JP2611431B2 - Uniform partial electroplating method - Google Patents

Description

The present invention relates to a uniform partial electroplating method.

[Prior art] Transistor and IC lead frame manufacturing methods include a method in which a metal strip is punched out by a precision press or formed into a desired shape by etching, and then a metal plating layer is provided on a chip mounting portion. There is a method of punching after providing a strip-shaped plating layer on the strip. In particular, the method is suitable for manufacturing a lead frame material for an electronic device whose shape is not so complicated, such as a lead frame for a transistor and a capacitor. Generally, in this method, after the surface of an iron or copper alloy strip is cleaned by degreasing and pickling, a plating film of nickel, silver, copper or the like is provided on the entire surface or a part thereof by electroplating.

In the partial plating method, put the strips, which have not been plated, masked with a mechanical mask or adhesive tape into the plating tank,
A desired plating film is provided on a portion that is not masked. The metal strip is pressed into a lead frame shape in the next step, and the plated portion becomes a chip mounting portion and a soldering portion.

By the way, when the metal strip is put into the plating tank and energized, current concentrates on the end of the strip, and the plating thickness at the end of the strip becomes thick and the center of the strip becomes thin. This phenomenon occurs due to non-uniform primary current distribution. Also in the case where an unnecessary portion of plating is shielded with an insulator or an adhesive tape, the plating thickness of the masked portion of the shielded mask becomes thick and the plating thickness of the central portion of the strip becomes thin. Therefore, when the plating thickness at the center of the strip is adjusted to the value required by the user, the plating thickness at the end of the strip reaches several times that of the strip, and the current is concentrated. (Eg, wire bonding properties, solder wettability, etc.) are significantly reduced.

Therefore, in order to make the plating thickness distribution uniform, the present inventors have previously proposed to install a current shielding plate 3 as shown in FIG. 2 (see Japanese Patent Application No. 62-274098).

[Problems to be Solved by the Invention] However, when the metal strip is masked and partially plated, the current shielding plate 3 must be installed close to the strip 1 as shown in FIG. When the width of the partial plating is narrow, the flow of the plating solution becomes insufficient, and the supply of metal ions is reduced, so that a high current density cannot be obtained,
Forcibly energizing will result in burnt plating. On the other hand, if the current shielding plate 3 is made thinner in order to increase the flow of the liquid, the current shielding effect becomes smaller and the plating thickness distribution becomes non-uniform.

The object of the present invention is to provide a strip-shaped partial plating on a metal strip, perform sufficient stirring of the plating solution near the strip surface,
Another object of the present invention is to provide a uniform electroplating method for making the primary current distribution uniform.

[Means for Solving the Problems] In order to achieve the above object, according to the present invention, a current shielding plate having a partition wall surface extending vertically from a plating surface boundary portion of a cathode formed of a metal strip toward an anode side is provided. A configuration is adopted in which a nozzle is provided obliquely to the portion to be plated of the metal strip and a plating solution or compressed air is blown to the portion to be plated.

[Function] By ejecting the plating solution or air at a high speed from the nozzle of the current shielding plate, the supply amount of metal ions to the plate to be plated is increased, and the stirring state of the plating solution near the surface of the plate to be plated is increased. As a result, the limit current density increases, the primary current distribution of the portion to be plated becomes uniform, and the variation in plating thickness is suppressed.

[Embodiment] An embodiment of the present invention will be described below with reference to FIG. 1. The current shielding plate 3 is made of an electric insulator (for example, vinyl chloride resin). A nozzle 5 is provided obliquely to the plating strip 1, and a plating solution 10 is sprayed from the nozzle 5 toward the plating strip 1. The sprayed plating solution 10 is returned to the plating solution recovery tank 8,
From there, it is circulated again by the pump 6.

Since a plurality of the nozzles 5 are provided in the current shielding plate 3 at equal intervals, the plating solution 10 is sprayed at a high speed onto the portion to be plated of the metal strip 1 while maintaining the current shielding effect, and the supply of metal ions is increased. The plating operation can be performed at a high current density while achieving a uniform increase in the plating thickness. In the figure, 2 is an anode, 4 is a masking tape, 9
Denotes a plating tank, and 11 denotes a heater.

Example 1 A metal condition (width 40 mm, thickness 0.5 mm) made of a copper alloy was cleaned by electrolytic degreasing and pickling, then only the portion to be plated was exposed, and the portion not requiring plating was shielded with a masking tape. As shown in FIG. 1, as shown in FIG. 1, it is installed in a Ni plating tank provided with a current shielding plate 3 with a nozzle 5 which can be changed according to the width of a portion to be plated, and the strip is placed in a tank filled with a Ni plating solution. Ni plating was performed while moving at a speed of 3 m / sec in the longitudinal direction. At this time, Ni is pumped from the nozzle 5 using the pump 6.
The plating solution was jetted at a flow rate of 2 m / sec. Ni plating bath composition / nickel sulfate _{(NiSO 4 · 6H 2 O)} 240g, nickel chloride _{(NiCl 2 · 6H 2 O)} 50g /, boric acid (H ₃ BO ₃₎ is 50 g / standard Watts bath. The current was set so that the Ni plating thickness was 3 μm. The bath temperature was 55 ± 2 ° C.
The Ni plating thickness distribution in the width direction of the partially plated strip obtained by removing the masking tape after Ni plating (see FIG. 4) was measured with a fluorescent X-ray film thickness meter. The results are shown in FIG. From this result, it was confirmed that the Ni plating thickness was substantially uniform at both the plating end portion and the center portion, and the plating thickness distribution could be made uniform even in partial plating with a narrow width.

Example 2 Using the apparatus shown in FIG. 1, the current density at the time of Ni plating was increased stepwise, and the limit current density was examined. Plating conditions other than the pretreatment method and the current density of the metal strip 1 are the same as those in the first embodiment. As a result, up to 40 A / dm
Plating could be obtained. When the current density was increased to 50 A / dm ² , the plated surface became slightly rough and slightly black. From this result, the nozzle 5 inside the current shielding plate 3
It was confirmed that the supply of plating metal ions to the metal strip 1 was remarkably increased by ejecting the plating solution from the above, and the limiting current density was increased.

[Effects of the Invention] As described above, according to the present invention, even when the width of the partial plating is narrow, the plating at the plating boundary portion (the portion separated by the masking tape) does not become granular due to burn plating, and the appearance is improved. Very uniform plating is obtained. In addition, since the current density can be set high, the length of the plating tank can be shortened, so that it is economical and the work efficiency is good.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing an embodiment of the present invention, FIG. 2 and FIG.
FIG. 4 is an explanatory view showing a conventional example, FIG. 4 is a cross-sectional view of a partially plated strip, and FIG. 5 is a graph showing measurement results of Ni plating thickness distribution. 1: Metal strip, 2: Anode, 3: Current shielding plate, 4: Masking tape, 5: Nozzle, 6: Pump, 7: Plating tank, 8: Plating solution recovery tank, 9: Plating tank, 10: Plating solution , 11: heater.

Continuation of the front page (56) References JP-A-62-274098 (JP, A) JP-A-61-270889 (JP, A) JP-A-53-7543 (JP, A)

Claims (1)

(57) [Claims] Claims: 1. A plating unnecessary portion of a metal strip is masked,
A uniform partial electroplating method of arranging a current shielding plate having a partition wall extending vertically toward the anode side from a plating surface boundary portion of the cathode formed of the metal strip and partially plating the metal strip, A uniform partial electroplating method, characterized in that a nozzle is provided in the current shielding plate obliquely with respect to a portion to be plated of the metal strip and a plating solution or compressed air is blown to the portion to be plated of the metal strip.