Issue link: https://iconnect007.uberflip.com/i/1243344
94 SMT007 MAGAZINE I MAY 2020 to be captured a few rows into the package. This visual inspection tool is especially use- ful when neighboring components are only a few millimeters from the perimeter of the BGA. Both direct and indirect lighting methods can provide the necessary illumination to capture meaningful solder ball images. The quality of the images obtained depends on the qual- ity of the light, the mirrors used on the end of the endoscope, the lenses, and the quality of the light going to the imaging area. In addi- tion to these visual techniques, X-ray imaging will also help to diagnose and troubleshoot the process being investigated. Transmissive X-ray imaging is a widely-used non-destructive imaging tool that allows for all of the solder and solder balls to be seen under- neath the BGA package. There are numerous anomalies and defects that can be seen through the use of X-ray inspection. X-ray inspection of the entire device field using a wide field of view generally is the beginning point of the BGA X-ray inspection process. This is followed by closer, higher magnification inspection of "areas of interest." Shorts and violations of minimum electrical clearance are common problems which can be measured and found using X-ray inspection. More subtle defects also show up on X-ray inspection, such as incomplete or inadequate wetting or head-in-pillow non-coalescing sol- der joints. Furthermore, measurements of the solder ball diameters and collapse height as well as sphericity, void percentage, and other attributes can be determined via careful X-ray inspection using higher-end X-ray equip- ment. Destructive testing could augment both the visual and X-ray inspection methods for Figure 1: Dye penetrant in corners of the BGA package indicating opens in the corner of the package.