From the PWB point of view we see changes in capacitance associated with
material damage caused by assembly and rework. Frequently crazing,
cohesive failure and delamination occur in the central zone of the PWB.
Material degradation is more prevalent in lead free applications. Some
of the high Tg, phenolic cured epoxy systems have a propensity to
material damage.

Could material damage account for the vagrancies you are seeing?


Sincerely, 
Paul Reid 

Program Coordinator 
PWB Interconnect Solutions Inc. 
235 Stafford Rd., West, Unit 103 
Nepean, Ontario 
Canada, K2H 9C1 
613 596 4244 ext. 229 
Skype paul_reid_pwb 
[log in to unmask] <mailto:[log in to unmask]> 


-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Pete
Sent: March 22, 2011 11:18 AM
To: [log in to unmask]
Subject: [TN] Fabrication failures in one area of board?

We are trying to get an RF board functioning, and are having
difficulties in the 
same area of a couple boards.  The circuit turns on, but with drastic 
performance differences

This board has 4 identical TX Channels, Channel 1, at the edge of the
board 
works every time, but as we move inward, we experience more failures.  
Channel 4, at the center of the board will not perform properly on any
board.

A visual examination doesn't show any differences that might impact 
performance.  The soldering process looks OK.

Is there something that could likely vary in the fabrication process
that might 
cause this?  It's (supposed to be) a standard 170Tg, non-dicy, RoHS fab.

High copper density, but the center channels are near an area of less
copper 
density.  Could an epoxy curing variation occur, that might impact
getting a 
consistent dielectric result?  What should I be looking for?  These
boards were 
not ordered from our qualified vendor, and I have some concerns.  We had

issues with them before.

Pete

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