Surface Finishes for Soldering and Wire Bonding

Since the invention of the printed circuit board, there has been a parallel interest in developing a means of protecting the copper surfaces from hostile environment and in maintaining solder ability of those surfaces during storage and throughout the life of the assembly.

HASL - Hot Air Solder Leveling - with eutectic tin/lead is still the number one in number of square feet PCB's produced, but a number of newer surface protections exists to day.

Chemitalic offers the following surface finishes:

* Hot Air Solder Leveling with eutectic tin/lead, 63% tin and 37% lead in a horizontal and in a vertical process. It is suitable for wave soldering and SMT reflow of low and medium pitch components.

* Electroless Nickel/gold, this process deposits a uniform electroless nickel/gold coating over exposed copper surfaces as well as in plated through holes. The thickness of the nickel layer is 3-7 micron, the thickness of the gold layer is 0,07 - 0,15 micron. The flatness is excellent.

It is suitable for wave soldering, SMT reflow of fine pitch components and wirebonding. With careful design it is also suitable as a contacting surface.

* Immersion tin, this process deposits a uniform pure tin coating with a nominal thickness of 1 micron, the flatness is excellent and it is suitable for wave soldering and SMT reflow of fine pitch components. Immersion tin is not suitable as a contacting surface or as a bonding surface.

A comparison of attributes for different surface finishes are shown in the table below.