Advancing Electronic Packaging Using Microsolder Balls: Making 25-nm Pitch Interconnection Possible

Electronic packaging technology has advanced in the direction of integrating diverse components into one package to satisfy market demands for multifunctionality as well as portability. For this reason, various packaging structures have been introduced, such as multichip modules, package on package, package in package, and eventually three-dimensional (3-D)-chip stacks. All of these approaches require increased input/output (I/O) counts, resulting in fine-pitch assembly. Therefore, the most critical issue in current electronic packaging is how to assemble fine-pitch components while avoiding an electrical short circuit in the x-y direction. Much research has been done on fine-pitch interconnecting technology using microsolder balls smaller than 200 nm, but the problems of solder-ball handling and low yield remain. In addition, there have been few reports so far about the fine-pitch interconnection below 25-nm pitch using microsolder balls. Three-dimensional-chip stacks require an additional microsolder and copper hybrid bumping and patterning processes on through silicon via (TSV), which increases the processing cost.