The other 3 channels, do they perform to spec, or at least uniformly?
Ie, are all Channel 1's at the right level, Channel 2 is always 3dB
down, Channel 3 is 10dB low, and 4 is always dead?  Or is every board
different?

Is it possible that it was a design mistake in Channel 4, which is
causing it to not work?

RF transmitter, is it low enough frequency that some work with an
o-scope can be done, to determine where the signal starts to give out?
It sounds like it's sub-GHz, if it's standard FR-4 (or at least not many
GHz).

[I have to ask--as a board designer, I'm used to hearing "your board
doesn't work" only to find out a component was installed wrong, or some
wire was broken elsewhere in the system.  Maybe Channel 4 was populated
wrong?  Test setup failure?]

I'd think a curing issue would show up "randomly", since, if this board
isn't the same size as a panel, then the design was panelized and cut
out.

Shawn Upton, KB1CKT
Test Engineer
Allegro MicroSystems, Inc
[log in to unmask]
603.626.2429/fax: 603.641.5336


-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Pete
Sent: Tuesday, 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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