JP2000286542A - Soldering method and soldering substrate - Google Patents

Abstract

(57) [Summary] A nickel film layer is formed on a surface of a base material mainly composed of copper, and gold,
A thin layer of silver, palladium or tin is formed as a soldering base material, and the soldering base material is soldered with tin-zinc solder. [Effect] A tin-zinc solder can be satisfactorily bonded to a base material mainly composed of copper, and the copper-zinc compound can be suppressed by suppressing the diffusion of copper when left in a high-temperature atmosphere after the bonding. The growth of the layer can be prevented, and the occurrence of cracks and the like based on the difference in strength between copper and the compound layer can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for soldering an electronic component on a printed circuit board with a tin-zinc solder, and an electronic component for the soldering and a soldering base in the printed circuit board. It is about materials.

[0002]

2. Description of the Related Art Conventionally, in the production of various electronic devices,
2. Description of the Related Art Soldering electronic components on printed wiring boards is widely performed. And in the soldering, tin-
Lead-based solder is widely used.

[0003] Tin-lead-based solder has excellent bonding properties with copper, has little change in the bonding state over time, and is evaluated as having extremely excellent stability. There is a concern that lead may have an adverse effect on the human body and an adverse effect on the environment, and the use of lead-free solder is required. As a lead-free solder, a tin-zinc solder is considered to be most promising in terms of melting point and cost.

[0004]

The tin-zinc solder contains tin as a main component and zinc added, and is similar to the conventional tin-lead solder in terms of metal properties and operability. At high temperatures, cracks may form in the joints, resulting in poor joints.

[0005] That is, when a tin-zinc solder is bonded to the surface of copper of a base material, a compound layer of copper and zinc is formed at the boundary, and the compound layer grows remarkably at a high temperature, and the compound layer grows. A difference in strength occurs between copper and copper, and the impact causes cracks along the interface between the compound layer and copper.

The present invention has been made in view of the above circumstances, and has as its object to prevent excessive growth of a compound layer at a high temperature and to prevent a crack from being formed in a joint portion and to prevent a joint failure. Things.

[0007]

According to the soldering method of the present invention, a nickel film layer is formed on the surface of a base material mainly composed of copper, and gold, silver, and palladium are formed on the surface of the nickel film layer. Alternatively, a thin layer of tin is formed and used as a soldering base material.
The present invention is characterized in that the soldering base material is soldered with a zinc-based solder.

In the soldering substrate of the present invention, a nickel coating layer is formed on the surface of a base material mainly composed of copper, and a thin layer of gold, silver, palladium or tin is formed on the surface of the nickel coating layer. It is characterized by having done.

According to the present invention, a base material to be subjected to soldering forms a nickel film layer on a surface of a base material mainly composed of copper,
It is characterized in that a thin layer of gold, silver, palladium or tin is formed on the surface of the nickel coating layer.

The base material is mainly composed of copper, and has a nickel film layer formed on the surface thereof. The nickel coating layer can be formed by plating, and its thickness is suitably 1 to 10 μm. If the thickness of the nickel coating layer is less than 1 μm, the diffusion of copper cannot be suppressed, and if it exceeds 10 μm, the nickel coating layer will hinder the joining between the copper and the solder.

The thin layer is made of gold, silver, palladium or tin, and can be formed singly or by stacking a plurality of materials. The thickness of the thin layer is suitably about 0.01 to 0.5 μm. If the thin layer is too thin, the bonding will be insufficient, and if it exceeds 0.5 μm, the effect will not be further improved.

Then, the base material is soldered. In the present invention, a tin-zinc-based solder is used as the solder for soldering. As the tin-zinc solder, a eutectic alloy of about 91% tin and about 9% zinc can be used, and based on this, other metals can be added.

The method of soldering can be the same as the method conventionally used for soldering electronic components to a printed circuit board. For example, printing solder paste on a printed circuit board, mounting electronic components on it,
It can be reflowed and soldered.

[0014]

In the present invention, since a nickel film layer is formed on the surface of a base material containing copper as a main component, copper is diffused in the nickel film layer by the solder adhering to the base material. To form a compound with zinc in the solder.
Therefore, the connection between the base material and the solder is reliably performed.

When the tin-zinc solder is directly bonded to the copper base, the copper diffuses into the compound layer and the compound layer grows as described above, when left in a high-temperature atmosphere after the bonding. However, according to the present invention, the nickel coating layer acts as a barrier to suppress copper diffusion and prevent the compound layer from growing excessively. You do it.

Although the formation of the nickel coating layer on the surface of the copper substrate alone has the effect of suppressing the growth of the compound layer, the tin-zinc-based solder has insufficient wettability with respect to nickel. We cannot secure enough.

Therefore, in the present invention, since a thin layer of gold, silver, palladium or tin is formed on the surface of the nickel film layer, the wettability of the solder to the surface of the base material is improved and the soldering is excellent. At the same time, the initial strength is improved.

[0018]

Thus, according to the present invention, a tin-zinc solder can be satisfactorily bonded to a base material mainly composed of copper. The diffusion can be suppressed to prevent the growth of the copper-zinc compound layer, thereby preventing the occurrence of cracks and the like based on the difference in strength between copper and the compound layer.

[0019]

EXAMPLES [Preparation of solder paste] Solder composition: 91% tin-9% zinc alloy Solder particle size: 20-40 μm Flux: RA type (chlorine content 0.2%) Solder paste composition: 88 weight of solder powder %-Flux 12% by weight

[Substrate test piece] Copper plate (0.3 mm) Nickel plating (5 μm) on copper plate (0.3 mm) Nickel plating (5 μm) on copper plate (0.3 mm)
Gold plating (0.1μm) on its surface Nickel plating (5μm) on copper plate (0.3mm)
Palladium plating (0.1 μm) on the surface, gold plating (0.03 μm) on the surface, nickel plating (5 μm) on a copper plate (0.3 mm),
The surface is tin-plated (0.2μm) Copper plate (0.3mm) is nickel-plated (5μm)
Silver plating on its surface (0.1μm)

[Joining of test pieces] From each board test piece, 50
A test piece A having a size of 30 mm × 30 mm and a test piece B having a size of 50 mm × 5 mm were collected, and a thickness of
A solder paste of 00 μm was printed, a 5 mm × 5 mm area at the end of the test piece B was superimposed thereon, and the solder paste was melted by heating to 230 ° C., and the test pieces A and B were joined.

[Test Conditions] The test pieces bonded as described above were left at 150 ° C. for 500 hours, and the bonding strength before and after the test pieces and the state of growth of the compound layer were measured.

[Joining strength] Test piece A was fixed and test piece B
Was vertically pulled up at a speed of 20 mm / sec, and the load at the time when the joint was broken was measured to determine the joint strength. Ten test pieces were prepared, and the average of the measurement results was obtained and evaluated. ◎: Joint strength 5 kg or more ○: Joint strength 3-5 kg △: Joint strength 1-3 kg ×: Joint strength 1 kg or less

[Growth of Compound Layer] The compound layer of copper and zinc at the interface of the joint was measured by EPMA analysis, the average compound layer thickness at the initial stage and after heating was measured, and the initial compound layer and the thickness after heating were measured. The difference in thickness from the compound layer was calculated and evaluated. ：: growth of compound layer 3 μm or less △: growth of compound layer 3 to 5 μm ×: growth of compound layer 5 μm or more

[Test Results] The results of the tests are shown in Table 1.

[0026]

[Table 1]

[Evaluation] From the above results, it can be understood that the formation of the nickel coating layer on the copper material suppresses the growth of the compound layer at the bonding portion, and the bonding strength does not decrease with time. .

However, when only a nickel coating layer was formed on a copper material, the nickel coating layer had poor initial wettability due to elimination of solder wettability, and was not usable. By further forming a thin layer, the wettability of the solder is improved and the initial strength is improved.

In particular, those formed with a thin layer of palladium and gold and those formed with a thin layer of tin have extremely good initial strength and maintain the initial strength over time. Very good results have been obtained.

Further, in the case of forming the thin layer of silver, although the remarkable improvement is not seen as in the case of (1) and (2), the initial strength shows the same bonding strength as that of direct soldering to copper. In addition, since the bonding strength is maintained over time, it is sufficiently good.

In the example in which the thin layer of gold is formed, a large number of voids are observed at the joint, and the joining strength is reduced due to this. However, the joining strength is lower than that of the case of only the nickel film layer. Has been improved.

Claims (2)

[Claims] 1. A nickel coating layer is formed on a surface of a base material containing copper as a main component, and gold,
A soldering method, comprising forming a thin layer of silver, palladium or tin as a soldering base material, and soldering the soldering base material with tin-zinc solder. 2. A nickel film layer is formed on a surface of a base material containing copper as a main component, and gold,
Solder base material characterized by forming a thin layer of silver, palladium or tin