JP2014024109A - Bi-Sb-BASED Pb-FREE SOLDER ALLOY - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a Bi-Sb-based Pb-free solder alloy having a melting point exceeding 265°C, materially withstanding a reflow temperature of about 270°C, and having excellent processability.SOLUTION: A Bi-Sb-based Pb-free solder alloy contains: Bi as a main component; Sb by 0.1-9.0 mass%; and at least one kind among Ag, Al, Zn, Sn, and Cu. When Ag is contained, its content is 0.01-4.00 mass%, and similarly for the rest, an Al content is 0.01-1.50 mass%, a Zn content is 0.1-5.0 mass%, a Sn content is 0.01-3.50 mass%, and a Cu content is 0.01-2.00 mass%.

Description

  The present invention relates to a high-temperature Pb-free solder alloy, and particularly to a Bi—Sb-based Pb-free solder alloy having a high melting point.

  In recent years, regulations on chemical substances harmful to the environment have become more and more stringent, and this regulation is no exception for solder materials used for the purpose of bonding semiconductor elements and the like to substrates. Pb has been used as a main component for solder materials for a long time, but Pb has already been a regulated substance under the Rohs Directive. For this reason, development of the solder which does not contain Pb, what is called Pb free solder, is performed actively.

  Solder used when bonding a semiconductor element to a substrate is roughly classified into high temperature (about 260 ° C. to 400 ° C.) and medium / low temperature (about 140 ° C. to 230 ° C.) depending on the limit temperature of use. Regarding the solder material, Pb-free solder mainly composed of Sn has been put into practical use. For example, in Patent Document 1, Sn is the main component, Ag is 1.0 to 4.0 mass%, Cu is 2.0 mass% or less, Ni is 0.5 mass% or less, and P is 0.2 mass%. Pb-free solder alloy compositions containing up to 10% are described. Patent Document 2 describes a Pb-free solder having an alloy composition containing 0.5 to 3.5% by mass of Ag, 0.5 to 2.0% by mass of Cu, and the balance being Sn.

  On the other hand, various research and development have been conducted on high-temperature Pb-free solder materials. For example, Patent Document 3 includes Bi / Ag containing 30 to 80% by mass of Bi and having a melting temperature of 350 to 500 ° C. Brazing material has been proposed. Patent Document 4 contains Zn in an amount of 0.4% to 13.5% by mass, Cu in an amount of 0.05% to 2.0% by mass, and P contains 0.5% by mass. There is described a Pb-free solder alloy which is not contained in excess and the balance is made of Bi except for inevitable impurities.

  Further, in Patent Document 5, a structure including a hole, an inner surface electrode formed on the inner wall of the hole, a lead wire inserted into the hole, and the inner electrode and the lead wire filled with the hole are fixed. It is composed of solder that does not contain lead, and the solder is composed of an alloy that does not shrink in volume during solidification, so that cracks do not occur at the interface between the inner surface electrode and the hole inner wall of the structure or inside the structure. An environmentally friendly soldering structure having sufficient inner surface electrode strength and containing no lead, and a feedthrough ceramic capacitor are described.

JP 1999-077366 JP-A-8-215880 JP 2002-160089 Japanese Patent No. 4807465 JP2007-181880

  As described above, many researches and developments have been made on Pb-free solder materials for high temperatures, but there are still points to be improved. That is, since a material having a relatively low heat-resistant temperature such as a thermoplastic resin or a thermosetting resin is generally used for a printed circuit board, the working temperature is preferably less than 400 ° C. when directly mounting a semiconductor element. Needs to be 370 ° C. or lower. However, for example, the Bi / Ag brazing material described in Patent Document 3 has a liquidus temperature as high as 400 to 700 ° C., so it is estimated that the working temperature at the time of joining is 400 to 700 ° C. or higher. It will exceed the heat resistance temperature of the substrate.

  Further, in the case of a solder alloy containing Bi as a main component, when bonding a semiconductor element to a substrate on which a Ni plating is formed on the semiconductor element mounting portion in order to enhance the bondability with the solder alloy, the bonding characteristics are caused by the reaction between Bi and Ni. There is a problem peculiar to Bi-based solder alloys in that the bonding characteristics deteriorate due to residual stress resulting from expansion during solidification of Bi. Specifically, the Ni layer reacts rapidly with Bi contained in the solder alloy to form a brittle alloy of Ni and Bi, and the Ni layer breaks or peels off and Ni diffuses into Bi. Strength will fall remarkably. A layer such as Ag or Au may be provided on the Ni layer. In this case, Ag or Au is thin because it aims to prevent oxidation of the Ni layer and improve the wettability of the solder, and immediately diffuses into the solder alloy. Therefore, there is almost no effect of suppressing Ni diffusion.

  As means for solving the problems peculiar to the above-described Bi-based solder alloy, the above-mentioned Patent Document 4 describes the fact that Zn reacts with the Ni layer preferentially over Bi to form an alloy. It is described that reaction and Ni diffusion into Bi are suppressed. This Bi-Zn solder alloy can withstand practical use, but it is considered that there is still room for improvement. For example, in the case of Bi—Zn solder alloy, the solidus temperature is 254.5 ° C., and the reflow temperature that can be endured is theoretically 254 ° C., and the temperature of the solder part is substantially lower than the reflow temperature in many cases. Therefore, it is estimated that the temperature is about 255 ° C to 265 ° C.

  However, the bonding conditions of the semiconductor element are various, and in some cases, the solder can withstand a reflow temperature exceeding about 270 ° C., that is, a solder capable of withstanding a reflow temperature higher than that which a Bi—Zn based solder alloy can withstand. There is a need for materials. Further, when the reaction between Ni and Bi is relatively difficult to proceed, such as when the Ni layer of the substrate is thin or the heating time at the time of bonding is short, or when the use environment as a semiconductor device is loose, the reaction between Ni and Bi proceeds to some extent. However, it is thought that the reliability which can be put into practical use can be obtained.

  Thus, a solder material that can withstand a reflow temperature higher than the temperature that the Bi—Zn-based solder alloy can withstand, for example, a reflow temperature exceeding 265 ° C., and does not need to completely suppress the reaction between Ni and Bi. Although there is a need, a Bi—Sb solder alloy can be cited as a material satisfying such characteristics. However, Bi—Sb based solder alloys are not sufficient to remarkably improve the characteristics of Bi by the addition of Sb because Sb exhibits properties similar to Bi.

  Particularly problematic is the workability of Bi—Sb solder alloys. Since Sb is very brittle like Bi, the elongation rate is 1% or less even for a Bi-Sb alloy. With such a small elongation rate, it is difficult to mass-produce into a shape actually used as a solder, for example, a wire shape. Patent Document 5 also describes this Bi—Sb solder alloy. As a feature of the alloy, the Bi—Sb alloy is solidified by alloying Bi with Sb by utilizing the expanding property of Bi during solidification. It is stated that it is possible to provide sufficient strength of the inner surface electrode without cracking at the interface between the inner surface electrode and the inner wall of the hole of the structure or the inside of the structure without contracting.

  However, according to the experiments by the present inventors, the elongation of the Bi-Sb alloy is 0.01 mass%, 0.3 mass%, 1.2 mass%, 3.1 mass%, and 4%. In each of the Bi-Sb alloys of 0.7 mass% and 6.5 mass%, the maximum was 2.1%, and most alloys were 1% or less. Therefore, with the Bi-Sb solder alloy described in Patent Document 5, even if solidification shrinkage can be improved, an elongation rate and excellent workability that can be mass-produced cannot be obtained, and high reliability is obtained. Is also considered difficult.

  As described above, when a semiconductor element and a substrate are bonded using a high-temperature Bi-based solder alloy that does not contain Pb, for example, the solidus temperature is 1 ° C. higher than that of a Bi—Zn-based solder alloy. There is a need for a solder material that can be processed into a wire shape or the like that allows the reaction between Ni and Bi of the solder alloy to be acceptable under predetermined conditions such as the thickness of the Ni layer.

  The present invention has been made in view of such circumstances, and in a Pb-free Bi-based solder alloy, it has a liquidus temperature exceeding 265 ° C. and can withstand a reflow temperature of about 270 ° C. An object of the present invention is to provide a Bi—Sb-based Pb-free solder alloy capable of suppressing the reaction between Ni and Bi and the diffusion of Ni into Bi to an acceptable level and having excellent workability.

  In order to achieve the above object, the Bi—Sb-based Pb-free solder alloy provided by the present invention contains Bi as a main component, and contains Sb in an amount of 0.1% by mass to 9.0% by mass, and Ag, Al, A Bi—Sb-based Pb-free solder alloy containing at least one of Zn, Sn, and Cu, and when containing Ag, the content is 0.01 mass% or more and 4.00 mass% or less, and Al is contained. In the case where the content is 0.01 mass% or more and 1.50 mass% or less, in the case where Zn is contained, the content is 0.1 mass% or more and 5.0 mass% or less, and in the case where Sn is contained, the content is 0 0.01 mass% or more and 3.50 mass% or less, and when it contains Cu, the content is 0.01% or more and 2.00 mass% or less.

  In addition, the Bi—Sb-based Pb-free solder alloy according to the present invention described above contains 0 as an optional component in addition to at least one of Bi as a main component and Sb as an essential component, and Ag, Al, Zn, Sn, and Cu. It can be contained up to .500% by mass.

  According to the present invention, as a high-temperature Bi-based solder alloy, it has a liquidus temperature exceeding 265 ° C., withstands a reflow temperature of about 270 ° C., and has practically no problem reliability. A Bi—Sb-based Pb-free solder alloy excellent in workability can be provided. In addition, the Bi—Sb-based Pb-free solder alloy of the present invention suppresses the reaction between the Ni layer formed on the substrate surface and Bi in the solder alloy and the diffusion of Ni into Bi, and the reaction and diffusion progress to some extent. Even so, it is possible to secure the bondability that does not cause a practical problem.

It is explanatory drawing of the method of measuring the diffusion state of Ni by EPNA line analysis about the solder alloy joined on the Cu board | substrate which has Ni layer.

  The Bi—Sb-based Pb-free solder alloy of the present invention contains Bi as a main component and Sb as an essential component, and contains at least one of Ag, Al, Zn, Sn, and Cu. The amount of Ag is 0.01% to 4.0% by weight, Al is 0.01% to 1.50% by weight, Zn is 0.1% to 5.0% by weight, and Sn is 0%. 0.01 mass% or more and 3.50 mass% or less, and Cu is 0.01% or more and 2.00 mass% or less. In addition, the Bi—Sb-based Pb-free solder alloy of the present invention can further contain P up to 0.500% by mass as necessary.

  As described above, the Bi—Sb-based Pb-free solder alloy of the present invention contains Bi as a main component and Sb as an essential component, thereby increasing the liquidus temperature and the solidus temperature to 270 ° C. or higher. it can. And various characteristics, such as workability and stress relaxation property, can be adjusted by selecting and containing 1 or more types from Ag, Al, Zn, Sn, and Cu. Below, each element related to the Bi-Sb system Pb free solder alloy of this invention is demonstrated in detail.

<Bi>
Bi is the main component of the high-temperature Pb-free solder alloy according to the present invention, that is, the first element. Bi belongs to the group 5B elements (N, P, As, Sb, Bi), and its crystal structure is a trigonal crystal (rhombohedral crystal) with a low symmetry and is a very brittle metal. It can be easily seen that the fracture surface is a brittle fracture surface. That is, pure Bi was poor in ductile properties, and the experimental results showed that the elongation rate of Bi was less than 1.0%.

  Bi is a special metal that expands during solidification, and the shrinkage rate during solidification (-means expansion and + means contraction) is -3.2% to -3.4%. Due to this expansion, residual stress is generated in the solder, which decreases the bonding strength and reliability. In addition, Bi has a problem that it easily reacts with Ni to form a brittle alloy and deteriorates the bondability and the like.

  On the other hand, Bi has a melting point of 271 ° C., which exceeds the reflow temperature of about 260 ° C., which is the use condition of the high-temperature solder. In order to take advantage of this advantage, by incorporating Sb described below, a basic alloy system in the Bi-Sb Pb-free solder alloy according to the present invention is obtained.

<Sb>
Sb is a second element that is an essential component of the high-temperature Pb-free solder alloy according to the present invention, and is contained for the purpose of further increasing the melting point of Bi at 271 ° C. Sb belongs to the same group 5B element as Bi, and its crystal structure is the same trigonal crystal as Bi. Since Bi and Sb are similar elements in this way, they are completely dissolved. Since the melting point of Sb is 631 ° C. and higher than Bi, when Sb is contained in Bi, the liquidus temperature and the solidus temperature rise monotonously. Therefore, Sb is the most suitable metal for adjusting the melting point of the Bi-based solder alloy in a region higher than the melting point of Bi. Furthermore, Sb also has an effect of suppressing the diffusion of Ni, and prevents the Ni layer formed on the substrate surface from becoming extremely thin during solder bonding.

  The Sb content in the solder alloy of the present invention is 0.1% by mass or more and 9.0% by mass or less. If the Sb content is less than 0.1% by mass, the content is too small, so that the effect of increasing the melting point of Bi cannot be substantially obtained. On the other hand, if the Sb content exceeds 9.0% by mass, the difference between the liquidus temperature and the solidus temperature becomes 50 ° C. or more, and a solder melting phenomenon occurs. In order to suppress the solder melting phenomenon as much as possible and to realize a better bonding, it is particularly preferable that the Sb content is 5.0% by mass or less.

  Thus, although the effect of adding and containing Sb is large, since Sb is similar in nature to Bi, the effect of improving the brittleness of Bi cannot be expected. Therefore, it is essential that the high-temperature Pb-free solder alloy of the present invention contains at least one element selected from the following third element group (Ag, Al, Zn, Sn, Cu). It is.

<Ag>
Ag is one of the elements of the third element group, and is very preferable as a metal to be contained for the purpose of improving workability and stress relaxation properties because it forms a eutectic alloy with Bi. However, since Ag forms an intermetallic compound with Sb, if the content of Sb and Ag is too large, the effect of improving the brittleness of the Bi—Sb solder alloy cannot be obtained. Furthermore, since the eutectic temperature of Bi—Ag is 262.5 ° C., it is necessary to adjust the Ag content while balancing the melting point and workability.

  The content of Ag in the solder alloy of the present invention is 0.01% by mass or more and 4.00% by mass or less. If the content of Ag is less than 0.01% by mass, the content is too small, so that the effect of adding and containing Ag is not substantially exhibited. On the other hand, if the Ag content exceeds 4.00% by mass, a large amount of brittle Sb-Ag intermetallic compounds are formed, and good bonding properties and reliability cannot be obtained, and the melting point becomes low. It is not preferable.

<Al>
Al is one of the elements of the third element group, is a soft metal, hardly dissolves in Bi, and forms a Bi—Al alloy to rapidly increase the melting point with a small content. Considering these effects in total, Al is an element that is preferably contained in a small amount. That is, by containing a small amount of Al, workability can be improved and the melting point can be further increased. In addition, when Zn, which will be described later, is added and contained, a Zn—Al eutectic alloy can be formed to further improve the workability.

  The Al content in the solder alloy of the present invention is 0.01% by mass or more and 1.50% by mass or less. If it is this range, desired melting | fusing point, workability, stress relaxation property, etc. will be obtained. When the Al content is less than 0.01% by mass, the above-described effect of adding and containing Al does not substantially appear. On the other hand, if the Al content exceeds 1.50 mass%, the particle size of the Al-rich phase becomes coarse and embrittles, or the liquidus temperature becomes too high, which is not preferable.

<Zn>
Zn is one of the elements of the third element group described above, and is preferable as a metal to be contained in the Bi—Sb alloy for the purpose of improving workability and stress relaxation properties in order to form a eutectic alloy with Bi as with Ag. . However, since Zn forms an intermetallic compound (Zn ₃ Sb ₂ ) having a high melting point with Sb, the content thereof needs to be taken into consideration. Since Zn ₃ Sb ₂ has a high melting point, it is easily generated at the bonding interface when the semiconductor element and the substrate are bonded. That is, Zn ₃ Sb ₂ is likely to be formed at the bonding interface where the temperature is low or cools the earliest during cooling. Then, the Zn ₃ Sb _2, like the common intermetallic compounds brittle, because poor stress relaxation properties, becomes liable to be cracked in the bonding interface.

The Zn content in the solder alloy of the present invention is 0.01 mass% or more and 5.00 mass% or less. The reason why the Zn content is within the above range is that if it exceeds 5.00 mass%, the above-described brittle intermetallic compound Zn ₃ Sb ₂ is generated in a large amount at the bonding interface, although it depends on the Sb content. It is. Moreover, if Zn content is less than 0.01 mass%, since the content is too small, the effect of addition inclusion does not appear.

<Sn>
Sn is one of the elements of the third element group and is preferably contained for the purpose of improving workability and stress relaxation properties in order to form a eutectic alloy with Bi, but it generates a low melting point phase. Therefore, it cannot be contained in large quantities. However, depending on the combination with other additive elements, 3% by mass or more can be contained. For example, the solidus temperature of a Bi—Sn alloy is 139 ° C., whereas the solidus temperature of an Ag—Sn alloy exceeds 700 ° C. Depending on the combination and content of such elements, and actual bonding conditions and use environment, Sn can be contained in an amount of 3% by mass or more.

  The Sn content in the solder alloy of the present invention is 0.01 mass% or more and 3.50 mass% or less. If the Sn content is less than 0.01% by mass, the content of the Sn content is too small, so that the effect of addition and inclusion does not appear. On the other hand, if the content exceeds 3.50% by mass, it is substantially difficult to withstand the reflow temperature, which is called high temperature, even if other elements are contained.

<Cu>
Cu is one of the elements of the third element group and exhibits an effect similar to Al. That is, Cu is a soft metal and hardly dissolves in Bi. In addition, the Bi-Cu alloy rapidly raises the melting point with a slight Al content. Because of these properties, the effect of improving workability and stress relaxation properties and increasing the melting point can be expected by adding a small amount of Cu.

  The content of Cu in the solder alloy of the present invention is 0.01% by mass or more and 2.00% by mass or less. If it is content of this range, there is no segregation of Cu or Cu compound, and desired workability, stress relaxation property, etc. can be obtained.

<P>
P is an element that may be contained as necessary, and the inclusion of P can further improve the wettability and bondability of the solder alloy of the present invention. The reason why the effect of improving wettability is increased by the addition of P is that P is very reducible and suppresses oxidation of the surface of the solder alloy by oxidizing itself.

  Furthermore, the addition of P has the effect of reducing the generation of voids during bonding. That is, as described above, since P easily oxidizes itself, oxidation proceeds preferentially over Bi, which is the main component of solder, at the time of bonding. As a result, oxidation of the solder mother phase can be prevented and wettability can be ensured, so that good bonding is possible and voids are hardly generated.

  P is very reducible, so even if it is added in a small amount, it exhibits the effect of improving wettability. However, even if it is added in a certain amount or more, the effect of improving wettability is saturated and does not change. There is a possibility that an oxide is generated on the solder surface, or P forms a brittle phase and becomes brittle. Therefore, the addition of P is preferably a trace amount.

  Specifically, the upper limit of the P content in the solder alloy of the present invention is 0.500% by mass. If P exceeds the upper limit of 0.500% by mass, the oxide of P covers the solder surface and conversely reduces wettability. Furthermore, since P has a very small amount of solid solution in Bi, if the content is large, brittle P oxide is segregated, and reliability is lowered. In particular, when processing into a wire shape, it tends to cause disconnection.

  The Bi-Sb-based Pb-free solder alloy for high temperature according to the present invention is practically used even when used under conditions such as an environment in which a heat cycle is repeated by being used for joining a semiconductor element and a substrate. It is possible to provide a semiconductor element assembly having no problem with durability and reliability. Moreover, when there is no Ni layer on the bonding surface of the substrate, the reaction between Ni and Bi and the diffusion of Ni into Bi under certain conditions, such as when the Ni layer is thin or when the Ag layer is formed on the Ni layer, etc. Can be suppressed to an acceptable level. Therefore, this semiconductor element assembly can be mounted on, for example, power semiconductor devices such as thyristors and inverters, various control devices mounted on automobiles, devices used in solar cells, and the like.

  As raw materials, Bi, Sb, Ag, Al, Zn, Sn, Cu having a purity of 99.9% by mass or more and P having a purity of 99.95% by mass or more were prepared. Large flakes and bulk-shaped raw materials were cut and pulverized, etc. so as to be uniform with no variation in composition depending on the sampling location in the alloy after melting, and were reduced to a size of 3 mm or less. Next, a predetermined amount of these raw materials was weighed and put into a graphite crucible for a high-frequency melting furnace.

  The crucible containing the raw material 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. In particular, when P is added, since P is easily oxidized, the flow rate of nitrogen gas is set to 1.2 liter / min or more per kg of the raw material. When the starting metal began to melt, it was thoroughly stirred 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 removed, and the molten metal in the crucible was poured into the solder mother alloy mold. A mold having the same shape as that generally used in the manufacture of solder alloys was used.

  Thus, each solder mother alloy of samples 1-22 was produced by changing the mixing ratio of each raw material. About each solder mother alloy of these samples 1-22, while analyzing a composition using an ICP emission spectroscopic analyzer (SHIMAZU, S-8100), liquidus temperature is measured using a differential scanning calorimeter (DSC). did. The obtained analysis results and measurement results are shown in Table 1 below.

  Next, for each of the solder mother alloys of Samples 1 to 22 shown in Table 1 above, evaluation of wire processability, evaluation of wettability (bondability), and EPMA line analysis (evaluation of Ni diffusion prevention effect) shown below. And a heat cycle test (evaluation of reliability). The evaluation of solder wettability and the like does not depend on the solder shape, and may be evaluated by the shape of a wire, a ball, a paste, or the like.

<Evaluation of wire workability>
Each solder mother alloy of Samples 1 to 22 shown in Table 1 above was set in an extruder and processed into a wire having an outer diameter of 0.75 mm. Specifically, the extruder was heated in advance to a temperature suitable for the solder composition, and each solder mother alloy was set. Since the wire-like solder extruded from the extruder outlet is still hot and easily oxidizes, the outlet of the extruder has a sealed structure, and an inert gas is allowed to flow therethrough.

  The extruder increased the pressure with hydraulic pressure and pushed out the solder mother alloy into a wire shape. The wire extrusion speed was adjusted in advance so that the wire was not cut or deformed, and at the same time, the wire was wound at the same speed using an automatic winder.

  In this way, each of the solder mother alloys of Samples 1 to 22 was processed into a wire shape, and when the obtained wire-shaped solder was wound up by 50 m with an automatic winder, the case where the wire was not disconnected once The case where “◯” was broken 1-3 times was evaluated as “Δ”, and the case where it was broken four times or more was evaluated as “x”. The obtained results are shown in Table 2 below.

<Evaluation of wettability (bondability)>
The wettability (joinability) evaluation was performed using each wire-shaped solder alloy of Samples 1 to 22 obtained by the above-described evaluation of wire workability. First, the wettability tester (device name: atmosphere control type wettability tester) is started, a double cover is applied to the heater part to be heated, and nitrogen gas is supplied from four locations around the heater part at a flow rate of 12 liters / minute. Washed away. Thereafter, the heater was set to 310 ° C. and heated.

  After the heater temperature was stabilized at 310 ° C., a Cu substrate (plate thickness: 0.15 μm) on which a Ni plating layer (layer thickness: 4.0 μm) and an Ag vapor deposition layer (layer thickness: 0.15 μm) were formed on the substrate surface. About 0.70 mm) was set in the heater section and heated for 10 seconds. Next, the solder alloy was placed on the Cu substrate and heated for 10 seconds. After the heating was completed, the Cu substrate was picked up from the heater part, temporarily moved to a place where the nitrogen atmosphere next to the Cu substrate was maintained, and cooled. After sufficiently cooling, it was taken out into the atmosphere and a joint portion between the Cu substrate and the solder was confirmed.

  Regarding the evaluation of the wettability (bondability), the joint portion between the Cu substrate and the solder was confirmed. When the Cu substrate and the solder could not be joined, “x”, when the joint could be joined but the wetting spread was poor (solder) Was evaluated as “◯”, and the case where the bonding was successful and wet spread (when the solder spread thinly on the Cu substrate) was evaluated as “◯”. The obtained results are shown in Table 2 below.

<EPMA line analysis (evaluation of Ni diffusion prevention effect)>
In order to confirm whether the Ni layer provided on the Cu substrate is thinned by reacting with Bi in the solder alloy or Ni diffuses into Bi, line analysis by EMPA is performed. It was. This analysis was performed using a Cu substrate to which a solder alloy was bonded (that is, a sample having a wettability evaluation of ◯ and Δ) among the Cu substrates obtained by the wettability evaluation.

  First, a Cu substrate to which a solder alloy was bonded in the wettability evaluation was embedded in a resin, and was polished using a polishing machine in order from coarse abrasive paper, and finally buffed. Thereafter, line analysis was performed using EPMA (device name: SHIMADZU EPMA-1600) to examine the diffusion state of Ni and the like. When the cross section of the Cu substrate to which the solder alloy is bonded is viewed from the side, the measuring method is that the bonding surface between the Cu substrate and the Ni layer is the origin 0, and the solder alloy side is the positive direction of the X axis (see FIG. 1). ). In the measurement, five points were arbitrarily measured and the average one was adopted.

  Regarding the evaluation of the Ni diffusion prevention effect by the above EPMA line analysis, the case where Ni reacts with Bi and the Ni layer thickness is reduced by 30% or more, or the Ni is layered and diffused in the solder is “×”. The case where the thickness of the Ni layer was hardly changed from the initial state and Ni was not diffused in the solder was evaluated as “◯”. The obtained results are shown in Table 2 below.

<Heat cycle test (reliability evaluation)>
In order to evaluate the reliability of solder joints, a heat cycle test was conducted. This test was performed using a Cu substrate to which a solder alloy was joined (that is, a sample having a wettability evaluation of ◯ and Δ) among Cu substrates obtained in the same manner as the wettability evaluation.

  First, with respect to the Cu board | substrate with which the solder alloy was joined, -40 degreeC cooling and +125 degreeC heating were made into 1 cycle, and this was repeated by predetermined cycle number (300 times and 500 times). Thereafter, the Cu substrate to which the solder alloy was bonded was embedded in the resin, the cross-section was polished, and the bonded surface was observed by SEM (device name: HITACHI S-4800).

  The reliability evaluation by the heat cycle test indicated that the case where the joint surface was peeled off or the solder was cracked was “x”, and there was no such defect, and the same joint surface as in the initial state was maintained. The case was evaluated as “◯”. The obtained results are shown in Table 2 below.

  As can be seen from Table 2 above, each solder alloy of Samples 1 to 14 which is an example of the present invention shows good characteristics in each evaluation item. That is, even if it was processed into a wire, it could be automatically wound without being cut and showed good workability. Further, the wettability was very good, and in particular, the sample 14 to which P was added spreads very quickly, and thinly spread when the solder alloy contacted the Cu substrate. In addition, the reaction between Bi in the solder alloy and the Ni layer formed on the surface of the substrate and the diffusion of Ni into Bi can be almost prevented, and it is possible to secure the bondability that causes no practical problems. . Furthermore, good results were also obtained in the heat cycle test and the heat resistance test in the air for reliability, and no defects appeared after 500 cycles in the heat cycle test.

  On the other hand, each of the solder alloys of Comparative Examples 15 to 22 that did not satisfy the requirements of the present invention resulted in an unfavorable result in at least one of the above characteristics. That is, when the mother alloy was processed into a wire, it was disconnected at least once, and the wettability was often poor except for the sample 19, and in the heat cycle test, all samples of the comparative example were defective up to 300 times. did.

Claims (2)

  A Bi—Sb Pb-free solder alloy containing Bi as a main component and containing Sb in an amount of 0.1% by mass to 9.0% by mass and containing at least one of Ag, Al, Zn, Sn, and Cu. When Ag is contained, the content is 0.01% by mass to 4.00% by mass, and when Al is contained, the content is 0.01% by mass to 1.50% by mass, and Zn is contained. When the content is 0.1 mass% or more and 5.0 mass% or less, when Sn is contained, the content is 0.01 mass% or more and 3.50 mass% or less, and when Cu is contained, the content is 0. A Bi—Sb-based Pb-free solder alloy characterized by being from 0.01% to 2.00% by mass.   The Bi-Sb-based Pb-free solder alloy according to claim 1, wherein P is contained in an amount of 0.500% by mass or less.

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