Performance of the stud bump bonding (SBB) process in comparison to solder flip chip technology

In flip chip on board, a flip chip packaging technology, a number of assembly techniques have been proposed using different bump materials, different techniques for the bump application and various methods for the electrical interconnection. Among these, the Stud Bump Bonding (SBB) process, which is widely used in Japan also for high volume production, is very interesting for several reasons and therefore is discussed in this paper. The stud bump bonding process uses Au bumps which are applied mechanically on the wafer or on the chip using a thermosonic ball bonder enabling fine pitch bumping. The process works with available chips, having peripheral bond pads of a pitch down to 80 μm, and does not need an under bump metallization (UBM). The SBB process with Au bumps uses mainly isotropically conductive adhesive (ICA) joining. The adhesive is applied by dip transfer. In the present work the total SBB process is evaluated. Besides the bumping, the flip chip assembly process covering the dip transfer of conductive adhesive, the pick and place as well as the underfill process are investigated with special emphasis on process automation. The reliability evaluation concentrates on thermo-mechanical and corrosion effects. The SBB process is compared to solder flip chip technology using solder bumps which are applied by the stencil printing of ultra-fine-pitch solder paste