PCB007 Magazine

PCB007-Mar2021

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54 PCB007 MAGAZINE I MARCH 2021 Although electrical testing provides a bene- ficial safeguard against an electrically inferior product reaching a customer, it does require adherence to critical processes. One of those processes is the inspection for witness marks or pin marks. e caveat of electrical test is that it needs to be done but at the same time, optimally, there should be no evidence it was performed. is can be a difficult process, es- pecially on some of the more delicate finishes such as immersion silver or so gold. e hor- rors of a complex multilayer order scrapping because of one stuck test pin during electri- cal test keeps sales personnel awake at night. erefore, a robust inspection process is nec- essary. In the past this was not as critical, as bare copper is ro- bust and HASL could easi- ly be reworked. However, as surface finishes have advanced and pad sizes reduced, a stuck fixture pin or overly aggres- sive flying probe compression can be catastrophic. In Figure 1, we see an example of severe damage caused by a malfunc- tioning test fixture. In most cases this scenario is fatal to the product. A live inspection process is the most successful approach to minimizing loss due to test damage. is is not just limit- ed to inspecting the product (which we do) but must include steps prior to that before prod- uct is even tested. Although this is more crit- ical with fixture testers, inspection of the test probes, clamping mechanism, and automat- ic handlers (if applicable) should be inspect- ed prior to testing on flying probes as well. For fixture testers it becomes more in-depth. First, you have the fixture itself which, depending on the scenario, may be a new build or an older repeat part where the fixture was stored for a length of time. is requires inspection of the fixture for missing or bent pins, faulty assem- bly, or damage incurred during storage. Next is the fixture integration to the fixture tester. Homing in on the Target Testing Todd by Todd Kolmodin, GARDIEN SERVICES USA Figure 1: Fixture damage.

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