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78 SMT007 MAGAZINE I SEPTEMBER 2021 X-ray imaging prior to the removal of a BGA for rework will help the rework technician point out potential issues which may be chal- lenges to successfully removing and replacing the BGA. X-ray imaging of the actual BGA lo- cation, as well as the surrounding area, is used to confirm rework challenges such as the prox- imity of neighboring devices, starved solder joints, and solder balls causing electrical shorts. ese images can point to potential root causes for the BGA rework including broken bond wires, or the popcorning or delamination of the package. Furthermore, soldering anoma- lies such as head-in-pillow or graping defects, which may be causing intermittent connec- tions, can be the cause of the failure. Devices on the opposite side of the BGA location will determine potential problem areas due to heat effects of the re- work process. For example, if a BGA is underneath a shield, X-ray will help determine the loca- tion of the BGA and the neighboring de- vices, as well as the margins for getting a nozzle into the rework location (if using a hot air rework reflow source). X-ray imaging will also provide clues to the physical board prob- lems such as lied pads or solder that has wick- ed down the dog bone of the PCB due to mask damage, as well as other anomalies. Not only does X-ray imaging provide some clues prior to rework of some of the challeng- es that may lie ahead, but it also confirms that the rework was completed correctly. Aer vi- sual and endoscopic inspection has been com- pleted, the BGA rework location is inspect- ed by manipulating the controls of the X-ray to where the component of interest is seen in X-ray Imaging and BGA Rework Knocking Down the Bone Pile by Bob Wettermann, BEST INC. Defects are clearly visible with the use of X-ray inspection. (Image courtesy of Creative Electron.)

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