Thermally stable PSA film with reduced adhesion after thermal and UV treatment

Abstract

Acrylic pressure-sensitive adhesives (PSAs), commonly used for their low glass transition temperature (T_g), often exhibit poor heat resistance. This poses challenges in high-temperature applications in semiconductor processing and enhancing the heat resistance of PSAs has been achieved through chemical crosslinking. In this study, PSAs were developed that maintains adhesion during thermal treatment and reduces adhesion after photo treatment, allowing easy separation from silicon wafers. The PSAs was synthesized by copolymerization of 2-ethylhexyl acrylate (2-EHA), acrylonitrile (AN), and 4-hydroxybutyl acrylate (4-HBA) with final composition ratios of 72.6, 12.3, and 15.1 mol% respectively. Hexamethylene diisocyanate (HDI) and 2-isocyanatoethyl methacrylate (MOI) were attached to the hydroxyl group of 4-HBA to control the degree of crosslinking. Corona-treated polyethylene naphthalate (PEN) was used as a base film, which was suitable for processing at high-temperatures of approximately 250 °C. The peel strength of PSAs decreased from 9.64 N/in. to 6.75 N/in. after thermal treatment. This decrease is attributed to increased crosslinking density through AN cyclization during the thermal treatment unlike conventional PSA which is inseparable after thermal treatment. After photo treatment, peel strength decreased from 6.75 N/in. to 3.62 N/in., indicating additional crosslinking due to intermolecular reactions of the methacrylate groups in MOI. The increase in crosslinking density was verified through gel fraction analysis, which showed a rise from 65.2 %, as prepared, up to 97.6 % after thermal and photo treatment. Trimethylolpropane triacrylate (TMPTA) was used to form additionally crosslinked networks during photo treatment. The final gel fraction increased with the TMPTA content, rising from 97.6 % without TMPTA to 99.1 % with 20 wt% TMPTA. The peel strength also decreased down to 1.50 N/in. with 20 wt% TMPTA with only 0.85 % residue. These results provide valuable insights for engineering PSAs with controlled adhesion characteristics, thereby enabling the development of advanced PSAs suited for semiconductor industry applications.