JP2002001520A - Soldering method and soldering structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of flux free soldering. SOLUTION: This method is to put a sheet of soldering foil between the faces to be connected of connecting materials 1, 1 and adhere closely the connecting faces by pressing with the pressing device 3 at a natural temperature of a preheating temperature lower than the melting point of soldering foil to bring them into close contact with each other, and melt the soldering foil by a heating furnace 4, while keeping the close adhesion, and cool down it after the pressing and heating conditions are kept for a specified time.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a soldering structure and a soldering method which does not require a flux or a reducing atmosphere.

[0002]

2. Description of the Related Art In soldering, it is essential to remove an oxide film from a surface to be joined in order to promote the wettability of molten solder. Conventionally, an oxide film on a surface to be joined is removed using a flux. At the same time, the surface to be joined and the molten solder are shielded from the air to prevent formation of an oxide film during heating. Conventionally, in assembling an IC, a lead frame plated with Ni or Au is used.
Although the lead frame is prevented from being oxidized by heating during the assembling process, when soldering the outer lead of the lead frame to an external circuit such as a wiring board, the oxidization due to heating during soldering is required. Flux is used to prevent Further, instead of using this flux, it has been proposed to perform soldering in a reducing atmosphere. Recently, it has been proposed to place a solder foil between the surfaces to be joined, heat and press these to melt the solder foil, and actively generate an intermetallic compound to perform soldering (Japanese Patent Laid-Open No. 2000-2000). −
No. 52027), this pressurized soldering method also requires a flux.

[0003]

However, in the soldering method using a flux, post-cleaning treatment is required in order to prevent deterioration of the soldering portion over time due to the flux residue. Recently, there has been a demand for flux-free soldering due to the problem of destruction. Further, as another environmental problem, there is a problem of harmfulness of lead ions eluted from a soldering portion of a waste electronic device, and in order to cope with this problem, lead-free solder is required.

An object of the present invention is to provide a flux-free soldering method in view of the above points. It is a further object of the present invention to provide a soldering method that enables flux-free soldering using Sn-based solder, which is a lead-free solder.

[0005]

According to the soldering method of the present invention, a soldering foil is disposed between surfaces to be joined, and the soldering is performed by a pressing jig at room temperature or under a preheating lower than the melting point of the soldering foil. The contact interface between the joining surface and the solder foil is tightly adhered by pressure, the solder foil is melted by heating while maintaining the tightly adhered state, the pressurized heating is maintained for a predetermined time, and then cooled. It is a configuration characterized by using a Sn-based solder foil having a thickness of 20 μm to 200 μm for the solder foil,
The pressing force of the pressing jig is 0.5 to 4 kg / mm ² , the preheating temperature is 230 ° C or lower, preferably 100 ° C or lower, and the heating temperature for melting the solder foil is 250 ° C or higher.
It is appropriate that the temperature is 450 ° C. and the heating and holding time is 5 to 600 seconds.
~ 80% by weight, or Au, A
One containing 0.1 to 5% by weight of any one or more of g, Cu, Ni, and In can be used.

[0006]

Embodiments of the present invention will be described below with reference to the drawings. (A) to (c) in FIG.
3 is a drawing showing a soldering method according to the present invention. In FIGS. 1A to 1C, reference numerals 1 and 1 denote materials to be joined;
Is a solder foil, 3 is a pressing jig (31 is an indenter, 32 is a table)
Numeral 4 denotes an elevating type heating furnace (for example, an electric heating type). To perform soldering according to the present invention,
First, as shown in FIG. 1 (a), a solder foil 2 is disposed between the surfaces to be joined of the materials 1 and 1 to be joined and pressed by a pressing jig 3 at room temperature. The contact interface between the joint surface and the solder foil is brought into tight contact with the solder foil. Then, while maintaining this tight contact state, as shown in FIG. 1 (b), the heating furnace 4 is lowered, and the work w is surrounded by the heating furnace 4, so that the solder foil 2 is melted.
The heating of the work w by the heating furnace 4 is maintained for a predetermined time,
Thereafter, as shown in FIG. 1C, the heating furnace 4 is raised to cool the work w to room temperature, and the soldering according to the present invention is completed.

In the above, air is eliminated from the contact interface between the surface to be joined and the solder foil by the clamping and pressing of the work at room temperature by the pressure jig. Therefore, the formation of an oxide film at the contact interface can be eliminated because of airlessness despite heating. The reason why the work is sandwiched and pressed at room temperature is to make the contact interface between the surface to be joined and the solder foil airless without forming an oxide film, and is substantially oxidized sufficiently lower than the melting point of the solder foil. It is also possible to preheat as long as the temperature can prevent the occurrence of the heat. Even during the heating by the heating furnace, the interface between the surface to be joined and the solder is shielded from the air by the sandwiching pressure by the pressing jig, so that the formation of a new oxide film is prevented. Further, the primitive oxide film existing from the beginning on the surface to be joined is broken by the clamping pressure by the pressing jig, so that the diffusion reaction between the surface to be joined and the solder is promoted, and the intermetallic compound grows. The growth of the intermetallic compound is governed by the diffusion reaction and depends on the temperature, and the thickness of the intermetallic compound is determined by the temperature and time. Thus, the molten solder foil portion that has not been consumed for the formation of the intermetallic compound under the predetermined temperature and the predetermined heating time is subjected to the intermetallic compound layer due to the pressurization during the heating and holding time. Although the thickness of about 10 μm remains as a solder layer, the thickness of the solder foil is reduced, the above-mentioned predetermined temperature is raised, or the predetermined heating time is prolonged to generate an intermetallic compound. If the entire thickness of the molten solder foil is consumed, the solder layer can be substantially eliminated.

Thus, in the soldering structure according to the soldering method according to the present invention, as shown in FIG.
An intermetallic compound layer 21 is formed between the metal layer and the solder layer 20, and exhibits excellent mechanical strength. That is, the intermetallic compound layer 21 has a high Young's modulus and is sufficiently tough, and the intermetallic compound layer 21 behaves mechanically in the same manner as the base material 1, reducing the tensile stress fz acting on the solder layer 20. On the other hand,
An x-direction stress fx for preventing the shrinkage of the solder layer 20 in the x-direction and a y-direction stress fy for preventing the shrinkage of the solder layer 20 in the y-direction are generated in the entire solder layer (solder layer 2).
Since the thickness t ₀ of 0 is as thin as not more than about 10 [mu] m), the results of stress generated in the solder layer 20 is a three-dimensional stress, the solder layer 20 comes to exhibit a strength of at least the mechanical strength of the solder itself. Therefore, according to the soldering method of the present invention, excellent strength soldering can be performed without using a flux or using a reducing atmosphere.

In the present invention, it is preferable to use a lead-free solder, for example, a Sn-based solder for the solder foil.
The thickness of this solder foil is usually 20 to 200 μm. If it is less than 20 μm, it is easily broken by pressurization by a pressure jig, and if it exceeds 200 μm, the ratio of being expelled from the intermetallic compound layer during heating and holding without increasing the intermetallic compound increases. is there. The pressing force of the pressing jig is usually set to 0.5 to 4 kg / mm ² . 0.5k
If it is less than g / mm 2, the contact pressure at the contact interface between the surface to be joined and the solder foil is too low to satisfactorily exclude air between them. If it exceeds 4 kg / mm ² , the contact pressure is too high and the solder foil This is because there is a fear that air may be broken and air may be trapped at the broken point. The preheating temperature for preheating the work is usually 230 ° C. or lower, preferably
100 ° C. or less. If the temperature exceeds 230 ° C., it is practically impossible to make the contact interface between the surface to be joined and the solder foil airless by pressurizing the pressing jig without forming an oxide film. If the temperature and time of the above-mentioned heating and holding are too small, the growth of the intermetallic compound cannot be expected and a substantial bond between the base material and the solder layer cannot be obtained. Since oxidation and deformation of
At 0 ° C. to 450 ° C., the heating and pressing holding time is set to 600 seconds to 5 seconds. If the temperature is less than 250 ° C., a time of 600 seconds or more is required, and the workability is inferior.
This is because it becomes difficult to control the heating time.

As the above-mentioned Sn-based solder, an Sn-based solder containing 2 to 80% by weight of In, for example, In, so that the heating temperature × retention time is 350 ° C. to 400 ° C. × 120 seconds to 300 seconds. -48Sn, Sn-5In or A
one containing at least one of u, Ag, Cu, Ni, and In in an amount of 0.1 to 5% by weight, for example, Sn-5
Cu-1Ni, Sn-1Ni, Sn-3Ag-4Cu-
0.5In or the like can be used.

In the soldering according to the present invention, an outer lead frame (for example, Fe—Ni—Co material) of an IC is used.
Soldering between the lead and the external conductor (copper conductor) of the wiring board
It can be used for sealing and sealing the lid plate with a ceramic case package of C. In particular, as is clear from the examples described later, when the surface to be joined is Ni-plated and the solder foil is the above-mentioned Sn-based solder, the heating temperature × the holding time is set to 35.
The thickness of the intermetallic compound (average value of t1 and t1 'in FIG. 2; hereinafter the same) is set to 1 to 15 μm, preferably 5 to 10 μm, and the thickness of the solder layer as 0 ° C. to 400 ° C. × 120 seconds to 300 seconds. The thickness can be reduced to 20 μm or less, preferably 5 μm or less, and soldering with excellent strength can be performed. Further, as is clear from the examples described later, when the surface to be joined is Au-plated and the solder foil is the above-mentioned Sn-based solder, the heating temperature × the holding time is set at 350 ° C. to 400 ° C. × 120 seconds to 300 ° C.
In seconds, the thickness of the intermetallic compound can be 1 to 15 μm, preferably 3 to 8 μm, and the thickness of the solder layer can be 20 μm or less, preferably 10 μm or less, and soldering with excellent strength is possible. Further, as is clear from the examples described later, when the surface to be joined is Cu-plated and the solder foil is the above-mentioned Sn-based solder, the heating temperature × the holding time is set to 350 ° C. to 400 ° C.
× 120 seconds to 300 seconds and the thickness of the intermetallic compound is 1 to
The thickness of the solder layer can be reduced to 15 μm, preferably 7 to 15 μm, and the thickness of the solder layer can be reduced to 20 μm or less, preferably 8 μm or less, so that soldering with excellent strength is possible.

[0012]

[Example 1] A Ni-plated lead frame material (Ni plating thickness of about 2 to 6 μm, lead frame material Fe-Ni-Co) was used as a material to be joined, and In-48 was used as a solder foil.
Sn, a thickness of 60 μm, and a plane dimension of 1 mm × 2 mm were used. As the pressing jig, a stainless steel indenter having a tip outer diameter of 1.2 mm and a stainless steel receiving table was used, and as the heating furnace, an electric furnace having a heating temperature of 350 ° C. was used. Using this pressing jig, a soldering force of 2.7 kg /
was clamped in mm ^2, then word in a heating furnace - surrounding the click, the pressurizing and heating was maintained for 15 seconds, then而Ru, word by removing the heating furnace - cooling the click. The peel strength of the soldered joint of this example at room temperature and 25 ° C. was 233 g, which was 10 times or more the strength of the solder (In-48Sn) itself.
The thickness of the intermetallic compound layer at the solder joint is 5 μm.
m, and the thickness of the solder layer was 5 μm.

[Comparative Example] In comparison with Example 1, a heater was added to the stainless steel indenter of the pressing jig, and the work placed on the stainless steel pedestal was heated to 350 ° C. with the stainless steel indenter. The pressure was set to 2.7 kg / mm ^2, which is the same as in Example 1,
The heating / pressing holding time was set to the value in Example 1 (heating / pressing holding time: 15
The heating and pressurization was performed for an extremely long time of 120 seconds, and then the stainless steel indenter was released to cool the work.

Normal temperature 2 of the soldered joint of this comparative example product
The peel strength at 5 ° C. was practically zero. The result is
It is presumed that an oxide film was formed at the contact interface between the solder foil and the surface to be joined due to heating before the end of the air elimination because the work was heated while being pressed and held. On the other hand, in Example 1, since the heating was performed after the discharge of the air from the contact interface was completed, it is presumed that good soldering was performed without forming the oxide film.

Example 2 The procedure was the same as that of Example 1 except that the heating time under pressure was changed to 300 seconds. The peel strength at 300 ° C. of the soldered joint of Example 2 was 96 g. In the second embodiment, the thickness of the solder layer at the soldered joint is 2
μm, the thickness of the intermetallic compound layer is 8 μm, and 3
The reason why sufficient peel strength is exhibited even at 00 ° C. is presumed to be that the soldered joint is substantially composed of only the intermetallic compound layer.

Example 3 The procedure was the same as Example 2 except that a Ni plate was used as the material to be joined to Example 2 (the material to be joined was a Ni-plated lead frame material). Example 3
The peel strength at 300 ° C of the soldered joint of Example 2 was
Also, the thickness of the solder layer and the thickness of the intermetallic compound layer at the soldered joint were almost the same as in Example 2.

Example 4 Example 2 (Composition I of solder foil)
n-48Sn), the composition of the solder foil was changed to Sn-5In.
The same as Example 2 except that The peel strength at 300 ° C. of the solder joint of Example 3 was 43 g, and the thickness of the solder layer of the solder joint was 3 μm.
m, and the thickness of the intermetallic compound layer was 5 μm.

Examples 5 to 7 The same procedure as in Example 2 was performed except that the solder foil having the composition shown in Table 1 was used in Example 2 (composition of solder foil In-48Sn). Examples 5 to 7
Table 1 shows the peel strength at 300 ° C. and the thickness of the intermetallic compound layer of the soldered joint of Example 1. The thickness of the solder layer at the solder joints in Examples 4 to 7 was 2 μm.

Table 1 (Soldering joint of Ni plating material) Composition of solder foil 300 ° C peel strength Thickness of intermetallic compound layer Example 2 In-48Sn 96 g 8 μm Example 5 Sn-5Cu-1Ni 36 g 7 μm Example 6 Sn-1Ni 59 g 8 μm Example 7 Sn-3Ag-4Au-0.5In 90 g 8 μm

[Embodiments 8 to 10] Embodiments 2 and 5
For each of No. 7 (using a Ni-plated lead frame material for the material to be joined), the same procedure was used in each of the examples except that an Au-plated lead frame material was used for the material to be joined. That is, using a pressing jig composed of a stainless steel indenter having a tip outer diameter of φ1.2 mm and a stainless steel pedestal, a thickness of 60 μm
m, a solder foil having a composition shown in Table 2 having a plane dimension of 1 mm × 2 mm and a pressing force of 2.7 kg applied between the Au plating lead frame materials.
/ Mm ² , and then the work was surrounded by an electric furnace having a heating temperature of 350 ° C., the pressurized heating was maintained for 300 seconds, and then the electric furnace was removed to cool the work. The peel strength at 300 ° C. and the thickness of the intermetallic compound layer of the soldered joint of this example were as shown in Table 2, and the thickness of the solder layer was 5 μm.

Table 2 (Soldering of Au plating material) Composition of solder foil 300 ° C peel strength Thickness of intermetallic compound layer Example 8 In-48Sn 30 g 5 μm Example 9 Sn-5Cu-1Ni 40 g 5 μm Example 10 Sn-1Ni 45g 6μm Example 11 Sn-3Ag-4Au-0.5In 60g 6μm

Embodiments 12 to 15 Embodiments 2 and 5
7 to 7 (Ni plating lead frame on the material to be joined)
Use of Cu plate material for the material to be joined
In addition, the same was applied to each example. That is, outside the tip
A stainless steel indenter with a diameter of φ1.2 mm and a stainless steel cradle
Using a pressure jig made of
mx2mm solder foil with the composition shown in Table 2
Pressure 2.7 kg / mm ², Then heating temperature 3
The work was surrounded by an electric furnace at 50 ° C.
Hold for 0 seconds, then remove the electric furnace and remove the work
Cool. 300 ° C of the soldered joint of this example product
The peel strength and the thickness of the intermetallic compound layer are as shown in Table 3.
And the thickness of the solder layer was 3 μm.

Table 3 (Soldering joint of Cu material) Composition of solder foil 300 ° C peel strength Thickness of intermetallic compound layer Example 12 In-48Sn 168 g 10 μm Example 13 Sn-5Cu-1Ni 174 g 10 μm Example 14 Sn −1Ni 178 g 12 μm Example 15 Sn-3Ag-4Au-0.5In 192 g 11 μm

[0021]

According to the present invention, soldering can be performed without using a flux, and a washing process of a flux residue in a mounting and assembling process of an electronic component can be omitted to improve work efficiency. The problem of ozone layer destruction due to the cleaning liquid can be solved. In particular, according to the second to fourth aspects of the present invention, soldering of flux-free can be performed by Sn-based solder, and environmental protection can be promoted also from the viewpoint of lead-free soldering.

[Brief description of the drawings]

FIG. 1 is a drawing showing a soldering method according to the present invention.

FIG. 2 is a view showing a soldering joint structure by a soldering method according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Joining material 2 Solder foil 3 Pressing jig 4 Heating furnace

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H05K 3/34 507 H05K 3/34 507C 512 512C

Claims (8)

[Claims] A solder foil is disposed between surfaces to be joined, and a contact interface between the surface to be joined and the solder foil is pressed by a pressing jig at room temperature or under preheating lower than the melting point of the solder foil. A soldering method wherein the solder foil is melted by heating while maintaining the tightly adhered state, the pressurized heating is maintained for a predetermined time, and then cooling is performed. 2. A solder foil having a thickness of 20 .mu.m to 200 .mu.m.
Use n-type solder foil and set the pressing force of the pressing jig to 0.5-4.
kg / mm ² , the preheating temperature is 100 ° C. or less, and the heating temperature for melting the solder foil is 250 ° C.
The soldering method according to claim 1, wherein the temperature is 450 ° C., and the heating and holding time is 5 to 600 seconds. 3. The soldering method according to claim 2, wherein said Sn-based solder contains 2 to 80% by weight of In. 4. Sn, solder, Au, Ag, Cu, N
3. The soldering method according to claim 2, wherein a material containing 0.1 to 5% by weight of at least one of i and In is used. 5. The soldering method according to claim 1, wherein no flux is used. 6. A joint surface is a Ni surface, the solder is a Sn-based solder, and a thickness of 1 to 15 is provided between the solder layer and the Ni surface.
A soldering structure in which a μm alloy layer is formed and the thickness of the solder layer is set to 20 μm or less. 7. The bonding surface is an Au surface, the solder is a Sn-based solder, and a thickness of 1 to 15 is provided between the solder layer and the Au surface.
A soldering structure in which a μm alloy layer is formed and the thickness of the solder layer is set to 20 μm or less. 8. The bonding surface is a Cu surface, the solder is Sn-based solder, and a thickness of 1 to 15 is provided between the solder layer and the Cu surface.
A soldering structure in which a μm alloy layer is formed and the thickness of the solder layer is set to 20 μm or less.