Preparation Of Castor Oil-Based Fully Cross-Linked UV Induced Peelable Adhesive

UV-induced peelable adhesive is a type of adhesive,which shows high adhesion normally,but the adhesion drops sharply after UV irradiation.It is widely used in wafer cutting field.With the increasing demand for size reduction in the semiconductor wafer manufacturing process,the wafers are getting thinner and thinner,and they are easily damaged during the cutting and picking stages.Therefore,the properties of the peelable adhesives should be improved.However,the peel adhesives developed in China still lag far behind the commercialization requirements for wafer cutting in the core indicators such as normal adhesion,adhesion reduction performance through UV irradiation and residual adhesive amount.Aiming at the above technical bottleneck restricting the development of UV-induced peelable adhesives for thin wafer dicing,a heat/light dual-curable castor oil-based polyurethane acrylate oligomer was designed and synthesized based on the unique properties of castor oil in this work.The preparation,performance and curing mechanism of UV-induced peelable adhesive with a fully cross-linked structure based on this oligomer were carried out.Firstly,under solvent-free conditions,through the condensation reaction between the hydroxyl group in castor oil(CO)and the NCO in isophorone diisocyanate(IPDI),a polyurethane oligomer(CO-PU)containing NCO groups was obtained.The appropriate amount of hydroxyethyl acrylate(HEA)was dded to partially end-capping CO-PU,a heat/light dual-curable castor oil-based polyurethane acrylate oligomer(CO-PUB)containing both NCO and acrylate groups was prepared.Besides,a mixture of castor oil-based polyurethane oligomer and IPDI/HEA adduct(HEA-IPDI-HEA)was prepared using the "one-pot method" by making IPDI excessive.For subsequent comparative studies,both castor oil acrylate oligomer(CO-MA)and polyurethane acrylate oligomer(CO-PUA)containing acrylate groups were prepared.The oligomers were characterized by infrared spectroscopy,nuclear magnetic resonance spectroscopy and mass spectrometry,which proved that the above-mentioned oligomers were successfully prepared.Then,CO-PUB was used as a crosslinking agent and mixed with hydroxyl-containing acrylate copolymer base adhesive.A photo-polymerizable network structured pressure-sensitive adhesive was prepared through NCO/OH thermal curing reaction.A fully crosslinked UV-induced peelable adhesive for silicon wafer cutting was prepared by mixing with multifunctional acrylate copolymer monomer and photoinitiator in a certain proportion.The results showed that this new type of fully cross-linked UV-induced peelable adhesive had high adhesion before irradiation and could meet the fixed requirements of silicon wafer cutting process.The peel strength before UV irradiation was up to 34 N/25 mm,which was higher than other reported UV-induced peelable adhesives.In addition,the UV dose required for photocuring of the peeling adhesive was low.After UV irradiation,the curing shrinkage rate of the adhesive film was high,and the peel strength was greatly reduced(less than 1 N/25 mm).Good peeling performances were found and no adhesive residue was observed.In addition,by using a mixture of castor oil-based polyurethane prepolymer and HEA-IPDI-HEA prepared by the "one-pot method" to instead of CO-PUB,UV-induced peelable adhesives with good peeling properties were also be prepared.