Sorry to annoy,
I don't understand why flux can contaminate Aluminum pads.
But apparently, Aluminum pads got some unremovable marks and after FIB
analysis, these marks look pits or dents.
Most of engineers think those pits perhpas come from the raw material; however,
I don't think those are from wafer making processes because we never saw
similar defect in another Assembly house in Thai.
This thing really distrubed me for a while.
I am the only one think these defects come from the flux, but I can't explain
why flux was on Aluminum pad because the distance between bumps and pads are
1mm away.
Therefore, I have to go to the production line to look at why flux stays on
Aluminum pads. Then I can persuade everybody the defects are flux, actually.