Investigations on Fluxless Flip Chip and Chip-on-Substrate Assembly using solder joints under different atmospheres in a vacuum/overpressure Solder Reflow Oven

摘要

New applications in the field of optoelectronic and power module packaging as well as environmental concerns lead to a growing interest in fluxless solder assembly processes. For the successful realization the metallurgy of the solder joints and the surrounding atmosphere are important factors. The scope of this paper is to investigate the influence of the atmosphere and pressure during reflow soldering on the resulting solder joints. The Joint geometry as well as the solder surface and the occurrence of pores in the solder will be analyzed. The Flip Chips will be positioned using a simple pick and place tool. Using the self-alignment mechanism of the solder, cost effective flip chip assembly with high accuracy can be realized, as the process requires only coarse prepositioning. The subsequent reflow processes will be performed in nitrogen, hydrogen and activated nitrogen. The resulting matrix of experiments leads to the determination of optimum process parameters for best soldering results.