Fully cross-linked UV-induced peelable acrylic PSA prepared from a dual curable castor oil based urethane acrylate oligomer for wafer dicing

Abstract

For UV-induced peelable pressure sensitive adhesive (PSA) used in the wafer dicing process, improving the peel performance can effectively increase the process reliability and the yield of subsequent packaging process. In this work, a NCO-containing castor oil-based urethane acrylate oligomer called CO-PUB with dual curable functions (UV-induced polymerization and NCO/OH reaction) was obtained by partially sealing a castor oil-based urethane oligomer with hydroxyethyl acrylate. Fourier transform infrared spectroscopy (FTIR) and nuclear magnetic resonance spectrometer (NMR) results indicated that CO-PUB was successfully prepared. CO-PUB, OH-containing acrylic copolymer, multifunctional acrylate monomer and photo-initiator were used to construct a UV-induced peelable adhesive for silicon wafer dicing. The results showed that NCO groups in CO-PUB underwent the NCO/OH reaction with the acrylic copolymer to obtain a vinyl pendant cross-linked acrylic copolymer. The peel strength of this peelable adhesive before UV irradiation could exceed 20 N/25 mm. After UV irradiation, the unsaturated vinyl bonds contained in it were copolymerized with the multifunctional acrylate monomer to form a fully cross-linked adhesive film and the peel strength could be reduced to below 1 N/25 mm. Compared with UV-induced peelable adhesives prepared by other reported curing agents, the adhesive prepared from CO-PUB reduced UV dose required for curing. The cross-linking degree of cured adhesive film was also increased and the gel content was up to 95%. The residual adhesive after peeling off could be reduced to about 0.32%. In addition, CO-PUB used renewable castor oil as polyol and did not need to add any organic solvent during the preparation process, providing a new idea for the green preparation of UV-induced peelable adhesive with excellent performances.