Plated material for connectors

Details Plated material for connectors Plated material for connectors

2000-06-14

2002-06-11

Jones, Deborah (Department: 1775)

Stock material or miscellaneous articles

All metal or with adjacent metals

Composite; i.e., plural, adjacent, spatially distinct metal...

C428S648000, C428S610000, C439S886000, C439S887000

Reexamination Certificate

active

06403234

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a Sn plated material for terminals and contacts in connectors, and more particularly, relates to a Sn plated material in which less insertion force is necessary when the material is employed as a connector.
BACKGROUND ART
Sn plated materials, in which Sn is plated on Cu or Cu alloy, are widely used for contacts (electrodes), such as connectors for automobiles.
These Sn plated materials are produced by continuously plating in a Sn coating line and are generally produced by a method as described below. A strip of Cu alloy plating base metal such as brass or phosphor bronze is degreased and pickled as a pretreatment, Cu substrate plating is formed on the base metal by an electroplating method as an intermediate layer, or no intermediate layer is provided thereon, and subsequently, a Sn plating layer is formed on the surface thereof. As a method for forming the Sn plating layer, a method in which reflow (heat-melting) treatment is carried out after plating is mainly employed. This is because whiskers are not produced on the reflowed Sn plated material, etc.
Cu alloy strip in which Sn is plated is pressed into the shape of a contact at a connector manufacturer and is molded with resin, thereby forming a connector. These Sn plated connectors are employed primarily for electrical wiring parts for automobiles at present.
However, in connectors formed of Sn plated material, it is noted that a large insertion force must be applied when the connector is connected. In assembly lines for automobiles, the connectors are usually manually connected at present. Therefore, in the case in which the insertion force necessary for the connector is too large, workers on the assembly line are burdened thereby, and it is also possible that work-related health problems will occur.
Since Sn is a soft metal, a Sn film produces a sliding resistance when a contact point is slid on the Sn film. Therefore, in the Sn plated terminals or connectors, insertion and withdrawal force necessary therefor is higher than that for Au plated connectors, etc.
Recently, connectors tend to have multiple cores, whereby insertion force necessary therefor is increased. Therefore, there is a much stronger demand to decrease the insertion force necessary for connectors.
DISCLOSURE OF INVENTION
The present invention was made in view of the above-described circumstances, and it is an object thereof to provide a Sn or Sn alloy plated material for terminals or connectors in which the insertion force necessary for connector assembly can be reduced.
As a result of the inventors' research to solve the above problems, the present invention provides a plated material for connectors having superior insertion and withdrawal properties, comprising: an intermediate layer consisting of Ni or Ni alloy plating having a Vickers hardness of 450 to 750 Hv and a thickness of 0.3 to 2 &mgr;m provided on a base metal consisting of Cu or Cu alloy; a reflowed Sn or Sn alloy plated surface layer provided thereon; and an alloy layer consisting primarily of Sn—Ni and having a thickness of 0.05 to 2 &mgr;m formed by diffusion between the intermediate layer and the surface layer, in which average grain size of Sn—Ni compound is 0.05 to 1 &mgr;m.
According to an embodiment of the present invention, an intermediate layer is made of an alloy consisting of P in an amount of 0.05 to 15% by weight; B, Zn, and Cu, in a total amount of 50% by weight or less; and the balance consisting of Ni and inevitable impurities, or consisting of Ni, Co, and inevitable impurities.
Furthermore, according to another embodiment of the present invention, the content of at least one of P and B in Sn or Sn alloy plating measured by Glow Discharge Mass Spectrometry (GDMS) is 0.001 to 0.2% by weight in total.
Moreover, according to another embodiment of the present invention, the content of at least one of P and B in an oxide layer formed on the surface of a Sn or Sn alloy plating layer by diffusion from the inside is 0.001 to 0.1% by weight in total.
It was found that the insertion force necessary for connector can be reduced according to the present invention.
As described above, since Sn is a soft metal, a Sn film produces sliding resistance when a contacted point (metal) is slid on Sn plating. The higher the hardness of the substrate, the smaller this function (lubricating property of a metallic thin film). Therefore, when a Sn plated connector has a hard substrate, the insertion force necessary therefor is reduced. In the present invention, a Ni alloy intermediate layer having suitable hardness is formed as a substrate for the Sn or Sn alloy plating, whereby the insertion force necessary for the connector is reduced. A plated material according to the present invention is satisfactory as long as an alloy layer containing Ni exists under the Sn or Sn alloy plating layer at the surface. That is to say, the present invention is effective even if another plating layer exists between the Ni alloy layer and the base metal consisting of Cu alloy.
As a Ni alloy intermediate layer, Ni alloy (or Ni—Co alloy) containing at least one of P and B may be mentioned. Ni—P alloy (or Ni—P—B alloy, etc.) plating has a Vickers hardness of 450 to 750 Hv and has a hardness suitable for decreasing the insertion force necessary for connectors. Furthermore, in Sn plated material having this intermediate layer, P or B diffused to the surface of Sn plating by reflow (heating) process in Sn plating lines, and a film consisting of P compound or B compound, is formed at the surface. P compounds, etc., have lubricating effects, whereby this film works as a lubricating film and the insertion force necessary for connectors is reduced without increasing contact resistance at the surface of the Sn plating.
The hardness of the intermediate layer is preferably 450 to 750 Hv. When the hardness is less than 450 Hv, the insertion force necessary for connectors is not satisfactorily decreased. In contrast, when it exceeds 750 Hv, defects such as plating cracks, etc., occur during pressing.
It is necessary that the thickness of the intermediate layer be 0.3 &mgr;m or more, and it is more preferable that it be 1.0 &mgr;m or more. When the thickness is less than 0.3 &mgr;m, the above insertion force decreasing effect is lessened. Since pressing properties are inferior when the thickness is too great, the upper limit therefor is preferably up to 2 &mgr;m. Moreover, structures having multiple plating layers can be constituted by forming another plating layer, for example, a Cr plating layer, etc., between an intermediate layer and a base metal.
When the Sn plating having a Ni alloy intermediate layer is reflowed (heated), an alloy layer consisting primarily of Ni—Sn is formed between the Sn plating layer and the intermediate layer by diffusing Ni. This alloy layer also affects the insertion force necessary for connectors as does the intermediate layer. The thickness of this alloy layer is preferably 0.05 to 2 &mgr;m. The insertion force necessary for connectors increases when the thickness is less than 0.05 &mgr;m , and the contact resistance in connectors in high temperature environments may be easily increased when it exceeds 2 &mgr;m.
In the alloy layer, crystals of Ni—Sn compound are generated and the average grain size of these crystals is 0.05 to 1 &mgr;m. The insertion force necessary for connectors increases when the average grain size is less than 0.05 &mgr;m, and the contact resistance may be easily increased when it exceeds 1 &mgr;m. The thickness of the alloy layer and the average grain size can be adjusted by controlling the heating temperature and the heating period during plating reflow processing.
Of elements constituting the intermediate layer, Ni or Co is a base element for adding P, B, Cu, or Zn in the intermediate layer, and can be alloy-plated with each element. An alloying ratio in a Ni—Co alloy can be optionally chosen. Furthermore, as a function of Ni or Co, there is also a suppressive effect for diffusing Cu in Sn plating, that is to say, an effec

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