Hi Pete,
Could look into copper pattern causing differential press pressures
resulting in resin starved/glass rich areas in one area and areas of
higher resin content in others. As Dk depends upon this mix, could be
affecting at RF. Look through the stack and identify consistently high
copper density areas. Also, find out how many fabricator put into
daylight of press - if too many or with "soft" dielectrics, the pressure
transfer varies from outer to middle as does the heat transfer.
Best Regards,
Phil.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Pete
Sent: 22 March 2011 15:18
To: [log in to unmask]
Subject: [TN] Fabrication failures in one area of board?
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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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