Increasing the bonding strength of chips and flex substrates assembly with a non-conductive paste by argon surface activation

Abstract

To increase the bonding strength of chips and flex substrates with a non-conductive paste, the Argon plasma was selected to perform the surface activation on the surface of flex substrates in this study. After flex substrates were activated with the argon plasma, several analytical methods were applied to verify the effective of argon plasma activated technology on the bonding surface of flex substrates, such as the contact angle was measured to verify the wettability of flex substrates, the ESCA was employed to determine the compositions on the surface of flex substrates, the AFM was conducted to examine the changes of roughness on the bonding surface of flex substrates, and die-shear test was used to evaluate the bonding force of chips and flex substrates assembly. With Appropriate bonding parameters, a sound bonding interface with sufficient bonding strength can be achieved for chips and flex substrates assembly combining with NCP and thermal compression bonding process. Neither porosity nor delamination was found at bonding interface between gold bumps and copper electrodes of flex substrates. The NCP was removed from the surface of the flex substrates, and then gold bumps bonded onto flex substrates directly. An electrical path between chips and the flex substrates was obtained. Die-shear forces were significant enhancement for chips and flex substrates activating with the argon plasma. A low contact angle can be determined on the surface of flex substrates for flex substrates activating with the argon plasma, indicating the containments can be removed by argon plasma, and then a clean bonding surface was achieved. For flex substrates subjected to the argon plasma activation, the residual NCP can be found on the both sides of chips and flex substrates that implying the bonding strength of NCP and flex substrates is even higher than the strength of NCP itself. These experimental results can be used to interpret that argon plasma activation is an effective scheme to improve the bonding strength of chips and substrates assembling with NCP and thermal compressing bonding process.