Tailoring peel strength in UV-responsive, nonconductive adhesives via photocleavable epoxy for micro-LED bonding and repair

To develop a UV-responsive epoxy-based nonconductive adhesive (NCA) with adjustable peel strength, a bifunctional epoxy (NBE) was synthesized. This compound included an ortho-nitrobenzyl ester that decomposes upon UV absorption, exhibiting absorption in the 240350 nm wavelength range and a thermal decomposition temperature at 1% weight loss of 214 ℃. When coupled with an imidazole catalyst, the curing of NBE began at 100 ℃ and reached a maximum exothermic peak at 136 ℃. The NCA was formulated using NBE together with bisphenol F epoxy, cresol novolac epoxy, and nadic methyl anhydride as a curing agent. Despite the increasing NBE content in the NCA, the curing behaviour remained almost the same. However, the decomposition temperature of the NCA decreased in proportion to the NBE content. NCA tapes bonded to quartz glass substrates exhibited a 90° peel strength of 7.1910.39 N/in, depending on the NBE content. When exposed to excimer laser irradiation at 100 mJ/cm2, the 90° peel strength decreased significantly to nearly 0 N/in. [Display omitted]