JPS6226449Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a mask plate used when partially plating lead frames for integrated circuits.

Lead frames for integrated circuits (hereinafter abbreviated as IC) are press punched from materials with high thermal conductivity such as 42 alloy (42% Ni, remaining Fe), Kovar (29% Ni, 17% Co, remaining Fe), and phosphor bronze. After forming a predetermined pattern by etching, the part on which the IC chip is placed (island) and the inner lead part are bonded together, and precious metals such as gold and silver are plated locally for the purpose of imparting electrical conductivity and preventing corrosion and heat dissipation. It is common to do so. Since these platings are quite expensive, they must be applied accurately to the minimum required area. The present invention relates to a mask plate for partial plating that meets this requirement.

Before showing the mask plate of the present invention, I would like to explain the conventional method.

Conventionally, mask plates for partial plating of IC lead frames have been made of heat-resistant and chemical-resistant insulating plates (polypropylene, polyethylene, acrylic, polycarbonate, polyester, epoxy resin laminated with glass fibers) having a thickness of 3 to 20 mm as the substrate 1. board, polyester laminate with glass fiber)
The desired holes were made by machining. As shown in FIG. 1, in partial noble metal plating, plating liquid 7 is injected from a nozzle 6 (anode) facing hole 2 of substrate 1 with an interval of 5 to 20 mm and passes through hole 2. The lead frame 4, which is the plating body (cathode), is collided with, but current is currently energized during this time to obtain the partial plating layer 8 of the desired thickness. Note that 5 in the figure is a backing plate. At this time, if the lead frame 4 is placed directly on the substrate 1, the plating liquid 7 will
It will penetrate laterally and end up sticking to unnecessary areas.

In order to prevent this, in conventional methods, a resin 3 having heat resistance and chemical resistance such as silicone is applied to the substrate 1 by spraying as shown in Fig. 1, or a resin 3 having heat resistance and chemical resistance such as silicone is applied in advance as shown in Fig. 2. A process was performed in which a resin sheet 10 made of silicon or the like with holes was laminated to the substrate 1 to form a mask plate.

However, such treatment was also insufficient for the following reasons. In other words, a mask plate made by applying silicone or the like to a thickness of about 0.1 to 1 mm using a spray coating method, like the mask plate shown in Fig. 1, has poor surface properties, especially the edges of the holes, which cannot be formed sharply and are completely dry. Although it is better than not applying silicone, the plating solution penetrates into this area, causing electrodeposit to occur in areas other than those where it is needed.

In the case of the mask plate shown in Fig. 2, holes are made in the resin sheet 10 using a punch or other mechanical processing to match the holes in the resin substrate, and the holes are carefully bonded to the substrate 1.
Although the accuracy was good in some areas, there were times when the position was slightly different. When plating is applied, precious metals are deposited in areas other than the desired areas, resulting in an unnecessary increase in material costs.

In view of these circumstances, the purpose of the present invention is to provide a mask plate for partial plating that can accurately plate the minimum required area.

The present invention will be explained using FIGS. 3 to 5. FIG. 3 is a sectional view of the mask plate of the present invention.
The resin substrate 11 having heat resistance and chemical resistance is made of polypropylene, polyethylene, acrylic, polyarbonate, polyester, an epoxy resin laminate with glass fibers, a polyester laminate with glass fibers, etc., as shown in FIG. Continuous slit-like holes 16 or individual independent holes 17 are formed that are slightly larger than the mating area. Lead frames come in a variety of shapes, and in the conventional method, a dedicated mask plate was manufactured and used for each lead frame, but in the present invention, a hole slightly larger than the desired plating area is used. Since the substrate 11 having the following characteristics is used, one substrate 11 can be used with all types of lead frames. The mask plate of the present invention consists of the above-mentioned substrate 11 and a cushion plate 12 having the desired areas described below. The cushion plate 12 may be made of any material as long as it has heat resistance, chemical resistance, and cushioning properties, and includes, for example, silicone resin, fluorine resin, urethane resin, and the like. In the center or on one side of this cushion plate 12, a corrosion-resistant metal (stainless steel, nickel, chrome plated on a copper plate) is used as a reinforcing material 13.
Alternatively, a plastic plate (heat-resistant polyvinyl chloride, polypropylene, polyester, epoxy resin laminate with glass fibers) is provided. First, if the reinforcing material 13 is made of metal, the part corresponding to the predetermined plating area is formed into the through hole 15 by etching or punching, or if it is a plastic plate, by machining.
to be drilled. After that, the reinforcing material 13 is inserted into the mold, and a cushioning resin such as silicone resin, fluorine resin, urethane resin, etc. described above is poured into one or both sides of the reinforcing material 13 by a casting method, and is hardened to provide cushioning properties. A resin layer 14 is formed to cover the resin layer 14 . Because of the reinforcing material 13, it does not sag in the center, and
Resin shrinkage during curing and expansion due to pressure and heat during plating are alleviated. At this time, the thickness of each part constituting the mask plate is 1 to 20 mm for the substrate 11 and 1 to 20 mm for the reinforcing material 1.
3 is 0.05 to 1 mm, and the cushioning resin layer 14 is
0.1 to 3 mm (both on one side and both sides). Also, the reinforcing material 13 does not need to have holes except for the plating area 15, but if resin is formed on both sides, it is better to have small holes 18 of 0.5 to 5 mmφ as shown in Fig. 5 for better cushioning properties. Better adhesion with resin layer 14 (resin sticks through small holes 18)
Therefore, small holes 18 are provided as necessary. The cushion plate 12 produced as described above is attached to the substrate 11. It can be said that it is convenient to attach the cushion plate 12 by providing a notch 19 in the substrate 11 and fitting the cushion plate 12 into the notch 19.

As described above, the mask plate of the present invention can be applied to any lead frame as a substrate, and can be manufactured at low cost since only the cushion plate needs to be manufactured. In addition, the edges of the plating area on the cushion plate created by the casting method are sharp, there is no leakage of plating liquid, and the desired area can be accurately plated. Other benefits include reducing the time required to replace masks and reducing the cost of precious metal materials.

[Brief explanation of the drawing]

Figures 1 and 2 are explanatory cross-sectional views showing the configuration of partial plating using a conventional mask plate, and Figure 3 is an example of a mask plate for partial plating according to the present invention. 4a and 4b are plan views showing two examples of the substrate of the mask plate for partial plating of the present invention, and FIG. 5 is a cross-sectional view of the reinforcing material of the mask plate for partial plating of the present invention. It is a top view showing an example. 1... Board, 2... Hole, 3... Resin, 4... Lead frame, 5... Backing plate, 6... Nozzle,
7... Plating liquid, 8... Partial plating layer, 9... Electrodeposit, 10... Resin sheet, 11... Substrate, 12
...Cushion plate, 13...Reinforcement material, 14...Cushion resin layer, 15...Through hole, 16...
Slit-like hole, 17...Independent hole, 18...
Small hole, 19...notch part.

Claims (1)

[Scope of utility model registration request] It consists of a substrate having holes larger than the desired partial plating area, and a cushion plate having holes in the desired partial plating area, and the cushion plate is cast on one or both sides of the reinforcing material to provide cushioning properties. 1. A mask plate for partial plating, characterized in that it is coated with a resin layer.