Argon plasma was selected to perform the surface activation on flex substrates in this study. The argon plasma activation was expected to remove the surface contaminants, and then to reduce the bonding barrier between flex substrates and the non-conductive paste (NCP). The bonding strength of chips and flex substrates assembly was thus improved. The reliability of chips and flex substrates assembly with NCP was also verified, including high temperature storage (HTS), high temperature/high humidity (HT/HH) and pressure cooker test (PCT). After flex substrates were activated with argon plasma, several analytical methods were applied to verify the effective of argon plasma activated 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, an integral bonding interface with sufficient bonding strength can be obtained for chips and flex substrates assembling using NCP and thermal compression bonding process. Neither porosity nor delamination was found at bonding interface between chips and flex substrates. The NCP can be removed from the surface of flex substrates during thermal compression bonding process, and gold bumps bonded onto flex substrates directly. In contrast to low die-shear forces for flex substrates without argon plasma activated, the die-shear force was significant enhancement for chips and flex substrates were both activated with argon plasma. A low contact angle can be determined on the surface of flex substrates, indicating the containments can be removed by argon plasma, and then a clean bonding surface was achieved for flex substrates activating with argon plasma. After die-shear test, the NCP was peeling off from the surface of flex substrates for flex substrates without activating with argon plasma, indicating the bonding strength of NCP and flex substrates is poor. For flex substrates subjected to argon plasma activation, the residual NCP can be found on the both sides of flex substrates and chips, indicating 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 IV argon plasma activation was an effective scheme to improve the bonding strength of chips and substrates assembly using NCP and thermal compressing bonding process. After specimen subjected to the HTS test, the die-shear forces of chips and flex substrates assembly were decreased slightly with increasing the durations for they were activated with argon plasma, and the die-shear forces for flex substrates treated with argon plasma is higher than those without argon plasma activation. This experimental result indicated that argon plasma activation is an effective way to improve the reliability of HTS test for chips bonded to flex substrate with NCP and the thermal compressional boding process. As prolong the durations of HTS, the fracture occurred at bonding interface between chips and gold bumps due to the high thermal stress was formed, and then the die-shear force was decreased. The specimen of chips and flex substrates cannot withstand the high temperature, high pressure and moisture during the PCT. The delamination can be found at the corner between the chip and the NCP for specimen subjected to 96 hr PCT, and then the moisture penetrated into the bonded interface between chips and gold bumps. The NCP lost its adhesion and the gold bump peeled off from the bond pads of chips, and then the die-shear force of chips and flex substrates assembly was degraded. Similarity, the die-shear force of chips and flex substrates assembly was decreased with increasing the durations of HT/HH. A delamination can be found at bonding interface between chips and the NCP. Increasing the HT/HH durations, the major fracture mode was gold bumps peeling off from the bond pads of chips and a part of NCP peeled off from the surface of flex substrates, indicating that bonding performance among chips, NCP and flex substrates was poor. With argon plasma activation, chips can be well bonded onto flex substrates using NCP and thermal compressional bonding process and its reliability was better than those without argon plasma activation. This scheme has great potential to be applied to chips and flex substrates assembly.