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Wirelife due to Au peel off
(-----) January 16, 2008
I'm not sure this is the right place but I'll try anyway. Currently I'm having issue with wirelift on the FR4 Type PCBA gold bond pad. During my investigation of the wirelift, I find that the gold is peeling off from the wire. This may mean that the gold from the bond pad is peeling off. I would like to know what are the potential areas in the plating process that can cause bad adhesion. This will help to to investigate the issue better. Below are the overview process flow of our plating line. Appreciate anyone help.
3.Cu Plating (thickness 15-40um)
6.Ni Plating (thickness 2.5-15um)
9.Au plating (flash gold thickness 0.03-0.15um)
Engineer - Malaysia
January 18, 2008
The most common reason for Au peeling from Ni is that the nickel layer becomes passive before gold plate, thereby losing adhesion values. Why is there a cleaning process after nickel? This should not be necessary, and may be actually be hurting you. It is best to go right into the gold after proper rinsing and activation. With the use of an activator, from nickel to gold should not exceed 2 minutes.
One other cause (not real common) is that the gold deposit is too hard and could be brittle.
1) Gold concentration too low, brighteners or metallic impurities too high.
2) Current density too high.
3) Organic contamination.
I would concentrate on process timing first as the culprit. Good Luck!
Process Engineer - Syracuse, New York