>I am interested in finding out potential causes of contamination of PCB,s
>with sulphur. What typical fabrication or assembly processes may introduce
>this contaminant to the board. What are the long term potential effects of
>sulphur contamination and are there any studies I could reference.
>
>Any suggestions or papers would be appreciated.
We used to experience extreme loss of solderability of components and PWBs
when they were stored in paper bags or envelopes.  Most brown, yellow, or
manila paper (maybe others but we've never checked) are high in sulfur
content and turn the tin and lead into sulfides which are difficult to
impossible to remove.

Howard S. Feldmesser
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Compulsory unification of opinion achieves only the unanimity of the
graveyard. - US Supreme Court 1942