At 09:23 PM 11/20/2016, you wrote:
>We occasionally find an open PCB trace (or perhaps via). Of course, the
>problem is on an inner layer. We can tell from continuity measurements
>that we have a problem between one via and the next. But where is the
>break? At one of the vias, on the trace? Is there a tracing device where
>we can inject a signal at a via and then follow it down the trace? I've
>seem something like this for tracing cable pairs in telephone cables. Is
>there something like this to find a problem in a PCB?
>
>Thanks!
>
>Harold

There's the BFI (Brute Force and Ignorance) method- just check continuity
at untented  vias or scratch through the solder mask like an animal until
you find the break. Get the PCB artwork up on the screen, divide and conque=
r.

If it's a bad via, consider strongly discarding the board and maybe the
entire batch. Bad vias have a way of multiplying (it's usually due to bad
controls at the PCB maker which causes cracks at the edges of the hole-
it's easy for there to be many marginal vias which pass 100% test but open
up later or under temperature). Broken traces are usually due to=20
sloppy handling
and are cause for reconsidering the supplier next order, but not as much
immediate concern.

--sp =20

--=20
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