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August 1998

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Subject:
From:
"Dhawan, Ashok" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum." <[log in to unmask]>, "Dhawan, Ashok" <[log in to unmask]>
Date:
Fri, 21 Aug 1998 11:54:11 -0500
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First of all many thanks for feedback on OSP  and Immersion gold as
finish -HASL Alternatives.


I am looking for info on another problem. The description is as follow:

We are using HASl finish on a board using 15.7 mils and 0603 components.
(That is why I asked opinion on Finish earlier).

The board is having all the untested vias solder masked  on pads. In
recent lots from One board vendor, our inspectors have observed black
residue or coloration on a portion of via . Some of the masked vias are
having black residue.It appears to be molten mask -turned black from its
original green color. Some other places, the greenish tinge is reduced
in intensity and thiose are places where it is affected to lesser
degree. If we probe or smear gently the blackish portion, the mask comes
off (peel off) very easily exposing the copper.The material is tacky,
paste like . Anybody there who can help us what it could be.

The board manufacturer is saying that the residue is non-ionic .

My question is:

- Anybody came across this / similar problem ?Is it common problem with
masked vias with hole open ?The solder pad is 25 mils and hole is 12
mils ( 1 mil = one thousandth of an inch).

- the concern for reliability is valid or not --even if the black
residue --flux or solder mask or any contamination --is passing the
ionic test.Do you have any suggestions on other tests which we can
suggest board vendor to carry out ? e.g. SEM ??

Please post your replies on IPC Technet .

thanks

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