JPS5919193B2 - Method for modifying impact plating film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for modifying an impact plating film, and its purpose is to heat-treat and modify a tin or tin-lead alloy (solder) layer plated on a metal substrate by impact plating. The purpose is to improve solderability and corrosion resistance.

In recent years, impact plating (Mcchanical Platinum) has been developed by 3M Corporation as a plating for items that are particularly sensitive to hydrogen embrittlement, such as structural parts of automobiles.
g) has become widely used.

Impact plating is a method of plating by placing the object to be plated, fine particles or powder of the metal to be plated, and glass beads as impact media in a ball mill or rotating barrel, and rotating them. Glass beads collide with fine metal particles for plating that are loosely attached to the surface of the object to be plated, and the impact causes the fine metal particles to become flakes and adhere to the substrate.The fine metal particles adhere to each other, forming a plating layer. It is considered that In impact plating, the type of metal to be plated can be changed for each batch, so it is possible to plate many types of metal with one plating device (ball mill or rotating barrel), which is different from ordinary electroplating. That's impossible. In addition, impact plating has a lighter burden on wastewater treatment than electric plating, so it is likely to be used more widely in the future. However, as expected from the plating method, impact plating is limited to soft metals with low hardness.

On the other hand, in the electronic equipment industry, platings such as tin, zinc, tin-lead alloy (solder), copper, nickel, and silver are used in large quantities. Possible materials include tin, tin-lead alloy, copper, and zinc, but copper plating is often used as a base plating.
Furthermore, since galvanizing can be treated with chromate for corrosion resistance, it is thought that there will be no major problems when applying it to electronic parts. However, in the case of tin plating or tin-lead alloy plating, good solderability is required in addition to corrosion resistance. In recent years, with the development of electronic devices, a method has been adopted for assembling electronic devices in which various electronic components are temporarily attached to a printed circuit board and finally soldered all at once using a solder bath. Solderability is becoming increasingly strict. However, tin plating using impact plating has very poor solderability, and compared to tin plating using electroplating, it has the disadvantage of extremely poor solderability. Therefore, when the surface of a part made of annealed copper was plated with tin by impact plating, the cross section of the plating film was observed under a microscope and it was found that the tin particles were not tightly bonded to each other and there were many voids between the tin particles. I realized what I was doing. Therefore, due to poor heat conduction and the oxidation of the surface of tin particles during the plating process,
It is thought that the solderability has deteriorated. In addition, impact tin plating has poor surface roughness and has many voids between tin particles as described above, so it has disadvantages such as slightly inferior corrosion resistance compared to electric tin plating. The present invention has been made in view of the above points, and involves immersing a workpiece plated with tin or tin-lead alloy in a heat treatment bath so that the tin or tin-lead alloy particles in the plating layer are mutually removed. The above-mentioned drawbacks are solved by making the plating layer dense by fusion bonding.

As a heat treatment method for the above purpose, a method of heating in a vacuum atmosphere or a cyclic atmosphere is also considered, but in that case, the heat treatment time and high temperature (230 to 250
It takes time and space to cool the object heated to 10°C (°C) from that temperature to room temperature without oxidizing the plating metal, which is a big problem when considering mass production equipment. In consideration of the above points, the present invention uses a heat-resistant oil or fat-like substance for heat treatment, and prevents the plating layer from being oxidized in the air when the object to be treated is cooled after the heat treatment. It is designed to prevent this by the oily pancreas (or oily film) that adheres to the surface of the plating.

In addition, the oil or fat-like substance for heat treatment should be non-oxidizing so that tin or tin-lead alloy plating is not oxidized during heat treatment, and do not change in quality at high temperatures (230 to 250 degrees Celsius) and have low evaporation. need to use something. Experiments have shown that natural apricot oil, which is a mixture of unsaturated fatty acids such as oleic acid and linoleic acid and saturated fatty acids such as palmitic acid and stearic acid in an appropriate ratio, is suitable as the fat for the above purpose. I figured it out.

Next, to explain heat treatment, the object to be treated is plated with tin or tin-lead alloy by impact plating, and the above-mentioned fat or oil-like substance is heated to a temperature higher than the melting point of the tin or tin-lead alloy. 30 seconds to 4 minutes in a heat treatment bath set up in
After being immersed for about a minute, the metal particles to be plated are taken out and left to cool. During the heat treatment, the metal particles to be plated are isolated from the outside air, and adjacent particles are fused to each other, gradually turning into a continuous plated layer.
Modified into a dense plating layer.

Next, examples of the present invention will be described.

Example 1 A plurality of electronic device parts made of mild steel were plated with tin to a thickness of approximately 8 μm by impact plating, and then heated with natural perilla oil at 230 to 250°C (performer oil was heated at temperatures exceeding 250°C). In a heat treatment bath heated to
After being immersed for 30 seconds to 4 minutes, it was taken out and allowed to cool.

When we conducted a soldering test on each object that had been heat-treated for different times after returning to room temperature, we found that the solderability of each object was significantly better than that of the untreated object. I understood. Note that the thin oil film that adheres during the heat treatment does not have to be removed after being left to cool for soldering. Example 2 A plurality of objects to be treated, which were electronic device parts made of mild steel and plated with tin-lead alloy (SU4O (Ft), Pb6O (Fb)) by impact plating, were immersed in the same heat treatment bath as in Example 1. When we compared the solderability of each object to be processed, which was heat-treated under the same conditions and then allowed to cool, to an impact-plated sample that was not heat-treated, it was found that the solderability was significantly improved.

The plating layer heat-treated in Examples 1 and 2 was denser and the furnace corrosion resistance was improved.

However, when a steel substrate is heat-treated by impact plating with tin or tin-lead alloy plated by immersing it in a heat treatment bath heated to 230 to 250°C,
At ~250°C, an alloy layer is not formed between the mild steel base and the plating metal layer, and due to the surface tension of the molten plating metal, if the immersion time is 30 seconds or more, the molten plating on the mild steel base will melt. It was found that the fine metal particles began to partially aggregate to form spherical particles, and as the immersion time became longer, the spherical particles merged to form even larger spherical lumps, and the surface of the plated metal layer became rough. Ivy.

For this reason, it has been found that in the case of objects to be treated that require a smooth surface in appearance, the heat treatment time is limited and management requires skill. Therefore, when heat-treating a workpiece made of mild steel and tin-plated by impact plating using the above method, it is necessary to control the temperature of the heat treatment bath and the heat treatment time (immersion time). We have developed a method that is easy to use, does not damage the appearance of the surface of the object to be processed, and can improve solderability and corrosion resistance.

The development method is to first plate the mild steel base of the object to be treated with copper as a base plating, then apply tin plating on the copper plating by impact plating, and then place the object to be treated in the same manner as above. A method of heat treatment by immersion in a heat treatment bath. In this case, when heated, the copper of the base plating diffuses into the tin that has melted into a liquid phase, forming a solid solution rich in tin. A tin-copper alloy is formed. As in the case of single-phase tin plating, spherical particles are formed by short-term heat treatment, but at the same time an intermetallic compound called η phase (CO6Sn5) is generated near the boundary between the copper layer and the tin layer. (This was revealed by X-ray diffraction, SEM observation, etc.) The spherical particles formed by the relatively long heat treatment are absorbed by the copper plating layer, causing the surface of the tin plating layer to become rough. It is possible to suppress deterioration of the appearance due to In addition, when 1 copper plating is performed by impact plating, if the underlying copper plating layer is thicker than the tin plating layer and the stoichiometric composition of the intermetallic compound (Cu6SO,) cannot be satisfied, After heat treatment, if an external impact is applied to the object, intermetallic compounds (C
Peeling occurs from the copper plating layer that is not supported by the formation of u6Sn5). Therefore, in order to maintain the tin-rich state rather than the stoichiometric composition of the intermetallic compound (Cu6SO5),
The thickness of the copper plating should be as thin as possible, and in consideration of ease of control, approximately 0.5 to 1 μm is practically appropriate. Note that it goes without saying that the underlying copper plating may be performed by electroplating, non-electrolytic plating, etc., when there is no need to particularly consider the problem of hydrogen embrittlement. Then as above,
An example will be described in which a copper base plating is applied to a mild steel substrate. Example 3 A plurality of electronic device parts made of mild steel were plated with a copper base plating to a thickness of about 1μ by impact plating, and then tin was plated to a thickness of 8 to 10μ using the same impact plating. The object to be treated was immersed for 1 to 4 minutes in a heat treatment bath prepared by heating natural bean oil to 230 to 250°C, and then taken out and allowed to cool.

After cooling, the appearance of the plating and soldering tests were conducted, and it was found that no spherical lumps or spherical particles were formed in the plating layer of each object treated with different heat treatment times, and the surface was relatively smooth. , solderability was significantly improved, and
It was found that corrosion resistance was also improved. Therefore, heat treatment management has become significantly easier. Of course, the above-mentioned method for undercoating copper can also be applied to tin-lead alloy (solder) plating, which has a melting point close to that of tin and forms an alloy with copper.

As described above, the method for modifying a plating film by impact plating of the present invention is to modify a plating metal layer made of tin or tin-lead alloy, which has poor solderability and corrosion resistance, by impact plating.
By immersing it in a heat treatment bath made of heated oil or fat-like substance and heat-treating it, it is easy to use in terms of equipment.
Heat treatment is also easy and can significantly improve the solderability and corrosion resistance of the plated metal layer. In addition, when impact plating tin or a tin-lead alloy on an article made of mild steel and heat treating it, it is possible to significantly improve the solderability and corrosion resistance of the plated metal layer. The method of underplating with copper improves solderability and corrosion resistance, and facilitates heat treatment management, without damaging the appearance of the tin or tin-lead alloy plating metal layer.

Claims (1)

[Scope of Claims] 1. A workpiece plated with tin or a tin-lead alloy by impact plating on a mild steel substrate, which is non-oxidizing and heat-resistant to the plated metal layer made of tin or tin-lead alloy. The plated metal layer is heated to a temperature equal to or higher than the melting point of the plated metal layer and heat-treated for an appropriate time to remove the A method for modifying an impact plating film, which comprises forming a dense plating film by fusing the particles of the plating metal in the plating metal layer to each other. 2. The workpiece plated with tin or tin-lead alloy by impact plating is heated with coconut oil above the melting point of tin or tin-lead alloy.
A method for modifying an impact plating film according to claim 1, characterized in that the heat treatment is carried out by immersing the workpiece in a heat treatment bath heated to a temperature of 250° C. or lower. 3. The object to be treated is prepared by base-plating copper on a mild steel substrate, plating tin or tin-lead alloy on the copper plating by impact plating, and applying a non-oxidizing material to the plated metal layer made of tin or tin-lead alloy. The tin or tin in the plated metal layer is heated to a temperature higher than the melting point of the tin or tin-lead alloy and heat-treated. Fusing tin-lead alloy particles to each other and forming a tin-copper alloy layer or a tin-copper-lead alloy layer between the copper plating layer to make the plating layer dense and smooth. A method for modifying an impact plating film, characterized by: 4. A workpiece prepared by base-plating copper on a mild steel substrate and plating tin or tin-lead alloy by impact plating on the copper plating is heated with coconut oil at 250° C. above the melting point of tin or tin-lead alloy.
4. The method for reforming an impact plating film according to claim 3, wherein the heat treatment is carried out by immersing the workpiece in a heat treatment bath heated to a temperature of .degree. C. or lower.