SMT007 Magazine

SMT-Apr2014

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32 SMT Magazine • April 2014 As a result, semiconductor and electronics suppliers are constantly shrinking their prod- ucts and adding more functionality to comply with market demands. For CMs and EMS pro- viders, it means moving toward smaller form- factor boards populated with such advanced, but smaller component and device packaging as micro-BGAs, micro-CSPs, package-on-package (PoP), 01005s, and others. Finding the Defect and Saving the Design Conventional inspection methodologies on the assembly floor include using advanced X-ray and automatic optical inspection or AOI and continue to be at the forefront for most PCB designs. Yet, because these advanced inspection and analysis systems aren't able to deliver, a new- er form of inspection is making its presence known in our industry. We call the new form forensic analysis. Here are just a few examples of the extremely small flaws and defects that forensics can locate. • Micro hairline crack in a BGA ball (Figure 2) • Voids due to air gaps created inside the solder due to poor plating (Figure 3) • Trapped air bubbles between via walls (Figure 4) • Head-on-pillow defect in assembly (Figure 5) • Contaminated plating with air gaps on an ENIG PCB surface (Figure 6) Detecting Elusive Flaws and Defects An OEM might be completely unaware of a small defect or flaw that crept in during as- sembly or was inadvertently included during design/layout. In a number of cases, OEMs basi- cally throw up their hands and give up because they simply cannot find the problem; they start all over again, thus sacrificing thousands of dol- lars. But if there's an assembly error or even a miscue after the design is sent to manufactur- ing, forensics is standing by to uncover those potentially unsolvable issues that convention- al inspection failed to catch and unwittingly passed. Some of these defects could be hard to find and some are intermittent, which makes it difficult to catch or duplicate them for doing the root cause analysis. Take a PoP-populated PCB, for example. You determine that the pass rate and yields are extremely low; the product is not performing or is failing. A cross-section view of the PoP is taken to provide physical evidence and a root cause of the failure mode. Plus, the cross-sec- tion shows the failure site location, and then isolates it from suspected versus non-suspected devices. As shown in Figure 5, two BGA balls FOrENSiCS UNCOvErS ElUSivE DEFECTS aND SavES pCB DESiGNS continues fEATurE figure 2. figure 3.

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