Carl -- have you thot about an epoxy dot as strain releif? cheap
insurance perhaps, tho a tru RC is more elegant -- cheers -- Ian
Carl VanWormer <[log in to unmask]>
Sent by: TechNet <[log in to unmask]>
08/26/2010 10:38 AM
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[TN] soldered battery wire - breaking problem
We produce a small module that is powered by a small battery in a
plastic battery holder that has the standard red & black wires, which
solder into two holes in in our PC board. After initial functional
testing, the board (with battery holder attached) is sent out for
conformal coating, then the boards are re-tested before inserting into
our plastic enclosure. The most recent run of 50 boards returned from
conformal coating with about 10 broken wires, with the break leaving
Copper colored ends visible where the strands were ripped from the
solder filled mounting hole. Since this problem is new, something in
the assembly process (or conformal coating process) must have changed.
Once the battery holder and board are assembled into the plastic case,
there is no more strain on the wires, so this is only a production and
handling problem.
In reviewing the recent wire solder joints, compared to 2 samples from
previous runs that did not exhibit this problem, I noticed that the
"bad" assemblies had been heated enough to flow solder up into the wire
strands, while the "good" assemblies had solder on the wire ends on the
back side of the board, but the solder did not flow up the strands on
the front side of the board. I'm guessing that the fused wire strands
are stiffer, and this is the cause of the breakage during handling for
the conformal coating process.
Many of us "old timers" remember the classic strain relief approach used
in the battery wires for transistor radios, where the two wires were
laced through a strain relief hole before being soldered onto the board.
Since our board has no room for the extra strain relief holes, and since
we have made hundreds of these things without problems, I'm looking for
suggestions on the best approach to solder the wires onto the board to
help eliminate the problem.
Are there any IPC standards for attaching battery holder wires?
Thanks,
Carl
Carl Van Wormer, P.E., AE7GD
Senior Hardware Engineer
Cipher Systems
1800 NW 169th Place, Suite B-100
Beaverton, OR 97006
Cipher Systems (503) 617-7447 x 5163
Direct Line (503) 425-5163
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