SMT Unlimited

When contract manufacturer SMT Unlimited L. P. ran into a high failure rate on a densely populated telecommunications board, Hom-Ming Chang, Vice President of Test Engineering and Information Systems, wasn't sure what he could do to solve the problem.

"We really don't have boundary scan (IEEE 1149.1 JTAG) expertise on our staff here," Mr. Chang said. "So we turned to Ensure DFT to help us and they developed a test program for us that's been very successful. In one case, we've gone from having an unacceptably high failure rate to a failure rate close to zero. I'd say that was very successful."

The board in question was densely populated with fine-pitch integrated circuits (ICs) and ball grid arrays (BGAs). Physical access to test points and to many of the devices themselves was nonexistent. As a result, SMT's in-circuit test (ICT) equipment could not be used to locate and diagnose the problems that were causing the high failure rate.

"We use ICT equipment extensively, but for some boards, we just don't have the access that an ICT system needs," Mr. Chang explained. "That's when we turn to boundary scan. We use ICT and boundary scan as complements to each other and that has worked very well for us. With more and more ICs having boundary scan cells and the increasing density of board designs, we are turning to boundary scan more often. And whenever we use boundary scan, we turn to Ensure DFT."

The boundary scan test program developed and implemented by Ensure DFT personnel using the ASSET boundary scan test and in-system programming system was able to locate many of the opens and shorts that were causing problems on the telecommunications board. And when the test program could not pinpoint the exact failure, the ASSET debug capability was used to troubleshoot the board until the problem was fixed. As a result, the yields on this particular telecommunications board have increased dramatically.

SMT has run into similar problems with other designs, most notably a densely populated board for a laptop computer that featured active components on both sides of the board. In this and successive instances, the relationship with Ensure DFT has paid off handsomely.

"We don't necessarily want to develop in-house boundary scan expertise, but every time we need help on a project, Ensure has come through for us. They have been very responsive and worked very hard to assure our success," Mr. Chang concluded.

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