It’s hard to get excited about the introduction of a new probe for in-circuit test fixtures. After all, most test fixtures have hundreds of probes, and densely populated fixtures can sport thousands of them. In some companies where multiple test fixtures are used on a daily basis, probes are stocked as commodity items. As the owner of one of our local tire stores would say if he were selling probes instead of tires, “Probes ain’t pretty.”
Any test engineer will tell you that defective or intermittent probes account for most of the problems during board test. Whenever a board fails in-circuit test, it probably is the result of a malfunctioning fixture. Most likely, the test operator will perform a probe check of the fixture before retesting the board. Only if the fixture checks OK will the operator reject the board. And even then, it may be a false failure.
Of course, today’s boards present formidable obstacles for test-fixture designers. Now, boards are crammed with surface-mount components, fine- pitch ICs, and consequently, smaller test targets. Designing test fixtures is more difficult because of the limited access on these boards.
Well, the folks at Interconnect Devices (IDI) have introduced a probe that was specifically designed to address today’s in-circuit testing challenges. Dubbed ICT for in-circuit test, the probe features a patent-pending design that the company claims will outperform other spring contact probe designs. It is compatible with existing probe systems; current test fixtures will readily accept ICT probes.
What makes this probe different is its bifurcated design. It features a bifurcated barrel that is cut into four contact beams, which are coined to perfect center. When depressed, the bifurcated barrel beams guide the plunger to center while maintaining electrical contact.
This design offers a number of significant advantages. Topping the list is its pointing accuracy of ±0.00095″. With this pointing accuracy, the probe is able to contact smaller pads and vias. Also, the bifurcated design reduces the scraping and wearing that result from sideloading or biasing of the plunger.
The electrical resistance of the probe, according to the company, is the lowest in the industry. IDI conducted numerous tests to support this claim. In tests measuring the variation of resistance over 50,000 cycles, the probe consistently remained within 5 mW of nominal.
The design of the ICT seals out contaminants from getting into the probe barrel. This not only permits operation in dirty test environments, but also extends the life of the probe.
The company has compiled the results of beta-site testing of the probe and posted the performance reviews on its web site at www.idinet.com. On the web site, you also can play “what if” with an interactive Cost of Ownership Worksheet for the ICT probes. Interconnect Devices, (913) 342-5544.
Copyright 1998 Nelson Publishing Inc.
July 1998