Printed Wiring Assemblies (PWAs)
Chlorine Contamination

Chlorine contamination inside this part introduced during the manufacturing process resulted in the gold ball-bond separating from the aluminum pad in this transistor. The ionic contamination weakened the intermatallic layer between the gold lead and aluminum base bond pad causing the failure.

Reference :
NASA-STD-8739.2,
7.4 PWB Preparation
1. Prior to use, the PWB shall be examined for:
a. Oxidation.
b. Discoloration.
c. Damage.
d. Contamination.
e. Flatness.