TABLE OF CONTENTS Tin (Sn) is a very attractive option as a lead-free surface finish. Merits of Sn include:
It s lead free.
It has good solderability.
It has good corrosion resistivity.
It has reasonably good electrical conductivity.
It has good mechanical strength.
It is nontoxic.
It is abundant in supply and low in cost.
It is compatible with virtually all solders, particularly Sn-bearing alloys.
It has a long history, with reliability data available.
It has the option of being a metal etch resist.
It is fusible, if needed.
It provides a flat surface contour.
However, the following three concerns have to be addressed before full acceptance is possible:
Tin whisker
Tin pest
Sliver
Several decades ago, electroplated tin was used as a final surface finish. It was abandoned later as final finish due to problems with current distribution thickness and deposit stability, besides the whisker and tin pest problems.76 Today, improved versions of electrolytic tin processes are reintroduced as an option for lead-free surface finishes, mainly driven by the global lead-free soldering move. The thickness of a tin layer may vary from 3 m for the SnTech Sn Satin Bright (SB) process to 7.5 m to as much as 8 to 15 m, depending on the process and chemistry.76 78
Fabrication Process. There is a wide variety of plating chemistry for electroplating tin in the electronics industry. Baths using pyrophosphate, potassium stannate, sodium stannate, and phenol sulfonic acid have been used in the past. However,...
