Steve,

See you're keeping real busy these days doing more advanced/challenging
stuff. That'l broaden your horizon - good for you. I just thought you and
Paul would be interested in one of our normal MLB's.

Earl
----- Original Message -----
From: Stephen R. Gregory <[log in to unmask]>
To: <[log in to unmask]>
Sent: Monday, September 20, 1999 5:46 PM
Subject: [TN] Internal Fab Shorts...a follow-up...


> Ahhhh, Monday, Monday...can't trust that day...'member that song? (OOPS,
I'm
> dating myself!) Oh well, I'm a ol' fart and I know it...hehehe.
>
> Just spent the better part of the afternoon and well, early evening with
the
> internal short problem I asked about a week ago. This was a meeting
between
> the fab vendor, our customer, and us.
>
> Sent one of the suspect assemblies to Trace labs for a few microsections
and
> they showed fracturing within the laminate at just about every large
diameter
> plated through hole of the terminal blocks that are installed on the
> assembly. Plating chemicals were trapped within the fractures in the
> laminate, and upon power-up the assembly shorted within just a few hours
> after voltage was applied.
>
> A number of key points were brought-up that were deemed contributors to
this
> problem, and I wanted to share them with ya'll so maybe you won't wind-up
in
> the same creek that we're in now:
>
> 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.
>
> 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.
>
> 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.
>
> Hey Earl! Maybe you're right...I might become a PC Fab guy after all! Boy
> though, this sure is a tough way to learn about this stuff!
>
> -Steve Gregory-
>
> ##############################################################
> TechNet Mail List provided as a free service by IPC using LISTSERV 1.8c
> ##############################################################
> To subscribe/unsubscribe, send a message to [log in to unmask] with
following text in
> the body:
> To subscribe:   SUBSCRIBE TECHNET <your full name>
> To unsubscribe:   SIGNOFF TECHNET
> ##############################################################
> Please visit IPC web site (http://www.ipc.org/html/forum.htm) for
additional
> information.
> If you need assistance - contact Gayatri Sardeshpande at [log in to unmask] or
> 847-509-9700 ext.5365
> ##############################################################