Performance of the Stud Bump Bonding (SBB) process in comparison to solder flip chip technology

In flip chip on board resp. flip chip in package 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 will therefore be discussed in the following paper. The stud bump bonding process is using 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 mum, and does not need an under bump metallization (UBM). The SBB process with Au bumps is using 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 & place as well as the underfill process is investigated with special emphasis on process automation. The reliability evaluation is concentrating on thermo-mechanical and corrosion effects. The SBB process is compared to solder flip chip technology using solder bumps which are applied by stencil printing of ultra-fine-pitch solder paste.