Novel Low-volume solder-on-pad for fine pitch Cu pillar bump

Novel low-volume solder-on-pad (SoP) process is proposed for a fine pitch Cu pillar bump interconnection. A novel solder bumping material has been developed for the 60 μm pitch SoP using screen printing process. Solder bumping material which is composed of the Sn3.0Ag0.5Cu (SAC305) solder powder and polymer resin is a paste material to perform the fine pitch SoP in place of the electroplating process. The Si chip and substrate with daisy-chain pattern are fabricated to develop the fine pitch SoP process and to evaluate the fine pitch interconnection. The fabricated Si substrate has 6724 under bump metallization (UBM) in 45 μm diameter and on 60um pitch. The Si chip with Cu pillar bump is flip-chip bonded with the SoP formed substrate using an underfill material that has fluxing features. Using the fluxing underfill material is advantageous since it eliminates the flux cleaning process and capillary flow process of underfill. The optimized interconnection process has been validated by the electrical characterization of the daisy-chain pattern. The development of fine pitch SoP and micro bump interconnection using screen printing process is newly reported.