JPH0522322B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to a tin-plated contact for a connector in which a liquid lubricant is applied to a tin-plated film.

TECHNICAL BACKGROUND Contact materials for connectors are generally constructed by coating the surface of a base metal with a metal plating film that has a low coefficient of friction and is durable.
Even in this configuration, if the plating film is softer than the base metal, the friction coefficient of the plating film can be further reduced by appropriately thinning the plating film. This occurs because the thin film of soft metal (corresponding to the plating film here) acts as if it were a lubricant, and this phenomenon is generally widely known as the metal thin film lubrication effect.
Generally, the lubricating effect of such a thin metal film is
This is a phenomenon that occurs when hard metals whose surfaces are coated with a thin film of soft metal are brought into contact with each other and slid, and the coefficient of friction is smaller than when the coating is thick.

Gold is generally used for the plating film of contact materials for connectors, but due to rising prices, tin-based metals have come to be used.

Prior Art and Problems A tin-based contact is constructed by forming a base plating film of nickel or copper on a base material such as phosphor bronze, and then plating a tin-based metal thin film. Here, the tin-based plating film includes tin containing 5% by weight of tin and lead 10%, which is generally used for connectors at present.
Includes all tin-lead alloys, such as tin containing % lead by weight or tin containing 40% lead by weight. Tin or tin-lead alloys are softer than the underlying metal and exhibit a metal thin film lubrication effect. However, tin or tin-lead alloys have a higher coefficient of friction than gold, and therefore cause significant friction. Since the insertion and removal life of contacts is important, conventional connectors with tin-based contacts have a film thickness of 5 to 10 μm so that the plating film can be maintained even after some wear.

It also has the disadvantage of fretting corrosion due to tin oxidation. Liquid lubricant is applied to reduce the friction of the metal plating film or to prevent fretting corrosion, but in conventional contacts, when applying liquid lubricant, tin or tin-lead is used. No consideration was given to the thickness of the alloy plating film.

OBJECTS OF THE INVENTION It is an object of the present invention to reduce the coefficient of friction of tin or tin-lead alloy plated contacts for connectors in which a liquid lubricant is applied to the tin or tin-lead alloy plated film.

Structure of the Invention The above object of the present invention is to set the thickness of the tin or tin-lead alloy plating film to 2 to 4 μm, and to coat the tin or tin-lead alloy plating film with a liquid lubricant most suitable for tin-based contacts. This is achieved by the characteristic tin-based plated contacts for connectors.

The liquid lubricant is based on polyphenyl ether, and 0.5% by weight or more of a phosphate ester type surfactant having a benzene ring in the lipophilic group is added.

The phosphate ester type surfactant can be a mixture of a phosphoric monoester, a phosphoric diester, and a trace amount of a phosphoric triester.

For example, phosphoric acid monoester is represented by the following formula, Also, phosphoric acid diester Here, R is an alkylphenyl group having 8 to 30 carbon atoms.

It is advantageous to add the phosphate ester type surfactant after neutralization with triethanolamine.

Example 1 The contact was made by plating copper or nickel to a thickness of 2 μm on a phosphor bronze base material, and a contact pin was formed by plating a tin film to a thickness of 3 μm on top of this, and the load was 150 g.
The friction coefficient was measured after 5 insertions and withdrawals.

In FIG. 1, for both curves a and b, the base is copper for the circles marked with black, and the base is nickel for the circles marked with ○. Curve a is
A contact material with a tinned film coated with a lubricant, curve b is a sample without a lubricant applied, and both a and b were tested with different tin film thicknesses.

For polyphenyl ether as a lubricant,
A phosphoric acid ester type surfactant (GAFAC RE-610 manufactured by Toho Chemical Co., Ltd.) having a benzene ring in its lipophilic group was added in an amount of 1% by weight. This lubricant is one of the best for tin-based contacts.

The friction coefficient is small when the tin film thickness is in the range of 1 to 4 μm, but when it exceeds 4 μm, both curves a and b begin to increase, and when curve a exceeds 7 μm and curve b exceeds 5 μm, the friction coefficient remains almost constant. Indicates a high value. In this way, whether the base plating film is made of nickel or copper, the coefficient of friction shows the same tendency up to a thickness of 4 μm.

Figure 2 shows the nickel plating base film shown in Figure 1.
The friction coefficient was measured after 5, 50, and 100 insertions and withdrawals for sample a, in which the same lubricant as shown in Figure 1 was applied on contacts plated with different tin film thicknesses, and sample b, in which no lubricant was applied. Show the results. Insertion and removal 5 times (○ mark)
are the results shown in FIG. Insertion and removal 50 times (□
The coefficient of friction after 100 times (marked with a mark) and 100 times (marked with an x) is the same as after 5 times (marked with an ○) for lubricant coated sample a, but
When no lubricant is applied, the low friction coefficient increases with the increase in the number of insertions and withdrawals for samples with a tin film thickness of 1 to 4 μm. On the other hand, it was confirmed that the friction coefficient of the tin-plated film coated with lubricant is small when the tin film thickness is in the range of 1 to 4 μm, and begins to increase when the tin film thickness exceeds 4 μm. It was also confirmed that the friction coefficient of the tinted film coated with this lubricant was the same as the initial value even after 100 insertions and withdrawals.

Example 2 As a lubricant, 1% by weight of the surfactant used in Example 1 was neutralized with triethanolamine.
Measurements were carried out in the same manner as in Example 1 except that the added polyphenyl ether was used, and the same results as in Example 1 were obtained. Note that this lubricant is also one of the most suitable for tin-based contacts.

In addition, in these Examples, when the film thickness was 1 μm, a portion where the underlying _Ni film was exposed could be observed in a part of the friction trace after 100 insertions and withdrawals. Therefore, the film thickness is 2
~4μm is desirable.

Effects of the Invention According to the present invention, the friction of the contacts can be kept low even after many times of insertion and removal, and the insertion and removal force can be small even in a connector having a large number of contacts.
It is possible to realize a multi-pin connector for use in electronic devices in which elements are mounted at high density.

[Brief explanation of drawings]

Figure 1 shows the contact material with a tin-plated film when the base plating film is nickel or copper.
This is a graph showing the relationship between the tinted film thickness and the coefficient of friction depending on the presence or absence of lubricant. Figure 2 shows the relationship between the tinted film thickness and the coefficient of friction depending on the presence or absence of lubricant. Accordingly, it is a graph showing the relationship between the tinted film and the coefficient of friction by changing the number of insertions and withdrawals. a...Contact sample with lubricant applied, b...Contact sample without lubricant, ●...Copper plating base film, after insertion and removal 5 times, ○...Nickel plating base film,
After 5 insertions and removals, □...Nickel-plated base film, after 50 insertions and removals, ×...Nickel-plated base film, after 100 insertions and removals.

Claims (1)

[Claims] 1. A nickel or copper underplating film is formed on the contact substrate, and a tin or tin-lead alloy solder film with a thickness of 2 to 4 μm is plated thereon. For connectors, characterized in that a liquid lubricant made of polyphenyl ether as a base material and containing 0.5% by weight or more of a phosphate ester surfactant having a benzene ring in its lipophilic group is applied to the sticky film. Tin-based plated contacts. 2. The tin-based plated contact according to claim 1, wherein the phosphate ester type surfactant is a mixture of a phosphoric acid monoester, a phosphoric diester, and a trace amount of a phosphoric triester. 3. The tin-based plated contact according to claim 1, in which a phosphate ester type surfactant is added after being neutralized with triethanolamine.