Wee Mei,

It would be helpful if we knew what the test protocols were (Temp, Rh, time, etc.).

1B31 has a low Tg ( ~15 degrees C ).
Above this temperature it's protective abilities are very limited.

Are you finding CAF or dendrites? They are two different failure modes.
Basically, CAF occurs internally in laminants while a dendrite forms on the surface.

David A. Douthit
Manager
LoCan LLC


Lum Wee Mei wrote:

> 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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