Influences of argon plasma cleaning on the die-shear force of chip and copper/polyimide flexible substrate assembly using a non-conductive film

A non-conductive film (NCF) and a thermal compression process were combined to assemble a chip onto a flexible substrate. To achieve direct bonding and to enhance the adhesion of a chip on the flexible substrate with NCF, argon plasma was used to clean copper electrodes over a flexible substrate. For flexible substrates which received argon plasma cleaning, low contact angles were obtained, and gold bumps directly contacted copper electrodes to form active input/output (I/O) paths, indicating the contaminants on the flexible substrate were removed and a clean bonding surface could be achieved. Neither delamination nor porosity was observed at the bonding interface between the NCF and copper electrodes. A sound bonding interface with satisfactory die-shear force was achieved. The argon plasma cleaning led to a significant improvement of the die-shear force of a chip bonded onto the flexible substrate using NCF.