JPH0317298A - Uniform electroplating method - Google Patents

Abstract

PURPOSE:To well stir a plating soln. near the surface of a bar to be partially plated and to make primary current distribution uniform by fitting nozzles in current shielding plates and spouting the plating soln. or compressed air on the part to be plated. CONSTITUTION:When a metal bar 1 is partially plated, nozzles 5 are fitted in current shielding plates 3 made of an electric insulator so that the nozzles 5 are inclined to the bar 1. A plating soln. 10 or compressed air is spouted on the bar 1 from the nozzles 5. The spouted plating soln. 10 is returned to a recovery tank 8 and circulated by a pump 6. The nozzles 5 are fixed at regular intervals, spouts the plating soln. 10 on the part of the bar 1 to be plated without reducing the current shielding effect of the plates 3 and increase the feed of metal ions. The thickness of a plating film is made uniform and electroplating can be carried out at high current density.

Description

[Detailed description of the invention] [Industrial usage ff] The present invention relates to a uniform electroplating process.

[Prior Art] Methods for producing lead frames for transistors and ICs include: (1) punching out a metal strip with a precision press or forming it into a desired shape by etching, and then providing a metal plating layer in the chip storage area; (2) There is a method in which a plating layer is provided in advance on a metal strip in a square shape and then punched out. In particular, the square width (■) is suitable for manufacturing lead frame materials for electronic devices whose shapes are not too ordinary, such as lead frames for transistors and capacitors. Generally, this square is made by degreasing the surface of an iron or copper alloy strip and cleaning it by pickling, and then applying a plating film of nickel, silver, copper, etc. to the entire surface or a portion thereof by electroplating.

In the partial plating method, a strip whose parts not to be plated are masked with a machine mask or adhesive tape is put into a plating plate, and the unmasked parts are provided with a desired plating film. The metal strip is pressed into the shape of a lead frame in the next step, and the plated part becomes a chip mounting part or a soldering part.

By the way, when a metal strip is placed in a plating bath and energized, the current concentrates at the ends of the strip, causing the problem that the plating thickness at the ends of the strip becomes thicker and the center portion of the strip becomes thinner. This phenomenon occurs due to the non-uniformity of the primary current distribution. When shielding unnecessary parts with an insulator or adhesive tape, the thickness of the plating at the edges of the shielded mask becomes thicker, and the thickness of the plating at the center of the strip becomes thinner. Therefore, if the plating thickness at the center of the strip is adjusted to the value requested by the user, the plating thickness at the ends of the strip will reach several times that value, and the current will be absorbed, resulting in burnt plating in some cases, making it difficult to use as an electronic component. The functionality (e.g. wire bondability, solder wettability, etc.)
decreases significantly.

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

[Problems to be Solved by the Invention] However, when partially plating a metal strip by masking it, the current shielding plate 3 is attached to the strip 1 as shown in FIG.
However, if the convergence of partial plating is narrow, the flow of the plating solution will be insufficient and the supply of metal ions will be affected, making it impossible to obtain a high current density and forcing the current to flow. This results 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 will be reduced and the plating thickness distribution will be uneven.

An object of the present invention is to provide a uniform electroplating method that sufficiently stirs the plating solution near the surface of the strip and makes the primary current distribution uniform when partially plating a metal strip in the form of a strip. This is what I am trying to do.

[Means for Solving the Problems] In order to achieve the above object, the present invention adopts a method in which a nozzle is provided on the current shielding plate pile and a plating solution or compressed air is sprayed onto the plating portion.

[Function] By ejecting the plating solution or air at high speed from the nozzle of the current shielding plate, the supply level of metal ions to the lance-plated strips is increased, and the agitation state of the plating solution near the surface of the limb-plated strips is increased. , so that the critical rs flow density increases and the primary current distribution in the limb plating portion becomes uniform, suppressing variations in the plating thickness.

[Example] Hereinafter, an example of the present invention will be described with reference to FIG. A nozzle 5 is provided in the current shielding plate 3 at an angle to the plating strip 1, and a plating solution 10 is sprayed from the nozzle 5 toward the plating strip 1. The mixed solution 10 is returned to the plating collection tank 8, and from there it is plated 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 material 10 is sprayed at high speed onto the plated portion of the metal strip 1 while maintaining the current shielding effect, thereby supplying metal ions. Plating work can be performed at high current density while increasing deposition dramatically and making the plating JV uniform. In the figure, 2 is an anode, 4 is a masking table,
9 is a plating bath, and 1l is a heater.

Example 1 Metal strip made of copper alloy (radius 40n++n, thickness 0.5
a + m) by electrolytic degreasing and pickling to expose only the part to be plated, and cover the unnecessary part with masking tape, as shown in Figure 1, according to the width of the part to be plated. Comes with 5 nozzles that can be adjusted by
The strip was installed in a Ni plating machine equipped with a temporary d-flow shield 3, and the strip was heated at 3 m/s in the longitudinal direction in a tank filled with Ni plating solution.
I performed N1 Mepki without moving at the speed of ee. At this time, the Ni agate liquid is applied from the nozzle 5 using the pump 6 at a flow rate of 2.
It was ejected at m/scc. The Ni plating bath composition is nickel sulfate (NiSO 6H20) 240 g/
I! , 50 g/J of nickel tetrachloride (NiCl 6H20), and 50 g/17 of diboric acid (H BO3). Note that the current was set so that the Ni plating thickness was 3 μm. Further, bath 14 was set at 55±2°C. N
After i-plating, the masking tape was removed and the partially plated strip (see FIG. 4) was obtained.The Ni plating thickness in the width direction was determined as 1111 using a fluorescent X-ray film thickness meter. The results will be shown to the fifth country. From this result, it was confirmed that the Ni plating thickness was uniform both at the plating ends and in the center, and it was possible to make the plating thickness uniform even in partial plating in a narrow area.

Example 2 Using the apparatus shown in FIG. 1, the current density during Ni plating was increased stepwise to reach a critical current density of 53. The pretreatment method for the metal strip 1 and the plating conditions other than the current density were the same as in Example 1. As a result, it was possible to obtain Ni plating with no abnormalities on the outer shell up to 40 A/dm2. In addition, 50
When the current density was increased to "A/dm", the plated surface became slightly rough and slightly blackened. From this result, it was found that the plating solution was jetted from the nozzle 5 inside the current shielding plate 3 to coat the metal strip 1. It was confirmed that the supply of plating metal ions increased significantly and the critical current density increased.

[Effects of the Invention] As explained above, according to the present invention, even when the convergence of partial plating is narrow, the plating at the plating boundary (the part separated by the masking tape) does not become granular due to burnt metal, and the outer plating does not become granular. A very uniform plating of il-I is obtained.

In addition, since the current density can be set high, the length of the plating process can be shortened, which is economical and has good work efficiency.

[Brief explanation of the drawing]

Figure 1 is an explanatory diagram showing an embodiment of the present invention, Figures 2 and 3 are
The figure is an explanatory diagram showing a conventional example, FIG. 4 is a cross-sectional view of a partially plated strip, and FIG. 5 is a graph showing the results of all determination of Ni plating thickness Vii. : Metal strip, anode, : Current shielding plate, : Masking tape, : Nozzle, bomb, plating film, : Plating solution recovery tank, plating tank, second plating solution, ; Heater.

Claims (1)

[Claims] 1. In a uniform electroplating method in which a current shielding plate having a partition wall surface extending from the boundary of the plating surface of the cathode consisting of a metal strip toward the anode side is arranged and plated, a nozzle is provided in the current shielding plate and plating is performed. A uniform electroplating method characterized by spraying liquid or compressed air onto the portion of the metal strip to be plated.