JPH0467726B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a method for manufacturing a contact with excellent electrical connectivity, and in particular, it is aimed at manufacturing a contact that has low contact resistance and is stable even under low contact pressure. be. [Prior Art] Composite materials obtained by electroplating copper or copper alloy with tin or tin-lead alloy as a contact metal and then subjecting the composite to heating and melting treatment are often used as contacts in consumer electronic devices. On the other hand, gold, gold,
Silver, rhodium, etc. are used. [Problems to be solved by the invention] Composite materials in which copper or copper alloys are plated with tin or tin-lead alloys are susceptible to corrosion in various corrosive environments because tin or tin-lead alloys have lower corrosion resistance than noble metals. There is a problem that the contact resistance is difficult to stabilize at low contact pressure due to products and micro-sliding wear and corrosion.Also, gold, silver, rhodium, etc. have low and stable contact resistance at low contact pressure, but are expensive. There is. [Means for Solving the Problems] The present invention was made to solve the above problems, and is a composite material in which copper or copper alloy is plated with tin or tin-lead alloy. The purpose is to provide a contact with low and stable contact resistance under contact pressure, and a method in which tin or tin-lead alloy is electroplated on copper or copper alloy, and then the plating layer is heated and melted. The degree of variation in plating thickness due to poor wetting of molten tin or molten tin-lead alloy during heating and melting, that is, the difference between the maximum and minimum values of the plating layer thickness, is 0.07 to 0.3 μm per cm ² . This is a method for manufacturing a contactor. Various types of copper alloys such as phosphor bronze, brass, nickel silver, beryllium copper, and titanium copper are used as the copper alloy, but in the present invention, these copper alloys are coated with tin or tin directly or after being plated with a copper undercoat. - Electroplating lead alloys. Next, this is maintained at a temperature higher than the melting point of tin or tin-lead alloy, and when the thickness of the copper-tin alloy layer and the degree of wettability reach the desired state, it is cooled with water. The conditions for copper undercoat plating, tin plating, and tin-lead alloy plating are well known, and can be appropriately selected from these. Tin-lead alloy plating is generally called solder plating, and is 90wt% tin - 10wt% lead or 60wt% tin.
Those with a composition of 40wt% lead are most often used. In addition to a direct-fired furnace using heavy oil, butane, or the like, an electric furnace, an infrared furnace, a high-frequency heating furnace, or the like may be used for the heating and melting treatment, and the present invention is not limited by these. When a tin or tin-lead alloy layer on copper or copper alloy is heated and melted, one of the accompanying phenomena is "wetting failure". This is also called "dewetting" or "repelling" and occurs when molten tin or tin-lead alloy aggregates into small droplets due to poor wetting with the base material or substrate. Since defective wetting is unfavorable from the viewpoint of quality such as appearance and solderability, many attempts have been made to suppress its occurrence. However, in the present invention, from the viewpoint of contactability,
It has been found that nonuniform plating thickness due to poor wetting is rather preferable. The range is from 0.07 ^per cm2
0.3 μm is appropriate. If it is less than 0.07 μm, the effect will be low, and if it is more than 0.3 μm, the appearance will deteriorate significantly, which is not preferable. When the non-uniformity of the plating thickness is within the above range, it is considered that an effect of reducing boundary resistance and concentrated resistance occurs at the contact portion of the contact. When tin or tin-lead alloy layer on copper or copper alloy is heated and melted, Cu ₆ Sn ₅ phase, Cu ₃ Sn phase and other matrix are formed as diffusion products between base metal or underlying copper and tin in plating layer. A copper-tin alloy layer containing the material element is formed. Normally, even if the plating layer is water-cooled and solidified immediately after melting, an alloy layer with a thickness of about 0.1 to 0.3 μm is produced, but if this is held in the molten state for several seconds to more than 10 seconds, the thickness of the alloy layer becomes 0.4 to 1.2 μm. It becomes μm. The Vickers hardness of these formed alloy layers is
It has a hardness of 350 to 450, which is significantly harder than the tin or tin-lead alloy layer remaining above it, which has a hardness of 50 or less. Therefore, it is thought that a thin film metal lubrication effect is generated by both layers, and when they are brought into contact with each other by applying contact pressure as an electric contact, sliding or fitting is smooth and the contact resistance is low. Such an effect is not observed when the thickness of the alloy layer is less than 0.4 μm. If it exceeds 1.2 μm, the contact resistance is good, but the appearance tends to deteriorate, making it undesirable as a contact material. Tin or tin-lead alloy plating, which is applied directly to the copper alloy base material without the copper undercoat plating, is preferable because poor wetting conditions can be adjusted by plating pretreatment. In addition, the base material is phosphor bronze (1 to 8 wt% tin, phosphorus).
0.03 to 0.35 wt%), the growth of the alloy layer is rapid, and when used as a contact, the contact resistance is low and stable compared to conventional products. [Example] Copper, German silver, and phosphor bronze plates with a thickness of 0.2 mm were subjected to alkaline degreasing, electrolytic degreasing, and pickling neutralization, followed by electroplating. Various plating conditions are as follows. Copper plating bath composition: Copper sulfate 240g/sulfuric acid 80g/bath temperature: 30℃ Current density: 5A/dm ^2Tanning bath composition: tinnous sulfate 60g/sulfuric acid 70g/additive 15g/bath temperature: 20 °C Current density: 2A/dm ^2Solder (tin-lead alloy) plating bath composition: Lead borofluoride 54g/tin borofluoride 130g/borofluoric acid 90g/additive 30g/Bath temperature: 20℃ Current density: 5A/dm ^2Electrical The heating and melting process after plating is carried out in an electric furnace at 600°C.
The copper-
After forming the tin alloy layer, it was cooled with water and dried with hot air.
The thickness of the copper-tin alloy layer was determined by an electrolytic thickness measurement method. The contact resistance was measured by moving a platinum ring with a radius of 5 mm, loaded with a load of 50 g, on the sample surface and reciprocating it over a distance of 5 mm at a speed of 10 mm/min, passing a direct current of 10 mA, and measuring the contact resistance. The number of round trips was 500. Contact resistance varies with movement and reciprocation, so it is shown as a range. At that time, a strain gauge was brought into contact with the sample to measure the frictional resistance, which was expressed in relative magnitude. The results are shown in Table 1. As is clear from the results in Table 1, the contact resistance of the example is lower than that of the comparative example.
And there are few fluctuations. Furthermore, the frictional resistance is low, so
It is suitable as a composition for contacts.

[Table] [Effects of the Invention] According to the present invention, a material with low contact resistance, little fluctuation, and low frictional resistance and excellent properties as a contactor can be obtained.

Claims (1)

[Scope of Claims] 1. In a method of electroplating tin or a tin-lead alloy on copper or a copper alloy and then heating and melting the plating layer, poor wetting of the molten tin or the molten tin-lead alloy occurs during heating and melting. A method for manufacturing a contact, characterized in that the difference between the maximum value and the minimum value of plating thickness due to the phenomenon is 0.07 to 0.3 μm per cm ² . 2. Manufacture of a contact according to claim 1, wherein the alloy layer formed by diffusion of tin atoms in the plating layer and copper atoms of the base material or base material during heating and melting has a thickness of 0.4 to 1.2 μm. Method. 3. A method for manufacturing a contact according to claim 1 or 2, using phosphor bronze as the copper alloy.