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August 2005

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Subject:
From:
Peter Lee <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Peter Lee <[log in to unmask]>
Date:
Mon, 8 Aug 2005 18:56:09 -0700
Content-Type:
text/plain
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text/plain (74 lines)
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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