Effects of anchor pads in micro-scale BGA

Micro-scale EGA has attracted more and more interest due to their high performance/area ratio. This technology is essential for the next generation of portable devices, such as cellular phones, wireless terminals, palm computers, global position systems, and other hand-held devices. With the decrease of solder ball sizes, however, the reliability problem becomes the major concern for this kind of packages. Also with the decrease of solder volume, the function of self-alignment of solder is reduced in solder reflow process. One solution to these problems is introducing an anchor pad at each corner of packages, which is used only for mechanical connection. In this study, 3-D finite element models are used to access the effects of anchor pads to solder joint reliability of micro-scale EGA. Three configurations are considered here: normal 144 I/O EGA, 144 I/O EGA with anchor pads, and 144 I/O EGA without anchor pads. Two creep mdoels are considered for solder joint modeling. It was found that the maximum creep strain in critical solder joints is greatly reduced after introducing anchor pads at the corner. Therefore, it is a good option to introduce the anchor pads to improve the reliability of solder joints in micro-scale EGA.