Effects of Ceramic Ball-Grid-Array Package’s Manufacturing Variations on Solder Joint Reliability

The effects of manufacturing variations on the reliability of solder joints between a ceramic ball grid array (BGA) package and a printed wiring board (PWB) are investigated. Two cases are studied, namely, with and without spacers between the BGA package and the PWB to maintain the solder joint height. Manufacturing variations considered include changes in solder volume, joint height, and pad size. To evaluate the effect of manufacturing variations on reliability, every possible solder joint profile is first derived. The maximum strain is calculated next. Finally, the fatigue life is predicted. The calculations show that these manufacturing variations change the joint profile, and subsequently affect the fatigue life. Since the package is heavy, the use of spacers is necessary to control the solder joint height for reliable connections, and to maintain a large gap for cleaning. The solder joints formed with the use of spacers, may have convex, cylindrical or concave profiles. The concave solder joints are preferred, since they have long fatigue lives and are less sensitive to the manufacturing variations. For the convex solder joints, their fatigue lives are strongly affected by the joint height variation caused by package warpage and by the combined effects of solder volume and pad size.