Do the pads on the non-soldered parts have any visible foreign material or discoloration?  Are the terminations of the parts wetted at all?  Are the parts with no solder the same parts and/or locations?  What are the package types?  Have you verified screen printing?  What volume are you stenciling down?  What are your stencil spec's (aperture, thickness, etc)  Do you have any pictures of the non soldered locations?  What is the primary side profile?  Do you see anything on the pads after first reflow?  What type of paste are you using?  

Kathy

>>> [log in to unmask] 03/26/01 10:01AM >>>
I could use some thoughts from those of you involved on the assembly side.
We have a customer who appears to have solderability issues with a
particular board we have built.  We have supplied this product over the last
several months using three different surface finishes; white tin, HASL and
ENIG.  His issue is the same regardless of the surface finish.  His first
side produces acceptable solderability however the second side exhibits
non-wetting and partial wetting.  I have one of the ENIG boards after
assembly and it shows absolute absence of solder on multiple areas of the
secondary side, while adjacent areas are excellent.  I have little specific
information regarding assembly, except as follows:

Screen solderpaste on backside
Inspect
Pick and place components
IR reflow
Aqueous clean
Screen topside with solderpaste
Inspect
Pick & place components
IR reflow
Aqueous clean.

I'm told the customer bakes his boards prior to paste screening, however, I
have no profile specifics etc.

The product in question has no unusual attributes.  It's an .062 ten layer
board, no thru-hole, SMT two sides, s single BGA and QFP and the typical
other passives.  Process sequence is typical SMOBC with no via plugging etc.

Mike Bailey
Director of Engineering
TTM Technologies
2630 S. Harbor Blvd.
Santa Ana, CA 92704
Phone(714) 241-0303
FAX (714) 241-0708
[log in to unmask]

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