Finite element modeling of temporary bonding systems for flexible microelectronics fabrication

One promising route to enable the manufacture of flexible microelectronics is through temporary bonding-debonding of flexible plastic substrates to rigid carriers, which facilitates effective substrate handling by automated tools. Understanding the thermomechanical properties of the temporary bonding system (flexible substrate-adhesive-carrier) could allow for improved control of bow and distortion of the flexible substrate that can adversely impact device fabrication. In this study, a thermomechanical analysis of this temporary bonding system is performed using finite element modeling (ANSYS) to understand how to control the stress-induced bow of the bonded system. This stress is developed during high temperature processing predominately through thermal mismatches between the carrier and substrate. However, viscous flow of adhesive can relax some stress to decrease the total extent of bowing of the bonded system. Interestingly, the viscoelasticity of flexible plastic substrate appears to be critical to the stress-induced bowing; viscous flow of the plastic substrate relaxes some stress of the bonded system and must be taken into account to achieve good agreement between simulated and experimental bow. By variation in the relaxation time (@t) and the relative relaxation modulus (@a) of the adhesive, the simulation shows a limited range for the relaxation parameters over which the bow can be tuned for a specified carrier-flexible substrate system. These results suggest that further engineering of the adhesive is unlikely to dramatically decrease the bow of the bonded system as would be necessary for extension to large form sizes. Therefore, efforts should focus on new flexible substrates and rigid carriers; the model developed here can be utilized as a screening tool for this purpose.