Polyurethane-Modified Acrylic Resins: High-Adhesion and Low-Dielectric Solder Resists for Advanced Packaging

The advancement of integrated circuit (IC) packaging necessitates solder resist (SR) materials with exceptional adhesion, flexibility, thermal stability, and low dielectric constants. In this work, we reported the development of an acrylic resin featuring hydroxyl-functionalized side chains, further modified with isocyanatoethyl methacrylate (IEM) and cis-1,2,3,6-tetrahydrophthalic anhydride (DMPA). By systematically adjusting the DMPA/IEM molar ratio, we achieved SR materials with excellent mechanical, thermal, adhesion, and dielectric properties. When the molar ratio of DMPA/IEM is 0.6:0.4 (SR-4), compared to the unmodified resin (SR-0), SR-4 exhibited a 38.2% increase in peel strength (0.37–0.51 N/mm), an 89.5% improvement in the elongation at break (1.9–3.6%), and a 10.2% reduction in the dielectric constant (3.03–2.72 at 20 GHz). The enhanced adhesion is attributed to hydrogen-bonding interactions between polar groups in the resin and the copper substrate, while the incorporation of flexible polyurethane chains improved toughness and reduced the molecular packing density, contributing to the lower dielectric constant. Furthermore, the SR-4 material demonstrated high thermal stability (Td5% = 319.26 °C), excellent hydrophobicity, and outstanding lithographic performance (40 μm), enabling high-resolution patterning with minimal defects. This study provides a robust framework for designing high-performance SR materials.