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92 SMT007 MAGAZINE I MAY 2020 When potential process defects begin show- ing up underneath BGAs in electronic assem- blies, there are numerous failure analysis tests that can be used to troubleshoot process prob- lems. These investigative methods begin with non-destructive test methods and progress to destructive methods as some of the possible root causes are eliminated. After electrical testing has been performed, there are numerous inspection methodologies spelled out in the IPC-A-610 [1] to use in deter- mining potential assembly defects at BGA loca- tions. These inspection methodologies include visual inspection via a microscope and bore- scope, as well as X-ray analysis. The first level of BGA failure analysis is visual inspection with the aid of a microscope or borescope. Visual inspection criteria per the IPC A-610 can be found in the SMT portion of the IPC-A-610. In most cases, BGAs are inspected to see the uniformity of collapse along the outer row of the package, with special attention being paid to the corner locations. This can be done when the view is unobstructed via a microscope. The magnification and lighting will be crucial to seeing the outside row of the BGAs. As long as the flux residue has been cleaned and the conformal coating is not obstructing the view- ing area, criteria—such as the uniformity of the ball collapse, the distance between balls, and the distance from balls to any neighboring ungrounded surface—can be seen using visual inspection. The next level of visual inspection, which may, in some cases, allow for inspection into the third row of the area array device, will be via a borescope. A borescope, borrowed from the medical industry, allows for images Getting to the Root Cause of BGA Assembly Problems Knocking Down the Bone Pile by Bob Wettermann, BEST INC.

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