COB Issue's (non-sticking)

Hello,

I have been having random yeild problems with my COB process where we have non-sticking issues and no parameters have been changed on the machine from one assembly to the next. I recently inquired to the board manufacturer's about thier process and the responses I recieved from two of the vendors was 150-200uinch's of nickel and 1-2uinch's of gold and electroplated, the third vendor stated 80-160uinch's of nickle and 2-3uinch's of gold using ENIG process. From what I have previously read in the forums shows that all of these responses could be process indicators for my random yield problems. Can anyone with good knowledge of this process respond with insight that I can pass onto my board house since I have no experieince with COB?

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