In a message dated 10/05/1999 9:42:32 AM Central Daylight Time,
[log in to unmask] writes:

>>Stupid questions, sorry...

Hey James!

Not stupid questions at all...hell, I didn't know either...just learned about
this stuff. I found out about this when an assembly we were building
internally shorted at the customers when it was powered-up at the full
operating voltages (150-volts plus). Everything tested fine here before we
shipped them. We discovered fractures within the laminate after
microsectioning one of the failed assemblies...

>>1.) "...should be more vocal about large holes (as one example, bigger than
>>.125") in GIL systems and the risks involved,..."

Risks involved -- The laminate that was used is a high Tg GIL polyimid, very
brittle and difficult to drill and/or machine. The fab vendor is going to use
a GIJ on a re-run of these boards which was stated is easier to drill.

The angle of the cutting flutes at the drill bit tip changes from smaller
diameters to larger diameters. This is standard with the drill bits used in
the industry. On smaller holes I believe they're 65-degrees, but on the
larger diameters I believe the angle that was stated is 145-degrees. Which
contributes to the crushing effect that drilling larger holes experience,
especially in hard, brittle resin systems.

>>2.) "... and the associated risks when there isn't the support of un-used
>>pads left in the artwork...I found this out the hard way."

Found out ---The holes in question had the un-used pads removed in the
artwork of the inner layers. If they were left intact, they may have provided
some additional support in the barrels during drilling to prevent the
fracturing, as the fractures appeared to have originated from where the pads
were removed.

Also, the test coupon did not have a full representation of all the hole
diameters that were drilled into the fab...only the smaller diameters where
there wasn't an issue, mainly because of the different drill bit design of
smaller diameter bits. So the issue didn't show itself in the microsections
done on the coupons by the fab house.

-Steve Gregory-

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