JPH11158685A - Mask plate for partial plating - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a mask plate for partial plating capable of well applying partial plating to a lead frame without lodging in of the support bars of the lead frame into the elastic member of the mask plate even when the lead frame is pressurized by the mask plate and a back plate at the time of partial plating. SOLUTION: The mask plate 11 has apertures 10 corresponding to the plating areas 8 of the lead frame 1a. The mask plate 9 for partial plating is constituted by mounting the elastic member 12 likewise having the apertures 10 corresponding to the plating areas 8 at the surface of the lead frame 1a for contact with an object to be plated. The points of the mask plate 9 corresponding to the support bars 4 of the mask plate 11 are provided with projecting parts 17 having nearly the same width as the width of the support bars 4.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a partial plating mask plate for partially plating a lead frame for a semiconductor device.

[0002]

2. Description of the Related Art A lead frame for a semiconductor device is usually plated with a noble metal such as gold or silver for the purpose of improving electrical characteristics. However, since such a noble metal material is expensive, it is common in recent years to mask an unnecessary portion and perform a plating process only on a truly necessary portion.

FIG. 7 is a view showing a lead frame for a semiconductor device. The lead frame 1 shown here comprises a pair of frames 2 which are separated from each other and extend along the longitudinal direction, a pad 3 for mounting a rectangular semiconductor element having sides facing each other, and a frame 2 of the pads 3. A pair of support bars 4 that extend from opposite sides arranged in parallel and support pads 3 that are connected to the frame 2 at substantially right angles, and inner leads 5 that are arranged around the pads 3 and extend radially;
The tie bar 6 connects the inner leads 5 and the outer leads 7 connected to the respective inner leads 5. Normally, plating made of a noble metal such as gold or silver is applied only to a portion corresponding to a plating area 8 indicated by a hatched portion at the tip of the pad 3 on which the semiconductor element is mounted and the inner lead 5 for wire bonding. In the normal manufacturing process, the lead frame 1
Are formed in a short state in which a plurality of pieces are connected, and each processing is performed.

FIG. 4 shows a mask plate and a plating apparatus used for masking an object to be plated in such partial plating. The mask plate shown here is for plating a short lead frame 1a, that is, the mask plate 9 has a plurality of openings 10 corresponding to the plating area 8 of the lead frame 1a. A mask plate 11 made of a heat-resistant and chemical-resistant hard material such as a glass epoxy resin, and a plating area of a lead frame 1 a, which is also an object to be plated, which is mounted on the surface of the mask plate 11 that contacts the object to be plated. And an elastic member 12 made of silicon rubber or the like provided with a plurality of openings 10 corresponding to 8. Note that such an elastic member 12 is generally formed on one surface of the mask plate 11 by a molding method using a mold or the like.

A partial plating method using such a mask plate 9 will be described. First, as shown in FIG. 4, the mask plate 9 is mounted on a top plate 13. The top plate 13 also has a plurality of openings 10 corresponding to the openings 10 provided in the mask plate 9.
Then, the plating surface of the lead frame 1a is placed on the elastic member 12 of the mask plate 9 with the plating surface in contact with the plating member. The back plate rubber 15 mounted on the plate 14 is brought into contact with the plate contacting surface, and the lead frame 1a is sandwiched.

In this state, the back plate 14 is pressurized from above, and the elastic member 12 of the mask plate 9 and the back plate rubber 15 of the back plate 14 are respectively brought into close contact with the lead frame 1a to mask the plating-free area of the lead frame 1a. I do. At this time, the plating area of the lead frame 1a, that is, the area corresponding to the plating area 8 at the tip of the pad 3 and the inner lead 5 of the lead frame 1a is not masked, and as shown in FIG. It is projected into the opening 10. The plurality of openings 10 provided in the mask plate 9
A plating solution is spouted from the nozzle (not shown) corresponding to the opening 10 into the opening 10, whereby a desired thickness is formed at a position corresponding to the plating area 8 of the lead frame 1 a protruding into the opening 10. Then plating is applied.

When partial plating is performed as described above, the elastic member 12 and the back plate rubber 15 need to be brought into close contact with each other by applying a sufficient pressure in order to properly mask a region not requiring plating. As shown in the drawing, at a portion corresponding to the plating area 8 of the lead frame 1a located at the opening 10 of the mask plate 9, a part of the inner lead 5 (not shown in FIG. 5) is barely formed by the mask plate 9. Although supported, the pad 3 has no support from below, and is only connected to and supported by the frame 2 of the lead frame 1a by the thin and fragile support bar 4, so that the plating is performed as described above. When a partial pressure is applied to the back plate 14 of the apparatus by applying a sufficient pressure, the pad 3 is attached to the back plate mounted on the surface of the back plate 14. Thus extruded downward (mask plate 9 side) not completely support the elastic force of the rubber 15. At this time, the support bar 4 that supports the pad 3 also moves downward as the pad 3 moves down, and as a result, the support bar 4 sinks into the elastic member 12 of the mask plate 9.

As described above, the support bar 4 is connected to the elastic member 12.
If the partial plating is performed in a state of being entrapped, a gap is generated between the back plate rubber 15 and the support bar 4, and it is not possible to sufficiently mask the plating unnecessary area on the back surface of the support bar 4, and as a result, As shown in FIG. 6, the plating solution 16 leaks to the periphery of the back surface of the support bar 4.
A phenomenon called so-called back leakage occurred.

[0009]

In the worst case, the plating solution 16 also leaks to the periphery of the back surface of the pad 3 as shown in FIG. If the plating solution 16 leaks from the back surface of the support bar 4 or the pad 3 in this way, the problem of wasting the expensive plating solution 16 will of course occur. When a plurality of lead frames 1a are stacked and transported, there is a problem that the plating applied to the surface of the pad 3 and the plating leaking from the back surface of the pad 3 in contact with the surface of the pad 3 are stuck. Was. If the plating adheres to each other as described above, for example, when a plurality of lead frames 1a are stacked in a subsequent step, and the lead frames 1a are taken out one by one and conveyed to each processing step, the stacked lead frames 1a are good. Therefore, there is a problem that the lead frame 1a is frequently fed by two sheets.

As a result of such back leakage, the plating solution 16 adheres to the heat block and contaminates the heat block in the die bonding step and the wire bonding step, which leads to poor deformation of the lead frame 1a, There is also a problem that a wire breakage failure, a feeding failure, and the like are induced. The present invention has been made in view of the above-mentioned circumstances, and solves the above-described problem. Even when the lead frame is pressed by the back plate during partial plating, the pad is prevented from being pushed downward and supported. It is an object of the present invention to provide a partial plating mask plate capable of satisfactorily performing partial plating without the bars being entrapped in the elastic member.

[0011]

In order to achieve the above object, in the mask plate for partial plating of the present invention, the thickness of the elastic member at the portion corresponding to the support bar is made thinner than the other portions. I have. Thus, the support bar can be prevented from being sunk into the elastic member, and the entire lead frame, in particular, the plating-free area of the support bar and / or the pad portion can be masked well.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention relates to a resilient plate having an opening corresponding to a plating area on a surface of a mask plate having an opening corresponding to a plating area of a lead frame to be plated. In a partial plating mask plate on which a member is mounted, a projection having substantially the same width as the width of the support bar is provided at a position corresponding to the support bar of the mask plate.

In the width direction of the support bar 4, the size of the projection 17 is the same as the width of the support bar 4, or the inner leads 5 on both sides of the support bar 4.
May be formed wide enough not to interfere with the pattern. Further, the longitudinal direction of the support bar 4 can be appropriately set in a portion where the support bar 4 is in contact with the mask plate 11, that is, in a range from an end of the opening 10 of the mask plate 11 to a portion connected to the frame 2. May be set longer than the entire length of the support bar 4.

However, in order to support the support bar 4 well, the mask plate 1 of the support bar 4 is required.
1, that is, the dimension from the end of the opening 10 of the mask plate 11 to the portion connected to the frame 2, based on the end of the opening 10 of the mask plate 11. It is preferable to set the size of the portion to at least 1/3 or more, preferably 1/2 or more. In order to improve the adhesion between the convex portion 17 and the elastic member 12, the end of the contact portion of the convex portion 17 on the opening 10 side should be 0.2 to 0.2.
It is desirable to set the length to about 0.5 mm shorter than the end of the opening 10 of the mask plate 11. Further, the dimension in the height direction is set to 3/5 to 4/4 of the thickness of the elastic member 12 in consideration of the balance between masking of the support bar 4 and prevention of indentation.
It is preferably about 5.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A partial plating mask plate of the present invention will be described below in detail with reference to the drawings. The same parts as those in the conventional example will be described using the same reference numerals. In the present embodiment, the basic configuration of the mask plate is the same as that of the conventional example, that is, the mask plate 9 has a plurality of openings 10 corresponding to the plating areas 8 of the lead frame 1a as shown in FIG. Plate 11 made of a heat-resistant and chemical-resistant hard material such as a glass epoxy resin provided with a glass plate, and a lead frame 1a, which is also an object to be plated, which is mounted on the surface of the mask plate 11 to be in contact with the object to be plated. Openings 10 corresponding to the plating areas 8
And an elastic member 12 made of silicon rubber or the like. Note that such an elastic member 12 is generally formed on one surface of the mask plate 11 by a molding method using a mold or the like.

In this embodiment, as shown in FIG. 1, a projection 17 is formed at a position corresponding to the support bar 4 of the lead frame 1a, which is an object to be plated, on the mounting surface of the elastic member 12 of the mask plate 11. Is provided. In the present embodiment, the convex portion 17 has a rectangular shape having substantially the same dimensions in the width direction and the longitudinal direction as the contact portion of the support bar 4 with the mask plate 11, and the height is 4 / (thickness) of the thickness of the elastic member 12. 5 are formed.

The partial plating method using such a mask plate 9 is the same as in the conventional example. First, the mask plate 9 is mounted on the top plate 13 as shown in FIG. The top plate 13 also has a plurality of openings 10 corresponding to the openings 10 provided in the mask plate 9. Then, the plating surface of the lead frame 1a is placed on the elastic member 12 of the mask plate 9 with the plating surface in contact with the plating member. The back plate rubber 15 mounted on the plate 14 is brought into contact with the plate contacting surface, and the lead frame 1a is sandwiched.

In this state, the back plate 14 is pressurized from above, and the elastic member 12 of the mask plate 9 and the back plate rubber 15 of the back plate 14 are brought into close contact with the lead frame 1a, thereby masking the plating-free area of the lead frame 1a. I do. At this time, a portion corresponding to the plating area 8 of the lead frame 1a is projected into the opening 10 of the mask plate 9, as shown in FIG.

Here, in the mask plate 9 of the present invention, since the projection 17 is provided at a position corresponding to the support bar 4 of the lead frame 1a of the mask plate 11, the lead frame 1a is connected to the back plate 14 and the mask plate. 9
Even when pressurizing with
The portion where the convex portion 17 exists is more elastic than the other portion.
Is formed to be thin, and the back plate rubber 15 mounted on the contact surface of the back plate 14 with the lead frame 1a protrudes below the pad 3 (to the side of the mask plate 9) due to the elastic force of the back plate rubber 15 and the accompanying protrusion. The support bar 4 can be prevented from being embedded into the elastic member 12, and as a result, the pad 3, the support bar 4 and the back plate rubber 1 can be prevented.
5 can be satisfactorily plated without deteriorating the adhesiveness to 5.

In this state, a plating solution is ejected from the nozzles (not shown) corresponding to the plurality of openings 10 provided in the mask plate 9 into the openings 10, whereby the plating liquid is injected into the openings 9. Lead frame 1 protruding
A portion corresponding to the plating area 8 on the surface to be plated a is plated with a desired thickness.

In this embodiment, an example in which the lead frame is formed in a short shape has been described. However, the present invention is not limited to this, and the present invention can be applied to a case in which the lead frame is formed in a band shape or a single unit. In this embodiment, the description has been given of the lead frame of the type in which the lead extends in two directions. However, the present invention is not limited to this type. For example, the lead frame may be extended in one direction or four directions. The invention is applicable. When the leads extend in four directions, the protrusions 17 are arranged as shown in FIG. 3 corresponding to the shape of the support bar.

Further, in this embodiment, glass epoxy resin is used as the material of the mask plate 11. However, the material is not limited to this, and any other material that can satisfy chemical resistance, heat resistance, and insulation properties can be used. It can be replaced by a material. Further, as for the material of the elastic member 12, other than the silicone rubber used in the present embodiment, synthetic rubber, natural rubber, urethane, fluorine-based resin and the like can be applied.

[0023]

As described above, according to the mask plate for partial plating of the present invention, since the projection corresponding to the support bar of the mask plate is provided, the elastic member at this location is provided. Since the thickness can be made thinner than other parts, even when the lead frame, which is the object to be plated, is pressed by the back plate during partial plating, the support bar is attached to the elastic member of the mask plate. As a result, the partial plating can be performed well without impairing the adhesion between the back plate rubber and the support bar and / or the pad of the lead frame.

Further, by providing the projections on the mask plate as described above, the effect that the adhesion between the mask plate and the elastic member can be improved is also effective.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a configuration of a mask plate for partial plating of the present invention.

FIG. 2 is a sectional view showing a partial plating method using a partial plating mask plate of the present invention.

FIG. 3 is a perspective view showing another embodiment of the present invention.

FIG. 4 is a perspective view showing a partial plating apparatus.

FIG. 5 is a cross-sectional view showing a conventional partial plating method using a partial plating mask plate.

FIG. 6 is a plan view showing leakage of plating.

FIG. 7 is a plan view showing a lead frame for a semiconductor device which is an object to be plated;

[Explanation of symbols]

 1, 1a, 1b lead frame 2 frame 3 pad 4 support bar 5 inner lead 6 tie bar 7 outer lead 8 plating area 9 mask plate 10 opening 11 mask plate 12 elastic member 13 top plate 14 back plate 15 back plate rubber 16 plating solution 17 convex part

Claims (1)

[Claims] 1. A partial plating mask plate comprising: a mask plate having an opening corresponding to a plating area; and an elastic member having an opening corresponding to the plating area is mounted on a surface of the mask plate contacting an object to be plated. A mask plate for partial plating, wherein a protrusion having substantially the same width as the width of the support bar is provided at a position corresponding to the support bar of the plate.