[sdiy] Importance of electrical test at PCB manufacturing?

[cheater cheater]

> Dave (only been doing this as an engineer or manager since 1982, so what do
> I know?) Manley

Dave, are you saying in 27 years of that, you've never come across
someone who wanted to rip you off or push gear that didn't meet your
expectations but satisfied contract fine print?

I've had people trying to pull contract loophole bs on me several
times a year since.. well, just about forever! Just today is the
latest one, actually! Beware of contracts :P

D.

On Wed, Oct 7, 2009 at 4:38 PM, Dave Manley <dlmanley at sonic.net> wrote:
> Colin f wrote:
>>
>>
>>>
>>> One thing I have done in the past, when a proper test point is not
>>> available, is to pull up the design files and locate a via which will give
>>> me access to the point in circuit. With more complex boards there is almost
>>> always a via to tap in at...
>>>
>>
>> Was just about to say the same thing...
>> I would add putting a silkscreen label next to vias that carry potentially
>> useful troubleshooting signals will only cost you a few minutes when
>> laying
>> out a board, and could make life much easier at repair.
>
> Also, make sure you do not have soldermask over your test vias.  It also
> helps to set your via size large enough to solder a fine wire into.  Then
> you can clip a scope probe to the wire.  It also makes rework easy.  If your
> board is large also put tenth inch posts connected to ground spread around
> your board so you always have a place to clip your scope probe's ground
> lead.  If you are running at very high frequencies, you may want a ground
> pad next to any high speed signal you want to probe, so you can minimize the
> length of the probe's ground lead.  Probe manufacturers often make special
> ground clips that fit directly to the tip of the probe, or you can get
> creative with a paper clip bent into the proper shape.
>
> In the 'old' days in my telecom equipment work we were required to put
> dedicated test points, a square pad 5-20 mils on a side, on every net for
> automated board test access - this was for 'bed of nails' testing.  The PCB
> layout guys did not always appreciate having to place all these pads.   The
> boards were tested in a clam-shell that could simultaneously probe the top
> and bottom of the board.  Later, as the density of the boards became greater
> and there was not always room for dedicated test points, the test technology
> advanced to where they could directly probe vias.  The PCB guys liked this
> option.  :-)  The test vias were a little larger with no solder mask.  Part
> of the board release process required testability analysis that guaranteed
> there was complete test access to every node.  There are innovative test
> techniques for BGA devices, one which puts a metal plate over the device and
> drives it with a high frequency signal that gets capacitively coupled
> through the device, through the balls, hopefully through solder, and then to
> the trace, where the signal can be detected.
>
> Dave (only been doing this as an engineer or manager since 1982, so what do
> I know?) Manley
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