CN107460368A - Brazing filler metal alloy and use its assembling structure - Google Patents

Abstract

To provide a solder alloy capable of realizing a solder joint excellent in thermal fatigue resistance in a high-temperature environment up to 150° C. in a mounting structure using a metal base substrate. It is a solder alloy containing Sn, Ag, Bi, In, and Cu, and is characterized in that each content rate (mass %) is expressed as [Sn], [Ag], [Bi], [In], For [Cu], it contains Ag in the range of 1.0≤[Ag]≤4.0 and Cu in the range of 0.5≤[Cu]≤1.2. When 0.5≤[Cu]≤1.0, it satisfies 6.74‑1.55×[Cu]≤[In ]≦6.5, 1.0<[Cu]≦1.2, it contains In in the range of 5.168≦[In]≦6.5, Bi in the range of 1.5≦[Bi]≦3.0, and the balance is composed of Sn.

Description

Solder alloy and mounting structure using same

technical field

The present invention mainly relates to a lead-free solder alloy used for soldering electronic components to a metal base substrate on which a circuit is formed, and a mounting structure using the solder alloy.

Background technique

In recent years, in the field of lighting equipment, from the viewpoint of energy saving, the adoption of light emitting diodes (Light Emission Diode, LED) has been carried out. Unlike conventional fluorescent lamps and incandescent lamps, LED chips are soldered to a substrate to form an LED substrate. In the soldering of LED substrates, Sn-Ag based solders are widely used from the viewpoint of melting point, wettability, thermal fatigue resistance, etc., and Sn-3.0% by mass is widely used as a standard lead-free solder alloy. Ag-0.5 mass % Cu.

Since the LED emits heat when emitting light, the temperature of the LED substrate rises when the LED chip is used. As the luminous efficiency of LEDs evolves, the amount of heat generated increases. However, the heat-resistant temperature of a general LED chip is 150° C. or lower. Therefore, it is preferable that the LED substrate has high heat dissipation. In recent years, in addition to heat dissipation, copper and aluminum are used as base metals from the viewpoint of cost and weight. Development of metal base substrates is ongoing.

The term "metal base substrate" refers to a substrate in which a metal layer is disposed on a base metal with an insulating resin layer interposed therebetween, whereby circuits are formed on the base metal. The metal base substrate has excellent heat dissipation compared with a glass epoxy resin board which is a general circuit board, and on the other hand has a larger linear expansion coefficient than a glass epoxy resin board. Therefore, in a metal base substrate to which an electronic component such as an LED chip having a small linear expansion coefficient is soldered, a large difference in linear expansion coefficient occurs between the electronic component and the metal base substrate. The difference in coefficient of linear expansion in such a mounting structure is larger than the difference in coefficient of linear expansion in a mounting structure in which electronic components are soldered to a glass epoxy resin board. From lower temperatures, the solder material that joins between the substrate electrodes on the metal base substrate and the component electrodes of the LED chip is subjected to large thermal stress.

Therefore, in addition to thermal fatigue resistance at 150° C., resistance to high stress at low temperatures is required for lead-free solder alloys used for soldering LED chips to metal base substrates. However, conventional solder alloys do not have sufficient characteristics for use in such severe environments.

As a conventional lead-free solder material excellent in thermal fatigue resistance, Patent Document 1 describes a lead-free solder alloy for soldering with an Au electrode having Au plating on Ni plating containing P. A brazing material characterized in that,

Assuming that the content (mass %) of Ag, Bi, Cu, and In in the brazing material is [Ag], [Bi], [Cu], and [In] respectively, the content of

Ag of 0.3≤[Ag]<4.0 (except for the cases where Ag is 0.5% by mass and 1.0% by mass),

0≤[Bi]≤1.0 Bi,

Cu with 0.2≤[Cu]≤1.2,

In the range of 0.2≤[Cu]<0.5, containing In in the range of 6.0≤[In]≤6.8,

In the range of 0.5≤[Cu]≤1.0, containing In within the range of 5.2+(6-(1.55×[Cu]+4.428))≤[In]≤6.8,

In the range of 1.0<[Cu]≤1.2, containing In in the range of 5.2≤[In]≤6, 8,

The balance is only 87% by mass or more of Sn.

In addition, Patent Document 2 describes a lead-free solder alloy, which is a lead-free solder having a composition of Sn-Ag-Bi-In-Cu in which Cu and In are added to a Sn-Ag-Bi alloy. The composition ratio of Sn, Bi, Ag, Cu, In is,

1.0% by weight ≤ Bi ≤ 12.0% by weight,

0.5% by weight ≤ Ag ≤ 6.0% by weight,

0.1 wt% ≤ Cu ≤ 3.0 wt%,

0.5 wt% ≤ In ≤ 10.0 wt%,

The remainder consists essentially of tin.

prior art literature

patent documents

Patent Document 1: Japanese Patent No. 5732627

Patent Document 2: Japanese Patent Application Laid-Open No. 10-314980

The problem to be solved by the invention

The lead-free solder alloy described in Patent Document 1 is a solder alloy containing Ag, Bi, Cu, and In at arbitrary content ratios, and the balance is only Sn, and is used to prevent soldering that occurs when soldering Au substrate electrodes. The reduction of the In content of the material. The solder alloy is considered to be no problem for use in the case of soldering LEDs to glass epoxy substrates, but for the large difference in linear expansion coefficient produced in the case of soldering LEDs to metal base substrates, then No countermeasures are mentioned, so it is considered difficult to maintain the thermal fatigue resistance even at a temperature of 150°C.

In Patent Document 2, it is disclosed that the content of Sn, Bi, Ag, Cu, and In of the lead-free solder alloy ranges, and this range is based on having a melting point equivalent to that of a Sn-Pb-based solder alloy and excellent wettability. Moisture, mechanical strength for the purpose. In particular, Cu and In are added for the purpose of lowering the melting temperature of the brazing material and improving the wettability of the solder melt. This solder alloy takes into account that there is no problem with soldering LEDs to glass epoxy boards, but there is no mention of the large difference in coefficient of linear expansion that occurs when soldering LEDs to metal base substrates Any countermeasures, therefore, are considered to be difficult to maintain thermal fatigue resistance even at a temperature of 150°C.

Therefore, when using existing solder alloys for soldering LED chips to metal base substrates, since the thermal fatigue resistance of the solder alloys cannot be maintained at a temperature of 150°C, it is necessary to suppress the output power of the LED chips, and to use Small-sized LED chips reduce thermal stress, so there is a problem that the performance of LED chips cannot be fully utilized.

Contents of the invention

An object of the present invention is to provide a solder alloy that maintains excellent thermal fatigue resistance in a high-temperature environment of up to 150° C. when used for soldering electronic components to metal base substrates.

means to solve the problem

A gist of the present invention is to provide a kind of solder alloy, and it contains Ag, Bi, In and Cu, and surplus is made of Sn, satisfies following formula:

1.0≤[Ag]≤4.0 (1)

0.5≤[Cu]≤1.2 (2)

1.5≤[Bi]≤3.0 (3)

(wherein, [Ag], [Cu], and [Bi] represent the contents (mass %) of Ag, Cu, and Bi, respectively),

When 0.5≤[Cu]≤1.0, the following formula is satisfied:

6.74-1.55×[Cu]≤[In]≤6.5 (4)

When 1.0<[Cu]≤1.2, the following formula is satisfied:

5.168≤[In]≤6.5 (5)

(In the formula, [In] represents the content rate (mass %) of In).

In one form of the present invention, the solder alloy also satisfies the following formula:

2.0≤[Bi]≤3.0 (6)

8.0≤[In]+[Bi] (7)

In one form of the present invention, the solder alloy further contains Sb and satisfies the following formula:

0.5≤[Sb]≤1.25 (8)

([Sb] in the formula represents the content rate (mass %) of Sb).

In one aspect of the present invention, a solder alloy is used for soldering electronic components to a metal base substrate.

According to another aspect of the present invention, there is provided a mounting structure in which a component electrode of an electronic component and a substrate electrode of a metal base substrate are soldered by the solder alloy according to any one of the above aspects.

In addition, in this specification, adding [] to the element constituting the solder alloy means the content rate (mass %) of the element in the solder alloy.

In addition, the "brazing filler metal alloy" in the present invention may contain a trace amount of unavoidable inclusion of metals as long as its metal composition is substantially composed of the listed metals. The solder alloy can have any form, and can be used for soldering alone or together with components other than metal (for example, flux, etc.).

Invention effect

According to the present invention, in the solder alloy containing Sn, Ag, Bi, In, Cu, and Sb, a predetermined content rate is selected for each element except Sn, and the Bi content rate is 1.5% by weight or more and 3.0% by mass. % or less, the Cu content is not less than 0.5% by mass and not more than 1.2% by mass, especially when the In content is 0.5≤[Cu]≤1.0, the In content satisfies the formula (4), and when 1.0<[Cu]≤1.2, the In content satisfies the formula (5), more particularly, the Bi content and the In content satisfy the formula (7), thereby providing a solder alloy for brazing a metal base substrate facing aluminum and copper as a base material. In the case of an electronic component partially made of ceramics, excellent thermal fatigue resistance is maintained at a temperature of 150°C.

Description of drawings

FIG. 1 is a view showing the structure state of a conventional lead-free solder alloy.

FIG. 2 is a view showing the structure state of the lead-free solder alloy according to the embodiment of the present invention.

FIG. 3 is a graph showing mechanical properties of a solder alloy according to an embodiment of the present invention at room temperature.

FIG. 4 is a graph showing mechanical properties at 150° C. of a solder alloy according to an embodiment of the present invention.

FIG. 5 is a graph showing mechanical properties of a solder alloy according to an embodiment of the present invention at room temperature.

FIG. 6 is a graph showing mechanical properties at 150° C. of a solder alloy according to an embodiment of the present invention.

FIG. 7 is a graph showing mechanical properties of a solder alloy according to an embodiment of the present invention at room temperature.

FIG. 8 is a graph showing mechanical properties at 150° C. of a solder alloy according to an embodiment of the present invention.

FIG. 9 is a diagram showing a mounting structure in which a reliability test of the solder alloy according to the embodiment of the present invention is carried out.

detailed description

As a result of research and development by the inventors of the present inventors on the mechanical properties and microstructure at temperatures below room temperature and at a temperature of 150°C, they have newly found that in lead-free solder alloys whose main component is Sn, by containing In, Cu, and Bi can achieve improvements in mechanical properties that have not been achieved until now. The following describes the advantageous effects of including In, Bi, Cu, Ag, and Sb at the content rates specified in the present invention in a lead-free solder alloy whose main component is Sn.

(In content, Bi content)

In a solder alloy mainly composed of Sn, in the low In content region where the In content is about 15% by mass or less, the β-Sn phase, which is an alloy phase in which In is dissolved in Sn, is formed at a temperature around room temperature . FIG. 1 is a view showing the structure state of a conventional solder alloy containing Sn and In. In the figure, the region indicated by the blank indicates the β-Sn phase.

The term "solid solution" in this specification refers to a phenomenon in which a part of the crystal lattice of the base metal is substituted by a solid solution element at the atomic level. In the crystal structure in which solid solution occurs, the lattice of the parent element is distorted due to the difference in atomic diameter between the matrix metal element and the solid solution element, and due to this distortion, the movement of crystal defects such as dislocations during stress loading is suppressed, so The occurrence of solid solution leads to an increase in the strength of the alloy. On the other hand, ductility under stress load decreases. The strength of the solder alloy due to solid solution increases, and increases as the content of solid solution elements increases.

When In is dissolved in a Sn-based brazing filler metal at a predetermined content rate, a phase transformation to a γ phase (InSn ₄ ) of a different structure occurs when the temperature exceeds 100°C. That is, it becomes a two-phase coexistence state (γ+β-Sn) in which different two phases coexist (right in FIG. 1 ). Since this two-phase coexistence state causes slip to easily occur at the grain boundary, an alloy in which In is dissolved in a predetermined content in the Sn-based solder exhibits improved ductility at a temperature exceeding 100°C.

When the In content in the Sn-based solder is greater than a predetermined content, the transformation to the γ phase occurs excessively. In this case, since the volumes of the lattice structures of the γ phase and the β-Sn phase are different, repeated heat cycles are applied, and self-deformation of the solder alloy occurs. This self-deformation causes internal fractures of the solder joints and short circuits between adjacent solder joints, so excessive phase transformation in the alloy is not preferable.

When In is dissolved in the Sn-based brazing filler metal at a predetermined content rate, not only the ductility at a temperature exceeding 100° C. is improved, but also the strength of the brazing filler metal alloy is improved. However, when used in a temperature environment exceeding 100° C., there is a limit to improving the strength by increasing the In content because the above-mentioned excessive phase transformation occurs. In the solder alloy of the present invention, the ductility of the solder alloy at a temperature exceeding 100° C. is improved without excessive phase transformation, and the In content that can increase the strength of the solder alloy is preferably 5.168% by mass. Above, more preferably 5.3% by mass or more, and preferably 6.5% by mass or less, more preferably 6.2% by mass or less.

As a result of repeated research and development on this problem, the inventors of the present invention have found that this problem can be solved by including Bi element in the alloy within a predetermined range, and the ductility at high temperature can be further improved.

Like In, Bi is solid-dissolved in a certain amount in the solder alloy mainly composed of Sn. The solid solution of Bi and In leads to an increase in strength, but on the other hand, generally leads to a decrease in ductility.

FIG. 2 is a view showing the structure state of a solder alloy containing Sn, In, and Bi in the present embodiment. At low temperatures around room temperature, a certain amount of Bi is uniformly solid-dissolved in the β-Sn phase (Fig. 2 left). Therefore, similarly to In, the strength of the lead-free solder alloy is improved. The Bi content of the solder alloy when Bi is dissolved in the β-Sn phase without segregation at room temperature is 3.0% by mass or less. In addition, when the Bi content of the solder alloy is 1.5% by mass or more, preferably 2.0% by mass or more, a favorable effect of improving strength can be obtained.

At a temperature exceeding 100°C, a part of the β-Sn phase will change to the γ phase, but in this case, Bi will not dissolve in the γ phase, but only in the β that has not phased into the γ phase. -Solid solution in the Sn phase (Figure 2 right). Therefore, since the amount of Bi solid-dissolved in the β-Sn phase that has not transformed into the γ phase increases, the strength of the β-Sn phase further increases. Thus, it was found that the above-mentioned grain boundary slip tends to occur due to the widening of the difference in strength between the β-Sn phase and the γ phase, so that the ductility at high temperature is contrary to expectations.

(Cu content rate)

By including Cu in the brazing filler metal, the melting point during brazing can be lowered, and the selectivity of the material of the material to be joined can also be improved.

The material to be joined by brazing is mainly a material in which Cu or Ni as a base material has been subjected to various plating and pre-flux treatments. When the base material of the object to be joined is Ni, a solder alloy containing In is used for brazing, and a part of In contained in the solder alloy is absorbed by the interface reaction layer (Ni ₃ Sn ₄ ). As a result, the mechanical properties of the solder joint after brazing will change. Therefore, in the brazing of the joined body whose base material is Ni, the brazing filler metal used needs to contain a lot of this material that is absorbed by the alloy interface reaction layer. The amount of In. However, since various electronic components are mounted on a single circuit board in an actual circuit board, it is difficult to preliminarily adjust the In content when mounting electronic components whose base materials are Cu and Ni.

In the present invention, a certain amount of Cu is contained in the solder alloy, whereby a Cu ₆ Sn ₅ alloy layer is formed in the interface reaction layer during brazing. Incorporation of In can be prevented by this alloy layer, and the selectivity of the solder alloy to be joined can be improved. In order to prevent In incorporation by the method described above, the preferred Cu content is 0.5% by mass or more, and the upper limit of the Cu content is preferably 1.2% by mass. By setting this upper limit, the wet spread of the brazing filler metal at the time of brazing can be maintained.

Therefore, the range of the preferable Cu content rate in the solder alloy of this invention is represented by Formula (2).

0.5≤[Cu]≤1.2 (2)

The incorporation of In leads to a decrease in the In content of the solder alloy, which is most notable when the base materials of both the substrate electrode and the component electrode are Ni. In this case, when the Cu content is in the range of 0.5≤[Cu]≤1.0, the (In reduction rate) is given by

(In reduction rate) = 1.572-1.55 x (Cu content rate) (9) represents.

In this specification, the reduction rate of an element means (the content rate of the element in the solder alloy before reduction)-(the content rate of the element in the solder alloy after reduction).

When the Cu content is 1.0<[Cu]≦1.2, it can be seen that the decrease in the In content of the solder alloy hardly occurs.

When solder alloys are used to join any kind of objects to be joined, it is required to ensure reliability. In order to maintain reliability when the decrease in the In content is the most significant, the minimum value of the In content of the solder alloy takes into account the above-mentioned In content in the range of 0.5≤[Cu]≤1.0 where the decrease in the In content occurs. The reduction rate is represented by the following formula (10).

(Minimum value of In content)＝5.168+(1.572-1.55×[Cu])

=6.74-1.55×[Cu] (10)

In order to ensure the reliability of the solder alloy when joining any kind of objects to be joined, it is preferable that the content of the solid-solutionable element in the solder alloy is higher than 8.0% by mass.

Therefore, in the solder alloy of the present invention, it is preferable that the In content and the Bi content satisfy the formula (7).

8.0≤[In]+[Bi] (7)

Therefore, in the range of 0.5≦[Cu]≦1.0 where the decrease in the In content occurs, the following formula holds.

8.0≤6.74-1.55×[Cu]+[Bi] (11)

Therefore, the preferred Cu content and Bi content in the solder alloy of the present invention are, respectively,

0.5≤[Cu]≤1.2 (2)

1.5≤[Bi]≤3.0 (3)

more preferably

0.5≤[Cu]≤1.2 (2)

2.0≤[Bi]≤3.0 (6)

The preferable In content rate in the solder alloy of the present invention is when 0.5≤[Cu]≤1.0 is

6.74-1.55×[Cu]≤[In]≤6.5 (4)

When 1.0<[Cu]≤1.2, it is

5.168≤[In]≤6.5 (5)

Furthermore, it is more preferable that the In content and the Bi content of the solder alloy of the present invention satisfy the formula (7).

8.0≤[In]+[Bi] (7)

(Ag content rate)

The solder alloy of the present invention contains Ag in the form of Ag ₃ Sn or Ag ₂ In in the solder alloy. By containing Ag in the solder alloy, the wettability during brazing can be improved, and the melting point can be lowered.

In order to uniformly melt the solder alloy by reflow, it is preferable to set the reflow peak temperature at a temperature higher than the liquidus temperature of the solder alloy by 10° C. or more. Considering the heat resistance temperature of electronic components, the reflow peak temperature is preferably 240°C or lower, and therefore, the liquidus temperature of the solder alloy is preferably 230°C or lower. In the solder alloy of the present invention, the preferred range of Ag content for achieving the liquidus temperature is as follows.

1.0≤[Ag]≤4.0 (1)

When the Ag content is in the above range, there is no difference of 10° C. or more between the liquidus temperature of the solder alloy and the reflow peak temperature, and the solder alloy can be uniformly melted by reflow soldering.

(Sb content rate)

By including Sb in the solder alloy containing Sn as the main component and containing In, the temperature at which the phase transformation between the β-Sn phase and the γ phase occurs can be raised. Since the chip bonding portion of the LED in the LED chip deteriorates due to repeated heat cycles, if an increase in heat generation occurs, the inclusion of Sb prevents excessive phase transformation from occurring, thereby preventing deterioration of the soldered portion. In the solder alloy of the present invention, the preferred range of Sb content for increasing the temperature at which transformation occurs is as follows.

0.5≤[Sb]≤1.25 (8)

If it is lower than this range, the temperature at which the phase transformation occurs cannot be raised sufficiently, and the deterioration of the brazed joint cannot be prevented. If it exceeds this range, In and Sb in the solder alloy form a compound InSb, resulting in a reduction in ductility.

【Example】

(Example 1)

In order to clarify the influence of the Bi content on the strength and elongation at 150° C. of a solder alloy containing Sn as a main component, a solder alloy of the present invention was prepared by the method shown below and tested.

make

The elements [Ag], [Bi], [In], and [Cu] contained in the solder alloy are 3.5, 0.5 to 4.0, 6.0, and 0.8, respectively, and the balance is Sn, and the total is 100g and weighed .

The weighed amount of Sn was put into a ceramic crucible, and the crucible was set in a nitrogen atmosphere in an electric jacketed heating furnace whose temperature was adjusted to 500°C. Add each element in order of melting point from low to high, and stir for 3 minutes for each one. After all the constituent elements were charged, the crucible was taken out from the electric jacketed heating furnace, immersed in a container filled with water at 25° C., and cooled to prepare a brazing filler metal alloy.

test

The prepared brazing filler metal alloy was put into the crucible again, heated to 250° C. to melt in an electric jacketed heating furnace, and poured into a graphite mold processed into a tensile test piece shape to prepare a tensile test piece. The sheet for the tensile test was in the shape of a round bar with a diameter of 3 mm and a length of 15 mm having a constricted portion. In order to evaluate the mechanical properties (tensile strength and elongation) of the prepared tensile test pieces, tensile tests at room temperature and 150° C. were performed using a tensile testing machine. The results are shown in Table 1, Figure 3 and Figure 4.

【Table 1】

As shown in Table 1, the tensile strengths of Existing Example 1, Existing Example 2, Examples 1-1, 1-2, and Comparative Example 1-2 containing Bi are all higher than those of Comparative Example 1-1 not containing Bi. high tensile strength. On the other hand, Comparative Example 1-2 having a significantly lower elongation than Comparative Example 1-1 and having a Bi content of 4.0% by mass exhibited brittle fracture. In Conventional Example 1, Conventional Example 2, and Examples 1-1 and 1-2 in which the Bi content was 0.5 to 3.0% by mass, no significant decrease in elongation was observed.

As shown in Table 1, the tensile strength at 150° C. of Bi-containing Conventional Example 1, Conventional Example 2, Examples 1-1, 1-2, and Comparative Example 1-2 was significantly higher than that of the Comparative Example not containing Bi. The 150°C tensile strength of 1-1 did not change significantly. On the other hand, the elongation at 150°C of Bi-containing Conventional Example 1, Conventional Example 2, Examples 1-1, 1-2, and Comparative Example 1-2 can be compared with that of Comparative Example 1-1 at 150°C. The lower elongation has been increased. In particular, when the Bi content is 2.0% by mass or more, the elongation at 150° C. increases significantly.

(Example 2)

Next, in order to clarify the influence of the In content on the tensile strength and elongation at 150°C of a solder alloy mainly composed of Sn, [Ag], [Bi], [In], and [Cu] are respectively 3.5, 2.0, 5.0 to 7.0, 0.8, or 0.5, and the balance is Sn, each element is weighed, and a brazing filler metal alloy is produced by the same method as in Example 1. The prepared solder alloy was tested by the same method as in Example 1, and the test results are shown in Table 2, FIG. 5 and FIG. 6 .

【Table 2】

As shown in Table 2, as the In content increases, the tensile strength increases. On the other hand, a significant decrease in elongation with an increase in the In content was not observed.

As shown in Table 2, the tensile strength at 150° C. increases as the In content increases. Comparative Examples 2-1 and 2-2 have lower elongation than Conventional Examples 1 and 2, while Examples 2-1 to 2-3 show higher elongation than Conventional Examples 1 and 2. value.

(Example 3)

Next, in order to clarify the influence of the In content on the strength and ductility at high temperature of a solder alloy mainly composed of Sn having a Bi content of 3.0, [Ag], [Bi], [In], [ Cu] was 3.5, 3.0, 5.0 to 7.0, 0.8, or 0.5, and the balance was Sn, and each element was weighed, and a solder alloy was produced by the same method as in Example 1. For the prepared solder alloy, the test was carried out in the same manner as in Example 1, and the test results are shown in Table 3, Fig. 7 and Fig. 8 .

【table 3】

As shown in Table 3, the tensile strength increases as the In content increases. On the other hand, a significant decrease in elongation with an increase in the In content was not observed.

As shown in Table 3, the tensile strength at 150° C. increases as the In content increases. When the In content is 5.0 to 6.0, the elongation at 150° C. increases significantly with the increase of the In content, but when the In content exceeds 6.0, a significant decrease is seen.

In the above (Example 1) to (Example 3), the effects of the In content and the Bi content on the properties of the solder alloy will be examined below.

The tensile strength at room temperature increases as the Bi content increases. This is considered to be because the amount of Bi solid-dissolved in the β-Sn phase increases as the Bi content increases, and the β-Sn phase becomes stronger. On the other hand, the elongation at room temperature hardly changes in a solder alloy having a Bi content of 3.0% by mass or less, and decreases in a solder alloy having a Bi content of more than 3.0% by mass. This is considered to occur due to segregation of Bi.

The increase in the tensile strength at 150° C. due to the increase in the Bi content was hardly visible. This is considered to be because Bi is solid-dissolved only in the β-Sn phase and therefore has no influence on the strength of the γ phase. On the other hand, the elongation at 150°C of an alloy with a Bi content of 2.0 to 3.0% by mass is higher than room temperature when the In content is 5.5 to 6.5% by mass, but is When it is 5.0 or 7.0 mass %, it does not necessarily improve compared with room temperature. This is considered as follows.

In the improvement of the elongation at a temperature of 150°C of a solder alloy containing Sn as a main component, it can be seen that the grain boundary formed by the coexistence of the β-Sn phase and the γ phase at a temperature of 150°C has an influence slip. When Bi is contained in such a solder alloy, when the γ phase is generated as the temperature rises, since Bi is solid-dissolved only in the β-Sn phase, the Bi concentration in the β-Sn phase increases, and only the strength of the β-Sn phase improve. In this way, the difference in strength between the β-Sn phase and the γ phase is enlarged, and the grain boundary slip is promoted, so that the elongation increases as the temperature rises. The improvement in the elongation at 150° C. of the alloys having a Bi content of 2.0 to 3.0 mass % seen in Examples 1 to 3 above is considered to be attributable to the promotion of grain boundary slip. On the other hand, when the In content was 5.0% by mass or 7.0% by mass, the elongation did not necessarily increase. This is considered to be because the ratio of γ to the β-Sn phase is too small or too high, so compared with the case where the In content is 5.5 to 6.5% by mass, there are few grain boundaries between the two phases, and the above-mentioned grain boundary cannot be effectively obtained. The improvement of elongation brought about by the promotion of boundary slip.

(Example 4)

In a mounting structure in which an electronic component is soldered to a metal base substrate using a solder alloy mainly composed of Sn, in order to evaluate the influence of the Bi content and the In content on the thermal fatigue resistance, the following The mounting structure used for the test of the thermal fatigue resistance characteristic was produced by the method.

make

Set [Ag], [Bi], [In], [Cu] to 3.5, 0.5-3.5, 5.0-7.0, and 0.8, respectively, and make the balance Sn, weigh each element, and make it by the same method as in Example 1. Brazing alloy. The prepared solder alloy was processed into a solder powder of several 10 μm, and the solder powder and flux were weighed in a weight ratio of 90:10 and mixed to prepare a solder paste.

Using a metal mask with a thickness of 150 μm, the circuit board electrode 102 was prepared on the metal base 101 through an insulating layer. The produced solder paste was printed on the substrate electrode 102 on the metal base substrate 100 having a thickness of 1.6 mm. On the printed solder paste, a chip resistor 103 with a size of 1608 (1.6mm×0.8mm) was bonded, and reflow heating was performed at a maximum temperature of 240°C to form a soldered head 105 to produce a mounting structure. The base material of the substrate electrode 102 of the metal base substrate 100 is Cu, and the base material of the metal base 101 is aluminum.

The mounting structure manufactured in the above manner for carrying out the reliability test of the solder alloy is shown in FIG. 9 . 100 denotes a metal base substrate, 101 denotes a metal substrate, 102 denotes a circuit board electrode, 103 denotes a chip resistor, 104 denotes a component electrode, 105 denotes a solder joint, and 106 denotes an insulating layer.

test

The reliability test was performed by repeating a heat cycle with a load of -40°C on the low temperature side and 150°C on the high temperature side for 30 minutes each. Table 4 shows the results. The resistance value is measured for each load thermal cycle, and the number of cycles at which the resistance value rises to more than 2 times is regarded as the service life. In the judging criteria column, the case where no increase in the resistance value was observed after 2,000 cycles was described as ○, and the case where no increase in the resistance value was observed after 2,500 cycles was described as ◎. In addition, with regard to the deformation caused by the phase transformation of the solder alloy containing Sn as the main component and containing In seen in the prior literature, the presence or absence of deformation in 2000 cycles was also evaluated.

【Table 4】

As shown in Table 4, the lifetimes of Conventional Examples 4-1 to 4-4 were 2000 cycles or less, while Examples 4-1 to 4-12 all had lifetimes of 2000 cycles or more. [Ag], [Bi], [In], and [Cu] are 3.5, 2.0-3.0, 5.5-6.5, and 0.8, respectively, and the balance is Sn. The life of Examples 4-5 to 4-12 is particularly excellent, being 2500 more than one cycle. On the other hand, as shown in Comparative Examples 4-2 and 4-5, even if the In content is 5.5 to 6.5% by mass, if the Bi content is 1.0% by mass or less, the lifetime is still less than 2000 cycles. This is considered to be due to the fact that the amount of Bi is too small, and thus the improvement in mechanical properties obtained becomes small. In addition, as shown in Comparative Examples 4-16, 4-17, and 4-18, even if the In content rate is 5.5 to 6.5 mass%, if the Bi content rate is 3.5 mass% or more, although the effect of improving the mechanical properties can be obtained, But the lifetime will still be less than 2000 cycles. This is considered to be because the amount of Bi is too large, and repeated exposure to high temperature causes Bi to segregate at the crystal grain boundaries, and the ductility decreases with time.

As shown in Table 4, Comparative Examples 4-1, 4-4, 4-7, 4-9, 4-11, 4-13, and 4-15 having an In content of 5.0% by mass regardless of the Bi content, The life span is less than 2000 cycles. From these results, it can be seen that when the In content is small, the elongation at high temperature cannot be improved regardless of the Bi content. In addition, in Comparative Examples 4-3, 4-6, 4-8, 4-10, 4-12, 4-14, and 4-19 with an In content of 7.0% by mass, regardless of the Bi content, the lifetime was lower than that of 2000 cycles. In these comparative examples, the deformation of the solder alloy was also seen, so it is considered that the phase transformation from the β-Sn phase to the γ phase occurred excessively.

(Example 5)

Table 5 shows the results of preparing solder alloys containing each element in a range suitable for the effect of the solder alloy of the present invention and evaluating the thermal fatigue resistance. The preparation method and test method of the solder alloy are the same as in Example 4. The base material of the circuit board electrode 102 of the metal base substrate 100 is Cu and Au/Ni, and the base material of the metal base 101 is aluminum.

【table 5】

As shown in Table 5, Examples 5-1 to 5-11 containing each element in a range suitable for the effect of the solder alloy of the present invention exhibited a lifetime of 2000 cycles or more. Particularly embodiment 5-2, 5-4, 5-5, 5-8, all have the life-span of more than 3000 cycles when the base material of substrate electrode is Cu, Au/Ni, carry out Examples 5-1, 5-6, 5-7, 5-10, and 5-11 had a lifetime of 3000 cycles or more when the base material of the substrate electrode was Cu. On the other hand, in Comparative Examples 5-1 to 5-7 and Conventional Example 5-1, certain elements contained are out of the range in which the effect of the solder alloy suitable for the present invention is exhibited, and therefore, the base material of the substrate electrode is In the case of Cu or Au/Ni or any of Cu and Au/Ni, the lifetime in the reliability test was less than 2000 cycles. In the range of 0.5 ≤ [Cu] ≤ 1.0, considering that the decrease in the In content based on the formula (9) occurs in the Au/Ni electrode, it can be seen that in order to express the effect of the solder alloy of the present invention, even if the above decrease occurs, the Preferably, the In content is 5.168 or more.

From the above, in the preferred solder alloy of the present invention, the Bi content, the Cu content, and the Ag content are respectively

1.5≤[Bi]≤3.0 (3)

0.5≤[Cu]≤1.2 (2)

1.0≤[Ag]≤4.0 (1)

In content rate, when 0.5≤[Cu]≤1.0,

6.74-1.55×[Cu]≤[In]≤6.5 (4)

When 1.0<[Cu]≤1.2,

5.168≤[In]≤6.5 (5)

The balance is Sn.

In the more preferable solder alloy of the present invention, the Bi content, the Cu content, and the Ag content are respectively

2.0≤[Bi]≤3.0 (6)

0.5≤[Cu]≤1.2 (2)

1.0≤[Ag]≤4.0 (1)

In content rate, when 0.5≤[Cu]≤1.0,

6.74-1.55×[Cu]≤[In]≤6.5 (4)

When 1.0<[Cu]≤1.2,

5.168≤[In]≤6.5 (5)

The above [In] and [Bi] satisfy 8.0≤[In]+[Bi] (7)

The balance is Sn.

In addition, in the solder alloy of the present invention, part of Sn may be substituted by Sb within the range of 0.5≤[Sb]≤1.25 (8).

Industrial availability

The solder alloy of the present invention can realize a solder joint having excellent thermal fatigue resistance at a temperature of 150° C. and a mounting structure having the same, for example, in a device equipped with components with large heat dissipation such as LEDs and power devices. It is useful for the utilization of installation structures, etc.

Symbol Description

100 metal base substrate

101 aluminum substrate

102 Circuit Board Electrodes

103 chip resistor

104 Component electrodes

105 brazed head

106 insulating layer

Claims (5)

1. a solder alloy, wherein, contains Ag, Bi, In and Cu, and surplus is made of Sn, satisfies following formula: 1.0≤[Ag]≤4.0 0.5≤[Cu]≤1.2 1.5≤[Bi]≤3.0 In the formula, [Ag], [Cu] and [Bi] represent the mass percent content of Ag, Cu and Bi, respectively, When 0.5≤[Cu]≤1.0, the following formula is satisfied: 6.74-1.55×[Cu]≤[In]≤6.5 When 1.0<[Cu]≤1.2, the following formula is satisfied: 5.168≤[In]≤6.5 In the formula, [In] represents the mass percent content of In. 2. solder alloy according to claim 1, wherein, Bi and In also satisfy following formula: 2.0≤[Bi]≤3.0 8.0≤[In]+[Bi]. 3. The solder alloy according to claim 1 or 2, wherein a part of Sn is replaced by Sb, and Sb satisfies 0.5≤[Sb]≤1.25 In the formula, [Sb] represents the mass percent content of Sb. 4. The solder alloy according to any one of claims 1 to 3, which is used for soldering electronic components to a metal base substrate. 5. A mounting structure in which a component electrode of an electronic component and a substrate electrode of a metal base substrate are soldered by the solder alloy according to any one of claims 1 to 4.