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May 2014 • SMT Magazine 81 addition to existing structural tests would be a real gain. How did the move towards lead-free sol- der impact the test/inspection process? Did it entail a complete process change and present new defects that need rectification? The move to lead-free did present several challenges to the test sectors within SMTC. As you know, the transition to lead-free introduced many new materials to the assembly process, from chemistry to raw laminates that required elevated thermal cycles and tended to cause increased PCB warpage, leave harder residues, and chang component termination/surface fin - ishes. This transition introduced a set of defects around cracked joints or internal trace separa- tion on higher layer boards, test pad contact is- sues due to harder residues. Changes to our DFM and Test (DFX) rules required increased probe maintenance and required us to revisit compo- nent pad to test point clearances; in some cases, it drove increased keep out or cleaning that did not require this process before. Through the application of design of ex- periments (DOE), root cause corrective action (RCCA), and the introduction of second and third generation materials, these areas were able to be addressed. As a result, our design guidelines have been updated to reflect SMTC's recommendations for lead-free chemistries and are in volume production today at very high quality levels. Would you say that in-circuit testing has come to its limits in terms of board accessibil- ity and utilization flexibility, and that bound- ary scan is the logical successor or makes the most sense for achieving the highest possible test coverage? In-circuit test [ICT] is still the benchmark tool for component-level electrical testing, and in most cases, still provides a high level of cov- erage and access primarily though advances in fixturing and tighter tolerances. We see bound- ary scan/JTAG as complimentary test technolo- gies in combination with ICT to provide the required levels of coverage. While boundary scan is important, it misses discrete component testing and analog parts where the majority of the defects still occur today. On their own, they provide a piece of the puzzle; we believe the best solution is the continued use of JTAG within ICT. On lower-density products, we commonly look to lower-cost test solutions where ICT may not be appropriate or has an undesirable return on investment due to lower product volumes and higher mix products. In these cases, test so- lutions including AOI, flying probe (fixture-less ICT) or MDA can deliver a comprehensive and cost-effective solution to our customers. What about testing cost? Does it still have a significant impact in your process? Test cost is commonly viewed as being limited to the cost to perform the test on the manufacturing floor, but this is only part of the total test costs, and minimizing these costs may in fact increase the overall costs of the product over the entire supply chain. Since the purpose of test is to provide a level of quality both dur- ing manufacturing and out in the field, the ob- jective should be to minimize the total cost of quality (COQ). Minimizing the overall COQ for our customer is best practice for defining the process and test strategy. A typical product COQ will include the costs of the test itself, costs associated with pro- cess fallout/repair and re-inspection, product scrap costs, costs associated with test fallout/ repair and re-test and field failures. Our experi- ence has shown that field failures are at least four times more expensive to repair whereas early detection of defects upstream is a fraction of that cost. To minimize the overall cost of quality, de- fect detection should be driven up the supply chain, ideally to the point of use. An effective test plan utilizes the effective access to develop and address coverage gaps to allow early detec- tion of problems in, say, sub component qual- ity, and provide an efficient and effective closed loop to prevent escapes. This greatly decreases the risk to the customer and limits opportuni- ties for large field issues requiring recalls and associated costs. THE FUTURE oF TEST continues feATuRe