TW201742930A - Solder alloy and mounting structure using the same realizing a solder joint excellent in thermal fatigue resistance under a high temperature environment - Google Patents

Abstract

This invention aims to provide a solder alloy for realizing a solder joint excellent in thermal fatigue resistance under a high temperature environment of 150 DEG C even in a mounting structure using a metal base substrate. The solution is to provide a solder alloy, which is characterized by having the solder alloy composed of Sn, Ag, Bi, In, and Cu, wherein when each content (mass%) is defined as [Sn], [Ag], [Bi], [In], [Cu], Ag is in the range of 1.0 ≤ [Ag] ≤ 4.0; Cu is in the range of 0.5 ≤ [Cu] ≤ 1.2; and In is in the range when 0.5 ≤ [Cu] ≤ 1.0 , 6.74-1.55 × [Cu] ≤ [In] ≤ 6.5 and when 1.0 <[Cu] ≤ 1.2, 5.168 ≤ [In] ≤ 6.5; and Bi is in the range of 1.5 ≤ [Bi] ≤ 3.0; and then the remaining part is Sn.

Description

Solder alloy and mounting structure using the same

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lead-free solder alloy mainly used for soldering electronic parts to a metal base substrate on which an electric circuit has been formed, and a mounting structure using the solder alloy.

BACKGROUND OF THE INVENTION In recent years, based on the viewpoint of energy saving, the use of Light Emission Diode (LED) has been expanded in the field of lighting machines. The LED chip is different from a conventional fluorescent lamp or a white thermal ball, and can be soldered on a substrate to form an LED substrate. From the viewpoints of melting point, wettability, and heat fatigue resistance, Sn-Ag solder is widely used for soldering of LED substrates, and Sn-3.0% by mass of Ag-0.5% by mass of Cu is widely used for standard lead-free solder alloys.

Since the LED generates heat when it emits light, the temperature of the LED substrate rises when the LED chip is used. As the luminous efficiency of LEDs increases, the heat generated is stronger. However, since the general LED chip has a heat resistance temperature of 150 ° C or less, the LED substrate preferably has a high heat release property. In recent years, a metal base substrate using copper or aluminum as a base metal has been developed from the viewpoint of heat release property and cost and weight.

The metal base substrate refers to a substrate on which a metal layer is disposed on the base metal through the insulating resin layer to form a circuit on the base metal. The metal base substrate has excellent heat release properties compared to a circuit substrate of a general glass epoxy substrate, and has a larger coefficient of linear expansion than a glass epoxy substrate. Therefore, a metal base substrate such as an electronic component such as an LED chip having a small coefficient of linear expansion is welded, and a significant difference in linear expansion coefficient is generated between the electronic component and the metal base substrate. The difference in linear expansion coefficient of such a mounting structure is larger than the difference in linear expansion coefficient of the mounting structure in which the electronic component is soldered on the glass epoxy substrate, so the metal base substrate is lower than the case where the glass epoxy substrate is used. When the upper substrate electrode is bonded to the component electrode of the LED chip, a large thermal stress is applied to the bonded solder material.

Therefore, for the lead-free solder alloy for soldering the LED wafer to the metal base substrate, in addition to the thermal fatigue resistance of 150 ° C, it is necessary to have resistance to withstand a large stress generated from a low temperature. However, conventional solder alloys have not yet fully possessed the characteristics used in such harsh environments.

As a lead-free solder material excellent in heat fatigue resistance, Patent Document 1 describes a lead-free solder alloy which is used for soldering an Au electrode having an Au plating material to a Ni-containing plating material containing P. When the content ratio (% by mass) of Ag, Bi, Cu, and In in the solder material is [Ag], [Bi], [Cu], or [In], respectively, 0.3: [Ag] < 4.0 Ag (except for the cases where Ag is 0.5% by mass and 1.0% by mass), 0 ≦ [Bi] ≦ 1.0 Bi and 0.2 ≦ [Cu] ≦ 1.2 Cu; and, in the range of 0.2 ≦ [Cu] < 0.5 Inside, containing In in the range of 6.0 ≦ [In] ≦ 6.8; in the range of 0.5 ≦ [Cu] ≦ 1.0, containing 5.2 + (6-(1.55 × [Cu] + 4.428)) ≦ [In] ≦ 6.8 In; in the range of 1.0 < [Cu] ≦ 1.2, contains In in the range of 5.2 ≦ [In] ≦ 6.8; and the remainder is only 87% by mass or more of Sn.

Further, Patent Document 2 describes a lead-free solder alloy characterized by being a lead-free solder composed of Sn-Ag-Bi-In-Cu containing Cu or In as a Sn-Ag-Bi-based alloy, and Sn, Bi, and Ag. The composition ratio of Cu, In is 1.0% by weight ≦Bi≦12.0% by weight, 0.5% by weight ≦Ag≦6.0% by weight, 0.1% by weight ≦Cu≦ 3.0% by weight, 0.5% by weight ≦In≦10.0% by weight and the remainder It consists essentially of tin. Prior Technical Literature Patent Literature

Patent Document 1: Japanese Patent No. 5732627 Patent Document 2: Japanese Laid-Open Patent Publication No. Hei 10-314980

SUMMARY OF THE INVENTION PROBLEMS TO BE SOLVED BY THE INVENTION The lead-free solder alloy described in Patent Document 1 is a solder alloy having Ag, Bi, Cu, and In at an arbitrary content and having only Sn in the remaining portion, which can prevent solder generated when the Au substrate electrode is soldered. The In content is reduced. Although the solder alloy can be used to solder the LED to the glass epoxy substrate undoubtedly, no significant countermeasures have been proposed for the difference in linear expansion coefficient generated when the LED is soldered to the metal base substrate, so it is expected to be at a temperature of 150 ° C. It is also difficult to maintain the heat fatigue resistance.

Patent Document 2 discloses a range of content ratios of Sn, Bi, Ag, Cu, and In which the lead-free solder alloy has a melting point, excellent wettability, and mechanical strength similar to those of the Sn—Pb-based solder alloy. In particular, Cu and In are added in order to reduce the melting temperature of the solder material and to improve the wettability of the solder melt. Although the solder alloy can be used to solder the LED to the glass epoxy substrate undoubtedly, no significant countermeasures have been proposed for the difference in linear expansion coefficient generated when the LED is soldered to the metal base substrate, so it is expected to be at a temperature of 150 ° C. It is also difficult to maintain the heat fatigue resistance.

Therefore, if a conventional solder alloy is used for soldering an LED wafer to a metal base substrate, the thermal fatigue resistance of the solder alloy cannot be maintained at a temperature of 150 ° C, so it is necessary to suppress the output power of the LED wafer or use a small-sized LED. Since the wafer is used to reduce thermal stress, there is a problem that the performance of the LED chip cannot be sufficiently exhibited.

An object of the present invention is to provide a solder alloy which can maintain excellent heat fatigue resistance in a high temperature environment of up to 150 ° C even when it is used for soldering electronic parts to a metal base substrate. Means to solve the problem

According to one of the gist of the present invention, a solder alloy containing Ag, Bi, In, and Cu and the remainder consisting of Sn and satisfying the following formula: 1.0 ≦ [Ag] ≦ 4.0 (1) 0.5 ≦ [Cu] ≦ can be provided. 1.2...(2) 1.5≦[Bi]≦3.0...(3) (wherein, [Ag], [Cu], and [Bi] respectively indicate the contents of Ag, Cu, and Bi (% by mass)); 0.5≦[ When Cu]≦1.0, the following formula is satisfied: 6.74-1.55×[Cu]≦[In]≦6.5...(4); 1.0<[Cu]≦1.2, the following formula is satisfied: 5.168≦[In]≦6.5...( 5) (In the formula, [In] represents the content ratio (% by mass) of In).

In one aspect of the invention, the solder alloy more satisfies the following formula: 2.0 ≦ [Bi] ≦ 3.0 (6) 8.0 ≦ [In] + [Bi] (7).

In one aspect of the invention, the solder alloy further contains Sb and satisfies the following formula: 0.5 ≦ [Sb] ≦ 1.25 (8) (wherein [Sb] represents the content ratio (% by mass) of Sb).

In one aspect of the invention, a solder alloy can be used to solder 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 a solder alloy described in any one of the above aspects.

In addition, in the present specification, the element symbol [01] constituting the solder alloy indicates the content ratio (% by mass) of the element in the solder alloy.

Further, the "solder alloy" in the present invention means that the metal composition is substantially composed of the listed metal, and may contain a trace amount of metal which cannot be prevented from being mixed. The solder alloy may have any form, such as may be used alone for soldering or may be used for soldering together with other components other than metal (such as flux). Effect of the invention

According to the present invention, it is possible to provide a solder alloy in which a predetermined content ratio is selected in each of the elements other than Sn in a solder alloy containing Sn, Ag, Bi, In, Cu, and Sb, and the Bi content is 1.5% by weight or more and 3.0% by mass. Hereinafter, the Cu content is 0.5% by mass or more and 1.2% by mass or less, and particularly, when 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). In particular, the Bi content and the In content satisfy the formula (7), whereby even if it is used for soldering a partially ceramic-made electronic component to a metal base substrate made of aluminum or copper as a substrate, Excellent thermal fatigue resistance at 150 °C.

The present inventors have made research and development on the mechanical properties and the state of the structure at a temperature lower than room temperature and a temperature of 150 ° C, and found that the lead-free solder alloy having a main component of Sn is respectively The predetermined amount contains In, Cu, and Bi, and it is possible to achieve an improvement in mechanical properties that have not been achieved so far. The following is a description of the advantageous effects of containing In, Bi, Cu, Ag, and Sb in the content ratio specified by the present invention in a lead-free solder alloy having a main component of Sn.

(In content and Bi content) In the solder alloy containing Sn as a main component, in the low In content region where the In content is about 15% by mass or less, the solid is dissolved in the Sn at a temperature near room temperature. The β-Sn phase of the alloy phase. Fig. 1 is a view showing a state of a structure of a conventional solder alloy containing Sn and In, and a region shown by a white background in the figure is a β-Sn phase.

In the present specification, "solid solution" means a phenomenon in which a part of a parent metal lattice is replaced by a solid solution element at an atomic level. In the crystal structure in which solid solution occurs, strain occurs in the mother element lattice due to the atomic diameter difference between the parent metal element and the solid solution element, and the strain can suppress the movement of crystal defects such as the difference in load stress, so The strength of the alloy is increased by the occurrence of solid solution energy. However, the load stress delay is reduced. The higher the content of the solid solution element, the greater the strength of the solder alloy obtained by solid solution.

When In is dissolved in the Sn-based solder at a predetermined content ratio, the γ phase (InSn ₄ ) having a different structure is phase-transformed from the time point when the temperature exceeds 100 °C. In other words, it will become a two-phase coexistence state (γ+β‐Sn) in which two phases are mutually different (Fig. 1 right). Since the two-phase coexistence state is easy to cause slippage at the grain boundary, the alloy in which In is solid-dissolved in the Sn-based solder at a predetermined content ratio can exhibit ductility improvement at a temperature of 100 ° C or higher.

When the In content of the Sn-based solder is larger than the predetermined content ratio, the phase change state becomes a γ phase excessively. At this time, since the lattice structure volume of the γ phase and the β-Sn phase is different, the solder alloy will be autonomously deformed by applying a reverse thermal cycle. This autonomous deformation is the cause of the fracture inside the welded joint and the short circuit between the adjacent welded joints, so that an excessive phase transition state is unlikely to occur in the alloy.

When In is dissolved in the Sn-based solder at a predetermined content, not only the ductility at a temperature of 100 ° C or higher but also the strength of the solder alloy can be improved. However, when it is used in a temperature environment of 100 ° C or higher, it is understood that the strength increase by increasing the In content has a limit based on the reason that the excessive phase transition may occur. In the solder alloy of the present invention, the excessive phase transformation state does not occur, and the ductility of the solder alloy at a temperature of 100 ° C or higher can be improved, and the In content of the solder alloy strength can be increased and preferably 5.168 mass % or more. It is 5.3 mass% or more and 6.2 mass% or less, and is preferably 6.5% by mass or less.

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

Bi is a solder alloy which is solid-dissolved in a Sn as a main component in the same manner as In. Although it is possible to increase the strength by solid solution of Bi and In, it usually causes a decrease in ductility.

Fig. 2 is a view showing the state of the structure of a solder alloy containing Sn, In, and Bi according to the embodiment. At a low temperature near room temperature, a fixed amount of Bi is uniformly soluble in the β-Sn phase (Fig. 2 left). Therefore, the strength of the lead-free solder alloy can be improved in the same manner as In. When Bi is not segregated at room temperature and is dissolved in the β-Sn phase, the Bi content of the solder alloy is 3.0% by mass or less. Moreover, the Bi content of the solder alloy is 1.5% by mass or more, and preferably 2.0% by mass or more, whereby an effective strength improving effect can be obtained.

At temperatures above 100 °C, the β-Sn phase will be partially phase-transformed into the γ phase. However, even in this case, Bi will not be dissolved in the γ phase and will only be dissolved in the β phase of the untransformed state into the γ phase. Sn phase (Figure 2 right). Therefore, the Bi dissolved in the β-Sn phase which is not transformed into the γ phase will increase, and the β-Sn phase intensity will become higher. As apparent from the above, by increasing the difference in strength between the β-Sn phase and the γ phase, slippage is likely to occur at the above-mentioned grain boundary, and the ductility at a high temperature is unexpectedly increased.

(Cu content) The Cu content of the solder alloy can reduce the melting point at the time of soldering, and can increase the material selectivity of the material to be joined.

The welded joint body is mainly made of various plating or pre-flux treatments such as Cu or Ni. When the base material of the bonded body is Ni, if a solder alloy containing In is used for soldering, a part of In contained in the solder alloy is intruded into the interface reaction layer (Ni ₃ Sn ₄ ). As a result, the mechanical properties of the welded joint portion after welding are changed. Therefore, when the solder base material is a Ni-joined body, it is necessary to use a solder alloy containing a large amount of In which is intruded by the interface reaction layer in advance. However, in an actual circuit board, various electronic components are mounted on one circuit board. Therefore, it is difficult to adjust the In content rate in advance when each of the base materials Cu and Ni is mounted.

In the present invention, the solder alloy contains a fixed amount of Cu, whereby a Cu ₆ Sn ₅ -based alloy layer can be formed in the interface reaction layer during soldering. By the alloy layer, In is prevented from being drawn, so that the selectivity of the solder alloy to be joined can be improved. The ideal Cu content of In which is prevented from being drawn by the above method is 0.5% by mass or more, and the upper limit of the Cu content is preferably 1.2% by mass. Set to this upper limit to maintain the wet spreadability of the solder during soldering.

Therefore, the ideal Cu content ratio in the solder alloy of the present invention is as shown in the formula (2). 0.5≦[Cu]≦1.2...(2)

When In is drawn, the In content of the solder alloy is reduced, and it is most remarkable when both the substrate electrode and the component electrode are made of Ni. In this case, when the Cu content is in the range of 0.5 ≦ [Cu] ≦ 1.0, the (In reduction ratio) is represented by the following formula. (In reduction rate) = 1.527 - 1.55 × (Cu content rate) (9). In the present specification, the element reduction rate means (in terms of reducing the element content in the former solder alloy) - (the element content ratio in the solder alloy after reduction).

It is known that when the Cu content is 1.0 < [Cu] ≦ 1.2, the In content of the solder alloy hardly decreases.

Solder alloys must ensure reliability regardless of which bonded body is joined. In order to maintain the reliability when the In content reduction is most conspicuous, the above-mentioned (In content reduction rate) is considered in the range of 0.5 ≦ [Cu] ≦ 1.0 in which the In content is reduced, and the solder alloy ( The In content minimum value can be expressed by the following formula (10). (In content minimum value) = 5.168 + (1.572 - 1.55 × [Cu]) = 6.74-1.55 × [Cu] ... (10)

The element content ratio in which the solid solution occurs in the solder alloy is preferably more than 8.0% by mass, so that the reliability of the solder alloy can be ensured regardless of the bonded body.

Therefore, the In content and the Bi content in the solder alloy of the present invention preferably satisfy the formula (7). 8.0 ≦ [In] + [Bi] (7) Therefore, the following formula can be satisfied in the range of 0.5 ≦ [Cu] ≦ 1.0 in which the In content is reduced. 8.0≦6.74-1.55×[Cu]+[Bi]...(11)

Therefore, in the solder alloy of the present invention, the ideal Cu content and Bi content are 0.5 ≦ [Cu] ≦ 1.2 (2), 1.5 ≦ [Bi] ≦ 3.0 (3), and preferably 0.5 ≦ [ Cu]≦1.2...(2), 2.0≦[Bi]≦3.0...(6). In the solder alloy of the present invention, when 0.5 ≦ [Cu] ≦ 1.0, the ideal In content is 6.74-1.55 × [Cu] ≦ [In] ≦ 6.5 (4); 1.0 < [Cu] ≦ 1.2, ideal In The content rate is 5.168 ≦ [In] ≦ 6.5 (5). Further, it is preferable that the In content and the Bi content of the solder alloy of the present invention satisfy the following formula (7). 8.0≦[In]+[Bi]...(7).

(Ag content) The solder alloy of the present invention contains Ag in the form of Ag ₃ Sn or Ag ₂ In in the solder alloy. The inclusion of Ag in the solder alloy improves the wettability at the time of soldering and lowers the melting point.

When the solder alloy is uniformly melted by reflow soldering, it is preferable to use a temperature higher than the liquidus temperature of the solder alloy by 10 ° C or higher as the reflow soldering peak temperature. When considering the heat-resistant temperature of the electronic component, the temperature of the reflow soldering peak should be set to 240 ° C or less, so the liquidus temperature of the solder alloy should be 230 ° C or less. In the solder alloy of the present invention, the desired Ag content required to achieve the liquidus temperature is in the range of 1.0 ≦ [Ag] ≦ 4.0 (1). By the Ag content being within the above range, the difference between the liquidus temperature of the solder alloy and the reflow soldering peak temperature does not occur at 10 ° C or more, and the solder alloy can be uniformly melted by reflow soldering.

(Sb content rate) The solder alloy containing Sn as a main component and containing In contains Sb, and the temperature at which the phase transition state of the β-Sn phase and the γ phase occurs can be increased. In the case where the heat-releasing portion of the LED in the LED wafer is deteriorated by the reverse thermal cycle to increase the amount of heat released, the phase change state can be prevented without excessively occurring, so that the welded joint portion can be prevented from deteriorating. In the solder alloy of the present invention, the ideal Sb content required for the temperature rise of the phase transition state is 0.5 ≦ [Sb] ≦ 1.25 (8). If it is less than this range, the temperature at which the phase transformation occurs may not be sufficiently increased, and the deterioration of the welded joint portion may not be prevented. If it is higher than this range, In and Sb in the solder alloy form the compound InSb to lower ductility. Example

(Example 1) In order to clearly show the influence of the Bi content and the elongation of the solder alloy containing Sn as a main component and the elongation at 150 ° C, the solder alloy of the present invention was produced by the following method and tested.

Production The elements contained in the solder alloy were weighed so that [Ag], [Bi], [In], and [Cu] were 3.5, 0.5 to 4.0, 6.0, and 0.8, respectively, and the remainder was Sn and the total amount was 100 g.

After the scale Sn was placed in a ceramic crucible, the crucible was placed in a power-type superheating heater adjusted to a temperature of 500 ° C in a nitrogen atmosphere. Each element was placed in the order of low melting point, and stirred for 3 minutes for each type. After all the constituent elements were charged, the crucible was taken out from the electric coating heater, immersed in a container filled with water at 25 ° C, and cooled to prepare a solder alloy.

In the test, the solder alloy was placed in a crucible again, heated to 250 ° C by an electric heating heater, and then poured into a graphite mold which was processed into a tensile test piece shape to prepare a tensile test piece. The tensile test piece was formed into a round bar shape having a diameter of 3 mm, a length of 15 mm, and a constricted neck. A tensile test at room temperature and 150 ° C was carried out using a tensile tester to evaluate the mechanical properties (tensile strength and elongation) of the tensile test piece produced. The results are shown in Table 1, Figure 3 and Figure 4. [Table 1]

As shown in Table 1, the tensile strengths of the conventional example 1, the conventional example 2, the examples 1-1, 1-2, and the comparative example 1-2 containing Bi were all larger than those of the comparative example 1-1 containing no Bi. Tensile Strength. Further, Comparative Example 1-2 having a Bi content of 4.0% by mass was significantly lower in elongation than Comparative Example 1-1, and was brittle. The elongation of the conventional example 1, the conventional example 2, and the examples 1-1 and 1-2 of the Bi content of 0.5 to 3.0% by mass was not significantly lowered.

As shown in Table 1, the tensile strength at 150 ° C of the conventional example 1, the conventional example 2, the examples 1-1 and 1-2, and the comparative example 1-2 containing Bi, and the comparative example containing no Bi There was no significant change in the tensile strength of 1-1 at 150 °C. Further, the elongation of the conventional example 1, the conventional example 2, the examples 1-1 and 1-2, and the comparative example 1-2 containing Bi at 150 ° C was compared with the elongation at 150 ° C of Comparative Example 1-1. The rate has increased. In particular, when the Bi content is 2.0% by mass or more, the elongation at 150 ° C is markedly increased.

(Example 2) Next, in order to clearly show the influence of the In content on the tensile strength of the solder alloy containing Sn as a main component and the elongation at 150 ° C, [Ag], [Bi], [In] Each element was weighed in such a manner that [Cu] was 3.5, 2.0, 5.0 to 7.0, 0.8 or 0.5 and the remainder was Sn, and a solder alloy was produced in the same manner as in Example 1. The solder alloy thus prepared was tested in the same manner as in Example 1 and the results obtained are shown in Table 2, FIG. 5 and FIG. [Table 2]

As shown in Table 2, as the In content increases, the tensile strength increases. In addition, no elongation was observed to decrease significantly as the In content increased.

As shown in Table 2, as the In content increased, the tensile strength at 150 ° C increased. The elongation ratios of Comparative Examples 2-1 and 2-2 were lower than those of the conventional examples 1 and 2, whereas the examples 2-1 to 2-3 showed higher values than the conventional examples 1 and 2.

(Example 3) Next, in order to clearly show the influence of the In content, the Bi content of 3.0 and the strength of the solder alloy containing Sn as a main component and the ductility at a high temperature, [Ag], [Bi], [ Each of the elements was weighed in such a manner that In] and [Cu] were 3.5, 3.0, 5.0 to 7.0, 0.8 or 0.5 and the remainder was Sn, and a solder alloy was produced in the same manner as in Example 1. The solder alloy thus prepared was tested in the same manner as in Example 1 and the results obtained are shown in Table 3, FIG. 7 and FIG. [table 3]

As shown in Table 3, as the In content increases, the tensile strength increases. In addition, no elongation was observed to decrease significantly as the In content increased.

As shown in Table 3, as the In content increased, the tensile strength at 150 ° C increased. When the In content is 5.0 to 6.0, the elongation at 150 ° C significantly increases as the In content increases, but there is no significant decrease in the In content exceeding 6.0.

In the following (Example 1) to (Example 3), the effects of the In content and the Bi content on the characteristics of the solder alloy were examined.

The tensile strength at room temperature increases as the Bi content increases. This is considered to be because the amount of Bi dissolved in the β-Sn phase increases as the Bi content increases, and the β-Sn phase is strengthened. In addition, the elongation at room temperature hardly changes when the Bi content is 3.0% by mass or less, but decreases when the Bi content is more than 3.0% by mass. This is considered to be due to the occurrence of Bi segregation.

It is almost impossible to increase the tensile strength at 150 ° C as the Bi content increases. This is considered to be because Bi is only dissolved in the β-Sn phase, so it does not affect the strength of the γ phase. In addition, the elongation at 150 ° C of the alloy having a Bi content of 2.0 to 3.0% by mass is improved when the In content is 5.5 to 6.5% by mass, but is higher than that at room temperature, but the In content is 5.0 or When it is 7.0% by mass, it is not necessarily higher than room temperature. For this phenomenon, we explain the following.

The elongation of the solder alloy containing Sn as the main component and containing In at 150 ° C is obviously affected by the grain boundary slip caused by the coexistence of the β-Sn phase and the γ phase at a temperature of 150 ° C. When the solder alloy contains Bi, even if the γ phase is generated as the temperature rises, since Bi is only dissolved in the β-Sn phase, the concentration of Bi in the β-Sn phase is increased, and only the strength of the β-Sn phase is increased. Upgrade. In this way, the grain boundary slip can be promoted by the expansion of the intensity difference between the β-Sn phase and the γ phase, so that the elongation can be increased with the temperature rise. It is considered that the elongation of the alloy having a Bi content of 2.0 to 3.0% by mass as seen in the above Examples 1 to 3 at 150 ° C is promoted by the grain boundary slip. Further, when the In content is 5.0% by mass and 7.0% by mass, the elongation does not necessarily increase. This is considered to be because the γ ratio is too small or too large with respect to the β-Sn phase, so the grain boundary between the two phases is less than the case where the In content is 5.5 to 6.5% by mass, and the above-described Increased elongation due to grain boundary slip promotion.

(Example 4) In order to evaluate the influence of the Bi content and the In content rate on the heat-resistant fatigue property, the mounting structure of the electronic component was soldered to the metal base substrate using a solder alloy containing Sn as a main component, and the following method was used. A mounting structure for the thermal fatigue resistance test was produced.

The elements were weighed so that [Ag], [Bi], [In], and [Cu] were 3.5, 0.5 to 3.5, 5.0 to 7.0, and 0.8, and the remaining portion was Sn, and were produced in the same manner as in Example 1. Solder alloy. The solder alloy prepared was processed into a solder powder of several 10 μm, and the solder powder and the flux were weighed at a weight ratio of 90:10, and then kneaded into a solder paste.

The circuit substrate electrode 102 is prepared on the metal substrate 101 via an insulating layer using a metal mask having a thickness of 150 μm. The prepared solder paste was printed on the substrate electrode 102 on the metal base substrate 100 having a thickness of 1.6 mm. A 1608-size (1.6 mm × 0.8 mm) wafer resistor 103 was bonded to the printed solder paste, and reflow soldering was performed at a temperature of up to 240 ° C to form a solder joint portion 105 to fabricate 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 substrate 101 is aluminum.

Fig. 9 shows a mounting structure manufactured in the above manner in order to carry out a reliability test of a solder alloy. 100 denotes a metal base substrate, 101 denotes a metal substrate, 102 denotes a circuit substrate electrode, 103 denotes a wafer resistor, 104 denotes a component electrode, 105 denotes a solder joint portion, and 106 denotes an insulating layer.

The test reliability test was carried out under a load-reversal thermal cycle of -40 ° C on a low temperature side and 150 ° C on a high temperature side, and the results are shown in Table 4. The resistance value is measured every time the thermal cycle is loaded, and the number of cycles in which the resistance value is increased by more than 2 times is taken as the service life. In the judgment standard column, if the resistance value was increased by 2000 cycles and the resistance value was not increased, it was recorded as ○, and after 2,500 cycles and no resistance value increase was observed, it was recorded as ◎. Further, the deformation caused by the phase change of the solder alloy containing Sn as a main component as seen in the prior literature was evaluated by the presence or absence of deformation at 2000 cycles. [Table 4]

As shown in Table 4, the service life was 2,000 cycles or less with respect to the conventional examples 4-1 to 4-4, and the service life in the examples 4-1 to 4-12 was 2000 cycles or more. The service life of the examples 4-5 to 4-12 in which [Ag], [Bi], [In], and [Cu] are 3.5, 2.0 to 3.0, 5.5 to 6.5, and 0.8, and the remainder is Sn is particularly excellent at 2,500. Loop above. Further, as shown in Comparative Examples 4-2 and 4-5, even if the In content is 5.5 to 6.5% by mass, the Bi content is 1.0% by mass or less, and the service life is less than 2,000 cycles. This is considered to be because the amount of Bi is too small, so the mechanical properties obtained are only slightly improved. Further, as shown in Comparative Examples 4-16, 4-17, and 4-18, even if the In content is 5.5 to 6.5% by mass, the Bi content is 3.5% by mass or more, and the mechanical properties can be improved. The life expectancy is still below 2000 cycles. This is considered to be because the amount of Bi is too large, and it is repeatedly exposed to high temperature to segregate Bi at the grain boundary, resulting in a decrease in ductility over time.

As shown in Table 4, in Comparative Examples 4-1, 4-4, 4-7, 4-9, 4-11, 4-13, and 4-15 in which the In content was 5.0% by mass, regardless of the Bi content rate, The service life is less than 2000 cycles. From this result, it is understood that if the In content is small, the elongation at a high temperature cannot be improved regardless of the Bi content. Further, in Comparative Examples 4-3, 4-6, 4-8, 4-10, 4-12, 4-14, and 4-19 in which the In content was 7.0% by mass, regardless of the Bi content rate, the service life was also All are below 2000 cycles. In these comparative examples, the solder alloy was also found to be deformed, so that it was considered to be excessively transformed from the β-Sn phase to the γ phase.

(Example 5) A solder alloy containing each element in a content range in which the effect of the solder alloy of the present invention was exhibited was evaluated to evaluate the thermal fatigue resistance. The results are shown in Table 5. The manufacturing method and test method of the solder alloy were the same as in the fourth embodiment. The base material of the circuit substrate electrode 102 of the metal base substrate 100 is Cu and Au/Ni, and the base material of the metal base material 101 is aluminum. [table 5]

As shown in Table 5, Examples 5-1 to 5-11 each having a content of a desired range in which the effect of the solder alloy of the present invention is contained have a service life of 2000 cycles or more. In particular, in Examples 5-2, 5-4, 5-5, and 5-8, when the substrate electrode base material is Cu or Au/Ni, the service life is 3000 cycles or more, and Examples 5-1 and 5- 6, 5-7, 5-10, and 5-11 have a service life of 3000 cycles or more when the substrate electrode base material is Cu. Further, in Comparative Examples 5-1 to 5-7 and Conventional Example 5-1, since either of the contained elements was not in the ideal range in which the effect of the solder alloy of the present invention was exhibited, the service life of the reliability test was The case where the substrate electrode base material is Cu or Au/Ni or both of Cu and Au/Ni is less than 2000 cycles. In the range of 0.5 ≦ [Cu] ≦ 1.0, it is considered that even if the In content of the formula (9) is decreased at the Au/Ni electrode, the effect of the solder alloy of the present invention is exhibited even if it occurs. With the above reduction, the In content should also be 5.168 or more.

As described above, in the solder alloy of the present invention, the Bi content, the Cu content, and the Ag content are 1.5 ≦ [Bi] ≦ 3.0 (3), 0.5 ≦ [Cu] ≦ 1.2 (2), and 1.0 分别, respectively. [Ag]≦4.0...(1), and, when 0.5≦[Cu]≦1.0, the In content is 6.74-1.55×[Cu]≦[In]≦6.5...(4);1.0<[Cu]≦1.2 In the case, the In content is 5.168 ≦ [In] ≦ 6.5 (5), and the remainder is Sn. In the 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), and, when 0.5≦[Cu]≦1.0, the In content is 6.74-1.55×[Cu]≦[In]≦6.5...(4); 1.0<[Cu]≦1.2, The In content is 5.168 ≦ [In] ≦ 6.5 (5), and the above [In] and [Bi] satisfy 8.0 ≦ [In] + [Bi] (7), and the remainder is Sn. Further, the solder alloy of the present invention can replace a portion of Sn with Sb in the range of 0.5 Å [Sb] ≦ 1.25 (8). Industrial availability

The solder alloy of the present invention can realize a welded joint having excellent heat fatigue resistance even at a temperature of 150 ° C and a mounting structure having the same, and can be effectively utilized for, for example, a component having a large heat release such as an LED or a power component. Install the structure, etc.

100‧‧‧Metal base substrate
101‧‧‧Aluminum substrate
102‧‧‧ circuit substrate electrode
103‧‧‧ Chip resistor
104‧‧‧Part electrode
105‧‧‧Welded joints
106‧‧‧Insulation

Fig. 1 is a view showing the state of the structure of a lead-free solder alloy of a conventional example. Fig. 2 is a view showing the state of the structure of a lead-free solder alloy according to an embodiment of the present invention. Fig. 3 is a view showing mechanical properties of a solder alloy according to an embodiment of the present invention at room temperature. Fig. 4 is a view showing mechanical properties of a solder alloy according to an embodiment of the present invention at 150 °C. Fig. 5 is a view showing mechanical properties of a solder alloy according to an embodiment of the present invention at room temperature. Fig. 6 is a view showing mechanical properties of a solder alloy according to an embodiment of the present invention at 150 °C. Fig. 7 is a view showing mechanical properties of a solder alloy according to an embodiment of the present invention at room temperature. Fig. 8 is a view showing mechanical properties of a solder alloy according to an embodiment of the present invention at 150 °C. Fig. 9 is a view showing a mounting structure for carrying out a reliability test of a solder alloy according to an embodiment of the present invention.

Claims (5)

A solder alloy containing Ag, Bi, In, and Cu and the remainder consisting of Sn and satisfying the following formula: 1.0 ≦ [Ag] ≦ 4.0 0.5 ≦ [Cu] ≦ 1.2 1.5 ≦ [Bi] ≦ 3.0 (wherein [ Ag], [Cu], and [Bi] respectively indicate the content ratio (% by mass) of Ag, Cu, and Bi); 0.5 ≦ [Cu] ≦ 1.0, which satisfies the following formula: 6.74-1.55 × [Cu] ≦ [In] ≦6.5; 1.0<[Cu]≦1.2, the following formula is satisfied: 5.168 ≦ [In] ≦ 6.5 (wherein [In] represents the content ratio (% by mass) of In). The solder alloy of claim 1, wherein Bi and In satisfy the following formula: 2.0 ≦ [Bi] ≦ 3.0, 8.0 ≦ [In] + [Bi]. A solder alloy according to claim 1 or 2, wherein a part of Sn is substituted by Sb, and Sb satisfies 0.5 ≦ [Sb] ≦ 1.25 (wherein [Sb] represents a content ratio (% by mass) of Sb). A solder alloy according to any one of claims 1 to 3, which can be used for soldering electronic parts to a metal base substrate. A mounting structure in which a component electrode of an electronic component and a substrate electrode of a metal base substrate are soldered by a solder alloy according to any one of claims 1 to 4.