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April 2004

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Thu, 22 Apr 2004 01:44:58 EDT
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1. If nothing dissolves the haze- alcohol, flux thinner, acetonitrile, water-
then it is time to trot out the hair drier to see if that does the trick. Run
a scrap board through the wave, make sure it has the white haze, then turn
the hair drier on and aim it at a spot on the PWB surface. If what you are
seeing is underdeveloped solder mask, the white stuff is the fumed silica used as a
thickening agent in the LPI mask.
[If the mask is not completely cured/cross-linked, then the flux and its
solvents will dissolve away the mask, exposing the whitish thickener or skeleton
of the mask. Heat up the material and the white residue will sink into the body
of the mask and disappear. Check the UV lamp output to ensure you are or your
PWB supplier is completely curing the mask.]
2. Another possible (if naught else works out from TechNet) is OA material
cross linking to give large insoluble polymers. This was described by one of
IBMs leading scientists at an InterNEPCON conference in the UK. I still have the
paper in my copies of all NEPCON proceedings back to 1977. If this turns out
to be the case, alternative OA flux formulations may need to be tried.

Bill Kenyon
Global Centre Consulting
3336 Birmingham Drive
Fort Collins, CO   80526
Tel: 970.207.9586     Cell: 302.377.4272

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