JPH0740077A - Solder material and its production - Google Patents

Abstract

PURPOSE:To enhance the dispersibiity of a reinforcing material and to improve strength and thermal fatigue resistance by dispersing the reinforcing material having a composite structure enclosed with metal having good joinability with a solder member into a solder base metal. CONSTITUTION:Reinforcing material forming elements or their comps. and the metal having the good joinability with the solder member are mixed and melted. This molten metal is cooled at >=10<2> deg.C/sec cooling rate to precipitate the metal having the good joinability with the solder member around the reinforcing material, by which the composite reinforcing material is formed. This composite reinforcing material is dispersed into the base metal. A Pb-Sn alloy, etc., are used as the solder member. A Cu-Sn alloy, Ni-Sn alloy, etc., are used as the reinforcing material. Ni and Cu or Sn, In, etc., which are elements forming an intermetallic compd. with Fe are used as the metal having the good joinability with the solder member.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solder material used for soldering electronic parts mounted on automobiles and the like, and a method for manufacturing the same.

[0002]

2. Description of the Related Art At present, electronic parts used for various purposes are harsh from low temperature to high temperature, as represented by electronic parts mounted on automobiles. In addition, the size of solder joints is becoming tens of μm or less due to miniaturization and miniaturization of electronic components.

Under such circumstances, when the conventional solder is applied to electronic parts, cracks are likely to occur due to vibration and the like, and the circuit is easily damaged. In particular, under a cold heat cycle, thermal stress is generated based on the difference in thermal expansion coefficient between the base material of the material to be joined and the solder base material. Originally, the melting point of the solder was about 200 ° C., and the room temperature exceeded the recrystallization temperature, so that it was very unstable in terms of metallographic structure and was easily deformed by thermal stress. Repeated application of such thermal stress causes fatigue failure. Therefore, the range of use of the solder material is limited.

As a method for increasing the strength and improving the thermal fatigue resistance of this solder material, (1) a method of adding an alloy element (JP-A-3-204194), or (2) a reinforcing material such as particles is dispersed. Method (JP-A-2-142698
Japanese Patent Laid-Open No. 3-169500, Japanese Patent Laid-Open No. 3-20419
No. 3) etc. have been tried.

[0005]

However, in the method of adding the alloying element of (1), the structure of the solder base material is apt to change, so that sufficient strength cannot be obtained.

In the method (2) for dispersing the reinforcing material, it is difficult to obtain the bondability between the reinforcing material and the solder base material, and the dispersibility of the reinforcing material and the reinforcing effect are not sufficient. In addition, although a method of using an intermetallic compound as a reinforcing material has also been reported, it is generally said that the wettability between the intermetallic compound and the solder material is low, the dispersibility is poor even when mixed with the solder, and the strengthening effect is obtained. Is also small. In particular, when a single-phase reinforcing material such as an intermetallic compound was used, a part of the reinforcing material was discharged to the outside of the solder and the dispersed state was not sufficient.

Further, in Japanese Patent Laid-Open No. 3-169500, a high energy ball mill is used to promote mixing, but there is a problem that it takes time and cost.

It is an object of the present invention to provide a solder material having improved strength and thermal fatigue resistance by improving the dispersibility of the reinforcing material, and a method for producing the same.

[0009]

The first invention (the invention according to claim 1) includes a solder base material and a metal dispersed in the solder base material and having a good bonding property with the solder base material. It is a solder material characterized by consisting of a rare reinforcing material.

The second invention (the invention according to claim 2) is
And one or both of the elements or a compound thereof to form the reinforcement, mixing a good metal bondability with solder preform, by melting, a first step of forming a melt, a solution water 10 ² By cooling at a cooling rate of ℃ / sec or more, a metal having a good bonding property with the solder base material is deposited around the reinforcing material, and the bonding property between the reinforcing material and the solder base material deposited around the reinforcing material is improved. A method of manufacturing a solder material, comprising: a second step of forming a composite reinforcing material made of a good metal; and a third step of dispersing the composite reinforcing material in a solder base material.

[0011]

[Action]

(Operation of First Invention) Since the solder material of the first invention is a composite structure in which a metal having good bondability (wettability) with the solder base material is arranged around the reinforcing material, the periphery of each reinforcing material is The surrounding of the molten solder improves the dispersibility of the reinforcing material. Since the dispersibility of this reinforcing material is good, the strength and thermal fatigue resistance of the solder material are significantly improved.

(Operation of the Second Invention) In the second invention, the second
A strengthening material is formed by rapidly cooling the molten metal of one or both of the element or its compound forming the strengthening material of the process and the metal having good bonding property to the solder base material It is possible to obtain a composite structure in which a metal having a good bondability with the solder base material is deposited. Therefore, a solder material excellent in strength and thermal fatigue resistance can be manufactured without spending time and cost.

[0013]

【The invention's effect】

(Effect of the first invention) The solder material of the first invention is excellent in strength and thermal fatigue resistance.

(Effect of Second Invention) In the second invention, a solder material excellent in strength and thermal fatigue resistance can be manufactured without spending time and cost.

[0015]

EXAMPLES Specific examples of the present invention will be described below.

(Specific Example of First Invention) The first invention is a solder material in which a reinforcing material having a composite structure in which a metal having a good bondability with the solder base material is wrapped is dispersed in the solder base material. .

The composition of the solder base material is not particularly limited. For example, a generally used lead (Pb) -tin (Sn) -based alloy having a basic composition and containing various additive elements may be used.

As the reinforcing material, one having a specific gravity similar to that of the molten solder base material is desirable in order to prevent uneven distribution of the reinforcing material (reinforcing phase) due to gravity during soldering.
For example, copper (Cu) -tin (Sn) alloy, nickel (Ni) -tin (Sn) alloy, iron (Fe) -tin (S).
An intermetallic compound such as n) -based alloy may be used, and at least one of them is used.

The shape of the reinforcing material may be any shape such as granular or fibrous. However, in order to enhance the reinforcing effect, the size of the reinforcing material (average particle diameter in the case of granules, fibrous shape) The average diameter) is preferably 30 μm or less. According to the theory of composite strengthening, it is generally said that the reinforcing material is preferably a fibrous material having a large aspect ratio (length / diameter). However, if anisotropy occurs or random orientation occurs, the composite amount is limited. Further, the granular material is preferable in order to obtain the reinforcing material relatively easily. In this case, if the fine particles are densely dispersed, the reinforcing effect is large. On the other hand, if the particles become too fine, it becomes very difficult to uniformly mix and disperse them. Therefore, the average particle size of the particles is preferably 30 μm or less.

The reinforcing material may be a composite of a plurality of different types.

It is assumed that the reinforcing material has a composite structure surrounded by a metal having a good bondability with the solder base material. That is, the composite reinforcing material is formed by the reinforcing material and the solder base material that wraps the reinforcing material and the metal having good bondability.
This composite structure (composite reinforcing material) facilitates the mixing of the reinforcing material in the solder base material and improves the dispersibility of the reinforcing material.

Examples of the metal having good bondability (wettability) with the solder base material are tin (Sn) and indium (In) which are elements forming an intermetallic compound with Ni, Cu or Fe.
Etc., and at least one of them is used.

Further, as the composite structure, it is desirable that almost all of the periphery of the reinforcing material is wrapped with a metal having a good bonding property with the solder base material. In order to further improve the dispersibility of the reinforcing material, it is desirable that the reinforcing material is contained solely and the periphery thereof is surrounded by a metal having a good bondability with the solder base material. But,
In terms of practicality, even if a plurality of reinforcing materials are present in contact with each other, the reinforcing effect does not cause much problem.

In the above composite structure (composite reinforcing material), the mixing ratio of the metal having a good bondability to the solder base material and the reinforcing material is
There is no particular limitation. For example, the above mixing ratio can be selected according to the rigidity, strength, coefficient of thermal expansion, etc. of the solder required for soldering. Among them, the ratio (weight ratio) of metal: reinforcing material having good bondability to the solder base material: weight ratio is from 1: 9.
The effect as a composite structure is high in the range of 9: 1.

When the density difference between the reinforcing material and the solder base material is large, the reinforcing material may float or sink after mixing the two, and uneven distribution of the reinforcing material may occur in the solder base material. . In that case, by making the density of the reinforcing material substantially the same as the density of the molten material of the solder base material, uneven distribution of the reinforcing material after mixing can be prevented.

The solder material of the first invention can be manufactured by the following method in addition to the manufacturing method of the second invention described below.

First, a metal layer is formed by coating the surface of the reinforcing material with a metal (Sn or an alloy thereof) having a good bondability with the solder base material by plating or the like. By forming a metal layer on the surface of the reinforcing material, a composite structure in which the periphery of the reinforcing material is wrapped with a metal having a good bonding property with the solder base material is generated. As a coating method, generally, there is a method in which a reinforcing material is manufactured and then electroless plating or electrolytic plating is performed. Then, the reinforcing material is dispersed in the molten solder base material, or is mixed with the solder base material powder and then remelted to disperse the reinforcing material in the solder base material.

The solder material according to the first aspect of the present invention can be used for soldering electronic components mounted on automobiles and the like. For example, the application range of the solder material is determined by the form of the solder material. If it is a paste-like solder, it is used in the conventional printing and reflow method. Further, if it is a solid solder, it can be handled in the same manner as conventional solder.

(Specific Example of Second Invention) In the second invention, one or both of an element or a compound forming a reinforcing material, a solder base material and a metal having good bonding property are mixed and melted ( The first step), the obtained molten metal is rapidly cooled at a cooling rate of 10 ² ° C / sec or more (second step), and the obtained mixture is dispersed in the solder base material (third step).
It is a method of manufacturing a solder material.

In the second aspect of the present invention, the number of steps can be reduced as compared with the above-mentioned method using plating or the like, which is advantageous in terms of cost.

Also in the second invention, the same solder base material, reinforcing material, and metal having a good bondability with the solder base material as shown in the specific example of the first invention can be used.

In the first step, one or both of an element or a compound forming a reinforcing material and a solder base material and a metal having good bonding property are mixed to form a molten metal.

As the compound forming the reinforcing material, Cu-
Sn-based _{(Cu 3 Sn, Cu 6 Sn} 5), Ni-Sn -based _{(Ni 3 Sn, Ni 3 Sn} 2, Ni 3 Sn 4), Ag-
Sn-based _{(Ag 3 Sn, Ag 6 Sn} ), Fe-Sn system (F
_{eSn, FeSn 2), Ni-} In -based (Ni ₃ In, N
iIn, NiIn ₃ , Ni ₂ In, Ni ₃ In ₇ ), A
g-an In-based _{(Ag 3 In, Ag 2 In} , AgIn 2) and the like, use at least one of these.

The molten metal may be formed by a general method.

In the second step, the obtained molten metal is rapidly cooled.
In this quenching, a molten metal having an alloy composition that forms the reinforcing material is solidified non-equilibrium to form the reinforcing material and it is possible to dispose a metal having good bondability with the solder base material around the reinforcing material. Is. Therefore, the reinforcing material becomes a composite structure in which the solder base material is wrapped with a metal having a good bonding property, and a composite reinforcing material including the reinforcing material and the solder base material enclosing the reinforcing material and a metal having a good bonding property is obtained. For example, Cu ₆ Sn ₅
The or Ni ₃ Sn ₄ or the like by using a melt of the alloy composition crystallizes,
When powdered at a solidification rate of about 10 ² ° C / sec, a composite structure composed of a compound having a size of several μm and a Sn-rich phase surrounding it is obtained.

The cooling rate is 10 ² ° C / sec or more, preferably 10 ⁴ to 10 ⁶ ° C / sec. As a result, the reinforcing material becomes finer and the composite reinforcing effect is easily obtained.

In the third step, the composite reinforcing material is dispersed in the solder base material.

As a method for dispersing the composite reinforcing material in the solder base material, a general composite material manufacturing method in which the reinforcing material is dispersed and strengthened can be used. For example, the composite reinforcing material is dispersed in the molten solder base material, or the composite reinforcing material and the powder of the solder base material are mixed and then remelted to form a composite. It may be used for joining after compounding, or compounding and joining may be performed at the same time. Also, the following two types of methods can be used.

This is selected depending on the intended use of the solder material. The first is paste-like solder, which is indispensable for high-density mounting these days. In this case, the particles of the solder base material and the particles of the composite reinforcing material may be mixed first, and then flux may be added and kneaded, or mixing and flux addition may be performed at the same time.

The second is a case of using a plate-shaped, rod-shaped, or thread-shaped solder. This is done by mixing the composite reinforcement with the molten metal of the solder base metal as described above, or by mixing the particles of the composite reinforcement and the particles of the solder base metal, solidifying by powder metallurgy, rolling, and extruding. It is a method of forming a predetermined shape by the above.

Examples of the present invention will be described below.

(Example 1) Ni and Sn were mixed in an atomic mixing ratio of Ni: Sn = 3: 4 and melted in nitrogen gas so that the cooling rate was about 10 ⁴ ° C / sec. To produce a powder. Micrographs showing the metal structure in the cross section of this powder are shown in FIGS. 1 and 2. 1 and 2 that Sn surrounds the periphery of the fine intermetallic compound (Ni ₃ Sn ₄ ).

This powder was classified to have an average particle size of about 25 μm or less and used as a composite reinforcing material.

The powder of the composite reinforcing material and the solder powder of the eutectic composition were mixed in a ball mill for about 1 hour. Using this mixed powder, the following two types of composite solders (1) and (2) were manufactured.

(1) A flux was added to the mixed powder and kneaded to obtain a paste solder. This solder was printed on a copper plate, a chip was placed on the copper plate, and fusion bonding was performed in a reflow furnace.
FIG. 3 shows a micrograph showing the metal structure in the cross section of the joint between the copper plate and the chip. It can be seen from FIG. 3 that the reinforcing material Ni ₃ Sn ₄ is uniformly dispersed without being discharged.

For comparison, the same joining was carried out also with a paste-like solder made of only solder powder. As a result, the static strength of the joint was about 50% or more when the reinforcing material was included.

(2) The mixed powder is compacted and extruded,
Plate-shaped solder was produced by rolling. In this case, the weight ratio of the composite reinforcing material and the solder base material was changed to composite reinforcing material: solder base material = 5: 95, 15:85, 25:75. The hardness, thermal expansion coefficient, and cross-sectional structure of this plate-shaped solder were examined. The results are shown in FIG. 4 (hardness), FIG. 5 (coefficient of thermal expansion), and FIGS. 6 to 8 (micrographs showing the metal structure in the cross section of the solder).

From FIG. 4 it can be seen that the hardness of the solder increases as the amount of composite reinforcement increases. Also, FIG.
It can be seen that the coefficient of thermal expansion of the solder decreases as the amount of composite reinforcement increases. Further, from FIGS. 6 to 8, it can be seen that in the solder of this example, the reinforcing material is uniformly dispersed in the solder base material.

Further, a part of the produced solder was further processed to produce a thread-shaped solder having a diameter of 1 mm.

A copper plate and a chip were joined using these solders, and the strength was measured.

For comparison, the same joining was also performed with solder prepared only with solder powder. As a result, it was confirmed that the material containing the reinforcing material increased the strength by about 50% or more.

(Comparative Example) A paste-like solder was manufactured and melt-bonded in the same manner as in Example 1 except that powder consisting of only the Ni ₃ Sn ₄ compound was used. As a result, most of the compound powder was discharged into the flux residue other than the joint portion, resulting in a joint state in which the dispersibility of the reinforcing material was poor. Further, FIG. 9 shows a micrograph showing the metal structure in the cross section of the joint between the copper plate and the chip. From FIG. 9, it can be seen that the reinforcing material is discharged and the reinforcing material is not uniformly dispersed.

(Example 2) Cu and Sn were mixed in an atomic mixing ratio of Cu: Sn = 6: 5, and a powder was prepared in the same manner as in Example 1. Paste-shaped, plate-shaped, and thread-shaped solders were prepared and compared with solders that do not contain a reinforcing material. As a result, the strength was improved by about 50% or more by adding the reinforcing material.

[Brief description of drawings]

FIG. 1 is a micrograph showing a metal structure of a cross section of a composite reinforcing material powder in an example of the present invention.

FIG. 2 is a micrograph showing a metal structure of a cross section of a composite reinforcing material powder in an example of the present invention.

FIG. 3 is a micrograph showing a metal structure of a cross section of a solder joint in an example of the present invention.

FIG. 4 is a diagram showing the relationship between the weight fraction of the composite reinforcing material and the hardness of the solder material in the example of the present invention.

FIG. 5 is a diagram showing the relationship between the weight fraction of the composite reinforcing material and the thermal expansion coefficient of the solder material in the example of the present invention.

FIG. 6 is a micrograph showing a metal structure of a cross section of a solder material in an example of the present invention.

FIG. 7 is a micrograph showing a metal structure of a cross section of a solder material in an example of the present invention.

FIG. 8 is a micrograph showing a metal structure of a cross section of a solder material in an example of the present invention.

FIG. 9 is a micrograph showing a metal structure of a cross section of a solder joint in a comparative example.

Claims (2)

[Claims] 1. A solder material comprising: a solder base material; and a reinforcing material dispersed in the solder base material and surrounded by a metal having a good bondability with the solder base material. 2. A first step of forming a molten metal by mixing one or both of an element forming a reinforcing material or a compound thereof and a solder base material and a metal having good bondability, and melting the mixture. By cooling the molten metal at a cooling rate of 10 ² ° C / sec or more, a metal having a good bonding property with the solder base material is deposited around the reinforcing material, and the reinforcing material and the solder matrix deposited around the reinforcing material. A method for producing a solder material, comprising: a second step of forming a composite reinforcing material composed of a metal and a metal having good bondability, and a third step of dispersing the composite reinforcing material in a solder base material.