appears more remarkably.

  Sn forms a eutectic alloy composed of an Al solid solution and a Sn solid solution with Al, and the eutectic temperature is 228 ° C., which is very low. And only a little is dissolved in Cu. If the content of Sn is small, the Sn—Cu intermetallic compound does not adversely affect the strength. In addition, Sn generally exhibits high reactivity with materials such as Cu and Ni constituting the uppermost surface of the substrate, so that wetting and spreading are improved and bonding properties are improved.

  The Sn content necessary to obtain such an effect of addition of Sn is not less than 0.01% by mass and not more than 3.0% by mass. When the Sn content is less than 0.01% by mass, the effect of inclusion is hardly exhibited, and when it exceeds 3.0% by mass, the intermetallic compound becomes too hard, the reaction layer with the substrate becomes too thick, and the stress of the solder The relaxation property may be extremely lowered. If the Sn content is 0.2% by mass or more and 1.5% by mass or less, it is preferable because the above-described effect of adding Sn appears more remarkably.

  Zn forms a eutectic alloy with Al. And it dissolves in Cu at 30% by mass or more. Thus, since Zn forms a eutectic alloy with Al or Cu or dissolves in a large amount, even if it is contained in the solder alloy, it does not have an adverse effect at the time of bonding if it is 20% by mass or less. The merit of containing Zn is to improve the bondability and workability. In other words, Zn is more reactive with a material constituting the uppermost surface of the substrate such as Cu than Ag or Sn. For this reason, it reacts with a board | substrate and a chip | tip back surface rapidly at the time of joining, and strong joining is implement | achieved.

  However, if the Zn content is too high, the oxide layer of the solder alloy becomes too thick, causing problems such as a decrease in wettability. For this reason, the upper limit of Zn content is 20.0 mass%. On the other hand, the lower limit of the Zn content is 0.01% by mass, and if it is less than this value, there is too little even if it is contained, and substantially no effect appears. It is preferable that the Zn content is 0.5% by mass or more and 12.0% by mass or less because the effect of containing Zn described above appears more remarkably.

<In>
In is an element that is appropriately contained for improving or adjusting various properties in the present invention, and the main effect of containing In is to improve flexibility, workability, and stress relaxation. In is only slightly dissolved in Al, and its solidus temperature is as low as 156 ° C. Then, several mass% is dissolved in Cu. In is a very soft element and, as described above, dissolves in Cu by several mass%. Therefore, by incorporating it into a solder alloy, workability and stress relaxation can be improved. However, since Al forms an alloy with a solidus temperature of 156 ° C. and a very low melting point, it cannot be contained in a large amount, and the upper limit of the In content is 1.0% by mass. On the other hand, the lower limit of the In content is 0.01% by mass, and if it is less than 0.01% by mass, the content is too small and the effect of inclusion is not substantially exhibited. If the In content is 0.1% by mass or more and 0.7% by mass or less, the above-described effects due to the inclusion of In are more apparent, which is preferable.

<Ni>
Ni is an element that is appropriately contained for improving or adjusting various properties in the present invention, and the main effect of containing Ni is to improve workability, reliability and the like by crystal refining. Ni hardly dissolves in Al. Ni has a very high melting point of 1455 ° C. When Ni melts and cools the solder alloy containing Ni due to its high melting point, Ni dispersed in the molten solder alloy is first precipitated, and this serves as a nucleus to grow crystals. For this reason, there is a crystal refinement effect, and reliability and the like can be improved. However, if a large amount of Ni is contained, the crystal becomes coarse, or a large amount of intermetallic compounds are produced and become too hard. For this reason, the upper limit of Ni content is 0.7 mass% or less. On the other hand, the lower limit of the Ni content is 0.01% by mass, and if it is less than 0.01% by mass, the content is too small and substantially no effect appears. If the Ni content is 0.1% by mass or more and 0.5% by mass or less, it is preferable because the above-described effect of adding Ni appears more remarkably.

<Ge, Mg, Sb>
Ge, Mg, and Sb are elements that are appropriately contained in the present invention in order to improve or adjust various properties. The main effects of containing these elements are almost the same, and the improvement is in wettability. Ge produces an eutectic alloy composed of an Al solid solution and a Ge solid solution, and the eutectic temperature is 420 ° C. And eutectic alloy is made with Cu. Thus, Ge that forms a eutectic alloy with Al or Cu, which is the main component of the solder alloy of the present invention, is contained in the solder alloy, so that the workability is not lowered and the content of Al that is relatively easily oxidized. It is possible to improve the wettability by lowering.

  The Ge content exhibiting such an effect is not less than 0.01% by mass and not more than 10.0% by mass. When the Ge content is less than 0.01% by mass, the effect of inclusion does not appear substantially. When the Ge content exceeds 10.0% by mass, the influence of the hard and brittle nature of Ge, which is a semimetal, starts to become noticeable. And reduce reliability. Furthermore, it is preferable if the Ge content is 0.3 mass% or more and 7.0 mass% or less because the effect of containing Ge described above appears more remarkably.

  Mg is an element with very strong reducibility. For this reason, when Mg is contained in the solder alloy, Mg is oxidized by itself to form a thin oxide layer on the solder surface, thereby improving the wettability of the solder alloy. Furthermore, since Mg dissolves in several mass% in Al and also dissolves in Cu several mass%, the strength of the solder alloy can be increased by solid solution strengthening. Although Mg has such excellent characteristics, Mg makes many intermetallic compounds with other metals, and generally this Mg intermetallic compound is very hard, so Mg is contained in the solder alloy in a large amount. It is not possible.

  For the above reasons, the Mg content is 0.01% by mass or more and 0.5% by mass or less. If the Mg content is less than 0.01% by mass, the effect of inclusion does not substantially appear. If the Mg content exceeds 0.5% by mass, the effect of solid solution strengthening increases or the amount of intermetallic compounds produced increases. It becomes too hard and causes cracking of the chip. If the Mg content is 0.1% by mass or more and 0.3% by mass or less, it is preferable because the above-described effect of adding Mg appears more remarkably.

  Sb forms an AlSb intermetallic compound having a high melting point of 1063 ° C. with Al. And it dissolves in Cu several percent. The effect of containing Sb is improvement of wettability. That is, wettability can be improved by reducing the Al content by incorporating Sb into the solder alloy. However, if the Sb content is too high, an intermetallic compound having a high melting point is formed, and during the joining, particles of the high melting intermetallic compound cause tilting of the chip, or the solid intermetallic compound causes the molten solder to melt away. Or segregate. For this reason, the upper limit of content of Sb is 5.0 mass%. On the other hand, the lower limit of the Sb content is 0.01% by mass, and if it is less than this value, the effect of containing Sb does not substantially appear. If Sb content is 0.5 mass% or more and 3.0 mass% or less, since the effect by containing Sb mentioned above appears more notably, it is preferable.

<P>
P is an element appropriately contained for improving or adjusting various properties in the present invention, and its main effect is improvement of wettability. The mechanism by which P improves wettability is as follows. That is, P is more reducible than Al and Cu, and suppresses oxidation of the solder alloy surface by oxidizing itself during bonding. Moreover, P has a function of carrying oxygen away from the bonding surface or solder as gaseous phosphorus oxide, and can reduce and remove the Cu substrate and the Ni plating surface oxide film. For this reason, wettability can be improved without using a forming gas (a gas containing hydrogen to reduce the oxide film on the substrate) during bonding. As described above, P has an extremely high wettability improving effect. Therefore, when sufficient wettability cannot be secured in the solder for sealing a crystal resonator that requires excellent wettability, P is used. The effect of improving wettability due to the inclusion is large.

  In addition, the inclusion of P also has the effect of reducing the generation of voids during bonding. That is, as described above, oxidation of P proceeds preferentially over Al and Cu, which are the main components of the solder alloy at the time of joining, so that the solder mother phase is prevented from being oxidized and the joint surfaces of electronic parts and the like are reduced and wetted. Sex can be secured. As a result, since the solder and oxides on the surface of the joint surface are eliminated, gaps (voids) formed by the oxide film are less likely to be generated, and jointability, reliability, and the like can be improved. Note that when P is reduced to an oxide by reducing a solder alloy such as Al or Cu or a substrate, it is vaporized and flowed into the atmosphere gas, so that it does not remain on the solder or the substrate surface. For this reason, there is no possibility that the residue of P adversely affects reliability and the like, and P can be said to be an excellent element from this point.

  Content in the case of containing P shall be 0.5000 mass% or less. Since P is very reducible, the effect of improving wettability can be obtained if it is contained even in a trace amount. However, even if the content exceeds 0.5000% by mass, the effect of improving the wettability does not change so much, and excessive inclusion may generate a large amount of P or P oxide gas and increase the void ratio. There is a possibility that P forms a fragile phase and segregates, embrittles the solder joint and reduces reliability. In particular, it has been confirmed that wire breakage is likely to occur when processing into a shape such as a wire. If it is 0.3000 mass% or less, the effect appears further and it is preferable.

  As raw materials, Al, Cu, Ag, Sn, Zn, In, Ni, Ge, Mg, Sb, P, and Au each having a purity of 99.9% by mass or more were prepared. Large flakes and bulk-shaped raw materials were reduced to a size of 3 mm or less by cutting and crushing while paying attention to ensure that the alloy after melting did not vary in composition depending on the sampling location. Next, a predetermined amount of each of these raw materials was weighed and placed in a graphite crucible for a high-frequency melting furnace.

  The crucible containing the various raw materials was placed in a high-frequency melting furnace, and nitrogen gas was flowed at a flow rate of 0.7 liter / min or more per kg of the raw material in order to suppress oxidation. In this state, the melting furnace was turned on to heat and melt the raw material. When the metal began to melt, it was stirred well with a mixing rod and mixed uniformly so as not to cause local compositional variations. After confirming sufficient melting, the high frequency power supply was turned off, the crucible was quickly taken out, and the molten metal in the crucible was poured into the mold of the solder mother alloy. A mold having the same shape as that generally used in the production of a solder mother alloy was used.

  In this way, each Pb-free Al—Cu solder mother alloy of Samples 1 to 48 was produced by changing the mixing ratio of the above various raw materials. The composition of the obtained samples 1 to 48 was subjected to composition analysis using an ICP emission spectroscopic analyzer (SHIMAZU S-8100). The obtained composition analysis results are shown in Tables 1 and 2 below.

  Each solder mother alloy of Samples 1 to 48 was processed into a ball shape using a submerged atomizer by the following method. As the liquid at that time, oil having a large effect of suppressing the oxidation of the solder alloy was used. The obtained balls of each sample were classified into a predetermined particle size by the following method, the yield was examined, and the workability was evaluated.

<Ball manufacturing method>
Each mother alloy (diameter 24 mm, length 80 mm) of the prepared samples 1 to 48 was put into a nozzle of a submerged atomizer, and this nozzle was heated to 380 ° C. above the quartz tube containing oil (of the high frequency melting coil). Middle). The mother alloy in the nozzle was heated to 650 ° C. by high frequency and held for 3 minutes, and then atomized by applying pressure to the nozzle with an inert gas to obtain a ball-shaped solder alloy. The ball diameter was set to 0.30 mm, and the nozzle tip diameter was adjusted in advance.

<Evaluation of workability (ball yield)>
In order to evaluate the workability of the solder alloy, the balls obtained by the above method using a biaxial classifier are classified within a range of diameter of 0.30 ± 0.015 mm, and the yield of the balls obtained by classification is determined. It was calculated by the following calculation formula 1.

[Calculation Formula 1]
Ball yield (%) = ball weight of diameter 0.30 ± 0.015 mm ÷ classified ball weight × 100

  Next, using each of the ball-shaped solder alloys of Samples 1 to 48 described above, after bonding to the substrate, the aspect ratio of the solder after bonding was measured by the method shown below to evaluate wettability, The void ratio was measured to evaluate the bondability. Furthermore, reliability evaluation by the heat cycle test was performed by the method shown below using the board | substrate and solder joined body obtained by the said joining test.

<Evaluation of wettability (measurement of aspect ratio)>
A laser soldering apparatus (manufactured by Apollo Seiko Co., Ltd.) was started and nitrogen gas was allowed to flow at a flow rate of 50 L / min. Then, a Cu substrate 1 having a Ni plating layer 2 (film thickness: 3.0 μm) (plate thickness: 0.3 mm) is automatically conveyed to a laser irradiation unit, and then a ball sample is supplied to the Ni-plated Cu substrate. After being heated and melted by laser for 0.3 seconds after being placed on the substrate 1, the Cu substrate 1 is automatically conveyed from the laser irradiation unit and cooled by a conveyance unit in which a nitrogen atmosphere is maintained and sufficiently cooled. Removed into the atmosphere.

  The aspect ratio of the solder alloy 3 was determined for the obtained joined body, that is, the joined body in which the solder alloy 3 was joined to the Ni layer 2 of the Cu substrate 1 as shown in FIG. Specifically, the maximum solder height Y shown in FIG. 3, the maximum solder wetting spread length X1 and the minimum solder wetting spread length X2 shown in FIG. 4 were measured, and the aspect ratio was calculated by the following calculation formula 2. It can be determined that the higher the aspect ratio, the thinner the joined solder and the wider the area, and the better the wettability.

[Calculation Formula 2]
Aspect ratio = [(X1 + X2) ÷ 2] ÷ Y

<Evaluation of bondability (measurement of void fraction)>
For the joined body shown in FIG. 2 obtained in the same manner as in the evaluation of the wettability, the void ratio of the Cu substrate to which the solder alloy is joined is measured using an X-ray transmission device (TOSMICRON-6125, manufactured by Toshiba Corporation). Measured. Specifically, X-rays were transmitted vertically through the joint surface of the solder alloy and the Cu substrate from above, and the void ratio was calculated using the following calculation formula 3.

[Calculation Formula 3]
Void ratio (%) = void area / (void area + solder alloy / Cu substrate bonding area) × 100

<Reliability evaluation (heat cycle test)>
The joined body shown in FIG. 2 obtained in the same manner as in the evaluation of the wettability was repeated a predetermined number of cycles, with -40 ° C. cooling and 250 ° C. heating taken as one cycle. Thereafter, the Cu substrate to which the solder alloy was bonded was embedded in the resin, cross-section polishing was performed, and the bonding surface was observed with SEM (S-4800, manufactured by Hitachi, Ltd.). The case where the joint surface was peeled off or the solder alloy was cracked was indicated as “X”, and the case where there was no such defect and the same joint surface as in the initial state was maintained as “◯”. The evaluation results are shown in Tables 3 and 4 below together with the results of the above-mentioned ball yield (workability evaluation), aspect ratio (wetability evaluation), and void ratio (bondability evaluation).

  As can be seen from Tables 3 and 4 above, the solder alloys of Samples 1 to 33 of the present invention all show good characteristics in each evaluation item. That is, the ball yield, which is an evaluation of workability, is high, and sample 47 (Au-12.5 mass% Ge) and sample 48 (Au-20 mass% Sn) of comparative examples currently used as Au-based solder are used. Even if it compares, it turns out that it is a high yield. Further, all the aspect ratios were 6.3 or more, the solder was thin and widely spread, and had good wettability. The highest void ratio was 0.2%, indicating good bondability. And in the heat cycle test which is a test regarding reliability, no defect appeared even after 500 cycles, and good results were obtained.

  On the other hand, each of the solder alloys of the samples 34 to 46 (excluding the samples 47 and 48 among the comparative examples), which is a comparative example, resulted in an undesirable result in at least one of the characteristics. That is, even if the ball yield was high, it was 43%, which was lower than that of all the samples of the present invention, and the void ratio was 2.5 to 7.3%, which was clearly worse than that of all the samples of the present invention. All the aspect ratios were 5.2 or less, and it was 4.0 or less excluding the sample 34. In the heat cycle test, defects occurred in all samples at 300 times. In addition, it is clear that the solder alloys of Samples 1 to 33 of the present invention do not contain Au and are very inexpensive, and can be said to be a highly practical solder alloy.

Claims (10)

  A Pb-free Al—Cu solder alloy, characterized in that the Cu content is 24.0% by mass or more and 42.0% by mass or less, and the balance is Al and inevitable impurities.   It further contains one or more of Ag, Sn and Zn, and when it contains Ag, its content is 0.01 mass% or more and 8.0 mass% or less, and when it contains Sn, its content 2 is 0.01 mass% or more and 3.0 mass% or less, and when Zn is contained, the content thereof is 0.01 mass% or more and 20.0 mass% or less. Pb-free Al—Cu solder alloy.   The Pb-free Al-Cu solder alloy according to claim 1 or 2, further comprising 0.01 mass% or more and 1.0 mass% or less of In.   The Pb-free Al-Cu solder alloy according to any one of claims 1 to 3, further comprising Ni in an amount of 0.01 mass% to 0.7 mass%.   It further contains at least one of Ge, Mg and Sb, and when it contains Ge, its content is 0.01 mass% or more and 10.0 mass% or less, and when it contains Mg, its content Is 0.01 mass% or more and 0.5 mass% or less, and when Sb is contained, the content thereof is 0.01 mass% or more and 5.0 mass% or less. The Pb-free Al—Cu solder alloy according to any one of the above.   The Pb-free Al—Cu solder alloy according to claim 1, further comprising P in an amount of not more than 0.5000 mass%.   It has the Si semiconductor element, SiC semiconductor element, or GaN semiconductor element joined using the Pb free Al-Cu type solder alloy of any one of Claims 1-6, It is characterized by the above-mentioned. To be joined.   A semiconductor device comprising the joined body according to claim 7 mounted thereon.   A crystal resonator sealing element, wherein the crystal resonator is sealed using the Pb-free Al—Cu solder alloy according to claim 1.   An electronic component comprising the crystal resonator sealing element according to claim 9.

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