JPH0245708B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of manufacturing a metal product having a desired shape having a precious metal plated portion, and particularly relates to a method suitable for manufacturing a lead frame having a precious metal plated portion at the lead end. .

Conventionally, a lead frame 1 as illustrated in FIG. 1 has been used for packaging semiconductor integrated circuit (IC) elements. This lead frame 1
is the island part 2 in the center where the IC element is mounted.
A large number of external leads 3 connected to the electrodes on the IC element and the connector wires are continuously formed around the island part 2 and the tips of the external leads 3 on the island side. (However, the island portion 2 may not be plated with precious metal.) Conventionally, such a lead frame 1 is made of a thin plate or strip of iron, iron alloy, copper, or copper alloy, and after photo etching or press punching is performed on this material to cut out unnecessary parts, at least the lead tips are cut out. It is manufactured by performing a plating process (this is called partial plating) using a mask that exposes the surface. In recent years, as the degree of integration of IC devices has improved, lead frames with a large number of leads have become necessary, and the thickness and width of the leads have become thinner and narrower. If partial plating is attempted on a lead frame having such delicate leads, the chances of handling will increase and defects such as lead bending will inevitably occur. Furthermore, according to the above-described partial plating method, as shown in FIG. 2, the precious metal is plated not only on the top surface 4 of the lead 3 but also on the side surface 5, but this plating on the side surface 5 is originally completely unnecessary. , you are wasting precious metals.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method that eliminates the drawbacks of the conventional methods described above and can manufacture delicate metal products such as lead frames with a high yield in which precious metal plating is applied only to necessary parts. In order to achieve this object, the present invention applies photoresist to a thin plate or strip made of iron, iron alloy, copper, or copper alloy, and exposes the area to be plated with precious metal by exposing and developing the photoresist. This exposed area is plated with precious metal, and a desired pattern is exposed and developed on the photoresist to expose a part of the metal surface of the material. After etching is performed using the photoresist as a mask, the remaining photoresist is removed. It is characterized by peeling off.

The present invention will be described below with reference to the case of manufacturing a lead frame.

Figure 3 is a cross-sectional view conceptually showing each of the following steps (A) to (F) in the manufacturing process of a lead frame in which precious metal plating is applied only to the top surface of the lead tip using the method of the present invention. be.

(A) Photoresist 7 is applied to the entire surface of material 6 made of iron, iron alloy, copper, or copper alloy. The coating thickness may be approximately several microns. There are two types of photoresists: negative type and positive type, and either method may be used as long as it is properly combined with an exposure mask. Here, we will discuss the case of using a positive photoresist.

(B) Part 8 of the lead tip where precious metal plating should be applied
Using a photomask with a pattern in which only the lead tip is exposed and other parts are not exposed, the exposed photoresist part is removed with a solvent (this is called development), and the part 8 of the lead tip to be plated with precious metal is removed. The material 6 is exposed.

(C) This material is subjected to a plating device, and the noble metal 9 is electrodeposited on the exposed portion of the material 6. Base plating may be applied before precious metal plating. The plating device may be either a batch type or a continuous type depending on the shape of the material.

(D) Next, both sides are exposed using a photomask with a lead frame pattern, and developed to expose the material 10 between the leads and between the leads and the islands. (Exposure alignment in steps (B) and (D) is important, but this alignment can be done by normal means.) (E) If this is subjected to etching, the material 6 will have exposed areas on both sides. Starting from 10, it is etched towards the inside in order,
At the end, the etched holes on both sides pass through. When ferric chloride is used as an etching solution, it can be applied to both iron-based and copper-based materials.

(F) By peeling off the remaining unexposed photoresist, a lead frame 11 having noble metal plated portions 9 only on the top surfaces of the tips of the leads 3 as shown in FIG. 4 is obtained.

If the precious metal to be plated is silver, the surface will be oxidized by the etching solution in the above etching step (E), so the step (E) to remove the oxide film or
(F) It can be added after the process. The silver oxide film can be easily removed with dilute nitric acid or other chemical polishing liquid.

In addition, in the etching process (E) above, the noble metal plating layer acts as a mask, but if the plating layer and photoresist are not in close contact, the etching solution will penetrate into the boundary, creating a depression around the plating layer due to etching. There is. To prevent this, it is recommended to perform a baking process on the photoresist immediately before the step (E). For example, heat treatment at 150°C for about 30 minutes.
In this way, the plating layer and the resist around it will be in close contact with each other.

According to the present invention, precious metal plating is performed on the material in the form of a thin plate or strip, and unnecessary parts are cut out in the final process, so precious metal is not wasted and the frequency of lead bending is greatly reduced. In particular, it can greatly contribute to lowering the manufacturing cost of fine metal products having precious metal plated parts.

[Brief explanation of the drawing]

Figure 1 shows a conventional lead with precious metal plating at the tip.
FIG. 2 is an enlarged perspective view of the tip of the lead frame; FIG. 3 is a schematic diagram showing changes in the material according to the method of the present invention in cross-section of the material at each step; FIG. 4 FIG. 1 is a plan view of a lead frame in which precious metal plating is applied in spots only to the top surface of the lead tips according to the present invention. 3...Lead; 6...Material; 9...Precious metal plating part.

Claims (1)

[Claims] 1 Apply photoresist to a thin plate or strip made of iron, iron alloy, copper, or copper alloy, expose the area to be plated with precious metal by exposing and developing the photoresist, and plate this exposed area with precious metal. , further comprising exposing and developing a desired pattern on the photoresist to expose a part of the metal surface of the material, etching using the photoresist as a mask, and then peeling off the remaining photoresist. A method for manufacturing metal products with plating parts.