Designed experiment to assess the surface mount attachment reliability of 14 mil pitch (1000 I/O) underfilled DCA

To accommodate increasing I/O and maintain die sizes at as small as practicable levels, the use of area array solder bump flip chip is increasingly being used to bond large ASIC and microprocessor devices to a BGA substrate. In conjunction with thermal cycling, an orthogonal array design with different combinations of assembly choices and underfill materials has proven useful in screening material and assembly parameter choices for these high I/O flip chip applications. Preliminary failure mode analysis (FMA) of assemblies subjected to thermal stress was carried out using metallurgical cross sections and CSAM examinations of the failed devices. Underfill delamination from the chip surface is the primary cause of failure, even though several other failure modes were also seen. The highest characteristic lives were found using the thin film applicator (TFA) technique in combination with underfill A. Reducing flux residues below the level found using the TFA technique did not significantly improve performance.