Issue link: https://iconnect007.uberflip.com/i/288471
34 SMT Magazine • April 2014 are shown with a head-on-pillow defect, which causes an intermittent connection. An inter- mittent connection refers to a faulty connec- tion existing between and among a BGA's balls. This is among the top and most prevalent issues associated with BGAs and micro-BGAs, which is preventable if OEMs select their EMS providers properly with due diligence. Forensics is also known as "destructive in- spection." In this case, an assembled board is cut apart along with its components so that in- spectors can look inside it via SEM or scanning electron microscope and/or cross-section image to start their detective work. Cross-sectioning is a key part of this failure analysis. It provides the physical evidence of failure mode and site location along with empirical measurement, as well as isolates suspected versus non-suspected devices. Forensic analysis uncovers an innumerable number of defects or failures that conventional inspection cannot. At the board level, it inves- tigates thickness of Cu plating on the through- holes and vias; if it's a gold immersion surface board, it verifies out the thickness of the gold plating to determine whether or not the ade- FOrENSiCS UNCOvErS ElUSivE DEFECTS aND SavES pCB DESiGNS continues fEATurE figure 4. figure 5. figure 6.