Yincae Advanced Materials has launched UF 66L, a next-generation Optical Clear Underfill (OCU) designed for silicon photonics, optoelectronic packaging, image sensors, AR/VR modules and advanced flip-chip assemblies. Engineered to deliver both high transparency and thermal endurance, UF 66L withstands five reflow cycles at 260 °C without cracking, delamination or adhesion loss. It maintains over 95% light transmittance between 400–800 nm, ensuring minimal signal loss in optical pathways, while its non-yellowing stability preserves clarity even after repeated high-temperature exposure. The material offers excellent adhesion to silicon, glass and substrates. Formulated with a controlled modulus that reinforces delicate structures while minimizing stress and warpage, addressing the limitations of conventional epoxy underfills that degrade under thermal cycling. It is optimized for optical interconnect stability, waveguide coupling, photodetectors and other high-density optoelectronic packaging scenarios.