JPS6146055A - Semiconductor device - Google Patents

Abstract

PURPOSE:To prevent the damaging of a function as an external lead during custody for a prolonged term by forming the external lead in sectional structure in which a copper layer is shaped onto a blank metal, a silver layer is formed onto the copper layer and an alloy layer consisting of tin-lead is shaped onto the silver layer. CONSTITUTION:A copper layer 2 is formed onto a blank 1 composed of a copper group alloy containing zinc or Kovar, and a silver plating layer 4 onto the copper layer 2 and a plating 5 consisting of a tin-lead alloy onto the silver plating layer 4 are shaped. The content of lead is brought to a comparatively small value because tin reduces for the growth of an alloy of silver and tin in the content of lead in the tin-lead alloy 5. In such an external lead, the silver layer is interposed between the copper layer and the silver plating which have been brought directly into contact, and the alloying of noxious copper and tin is prevented while the tin-lead alloy is used in place of tin, thus obviating the generation of whiskers, then improving solderability.

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to a semiconductor device, and more particularly to the structure of an external lead drawn out of an exterior body for electrical connection.

Conventional technology Generally speaking, the external leads of semiconductor devices such as ICs and digital resistors have a structure in which the material Kovar or copper-based material is plated with gold or tin.The reason for this is that the external leads of semiconductor devices As a function, it prevents corrosion of the external leads from the external environment, facilitates the electrical connection between the external leads and the external circuit, and also ensures the soldering properties of the connections between the external leads and the external circuit. It's for a reason. However, since gold plating is expensive and plentiful, it is applied to products with special exteriors such as ceramic packages, but in general, tin plating is widely used. When using tin plating,
Generally, the structure is shown in the cross-sectional view of FIG. Second
In the figure, a copper plating 2 is applied on a material 1 made of Kovar or a copper-based material, and a tin plating 3 is applied thereon. Copper plating 2 is used to increase the adhesion of tin when the material is Kovar, and when the material is a copper-based material, zinc etc. in the copper-based material will diffuse into the tin plating, causing discoloration and soldering. This is provided to prevent this from occurring.

However, in this structure, during long-term storage, an alloy grows between the copper and tin, which may cause delamination between the copper and the copper-tin alloy, since the copper-tin alloy is hard and brittle. Also,
Copper-tin alloy has poor soldering properties and impairs the external lead function of semiconductor devices. To make matters worse, the growth of the alloy causes distortion during the tin etch, causing whiskers.

Problems to be Solved by the Invention In the conventional external lead having a surface layer structure in which tin is plated on a copper layer as described above, an alloy is formed between the steel and tin during long-term storage. The problem was that it began to impair its function as a lead.

20 Technical Means for Solving the Problems To solve the above problems, in the external leads of the semiconductor device of the present invention, a copper layer is provided on a material metal such as Kovar or a copper-based material, and a silver layer is provided on top of the copper layer. , and further has a cross-sectional structure with a tin-lead alloy layer provided thereon.

Function The copper layer in the external lead of the present invention improves the adhesion of silver plating and prevents impurity diffusion. - The tin-lead alloy on the outside of the hook has less cracking and has good soldering properties.

EXAMPLE Next, the present invention will be explained by way of an example. FIG. 1 is a sectional view of an example of the present invention. In FIG. 1, 1 is a copper-based alloy containing zinc, a casing or a material made of Kovar, and a copper layer 2 is provided thereon.
On top of II2, silver plating Ni4. Furthermore, a tin-lead alloy plating 5 is applied on the silver plating layer. The lead content of this tin-lead alloy 5 decreases due to the alloy growth of silver and tin, so if the lead content is too high, the melting point will decrease. Top 9: Since solderability deteriorates, a lead content of 2 to 50 wt% is appropriate.

1. Effects of the Invention In the external lead according to the present invention, a silver layer is interposed between the copper layer and the tin plating, which were conventionally directly bonded, to prevent harmful alloying of copper and tin, and to prevent tin plating. Instead, the tin-lead alloy prevents the generation of whiskers and improves solderability, and the external lead function does not deteriorate during long-term storage.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of an external lead according to an embodiment of the present invention;
Fig. 2 is a cross-sectional view of a conventional external lead.
...Tin plating layer, 4...Silver layer, 5...
・・Tin-gold layer with button.

Claims (1)

[Claims] In a semiconductor device having an external lead that is pulled out from the exterior body, the external lead is provided with a copper layer on a material metal, a silver layer on top of the copper layer, and a tin-lead alloy layer on top of the copper layer. A semiconductor device characterized by: