Re: repairing broken traces on a PCB


Frank Bemelman wrote:
"Spehro Pefhany" <speffSNIP@xxxxxxxxxxxxxxxxxxxxxxx> schreef in bericht
news:3i0vv195e58n088sddpu25m71tunhsf6hh@xxxxxxxxxx
On Fri, 24 Feb 2006 22:35:36 +0100, the renowned "Frank Bemelman"
<f.bemelmanq@xxxxxxxxxxxxxxxxx> wrote:

"samIam" <him@xxxxxxxx> schreef in bericht
news:pzHLf.17$Ry.12@xxxxxxxxxxx
I have broken traces on a PCB I recently etched. Just a handful ...

I am wondering how some of you repair them. Trying to tap into your
body
of experience with this.

More interesting is to hear about experiences in finding hairline
cracks in tracks.

I rather enjoy paying for 100% electrical inspection. Let the machines
find the problems.

Well, I have a board here worth $100 perhaps, that certainly passed
all tests, but fails now. When I bend it, it works. I should add, that
after bending it ~15 times it stayed in failure mode. I found one
decoupling cap standing in the air, some flux rubbish (?) between a few
legs of a TQFP, but nothing that causes the failure. Ditched it
already.

I wonder what the dropout percentage is for tested boards, and if
it is worth paying for. Difficult to anwer of course, I simply have
excellent experience with untested boards, even with 7mil tracks/distance.
Seems that more goes wrong with the assembly of parts, imo
.
--
Thanks, Frank.
(remove 'q' and '.invalid' when replying by email)

Hi

I debugged a similar intermittant failure a few years ago: Visually
inspected the PCB and solder joints with a microscope, found nothing.
Touched up all joints with a soldering iron anyway because I couldn't
see under the legs, no effect. As the via's weren't covered over with
solder resist I reflowed them with a little extra solder, this fixed
the problem. I had the via cross-sectioned and found cracks in the
barrel. The PCB manufacturer was drilling the via's with a 4 board
stack-up, which meant the bottom board was suffering burring from
excessive heat on the drill bit going through the boards above. They
changed it to drilling single boards and when we cross-sectioned the
new batch we had picture perfect via's.

Alan
www.electronic-eng.com

.

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