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November 2002

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Subject:
From:
Lum Wee Mei <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Sat, 30 Nov 2002 09:43:44 +0800
Content-Type:
text/plain
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text/plain (43 lines)
My colleague who presented the talk is not able to understand why
Magnesium is present on the conformal coated board on one of her test
sample. In addition, she found migration of Au ions between traces on
the coated board - the channel seems like bridges from the top of the
traces and not from the sides.

My opinions are as follows and I may be wrong in my deduction as I am
not a process gal :

1. Can the presence of Magnesium due to the presence of permanganate
used to desmear the drilled hole? If not, what is the possible cause of
their presence?

2. The presence of "brush hair from the coating brush" is rule out by
the engineer as the image does not correlate to that of a artist brush
used for coating. My opinions are:
- migration is due to hunidity, mositure and high temperature.
- CAF as the test coupon consists of comb patterns that are of 4/4mils,
5/5mils and 6/6mils. With such small spacing, the tendency of CAF when
bias is applied can occur. The engineer mentioned that resistance
measurement does not flag up such presence before coating. In my
opinion, if CAF is to be activated and in such small spacing between
traces, the time to coat and after coat (Humiseal IB31) is sufficient to
cause CAF with presence of humidity or moisture.

Well, the above are just my simple analogy from a non process gal. I
hope to hear and learn from you experts out there and sincerely
appreciate your feedback.

Thanks in adavnce and best regards,
Wee Mei

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