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112 SMT007 MAGAZINE I MARCH 2019 and replacement of the component, inspection of the newly placed component—whether it is a new component or a reballed component— needs to take place to ensure the replacement components' interconnections. X-ray inspection of BGAs post rework (Fig- ure 1) require inspection time to determine the acceptability of the solder interconnection. A "scan" of the BGA area from a far enough field of view to see the entire array is a good way to begin the BGA post rework inspection process. After this far field of view scan, the technician should zoom in to get a good visual indication at close range of the ball shape, size, and con- sistency. Starting at one corner, the technician manip- ulates the X-ray back and forth over the array until all of the balls have been scanned. More advanced X-ray systems can be programmed with acceptance/reject criteria to more fully automate this process. More automated X-ray systems can scan for concentricity (i.e., ball shape), ball diameter, pitch, and other param- eters (Figure 2). Summary Many of today's designs include a BGA or area array package. When this component needs to be swapped out for rework, the in- spection of the replaced BGA may include both visual as well as X-ray inspection. Following the customer agreed-upon inspection criteria, there may be visual, basic X-ray inspection, or more advanced automated inspection of the reworked location may need to be made to make a go/no-go determination of the inter- connection. SMT007 Bob Wettermann is the principal of BEST Inc., a contract rework and repair facility in Chicago. To read past columns or contact Wettermann, click here. Figure 2: Automated BGA X-ray inspection post-rework can catch a missing ball.