JPS59228315A - Method of producing partial silver lead frame - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing partially silver-plated lead frames used in semiconductors.

Traditionally, lead frames used for semiconductors were plated on the entire surface, but in order to reduce costs by reducing the amount of precious metals used, spot or stripe-like partial plating is used for gold and silver plating. is becoming mainstream. When selectively plating precious metals, the main parts of the metal are masked with an insulating material such as paint or tape, and plating is applied only to the intended areas. However, when masking is performed mechanically, the plating solution comes into contact with conductor surfaces other than the intended portions, resulting in substitutional precipitation of gold and silver there. Additionally, strike plating may be applied to the entire surface to improve adhesion.

Precious metals precipitated or remaining in areas other than these intended areas must be removed by peeling because of problems such as poor appearance and, especially in the case of silver, migration.

As a method of stripping, a method of chemically dissolving the material by immersing it in a lead-tree unevenness stripping 11Jt solution, a method of electrolyzing the conductor in a stripping solution using the conductor as an anode, etc. are used.

However, the chemical dissolution method has the problem that the dissolution rate changes over time, making it difficult to control, and that the lifetime of the solution is short.

On the other hand, with the method of peeling off by electrolysis, there is a problem that unevenness will occur unless the amount of silver dissolved in the necessary areas is large, and the gloss will deteriorate in the case of bright plating, so it is necessary to dissolve more than about 1 μm. . Unfortunately, during plating, it is necessary to plate approximately 1 μ thicker than the final target thickness, which causes an increase in cost.

An object of the present invention is to eliminate the above-mentioned drawbacks of the prior art and to obtain a partially-metallic lid frame with a good appearance with a small amount of melting.

That is, the present invention provides silver that is partially deposited on the surface of a conductor made of copper, copper alloy, or Fe-Ni alloy by electroplating, and then removes silver that has adhered to unnecessary portions of the conductor by substitution precipitation or strike plating. In the manufacturing method of a partially silvered lead frame for a semiconductor, which involves anodizing and peeling off, the anodizing process is carried out using a square wave current, a combination of direct current and square wave current, or a combination of direct current and alternating current. This is a method for manufacturing a featured partial silver IJ FS frame.

The present invention will be explained below.

The conductor for the lead frame used in the present invention includes copper,
Copper alloys such as phosphor bronze and Fe-Ni alloys are used. In the present invention, partial silver plating is performed on a lead frame base made of such a metal using a mechanical mask. Generally, prior to plating, the metal surface is cleaned by degreasing, pickling, etc., and then a copper strike or silver strike is applied to the lead frame base before partial plating to improve the adhesion of silver partial plating. In the present invention, after performing strike plating (referred to as strike plating), silver plating is performed using a cyan bath.

The partial silver meso obtained in this way was applied -r
Since silver and copper deposited or deposited on unnecessary parts due to strike plating or during partial plating remain on the frame, this is removed by the present invention. That is, the lead frame is immersed as an anode in a stripping solution, and between it and a cathode made of stainless steel, according to the present invention, a combination of rectangular wave, direct current, and rectangular wave radio current as illustrated in FIGS. 1 to 4 is applied. Alternatively, unnecessary portions of silver or copper can be dissolved and removed extremely effectively by passing a current using a combination of direct current and alternating current. The current density for stripping used in the present invention is 05
~4 A/dm, the period of square wave or alternating current is 6O-
It is desirable that it be about 10H2.

As the stripping solution, an aqueous solution or liquid of KON is generally used.

The present invention will be explained below using examples.

Example 1 A lead frame base made of phosphor bronze was subjected to pretreatment such as degreasing and pickling, and then copper strike plating was applied to the entire surface at 0.000.
0.05μ thick and then partially coated with bright silver plating to 3μ thickness using a mechanical mask.

Thus obtained - KON with F frame as anode
The silver plating is dissolved by periodic electrolysis in a stripping solution consisting of an aqueous solution of 20 g/z using a rectangular wave current with the waveform shown in Figure 1 or a current with a waveform of superimposed alternating current and direct current as shown in Figure 2. The amount and appearance of the silver-plated surface were determined and shown in Table 1. Note that, as a comparative example, results using a DC power source are also shown in the same manner. Further, the average anode current density during anodic melting in this example was 1 (Vdm2).

Table 1 Judgment ○: Glossy and uniform △: Not glossy but uniform ×: Glossy and uneven From the above results, the current during peeling electrolysis according to the present invention
It can be seen that by performing peeling by periodically changing the special waveform as described above, a lead frame with a good appearance can be obtained with a small amount of dissolved silver.

Example 2 After a lead frame base made of phosphor bronze was subjected to pretreatment such as degreasing and pickling, Ni plating was applied to the entire surface of the base to a thickness of 2 μm. Next, in order to improve adhesion, silver strike plating was applied to the entire surface to a thickness of 0.05μ, and then Example 1 was applied.
In the same way as above, some parts are plated with glossy silver to a thickness of 3μ.-P
Prepare the frame 1.

Next, in order to peel off the silver adhering to unnecessary parts, stripping electrolysis was carried out in the same stripping solution as in Example 1 using a current with the same waveform as in the example and using the lead frame as an anode. Table 2 shows the amount of silver dissolved and the appearance of the silver plating at this time.

The judgment in Table 2 is the same as in Table 1. From the above results, it can be seen that even when the silver strike plating layer is peeled off, partial silver plating with a good appearance can be obtained with a small amount of dissolved silver.

Example 3 This example shows the application of the present invention to copper stripping.

After performing pretreatment such as degreasing and pickling on the lead frame base made of Fe-42%N'i alloy, copper strike plating was applied to a thickness of 0.005μ, and then, as in Example 1, a glossy plate of 3μ was partially applied. Provide silver plating and prepare lead frame]7.

In order to peel off the copper from unnecessary parts of this lead frame,
ON 20 g/I! Stripping electrolysis was carried out in a stripping solution consisting of an aqueous solution using the saw 1 frame as an anode and a current having the same waveform as in Example 1. Table 3 shows the amount of silver dissolved and the appearance of silver plating in this case.

The results in Table 3 are similar to those in Table 1, and it can be seen from this result that the present invention is effective also when peeling off a copper strike layer provided on an iron-based material such as Fe--Ni. That is, the present invention can be applied not only to silver peeling but also to copper peeling.

In the above embodiments, the positive waveforms illustrated in FIGS. 1 and 2 were used as the current waveforms used in the present invention, but positive and negative rectangular waves as shown in FIG. It is also possible to use current in the form of a superimposed wave of positive and negative direct current and alternating current as shown in FIG.

According to the present invention, a partially silver-plated lead frame with a good appearance can be obtained with a small amount of dissolved silver, so that the thickness adjustment during silver plating can be made thinner, and the cost of the lead frame can be reduced. Furthermore, since the amount of dissolution is small, the peeling time is shortened and workability can be improved.

[Brief explanation of drawings]

1 to 4 are waveform diagrams showing various aspects of the waveform of the current for stripping electrolysis used in the present invention. Arithmetic 1 (21 Arithmetic 2 circuit 3rd 412th)

Claims (1)

[Claims] (1) After partially depositing silver on the surface of copper, copper alloy, or PE-Ni alloy as a conductor by electroplating, the silver adhering to unnecessary parts of the conductor is anodized by displacement deposition or strike plating. A method for manufacturing a partial silver lead frame for semiconductors that is processed and peeled off, characterized in that anodization during peeling is performed using a rectangular wave current, a combination of a direct current and a rectangular wave current, or a combination of a direct current and an alternating current. Ginri-P
How the frame is manufactured.