Steve,
As a user of GIL, I have seen suppliers have the same trouble with drilling this
material. It is often a problem of unfamiliarity with the material. As previously
mentioned, if you start to "punch" thru GIL with your drill bit, it will shatter the
GIL material. You are probably on the right track here as to HOW the defect was
created. Let's ask why the PWB supplier let the board out of his shop. The Fab shop
should be able to catch such errors.
So, lets swim a bit further up stream here. I was wondering if the hole is a mounting
hole that is plated thru and connected to the ground. I try to discourage the practice
of plating mounting holes. If it is a mounting hole, who torqued the bolts, Magilla
Gorilla? Torquing down a hole can increase your GIL cracking/crazing problems,
providing a reason the latent short occurred after assembly, and not at the board shop.
Lets talk electrical testing now. What isolation resistance threshold was used at
electrical test? 100 Megs is the norm. Now the next question. Was the board tested
with a flying probe machine? Many of these machines will only test adjacent nets for
isolation. This software driven algorithm greatly reduces test time, by not testing
nets that are on opposite corners of the board from each other. The problem with this
algorithm is that most of them do not recognize and test nets that pass near planes in
the vertical axis. For example, a trace that comes close to a ground via, may not get
tested for isolation to ground. It is quite possible, if your short is from a net to a
plane, that the resistance isolation between these were never tested.
Also, are you happy with the clearance area allowed by the design around the holes?
Finally Steve, who once graced the golden state, did California Dreaming come before or
after Monday, Monday?
George Franck
"My opinions are just that"
##############################################################
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
##############################################################
|
