JPH0119474B2 - - Google Patents

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a sealing method for spot-plating lead frames used in the manufacture of ICs, etc., and particularly to a method for spot-plating that prevents frame deformation and improves sealing effects. Concerning the sealing method.

<Conventional technology> When spot-plating a lead frame for an integrated circuit device used in the manufacture of ICs, etc., spot plating is applied to the part where the pellet element is mounted (hereinafter referred to as the tab) and the part where the thin metal wire is connected (hereinafter referred to as the inner lead). Partially gold plated etc. These spot plating methods involve using a plating mask to expose only the parts to be plated and covering the other parts on a lead frame in which a pattern is formed by etching or punching a thin metal plate such as Kovar, and then plating the exposed parts. A so-called high-speed spotting method, in which the liquid is jetted, is generally employed.

In this spot plating method, as shown in FIG. 2, a mask 1 is brought into close contact with the surface of the lead frame 3 to be plated, an elastic insulator such as sponge rubber 7 is brought into close contact with the opposite surface, and pressure applied by an air cylinder 6 or the like is applied. A method is adopted in which the lead frame 3 is sealed by pressure from the source.

However, recently, customer demands have increased regarding the appearance of the frame, and the following problems have surfaced regarding the sealing method that cannot be overcome with the conventional sealing method using sponge rubber.

(1) Bleeding on the frame due to plating liquid seeping out (2) Plating chipping at the tip of the inner lead pin that should be plated due to the sponge surface in contact with the frame peeling off and covering the lead pin (3) Especially when tab lowering In the lead frame,
Deformation of tabs and lead pins Problems with the conventional sealing method will be explained below using FIG. 2.

The frame 3, which is the object to be plated, is made of sponge rubber 7.
The air cylinder 6 presses the mask 1 through the air cylinder 6. During pressing, as shown in Figure 2a,
The sponge rubber 7 bulges at the opening of the frame 3 because it is released from pressure.

For this reason, as the number of times the sponge rubber 7 is used increases, when returning from the press, only the mask opening 9 is released from pressure, resulting in a structure 8 that bulges out compared to other parts. As shown in , the tab 3-2 is pressed more strongly than the inner lead pin 3-1, and the tab 3-2 is deformed toward the mask opening 9 side.

Generally, when the press pressure is small, it will return elastically,
Although tab deformation does not occur, there is a marked tendency for deformation when the tab suspension lead is long, when the frame film thickness is thin, or when the tab is lowered (tab downset).

The current ways to deal with the above problem are: (1) Replacing the sponge rubber as soon as possible (2) Using a special coating on the surface of the sponge (3) Considering the material of the sponge rubber 7 (4) Furthermore, there is pressure control of the air cylinder 6, which is the pressure generation source to be sealed.

However, with the above solutions, (1) the number of days the machine will be stopped for periodic replacement will increase, and costs will increase (2) If the pressure is increased, increasing the pressure may cause pin deformation, etc.
Pin tip plating is likely to chip, and if the pressure is weakened, the plating liquid may ooze out due to insufficient sealing, especially for thin (0.15mm thick) frames with tab-down-set seals. The problem is that it cannot be applied at all.

<Problems to be Solved by the Invention> The purpose of the present invention is to solve the above-mentioned drawbacks of the prior art, to significantly improve the sealing method for spot plating lead frames of ICs, etc. by a simple method, and to improve the quality. The purpose is to provide a sealing method for spot plating that greatly contributes to improvement.

<Means for Solving the Problems> The present invention covers one side of the object to be plated with a plating mask, and seals the other side of the object to be plated with a pressing member whose surface is covered with an elastic member. When spot-plating is performed through the mask opening of the mask, the plating is performed by applying the required pressure to the required part of the object to be plated using a pressing member having a hollow portion inside thereof corresponding to the mask opening. This is a method of sealing spots.

<Structure of the Invention> The present invention will be described in detail below with regard to preferred embodiments shown in the drawings.

When carrying out the method of the present invention, it is preferable to use the sponge rubber 4 shown in FIGS. 1 and 3 as the sealing pressing member.

FIG. 1 shows a longitudinal cross-sectional view when spot-plating a short rail lead frame 3 of 5 pieces per frame. The mask 1 masks the lead frame 3, and the masked lead frame 3 is exposed to light from the nozzle 2. It is spot-pecked by a squirt of plating liquid. The lead frame 3 is placed on the mask and includes a part of the inner lead 3-1 and a tab 3-1.
2 is correctly positioned in the mask opening 9. Sponge rubber that seals the lead frame 4
is fixed to the press upper die 5, and an air cylinder 6 generates pressure to seal the frame.

When the sponge rubber 4 seals the lead frame 3, a mask shape is considered on the inside of the sponge rubber 4 on the side that contacts the lead frame 3 in order to change the sealing pressure distribution to the required distribution according to the shape of the frame 3. It is preferable to use a specially shaped intermediate plate 4-1 for generating pressure distribution.

As an example, the intermediate plate 4-1 for generating pressure distribution uses three sponges that are 1/3 the thickness of conventional sponge rubber, and the middle sponge plate is placed at the center of the tab 3-2 of the lead frame 3. Hollow out approximately the size of the mask opening to match the hollow part 10.
shall be. The shape and position of this hollow portion 10 are appropriately determined depending on the shape of the lead frame, mask, etc. The remaining two pieces of sponge rubber 4-2 have the same shape as the conventional sponge rubber, and have a thickness of 1/3. 3 pieces of sponge rubber 4-1, 4-2, 4-
The relationship between lead frame 2 and lead frame 3 is shown in FIG. 3
The sponge rubber is the intermediate plate 4-1 for generating pressure distribution.
The three-layered sponge 4 (FIG. 1) is used for sealing the frame.

The thickness of one sheet of sponge rubber and the cutout area of the pressure distribution generating intermediate plate 4-1 can be easily obtained through several experiments. The cutout area only needs to correspond to the mask opening 9, and in particular does not need to be exactly the same size as the mask opening 9.

The pressing member such as the sponge rubber 4 used in the method of the present invention may be one that has at least the surface covered with an elastic member and has a hollow part corresponding to the mask opening on the inside. In addition, it may be made of sponge rubber laminated with two or four or more layers.

For particularly delicate pressure adjustment, it is also possible to use a sheet that uses an elastic member as a seal and has a hollow portion inside thereof that corresponds to the mask opening.

The intermediate plate 4-1 for generating pressure distribution does not need to be sandwiched between the sponge rubber 4-2, 4-2, and as shown in FIG.
It may be sandwiched between -2.

Sponge rubber 4- in contact with lead frame 3
Intermediate plate 4 for generating pressure distribution inside the second elastic member
The material of -1 may be an elastic body other than sponge rubber, or may be an insulating structure such as PVC.

Moreover, as shown in FIG. 6, the sponge rubber 4-
The press upper die 5 for pressing the elastic body 2 or the like may be processed to have a hollow portion corresponding to the mask opening, and in this case, the desired pressure distribution can be obtained using only one layer of conventional sponge rubber.

The sealing method of the present invention covers the object to be plated with a plating mask, and seals the opposite side of the plated object with a pressing member whose surface is covered with an elastic member at least, as long as it is a sealing method when spot plating is performed. It can be used not only for lead frames such as ICs but also for various other things.

<Operation of the Invention> The operation of the embodiment of the method of the present invention in which the three-layered sponge shown in FIG. 3 is used for sealing a lead frame will be described with reference to FIG. 4.

Sponge rubber 4 located in mask opening 9
Since there is a hollow portion 10 in the middle sponge rubber layer, pressure is dispersed in the sponge rubber on the side of the pressure distribution generation intermediate plate 4-1 in the opposite direction to the lead frame 3. Therefore, the pressing force against the tab 3-2 is weakened, preventing the tab from deforming, and at the same time, sealing is possible without weakening the pressure on the inner lead portion 3-1 at all. Furthermore, since the amount of elastic deformation of the sponge rubber between the inner lead portion 3-1 and the tab 3-2 is small, there is less occurrence of chipping of the pin tip plating, which occurs when the sponge rubber surface is cut and covers the pin tip. Become.

<Effects of the Invention> Compared to conventional techniques, the method of the present invention significantly extends the life of the sealing elastic body because the growth after deformation of the sealing elastic body is much smaller, and the damage caused by the breakage of the sealing elastic body surface is significantly reduced. There is less occurrence of pin tip plating chipping. The sealing effect can be enhanced while minimizing deformation of the lead frame tab and inner lead. Therefore, it is possible to prevent the plating liquid from seeping out, and furthermore, it is possible to easily perform spot plating of the lead frame of the tab-lowered product, which is difficult to perform, and it is possible to improve productivity and achieve economical efficiency with a simple method.

[Brief explanation of drawings]

FIG. 1 is a partial sectional view showing an apparatus for carrying out the method of the invention. FIG. 2 is a partial cross-sectional view of an apparatus for carrying out a conventional sealing method. FIG. 3 is a partially exploded perspective view of a pressing member used in the sealing method of the present invention. FIGS. 4a and 4b are partial cross-sectional views of the lead frame when it is pressed and when it is returned from the press, respectively. 5 and 6 are cross-sectional views showing other embodiments of the sealing method of the present invention. Explanation of symbols, 1...Mask, 2...Nozzle, 3
... Lead frame, 3-1 ... Inner lead, 3-2 ... Tab, 4 ... Sponge rubber (pressing member), 4-1 ... Intermediate plate for generating pressure distribution, 4-
2, 7...Sponge rubber, 5...Press upper mold, 6
... Air cylinder, 8 ... Deformed part of sponge rubber, 9 ... Mask opening, 10 ... Hollow part.

Claims (1)

[Scope of Claims] 1. One side of the object to be plated is covered with a plating mask, the other side of the object to be plated is sealed with a pressing member having at least the surface covered with an elastic member, and the mask opening of the mask is sealed. A sealing method for spot plating, characterized in that when spot plating is performed, the required pressure is applied to a required part of the object to be plated using a pressing member having a hollow portion inside thereof corresponding to the opening of the mask. 2. The spot plating sealing method according to claim 1, wherein the object to be plated is a lead frame.