电子封装 化学品

Potting (encapsulation) floods an electronic assembly with liquid resin that cures to a solid or gel, providing full environmental and mechanical protection. Conformal coatings are thin films (25–250 µm) applied by spray, dip, or selective coating to provide moisture and contamination protection while keeping assemblies accessible. Potting is preferred for harsh environments; conformal coating for general protection where component access is needed.

Low-viscosity liquid epoxy systems (bisphenol A/F, cycloaliphatic epoxy) with amine or anhydride hardeners are standard for general PCB potting. Flame-retardant formulations (UL 94 V-0) use reactive FR additives or aluminum trihydrate (ATH)-filled systems. Epoxy potting compounds with low CTE — achieved by silica or alumina filler — reduce thermal stress on components.

Silicone gels are preferred when thermal cycling over a wide temperature range (-55°C to +200°C), vibration, or flexibility is required — they have very low modulus and do not stress components. Silicone is the standard for automotive electronics, power modules, and LED drivers. Epoxy offers higher rigidity, adhesion, and chemical resistance for fixed installations. PU potting compounds bridge the gap with good flexibility and lower cost than silicone.

IPC-CC-830 is the primary standard for conformal coating qualification — specifying tests for moisture and insulation resistance, fungus resistance, thermal shock, and humidity. UL 746E qualifies coatings for use in UL-listed electronics. Coatings are classified by type: AR (acrylic), UR (urethane), SR (silicone), ER (epoxy), and SC (synthetic rubber), each with specific application advantages and performance trade-offs.

LED encapsulation uses transparent silicone gels or epoxy with high thermal stability and matched refractive index for light-extraction efficiency. Phenyl-modified silicones provide higher refractive index (n=1.53–1.55) for high-brightness LEDs. Yellow discoloration after thermal aging must be minimized — modern phenyl silicones maintain transmittance after 1000 h at 150°C. Curable optical adhesives are used for OLED display lamination.

Power electronics encapsulants must have low CTE (matched to silicon ~3 ppm/°C and copper ~17 ppm/°C) to minimize thermal stress during high power cycling. Silica-filled epoxy (typically 70–80% loading) achieves CTE of 12–25 ppm/°C. Modulus is tuned by filler loading and resin chemistry. Glass transition temperature (Tg) typically 130–180°C for high-temperature operation. UL flammability classification (V-0) is required for most commercial applications.