JPH0419318B2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a semiconductor integrated circuit (hereinafter abbreviated as IC).
The present invention relates to a method of manufacturing a mask plate used when performing partial noble metal plating on the island portion of a lead frame and the tip portion of an inner lead. IC lead frame is 42 alloy (42% Ni, remaining Fe),
After forming a predetermined pattern by press punching or etching a material with high thermal conductivity and strength such as Kovar (29% Ni, 17% Co, remaining Fe) or phosphor bronze, the island portion (IC chip) is formed. bonding part) and the tip of the inner lead (the part to be wire bonded), giving it conductivity,
It is common that noble metals such as gold, silver, and palladium alloys are partially coated for corrosion prevention and heat dissipation purposes. When partially plating the above areas, the 7th
As shown in the figure, the air is emitted from a nozzle-shaped or slit-shaped anode (plated with platinum on materials such as titanium, stainless steel, and tantalum) at a speed of 1 to 10 m/sec.
This is carried out by colliding a plating liquid flow 20 having a velocity of 1000 to a lead frame 18 set on the upper and lower mask plates 9 and 19 on which a desired pattern (holes) has been formed, and energizing the plated liquid flow 20. The conventional mask board is the first
The configuration shown in Figures 1 and 2 was used. That is, in FIG. 1, a resin substrate 1 (polypropylene, polyethylene, polyester, epoxy resin containing glass fibers, polyester resin containing glass fibers, vinyl chloride resin), in which only a predetermined plating area is hollowed out,
The cushion layer 2 is formed by spray coating silicone resin or the like. This mask board is
Although it is easy to manufacture, since the silicone resin is spray coated, the surface condition becomes uneven parts 3, and the silicone resin flows into the plating area (hole) 5, forming a protruding part 4. It was hot. This has caused inconvenience when partially plating an IC lead frame using this mask plate. In other words, since the silicon surface of the mask plate has uneven parts 3, the plating liquid leaks through the IC lead frame, resulting in the precipitation of expensive precious metals outside the plating area. Since there is a protruding portion 4 of silicone resin, there is a drawback that the tightening area becomes smaller than the set tightening area. On the other hand, after pasting the silicon sheet 6 on the perforated resin substrate 1 like the mask plate shown in FIG.
Another method is to cut the silicone sheet 6 by laser cutting or mechanical punching. Compared to the silicone resin spray coating method shown in FIG. 1 described above, the surface is smooth and the plating solution does not leak, which is an advantage. As with the spray coating method, it was difficult to accurately expose the sticking area. For this reason,
When conventional mask plates are used, an inconvenient situation arises in that more expensive precious metals than necessary are deposited, or conversely, a large number of defective products are produced due to the small plating area. In order to improve this situation, the present invention provides a method for manufacturing a mask plate having a silicon layer with a smooth surface and a precise plating area. More specifically, when performing partial plating, the IC lead frame body 18 is placed on the mask plate 9 as shown in FIG. Plating is performed by sandwiching the rubber 19 and jetting the plating liquid 20 from below. In this case, when the IC lead frame body 18 is placed directly on the perforated resin substrate 1, the plating liquid flows from the gap. leaks. In order to improve this problem, the present invention devises a method for forming the cushion layer 2, which plays an important role in partial plating, by imparting adhesion and cushioning properties to the mask plate 9. The details of the present invention will be explained based on the drawings. FIG. 3 shows a master mold 10 for obtaining a silicon layer with a smooth surface and a precise plating area. This master mold 10 may be manufactured by cutting using metal materials (aluminum, iron, copper, brass) or plastic materials (vinyl chloride resin, epoxy resin containing glass fibers), but many identical molds can be produced in a short time. When producing it, it is desirable to use a photosensitive resin. Add an explanation of how to make a matrix using photosensitive resin as the material. Commonly available commercially available photosensitive resins include polyester, nylon,
An example of this is to use a photosensitive resin plate such as polyvinyl alcohol. For example, Tokyo Ohka Kogyo Co., Ltd.
The product names include "Rigilon" by BASF, "nyloprint" by BASF, and "APR System G42, Mold 20" by Asahi Kasei Corporation. For patterning, a negative mask film is prepared so as to have a finish as shown in FIG. That is, matrix 10
The depth of the recess 13 (corresponding to the thickness of the silicon layer) is 0.3 to 2.0 mm, and the photosensitive resin plate also needs to be this thick. Due to the positional relationship of the mask film, the photosensitive resin surface that is in contact with the negative mask film will produce a pattern that matches the accuracy of the negative mask film, but the area below 0.3 to 2.0 mm will have a wider finished area due to the spread of the luminous flux. It gets bigger. Since the angle of inclination at this time is about 10 to 30 degrees, it is necessary to make the pattern of the negative mask film small in advance so that the area through which light passes is small. A negative mask film with a predetermined pattern formed on it is adhered to a photosensitive resin plate, exposed to ultraviolet light or a chemical lamp for several minutes, developed with a predetermined developing solution (alcohol, pure water, or weakly alkaline water), and dried. , exposure is performed to form a matrix 10 as shown in FIG. This matrix 10 is
A predetermined plating area is formed at the bottom 12 of the pattern with a depth of 0.3 to 2.0 mm, and the convex surface 1
1 is slightly smaller than the bottom portion 12 due to the above-mentioned spread of the light beam. Further, an outer frame 14 is provided to prevent leakage when silicone resin is poured. Concave portion 13 of the mother mold 10 obtained in this way
A hardening silicone resin, which is an important part of this method, is poured into the resin.Any silicone resin can be used as long as it hardens deep at room temperature. Silicone resin product name KE61RTV, KE119RTV, KE12RTV,
KE112RTV, Toray Silicone Co., Ltd. product name
SH9550, SH9551, SH9552, SH9555, SH9556
Examples include. After pouring the defoamed silicone resin into the mother mold 10, the resin on the convex surface 11 is scraped off with a rubber squeegee, a steel doctor, a rubber roll, etc., and the outer frame 1 of the mother mold 10 is removed as shown in FIG.
4 and the convex surface 11 at the same height as the silicone resin 15. On the other hand, a resin substrate 17 which is a mask base material
As in the conventional method, any material can be used as long as it has heat resistance and chemical resistance, and candidates include polypropylene, polyethylene, polyester, epoxy resin containing glass fibers, polyester resin containing glass fibers, and vinyl chloride. Hole 21 (plating area) provided in this resin substrate 17
When using the photosensitive resin plate described above as a matrix for forming a silicon layer, it must be set slightly smaller than the predetermined area for the reasons mentioned above, and the area must be the same as the pattern convex surface 11 of the matrix shown in FIG. Must be. If necessary, apply a brimer (for example, Brimmer T from Shin-Etsu Chemical Co., Ltd.) to the resin substrate 17 provided with the holes 21, and place the surface 16 of the silicone resin 15 at the same height as the convex surface 11 in the matrix 10 described above. Even though it is in a state where the silicone resin 1 is
The resin substrate 17 is overlapped with the resin substrate 17 as shown in FIG. 5 while the resin substrate 5 is in an uncured state maintaining fluidity. Applying a pressure of several 100 g to several kg/cm ² from above the resin substrate 17,
It is left to stand until a predetermined curing completion time of the silicone resin 15 is reached. After the silicone resin 15 has hardened, when the silicone resin 15 is peeled off from the mother mold 10 in a state that it is stuck to the resin substrate 17, as shown in FIG. 6, the surface of the silicone resin layer 22, which is the purpose of this method, is A mask plate is obtained that is smooth and has a precise plating area. When this mask plate is used to selectively plate an IC lead frame with precious metals (gold, silver, palladium alloy, etc.), the plating film will not spread to unnecessary areas and the plating area will be kept to a minimum. This resulted in a huge material savings. Also, by using this mask board, it is now possible to easily plate patterns with small plating areas (less than 5 mm on a side), which was previously impossible, and it is now compatible with all kinds of products. Example A photosensitive resin plate (Tokyo Ohka Kogyo Co., Ltd.) was used as the matrix material.
Co., Ltd. (trade name: Rigilon MX-100) was used. As a negative film, the light transmitting area (corresponding to the hole in the mask plate) is 0.8 per side from the specified plating area.
A square pattern (5 pieces lined up with a side of 9.2 mm and a pitch of 15 mm) smaller in mm was used. Place the negative film in close contact with the above resin plate and light it with a chemical lamp (wavelength 250-430mm, 40W, distance 4.5cm).
A 2.5 minute exposure was performed. Development was carried out using tap water at 40°C using a spray method. After drying at 90° C., post-exposure was performed again for 1 minute using the chemical lamp described above to complete a master mold 10. This matrix has convex surfaces 11 and 10 with a side of 9.2 mm as shown in Figure 3.
A pattern with a base 12 of mm was formed and its relief depth was 0.68 mm. Next, this matrix 1
Pour in silicone resin (KE61RTV, Shin-Etsu Chemical Co., Ltd.) that has been blended and degassed to 0. Using a steel doctor, remove excess silicone until it is at the same height as the pattern convex surface 11 of the matrix 10, as shown in Figure 4. resin 1
I scraped off 5. While the poured silicone resin 15 was still fluid, a previously prepared resin substrate 17 was placed on top of the resin substrate 17 and left at room temperature under a pressure of 500 g/cm ² for 24 hours, which is the time required to complete the curing of the resin. The resin substrate 17 is made of vinyl chloride with a thickness of 5 mm, and the size of the hole corresponding to the plating area is a square with one side of 9.2 mm on the side in contact with the silicone resin 15. After the silicone resin is completely cured, when the silicone resin 15 is peeled off from the mother mold 10 while it is stuck to the resin substrate 17, a mask with a smooth surface of the silicone resin layer 22 and a precise plating area as shown in FIG. 6 is obtained. Plate 9 was obtained. Using this mask plate 9, gold plating with a thickness of 2.5 μm was performed on a 42 alloy lead frame under the conditions shown in Table 1. As a result, the plating area was obtained with an error within 10μ from the set value (conventionally 100 to 200μ), and a good quality product with no plating leakage was obtained. At the same time, it also made a significant contribution to saving expensive money. 【table】

[Brief explanation of drawings]

FIG. 1 is a sectional view showing an example of a conventional partial plating mask plate formed by spray coating with silicone resin. FIG. 2 is a sectional view showing an example of a conventional mask plate for partial plating formed by laminating silicon sheets. FIG. 3 is a perspective view showing an example of a matrix for pouring silicone resin, which is the cushion of the mask plate of the present invention, and FIG.
FIG. 5 is a sectional view showing a mother mold into which the silicone resin of the present invention is poured, and FIG. FIG. 6 is a sectional view showing an embodiment of the mask plate according to the present invention. FIG. 7 is a sectional view showing partial plating to an IC lead frame. 10... Mother mold, 11... Convex surface, 12... Bottom, 13...
recess, 14...outer frame, 15...silicon resin, 16...
Surface of silicone resin, 17...Resin substrate, 21...
Hole, 22... silicone resin layer.

Claims (1)

[Claims] 1. Pour curable silicone resin 15 into a matrix 10 having a convex surface 11 corresponding to the plating area,
While the silicone resin 15 is in an uncured state, a resin substrate 17 provided with a hole 21 corresponding to a predetermined plating area is applied with high accuracy, and the silicone resin 15 is
A method for manufacturing a mask plate for partial plating comprising a silicone resin layer laminated on a resin substrate 17, characterized in that the mask plate is peeled off from a matrix 10 after the mask plate is cured. 2. The method of manufacturing a mask plate for partial plating according to claim 1, which uses a photosensitive resin plate as a matrix having a convex surface corresponding to the plating area.