JPS6023502B2 - Lead frame partial masking method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a lead frame, and particularly to a method for partially masking a lead frame for a semiconductor device.

A lead frame is used to attach a semiconductor to a punched metal strip with multiple legs, and some of the legs are provided with unplated parts (terminals) to prevent migration. There is a need.

Conventionally, plating resist ink was applied manually to such areas, or the metal strip was immersed in the plating solution so that this area was exposed above the plating solution level, but the efficiency of the plating work was reduced. is low and not suitable for mass production.

In particular, the latter method of controlling the position of the metal strip that is immersed in the plating solution is difficult, and it is difficult to control the liquid level position, making it impossible to obtain the precision of the boundaries of the plated parts. It cannot be provided in one plating process. In addition, some attempts have been made to mask the parts that are not to be plated by applying masking tape or sponge rubber tape, but since metal strips are thick, it is best to use elastic tape such as sponge tape. However, it is impossible to completely mask the sides of the terminal portion, and no simple and complete local masking method has been developed.

An object of the present invention is to provide a method for partially masking a lead frame that can cover a large number of terminal parts efficiently and accurately.The present invention is characterized by moving a punched metal strip. A pair of guides are installed on both sides of the path to guide and adhere the thread-like body impregnated with an electrically insulating hot-melt substance that does not dissolve in water to the terminal part of the metal strip, and to attach it to the terminal part of the metal strip within a time period before the hot-melt substance solidifies. , the guide may compress the filament to automatically fill the area around the terminal with the hot melt material.

FIG. 1 is a perspective view illustrating an embodiment of the present invention.

1 is a metal strip punched from a thin steel plate, which is moving in the direction of the arrow.

Stems 2 are formed at predetermined intervals on the upper part of the metal strip 1, and a part of the leg between the stem 2 and the diver 4 is a terminal part 3 that does not need to be plated.

A pair of guide frames 5 are installed with the terminal portion 3 in between, and a paraffin-impregnated masking thread 6 is guided by the guide plates 5 and attached to the surface of the terminal portion 3.

The masking thread 6 is made of a single willow cotton thread and is wound around a reel 8, and is guided to the guide plate 5 through a paraffin bath 7. Paraffin heated to 68 to 73 oo and liquefied is stored in the paraffin tank 7, so when the masking thread 6 leaves the paraffin tank 7, it is sufficiently impregnated with paraffin and is in a wet state. 2 is a plan view of FIG. 1, and FIG. 3 is a sectional view taken along the line AB of FIG. 2, and the same parts as in FIG. 1 are designated by the same reference numerals.

The guide plate 5 has a curved portion for introducing the masking thread 6, and a groove 10 for guiding the masking thread 6 is provided on the opposite surface thereof. Further, the spacing between the guide plates 5 is gradually narrowed in accordance with the flow direction of the metal strip 1. Therefore, the masking thread 6 smoothly moves into the groove 1.
While moving in close contact with the terminal portion 3 of the metal strip 1, the metal strip 1 is gradually compressed by the guide plate 5, so the impregnated paraffin is squeezed out and the area around the terminal portion 3 is filled. .

FIG. 4 is an enlarged view of section A in FIG. The terminal portion 3 between the stem 2 and the tie bar 4 is filled with paraffin squeezed out from the masking thread 6, and there is no gap. When the metal strip 1 is further moved and cooled, the terminal portion 3 is completely masked with the solid paraffin 9. Since the solid paraffin 9 of the metal strip 4 masked with paraffin is water-repellent and does not dissolve in water, even if it is immersed in the plating solution, the plating solution will not enter the terminal portion 3.

After finishing the plating work, when the metal strip 1 is passed through hot water of 90 qo or more, the paraffin is dissolved and floated, and the masking thread 6 is separated. Note that the masking thread 6 and paraffin can be reused.

FIG. 5 is an enlarged view of part A after removing the masking thread.

An unplated terminal portion 3 is formed at the bottom of the stem 2 with good dimensional accuracy, and if a lead wire is connected to this portion, migration will not occur.

The dimensions of the unplated terminals can be adjusted within the range of 0.3 mm in the case of a transistor lead frame of 300 m. As described above, the lead frame partial masking method of this embodiment involves plating by tightly solidifying two cotton threads impregnated with molten paraffin on the terminals of metal strips using a guide plate, thereby eliminating the need for plating. This has the effect that the terminal portion can be easily formed with good dimensional accuracy.

In the above example, the cotton thread was impregnated with paraffin, but even if one leg of the cotton thread was impregnated with ethyl cerosene compound having a melting point of 150 oo and masked in the same way, the 300 m long terminal part of the transistor lead frame could be fabricated with the same precision. was able to be formed.

In this case, the solidified ethyl cerosene compound could be easily removed by pulling the masking thread after cooling.

In addition, instead of cotton thread, one side of Tetoron (product name of Tijin Co., Ltd., Toyo Rayon Co., Ltd.) twisted yarn is used, and the thickness of 0.05
You can also use a polyester tape with a width of two ribs impregnated with paraffin or the like. Furthermore, Japanese paper twisted yarn on the 1st side ◇ can also be used. Note that a guide roll provided with a groove for holding the masking thread 6 may be used instead of the guide plate 5 shown in FIG.

Such a local masking method can be applied, for example, to the mass production of connector parts, and is an industrially useful method.

The lead frame partial masking method of the present invention has the effect that a portion of a thin sheet metal strip can be coated efficiently and with high precision.

[Brief explanation of the drawing]

FIG. 1 is a perspective view illustrating a partial masking method for a lead frame according to an embodiment of the present invention, FIG. 2 is a plan view of FIG. 1, and FIG. 3 is a sectional view taken along line A-B in FIG. 2. Figure 4 is the first
FIG. 5 is an enlarged view of part A after removing the masking thread. 1... Metal strip, 2... Stem, 3... Terminal part,
4... Tie bar, 5... Guide plate, 6... Masking thread, 7... Paraffin bath, 8... Reel, 9...
・Solid paraffin, 10...grooves. Figure 1 Figure 2 Figure 3 Figure 4 Figure 5

Claims (1)

[Claims] 1. In a method for manufacturing a lead frame that partially masks a metal strip formed by punching out a thin metal plate, a pair of guides are installed on both sides of a path for moving the metal strip, and the metal strip is immersed in water. A thread-like body impregnated with an electrically insulating heat-melting substance that does not melt is guided and adhered to the terminal portion of the metal strip, and the guide presses the thread-like body within a time period before the heat-melting substance solidifies. A method for partially masking a lead frame, characterized in that the periphery of the terminal portion is automatically covered with a heat-melting substance. 2. The lead frame partial masking method according to claim 1, wherein the filamentous body is a thin cotton thread. 3. The method for partially masking a lead frame according to claim 1, wherein the heat-melting substance is paraffin.