Peter,

This looks like a classic solder mask "blush". Try using a heat gun on the
surface or if possible bake the board at 250F for about 30 min and see if
disappears. This could be caused by an under cured solder mask or an
improperly mixed solder mask. You mentioned the coloration was somewhat
different and that would lead me to suspect the mixing.

If this is by chance a dry film solder mask, this is a fairly common
occurrence. On a dry film mask I would not expect this to cause reliability
issues. If however it is a liquid photoimageable, I would have some concern.
Have your vendor check with their solder mask vendor to suggest some tests
to insure the mask is functioning properly. Most common tests include tape
test and solvent resistance test.

Regards,

Bob Metcalf
Circuit Solutions
949-709-2544

-----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.



We have not seen this issue before this build. There was no PCB vendor
change & (known) process &.



Process details:

Reflow (x2 times)

Wave solder: preheat (120/130C), solder temp 260C, with fixture

Flux: no clean, halide free

Top side max PCB temp 110C

Wash&Rinse cycle 8min at 130F in DI with saponifier, Dry 1 min at 100F



Following link shows PCB images with white milky masks after wave soldering
AND WASH. It does not seem to be surface residues (IPA has no effect). PCB
vendor is currently investigating.



http://members.shaw.ca/ppwlee1/Images/Mask_color1.jpg

http://members.shaw.ca/ppwlee1/Images/Mask_color2.jpg

http://members.shaw.ca/ppwlee1/Images/Mask_color3.jpg



Has anyone seen this before? Any idea on what causes the mask discoloration
and its potential impact on the assembly?

Any comment is greatly appreciated.



Rgds,

Peter




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