hi,

here's a wag for you.  i assume the blind vias are filled with pure resin (ie, no reinforcement).  this pure resin has a relatively high coefficient of thermal expansion that could be sufficient to cause some separation within the laminate during the exposures to elevated temperature.

had any of these boards been assembled shortly after they were received with no problems encountered?

can i assume that you have not embraced jit? (thought i'd say this to satisfy your hunger for sarcasm)

phil

-----Original Message-----
From: Gfranck [mailto:[log in to unmask]]
Sent: Friday, March 03, 2000 5:49 AM
To: [log in to unmask]
Subject: [TN] Old PWB BV delamination.


Technetters,

We have a lot of a 12 layer PWB made from a High Tg Epoxy material, some 75 mil thick overall.  The board has 3 sequential laminations, and four drill operations to get the three Blind vias (BV) and thru holes in the board.  The BVs from
layer 1 - 10 terminations are visible thru the material from the Layer 12 side.  During the assembly prebake  process the tops of these little BVs delaminate.  A patteren of little white dots which closely matchs the 1-10 BV drill pattern
emerges.  I believe the BV drill size was 10 mil

Boards are 20 months old.  Assemblier was aware of the age of the boards, and the delamination occured during the pre-bake process, and thermal profile set up.

Would anyone want to discuss why a BV would be more prone to delamination than the rest of the board?

                         *** Warning: the follow contains sarcasm.***
*** For those unable or unwilling to understand sarcasm, please read no further.***

Current corrective action proposals:
1) Don't assembly old PWBs.
2) Add a ground plane between layer 11 and 12 to prevent the layer 10BV  terminations (and delaminations) to be visible from the outside of the board.
3) Blame the PWB supplier, and get them to replace the boards.
4) Willing to entertain other options.

Thanks,

George Franck

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