Core metal solder bumps for flip chip technololgy

: Zakel, E.; Nave, J.; Eldring, J.

Abstract
The invention relates to a solder bump containing an inhomogenous material composition, in particular for connecting terminal area metallizations of different electronic components or substrates in flip chip technology, and a process for producing such a solder bump. The invention is characterized by the fact that a solder bump according to the invention consists of a high-fusion solder bump core determining distance on which a layer of preferably low-fusion solder material is placed. The conditions required for soldering, e.g. solder deposit, bump height and soldering temperature, are thus all combined in the solder bump according to the invention. The low-fusion solder material also permits a reduction in the bonding forces and a self-adjustment in the molten state during soldering. The application of the solder bump core material and the solder material with software-supported mechnical bumping processes is extremely flexible and permits a fast and low-cost production of flipchip b onded prototypes and small batches. In particular, the invention also obviates the production of technologically complex solder deposits on the substrate, which, in the case of mixed SMD flip chip configurations, has the added advantage that the previously required process step involving the planarization of substrate solder bumps can be omitted.