WO2016185674A1

WO2016185674A1 - Solder alloy and package structure using same

Info

Publication number: WO2016185674A1
Application number: PCT/JP2016/002195
Authority: WO
Inventors: 清裕日根; 彰男古澤; 秀敏北浦
Original assignee: パナソニックＩｐマネジメント株式会社
Priority date: 2015-05-19
Filing date: 2016-04-26
Publication date: 2016-11-24

Abstract

A solder alloy which contains from 0.5% by mass to 1.25% by mass (inclusive) of Sb, In in an amount satisfying 5.5 ≤ [In] ≤ 5.50 + 1.06[Sb] in cases where 0.5 ≤ [Sb] ≤ 1.0, while satisfying 5.5 ≤ [In] ≤ 6.35 + 0.212[Sb] in cases where 1.0 < [Sb] ≤ 1.25 (in the formulae, [Sb] represents the Sb content (mass%) and [In] represents the In content (mass%)), from 0.5% by mass to 1.2% by mass (inclusive) of Cu, from 0.1% by mass to 3.0% by mass (inclusive) of Bi and from 1.0% by mass to 4.0% by mass (inclusive) of Ag, with the balance made up of Sn.

Description

Solder alloy and mounting structure using the same

The present invention mainly relates to a solder alloy used for soldering an electronic component to an electronic circuit board and a mounting structure using the same.

The electronic control of automobiles is advancing from the viewpoint of safety and comfort of automobiles and environmental impact. Electronic devices mounted on automobiles are required to have high reliability with respect to loads such as heat, vibration and shock in automobiles.

In response to such demands for automotive electronic devices, high reliability is required for solder alloys used for mounting circuit boards of automotive electronic devices. Since a solder alloy has a lower melting point than a printed circuit board or an electronic component as a member to be joined, the mechanical properties thereof are remarkably deteriorated in a high temperature environment. Also, since the solder alloy has a low elastic modulus, strain due to differences in linear expansion coefficient between components due to temperature changes in the automobile environment, loads due to vibration and impact are concentrated on the solder joints soldered with the solder alloy. Will be added. In particular, when a strain due to a difference in linear expansion coefficient between the constituent members is repeatedly applied, a crack may be generated in the solder joint portion, which may ultimately cause a disconnection. For this reason, solder alloys used in electronic equipment for automobiles are required to have heat-resistant fatigue characteristics against repeated strain generated by temperature changes, and require high strength and ductility in a high-temperature environment.

As a solder alloy having excellent heat fatigue resistance that can be used in conventional electronic equipment for automobiles, Ag is 1.0 to 4.0% by mass, In is 4.0 to 6.0% by mass, and Bi is 0.1 to 1%. Solder alloy consisting of 0.0 mass%, the total of one or more elements selected from the group consisting of Cu, Ni, Co, Fe and Sb being 1 mass% or less (excluding 0 mass%), and the balance of Sn The electrode part containing copper of the electronic component is joined to the electrode land containing copper of the substrate by the joint part formed using such a solder alloy. There is known an electronic component bonded body (mounting structure) in which the electrode portion of the electronic component and the electrode land of the substrate are at least partially blocked by the Cu—Sn intermetallic compound in this bonded portion (patent) Reference 1). Patent Document 1 describes that such a configuration can prevent the generation and extension of cracks in a temperature cycle test between −40 ° C. and 150 ° C.

In addition, as another solder alloy having excellent heat fatigue resistance, Sn—Ag—In containing 0.5 to 5% by mass of Ag, 0.5 to 20% by mass of In, and 0.1 to 3% by mass of Bi, with the balance being Sn. There is also known a Sn-based solder alloy characterized by containing 3% by mass or less of at least one selected from Sb, Zn, Ni, Ga, Ge and Cu (patent) Reference 2). Patent Document 2 describes that according to such a solder alloy, deformation of the solder alloy can be prevented in a temperature (cooling) cycle test between −40 ° C. and 125 ° C.

Japanese Patent No. 5280520 JP 2004-188453 A Japanese Unexamined Patent Publication No. 2015-1000083

An object of the present invention is to provide a solder alloy capable of obtaining sufficient reliability to withstand use at 175 ° C.

The present inventors have added both Sb and Cu to the Sn—Ag—Bi—In based solder alloy, and have strictly controlled the In content with respect to the Sb content. The inventors independently found that high reliability was obtained even at a high temperature that was not assumed, specifically, 175 ° C., and as a result of further intensive studies, the present invention was completed.

According to one aspect of the present invention,
0.5% by mass or more and 1.25% by mass or less of Sb;
The following formula (I) or (II):
In the case of 0.5 ≦ [Sb] ≦ 1.0 5.5 ≦ [In] ≦ 5.50 + 1.06 [Sb] (I)
When 1.0 <[Sb] ≦ 1.25 5.5 ≦ [In] ≦ 6.35 + 0.212 [Sb] (II)
(In the formula, [Sb] represents the Sb content (mass%), [In] represents the In content (mass%)), and
0.5% by mass or more and 1.2% by mass or less of Cu;
Bi of 0.1 mass% or more and 3.0 mass% or less;
There is provided a solder alloy containing 1.0% by mass or more and 4.0% by mass or less of Ag, the balance being Sn.

According to the present invention, in a solder alloy composed of Sn, Ag, Bi, In, Cu and Sb, a predetermined content is selected for each element except Sn, and in particular, the Sb content is 0.5 mass% or more. , 1.25 mass% or less, the In content is selected in relation to the Sb content so as to satisfy the above formula (I) or (II), and the Cu content is 0.5 mass% or more, 1.2 By setting the mass% or less, a solder alloy capable of obtaining sufficient reliability to withstand use at 175 ° C. is realized.

It is a graph showing the DSC measurement result of the solder alloy concerning embodiment of this invention. It is a graph which shows the result of the tension test in the 175 degreeC environment of the solder alloy concerning embodiment of this invention. It is a graph which shows the relationship (when Sb content rate is 0.5 mass%) of In content rate and the transformation temperature of the solder alloy concerning embodiment of this invention.

Prior to the description of the embodiment of the present invention, problems in the conventional solder alloy will be briefly described. The number of electronic devices mounted on automobiles is steadily increasing, and it is difficult to secure a mounting space for electronic devices in a limited space of automobiles. Therefore, it is possible to relatively expand the space by downsizing the electronic device, or to install the electronic device in a place where the conventional mounting was refrained from the viewpoint of reliability due to high temperatures such as in the engine room. It is being advanced. As a result, an increase in heat generation density of electronic devices due to miniaturization and an increase in ambient environment temperature occur, and electronic devices are exposed to higher temperatures. In order to cope with the future evolution of electronic devices, high reliability such as heat resistance, for example, even at temperatures higher than 125 ° C. and 150 ° C., specifically 175 ° C., which has been a standard for the past. There is a need for solder alloys that exhibit fatigue properties.

However, conventional solder alloys are not considered for use at such high temperatures. More specifically, the solder alloy described in Patent Document 1 is only supposed to be used up to 150 ° C., and the solder alloy described in Patent Document 2 is only supposed to be used up to 125 ° C. In such a conventional solder alloy, sufficient reliability cannot always be obtained at a temperature of 175 ° C.

The contents of Japanese Patent Application Laid-Open No. 2015-1000083 (US2015144388A1) are incorporated herein.

Hereinafter, a solder alloy and a mounting structure using the same according to an embodiment of the present invention will be described in detail with reference to the drawings.

In addition, in this specification, what added [] to the element symbol which comprises a solder alloy shall mean the content rate (mass%) of the said element in a solder alloy.

Further, in the present specification, in order to describe the metal composition of a solder alloy, a numerical value or a numerical range may be shown immediately before a metal element other than Sn, which is generally used in the technical field. As shown in the figure, the mass% (=% by weight) of each element in the metal composition is indicated by a numerical value or a numerical range, which means that the balance is made of Sn.

The solder alloy of this embodiment is
0.5% by mass or more and 1.25% by mass or less of Sb;
The following formula (I) or (II):
In the case of 0.5 ≦ [Sb] ≦ 1.0 5.5 ≦ [In] ≦ 5.50 + 1.06 [Sb] (I)
When 1.0 <[Sb] ≦ 1.25 5.5 ≦ [In] ≦ 6.35 + 0.212 [Sb] (II)
(In the formula, [Sb] represents the Sb content (mass%), and [In] represents the In content (mass%)).
In that satisfies
0.5% by mass or more and 1.2% by mass or less of Cu;
Bi of 0.1 mass% or more and 3.0 mass% or less;
1.0 mass% or more and 4.0 mass% or less of Ag are contained, and the remainder consists of Sn.

Conventionally, the effects on the physical properties that affect the heat fatigue characteristics such as the strength and ductility of the solder alloy itself have not been clarified. Further, the combined effect when Cu and Sb are combined is not verified. Under such circumstances, the present inventors conducted research and development on mechanical properties in a high-temperature environment required for automotive electronic devices, and as a result, each of In, Cu, and Sb has a certain relationship. It has been newly found that by containing it, mechanical properties at high temperatures, particularly ductility at high temperatures, which have not been clarified so far, are remarkably improved, and as a result, the thermal fatigue strength is improved.

In order to clarify the effect of the solder alloy of this embodiment, a solder alloy (sample) having a predetermined composition was prepared and evaluated.

The sample evaluated in this embodiment was manufactured by the following method.

Sn, Ag, Bi, In, Cu, and Sb contained in the solder alloy, Ag is 3.5% by mass, Bi is 0.5% by mass, In is 6.0% by mass, and Cu is 0.8% by mass. , Sb was 0.5 mass%, the balance was Sn, and weighed so that the total amount was 100 g.

The weighed Sn was put into a ceramic crucible, adjusted to a temperature of 500 ° C. and a nitrogen atmosphere, and placed in an electric jacket heater.

After confirming that Sn was melted, In was added and stirred for 3 minutes.

Bi was added and the mixture was further stirred for 3 minutes.

Ａ Ag was added and further stirred for 3 minutes.

Sb was added and further stirred for 3 minutes.

Cu was added and further stirred for 3 minutes.

Thereafter, the crucible was taken out from the electric jacket heater and immersed in a container filled with water at 25 ° C. to cool, thereby producing a solder alloy.

Hereinafter, this is referred to as “solder alloy A”, and the alloy composition is represented by Sn-3.5Ag-0.5Bi-6.0In-0.8Cu-0.5Sb.

For comparison, as an example of a conventional solder alloy, a solder alloy having a composition of Sn-3.5Ag-0.5Bi-6.0In-0.5Cu not containing Sb was produced in the same manner as described above. . This is referred to as “Conventional Example 1”.

In order to evaluate the transformation temperature, which is the temperature at which the β-Sn and γ phase transformations proceed rapidly, 10 mg of the solder alloy produced above was taken out and subjected to differential scanning calorimetry (DSC). The temperature increase rate at the time of measurement was 10 ° C./min, and the temperature was measured in the range from 25 ° C. to 250 ° C. The results are shown in FIG.

In FIG. 1, the transformation temperature was determined from the inflection point of a small peak (part A) generated from the low temperature (solid) side to the peak showing the melting point, and the transformation temperature of solder alloy A was 175 ° C. On the other hand, the transformation temperature of Conventional Example 1 was 165 ° C.

Next, 1 g of the solder alloy produced above was taken out and soldered at 250 ° C. using a commercially available flux on a Cu plate, and a temperature cycle test was conducted. The test condition is a temperature between −40 ° C. and 175 ° C., and each cycle is held at −40 ° C. and 175 ° C. for 30 minutes, respectively (the test under such conditions is referred to as “−40 / 175 ° C. temperature cycle test”). ), 500 cycles were performed.

As a result, in the solder alloy A, self-deformation was not observed at the stage after 500 cycles, whereas in the conventional example 1, self-deformation occurred. Together with the above results, it is understood that a solder alloy having a transformation temperature of 175 ° C. or higher does not self-deform in a temperature cycle test of −40 ° C./175° C. and can withstand use in a 175 ° C. environment.

Next, in order to evaluate the mechanical properties of the solder alloy, a tensile test was performed in a 175 ° C. environment using a tensile test piece. The tensile test piece was produced by putting the solder alloy produced above into a crucible, heating it to 250 ° C. with an electric jacket heater, melting it, and pouring it into a graphite mold processed into the shape of a tensile test piece. The tensile test piece had a round bar shape with a constricted portion having a diameter of 3 mm and a length of 15 mm. The result of the tensile test in a 175 degreeC environment is shown in FIG.

2. In FIG. 2, the horizontal axis indicates the stroke strain of the tensile tester, and the vertical axis indicates the tensile stress. The maximum values are measured as elongation at break and tensile strength, respectively. From FIG. 2, it can be seen that the solder alloy A has a tensile strength equal to or higher than that of the conventional example 1 even in the 175 ° C. environment. It can be seen that the breaking elongation of the solder alloy A is improved by several tens of percent compared to the conventional example 1, and the ductility at high temperature is improved.

From the above, it is confirmed that the solder alloy A does not self-deform even when repeatedly exposed to a high temperature of 175 ° C., and is excellent in the mechanical properties of the solder alloy such as strength and ductility at a high temperature. It becomes possible to improve the heat fatigue resistance.

Next, the alloy composition for expressing the effect of the solder alloy of this embodiment will be described.

(In content, Sb content)
First, the In content and the Sb content in the solder alloy will be described.

In a solder alloy containing Sn as a main component, an alloy (β-Sn phase) in which In is dissolved in Sn is formed in a low In content region where the In content is about 15% by mass or less.

Solid solution is a phenomenon in which a part of the crystal lattice of the base metal is replaced with a solid solution element at the atomic level. In general, the effect of solid solution elements is to suppress the movement of crystal defects such as transitions when stress is applied by generating strain in the crystal lattice of the parent element due to the difference in atomic diameter between the parent metal element and the solid solution element. Can do. As a result, the strength of the metal can be improved, while the ductility during stress loading is reduced. The strength improvement of the solder alloy by solid solution increases as the solid solution element content increases.

However, when In is dissolved in Sn-based solder, it depends on the In content, but when the temperature is gradually increased, it differs from the β-Sn phase from about 100 ° C or higher. Phase transformation to the γ phase (InSn ₄ ) of the structure proceeds. In other words, two different phases coexist to the same extent (γ + β-Sn). By being in this two-phase coexistence state, the contribution of slip at the grain boundary is increased, and ductility at high temperatures is improved.

On the other hand, when the In content is large, excessive transformation from β-Sn phase to γ phase occurs. In this case, since the volume of the crystal lattice structure of the γ phase and that of the β-Sn phase are different, the solder alloy undergoes self-deformation due to repeated thermal cycles. This is a problem because it causes a breakage in the solder joints and a short circuit between different solder joints.

In addition, Sb increases the transformation temperature in the Sn—In alloy, such as the transformation temperature of 165 ° C. in Conventional Example 1 and the transformation temperature of solder alloy A of 175 ° C.

This is because the state of the alloy structure is changed by containing Sb. When the Sb content is relatively small, Sb dissolves in Sn in the same manner as In in the Sn—In alloy. When the Sb content is further increased, In and a compound (InSn) are formed and precipitated in the alloy structure.

When Sb is dissolved in Sn together with In, the movement of Sn and In elements at the time of temperature change is suppressed, and the transformation start temperature of β-Sn phase and γ phase is changed.

The mechanical properties of the solder alloy improve the strength of the solder alloy by dissolving Sb in the same manner as the In solid solution. In addition, as will be described later, the present inventors have newly found that the solid solution of Sb further promotes the improvement in ductility at a high temperature seen at a specific In content.

When the Sb content is further increased, InSn precipitates like a pin between the crystal structures and suppresses deformation. On the other hand, since the ductility is lowered by the precipitation of InSb, excessive precipitation of InSb is not suitable for improving the thermal fatigue resistance.

In order to clarify the influence of the Sb content on the transformation temperature of the Sn—In solder alloy, solder alloys having the metal compositions shown in Table 1 were prepared and evaluated. The method for producing the solder alloy is the same as described above.

(In the table, “bal.” Represents the remainder. The same applies to the following tables.)
In the table, the transformation temperature of the produced solder alloy was evaluated as “◯” when the temperature was 175 ° C. or higher, and “X” when the temperature was less than 175 ° C. Further, regarding mechanical properties (tensile strength and elongation) at 175 ° C., the case where it was improved compared to the case of Conventional Example 1 was evaluated as “◯”, and the case where it was equal or less than “X” was evaluated, In particular, the case where the elongation at 175 ° C. was improved by 30% or more was evaluated as “◎”.

Furthermore, in the table, the transformation temperature of the produced solder alloy is evaluated at 175 ° C. and the mechanical properties (tensile strength and elongation) are evaluated and the results of comprehensive judgment are also shown. Judgment is made when the transformation temperature is 175 ° C. or higher and the mechanical properties are improved as compared with the case of the conventional example 1, especially when the elongation at 175 ° C. is improved by 30% or more. “◎” and the effect of the present invention is expressed. The case where the transformation temperature is less than 175 ° C. and the mechanical property value is less than the value in Conventional Example 1 is determined as “x”.

As shown in Examples 1-1 to 1-4, when Sb is contained in an amount of 0.50 to 1.25% by mass, the transformation temperature is 175 ° C. or more and the mechanical properties are improved. The effect is expressed. On the other hand, when the Sb content shown in Comparative Examples 1-1 and 1-2 is 0.25% by mass or less, the mechanical properties at 175 ° C. are good, but the transformation temperature is not sufficiently increased, and the transformation Since the temperature is less than 175 ° C., the determination is “x”. When the Sb content shown in Comparative Example 1-3 is 1.5% by mass, the generation of InSb becomes remarkable, the ductility at high temperature deteriorates, and the determination is “x”.

From the results shown in Table 1, it can be seen that the effect of the present invention is exhibited when the Sb content is in the range of 0.5 mass% or more and 1.25 mass% or less.

Further, from Examples 1-1 to 1-4 and Comparative Example 1-1, the increase in Sb content and the transformation temperature from the case where no Sb is contained have a relationship as shown in the following formula (1). I understand.

(Formula 1)
When 0.5 ≦ [Sb] ≦ 1.0:
ΔT _t = 20 × [Sb]
When 1.0 <[Sb] ≦ 1.25:
ΔT _t = 4 × [Sb] +16
(In the formula, ΔT _t represents the transformation temperature increase (° C.).)
Next, in order to clarify the influence of the In content, solder alloys having the metal compositions shown in Table 2 were prepared and evaluated. The Sb content is 0.50% by mass, which is the above-mentioned minimum, and the method for producing and evaluating the solder alloy is the same as that described above.

As shown in Table 2, when Example 2-2, where the Sb content is 0.5 mass%, is compared with Conventional Example 1, it can be seen that the transformation temperature increases due to the Sb content. When the Sb content was 0.5% by mass, the mechanical properties at the transformation temperature and 175 ° C. in Examples 2-1 and 2-2 in which the In content was 5.5% by mass and 6.0% by mass, respectively. Both (tensile strength and elongation) are improved. As the In content increases, the transformation temperature decreases, and in Comparative Examples 2-2 and 2-3 where the In content is 6.5% by mass and 7.5% by mass, respectively, the mechanical properties at high temperatures are good. However, since the transformation temperature is less than 175 ° C., the determination is “x”. Furthermore, in Comparative Example 2-4 having a large In content of 7.5% by mass, both the transformation temperature and the mechanical properties at 175 ° C. are not sufficient, and the determination is “x”. On the other hand, from the results of the evaluation of the mechanical properties (tensile strength and elongation), Comparative Example 2-1 with an In content of 5.0% by mass has a small effect due to the solid solution of In and is 175 compared with Conventional Example 1. The tensile strength at 0 ° C. is small, and the judgment is “x”.

Next, as shown in Table 3, a solder alloy was prepared and evaluated in the case where the upper limit of the Sb content was 1.25% by mass. The method for producing and evaluating the solder alloy is the same as described above.

As shown in Table 3, when Example 3-2 is compared with Conventional Example 1, it can be seen that the transformation temperature increases due to the Sb content. As in the case of the results shown in Table 2, the transformation temperature decreases as the In content increases, and in Comparative Examples 3-2 and 3-3 where the In content is 7.0% by mass or more, the transformation temperature is 175. Since it is less than ° C., the determination is “x”. Further, focusing on the mechanical properties of tensile strength and elongation, in the case of Comparative Example 3-1, in which the In content is 5.0% by mass, the In-solution effect is not sufficiently exhibited, and the tensile strength in an environment of 175 ° C. Since the intensity is smaller than Conventional Example 1, the determination is “x”.

Based on the results shown in Tables 2 and 3, the range of the In content that exhibits the effect of the present invention is as follows.

When the Sb content is 0.5 ≦ [Sb] ≦ 1.25, when attention is paid to the relationship between the In content and the mechanical properties, the In content is 5.5% in order to exhibit the effects of the present invention. % Or more, which is the relationship of (Equation 2).

(Formula 2)
[In] ≧ 5.5
Next, attention is focused on the relationship between the In content and the transformation temperature.

FIG. 3 is a diagram showing the relationship between the In content and the transformation temperature when the Sb content shown in Table 2 is 0.50 mass%. In FIG. 3, the horizontal axis indicates the In content (% by mass), and the vertical axis indicates the transformation temperature (° C.).

When the Sb content is 0.50% by mass, the relationship between the In content and the transformation temperature is expressed by the following formula 3.

(Formula 3)
T _t = −18.9 × [In] +289
(In the formula, T _t represents the transformation temperature (° C.).)
From Equation 1, the effect of increasing the transformation temperature due to the inclusion of Sb is 10 ° C. Therefore, when Sb is not contained, the relationship is as shown in the following Equation 4.

(Formula 4)
T _t = −18.9 × [In] +279
(In the formula, T _t represents the transformation temperature (° C.).)
From these results, in order to develop the effect of the present invention that improves the mechanical properties of the solder alloy with a transformation temperature of 175 ° C. or higher, the relationship shown in Equation 5 is necessary.

(Formula 5)
5.5 ≦ [In] ≦ 6.5
And 0.5 ≦ [Sb] ≦ 1.0:
−18.9 × [In] + 279 + 20 × [Sb] ≧ 175
When 1.0 <[Sb] ≦ 1.25:
−18.9 × [In] + 279 + 4 × [Sb] + 16 ≧ 175
From Formula 1, Formula 2, and Formula 5, it is necessary to satisfy | fill the relationship of following Formula 6 to In content rate (mass%) and Sb content rate (mass%) which express the effect of this invention.

(Formula 6)
0.5 ≦ [Sb] ≦ 1.25
And 0.5 ≦ [Sb] ≦ 1.0:
5.5 ≦ [In] ≦ 5.50 + 1.06 × [Sb]
When 1.0 <[Sb] ≦ 1.25:
5.5 ≦ [In] ≦ 6.35 + 0.212 × [Sb]
In order to clarify the composition range in which the improvement of ductility at high temperature, which is one of the effects of the present invention, is clarified, the Sb content as shown in Table 4 is 0.75 mass% and 1.0 mass. %, And a solder alloy in which the In content satisfies the relationship of Formula 6 was prepared, and the relationship with the In content was evaluated in detail. The method for producing and evaluating the solder alloy is the same as described above.

As shown in Table 4, in any of Examples 4-1 to 4-9, the transformation temperature and mechanical properties are increased as compared with Conventional Example 1. Further, focusing on the elongation at 175 ° C., it can be seen that when the In content is 6.0% by mass or more, the smaller the In content, the higher the elongation is. In particular, the In content is 6.1% by mass or less. In this case, the elongation at 175 ° C. was particularly large, and the evaluation was ◎.

From the results shown in Table 4, it is particularly desirable that the In content (mass%) and the Sb content (mass%) satisfy the relationship of the following formula 7 in order to exhibit the effects of the present invention.

(Formula 7)
0.5 ≦ [Sb] ≦ 1.0
And 5.5 ≦ [In] ≦ 5.50 + 1.06 × [Sb]
And [In] ≦ 6.1
(Cu content)
Cu is contained for the purpose of lowering the melting point during soldering and improving the selectivity of the material of the member to be joined.

As a member to be joined in soldering, a material obtained by subjecting the base material Cu or Ni to various plating or preflux treatment is mainly used.

Among these, in the case where the base material of the member to be joined is Ni, when soldering is performed using a solder alloy containing In and not containing Cu or containing a small amount, In in the interface reaction layer (Ni ₃ Sn ₄ ) Is partially captured. Therefore, a change in the mechanical characteristics of the solder joint after soldering occurs. When the base material of the member to be joined is Ni, it is necessary to contain a large amount of In in advance by an amount that is partially taken into the interface reaction layer. However, in an actual circuit board, various electronic components are mounted on a single circuit board. Therefore, when an electronic component of Cu or Ni is mounted on the base material, the In content ratio is determined in advance. Adjustment is difficult.

However, when a certain amount of Cu is contained in the solder alloy, Cu in the solder alloy forms a Cu ₆ Sn ₅ based alloy layer in the interface reaction layer at the time of soldering, and can prevent the incorporation of In. The selectivity of the joining member is improved.

In order to express such an effect of containing Cu, it is clarified in Japanese Patent Application Laid-Open No. 2015-1000083 that the present applicant has a Cu content of 0.5% by mass or more. Therefore, the lower limit of the Cu content is 0.5% by mass.

On the other hand, when Cu is excessively contained, the melting point increases, so that it is desirable that the content be 1.2% by mass or less.

Therefore, in the solder alloy of the present invention, the Cu content is 0.5 mass% or more and 1.2 mass% or less.

(Bi content)
Bi is contained for the purpose of improving the mechanical strength of the solder material and lowering the melting point. In the solder alloy, when the Bi content is relatively small at 3.0% by mass or less, it dissolves in β-Sn, and when the Bi content increases, Bi or Bi compounds are present in a precipitated form.

In order to obtain the effect of improving the mechanical strength due to the Bi content, it is necessary to contain Bi by 0.1% by mass or more, and the Bi content is preferably 0.1% by mass or more.

In addition, when precipitation of Bi or Bi compound occurs, the ductility at a high temperature is remarkably lowered because it shows a function of preventing the grain boundary from sliding. For this reason, the upper limit of the Bi content is desirably set to 3.0% by mass or less so that precipitation of Bi or Bi compound does not occur.

From the above, in the solder alloy of the present invention, the Bi content is 0.1 mass% or more and 3.0 mass% or less.

(Ag content)
Ag is contained for the purpose of improving wettability during soldering and lowering the melting point, and is present in the form of Ag ₃ Sn compound and Ag ₂ In in the solder alloy.

Usually, in order to uniformly melt the solder alloy by reflow soldering, it is preferable to set the reflow peak temperature of the liquidus temperature of the solder alloy + 10 ° C. or more. In view of the heat resistance temperature of the electronic component, the reflow peak temperature is preferably 240 ° C. or lower.

Therefore, the liquidus temperature of the solder alloy is preferably set to 230 ° C. or less. In the solder alloy of the present invention, the Ag content is set to 1.0% by mass or more and 4.0% by mass or less.

Based on the content of each element determined as described above, examples, comparative examples, and conventional solder alloys having the metal compositions shown in Table 5 were prepared, and the heat fatigue resistance was evaluated. The method for producing the solder alloy is the same as described above.

The evaluation method of heat fatigue resistance is as follows.

First, the produced solder alloy was processed into solder powder having a particle size of several tens of μm, the solder powder and the flux were weighed so as to have a weight ratio of 90:10, and these were kneaded to produce a solder paste. . This solder paste was printed on the circuit board electrode on the circuit board using a metal mask having a thickness of 150 μm. A chip resistor was mounted on the printed solder paste, and reflow heating was performed at a maximum temperature of 240 ° C. to produce a mounting structure. The base material of the circuit board electrode of the used circuit board was Cu and Ni.

The mounting structure thus fabricated was subjected to a temperature cycle test of −40 ° C./175° C., and the deformation of the solder joint after 2000 cycles was visually observed. When no deformation is observed by visual observation, the electrical connection is evaluated, and when there is a change in the resistance value of 10% or more from the initial value, the electrical failure is “present”, and there is no change or 10% Those that were less than were judged as electrical failure “none”. Note that “−” in the electrical failure column of Table 5 indicates that no evaluation was performed.

As shown in Table 5, in Examples 5-1 to 5-11 included in the composition range of the solder alloy determined as described above, self-deformation of the solder joint does not occur, and short-circuiting or disconnection occurs. There was no electrical failure.

On the other hand, in Comparative Examples 5-1 to 5-4 having different In and Sb contents, either self-deformation or electrical failure of the solder joint occurred.

In Comparative Example 5-5 that does not contain Cu, self-deformation of the solder joint did not occur, but disconnection occurred when the base material of the circuit board electrode was Ni.

Comparative Example 5-6 with a Cu content of 1.5% by mass, Comparative Example 5-7 without Bi, Comparative Example 5-8 with a Bi content of 3.5% by mass, Comparative Example without Ag In 5-9, an electrical failure occurred.

Also, in all of the conventional examples 1 to 5, self-deformation of the solder joint occurred.

Therefore, from the evaluation results shown in Tables 1 to 5,
0.5% by mass or more and 1.25% by mass or less of Sb;
The following formula (I) or (II):
In the case of 0.5 ≦ [Sb] ≦ 1.0 5.5 ≦ [In] ≦ 5.50 + 1.06 [Sb] (I)
When 1.0 <[Sb] ≦ 1.25 5.5 ≦ [In] ≦ 6.35 + 0.212 [Sb] (II)
(In the formula, [Sb] represents the Sb content (mass%), and [In] represents the In content (mass%)).
In that satisfies
0.5% by mass or more and 1.2% by mass or less of Cu;
Bi of 0.1 mass% or more and 3.0 mass% or less;
It was confirmed that the effect of the present invention is exhibited in a solder alloy containing 1.0 mass% or more and 4.0 mass% or less of Ag and the balance being Sn. Such a solder alloy can be composed of an alloy structure including at least a γ phase and a β-Sn phase in which Sb is dissolved at 150 ° C. or higher, and forms a joint having excellent heat fatigue resistance even in an environment of 175 ° C. It becomes possible.

More preferably, the solder alloy is
0.5% by mass or more and 1.0% by mass or less of Sb;
The following formula (I):
5.5 ≦ [In] ≦ 5.50 + 1.06 [Sb] (I)
In that satisfies
0.5% by mass or more and 1.2% by mass or less of Cu;
Bi of 0.1 mass% or more and 3.0 mass% or less;
1.0 mass% or more and 4.0 mass% or less of Ag are contained, and the remainder consists of Sn. Such a solder alloy can be composed of an alloy structure including at least a γ phase and a β-Sn phase in which Sb is dissolved at 150 ° C. or higher, and has a solder joint portion having further excellent heat fatigue resistance even in an environment of 175 ° C. It becomes possible to form.

Even more preferably, the solder alloy is
0.5% by mass or more and 1.0% by mass or less of Sb;
The following formula (I):
5.5 ≦ [In] ≦ 5.50 + 1.06 [Sb] (I)
And In which is 6.1% by mass or less,
0.5% by mass or more and 1.2% by mass or less of Cu;
Bi of 0.1 mass% or more and 3.0 mass% or less;
1.0 mass% or more and 4.0 mass% or less of Ag are contained, and the remainder consists of Sn. Such a solder alloy can be composed of an alloy structure including a γ phase and a β-Sn phase in which at least Sb is dissolved at 150 ° C. or higher, and has a particularly excellent solder joint property even in an environment of 175 ° C. It becomes possible to form.

The mounting structure of the present invention is characterized in that an electrode part of an electronic component and an electrode part of a circuit board are joined by the solder alloy described above. According to this, even in an environment of 175 ° C., it is possible to provide a mounting structure having a bonding superior in thermal fatigue resistance.

任意 Electronic components and circuit boards can be used arbitrarily. The electrode part of the electronic component and the electrode part of the circuit board may be made of any appropriate conductive material, and these may contain Cu and / or Ni as described above as the members to be joined. Good. Also, the solder alloy can have any form, alone (eg, in the form of powder, yarn solder, melt, preform solder, etc.) or together with flux (eg, solder paste or solder containing solder) Can be used for soldering. The soldering conditions can be appropriately selected.

In one embodiment of the present invention, the solder alloy may have an Sb content of 0.5% by mass or more and 1.0% by mass or less, and an In content satisfying the above formula (I).

In the above aspect of the present invention, the In content may further satisfy that it is 6.1% by mass or less.

The solder alloy of the present invention preferably has an alloy structure including a γ phase and a β-Sn phase in which at least Sb is dissolved at 150 ° C. or higher.

According to another aspect of the present invention, there is provided a mounting structure in which an electronic component is mounted on a circuit board, and the electrode portion of the electronic component and the electrode portion of the circuit board are joined by the solder alloy of the present invention. An implementation structure is provided.

In the present invention, the “solder alloy” may contain unavoidably mixed trace metals as long as the metal composition is substantially composed of the enumerated metals. The solder alloy can have any form and can be used for soldering, for example, alone or together with other components other than metal (eg, flux, etc.).

The solder alloy and mounting structure of the present invention can realize a solder joint having excellent mechanical characteristics even in a high temperature environment of 175 ° C. It is useful for use in a mounting structure of an automobile electrical component that is required to ensure conduction.

Claims

0.5% by mass or more and 1.25% by mass or less of Sb;
The following formula (I) or (II):
In the case of 0.5 ≦ [Sb] ≦ 1.0 5.5 ≦ [In] ≦ 5.50 + 1.06 [Sb] (I)
When 1.0 <[Sb] ≦ 1.25 5.5 ≦ [In] ≦ 6.35 + 0.212 [Sb] (II)
(In the formula, [Sb] represents the Sb content (mass%), and [In] represents the In content (mass%)).
In that satisfies
0.5% by mass or more and 1.2% by mass or less of Cu;
Bi of 0.1 mass% or more and 3.0 mass% or less;
A solder alloy containing 1.0% by mass or more and 4.0% by mass or less of Ag, the balance being Sn.
The solder alloy according to claim 1, wherein the Sb content is 0.5 mass% or more and 1.0 mass% or less, and the In content satisfies the formula (I).
The solder alloy according to claim 2, further satisfying that the In content is 6.1% by mass or less.
The solder alloy according to any one of claims 1 to 3, which has an alloy structure including at least a γ phase and a β-Sn phase in which Sb is dissolved at 150 ° C or higher.
A mounting structure in which an electronic component is mounted on a circuit board, wherein the electrode part of the electronic component and the electrode part of the circuit board are joined by the solder alloy according to any one of claims 1 to 4. Structure.