Novel Low-Volume Solder-on-Pad Process for Fine Pitch Cu Pillar Bump Interconnection

Abstract

Energy Harvesting Devices Research Section, Information & Communications Core Technology Research Laboratory218, Gajeong-ro, Yuseong-gu, Daejeon 305-700, Korea(Received June 10, 2015: Corrected June 17, 2015: Accepted June 19, 2015)Abstract: Novel low-volume solder-on-pad (SoP) process is proposed for a fine pitch Cu pillar bump interconnection.A novel solder bumping material (SBM) has been developed for the 60 µm pitch SoP using screen printing process. SBM,which is composed of ternary Sn-3.0Ag-0.5Cu (SAC305) solder powder and a polymer resin, is a paste material to performa fine-pitch SoP in place of the electroplating process. By optimizing the volumetric ratio of the resin, deoxidizing agent,and SAC305 solder powder; the oxide layers on the solder powder and Cu pads are successfully removed during thebumping process without additional treatment or equipment. The Si chip and substrate with daisy-chain pattern are fab-ricated to develop the fine pitch SoP process and evaluate the fine-pitch interconnection. The fabricated Si substrate has6724 under bump metallization (UBM) with a 45 µm diameter and 60 µm pitch. The Si chip with Cu pillar bump isflip chip bonded with the SoP formed substrate using an underfill material with fluxing features. Using the fluxing underfillmaterial is advantageous since it eliminates the flux cleaning process and capillary flow process of underfill. The optimizedinterconnection process has been validated by the electrical characterization of the daisy-chain pattern. This work is thefirst report on a successful operation of a fine-pitch SoP and micro bump interconnection using a screen printing process. Keywords: solder-on-pad, fine pitch bumping, micro bump interconnection