Is this LPISM ?
if so try a bake cycle and see if it goes away

On Fri, 15 Jan 1999, Paul Wareham wrote:

> Getting alot of white blister marks on a batch of boards.  All boards seem to be from the same date code of board manufacture.  The marks seem to occur over all areas, not just over copper.  There is no residue and does not scrape, it looks like it is subsurface.  To me, it looks as though there is some weakness in the solder mask which was brought out under the stress of wave solder.  The marks are only on the solder side, and only seem to appear after they've been washed.  Could a defective solder mask have been damaged by heat stress of the wave, then providing a home from moisture during the wash process?
>
> Any ideas?
>
> Paul Wareham
> DynaGen Systems Inc.
>

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