JP2013123741A - Pb-free solder alloy having excellent plastic deformation property - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high-temperature Pb-free solder alloy mainly composed of Zn having a melting point of about 300 to 400 ° C., excellent wettability and reliability, particularly excellent workability and stress relaxation properties.
A Pb-free solder alloy having an elongation of 50% or more and a tensile strength of 70 MPa or more, and Al is 1.0% by mass or more and 15.0% by mass or less, preferably 2.0% by mass or more and 9. It is contained in an amount of 0% by mass or less, and contains at least one of Ge, Cu, Ag, Ni, and P as required, and is made of Zn except for elements that are inevitably contained in the balance.
[Selection figure] None

Description

  The present invention relates to a so-called Pb-free solder alloy that does not contain Pb, and particularly relates to a Pb-free solder alloy that is excellent in plastic deformability and that is suitable for high temperature use and contains Zn as a main component.

  Starting with die bonding of power transistor elements, high temperature soldering is performed in soldering in the assembly process of various electronic components, and a solder alloy having a relatively high melting point of about 300 to 400 ° C. (hereinafter referred to as “high temperature”). Also referred to as “solder alloy”. 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 is a regulated substance in the RoHS directive. Corresponding to such a movement, in the field of assembling electronic components and the like, it is required to provide a Pb-free (lead-free) solder alloy, that is, a Pb-free solder alloy.

  As for a solder alloy for medium and low temperatures (about 140 to 230 ° C.), a Pb-free solder alloy containing Sn as a main component has already 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 alloys containing up to 10% are described. Patent Document 2 describes a Pb-free solder alloy 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, Bi-based solder alloys, Zn-based solder alloys, and the like have been developed by various organizations in order to realize Pb-free soldering alloys for high temperatures. For example, for a Bi-based solder alloy, Patent Document 3 discloses a Bi / Ag-based brazing material containing 30 to 80% by mass of Bi and having a melting temperature of 350 to 500 ° C. Patent Document 4 discloses a production method in which a binary eutectic alloy is added to a Bi-containing eutectic alloy and an additive element is further added to adjust the liquidus temperature and reduce variations. Yes.

  As for a Zn-based solder alloy, for example, Patent Document 5 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. ing. Patent Document 5 also describes that there is an effect of further lowering the melting point by further adding Sn or In.

  Specifically, in Patent Document 5, a Zn alloy containing 1 to 9% by mass of Al and 0.05 to 1% by mass of Ge, with the balance being Zn and inevitable impurities; 5 to 9% by mass of Al, Mg Zn alloy composed of 0.01 to 0.5% by mass with the balance being Zn and inevitable impurities; Al is 1 to 9% by mass, Ge is 0.05 to 1% by mass, Mg is 0.01 to 0.5% Zn alloy containing Zn and the balance consisting of Zn and unavoidable impurities; Al containing 1 to 9% by mass; Ge containing 0.05 to 1% by mass; Sn and / or In containing 0.1 to 25% by mass and the balance being Zn alloy composed of Zn and inevitable impurities; Al 1-9 mass%, Mg 0.01-0.5 mass%, Sn and / or In 0.1-25 mass%, the balance Zn and inevitable impurities Zn alloy comprising: Al 1-9 mass%, Ge 0.05-1 mass%, Mg 0.01-0.5 The amount%, Sn and / or In includes 0.1 to 25 wt%, and the balance are described Zn alloy consisting of Zn and unavoidable impurities.

  By the way, the solder is generally required to relax thermal stress. The reason is that, for example, since a joined body obtained by joining a semiconductor chip to a substrate with solder is used in various environments, the stress caused by thermal expansion / contraction of the substrate and the semiconductor chip caused by temperature changes is absorbed by the solder. It is necessary. For example, in Patent Document 6, as a solder material exhibiting excellent thermal stress relaxation properties, Zn containing 17 to 30 wt% Al-0 to 1.5 wt% Cu-0 to 0.5 wt% Mg—Zn is used. -Al eutectoid alloy bonding materials are described. This bonding material is characterized by bonding a target object using a superplastic phenomenon.

Japanese Patent Laid-Open No. 1999-077366 JP-A-8-215880 JP 2002-160089 A JP 2006-167790 A Patent No. 3850135 JP 2009-1113050 A

  Thermoplastic resins and thermosetting resins are often used as substrate materials for general electronic components, so that the working temperature during soldering is preferably less than 400 ° C., more preferably 370 ° C. or less. However, since the Bi / Ag brazing material of Patent Document 3 has a high liquidus temperature of 400 to 700 ° C., it is presumed that the working temperature at the time of bonding is 400 to 700 ° C. or higher, and the substrate material used is durable. It is considered that the temperature exceeds the allowable temperature. In addition, the method of Patent Document 4 becomes a quaternary or higher multi-component solder alloy only by adjusting the temperature of the liquidus, and the fragile mechanical characteristics of Bi are not effectively improved.

  Furthermore, the Zn-based solder alloy disclosed in Patent Document 5 often has insufficient wettability within the composition range. That is, Zn, which is the main component, has a strong reducibility, so that it is easily oxidized by itself, and as a result, the wettability is extremely deteriorated. And since Al is more reducible than Zn, for example, when 1 wt% or more is added, the wettability may be lowered.

  Moreover, it is considered that these oxidized Zn and Al cannot be reduced even if Ge or Sn is added in terms of thermodynamic equilibrium, and the wettability cannot be improved. However, when melting and solidifying in a very short time, such as soldering, the metal reaction is often a non-equilibrium reaction, and not all can be explained by equilibrium theory.

  In addition to the problem of wettability, the Zn-based solder alloy disclosed in Patent Document 5 also has problems with workability and stress relaxation as further important problems in solder bonding. That is, Zn and Al make a eutectic alloy and become a soft alloy with a certain degree of flexibility. However, since the bonding temperature is relatively high (eutectic temperature of Zn—Al alloy: 381 ° C.), after bonding, the semiconductor element mainly composed of Si and the substrate mainly composed of Cu are cooled to room temperature. Since the temperature difference is large, it is greatly affected by the stress due to thermal expansion. Therefore, much better stress relaxation properties are required as compared with the solder for medium and low temperatures.

  As described above, the Zn—Al-based alloy has a preferable melting point of about 300 to 400 ° C. (Zn—Al eutectic temperature: 381 ° C.), but is not necessarily an optimum alloy from the viewpoint of workability. . Further, when Mg or the like is added to the Zn—Al alloy, an intermetallic compound is formed and becomes extremely hard, and there may be a case where good workability and stress relaxation properties cannot be obtained. For example, when Mg is contained in an amount of 5% by mass or more, it is practically impossible to process into a wire shape or a sheet shape that is difficult to process.

  Furthermore, although the Zn-Al eutectoid alloy bonding material described in Patent Document 6 uses a superplastic phenomenon and is considered to be excellent in workability and stress relaxation properties, it contains liquid in an amount of 17 wt% or more. Since the temperature exceeds 460 ° C., the bonding temperature is too high to be used as a semiconductor bonding solder. More specifically, when a semiconductor element or a substrate is bonded using solder, it is necessary to sufficiently react the bonding surface with the solder to form an alloy of the solder and the bonding surface at the bonding interface. For this reason, the joining temperature is generally about 50 ° C. higher than the melting point of the solder. For this reason, the temperature in the case of joining a semiconductor element or the like using the solder of Patent Document 6 is expected to exceed 500 ° C. and exceeds the heat resistance temperature of the semiconductor element or its peripheral components. It can be said that the soldering temperature is too high to be used as a solder.

  As described above, Pb-free solder alloys for high temperatures, especially Pb-free solder alloys containing Zn as the main component, mainly improve workability and stress relaxation while balancing with various properties such as wettability. It has become a big issue, but this issue has not been solved yet. Thus, the actual situation is that a high-temperature solder alloy that can replace a Pb-based solder alloy typified by a conventional Pb-5 mass% Sn alloy has not yet been put into practical use.

  The present invention has been made in view of such circumstances, has a melting point of about 300 to 400 ° C. suitable for use in assembling various electronic components, and has excellent wettability and reliability, particularly workability and stress. An object of the present invention is to provide a Pb-free Zn—Al solder alloy for high temperature, which has excellent relaxation properties and does not contain Pb but contains Zn as a main component.

  In order to achieve the above-mentioned object, the Zn-based Pb-free solder alloy provided by the present invention has an elongation of 50% or more, a tensile strength of 70 MPa or more, and Al of 1.0% by mass or more and 15.0. It is characterized by being composed of Zn except for elements that are contained by mass% or less and the remainder is unavoidably contained.

  The Pb-free solder alloy containing Zn as a main component of the present invention does not contain Ge in excess of 8.00% by mass and Cu does not contain in excess of 3.00% by mass. Preferably, Ag is not included in excess of 4.00 mass%, Ni is not included in excess of 0.80 mass%, and P is not included in excess of 0.5000 mass%, Moreover, it is preferable to manufacture by the manufacturing method accompanied by plastic deformation. As a result, the solder alloy can be further improved in workability and stress relaxation properties.

  Furthermore, the Pb-free solder alloy containing Zn as a main component according to the present invention contains Al in an amount of 2.0% by mass to 9.0% by mass and includes at least one of Ge, Cu, Ag, Ni, and P. In the case of Ge, 0.01 mass% to 8.00 mass%, in the case of Cu, 0.01 mass% to 3.00 mass%, and in the case of Ag, 0.10 mass% to 4.00 mass%. In the case of Ni, it is preferable to contain 0.01 mass% or more and 0.80 mass% or less, and in the case of P, 0.0005 mass% or more and 0.500 mass% or less is preferable.

  According to the present invention, in addition to being excellent in wettability, bondability, reliability, etc., a Pb-free solder alloy that is particularly excellent in workability and stress relaxation properties and can sufficiently withstand a reflow temperature of about 300 ° C. Can be provided. Accordingly, it becomes possible to suitably perform high-temperature soldering in an assembly process of various electronic components such as die bonding of power transistor elements using a Pb-free solder alloy.

  The Pb-free solder alloy containing Zn as a main component according to the present invention does not contain Pb, contains a predetermined content of Al, and the balance is made of Zn except for elements that are inevitably contained in production. The rate is 50% or more, and the tensile strength is 70 MPa or more. This Pb-free solder alloy is preferably manufactured by a manufacturing method involving plastic deformation, and preferably contains at least one of Ge, Cu, Ag, Ni, and P as required.

  Zn has a disadvantage that its melting point is 419 ° C., which is too high for 300 to 400 ° C., which is the bonding temperature of electronic components and the like. In order to cope with such a defect of Zn, in the present invention, the melting point is lowered to a temperature that is easy to use as solder by containing Al. Further, in the joining with solder, when the solder is melted and then cooled and solidified, when it is cooled to the eutectoid temperature (277 ° C.) through the eutectic temperature (381 ° C.), a fine crystal is formed and processed. And stress relaxation properties are improved.

  Thus, by containing Al, an eutectic alloy with Zn is formed to lower the melting point to about 400 ° C. or less, and at the same time, the crystal is refined to improve workability and stress relaxation. Can be obtained. These processability and stress relaxation properties can be further improved by adding various limitations in addition to the addition of Al, as will be described below.

  That is, there are cases where sufficient workability and stress relaxation properties can be obtained by considering the solder manufacturing method. Specifically, at the time of manufacturing the solder, workability and the like can be improved by manufacturing by a processing method involving plastic deformation such as rolling. This is because the structure is refined by plastic deformation, and excellent workability and stress relaxation properties are obtained.

  There are various processing methods, such as press working, tensile working, or rolling work, to make plastic deformation, but in particular, the rolling work is performed at a rolling speed and a reduction ratio (when the work material is rolled and thinned, the thickness is reduced. Many ratios that can be adjusted, such as rolling temperature, and the like, and it is easy to control the crystal grain size and crystal structure. If the rolling temperature is too high, recrystallization will cause the crystal grains to become too large. Conversely, if the rolling temperature is too low, the crystals will be destroyed. Based on the above, a preferable rolling temperature is about 40 to 300 ° C, more preferably about 60 to 230 ° C. If rolling is performed in such a temperature range, not only a high elongation rate is exhibited, but also burrs and warps are hardly generated, and a high yield can be obtained.

  In addition, it is easier to use when you want to further improve the workability and stress relaxation of a binary alloy of Zn-Al, or when you want to adjust the melting point, wettability, bonding strength, reliability, etc. as appropriate. In order to obtain a solder material, it is effective to contain at least one of Ge, Cu, Ag, and Ni within a predetermined range in the Zn—Al alloy. Further, when it is desired to improve the properties of the solder alloy particularly from the viewpoint of wettability, it is effective to contain P within a predetermined range.

  That is, by containing a small amount of at least one of Ge, Cu, Ag, and Ni, after the solder is melted, these elements are first deposited at the time of cooling and solidification, and crystals are formed using the elements as nuclei. As a result, the crystal becomes finer and the flexibility of the solder is remarkably improved. On the other hand, since P is highly reducible, the wettability can be improved by suppressing oxidation of the solder alloy or the like. Each element added to the Zn—Al based solder alloy mainly composed of Zn of the present invention will be described in detail below.

<Al>
Al is an essential element that plays an important role in the Pb-free solder alloy containing Zn as a main component of the present invention, and its content is 1.0 mass% or more and 15.0 mass% or less. An alloy containing Al in this range is particularly excellent in elongation and depends on an additive element other than Al, but exhibits an elongation exceeding approximately 50%. If the Al content is less than 1.0% by mass, the melting point is not sufficiently lowered even if other elements are added, so that the bonding property is lowered and the composition is considerably deviated from the eutectic composition. No improvement in workability can be expected.

  On the other hand, if the Al content exceeds 15.0% by mass, the liquidus temperature of the Zn-Al alloy becomes too high, and it does not melt sufficiently at the actual bonding temperature of electronic parts, etc. Since it becomes too high or alloying of the joint portion becomes insufficient, joining that can withstand practical use cannot be performed. Furthermore, as a matter of course, since the proportion of Al is large, the crystal grains become coarse, and it becomes difficult to obtain the required workability.

  The Al content is more preferably 2.0% by mass or more and 9.0% by mass or less. This is because if the Al content is within this range, the eutectic point composition (Zn = 95% by mass, Al = 5% by mass) of the Zn—Al binary alloy is obtained, and the liquidus temperature decreases. In addition, the crystal is also refined to improve workability, and it is closer to an easy-to-use solder.

  The effect of containing Al is mainly the adjustment of the melting point as described above, that is, the melting point is lowered to the solidus temperature of 381 ° C. as a Zn—Al alloy, and the metal becomes soft because it becomes a eutectic alloy, The purpose is to improve elongation, workability and stress relaxation. However, since a high-temperature solder requires a higher bonding temperature than a medium-low temperature solder, a higher stress relaxation property is required for thermal stress due to a temperature difference. Therefore, each element described below is appropriately added to make a further excellent material.

<Ge>
Ge is an element that is preferably added to improve the workability and stress relaxation properties in addition to wettability in the Pb-free solder alloy of the present invention containing Zn as a main component. More specifically, when a small amount of Ge is contained in a Zn—Al alloy, Ge having a small specific gravity floats during solder melting and is preferentially oxidized over Zn. In the thermodynamic equilibrium theory, Zn and Al are more likely to be oxidized. However, since Ge is present in a relatively large amount on the surface of the solder due to the specific gravity, the rate at which Ge is oxidized increases. Oxidation of the main component Zn is suppressed and wettability is improved.

  Furthermore, when the content of Ge is small, the solder alloy is microcrystallized. Specifically, Ge has a higher melting point than Zn or Al (Zn melting point: 419 ° C., Al melting point: 660 ° C., Ge melting point: 938 ° C.), and after the solder alloy of the present invention is melted, a cooling process When solidifying at this time, this high melting point Ge is precipitated first, and this serves as a nucleus to grow crystals, so that the solder alloy is microcrystallized.

  Thereby, as will be described in detail in <Cu> below, the elongation, workability, and stress relaxation properties are improved. On the other hand, when the Ge content is relatively large, the composition approaches the eutectic point, and the elongation, workability, and stress relaxation properties are improved. As described above, by including Ge within a predetermined range, it becomes possible to improve wettability, elongation, stress relaxation, and the like.

  Specifically, the Ge content is preferably 0.01% by mass or more and 8.00% by mass or less. If this amount exceeds 8.00% by mass, there is a high possibility that the crystal grains will grow greatly and the elongation will decrease. On the other hand, if it is less than 0.01% by mass, the content is too small and the above effect does not appear.

<Cu>
Cu is an element that plays an important role in improving elongation, stress relaxation, and workability in the Pb-free solder alloy containing Zn as a main component of the present invention. Cu has a higher melting point than Zn and Al (Zn melting point: 419 ° C., Al melting point: 660 ° C., Cu melting point: 1084 ° C.), and has a high melting point when solidified in the cooling process after melting of the solder alloy. Cu is precipitated first, and this serves as a nucleus to form a crystal. Therefore, the crystal of the solder alloy becomes finer. By making the crystal finer, it becomes possible to obtain a soft solder in which cracks are difficult to progress.

  A solder alloy having such a flexible property exhibits very excellent properties in workability and stress relaxation properties. That is, when processing into a wire, a sheet, or the like, since the solder is soft, cracks and chips are hardly generated, and various processing speeds such as an extrusion speed to the wire and a rolling speed to the sheet can be increased as compared with a hard solder material. Thereby, it is excellent in productivity, and it becomes difficult to generate defective products, so that the yield can be increased.

  Furthermore, since it is easy to process with few burrs and warping when processing into a preform material, the quality inspection cost per unit amount can be reduced. In addition, since the soft solder alloy is easily deformed and the warpage of the solder is reduced when the semiconductor elements are joined, the substantial contact area can be increased. This makes it possible to obtain extremely high bondability.

  Also, Cu itself is a very soft metal among metals, and the softness of Cu itself is exhibited in the Zn-Al alloy. And since solder bonding is performed in a very short time, a non-equilibrium phenomenon occurs. Therefore, even if the Cu content is overwhelmingly smaller than Zn or Al, a Cu rich phase is formed depending on the solder composition and bonding conditions. Generated.

  As can be seen from the binary phase diagrams of Cu-Zn and Cu-Al, Cu has a large amount of Al and Zn, so the Cu-rich phase contains some Zn and Al. Thus, the stress applied to the solder can be absorbed in the Cu-rich phase. As a result, the solder alloy becomes softer.

  And it is stress relaxation that the flexible property of the solder alloy of the present invention appears most remarkably. In other words, a joined body such as an electronic component obtained by soldering a semiconductor element to a substrate is mounted on various devices such as automobiles and home appliances. Thermal stress is applied due to expansion and contraction due to changes in the outside air temperature. For example, an electronic component assembled with a substrate containing Cu as a main component and a semiconductor element containing Si as a main component has a coefficient of thermal expansion that is different by about five times, so that repeated thermal stress is also large. The solder alloy of the present invention is excellent in stress relaxation property that absorbs such a large thermal stress, and enables long-term use of electronic components in a severe environment.

  The Cu content is preferably 0.01% by mass or more and 3.00% by mass or less. As described above, the effect of addition of Cu is improvement of workability, flexibility, and the like by miniaturization of a solder alloy and generation of a Cu rich phase. Therefore, when giving priority to the refinement effect, the Cu content may be very small, and a lower limit of 0.01% by mass is sufficient. On the other hand, when giving priority to the effect of Cu-rich phase generation, the higher the Cu content, the better. However, if the limit is exceeded, the liquidus temperature becomes too high and good bonding cannot be performed. Mass%. Furthermore, if the Cu content is 0.03 mass% or more and 1.00 mass% or less, the above effect is more likely to appear, which is more preferable.

<Ag>
Ag is an element that is appropriately added when adjusting the various characteristics of the Pb-free solder alloy containing Zn as a main component of the present invention in accordance with the purpose, and the main effect of the addition is to improve wettability. In other words, as can be seen from the fact that Ag is used for the uppermost layer of the metallization of the substrate or semiconductor element, the effect of improving the wettability is great. This is due to the property of Ag that is difficult to oxidize. In addition, when the Ag content is increased on the Zn-rich side in the Zn-Ag alloy, the liquidus temperature increases monotonically, so Ag affects the melting point of the solder alloy of the present invention.

  As described above, it is better to increase the amount of Ag in terms of improving wettability, but it is preferable to reduce the amount of Ag in view of the melting point. Accordingly, Ag is contained in consideration of the balance between the melting point and the wettability, but if Ag exceeds 4.00% by mass, the liquidus temperature becomes too high even if Al is contained. Since it becomes difficult to obtain bonding, the Ag content is set to 4.0% by mass or less. On the other hand, if it is less than 0.10% by mass, the effect of adding Ag cannot be expected.

<Ni>
Ni is an element that plays an important role in improving elongation, stress relaxation, and workability in the Pb-free solder alloy containing Zn as a main component of the present invention. Ni has a higher melting point than Zn and Al (Zn melting point: 419 ° C., Al melting point: 660 ° C., Ni melting point: 1455 ° C.), and when the solder alloy of the present invention is solidified in the cooling process after melting. First, Ni having a high melting point is precipitated first, and this serves as a nucleus to form crystals, so that the solder alloy is microcrystallized. As a result, soft solder can be obtained. As a result, as described in the above <Cu>, very excellent properties in workability and stress relaxation properties are exhibited.

  The content of Ni that gives such excellent characteristics to the Zn—Al-based alloy is 0.01% by mass or more and 0.80% by mass or less. Since the purpose of containing Ni is to refine the solder alloy as described above, it is not necessary to contain a large amount. Conversely, if Ni is contained in an amount exceeding 0.80% by mass, Ni is segregated or the liquidus temperature is low. If it becomes high, the bondability, stress relaxation property, reliability, etc. will be lowered. However, if the content is less than 0.01% by mass, the content is too small and the effect does not appear.

<P>
P is an element added as appropriate when adjusting the various characteristics of the Pb-free solder alloy containing Zn as a main component of the present invention in accordance with the purpose, and the effect of the addition is in improving wettability. That is, P is highly reducing and suppresses oxidation of the solder alloy surface by being oxidized by itself. In particular, in the present invention, Zn that is easily oxidized is a main component, and Al that is more easily oxidized than Zn is contained. Therefore, when wettability is insufficient, the role of improving wettability by containing P is significant.

  Moreover, the effect of reducing the generation | occurrence | production of a void at the time of joining by containing P is also acquired. That is, as described above, P is easily oxidized by itself, and therefore, oxidation proceeds preferentially over Zn and Al, which are the main components of the solder alloy, at the time of bonding. As a result, it is possible to prevent the solder mother phase from being oxidized and reduce the bonding surface of the semiconductor element or the substrate to ensure wettability. At the time of this joining, oxides on the joining surface such as the solder surface and the semiconductor element are eliminated, so that voids formed by the oxide film are less likely to be generated, thereby improving the joining property and reliability. it can.

  As described above, P is not left on the surface of the solder or the substrate because it vaporizes and flows into the atmospheric gas when the joint surface of the solder alloy or the substrate is reduced to an oxide as described above. For this reason, there is no possibility that the residue of P adversely affects reliability and the like, and it can be said that this is an excellent additive element.

  When it contains P, it is preferable that the content is 0.0005 mass% or more and 0.5000 mass% or less. This is because, as described above, P has a very strong reducibility, and if a trace amount is contained, an effect of improving wettability can be obtained. However, if the content of P is less than 0.0005% by weight, the content is too small and the effect does not appear. On the other hand, even if the content exceeds 0.500% by mass, the effect of improving the wettability is not much changed, and excessive inclusion increases the generation rate of voids by generating a large amount of P and P oxide gases. There is a risk that P may form a fragile phase and segregate, embrittle the solder joint and reduce reliability. In particular, it has been confirmed that when processing into a shape such as a wire, it is likely to cause disconnection.

  As described above, by using the Pb-free solder alloy of the present invention for joining a semiconductor element and a substrate, even when used under severe conditions such as an environment in which a heat cycle is repeated, A durable and highly reliable bonded body can be provided. Therefore, by mounting this joined body on, for example, power semiconductor devices such as thyristors and inverters, various control devices mounted on automobiles, devices used under harsh conditions such as solar cells, these various devices Can be further improved in reliability.

  As raw materials, Zn, Al, Ge, Cu, Ag, Ni, and P 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 these raw materials was weighed and put into a graphite crucible for a high-frequency melting furnace.

  The crucible containing the raw materials was placed in a high-frequency melting furnace, and nitrogen was flowed at a flow rate of 0.7 liter / min or more per kg of the raw materials 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.

  Thus, the Zn-Al type solder mother alloy of samples 1-24 was produced by changing the mixing ratio of each above-mentioned raw material. The composition of each solder mother alloy of the obtained samples 1 to 24 was analyzed using an ICP emission spectroscopic analyzer (SHIMAZU S-8100). The analysis results of the obtained solder composition are shown in Table 1 below.

  Next, each solder mother alloy of Samples 1 to 24 is processed into a sheet with a predetermined thickness using a lathe without plastic deformation or a rolling mill with plastic deformation, and the following method The mechanical properties (tensile strength, elongation) were measured using a tensile tester. Further, for each solder alloy processed into a sheet shape, wettability (joinability) was evaluated by the following method and reliability was evaluated by a heat cycle test. The evaluation of solder wettability or bondability 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 mechanical properties>
In order to evaluate the mechanical properties, as described above, using a lathe or a rolling mill, the solder mother alloys (plate ingots with a thickness of 5 mm) of Samples 1 to 24 were each processed to a thickness of 0.5 mm. The sheet-like samples 1 to 24 of Zn-Al solder alloys were processed into a width of 3 mm by a slitter, and the length was cut to about 15 cm. In this way, a test piece for measuring the mechanical properties was produced. After visually confirming the presence or absence of scratches and cracks on each of the obtained test pieces, the tensile strength and elongation were measured with a tensile tester (Tensilon universal tester). Table 2 below shows the processing method and the evaluation results of the mechanical properties.

<Evaluation of wettability (bondability)>
Each solder alloy processed into a sheet shape as described above was evaluated using a wettability tester (device name: atmosphere control type wettability tester). In other words, a double cover is applied to the heater section of the wettability tester, and the heater set temperature is about 10 ° C. higher than the melting point of each sample while flowing nitrogen from four locations around the heater section at a flow rate of 12 liters / minute. Heated to set temperature. After the set heater temperature was stabilized, a Cu substrate (plate thickness: about 0.70 mm) was set in the heater section and heated for 25 seconds.

  Next, the solder alloy of each sample was placed on a Cu substrate and heated for 25 seconds. After the heating was completed, the Cu substrate was taken up from the heater part, and once installed in a place where the nitrogen atmosphere next to it was kept, it was cooled. After sufficiently cooling, it was taken out into the atmosphere and a joint portion was confirmed. The joint between the solder alloy of each sample and the Cu substrate is visually checked, and “X” indicates that the bonding cannot be performed, “△” indicates that the bonding is successful but the wetting spread is poor (the solder does not spread), The case where bonding was possible and the wet spread was good (when the solder was thin and spread) was evaluated as “◯”. The evaluation results are shown in Table 2 below.

<Heat cycle test>
A heat cycle test was conducted to evaluate the reliability of solder joints. This test was performed using two samples each having a solder alloy bonded to the Cu substrate in the above-described wettability evaluation (samples having a wettability evaluation of “◯” or “Δ”). That is, for one of the two Cu substrates to which the solder alloy of each sample is bonded, 300 cycles are required for confirming the heat cycle test in which one cycle includes cooling at −40 ° C. and heating at + 150 ° C. The same heat cycle test was repeated up to 500 cycles for the remaining one.

  Then, about each sample which performed the heat cycle test of 300 cycles and 500 cycles, Cu board | substrate with which the solder alloy was joined was embedded in resin, cross-sectional grinding | polishing was performed, and SEM (device name: HITACHI S-4800) performed the joining surface. Observations were made. As a result of this observation, the case where the joint surface is peeled off or the solder is cracked is indicated as “X”, and the case where there is no such defect and the same joint surface as in the initial state is maintained as “O”. did. The evaluation results are shown in Table 2 below.

  As can be seen from Tables 1 and 2 above, the solder alloys of Samples 1 to 13 that satisfy the requirements of the present invention exhibit good characteristics in all evaluation items. That is, it has been found that it has an elongation of 50% or more and a tensile strength of 70 MPa or more and is excellent in plastic deformability. Further, even when processed into a sheet shape, no scratches or cracks were generated, and the wettability and reliability were very good.

  The reason why the very high elongation rate was obtained as described above is considered to be due to the unique effect of the Zn-Al alloy. Especially in the samples 7 to 13, among Ge, Cu, Ag, Ni, and P It is considered that the inclusion of one or more types further promotes the refinement of crystals, and this has resulted in good effects.

  Also, in the heat cycle test, cracks etc. did not occur up to 500 times and showed good bondability and reliability, but this also absorbed the thermal stress repeatedly applied by the solder alloy with increased softness (elongation rate)・ It is thought to be due to the relaxation. In addition, the elongation rate of the solder alloys of Samples 4 to 13 produced by rolling was about twice or more larger than the solder alloys of Samples 1 to 3 produced by lathe processing. This is thought to be due to the refinement of the structure due to plastic deformation by rolling.

  On the other hand, each solder alloy of Samples 14 to 24 that does not satisfy the requirements of the present invention was not suitable for the content of any of Al, Ge, Cu, Ag, Ni, and P. It became. Specifically, the elongation was less than 50%, and the tensile strength was less than 70 MPa except for the samples 21 to 24. Regarding the wettability, 10 samples out of 11 samples were unfavorable. Especially in the heat cycle test, all samples (except samples 14, 16, 21, 23, and 24 that could not be joined) were up to 300 times. A defect occurred.

Claims (6)

Elongation rate is 50% or more, tensile strength is 70 MPa or more, Al is contained by 1.0 mass% or more and 15.0 mass% or less, and the balance is made of Zn except for elements inevitably contained. A Pb-free solder alloy mainly composed of Zn.   Ge is not included in excess of 8.00 mass%, Cu is not included in excess of 3.00 mass%, Ag is not included in excess of 4.00 mass%, Ni is not included. 2. The Pb-free solder alloy containing Zn as a main component according to claim 1, wherein the Pb-free solder alloy is not contained in an amount exceeding 0.80 mass% and P is not contained in an amount exceeding 0.50 mass%. .   3. The Pb-free solder alloy containing Zn as a main component according to claim 1, wherein the Pb-free solder alloy is manufactured by a processing method involving plastic deformation.   Al is contained in an amount of 2.0 to 9.0% by mass, and at least one of Ge, Cu, Ag, Ni, and P is contained. In the case of Ge, 0.01 to 8.0% by mass Hereinafter, in the case of Cu, 0.01 mass% to 3.00 mass%, in the case of Ag, 0.10 mass% to 4.00 mass%, and in the case of Ni, 0.01 mass% to 0.80 mass%. The Pb-free solder alloy containing Zn as a main component according to any one of claims 1 to 3, wherein the Pb-free solder alloy contains 0.0005 mass% or more and 0.5000 mass% or less in the case of P. .   A bonded body characterized by being bonded using a Pb-free solder alloy containing Zn as a main component according to any one of claims 1 to 4.   An apparatus comprising the joined body according to claim 5.