Stock material or miscellaneous articles – All metal or with adjacent metals – Composite; i.e. – plural – adjacent – spatially distinct metal...
Reexamination Certificate
1998-12-16
2001-03-27
Jones, Deborah (Department: 1775)
Stock material or miscellaneous articles
All metal or with adjacent metals
Composite; i.e., plural, adjacent, spatially distinct metal...
C428S620000, C428S628000, C428S680000, C439S887000, C257S677000
Reexamination Certificate
active
06207298
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a tin-nickel alloy and a component surface-treated with such an alloy and, more particularly, to an electronic component to be soldered on a substrate surface with the use of the surface mount technology.
2. Description of Related Art
Typical methods for mounting an electronic component such as a connector on a surface of a substrate include a dip soldering method and a surface mount technology (SMT).
In the dip soldering method, leads and the like of an electronic component are preliminarily inserted into holes formed in a substrate, and the substrate is then dipped in a solder melt in a solder bath. Thus, the solder adheres only onto desired portions to achieve electrical and mechanical connection between the electronic component and the substrate.
In the surface mount technology, a solder paste is preliminarily applied onto electronic component connection areas on a surface of a substrate, and then an electronic component is mounted on the substrate with its joint portions being in contact with the solder paste. Subsequently, the substrate and the electronic component mounted thereon are put in a hot air reflow oven, and maintained in an atmosphere at a peak temperature of about 250° C. for a predetermined period (e.g., 60 seconds to 120 seconds), whereby the solder paste is fused. In turn, the substrate is taken out of the hot air reflow oven and cooled for solidification of the solder paste. Thus, the electrical and mechanical connection between the substrate and the electronic component is achieved.
An electronic component such as a connector which includes a copper alloy base or an iron base, for example, is in some cases subjected to a surface treatment such as plating for improvement of the appearance thereof. In this case, a surface treatment layer (e.g., deposit layer) should have a certain level of solder wettability (particularly, solder wettability after the lapse of a predetermined time from the surface treatment) for easy mounting of the electronic component on a substrate.
Particularly where the surface mount technology is employed, the surface treatment layer should also have a heat resistance sufficient to withstand a treatment at a high temperature.
If the surface treatment layer has an insufficient heat resistance, the layer is melted so that it cannot maintain its good appearance. That is, the surface treatment layer becomes less lustrous, and is roughened or flaked off upon solidification thereof after the melting thereof. The roughening and flaking of the surface treatment layer impair the solderability of the electronic component.
Where an electronic component is mounted on the substrate with the use of the surface mount technology, a palladium deposit layer, which has a higher melting point (1550° C.) and a superior solderability, is conventionally employed as a surface treatment layer.
However, palladium is a very expensive metal, and it is therefore not economical to employ palladium for the formation of a surface treatment layer. Besides palladium, gold and silver are known to have high melting points (1064.4° C. and 961.9° C., respectively) and a satisfactory solderability, but are very expensive. Therefore, gold and silver also have the same drawback as palladium when they are employed for the formation of a surface treatment layer.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a tin-nickel alloy which has a sufficient heat resistance and a satisfactory solderability and is effective for cost reduction of a component.
It is another object of the present invention to provide a component which has been surface-treated so as to be imparted with a sufficient heat resistance and a satisfactory solderability.
To achieve the aforesaid objects, the tin-nickel alloy according to the present invention comprises not less than 75 wt % and less than 100 wt % of tin with the balance of nickel.
With this arrangement, the tin-nickel alloy has a satisfactory solderability and a sufficient heat resistance. In addition, a drastic cost reduction can be achieved in comparison with the use of palladium.
If the tin content in the tin-nickel alloy is less than 75 wt %, the solderability is impaired. Conversely, if the tin content is 100 wt %, the heat resistance is insufficient because the melting temperature of pure tin is relatively low (about 232° C.). In addition, the use of 100-wt % tin for the surface treatment layer of the component results in formation of whiskers. Therefore, particularly where the component is used in electric circuitry, a failure associated with a short circuit may occur.
The tin-nickel alloy preferably comprises 75 wt % to 95 wt % of tin with the balance of nickel. In such a case, the tin-nickel alloy has a melting temperature of not lower than about 250° C. and hence a sufficient heat resistance.
The tin-nickel alloy more preferably comprises 75 wt % to 88 wt % of tin with the balance of nickel. In such a case, the alloy has an improved solderability.
The component according to the present invention has a surface treatment layer formed of the aforesaid alloy on a base thereof.
With this arrangement, the surface treatment layer formed on the base of the component has a satisfactory solderability and a sufficient heat resistance, and the mounting of the component on a substrate surface is therefore facilitated.
Electronic components and other components are included as the component. Examples of specific electronic components include connectors, semiconductor IC packages, semiconductor IC chips, and conductive members (contacts and lead frames for semiconductor ICs) for electrical connection. The connector may have, for example, a main body of a resin, and metal components attached to the main body. The metal components include, for example, a metal shell covering the main body, and contacts fixed on the main body.
The surface treatment layer preferably has a thickness of not less than 0.1 &mgr;m and less than 0.5 &mgr;m.
It is preferred that an underlying layer is interposed between the surface treatment layer and the base of the component.
The underlying layer may be a deposit layer, preferably a nickel deposit layer which is lustrous.
Where the deposit layer formed on the surface of the component has a thickness of about 0.1 &mgr;m, for example, pin holes are formed in the deposit layer due to evolution of hydrogen gas during the plating process. This results in a deteriorated solder wettability. Therefore, the thickness of the surface treatment layer is preferably not less than 0.1 &mgr;m.
The aforesaid surface treatment layer tends to discolor in a high temperature atmosphere. The discoloration does not affect the performance of the surface treatment layer but, if remarkable, impairs the appearance of the layer. The discoloration is supposedly caused by such a mechanism that metal tin and metal nickel precipitated in the tin-nickel alloy deposit layer form a solid solution at a high temperature and then recrystallized.
It has experimentally been found that, if the thickness of the surface treatment layer is not less than 0.5 &mgr;m, the discoloration is noticeable (the discoloration is noticed only by comparing the appearances before and after the surface treatment layer is placed in the high temperature atmosphere), and, if the thickness is not less than 1.0 &mgr;m, the discoloration is distinct. Accordingly, the thickness of the surface treatment layer is preferably not less than 0.1 &mgr;m and less than 0.5 &mgr;m.
Therefore, the surface treatment layer having a thickness of not less than 0.1 &mgr;m and less than 0.5 &mgr;m does not suffer from the apparent discoloration even after the component is kept in the high temperature atmosphere, for example, for soldering the electronic component onto the substrate. Hence, the component has a good appearance and a surface state with a satisfactory solderability.
The underlying layer interposed between the surface treatment layer and the base of the component provides for ligh
Japan Solderless Terminal Mfg. Co., Ltd.
Jones Deborah
Rader Fishman & Grauer
Savage Jason
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