building a custom test fixture ?

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[FIXME: more tips on testing electronics, and building test jigs to help test them, need to go here ... pointers to test tools from simple LEDs to spectrum analyzers ...]

Subject:	[PROTEL EDA USERS]:  Test fixture design
From: Bob Puckette  on 2000-08-23 11:07:57 AM
Please respond to "Association of Protel EDA Users" <proteledausers at techservinc.com>

I've come up with a cute way to generate pogo pin test fixtures.
It's been working so far, but I'd like to see if anyone has any
contructive criticism for the scheme.

It goes like this:

1. Take a copy of the final artwork and delete everything but
   the tooling holes and the test pads.

2. Do a global change to change all the test pads into thru holes
   that will accomodate pogo pin sockets.

3. Route all the pogo pin sockets to whatever you test with on a
   bigger board that the production board. This is an easy job for
   the auto router.

4. Have a cheap quickturn fab (I use PCB Express) make two copies
   (a minimum order) of the board. The idea is to use stand-offs
   to make a pogo pin block out of the two boards. The pogo pin
   sockets will be held reliably in parallel by the sandwich of
   the two boards.

5. Cram rod stock through the tooling holes and, viola, you have
   guaranteed registration of all the pogo pins to the DUT.

6. One of the test boards is populated with connectors, and whatever
   test circuit you want up close to the board. My designs usually
   have a bunch of connectors to an Agilent data acq system, and a
   bunch of relays.

This seems to me to be easier than getting the pogo pin block machined
and then wiring point-to-point to the testhead.

Any comments....

Bob Puckette
345 SW Avery Ave
Corvallis OR, 97333

541.752.9000

The traditional test fixtures have individual wires run from each pogo pin to the test instrument I/Os. (see "Getting On-Board ATE Test Fixtures" http://www.evaluationengineering.com/archive/articles/0304/0304ATE.htm by Tom Lecklider for some nice pictures ).

More recent "wireless" fixtures have a "test" PCB, similar to the one described above, but with traces on the PBC running from the PCB to the test circuits, which may be on the same test PCB. See "Wireless Test Fixture Considerations" http://www.ectinfo.com/files/resource/technical/wireless_test.html by Gary St. Onge and Jeff Sendzicki , CIRCUITS ASSEMBLY, June 1998

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