Tin/lead plating and HAL are, as you know, entirely different animals. The spec for tin/lead
plating is still good as you indicated (.0003" minimum and, after fusing, tin/lead solder
coating covers all solder termination areas and becomes highly solderable). When the minimum
thickness requirement is met, fusing, when properly effected, always provides solderable
surfaces because the tin/lead is now "homogeneous" resisting oxidation for long periods.

There can be no true thickness spec for HAL by process definition. Simply, it must be capable
of supporting soldering operations, solder wetting, acceptable solder joints, and long term
reliability. It often is not capable of doing so. This is why so many seek alternative solder
termination area coatings.

Tin/lead plated board solder termination areas, that are reflowed (fused), provide excellent
solder wetting characteristics. It's the big hump that's unacceptable to SMT.

Earl Moon

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