We have seen this several times in the past. Same conditions except we were
using RMA flux. Pre bake made little or no difference. ( Bake was per Manuf.
Instruction, 250F 8 hr. The one thing that did make a difference although not
completely fixing the problem was cleaning with IPA and a brush before
Aqueous cleaning. We only rejected a very few for cosmetic reasons. Never had
a reliability issue and the boards passed ionic cleanliness test.

-----Original Message-----
From: Bloomquist, Ken [mailto:[log in to unmask]] 
Sent: Tuesday, 9 August 2005 8:38 AM
To: [log in to unmask]
Subject: Re: [TN] Solder Mask discoloration

Hi Peter,

We've seen the exact same thing from our CM and we determined that it
was most likely solder mask that was not quite fully cured. We did not
reject the assemblies and have had no issues with them.

KennyB

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Peter Lee
Sent: Monday, August 08, 2005 6:56 PM
To: [log in to unmask]
Subject: [TN] Solder Mask discoloration

Technet,

We have encountered what appears to be mask discoloration after wave
soldering.

The areas of concern coincide with the areas that were exposed
selectively
by fixtures during wave soldering, dominated by one date code of PCB
with a
slightly different green (lighter) solder resist. Other data code (same
PCB
vendor) with darker solder resist waved at the same time have less/no
discoloration.

Rgds,

Peter

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