JPS6041718B2 - Partial plating method for punched strips - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for partial plating of punched strips used, for example, in semiconductor lead frames.

Generally, when partially plating a metal strip, a mechanical masking method or a masking tape method is used.

However, these methods cannot be applied to punched strips of complicated shapes, such as semiconductor frames.

This is because the masking of the cut end faces of the punched strip is incomplete or completely impossible, making it impossible to obtain a partially plated strip with clear plating boundaries even on the end faces.

For example, in a semiconductor lead frame as shown in Fig. 1, if you do not want to plate the area a between the tie bar 5, the upper lead 1, and the die stem 4 (for example, if you do this to prevent migration in silver plating) )
There is.

In this case, if partial plating is attempted using the conventional mechanical masking method or masking tape method, gaps 8 that cannot be masked cannot be avoided, as shown in FIGS. 2 and 3.

In Figures 2 and 3, 6 is masking tape, 7 is sponge rubber or soft rubber, etc., but the plating solution enters the capillary through gaps 8 in the incomplete masking, causing the plating to protrude, displacement precipitation, etc. It is completely impossible to perform partial plating with clear plating boundaries up to the cut end face. The present invention has been made in view of these points.
The object of the present invention is to provide a partial plating method for punched strips that can facilitate partial plating with clear plating boundaries up to the cut end face.

The gist of the present invention is to apply paraffin to mask areas where plating is not required when continuously partially plating a part extending in the longitudinal direction excluding the cut portions of a punched strip having cut portions at intervals in the longitudinal direction. This is a partial plating method for punched strips, which is characterized by plating, followed by plating and finally removing paraffin.

In the above, paraffin can be applied by a dipping method using meltable paraffin or a coating method.

When paraffin is applied in this way, the cross section at part a in FIG. 1 is as shown in FIG. 4, and it can be seen that paraffin is completely applied to the cut end surface.

Paraffin can be removed by dipping in boiling water or heated water, or by stripping.

The range of paraffins includes those with melting points of 300C to 100C.

Next, an embodiment of the partial plating method for punched strips of the present invention will be described with reference to the accompanying drawings FIGS. 5, 6, and 7. FIGS. 5 and 6 show a masking process when manufacturing a semiconductor lead frame by partially plating silver on a copper strip 10, which is a punched strip having the shape shown in FIG. 1, respectively. be.

That is, to explain the paraffin coating method with reference to FIGS. 5 and 6, 10 is a running copper strip, and a coating roller 11 is in contact with this.

Around the circumference of the coating roller 11, a soft rubber 1"
is lined to improve contact with the copper strip 10. This coating roller 11 rotates in the direction of the arrow by contact with the running copper strip 10, and does not require any special driving.

Furthermore, a paraffin supply container 12 is rotated in contact with the outside of the coating roller 11 in the direction of the arrow as shown in the figure, and paraffin permeates through the through hole 16 and is supplied to the coating roller 11.

The paraffin supply device 12 is heated by a hot air blower 13, and the paraffin is maintained in a molten state. Punched copper strip 10 passed through this paraffin coating roller 11
As shown in FIG. 7, necessary areas are locally masked with paraffin 15, and then the next step, the plating step, is carried out.

In this example, by using such a method, one copper strip 1 shown in FIG.
A 300 m long semiconductor lead frame was manufactured on a continuous line by paraffin coating and partially plating with silver.

As another example, part b of the copper strip 10 shown in FIG. 1 was manufactured using a semiconductor lead frame 3007TL line in which the part b of the copper strip 10 shown in FIG. 1 was coated with paraffin by a local dipping method and partially plated with silver.

On the cut end face of the lead frame manufactured in accordance with this example, the plating boundary was extremely clear.

As described above, according to the partial plating method for punched strips of the present invention,
By masking with paraffin, it is possible to easily obtain a partially plated strip with clear plating boundaries on the cut end face.

Moreover, since paraffin can be reused, it is very economical compared to masking tape methods, etc., and its practical value is extremely large.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of a semiconductor lead frame, FIGS. 2, 3, and 4 are cross-sectional views of the masking part of the strip material, respectively.
FIG. 5 is a plan view illustrating an embodiment of the partial plating method for a punched strip according to the present invention, FIG. 6 is a front view, and FIG. 7 is a perspective view showing the masked state of the strip. 9: Paraffin, 10: Punched copper strip, 11: Coating roller, 1'': Soft rubber, 12: Paraffin supply container, 13: Hot air blower, 14: Rotating shaft, 15: Paraffin masking, 16: Through hole.

Claims (1)

[Claims] 1. When continuously partially plating a part of a punched strip having cut portions at intervals in the longitudinal direction, excluding the cut portions, apply paraffin to mask the areas where plating is not required, and then plate This is a partial plating method for punched strips, which is characterized by subjecting them to a process to finally remove paraffin.