Letter 20045

Ionic Contamination on PCBAs - acceptable level per ug/sq inch  

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What is the normal acceptable level of Ionic Contamination on a PCBA after solder reflow and normal wash operation? We have to meet an extremely high evironmental test specification requiring the PCB to withstand 300 to 400 hours at 85% Relative Humidity and fluctuating temperatures from -40 C to 85 C during powerup of 12.5 volts. Our PCBs are running around 10 ug/sq inch of ionic contamination currently, and we are seeing growth of Copper Oxide on the Au plating during/after the test. On the PCB for plating we have a base of Cu with 250 to 400 microinches of Ni and 3 to 8 microinches of Au.

Chad Leinbach
- Golden, IL, USA

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