Hi Marty! I have seen several RF designs which exhibit the same type of
behavior your are experiencing. Is the component's base soldered to the
board? The quality of that solder joint for grounding purposes can
sometimes be an issue. However, it is poor design practice and a
manufacturing nightmare (in terms of schedule and yields) to rely on a
"designed geometry" solder joint to produce a consistent, reproducible
electrical function. In the several similar RF cases I have worked on we
have found that the transceiver components were functioning at one end of
their specification parameters or that the pwb trace dimensions were
contributing to the performance variation.  Hope this helps, good luck.

Dave Hillman
Rockwell Collins
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Marty Brooks <[log in to unmask]>@IPC.ORG> on 03/28/2001 03:41:17 PM

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Subject:  [TN] RF Assembly Issues


We are experiencing a concerning variation from board to board in the
performance of our RF product.  We have investigated several causes of the
problem and are currently of the opinion that soldering quality of the
transceiver chip is the most significant contributing factor.  As an
example, on the last run of prototypes that was manufactured, the signal
frequency was at the upper limit of the allowable range.  We removed and
replaced the transceiver chip in-house and decreased the frequency closer
to
what we would expect.

I'm going to be making a visit to our contractor's facility next week to
investigate this problem and would like some feedback on possible causes or
process controls that I should look into.

The board is 4 layers, HASL finish, single side smt, solder paste used is
Alpha's UP78 no-clean.  The transceiver chip is a 20-pin device with
terminations flush along the bottom of the component.

Thanks for any advice.

Marty Brooks
Manufacturing Engineer
IDENTEC Solutions, Inc.
102, 1860 Dayton Street
Kelowna, B.C., Canada V1Y 7W6
Ph:(250)860-6567, Fax:(250)860-6541
www.identec.com

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