Introduction

ELECTRODEPOSITION of tin alloys is used to protect steel against corrosion or wear, to impart resistance to etching, and to facilitate soldering. Four types of tin alloys are available in commercial processes.

Tin-lead is the most commonly used of these processes because of its simplicity and low cost. It is especially popular in the electronics industry because of its excellent solderability, resistance to tin whisker growth, and resistance to tin pest (formation of a gray powder on the surface, also called tin disease). These properties make it a valuable coating for integrated-circuit leads, surface-mount (small outline transistor) components, and circuit board connections.

Tin-bismuth processes have been developed in recent years as a substitute for tin-lead. Bismuth as an alloying agent prevents the whiskering and tin pest that can occur in tin coatings.

Tin-nickel is used for corrosion-resistant coatings, especially in seawater environments. It has an attractive chromelike appearance and high lubricity when plated over bright nickel.

Tin-zinc provides outstanding corrosion protection, comparable to cadmium, and is a possible replacement for cadmium at a lower cost.

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