LED Encapsulation High-Transparency LSR Comparison

橡楚技术团队 5/8/2026 10 min read

Comparative analysis of optical-grade LSR silicone for LED encapsulation.

Performance Comparison and Selection Guide for High-Transmittance LSR Silicone in LED Packaging

The rapid development of LED lighting technology has placed higher demands on packaging material performance. High-transmittance LSR silicone, as the optical interface between LED chip and the outside world, directly affects LED luminous efficacy and lifespan through its refractive index, light transmittance, yellowing resistance, and high-temperature resistance.

I. Core Requirements for LED Packaging LSR

1. Optical Performance

Transmittance: ≥ 95% in visible light range (400-700nm)
Refractive index: 1.41-1.53, matching with LED chip and substrate affects light extraction efficiency
Yellowing index: YI ≤ 2 after 150°C × 1000 hours

2. Thermal Performance

Operating temperature: long-term 150-200°C, short-term up to 250°C
Thermal conductivity: 0.8-3.0 W/m·K (thermally conductive types), aiding chip heat dissipation
CTE matching with chip and substrate, reducing thermal stress

3. Reliability

UV aging resistance: transmittance decrease ≤ 3% after 365nm UV exposure 1000h
Damp heat aging: stable performance after 85°C/85% RH × 1000h
Sulfurization resistance: preventing LED chip silver reflector blackening

II. Mainstream LSR Packaging Silicone Comparison

ParameterMethyl LSRPhenyl LSRFluorosilicone LSR

Refractive index1.411.49-1.531.38-1.41

Transmittance (450nm)95-97%93-96%90-93%

Long-term temperature200°C250°C200°C

YI (150°C×1000h)3-51-22-4

UV resistanceGoodExcellentExcellent

CostLowHighHighest

Typical applicationLighting LEDHigh-power/UV LEDSpecial environment LED

III. Selection Strategy

1. General Lighting LED (White Light)

Methyl LSR recommended, refractive index 1.41, best cost-effectiveness. Focus on anti-yellowing performance, select formulations with antioxidants. Hardness Shore D 40-60, ensuring mechanical strength.

2. High-Power LED (>1W)

Phenyl LSR recommended, refractive index 1.50-1.53, improving light extraction efficiency by 5-10%. High temperature rating, withstanding chip junction temperatures of 150-200°C. Low stress characteristics, reducing thermal cycling package cracking.

3. UV LED (365-405nm)

Must select high phenyl content LSR with excellent UV resistance. Transmittance ≥ 90% in UV band. Avoid formulations containing UV absorbers.

4. Outdoor LED Displays

Weather-resistant methyl LSR recommended, with UV and sulfurization resistance. Salt spray and acid rain resistance needs specific verification. Anti-fouling surface design, reducing dust adhesion affecting luminous efficacy.

IV. Packaging Process Considerations

1. Dispensing Process

Methyl LSR viscosity 3000-8000 mPa·s, suitable for dispensing
Phenyl LSR higher viscosity (10000-30000 mPa·s), requires parameter adjustment
Vacuum degassing before dispensing, avoiding bubbles inside package affecting light output

2. Curing Conditions

Methyl LSR: 150°C × 30-60 min
Phenyl LSR: 150-180°C × 60-120 min, requires step-up heating
Post-cure after initial cure (200°C × 2-4h), reducing volatiles

3. Quality Inspection

Optical testing: integrating sphere for luminous flux and color temperature
Bubble inspection: X-ray or infrared detection of internal defects
Reliability verification: LM-80 standard 6000-hour lumen maintenance test

Selecting the appropriate LSR packaging silicone is fundamental to LED product performance and reliability, requiring comprehensive consideration of optical, thermal, and reliability requirements based on specific application scenarios.