Introduction

SELECTIVE PLATING, also known as brush plating, differs from traditional tank or bath plating in that the workpiece is not immersed in a plating solution (electrolyte). Instead, the electrolyte is brought to the part and applied by a hand-held anode or stylus, which incorporates an absorbent wrapping for applying the solution to the workpiece (cathode). A direct current power pack drives the electrochemical reaction, depositing the desired metal on the substrate. In practice, movement between the anode and cathode is required for optimum results when plating, stripping, activating, and so on. A schematic of the selective plating process appears in Fig. 1.

Fig. 1 Manual operation of selective plating process. Source: Ref 1

Currently, a broad range of elements and alloys can be brush plated; the majority are listed in Table 1. Even though selective plating can be done in a tank, labor-intensive masking and subsequent removal often make this option impractical.

Table 1 Energy factors for selective plating

Element or alloy

Energy factor

Cadmium

0.006

Chromium

0.200

Cobalt

0.014

Copper

0.013

Gallium

0.014

Gold

0.006

Indium

0.009

Iridium

0.069

Iron

0.025

Lead

0.006

Mercury

0.008

Nickel acid

0.047

Nickel alkaline

0.017

Nickel, black

0.025

Nickel, natural

0.025

Palladium

0.019

Platinum

0.015

Rhodium

0.030

Silver, noncyanide

0.750

Silver, pure

0.004

Babbitt

0.006

Brass

0.017

Bronze

0.017

Cobalt-nickel

0.019

Cobalt-tungsten

0.015

Nickel-cobalt

0.020

Nickel-tungsten

0.020

Tin-cadmium

0.007

Tin-indium

0.008

Tin-lead (90/10)

0.006

Tin-lead (60-40)

G.GG7

Tin-nickel

G.G1G

Note: The energy factor is the ampere-hours required to produce a deposit thickness of 0.003 mm (0.0001 in.) on a square inch of area.

0 0

Post a comment