Temporary bond-debond process for manufacture of flexible electronics: Impact of adhesive and carrier properties on performance

Manufacturing of microelectronics on flexible substrates is challenged by difficulties in maintaining alignment and conformity of the substrate through deposition, patterning, and etch processes. To address these difficulties, a temporary bond-debond method has been developed for effective automated handling of flexible substrate systems during electronics fabrication. The flexible substrate is temporarily bonded to a rigid carrier, which provides structural support and suppresses bending during processing. The photolithographic alignment of the bonded system is strongly dependent upon the viscoelastic properties of the bonding adhesive. An additional challenge is to control the stress developed during processing; these stresses evolve predominately through thermomechanical property mismatches between the carrier and flexible substrate. To investigate the role of the thermomechanical properties of the carrier and adhesive, the stress, and subsequent bowing of bonded systems (flexible substrate-adhesive-carrier) is examined systematically using different carriers and adhesives. Excellent registration of the flexible circuitry fabricated on the bonded system with low stress can be achieved by using a viscoelastic adhesive with a low loss factor $(tanδ)$ and a carrier with high modulus and coefficient of thermal expansion that is closely matched to the flexible substrate. This bond-debond process enables the high yield fabrication of flexible microelectronics on plastic substrates.