سایر صنایع

ZEMSIL® در روشنایی LED

کپسوله‌کننده‌های سیلیکونی با ضریب شکست بالا برای تراشه‌های LED، گریس حرارتی سیلیکونی برای هیت‌سینک و لنزهای سیلیکونی درجه اپتیک.

یافتن سیلیکون‌های روشنایی LED ←

Silicone Materials in LED and OLED Lighting

LED lighting has displaced incandescent and fluorescent sources in virtually every application — general illumination, automotive lighting, horticulture, UV curing, display backlighting, and medical phototherapy. Silicone is the dominant encapsulant and lens material for mid-power and high-power LED packages, selected over epoxy because of its superior optical stability at elevated temperatures and under high-flux blue/UV radiation.

The LED encapsulant market exceeds $500M annually, almost entirely served by silicone — primarily addition-cure silicone supplied as two-part A/B systems. Understanding the refractive index, transmittance, viscosity, and cure profile requirements for each LED segment is essential for procurement engineers and formulators selecting and qualifying silicone materials.

LED Package Encapsulation

Primary encapsulant (die-level): the silicone layer covering the LED chip directly. This material must have high refractive index (RI 1.50–1.54 for efficient light extraction from GaN, RI 1.41–1.43 for standard PDMS), >98% transmittance at 450 nm (blue primary), and stability against yellowingunder 10,000+ hours of operation at chip temperature 85–125 °C. Phenyl-modified silicone (PH series) provides the higher refractive index; standard PDMS gives 1.41 RI suitable for low-power LEDs.

Secondary encapsulant / lens: the dome or flat-top encapsulant over the LED package. Two-part addition-cure silicone with Shore A 30–80, mixed viscosity 500–5000 mPa·s for dispensing, and full cure in 60–150 minutes at 150 °C. Phosphor can be dispersed in the encapsulant for remote phosphor configurations.

Reflector and underfill: silicone reflector compounds (TiO₂-filled, white, Shore D 70–85) define the light cone and protect the bond wire. Silicone underfill beneath flip-chip LEDs provides mechanical support and thermal conduction to the substrate.

COB (Chip-on-Board) and Module Potting

COB LED arrays — used in stadium lighting, plant grow lights, cinema projectors, and UV LED systems — require potting over multi-chip arrays bonded directly to a metal-core PCB (MCPCB). Requirements:

Mixed viscosity: 1000–8000 mPa·s to flow around closely spaced chips without trapped voids.
Pot life: ≥60 minutes at room temperature to allow dispensing of large arrays.
Cure shrinkage: <0.5% volumetric to avoid stress on wire bonds and die adhesive.
Thermal conductivity: for high-power arrays (>10 W/cm²), lightly filled silicone (0.5–1.0 W/m·K) improves heat spreading toward the MCPCB.

SB-RTV2 addition-cure two-part systems are used as the base for LED potting formulations.

Optical and Thermal Performance Data

Application	RI Requirement	Transmittance (450 nm)	Thermal Conductivity	Key Grade
Low-power LED (SMD 2835/3030)	1.41	>98%	0.15 W/m·K	Standard PDMS encapsulant
High-power LED chip (>1 W)	1.50–1.54	>97%	0.15–0.5 W/m·K	Phenyl silicone (PH series)
UV LED (365–395 nm)	1.41–1.50	>90% at 365 nm	0.15 W/m·K	UV-stable low-phenyl grade
COB array potting	1.41	>97%	0.5–1.0 W/m·K	Filled RTV2 compound
LED driver thermal pad	—	—	3–6 W/m·K	Thermally conductive PDMS TIM

OLED Lighting and Encapsulation

OLED panels are extreme moisture-sensitive devices: a water vapor transmission rate (WVTR) >10⁻⁶ g/m²·day causes catastrophic dark spot formation. Silicone is used in OLED lighting in two roles:

Edge sealant: flexible silicone sealant at panel perimeter to absorb CTE mismatch between glass and substrate during thermal cycling, while a primary inorganic barrier handles moisture.
Backplane potting: for flexible OLED panels on plastic substrates, low-modulus silicone potting protects thin-film transistor (TFT) backplane during handling and use.

Silicone's inherent high WVTR (100–1000 g/m²·day) means it cannot serve as the primary moisture barrier for OLED — that role goes to ALD or PVD inorganic films — but its flexibility and optical clarity make it indispensable for mechanical protection layers.

Silicone Coupling Agents in LED Substrates

Silane coupling agents (CS-550, CS-560) are used to promote adhesion between silicone encapsulant and the following substrate materials in LED packages:

Aluminum-core PCB (MCPCB): alumina or anodized aluminum surface treated with aminosilane primer.
Ceramic substrates (AlN, Al₂O₃): silane coupling improves peel adhesion of silicone encapsulant by 2–4×.
EMC (epoxy-molded compound) reflector cups: silane treatment of the cup surface before dispense prevents delamination in humidity cycling.

Horticultural and UV LED Considerations

Plant grow lights (600–1200 µmol/m²·s PPFD) and UV LED curing systems impose higher stress on encapsulant materials than general lighting:

Photodegradation: UV-A and deep blue flux cleaves Si-phenyl bonds at rates dependent on flux density. UV-stable grades with minimal phenyl content or UV stabilizers are required.
Temperature: high-power arrays reach 100–150 °C at the encapsulant, requiring good compression set resistance to avoid cracking through thermal cycling.
Ozone generation: some UV LED systems generate ozone. FVMQ-based grades or ozone-resistant standard silicone with antioxidants are specified.