Finding faults in circuit card assemblies
Greg Reed, Contributing Technical Editor -- Test & Measurement World, 12/1/2006 2:00:00 AM
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Bill Curry President, Huntron Courtesy of Huntron. |
Testing circuit card assemblies (CCAs) requires a delicate balance between performing exhaustive fault detection and reining in total assembly cost. With shrinking card real estate accompanied by denser designs, having a well-stocked toolbox may be the test technician’s best defense. Bill Curry, president of Huntron for the past 21 years, offered some time-honored solutions in this exclusive interview.
Q: Which diagnostic technologies do you typically use to zero in on problem CCAs?
A: Our main core test technology is analog signature analysis (ASA). The products are called trackers. ASA is a “power-off” technique that applies a sine wave (AC) stimulus to a component, creating a voltage versus current signature. This technique allows a trained technician to locate damaged or marginal components.
ASA is used as a complementary test where functional test diagnostics typically end—at an ambiguity group or cluster of components. The technician changes to ASA test to complete the diagnostics and troubleshoots to find the component or components that need to be replaced.
Also, open-architecture robotic probers assist technicians in testing CCAs using ASA technology as well as interfacing with scopes, meters, RF, or other technologies. These can be used to automate what would otherwise be manual guided probing, increasing both accuracy and productivity of the technician.
Q: What are some inspection challenges raised by lead-free assembly?
A: There are obvious visual inspection and reflow process related issues. Our role here has been to provide tools to help the operator or technician to see more effectively. In the DoD’s gold disk program, 38% of all repairs are done using only visual inspection. As parts become smaller, boards become denser, and the inspection of lead-free is added, our customers have asked for help in finding new visual inspection tools.
Q: Since manufacturing processes and equipment differ, is it really possible to automate the repair and rework of CCAs?
A: Repair, rework, and diagnostics, by definition, means one at a time. So, to automate in the same way you automate a production line, “no.” How-ever, there are areas or steps in the repair and rework process where automation can make a huge difference.
Standard benchtop instruments are hand-probe or clips-and-cable testers. These testers become more effective by adding robotics systems. If the technician needs to be on pin 137 of a 200 pin device, automation can ensure that accuracy. This allows highly skilled labor to spend time diagnosing problems, not manually probing or using clips and cables.
Q: How does Huntron participate in design for test activities?
A: First, we recommend the use of boundary scan, a testing method that offers the advantage of structural device, board, and system-level access throughout a product’s life cycle without the need for any invasive nail fixtures common to in-circuit test. The result is a reduction in the cost of testing and an increase in test coverage.
Another option is using robotic systems and workstation software for fault injection, first article testing, and debugging. Robotic probing test systems provide a fixtureless test that can deal with short production runs and board revision changes.
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