JPH03106591A - Solder material - Google Patents

Abstract

PURPOSE:To improve the reliability of a soldered and brazed part by constituting the solder material of specific weight per cent of In, Sb, etc., and Ag, Au, Pb, and Sn and depositing secondary phases at the crystal grain boundaries of Pb and Sn after soldering. CONSTITUTION:The solder material is constituted, by weight per cent, of at least two kinds among the groups (1) to (3) consisting of (1) 0.01 to 10% MA (at least one kind of In and Ga), (2) 0.01 to 8% Ms (at least one kind of Sb and Bi) and (3) 0.01 to 10% at least one kind of Ag and Au, 10 to 95% Pb and the balance Sn. This material is a substantially solid soln. in a soldering state. The secondary phases 3 of the MA and/or Ms deposited after the soldering are made to exist mainly at the grain boundaries of the Pb crystal grains 1 and Sn crystal grains 2. The long-term stable use of the solder material without generating cracks is possible in this way.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to a solder material, and more specifically, it is used in environments where electrical components for automobiles are constantly exposed to vibrations and are prone to fatigue. This invention relates to a solder material whose structure is controlled to be suitable for soldering parts used in electronics, especially for joining electronic parts to printed circuit boards. (Prior technology) Generally, solder materials are Sn-Pb binary system. It is known that various ingredients are added to improve its properties.Japanese Patent Publication No. 40-25885 discloses that the copper of an electric iron tip for soldering melts into the solder, causing the solder to melt. It is disclosed that copper, silver, nickel, etc. are added to the solder material in order to prevent wear and tear.It is explained that the wear prevention effect is caused by finely uniform distribution of copper in the solder with silver and nickel. Japanese Patent Publication No. 45-2093 discloses that the corrosion resistance of solder at the soldered joint with an aluminum alloy is improved by adding Ag or sb, and the fluidity and workability of the solder material are improved by C.
It is disclosed that this can be improved by adding d. In particular, the following conventional techniques are intended to improve solder materials used in integrated circuits, printed circuit boards, etc. Japanese Patent Publication No. 52-30377 discloses the simultaneous addition of Cu and Ag in order to prevent thin copper wires to be soldered from being melted by solder, eroded, or having a decrease in strength. Cu suppresses the overlying soldering material from being eaten by the solder, while the addition of Cu increases the melting point of the solder, making it easier for the overlying soldering material to melt.
Cu and Ag can be prevented by their melting point lowering effect.
It is explained that the simultaneous addition of Japanese Unexamined Patent Publication 1983
The purpose of Publication No. 144893 is to eliminate the drawback that silver in the silver lead wire of a ceramic capacitor diffuses into the solder, worsening the characteristics of the capacitor or causing the silver surface to peel off, and to enable high-speed soldering. , S
We propose n-Sb-Ag-Pb based solder material. Japanese Patent Publication No. 5
Publication No. 9-70490 discloses SblN15%-Sn(In)1 as an inexpensive brazing filler metal with properties comparable to Au brazing filler metal used for joining components in semiconductor memories.
~65%-Pb and Sb-Ag-Sn(In)-
We propose a Pb-based component. JP-A-63-313689 discloses Pb62-72%,
The basic composition is Sn28-38%, and Cub. 05
% to 1.0%, SbO. O'5~1.0%, In0.0
5-1.0%, Cd0.05-1.0%, Fed. 05
We propose a solder alloy composition characterized by adding at least one type of solder in an amount of 1.0% to 1.0% to prevent bridging between lead terminals. The following are conventional technologies that refer to the structure of solder. In Japanese Patent Publication No. 40-25885, there is a problem when a Sn-Cu intermetallic compound is created because it obstructs the flow of solder, but if Cu is dispersed finely and uniformly by adding small amounts of Ag and Ni, It is explained that the defects caused by intermetallic compounds are not a problem. According to Japanese Patent Publication No. 52-30377, adding a large amount of Ag causes harm such as crystallization of intermetallic compounds, and adding more than 5.0% of sb causes intermetallic compounds to form in the molten solder. It is explained that primary crystals develop at the joint surface when exposed to large amounts. In this way, regarding the conventional solder structure,
In order to prevent the precipitation of intermetallic compounds that inhibit the flow of molten metal, efforts were made to reduce the amount added to some extent. (Problem to be Solved by the Invention) Regarding the characteristics of solder materials used for soldering integrated circuits and electronic components mounted on printed circuit boards, in recent years, it has been found that A problem that is attracting attention is that cracks occur in the battery, causing malfunctions due to poor electrical conduction. The reason for this is that stress is generated in the board and mounted components due to periodic changes in the operating temperature from around 100°C to around -30°C, and the solder, which is the joining material, takes on the stress. is constantly placed under stress, and it is presumed that fatigue failure will occur if used for a long period of time. Furthermore, thermal effects such as the rise in temperature of the soldered joint due to energization, heat generation of electronic components, and even mechanical effects such as vibration of the printed circuit board can accelerate fatigue failure during long-term use. it is conceivable that. It has become clear that the Sn-Pb binary solder material, which has a basic composition, has problems in terms of fatigue resistance when used in environments where it is exposed to long-term thermal and mechanical stress as described above. However, although it has been said that adding Cu or N1 to Pb-Sn binary alloys improves fatigue resistance, the structure has only been studied at or before soldering, and There has been no research conducted from the perspective of improving the structure of the solder after soldering, that is, improving the fatigue resistance in the environment in which the solder is exposed after soldering. (Means for Solving the Problems) As a result of intensive research into methods for improving the fatigue resistance of solder materials, the present inventors have found that, immediately after soldering, additive elements to Pb-Sn alloys are added to the Pb-Sn alloy in a solid solution state. We discovered that fatigue resistance could be improved by precipitating this as a secondary phase after soldering, and invented the following four types of solder materials.
1. ΦM^ (However, at least one type of In1Ga) 0
, Of~10%, ■Ml (However, at least one of sb and Bi) o. 01 to 8%, and [3] a group consisting of 0.01 to 10% of at least one of Ag and Au [1
] to [3], Pb10 to 95%,
The remainder (excluding O%) consists essentially of Sn, is substantially a solid solution in the soldered state, and contains the M1 and/or MA precipitated after soldering.
A solder material characterized in that a secondary phase consisting of and/or M exists mainly at the grain boundaries of Pb crystal grains and Sn crystal grains, and has excellent fatigue resistance (hereinafter referred to as the first invention) ．． 2. SbO. 01-3%, Al0.01-2%, Pb1
0 to 95%, and the remainder (excluding 0%) consists essentially of Sn, and is substantially a solid solution in the soldered state, and is mainly composed of a secondary phase of Al-sb intermetallic compounds precipitated after soldering. A solder material that exists at the grain boundaries of Pb crystal grains and Sn crystal grains and has excellent fatigue resistance. (Hereinafter referred to as the second invention). 3. AlO. Of~2%, Pb10~95%, balance (0
%) to Sn, is substantially a solid solution in the soldered state, and is precipitated after soldering.
A solder material characterized in that a secondary phase mainly exists at the grain boundaries of Pb crystal grains and Sn crystal grains, and has excellent fatigue resistance. (Hereinafter referred to as the third invention). 4. A solder material characterized in that the composition of the second and third inventions further contains 0.01 to 10% of at least one of Ag and Au (hereinafter referred to as the fourth invention). (Function) First, the reason for limiting the composition in the present invention will be explained. In the present invention, regarding the composition of the Pb-Sn basic system, P
b10 to 95% (percentages are weight percentages unless otherwise specified), Sn balance (excluding 0%) was selected as a certain range because in this composition range, it is significantly different from the eutectic composition of the Sn-Pb binary system. This is because soldering can be done at a relatively low temperature without causing any separation. However, from the viewpoint of solderability, Sn2%
The above is preferable, and Pb is 10 to 90%, especially 10 to 80%.
%, more preferably 20 to 60%. In addition, Pb is 30 to 50% as a eutectic system, preferably 3
When Pb is set at 0 to 45%, it is better in terms of solderability and ease of use, and the solder strength can be increased. On the other hand, when Pb is set at around 50% and 45 to 60%, cost is emphasized, This is advantageous for applications where soldering strength does not need to be very high. When using at high temperatures, increase the amount of Pb to 60
% or more, preferably 70 to 95%, can also be used. In addition, especially when fatigue resistance at high temperatures is required, it is desirable to have a small amount of Sn and a large amount of Pbm. For example, Sn is 3-9% and Pbso is ~90%. In the first invention, MA, MA, and Ag (Au) are used as additive elements, and the reasons for limiting their content (or total content if two types are added in each group) will be explained below. The lower limit of added elements is set to o. The reason why it is set at 0.01% is that if it is less than this, the fatigue resistance cannot be improved due to precipitation, which will be described in detail later. Furthermore, if the content of M& and Me is 10% or more and 8% or more, respectively, a large amount of additive elements will precipitate before soldering, resulting in a decrease in the flowability and solderability of the solder, or This causes the solder surface to become cloudy, making it easier for cracks to form. Then, in the state at the time of soldering, the precipitates become macroscopically segregated, and there are too many fatigue starting points where fatigue occurs in this part. For this reason, the secondary phase in which the additive elements are precipitated from the solid solution state after soldering becomes insufficient to protect fatigue starting points such as segregated areas by the areas with excellent fatigue resistance.
Since there is a tendency for fatigue resistance to decrease significantly, these contents were set as upper limits. The content of MA is preferably 5% or less, more preferably 3% or less. Further, the content of MA is preferably 5% or less, more preferably 3% or less. The upper limit of Ag and/or Au is also determined for the same reason. In particular, when the Ag content exceeds the upper limit, a large Ag-Sn intermetallic compound is generated, and a large amount of sinkholes, bottle holes, blowholes, etc. are generated, and the flowability of the solder is reduced. This may lead to a decrease in fatigue resistance. It becomes. Even if a large amount of Ag and Au is added, no significant improvement in performance can be expected for the added amount, and they are also expensive elements. Considering the overall solder performance including this economical point of view, the total amount of Ag and Au is preferably 5% or less,
More preferably, it is 3% or less. In addition, the component ranges of MA and individual additive elements of MA are as follows:
The content of In and the content of Ga are each preferably 0.01 to 5%, more preferably 0.03 to 1%, and even more preferably 0.05 to 0.9%. When increasing the MA content, it is better to add both In and Ga than to add only one. Among Mm, the preferable content of sb is 0. Ol~3%,
More preferably 0.03 to 1%, still more preferably 0.03% to 1%.
05-0.9%. When Sb is 3% or less, solderability becomes better, but when it exceeds 2%, a small portion may precipitate during soldering. Although this precipitation does not have much influence on the action of the secondary phase that is subsequently precipitated, in order to obtain a more preferable secondary phase, it is recommended that sb be 2% or less. The preferred content of %Bi in M1 is 0. Ol~5%,
More preferably 0.03 to 3%, still more preferably 0.03%.
05-1%. Similar to Sb, if 81 exceeds 3.5%, a small portion may precipitate during soldering. As for the component range of the individual additive elements of Ag and Au, the preferred content is o. 01-5%, more preferably 0.1-4
%, more preferably 0.5 to 3%. In the second invention, the lower limit of the additive elements sb and Al is set to 0.01% because if it is less than this, the fatigue resistance will be improved due to the precipitation of intermetallic compounds as a secondary phase, which will be described in detail later. That's because there isn't. Also, sb and Al
When the content of these elements exceeds 3% and 2%, respectively, it becomes difficult to dissolve most of the additive elements in the state at the time of soldering, and the precipitates formed by the additive elements that are not dissolved in the solid solution form. If the content is too high, the effect of the secondary phase tends to be destroyed and fatigue resistance decreases, so these contents were set as upper limits. A more preferable content of sb is 0.03 to 1%, more preferably 0.05 to 0.9%. If sb exceeds 2%, a small portion may precipitate during soldering. Although this precipitation does not have much effect on the action of the secondary phase that is subsequently precipitated, from the viewpoint of obtaining a more preferable secondary phase, it is recommended that sb be 2% or less. In the third invention, the lower limit of the additive element Al is 0.0
The reason why it is set at 1% is because if it is less than this, fatigue resistance cannot be improved due to the precipitation of an aluminum metal phase, which will be described in detail later. Furthermore, when the Al content exceeds 2%, it becomes difficult to form a solid solution for most of the added elements in the state at the time of soldering, and too many precipitates are formed, resulting in secondary phase formation. These contents were set as upper limits because they tended to destroy the effects of carbon dioxide and reduce fatigue resistance. In the second invention and the third invention, the Al content is desirably 0.01 to 1.5%, preferably 0.05 to 0.
65%, more preferably 0.05-0.2%. Note that when the amount of Sn added is small, the content of Al may be reduced. That is, when the Sn content is 50% or less, it is particularly recommended that the Al content be 1% or less. Ag and/or Au added as optional additive elements to the solder materials of the second and third inventions has the effect of further improving fatigue resistance. If the content (total amount when two types are added) is less than 0.01%, there is no effect;
On the other hand, if the content exceeds 10%, the effect of the secondary phase is destroyed and fatigue resistance tends to decrease, so these contents were set as upper limits. Moreover, especially when the upper limit of the Ag content is exceeded, a large Ag-Sn intermetallic compound is generated, which reduces fatigue resistance. Considering the solder performance comprehensively including the economical point of view, the total amount of Ag and Au is:
It is preferably 5% or less, more preferably 3% or less. Precepts other than those listed above are essentially impurities. Here, Cu
, Fes Nl, Mn, Mo, TI, Cd, Zn, etc.
Although a small amount may be mixed in as an impurity, it is of course possible to include it for a known purpose as long as it does not eliminate the effects of the present invention. If Cu is 3% or less, it does not destroy the effect of the secondary phase of the present invention, but it tends to produce crystallized Cu-Sn intermetallic compounds in the state at the time of soldering. It is preferable not to use it actively. Next, the organizational features of the present invention will be explained. Figure 1 (A)
Figure 1 (B) shows the structure of the solder material of the present invention after soldering.
is a diagram schematically showing the tissue after use. In the figure, 1 is P
b crystal, 2 is Sn crystal, and 3 is intermetallic compound secondary phase. Figure 2 (A) shows the structure of the conventional solder material after soldering.
Figure 2 (B) is a diagram schematically showing the structure after use.
In the figure, 1 is a Pb crystal, 2 is a Sn crystal, and 3 is a secondary phase. The structure of the solder material of the present invention has a solid solution structure in which the additive elements are supersaturated and dissolved in the Sn crystal and Pb crystal at the time of soldering. The secondary phase generated during soldering may be effective in improving static strength, but it is in the form of needle-like particles with sharp corners, and these sharp parts become notches and cause fatigue. Since this becomes the starting point of fracture, one of the features of the present invention is to avoid the generation of secondary phases at the time of soldering as much as possible and create a solid solution structure. The feature is that a secondary phase is precipitated from this solid solution structure after soldering. In the past, the alloy composition and structure were improved by focusing on the characteristics until soldering was completed. In particular, no research has been conducted that focuses on fatigue behavior after soldering. Therefore, the present inventors conducted research and found that Pb-
It was found that this fatigue behavior in Sn-based solder is dominated by the glowing phenomenon of the Pb phase. This is because, due to the temperature of the usage environment, the Sn phase and the Pb phase in the soldering part gather crystal grains of the same phase and gradually grow, and as a result, the Pb phase becomes coarser than the Sn phase. However, fatigue progresses from the Pb phase, which is weak against fatigue. Therefore, as a means to stop this particle growth, by forming the secondary phase after soldering,
The present invention was completed after discovering that it is possible to suppress the progress of fatigue in the soldered parts. In conventional solder materials, it has been recognized that crystallized substances such as intermetallic compounds are harmful and the amount of added elements should be limited to avoid their presence as much as possible. Generally, during use, solder is exposed to elevated temperatures (up to about 100°C) that can lead to grain growth, coalescence, etc. The weight of solder in one solder joint of a board on which electronic equipment is mounted is usually 100 to 1000 mg. At such a weight, the alloy structure is dominated by the cooling rate during soldering, and the grain size determined by this rate is usually 1 to 10 microns. When such crystal grains are exposed to high temperatures, the continuous portion of the Pb phase increases, especially due to the growth of the Sn phase, and cracks occur in the Pb phase, which is susceptible to fatigue. In this way, fatigue strength decreases. In addition, since electronic devices installed in automobiles are used in temperatures ranging from minus several tens of degrees Celsius to plus approximately 80 degrees Celsius, stress is applied to the solder due to the thermal expansion and contraction of the solder and element lead terminals, which can lead to fatigue failure. This is a major factor. Additionally, when solder is exposed to high temperatures for long periods of time, the solder is constantly exposed to constant stress and may break due to creep, which is also a major factor in fatigue failure.
Of course, in the solder material of the present invention, the initial strength of the solder is quite high due to solid solution strengthening, so fatigue failure does not occur rapidly, but even with solid solution strengthening, crystal grain growth occurs. In addition, significant reorganization of crystal grains occurs under the conditions of use at high temperatures, long periods of time, and repeated stress. The effect of fatigue resistance deterioration becomes noticeable. Therefore, in the solder material of the present invention, during long-term use after soldering, Pb crystal grains 1 and Sn
The secondary phase 3, such as an intermetallic compound, is present at the grain boundaries of the crystal grains 2, thereby preventing the growth of the crystal grains. Here, the growth of crystal grains and the generation of secondary phases do not proceed preferentially, but rather occur simultaneously, so at the point when fatigue strength tends to decrease due to coarsening of crystal grains, two The grain growth suppressing effect appears due to the secondary phase, and these effects compete with each other. Note that intermetallic compounds that precipitate during long-term use do not have sharp edges and form a block with approximately equal dimensions in all directions. The size of the secondary phase is preferably 10μ or less, preferably 5μ or less. If this is exceeded, the secondary phase itself may become the origin of fatigue. Preferably, if it is 3 μm or less, the growth suppressing effect will be even better. More preferably, it is 1μ or less. In the solder material of the representative embodiment of the present invention, 1
If the image is magnified approximately 0.000 times, a secondary phase of approximately 0.5 to 1 μm in size can actually be easily observed. Of course, there are secondary phases smaller than this, but they require expensive measuring equipment to observe them. The size of the secondary phase is this if it is fine and present in large quantities. The following may be used. The time required for secondary phase formation is greatly influenced by temperature. Under accelerated test conditions for testing the reliability of electronic components, the time specified by the specifications (for example, -30
The formation of a secondary phase was confirmed after 1000 cycles at ℃ to +80℃. In electronic components built into actual equipment, performance deterioration and precipitation within the solder alloy progress more slowly than in accelerated tests, so the formation of secondary phases can be observed several years after soldering. It is considered a thing. It is preferable for the secondary phase to form slowly in this way in order to prevent fatigue failure. On the other hand, after soldering, a low-temperature heat treatment may be intentionally performed so that a secondary phase is formed in a few hours to form a solder joint. In contrast to the present invention, in conventional Pb-Sn-Cu solder materials, almost all of the SnCu intermetallic compound is crystallized before soldering, and at the time of soldering, this crystallized material is in the matrix. There is virtually no solid solution in the soldering process, and the heat of soldering turns it into a coarse form. When the structure after soldering is observed, this coarse SnCu intermetallic compound exists randomly at grain boundaries and within the grain, and there is virtually no solid solution in the matrix. For this reason,
It cannot be precipitated after soldering, and the glow phenomenon of Pb grains due to the heat during use is seen to the same extent as Pb-Sn solder, and the coarse SnCu intermetallic compound has no grain growth suppressing effect. There wasn't. Similarly, in Pb-Sn-Ag solder, Ag-Sn intermetallic compounds are observed, but when observing the structure from immediately after soldering to after long-term use, it is found that they exist randomly at grain boundaries and within grains. However, due to the heat during use, this intermetallic compound itself becomes solid solution again and grows into coarse crystals with almost no effect on the grain boundaries of the Pb phase and Sn phase. In addition, there are cases where Ag-Sn intermetallic compounds migrate and grow. Therefore, the Ag-Sn intermetallic compound that existed alone in this form is P
No grain growth inhibitory effect was observed on the b-grain growing phenomenon. As described above, the SnCu intermetallic compound found in conventional soldering or the Ag-Sn intermetallic compound alone did not have the effect of extending fatigue life based on the effect of suppressing crystal grain growth. In contrast, the secondary phase of the present invention has a form that can be substantially solid-dissolved in the Pb phase and/or Sn phase at the time of soldering, and precipitated from this solid-solution structure by heat after soldering. As a result, most of it can exist at the grain boundaries of the Pb phase and Sn phase, and as a result, the effect of suppressing grain growth can be obtained. The performance required for the secondary phase, which is a feature of the present invention, is summarized as follows. ■Immediately after soldering, there is a substantial solid solution in the Pb phase and/or Sn phase, and due to low-temperature heat treatment after soldering or heat during long-term use, To produce by precipitation. ■Have a high melting point and be stable at high temperatures. Or, it must be at least stable enough to avoid being completely re-dissolved in the matrix against the heat applied during use.
Intermetallic compounds meet this requirement whether they are stoichiometric, non-stoichiometric, or contain solid solution elements. Even metals (solid solutions), such as Al, satisfy this requirement if they are more stable than Pb and Sn. ■Precipitates must be fine and dispersed. Secondary phases formed by precipitation during low-temperature heat treatment after soldering and secondary phases formed by precipitation during long-term use of soldered parts meet this requirement. The size of the precipitate is preferably 5 μm or less, preferably 3 μm or less, and particularly preferably 1 μm or less. If a large number of fine particles are dispersed and precipitated in the solder structure after soldering, they are likely to be arranged at grain boundaries.

Although it is necessary for the dispersed secondary phase to exist mostly at the grain boundaries of the matrix phase in order to obtain a high grain growth suppressing effect, it is not necessary for the dispersed secondary phase to precipitate at the grain boundaries from the beginning; As a result of the stopping effect, it only needs to exist at grain boundaries. In the present invention, a phase that satisfies these properties is referred to as a secondary phase. A specific example of the above secondary phase will be explained below. (1) Ma Ms type intermetallic compound; Sb-In, Sb-Ga, Bi-In, Bi-Ga type intermetallic compound. This intermetallic compound is a binary compound generated in the solder material of the first invention having an MA-MA-Pb-Sn composition. Moreover, this intermetallic compound is MA-Me-Pb-Sn-
Even in the case of an AM (Au) based composition, it is often produced as a binary compound that does not contain Ag (Au). In either case, thermal precipitation after soldering significantly increases fatigue strength. The size of the intermetallic compound (1) is preferably 3 μm or less. Usually 0.
1 to lua are observed. At this time, there are also cases of less than 0.1μ, but it is difficult to distinguish. In this way, the intermetallic compounds precipitated by heat after soldering are fine. Furthermore, when suppressing matrix particle growth, intermetallic compounds may grow to a very small extent, although this is not a problem. The intermetallic compound (1) is more preferable as a secondary phase. This is because, in addition to the functions of the secondary phase of the present invention, the fatigue strength of the secondary phase itself is high, the strength at the interface between the secondary phase and the Sn phase/Pb phase is high, and the growth rate of the secondary phase is high. It seems that the precipitation rate or formation rate from the solid solution is not so large, and secondary phases of appropriate size are formed sequentially from extremely fine secondary phases to enhance the particle growth suppressing function. It is speculated that when the Sn and Pb phases grow slightly, this secondary phase also grows slightly and has an additional function, such as increasing the effect of inhibiting the movement of the Pb phase. It will be done. (
2) M@-Ag (Au) type intermetallic compound; Sb-Ag. Bi-Ag, Sb-Au, Bl
-AU-based intermetallic compound. This intermetallic compound is MA-Pb-Sn-A of the first invention.
In the g(Au)-based compound, a part of the Ag(Au) is a binary compound that combines with MA and becomes active. The size of the intermetallic compound (2) is preferably 3 μm or less, and a size of 0.1 to 1 μm is usually observed. Furthermore, in the Ma-Me-Pb-Sn-Ag (Au) system composition, the compound (1) also exists, and the compound (2) often also exists. Therefore, in this composition, Ag (Au) has a greater tendency to combine with MA than to be incorporated into a part of the intermetallic compound of <<1>>. Due to the coexistence of these intermetallic compounds (1) and (2), the fatigue strength tends to be higher than when only the intermetallic compound (l) is formed. (3) Ma-Ag (Au) type intermetallic compound: In-
Ag1Ga-Ag, In-Au1Ga-AU intermetallic compound. This intermetallic compound is M a - P b - S n
- In an Ag-based composition, a part of Ag is a binary compound formed by combining with M&. However, the tendency of this compound to form is weaker than that of the intermetallic compound <<2>>, and even if the intermetallic compound <<2>> is formed, the intermetallic compound (3) may not be formed. The tendency of intermetallic compounds to form here is defined as the tendency of intermetallic compounds to form preferentially in the solder at component contents excluding those near the upper and lower limits of the composition of the present invention. Therefore, when the composition is near the upper or lower limit, intermetallic compounds are generated with a different priority order from the generation tendency described here. The intermetallic compound (3) is likely to be formed when the content of Ag (Au) and/or the content of Sn is high. The size of the intermetallic compound (3) is usually observed to be 0.1 to lμ■. (4) Mm-Sn-Ag(A
u ) type intermetallic compounds: Sb-Sn-Ag (Au), Bi-Sn-Ag (A
u) Intermetallic compounds. This intermetallic compound has a composition in which Ag (Au) is added to the MA-Pb-Sn system composition of the first invention, and
A compound is produced by the combination of MA and a portion of Sn in the matrix, and a compound is produced by the combination of Au, MA, and a portion of the Sn in the matrix. This compound is either a ternary compound or a solid solution of MA in a Sn-Ag (Au) binary compound.゜This tendency to form intermetallic compounds is stronger than (3) (2).
) is almost equivalent to (5) Ma-Sn-Ag (Au) type intermetallic compound: In-Sn-Ag (Au)* Ga-Sn-Ag
It corresponds to (Au)-based intermetallic compounds. This intermetallic compound corresponds to (4) in which M- is replaced with M1. It is easier to understand if you read MA in the explanation in (4) above as MA. (6) MAMl -Ag (Au) type intermetallic compound: Sb-In-Ag (Au), Sb-Ga -Ag
(Au), Bi-In-Ag (Au), Bi
-Ga-Ag (Au) based intermetallic compound. This intermetallic compound is a compound containing all the additive elements of the first invention. It has a weaker tendency to form than the MA MB type (1) and the MA Ag type intermetallic compounds (2), and may be formed only when the Ag content is extremely high. The reason why this compound has a weak tendency to form is thought to be because it is difficult for additive elements to react with each other because they are diluted in concentration compared to matrix components, and because the composition of the compound is complex, it is inherently difficult to form. ．． Similarly, even if the compound is composed of diluted elements, a compound with a simple composition like (1) has a high tendency to form. The above (1) to {6) may exist in a single form as a secondary phase, but they may coexist if there are many types of added elements. Overall, fatigue resistance performance tends to be higher when they coexist. Moreover, most of these precipitated secondary phases exist at the grain boundaries of the Sn phase and Pb phase due to the heat generated after soldering. The proportion of the precipitated secondary phase existing at grain boundaries is preferably 60% or more. Preferably, it is 70% or more, more preferably 80% or more, and still more preferably 90% or more. The operating environment may reach temperatures of 80 to 100 degrees Celsius.
If exposed to that environment for a long period of time, the proportion can increase to about 60% or more. If low-temperature heat treatment is performed, it can be easily controlled to about 80-95%. In cases where exposure to such temperatures is not possible, improvements can be made by combining this low-temperature heat treatment. (7) Ag-Sn type intermetallic compound Although this intermetallic compound does not increase fatigue strength when present alone, it has a fairly strong tendency to form, and Pb-Sn-
It also occurs with Ag-based solder materials. As mentioned above, when observing the structure of conventional Pb-Sn-Ag solder from immediately after soldering to after long-term use, it is found that Ag-Sn intermetallic compounds exist randomly at grain boundaries and inside grains. The intermetallic compound itself re-dissolves into solid solution due to the heat during use, and grows into coarse crystals with almost no effect on the grain boundaries of the Pb phase and Sn phase. In addition, the Ag-Sn intermetallic compound may move or lengthen. Therefore, the Ag-Sn intermetallic compound that existed alone in this form is Pb
No grain growth inhibitory effect was observed on the grain glowing phenomenon. However, when it coexists with the intermetallic compounds (1) to (6) above, the fatigue resistance of the solder is further improved. This is because (1) to (6) above are based on the particle growth suppressing effect of the Sn phase-Pb phase, and when there is movement and growth of the particles of the Ag-Sn intermetallic compound itself, the movement is suppressed by the bottling effect. (1) to (6) above during mobile growth.
absorbs Ag and forms or precipitates as a new secondary phase, suppressing migration and growth by a kind of buffering effect.
This buffering effect substantially expands the microscopic range of action of the secondary phase pinning effect that suppresses the movement and growth of the Sn and Pb phases. Although it is only for a short time until the precipitates of the Ag-Sn intermetallic compound whose movement is suppressed are re-dissolved into the matrix by heat, it becomes an auxiliary bottle for the grain growth of the Sn phase and Pb phase. Possible mechanisms of action include a stopping effect.

If this intermetallic compound is also generated in large quantities during soldering, Ag will be consumed in the formation of (7), inhibiting the formation of the secondary phase, or inhibiting the formation of the secondary phases of (1) to (6) above. Particular attention must be paid to the fact that even if the Moreover, regarding this (7), it was difficult to make it exist selectively at the grain boundaries of the Sn phase and Pb phase even with low-temperature heat treatment. (8) Al-Sb intermetallic compound This intermetallic compound is produced in the solder materials of the second and fourth inventions. The size of this intermetallic compound is usually 1-5μ
It is m. This secondary phase also becomes Sn phase and Pb phase due to the heat after soldering.
As a result, most of the phase exists at the grain boundaries of the phase. (9) In the third invention with a single Al phase, intermetallic compounds do not precipitate and an Al phase is generated. Also, in the fourth invention, an Al phase may be generated. As mentioned in (8) above, when sb exists, Al forms an intermetallic compound with it, but Al does not form an intermetallic compound with Sn and Pb, and the supersaturated solid solution of Al forms an intermetallic compound with Sn and Pb. Separates from the phase as metal crystals. The At phase separated in this way is morphologically similar to the secondary phase of intermetallic compound precipitates as shown in (3), and the morphological classification of the phases indicates that it is not a matrix phase but a secondary phase. Belong. Also, Al
The reason why the single layer (9) suppresses the grain growth of the matrix phase is because its properties are similar to those of intermetallic compounds. In other words, (9) precipitates finer than the matrix phase and is less likely to grow as a crystal, and in this respect has the same effect as an intermetallic compound. In addition, (9) is precipitated from the matrix phase and has the same effect as an intermetallic compound in that it is not re-dissolved. Therefore, (9) exists at the grain boundaries of the matrix phase and prevents its movement. Although Al alone is relatively inexpensive and the size of precipitates can be easily controlled in some respects, from the viewpoint of effectiveness, ease of soldering, amount of solid solution in the matrix, etc. It is preferable to select types 1) to (6). Next, with respect to the composition of the first invention, which type of intermetallic compound is actually produced is first determined by S n - P b
- S b - In The four-element set will be explained using an example. In this composition, the matrix phase is Sn phase and Pb
The secondary phase was the intermetallic compound phase (1).
Most of these secondary phases exist at the grain boundaries of the Sn phase and Pb phase. Next, S n-P b- S b -
In the r n-A g five-element composition, the matrix phase is
There are seven types of intermetallic compounds (1) to (7), which are the Sn phase and the Pb phase, and may exist as secondary phases. A
When the content of Ag is low, a three-phase structure exists in which only the intermetallic compound (1) is dispersed as a secondary phase, but when the content of Ag is high, Ag reacts with MA, one or both of MA. And a part of it also reacts with Sn. Depending on the blended composition, one or more intermetallic compounds selected from (1) to (6) will be present. Of course A
As the g content increases, (7) also tends to increase relatively. For (1), Ma and MA should be added in a predetermined amount or more. On the other hand, if you particularly want to generate (2) and (4), increase the MA
All you have to do is reduce MA or not mix it (3
). If (5) is particularly desired to be produced, it is sufficient to increase M1 and decrease MA or omit it. (4). (
If you particularly want to generate 5), you tend to be careful if you reduce the amount of Pb and relatively increase the amount of remaining Sn. Note that solder is an alloy with a lot of segregation and has not undergone heat treatment such as homogenization as it was originally cast.In solder joint parts, each component may react locally at a maximum temperature of around 100°C, which is the maximum concentration used. Because it is a metastable state, in reality, secondary phases different from those predicted by the theory of equilibrium phase diagrams may coexist and be created. Finally, we will talk about heat treatment. Heat treatment improves static mechanical properties, so it can improve basic fatigue resistance. It is practically difficult to expose only the solder to high-temperature heat treatment for soldered parts of printed circuit boards with electronic components mounted, and there is also concern about the effects of heat on the electronic components. Therefore, the fatigue resistance of printed circuit board solder can be improved by low-temperature heat treatment. For example, low-temperature heat treatment is performed at a low temperature of 80 to 120°C for a relatively long time of 5 to 6 hours. In this case, a part of the secondary phase will be formed to some extent at the time of product shipment, and the basic overall properties will be good, while unprecipitated solid solution will also remain, which is preferable. Note that if the secondary phase is rapidly cooled at a high temperature, it will essentially remain in solid solution and will only return to its state at the time of soldering, which will only have a thermal effect on electronic components, etc. There is no point in heat treatment. Furthermore, if heat treatment is carried out for an excessively long time, not only will productivity be reduced, but also the S content in the solder will be
This is undesirable because the n-phase and Pb phase may become coarse, which leads to a shortened fatigue life. (Examples) The present invention will now be explained in more detail with reference to Examples. The fatigue test was conducted using a test piece in which a phenolic resin substrate 5 shown in FIG. 3 and a lead II 7 that penetrates a land portion 6 made of IRW 3 formed on one surface of the substrate were soldered. The test method is to apply a tensile load to the lead wire using a fatigue testing machine at a repetition rate of 20 Hz (one-sided swing) and a constant temperature of 80°C, and calculate the number of repetitions until a crack occurs as the fatigue life. I did it with Note that cracks had occurred within the solder as shown by 9 in Figure 4. Here, the fatigue resistance value is 37%P obtained under these measurement conditions.
The fatigue life (1x106) of b-Sn solder is the fatigue resistance value l
This is the relative value when . The following table shows the composition, fatigue resistance value, and type of secondary phases (intermetallic compounds, etc.) of the test materials. Figure 5 is an electron micrograph (5000x magnification) of sample material 2 after soldering. The white parts are Pb crystal grains, and the gray parts are Sn crystal grains. The EPMA analysis results of this sample material showed that Pb, Sn, Sb, In, and Ag were all uniformly distributed, and it was therefore confirmed that the structure shown in Figure 5 was a solid solution structure. Figure 6 is an electron micrograph of sample material 2 after the test (magnification: 50
00 times). Grain boundaries of dark Sn crystal grains and gray Pb
Precipitates are observed at grain boundaries. Figures 7 and 8
The figure shows the atomic reflection images of sb and In obtained by EPMA analysis after each test. It can be seen that the locations where these elements are present in high concentrations are consistent with each other. Therefore, these elements were found to exist as intermetallic compounds. Similar EPMA analysis was also performed for Sn and Ag to investigate the locations where high concentrations were present. The elements whose local locations coincided were as follows. :Sb-InHSb-
AgHSb-Sn-Ag; In-Sn-Ag. Similarly, after soldering the solder material of sample material 2,
It was subjected to low-temperature heat treatment at 0°C (5 hours), then taken out into the atmosphere and slowly cooled. When similar EPMA analysis was performed, similar results were obtained. The fatigue resistance of this low-temperature heat-treated product was also superior to that of conventional solder materials. (Effects of the Invention) According to the present invention, when solder materials are used under harsh conditions ranging from low temperatures of minus several tens of degrees Celsius to plus hundreds of degrees Celsius, such as printed circuit boards mounted on automobiles, for example, It can also be used stably for a long time without cracking like conventional solder materials, improving the reliability of solder joints.

[Brief explanation of drawings]

FIG. 1(A) is a diagram schematically showing the structure of the solder material of the present invention after soldering, FIG. 1(B) is a diagram schematically showing the structure after use, and FIG. 2(A) is a diagram schematically showing the structure after soldering of the solder material of the present invention. A diagram schematically showing the structure of a conventional solder material after soldering. Figure 2 (B) is a diagram schematically showing the structure after use. Figure 3 is a diagram of a test piece subjected to a fatigue resistance test. , Figure 4 is a drawing of a test piece showing the crack occurrence area in the fatigue resistance test. Figure 5 is an electron micrograph (5000x magnification) showing the metallographic structure of sample material 2 immediately after soldering, and Figure 6 is an electron micrograph (3500x magnification) showing the metallographic structure of sample material 2 after testing. , Fig. 7, and Fig. 8 show the sb and I after the test, respectively.
The atomic reflection image obtained by EPMA analysis of n is shown, and sb and I
This is a metallographic photograph showing the localized structure of n. 1-Pb crystal, 2-Sn crystal, 3-secondary phase, 5-substrate,
6-Land, 7-Lead wire, 8-Solder, 9-Crack Figure 1 (A) Figure 1 (B) Figure 2 (A) 2 Figure 2 (B)

Claims (1)

[Claims] 1. In weight percentage, [1]M_A (However, In_1Ga
at least one kind of) 0.01 to 10%, [2]M_B(
However, at least one of Sb and Bi) 0.01 to 8%,
and [3] At least one of Ag and Au 0.01
It consists essentially of at least two of the groups [1] to [3] consisting of ~10%, Pb10~95%, and the balance (excluding 0%) Sn, and is substantially in a solid solution in the soldered state. The secondary phase containing M_A and/or M_B or consisting of M_A and/or M_B precipitated after soldering exists mainly at the grain boundaries of Pb crystal grains and Sn crystal grains, and has excellent fatigue resistance. A solder material characterized by: 2. Sb0.01-3%, Al0.01-3% by weight
2%, Pb10-95%, balance (excluding 0%) to Sn
It is essentially a solid solution in the soldered state, and the secondary phase of the Al-Sb intermetallic compound precipitated after soldering is mainly present at the grain boundaries of Pb crystal grains and Sn crystal grains. A solder material characterized by excellent fatigue resistance. 3. Al0.01-2%, Pb10-95 in weight percentage
%, the remainder (excluding 0%) is essentially Sn, and is substantially a solid solution in the soldered state, and the Al secondary phase precipitated after soldering mainly forms the grain boundaries of Pb crystal grains and Sn crystal grains. A solder material characterized by excellent fatigue resistance. 4. At least one of Ag and Au in weight percentage is 0
．． Claim 2 characterized in that it further contains 01 to 10%.
Or the solder material described in 3.