Toughening and Performance Enhancement of Epoxy Acrylate-Based Solder Resist Using Polyurethane Acrylate for Advanced Packaging

As packaging technology evolves to support higher integration and performance, demands on solder resist materials in FC-BGA (Flip Chip Ball Grid Array) substrates have intensified. These materials are now expected to combine mechanical strength, thermal resistance, dielectric stability, and fine resolution patterning to align with strict manufacturing requirements. In this study, hydroxyl-functionalized acrylic resins were synthesized via free-radical polymerization and chemically modified using cis-1,2,3,6-tetrahydrophthalic anhydride (THAPC) and isocyanoethyl methacrylate (IEM) to obtain alkali-soluble polyurethane acrylate (PUA) resins. The synthesized PUA was incorporated into photosensitive epoxy acrylate (PE) system to enhance its mechanical, thermal, dielectric, and lithographic performance for solder resist applications. The results indicate that with the addition of 20 wt% PUA, the modified PE based solder resist exhibits remarkable improvements across multiple performance aspects. The tensile strength reaches 97.72 MPa, while the elongation at break increases to 6.07%, demonstrating enhanced mechanical robustness. Meanwhile, the material also demonstrates excellent thermal stability, with a glass transition temperature (Tg) of 156.87°C and a 5% weight loss decomposition temperature (Td5%) of 349.41°C, indicating superior thermal resistance. Beyond mechanical and thermal enhancements, the low polarity and flexible molecular structure of PUA contribute to improved hydrophobicity and dielectric properties. The water contact angle increases to 86.55°, signifying enhanced moisture resistance, while at 10 GHz, the dielectric constant and dielectric loss reach 3.336 and 0.0256, respectively, ensuring favorable electrical insulation performance. Furthermore, the modified solder resist exhibits excellent photolithographic resolution, achieving well-defined micro patterns with a minimum feature size of 40 μm, demonstrating outstanding developability and imaging fidelity, which are critical for high-precision FC-BGA applications. These findings highlight the potential of PUA-modified epoxy acrylate-based solder resist in addressing the demanding requirements of FC-BGA advanced packaging, providing an effective strategy for optimizing mechanical, thermal, dielectric, and lithographic properties in next generation electronic applications.