Hi Pete,

While the '800 ohm short' does not quite fit the picture, you may have CAF [conductive anodic filament] problems.

Bad drilling certainly is a part of it—it separates the glass fibers from the resin matrix opening capillaries Cu can plate into, and that can open further with moisture and voltage differential. Close via spacing also figures into the equation [and .050" qualifies].



Werner

Future webinars:

September 15, “Fundamentals in Solder Joint Reliability”

September 16, “Root Cause Analysis of Solder Joint Failures”

September 17, “Solder Joint Reliability for Pb-Free Solders”

Future workshops:

September 24, IPC Midwest, Schaumburg, IL “Fundamentals in Solder Joint Reliability”







 





 



-----Original Message-----

From: [log in to unmask]

To: [log in to unmask]

Sent: Wed, Jul 29, 2009 11:09 am

Subject: [IPC-600-6012] Latent short question













I have an 8 layer assembled rigid flex board that developed a 800 ohm

'short' between two traces after 18 thermal cycles (-55 to + 65C)_.  The

short developed on the hot cycle (+65C) and we can occasionally get the

short back by moving it from room temp to +65. 



The short is between two  .010" traces / .015" spacing, the holes for

these traces are .050" centers all 1 ounce copper.  



We haven't ruled anything out, it could be  component related or FOD but

what has stuck with my customer is a
 corrective action this board shop

gave them about 6 years ago - at that time the board shop identified the

cause of latent shorts  to be from poor drilling - I'm having a hard

time wrapping my arms around poor drilling causing latent shorts - any

thoughts or comments on how this problem could be bare board related?





Thanks,

Pete 



 





Pete Menuez 

Supplier Quality Engineering Manager 

L-3 Communications Cincinnati Electronics 

7500 Innovation Way 

Mason, Ohio 45040 

[log in to unmask] 

513-573-6401 Voice 

513-573-6767 Fax