Reliability and analytical evaluations of no-clean flip-chip assembly

A process has been developed, qualified and implemented to replace traditional flip-chip (C4-Controlled Collapse Chip Connection) joining on ceramic carriers with a new no-clean technique. This important technical achievement overcomes existing cleaning limitations on attaching flip-chip C4´s at high melt soldering conditions. Previous no-clean assembly was limited to Direct Chip Attach (DCA) on organic substrates at low reflow eutectic (<300°C) soldering temperatures. Significant cost and environmental benefits have been realized with this process simplification. The new method uses a mild fluxing material and reducing atmosphere for flip-chip assembly. It is a tremendous advancement for mounting flip-chip C4´s with high lead content to corresponding copper pads at high reflow (>300°C) temperatures. The no-clean process enabled removal of cleaning steps which increased manufacturing efficiency and greatly reduced product cost. Also, elimination of chlorinated cleaning solvents has accomplished government mandated reductions on their usage. Assembly, analytical and reliability characterization has been performed to support this important development in flip-chip joining. These studies have provided a comprehensive understanding of process parameters, controls, reaction and yields while assessing component reliability. This thorough evaluation of no-clean assembly processing was critical to successful implementation of the breakthrough accomplishment