A thermode bonding process for fine pitch flip chip applications down to 40 micron

As the density of electronic packaging continues to increase interconnection technologies for finer pitches down to 40 micron are required. Solder joining is still the most common technology for flip chip assemblies. Stencil printing is appropriate down to pitches of 200 micron to create solder balls. For finer pitches smaller solder volumes and new assembly processes are needed. In this paper a cost effective maskless bumping technique to create thin solder caps and a fast thermode bonding process are presented. For the thermode bonding process in a first step noflow underfiller is applied on the substrate e.g. by stencil printing. Using a flipchip-bonder the chip is soldered on the substrate by fast heating of the tool and low pressures. This work is focused on the assembling process of flip chips with pitches down to 40 micron on different substrate types like silicon and flexible substrates. The effect of the small gap due to the thin solder caps and the increased influence of the formation of intermetallic compounds are studied. Results of reliability investigations such as thermal cycling and temperature humidity testing are shown.