YINCAE announced the release of UF 66L, a next-generation optical clear underfill (OCU) engineered for silicon photonics, optoelectronic packaging, image sensors, AR/VR modules and advanced flip-chip assemblies where optical clarity, thermal endurance and reliability are critical.

Technical Performance Highlights:

• Thermal Endurance: Withstands 5× 260°C reflow cycles without cracking, delamination or adhesion loss
• Optical Transparency: Maintains >95 percent light transmittance (400 to 800 nm), ensuring minimal signal loss through optical pathways
• Non-Yellowing Stability: Exceptional resistance to discoloration after repeated high-temperature exposure
• Reliability: Excellent adhesion to silicon, glass and substrate materials for enhanced package durability
• Mechanical Properties: Controlled modulus formulation reinforces delicate structures while minimizing stress and warpage.

UF 66L overcomes the limitations of conventional epoxy underfills, which often lose transparency or degrade under thermal cycling. It is specifically optimized for optical interconnect stability, waveguide coupling, photodetectors, and high-density optoelectronic packaging, enabling reliable performance in next-generation devices.

“UF 66L provides engineers with a robust, optically clear underfill that maintains mechanical integrity and optical performance under demanding processing and operational conditions,” said CTO at YINCAE.

YINCAE will showcase UF 66L at SMTAI 2025 in Chicago from October 21 to 23 at Booth #2551.