JP2001179483A - Packaging structural body for electronic parts and producing method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a packaging structural body of electronic parts having solder joints having excellent ductility and thermal fatigue resistance and moreover to provide a producing method capable of easily producing the packaging structural body. SOLUTION: In the packaging structural body of electronic parts having joints at which two or more components are joined by solder, the composition of solder alloy forming the joints is composed of, by weight, 40 to <50% Bi, 0.01 to 0.4% Cu, and the balance Sn with inevitable impurities. Soldering materials for joining composed of only Bi, Sn and inevitable impurities are brought into contact with the components in a molten state, and Cu contained in the components is eluted into the soldering materials for joining.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mounting structure in which electronic components are joined using solder and a method for manufacturing the same.

[0002]

2. Description of the Related Art JIS Z 3282 specifies a 42% by weight Sn-58% by weight Bi eutectic solder (symbol: H42Bi58A) for use in the electric and electronic industries.
Literature (Binary Alloy Phase Diagrams, Ed by BTMassa
In lski et al, vol. 2 (1996), the eutectic composition of the Sn-Bi binary alloy is 43% by weight Sn-57% by weight Bi (hereinafter, referred to as "Sn-57Bi"). The solder having the composition of Sn-58Bi has a low melting point (melting temperature: 139 ° C.), and is a Sn-37Pb eutectic solder (melting temperature: 183) which is widely used as an electronic solder.
C), it is possible to mount electronic components at a lower temperature.

[0003] Reducing the soldering operation temperature can reduce the thermal load on the electronic components, and can produce a more reliable circuit board. Performing the soldering operation at a lower temperature also has the advantage of reducing the amount of dross generated due to oxidation of the molten solder and improving the workability.

However, papers (for example, Journal of the Japan Institute of Metals, vol. 57 (1993), 455-462)
And the like, the Sn-Bi eutectic solder has a disadvantage of poor ductility. Due to the heat generated by the electronic components or the temperature change of the usage environment, the components and the board repeatedly undergo thermal expansion and contraction, so that repeated stress and distortion are generated at the solder joints, and solder fatigue may cause cracks in the solder due to thermal fatigue. is there. The peeling of the soldered portion due to thermal fatigue hinders electrical continuity and causes electronic devices to fail to perform their functions.

[0005] Therefore, it is required that the solder functions to relieve the stress and strain generated in the solder joint due to its ductility and to suppress the occurrence of cracks and the like.
That is, the fact that the solder has good ductility is an indispensable property for improving the thermal fatigue property of the joint.

[0006] As a technique for improving the ductility of Sn-Bi based solder, there has been a technique in which a third component is conventionally added. For example, JP-A-8-252688, JP-A-10-52791 and J.P. Electro
n. Mater. , Vol. 26 (1997), 954
Japanese Patent Application Laid-Open No. 8-150493 discloses a method of miniaturizing the structure by adding Ag shown in -958, a method of suppressing the transformation of Sn from β phase to α phase by adding Sb shown in JP-A-7-40079, and JP-A-8-150493. It is the one to which In shown in the gazette is added.

[0007]

SUMMARY OF THE INVENTION However, Japanese Patent Application Laid-Open No. Hei 8-2
When Ag or In is added as in JP-A-52688 and JP-A-8-150493, an increase in the cost of the solder alloy can be avoided when the amount of addition is large because Ag and In are expensive metals. In addition, since In is a rare metal, there is a problem in its supply property. In particular,
The technique disclosed in Japanese Patent Application Laid-Open No. 8-150493 aims at a Sn-Bi-In ternary alloy by adding In of several weight% or more, and the cost increase becomes remarkable. Also, JP-A-8-252688,
The inventor of the present invention has repeated the addition of Ag as disclosed in JP-A-527991, but no effect of improving the ductility due to the addition of Ag was found, and in some cases, the ductility was impaired.

[0008] Transformation suppression by Sb is disclosed in JP-A-7-400.
No. 79, which is a well-known technique before the filing of the application (for example, a highly reliable micro soldering technique, (199)
1), p44), and Sb is an item to be monitored in the environmental standards for water pollution based on the Basic Environmental Law, and it is not preferable to use it as an additional element in the solder alloy in that respect. Further, in Japanese Patent Application Laid-Open No. 7-40079, Ga is used as an essential fourth component element. However, the inventors have obtained an experimental result that even if the amount of Ga is small, the solderability is greatly impaired. There is a problem with the addition itself.

The present invention has been made in view of the above-mentioned circumstances, and while taking advantage of the characteristics of a Sn-Bi binary solder alloy having a low melting temperature, by adding a small amount of Cu, which is another element, to this, excellent ductility and It is an object of the present invention to provide a mounting structure of an electronic component having a solder joint having thermal fatigue resistance. Another object of the present invention is to provide a manufacturing method capable of easily manufacturing the mounting structure of the electronic component.

[0010]

An electronic component mounting structure according to the present invention is an electronic component mounting structure having a joint portion in which two or more components are joined by solder, wherein the joint portion is formed. The composition of the solder alloy is such that Bi is 40% by weight or more and 50% or more.
It is characterized in that Cu is less than 0.01% by weight and 0.4% by weight or less, with the balance being Sn and unavoidable impurities. That is, the mounting structure of the present invention has improved ductility and thermal fatigue resistance of the solder joint by forming the solder joint with a solder alloy containing a small amount of Cu in the Sn-Bi alloy.

It is considered that the solder joints of the mounting structure of the present invention are excellent in ductility and thermal fatigue resistance for the following reasons. The trace amount of Cu contained is Cu-
Finely dispersed in the Sn-Bi eutectic in the form of Sn-based intermetallic compound. The fine intermetallic compound in this eutectic is primary Sn
At the boundary between Sn and Sn-Bi eutectic. As a result, the solder joint of the mounting structure of the present invention has excellent ductility. Due to the heat generated by the electronic components or the temperature changes in the operating environment, the components and the board repeatedly undergo thermal expansion and contraction, so that repeated stresses and strains are generated in the solder joints, and cracks occur in the solder joints due to thermal fatigue due to this. May evolve. In contrast, the solder joints of the mounting structure of the present invention, due to their excellent ductility,
The generation and propagation of cracks in the solder joint as described above can be suppressed, and the heat-resistant fatigue characteristics are improved.

The method for manufacturing the mounting structure of the present invention is not particularly limited. Therefore, the mounting structure can be manufactured by a conventionally known solder bonding method using a solder material having a composition in the above-described appropriate range. However, when a joining solder material containing a small amount of Cu is manufactured in advance and components are joined using the same, the composition of the joining solder material becomes complicated, so that composition management is difficult. Therefore, it is desirable to manufacture the mounting structure of the present invention using the method described below.

A manufacturing method according to the present invention is a method for manufacturing a mounting structure as described above, wherein at least one of the components has at least a part of a portion to be joined to Cu or Cu.
A step of contacting a joining solder material comprising only Bi, Sn and unavoidable impurities with the component in a molten state, comprising an alloy, and eluted Cu contained in the component into the joining solder material; Solidifying the joining solder material to form a joint.

In other words, the manufacturing method of the present invention uses an alloy composed of Bi and Sn as a solder material for joining, and utilizes the elution of Cu from the component into the alloy in the joining step. When the composition of the solder alloy forming the joint is in the above-mentioned appropriate range, Bi is 40% by weight or more.
Less than 0 wt%, Cu is 0.01 wt% or more and 0.4 wt%
Hereinafter, the remainder is Sn and unavoidable impurities.

Therefore, when the manufacturing method of the present invention is used, the composition of the joining solder material can be simplified as compared with the case of using an Sn—Bi—Cu-based solder alloy as the joining solder material. The steps can be simplified, and the production of the mounting structure of the present invention is simplified when viewed comprehensively.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION <Mounting Structure of Electronic Component> The mounting structure of the present invention is a mounting structure of an electronic component having a joint portion formed by joining two or more components with solder. Examples of the mounting structure include a mounting board in which a capacitor, a diode, an IC package, and the like are soldered to a printed board.

[0017] The solder alloy forming the joint portion includes B
i is contained in an amount of 40% by weight or more and less than 50% by weight. Sn-
The Bi binary alloy has good wettability when the Bi amount is 10 to 50% by weight. Further, the occurrence of the lift-off or the like, which is a problem in mounting components using lead-free solder, can be controlled by setting the Bi amount to 40% by weight or more.
For this reason, it is desirable that the Bi content in the Sn—Bi-based solder alloy be 40% by weight or more and less than 50% by weight. On the other hand, the Sn—Bi binary alloy has a Bi amount of 30 to 4%.
5% by weight has the best mechanical properties (strength, elongation). Therefore, in consideration of the mechanical properties, it is more preferable to set the Bi amount to 40% by weight to 45% by weight.

In the mounting structure of the present invention, a small amount of Cu is contained in the solder joint in order to improve the ductility.
When a small amount of Cu is contained, the contained Cu is Cu-
Finely dispersed in the Sn-Bi eutectic in the form of Sn-based intermetallic compound. As described above, the fine intermetallic compound in the eutectic tends to cause slip at the boundary between the primary crystal Sn and the Sn-Bi eutectic. For this reason, the ductility of the solder joint containing a small amount of Cu is further improved.

The effect of improving the ductility by containing a trace amount of Cu is generated from a very small amount. However, in order to obtain a substantial effect of improving the ductility, it is desirable to contain 0.01% by weight or more of Cu. Conversely, when Cu is contained in an amount of 0.5% by weight or more, Cu is crystallized as a primary crystal and becomes coarse particles and is dispersed in the alloy, so that the ductility of the solder joint is lost. As will be apparent from the experimental results described later as an example, Cu
The effect of improving ductility is greatest when the content ratio is about 0.1% by weight. Therefore, in order to obtain a greater ductility improving effect, the content ratio of Cu is 0.05%.
It is more preferable that the content be not less than 0.2% by weight and not more than 0.2% by weight.

<Method of Manufacturing Mounting Structure> As described above, the manufacturing method of the mounting structure of the present invention is not particularly limited, but a bonding solder alloy containing a small amount of Cu in advance is used. When manufacturing and joining constituent parts using the same, the composition of the solder alloy for joining is complicated and composition management is difficult. Therefore, a simple manufacturing method of the mounting structure of the present invention will be described below.

The manufacturing method according to the present invention is the method for manufacturing a mounting structure according to the present invention, wherein at least one of the components has at least a part of a portion to be joined made of Cu or a Cu alloy; A step of bringing a joining solder material made of Bi and Sn into contact with the component in a molten state to elute Cu contained in the component into the joining solder material; and solidifying the joining solder material to form a joining portion And forming a.

As long as any one of the components to be joined contains Cu at a portion to be joined, even a portion of the surface that contacts the molten solder material contains Cu. Then, the manufacturing method of the present invention can be applied. For example, Cu or Cu
When an electronic component is soldered to a printed board having a current path made of an alloy, Cu elutes from the board side. Also, when soldering an electronic component containing Cu to the lead to the printed circuit board, Cu
Will elute. Further, even when any of the component parts does not contain Cu, the manufacturing method of the present invention can be applied as long as Cu or a solder containing Cu is coated on the surface of the portion to be joined.

In the present manufacturing method, when an element other than Cu is contained in a part to be joined of a component, the element can also be eluted into the joining solder material in a molten state. Since the mounting structure of the present invention and the method of manufacturing the same aim at including a trace amount of Cu in the solder alloy forming the joint, when an element other than Cu is eluted, the presence of the element is determined by the presence of the solder. In the mounting structure and the method of manufacturing the same according to the present invention, trace elements other than Cu are treated as unavoidable impurities as long as they do not affect the ductility of the joint.

A joining solder material made of Bi and Sn is brought into contact with the component in a molten state, Cu contained in the component is eluted into the joining solder material, and then the joining solder material is solidified and joined. The method of forming the portion may be a conventional soldering method. This method includes flow soldering, reflow soldering, manual soldering, and BGA bonding. In these methods, various shapes such as linear, rod, ribbon, wire, powder, and spherical are used depending on the application. Solder materials can be used.

The joining solder material comprising Bi and Sn can be prepared by a usual melting means in the art. For example, Sn and Bi weighed by weight may be put in a container being heated and melted. In this case, an alloy may be partially used. These metals can be melted using any conventional melting technique, and are manufactured by heating all of the metals until they become liquid and then pouring them into a suitable mold and cooling.

At the time of soldering, it is necessary that the solder for joining is in a molten state, Cu is eluted into the solder for joining in a certain amount, and the solder composition at the joint is required to be in the above-mentioned appropriate range. That is, at the joint, Cu is eluted from the component into the joint solder material, and the solder composition at the joint is 40% by weight or more and less than 50% by weight, and 0.01% by weight of Cu, which is an appropriate composition. The temperature, time, amount of solder for joining, and the like at the time of soldering may be controlled so that the content is 0.4% by weight or less and the balance is Sn. In the present manufacturing method, the temperature at the time of soldering is set to a value equal to or higher than the solidus temperature of the Sn—Bi-based alloy as a joining solder material + 20 ° C.
The temperature may be lower than or equal to ° C.

The embodiment of the electronic component mounting structure and the method of manufacturing the same have been described above. However, the above-described embodiment is merely an embodiment, and the electronic component mounting structure and the method of manufacturing the same according to the present invention are as follows. Starting with the above embodiment,
The present invention can be implemented in various forms with various modifications and improvements based on the knowledge of those skilled in the art.

[0028]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In order to evaluate the characteristics of a solder alloy forming a joint of a mounting structure of the present invention, various compositions of Sn-B
A solder alloy containing Cu in an i-based solder alloy was prepared, various tests were performed, and their properties were evaluated.
The following is an example.

<Evaluation of Mechanical Properties> Sn, Bi and Cu having a purity of 99.9% or more were mixed at various ratios to prepare Sn—Bi—Cu based solder alloys having various compositions. Bi in an amount of 40% by weight and Cu in an amount of 0.05% by weight, 0.1% by weight, 0.2% by weight and 0.3% by weight, respectively.
Those containing 1% by weight were referred to as Example 1-1, Example 1-2, Example 1-3, and Example 1-4, respectively. At the same time, in order to compare the performance with the solder alloy of the above embodiment,
Alloys with different compositions were also prepared. And Bi
Containing 40% by weight and containing no Cu, and Cu
Containing 0.5% by weight, 1.0% by weight, and 2.0% by weight of Comparative Example 1-1, Comparative Example 1-2, Comparative Example 1-3, and Comparative Example 1-4, respectively. Table 1 below shows the compositions of these alloys.

[0030]

[Table 1]

The mechanical properties of these Examples and Comparative Examples were evaluated by performing a tensile test to determine the strength (maximum tensile strength) and elongation (elongation at break). The tensile test piece was formed into a shape shown in FIG. 1 by machining from a 20 × 15 × 60 (mm) ingot cast by a mold. Three test pieces were collected from one ingot. After the mechanical processing, a heat treatment was performed at 50 ° C. for 24 hours in order to remove distortion due to the processing, and then left at room temperature for one week or more, and then subjected to a tensile test. The strain rate in the tensile test was set to 1 × 10 ⁻⁴ s ⁻¹ in order to reproduce the state at the solder joint, the test temperature was room temperature (25 ° C.), the number of n was 3, and the average was calculated.

As a result of this test, Bi was 40% by weight.
FIG. 2 shows the relationship between the content of Cu and the tensile strength and elongation when Cu is contained. As is apparent from FIG.
It can be seen that by controlling the Cu content in the n-Bi binary alloy, the ductility is improved without affecting the mechanical strength as compared with the case where Cu is not contained. For example, in an alloy containing 40% by weight of Bi, the ductility is most improved when the Cu content is about 0.1% by weight, and the elongation at room temperature is about 1.4 in the case of not containing Cu.
It is clear that the number is doubled. However, when the Cu content is too large, it is understood that the ductility improving effect is lost. For example, when the Cu content ratio is 0.5% by weight or more, the elongation becomes smaller than when Cu is not contained,
Ductility is impaired.

If the above results are comprehensively determined, Sn-B
It can be confirmed that the effect of improving ductility can be obtained by containing Cu in a ratio of 0.4% by weight or less in the binary solder alloy. Also, it can be confirmed that the content ratio of Cu having a greater improvement effect is 0.05% by weight or more and 0.2% by weight or less.

<Evaluation of Thermal Fatigue Properties> Sn-40Bi and Sn-45Bi alloys were used as joining solder materials,
A substrate whose joining portion is made of Cu and a chip component (shape 4532) in which the joining portion is plated with Ni are joined, and the solder composition of the joining portion is Sn-40Bi-0.1.
A mounting structure made of Cu and Sn-45Bi-0.1Cu was prepared. For comparison, a sample using an Sn-37Pb alloy as a joining solder material was also prepared.
As an example, FIG. 3 shows a temperature profile when joining is performed using a Sn-40Bi alloy and a Sn-37Pb alloy as joining solder materials.

The number of chip components evaluated was 5 for each solder, and the temperature cycle test was performed at -30 ° C to 80 ° C.
Up to 000 cycles were performed. One cycle is one hour,
The breakdown is that the time required to raise the temperature from -30 ° C to 80 ° C is about 5
Minutes, the time to hold the mounting structure at 80 ° C. is about 25 minutes,
Approximately 5 minutes to cool from 80 ° C to -30 ° C, -30 ° C
The holding time of the mounting structure was set to about 25 minutes. The analysis of the Cu content in the solder after joining was performed by EPMA (El
electronprobemicroanalysis)
Was performed.

When the solder composition at the joint is Sn-40Bi-
A mounting structure made of 0.1 Cu was used as Example 2-1 and a mounting structure having a solder composition of a joint portion made of Sn-45Bi-0.1Cu was used as Example 2-2. At the same time, in order to make a comparison with the above-mentioned mounting structure, a mounting structure having a bonding portion having a different composition from those was also prepared. The mounting structure in which the bonding solder material was Sn-37Pb was used as Comparative Example 2-1.

As a result of this experiment, FIG.
1 shows an appearance and a cross-sectional structure of a solder joint portion of a mounting structure of Example 1 and a mounting structure of Comparative Example 2-1 after a temperature cycle test. 4A shows the appearance of the solder joint of Example 2-1 and FIG. 4B shows the cross-sectional structure of the solder joint of Example 2-1. FIG. 4C shows the appearance of the solder joint of Comparative Example 2-1.
(D) shows the cross-sectional structure of the solder joint of Comparative Example 2-1. FIG. 4E is an enlarged view of a crack in Comparative Example 2-1. In Table 2 below, Example 2-1 and Example 2 are shown.
2 shows crack growth rates of solder joints of Comparative Example 2-1 and Comparative Example 2-1. The crack growth rate is 100% based on the assumption that the crack penetrates the solder joint in the cross section.
It is assumed that

[0038]

[Table 2]

As is clear from FIG. 4 and Table 2, Example 2 in which the solder composition was Sn-40Bi-0.1Cu
1, and the crack growth rate of the joint portion of Example 2-2 in which the solder composition is Sn-45Bi-0.1Cu is −30 ° C. or more.
It is 5% or less even after 3000 cycles at 80 ° C. On the other hand, the crack growth rate of the joint in Comparative Example 2-1 in which the joining solder material is Sn-37Pb is 50% or more. This indicates that the solder joints according to the mounting method of the present invention have excellent thermal fatigue resistance.

[0040]

According to the present invention, the solder joint of the mounting structure is made of a Sn-Bi-based solder alloy containing Cu, and the Bi content is 40% by weight or more and less than 50% by weight, and the Cu content is 0.01% by weight. % Or more and 0.4% by weight or less. With such a configuration, the solder joints of the mounting structure of the present invention are Sn-
While having the same level of mechanical strength as the Bi eutectic solder alloy, the ductility is greatly improved, and it has excellent thermal fatigue resistance.

[Brief description of the drawings]

FIG. 1 is a view showing the shape of a test piece subjected to a tensile test.

FIG. 2 is a diagram showing the relationship between Cu content and tensile properties of a Cu-containing Sn—Bi-based solder alloy.

FIG. 3 Sn-40Bi, Sn-
The figure which shows the temperature profile at the time of joining a board | substrate and a chip component using 37Pb.

FIG. 4 is a photograph showing the appearance and cross-sectional structure of a solder joint after a temperature cycle test of a mounting structure in which a substrate and a chip component are joined.

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[Procedure amendment]

[Submission date] May 19, 2000 (2005.1.
9)

[Procedure amendment 1]

[Document name to be amended] Drawing

[Correction target item name] Fig. 4

[Correction method] Change

[Correction contents]

FIG. 4

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) B23K 101: 36 B23K 101: 36

Claims (3)

[Claims] 1. A mounting structure for an electronic component having a joint formed by joining two or more components with solder, wherein the composition of a solder alloy forming the joint is 40% Bi.
A mounting structure for an electronic component, characterized in that the content is not less than 50% by weight, less than 0.01% by weight and not more than 0.4% by weight of Cu, and the balance is Sn and inevitable impurities. 2. The electronic component mounting structure according to claim 1, wherein the Cu content is 0.05% by weight or more and 0.2% by weight or less. 3. A solder joint comprising two or more component parts joined by solder, and the composition of the solder alloy forming the joint is:
Bi is 40% by weight or more and less than 50% by weight, and Cu is 0.01% by weight.
A method for manufacturing a mounting structure of an electronic component, which is not less than 0.4% by weight and not more than 0.4% by weight, with the balance being Sn and unavoidable impurities, wherein at least one of the component parts has at least one The part is made of Cu or Cu alloy, and a soldering material for joining consisting only of Bi, Sn and unavoidable impurities is brought into contact with the component in a molten state, and Cu contained in the component is eluted into the soldering material for joining. And a step of solidifying the bonding solder material to form a bonding portion. A method for manufacturing a mounting structure for an electronic component, comprising: