Issue link: https://iconnect007.uberflip.com/i/1406534
80 SMT007 MAGAZINE I SEPTEMBER 2021 a large field of view. e technician then ma- nipulates the X-ray system to where numerous solder balls can be seen on the screen as the rows are scanned back and forth. e techni- cian reviews the overall ball sizes to make sure they are consistent in size and shape. Anomalies such as small balls (Figure 1), oversized balls (Figure 2), and misshapen balls all will be caught by an experienced X-ray oper- ator. Especially critical to observe are the cor- ner solder ball locations. If these locations are full and round, then as a rule the overall ball collapse is sufficient. Smaller- sized balls may be a direct result of solder wetting down a dog bone pattern where the mask has been damaged, or in cases where a thermal via has wick- ed the solder down into the via hole. Oversized balls may be a result of neighboring balls hav- ing their solder squirt over to a neighboring ball location. Obvious anomalies like sol- der shorts, missing balls, or mis- shapen balls will also be picked out during this part of the inves- tigation. At this field of view the technician will next investigate areas around the device of inter- est. Skewed components, sol- der balls, or handling damage can all be picked up by examining the X-ray image. Solder may have "squirted" out of neighboring locations; such is the case when the board has been con- formally coated or neighboring or mirrored de- vices that are underfilled also show up clearly on X-ray images. Once this larger field of view inspection has been successfully completed, the BGA technician zooms in to review de- tails about the solder balls and their collapse. e technician is looking for misshapen balls, smaller or larger balls, a high voiding percent- Figure 1: Undersized solder balls. Figure 2: Oversized solder balls. Figure 3: Solder voids during close up (large field of view) inspection.