JPS602692A - Method for plating silver - Google Patents

Abstract

PURPOSE:To form a silver film with high adhesion by plating on an iron or Ni alloy material without carrying out striking by impressing ripple direct current as electric current for electrolysis in a periodically interrupted state. CONSTITUTION:When an Ag-Ni alloy material is plated with silver, ripple direct current is supplied as electric current for electrolysis in a periodically interrupted state. For example, on-time and off-time are set at 4-33millisec and 1.65- 23millisec, respectively, and the on-time is made equal to (1/2Xoff-time-1/2X off-time)+30millisec. By this method a silver film with high adhesion is formed without requiring a striking stage.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a secondary silver plating method for forming a silver coating with good adhesion on an alloy material containing iron and/or nickel.

Generally, 42 alloy and 5 alloy are used as lead frame materials for IC.
Iron-nickel alloys such as 2 alloy and copper-iron alloys such as 19470 are used. IC lead frame is ICE
The child mounting part and the wire bonding part are coated with precious metals such as gold and silver, but this precious metal coating has a
It is required to have adhesion that does not cause blisters when heated at 0° C. for 5 minutes. Conventionally, it has been believed that direct plating of silver on alloy materials containing iron and/or nickel as described above does not provide sufficient adhesion, so gold, fine, copper, etc. are used before silver plating. It was common practice to perform a so-called strike plating process in which a base plating was applied to cover the metal.

However, even when such strike plating is applied, the silver plating film may blister during a heating test.

The main reason for this is thought to be that the plating bath used for base plating has a low metal component concentration of J~5/l, and the optimum range of concentration is narrow, so it is easy to deviate from the optimum conditions. For this reason, we pay close attention to the management of the strike plating bath.

However, such consideration does not improve the adhesion itself, but is merely a consideration to reduce the variation. For this reason, it has been keenly felt that some means to essentially improve the adhesion itself is necessary.

In order to meet the above requirements, the present inventors successively examined a large number of plating conditions, and found that by combining the plating current waveform and its supply method, it was possible to achieve sufficient adhesion even when the strike plating was repeated. The present invention was achieved by discovering that the silver plating problem can be reduced. That is, the present invention is characterized in that when plating silver on an alloy material containing iron and nickel, a direct current with ripples is used as the electrolytic current, and the current is periodically interrupted to apply the current. shall be.

Here, DC current with ripples, three-phase half-wave rectification,
It is a current obtained by three-phase full-wave rectification, etc., and has small waves (ripples) or pulsations in its waveform. The pulsation rate is 18-21% for three-phase half-wave, and 4-4.5 for three-phase full-wave. The present invention periodically interrupts the rippled DC current to apply the ripple. The period of this interruption is ON time 4
It is preferable to set the OFF time within the range of 1.65 to 23 milliseconds, and set the OFF time within the range of 7 times the OFF time to 7 times the OFF time + 30 milliseconds. .

With a DC current without ripples, that is, with a normal rectangular pulse waveform, the heating temperature does not reach the sound range, and the adhesion is insufficient. Therefore, although it is doubtful that ripples have some kind of effect, it is still clear and powerful what this effect is. The period of interruption also contributes to improving the adhesion of single-layer plating. This is clear from the fact that if the interruption period is too long, the adhesion deteriorates. It was found that when the OFF time was less than 1 or 2×OFF time + 30 milliseconds or more, the adhesion decreased.

A circuit that periodically interrupts a DC current with ripples can be easily constructed, but the rectification method is, for example, six-phase half-wave rectification, and the circuit is kept ON for a certain number of pulses while counting the number of ripples with a pulse counter. O for a certain number of pulses after
If the circuit is configured to be FF, a relatively inexpensive power supply circuit can be obtained.

In the method of the present invention, either an ordinary cyan bath or a neutral bath can be used as a plating bath. According to the present invention, a silver coating with good adhesion can be obtained without performing strike plating, and the strike plating step can be omitted. Furthermore, it has been found that according to the present invention, it is possible to somewhat increase the shadow (gummy flow density (Dk)) during silver plating compared to the conventional method of striking silver plating. Even if the existing Dk value is increased to 3 oAyctm2 using the method of the present invention, there is no change in the appearance of the plating.Therefore, the method of the present invention not only allows the strike plating process to be omitted, but also reduces the time required for the silver plating process itself. The expected and powerful effects that can be achieved are obtained.

Examples of the present invention are shown below.

Example A plating power supply circuit consisting of a double star-shaped six-phase half-wave rectifier circuit, a pulse counter circuit, and two digital switches for setting the number of pulses for 08 hours and the number of pulses for OFF time was installed in a jet-type partial plating system. Connected to the bottom. This partial plating device is a type of device in which a material to be plated is held between a mask plate having an opening and a suppressing plate, and a plating solution is sprayed from below toward the opening of the mask plate, and the plating solution is sprayed from below. At almost the same time, electricity is applied between the material to be plated, which becomes the cathode, and the insoluble anode. The plating bath is Ag602/l,
The free cyanide was 80 l/l and the bath temperature was 60°C. 5 ws x 7 mm aperture as a mask plate in January
25 pieces x 200 as the material to be plated.
Using a 4270 plate of IIIIII, a 42mm alloy plate was degreased with alkali, washed with hydrochloric acid, and then subjected to plating, and approximately 7 μm of silver was electrodeposited at an average cathode current density of 5.5 A/(/II+”. Silver plating The prepared 42 alloy plate was heated at 500° C. for 5 minutes, and then observed under a stereomicroscope with a magnification of 40 times to determine the presence or absence of blisters and their positions to determine pass/fail.

Figure 1 summarizes the pass/fail results for the number of pulses during 08 hours and the number of pulses during OFF time. In Figure 1, the O mark indicates that no blisters were observed, the Δ mark indicates that there were 2 or less blisters with a diameter of 20μ or less at the edge of the plating area, and the x mark indicates that there were 7 blisters in the center of the plating area. Indicates a case where one or more sag is present and the criteria of the Δ mark are fully satisfied.

From the results in Figure 1, the number of pulses at 08 hours is 1.5 to 10.
, the number of pulses during the OFF time is within the range of 0.5 to 7 and 0.
It can be seen that the number of pulses for 8 hours is equal to the number of pulses during the OFF time by 1 to -x orr'tv time pulse time pulse amount + 91 times. Converting the amount of time to time,
I pulse is 333 milliseconds, ON time is 4-3
3 milliseconds, OF'F time is 1.65 to 23 milliseconds and OR14 time is 0FTi' time 7 to T x OFF time +3
The range is 0 milliseconds.

[Brief explanation of the drawing]

Fig. 1 is a graph showing the pass/fail judgment results for the presence or absence of 7 creases in the relationship between the number of pulses in the ON time and the number of pulses in the OB''F time. Patent applicant: Sumitomo Metal Scrap Mining Co., Ltd. Agent: Patent Attorney Kai Sando Tsuyasu: Patent attorney Hirayama - Ko 7 - Figure 1 OFF σ1 open No ψ L2 Nata 2

Claims (1)

[Claims] Silver plating method 0 in a method of silver plating an alloy material containing iron and/or nickel, characterized in that a DC current with a Rinnol is used as an electrolytic current and the current is periodically interrupted and applied.