Backfill & Optical Structural Bonding in Photonic Devices

EPO-TEK® 353NDP is the primary recommendation for optical structural bonding and backfill in high-speed data transceiver devices. It combines high optical transmission (≥98% at 800–1000 nm), strong humidity resistance (retaining 15 kg die shear after 2000 hours at 85°C/85%RH), and NASA ASTM E595 low outgassing compliance. Its pourable viscosity of 3,600 cPs allows it to flow into V-groove arrays and fine optical cavities without voids.

EPO-TEK® 353NDP demonstrates strong retention of adhesion after humidity exposure. Initial die shear strength is 38 kg, dropping to 32 kg after 7 days at 85°C/85%RH and retaining 15 kg after 2000 hours at the same conditions. This makes it suitable for long-term field deployment in telecom and datacom environments where condensation and thermal cycling are common.

Backfill bonding fills the void space around an aligned optical assembly to lock it in place after active alignment — preventing movement caused by thermal cycling or vibration. Optical structural bonding is the primary adhesive joint that mechanically holds an optical component (lens, prism, fiber, PLC chip) to a substrate or housing. In practice, the same adhesive — such as EPO-TEK® 353NDP — is often used for both purposes in photonic packaging.

Yes. EPO-TEK® 353NDP passes the NASA low outgassing standard ASTM E595 when properly cured at 120°C for 1 hour. Low outgassing is critical in sealed optical packages because condensed volatile residues can form contaminating films on optical surfaces, degrading transmission over time.

Yes. EPO-TEK® 353NDP is designed for sealing fiber into ferrules while transmitting light in the 800–1550 nm range — covering the standard O-band (1310 nm) and C-band (1550 nm) windows used in telecom and datacom systems. It is also suitable for V-groove arrays and environmental sealing of opto-packages in high-speed transceiver devices.

The recommended cure is 120°C for 1 hour. Alternative cure schedules include 150°C / 1 minute, 120°C / 5 minutes, 100°C / 10 minutes, and 80°C / 30 minutes — offering flexibility for temperature-sensitive assemblies. Note that alternative schedules may not achieve all listed performance properties.

According to EPO-TEK®’s own application guide for High-Speed Data Transmission Devices, Position 2 (Backfill / Optical Structural Bonding) is assigned to 353NDP, H70E-2 (heat cure), and VC-136. For optical path applications requiring high transmission and humidity resistance, 353NDP is the first choice. H70E-2 is preferred when thermal conductivity is also needed alongside structural bonding.