A study to stencil printing technology for solder bump assembly

In general, the stencil printing manufacturing in pre-WLCSP (wafer-level chip-scale packaging) is able to be integrated by 7-step processes, including two masks and one set of stencil plate. After the formation of solder ball, the specified professional probe card is needed to verify whether the electric functions of this packaged IC are good. After this step, the wafer grinding, the wafer cutting, the chip choice and the final test (F/T) are gradually adopted to proceed. Finally, due to the customer´s need, the shipping package type to customers is, generally, tray or tape and reel. Although the stencil printing technology can provide the mass-production capability, the mainly existing problems of this technology are the quality of manufacturing steel plate, the coating operation for solder paste, and the flatness of wafer surface. These issues usually constrain the minimization of the size of the solder ball and the pitch. Thinking to solve these issues, this package technology is still feasible in assembly competition.