Laxmisha M. Sridhar

By Laxmisha M. Sridhar, Andrew T. Slark and James A. Wilson

New reactive hotmelt (RHM) adhesives based on thermally reversible Diels-Alder networks comprising multifunctional furan and maleimide prepolymers are described. The prepolymer mixture is easy to apply in the bulk from the melt and after application to the substrates, the adhesive undergoes polymerization at room temperature resulting in crosslinked bonds. Due to their thermoplastic nature and low melt viscosity at hot melt application temperatures, the adhesives provide processing properties similar to moisture cured polyurethanes (PUR). The technology is isocyanate-free and does not require moisture to initiate the crosslinking. Bonding and tensile properties of the RHM adhesive can be readily tuned by prepolymer design and provide cure rates similar to PUR adhesives. The Diels-Alder adhesives provide versatile adhesion to a variety of substrates and good creep resistance up to the retro temperature. The adhesives show good thermal stability during application and can be recycled multiple times by simple heating/cooling of the bonds providing similar performance. Several furan and maleimide prepolymers were scaled up to multi-Kg quantities to demonstrate the potential for industrial scalability. The results demonstrate that furan-maleimide reversible chemistry can be used for RHM application as a more sustainable alternative to conventional moisture curing PURs which tend to contain harmful residual isocyanate monomers.

Part of the book: Furan Derivatives

By Laxmisha M. Sridhar and Timothy M. Champagne

A highly reliable and reworkable underfill adhesive based on thermoset epoxy resin possessing thermally reversible dicyclopentadiene (DCPD) moiety is described. The adhesive can be cured rapidly at moderate temperatures resulting in high Tg cured network, which gives high reliability to the bonded semiconductor components. The inherent thermal reversibility of DCPD moiety causes network breakdown at high temperatures enabling easy removal of defective semiconductor chips. A discernible trend between loading level of the thermally reversible epoxy resin and high-temperature die shear strength was observed. Using this novel adhesive system, both high reliability and reworkability can be achieved concurrently, which is normally not possible with other thermoset adhesive systems. The epoxy resin used in the study was scaled up to multi-kg quantities demonstrating industrial applicability of the approach.

Part of the book: Next Generation Fiber-Reinforced Composites