abstract: Temporary bonding-debonding of flexible plastic substrates to rigid carriers may facilitate effective substrate handling by automated tools for manufacture of flexible microelectronics. The primary challenges in implementing practical temporary bond-debond technology originate from the stress that is developed during high temperature processing predominately through thermal-mechanical property mismatches between carrier, adhesive and substrate. These stresses are relaxed through bowing of the bonded system (substrate-adhesive-carrier), which causes wafer handling problems, or through delamination of substrate from rigid carrier. Another challenge inherent to flexible plastic substrates and linked to stress is their dimensional instability, which may manifest itself in irreversible deformation upon heating and cooling cycles. Dimensional stability is critical to ensure precise registration of different layers during photolithography. The global objective of this work is to determine comprehensive experimental characterization and develop underlying fundamental engineering concept that could enable widespread adoption and scale-up of temporary bonding processing protocols for flexible microelectronics manufacturing. A series of carriers with different coefficient of thermal expansion (CTE), modulus and thickness were investigated to correlate the thermo-mechanical properties of carrier with deformation behavior of bonded systems. The observed magnitude of system bow scaled with properties of carriers according to well-established Stoney's equation. In addition, rheology of adhesive impacted the deformation of bonded system. In particular, distortion-bowing behavior correlated directly with the relative loss factor of adhesive and flexible plastic substrate. Higher loss factor of adhesive compared to that of substrate allowed the stress to be relaxed with less bow, but led to significantly greater dimensional distortion. Conversely, lower loss factor of adhesive allowed less distortion but led to larger wafer bow. A finite element model using ANSYS was developed to predict the trend in bow-distortion of bonded systems as a function of the viscoelastic properties of adhesive. Inclusion of the viscoelasticity of flexible plastic substrate itself was critical to achieving good agreement between simulation and experiment. Simulation results showed that there is a limited range within which tuning the rheology of adhesive can control the stress-distortion. Therefore, this model can aid in design of new adhesive formulations compatible with different processing requirements of various flexible microelectronics applications. / Dissertation/Thesis / Ph.D. Chemical Engineering 2011

Fiber reinforced polymer (FRP) composites have been of interest to the structural engineering society since the earliest days of FRP composites industry. The use of such systems has been implemented in both new construction and for repair and rehabilitation of existing structures. Since the 1980s, researchers have developed a significant body of knowledge to use FRP composites in infrastructure applications; however, most of this established knowledge was concentrated on the use of traditional epoxy (EP) systems (epoxy matrix FRPs and epoxy adhesives). FRP composites with polyurethane (PU) matrices and adhesives have recently attracted the attention of a few researchers due to their potential advantages in constructibility and mechanical properties. The deployment of these systems is currently limited by a lack of knowledge on mechanical and durability performance. The objective of this research is to quantify the mechanical behavior of PU composites utilized in externally-bonded repair of common flexural and flexural-axial reinforced concrete systems. In addition, the mechanical performance, strength, and failure modes are compared directly with an epoxy-based composite by subjecting reinforced concrete specimens utilizing each of the matrix types (EP and PU) to the same protocols. The study presented therefore allows an objective comparison (advantages and disadvantages) between the two composite system used for repair and rehabilitation of concrete infrastructure. An experimental research program was designed with different length scales. Small-scale experiments were utilized to characterize the component level properties of the materials and bond to concrete, which include the flexural behavior as well as the pure shear behavior. The results of these small scale experiments were used to calibrate analytical models of the interface behavior between FRP laminate and concrete, and paved the way for the next level of the research which studied the behavior of each composite system at larger scales. The large scale experiments included flexural retrofitting of reinforced concrete girders and retrofitting of circular columns using FRP laminates. The large-scale experimental specimens were mechanically damaged prior to FRP repair and testing, making the testing more appropriate compared to common practice of repairing undamaged specimens.