In a message dated 4/13/99 8:42:13 AM Pacific Daylight Time, [log in to unmask]
writes:
<< Hi TechNet,
We have a small multilayer (4, I think) GFG board which has 8 pressfit,
flared terminals installed along one edge, about 0.25" from the edge of the
board. After wave solder, these boards are being rejected for measling
around the hardware - typically between two terminals. The measling was
either not present before solder or was made more apparent by the wave solder
temperatures. The hardware is the correct size for the board thickness and
hole size & is being installed using the manufacturer's tool. We did not
observe this problem in previous batches but the board material has been
changed from FR4 to GFG [should have helped, I'd think]. Is it possible we
are doing mechanical damage to the boards during flaring? Thanks in advance
for your help!
Sheila Smith, Marconi Aerospace >>
Hi Sheila!
(nice name BTW, I gotta sister named Sheila...GRIN) You didn't say what kind
of FR4 you were using before, but I'm assuming it was either GFN, GFK, or GHN
which all have anywhere from 75-85ppm CTE's, and TG's of between 120-140 C..
So you're right from a CTE and TG perspective that a GFG would be better
since it's TG is 170-190 C. and it's CTE is down around 65ppm. But maybe it
one of them deals that since the GFG is so stable and stiff, that it doesn't
have the same sort of "give" that your earlier laminate did, so that's why
you're seeing the measling, just a guess. I kinda' equate it to a earthquake
proof building (since I'm in California), a stiff building will always be
damaged more in a earthquake than a flexible one will...crude analogy I
know...but you get my drift.
I gotta ask, why are ya' doing your pressing and swaging before wave? I know
you probably have a reason, but typically I've always done those sort of
operations after wave. Maybe ya' just need to do it after wave to keep from
getting rejected...
-Steve Gregory-
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