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62 PCB007 MAGAZINE I NOVEMBER 2021 Feature Interview by the I-Connect007 Editorial Team Alex Stepinski gives his thoughts on how test and inspection should be linked and reflects on how the process controls in fabrication are likely to change in the future. Barry Matties: Alex, as you know, there are two levels of test inspection: product and process. What is your philosophy around test and inspection? I think you have approached it differently. Alex Stepinski: e industry traditionally has relied on time zero testing. Defects that are 100% there, not latent defects; this is where things started in our industry. As time went on, methods were developed for latent defects. For instance, IBM originally started decades ago doing CAF testing, shorts testing in cham- bers. ey simulated reflow testing in cham- bers. As a big OEM, this drove reliability to their products. Gradually, these philosophies spread through the industry and more methods have been Alex Stepinski: A Philosophical View developed. Now, we do this OM test method on IPC D coupons for via reliability. e CAF method hasn't improved too much. It's slow and steady, however, it's much more preva- lent. But time zero is still what most people do. You generally do reliability through regression. It's not direct measurement, so there's a lot of inferences that need to be made; with the time zero work, you have a probe tester and a fixture tester. It runs against your parameters, what- ever they are—whether they're some advanced military parameters, IPC standard parameters, or something special. is is what people do. My philosophy is to rely less on this and more on sensors through- out the process to measure things non-destruc- tively, then build a model for how you're going to perform, and just validate against the model. It's the next step slowly happening worldwide. For instance, we've had 2D AOI for many years. Sometimes, this is complemented with electrical tests. Now, you start to see more 3D AOI happening. You see them putting more sensors on the AOI equipment for direct mea- surement. en, you also have the traditional signal integrity testing. e challenge with that

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