LSR Overmolding on Glass Molding Technology: Process Breakthroughs in Optical Packaging and Precision Protection

Liquid Silicone Rubber Overmolding on Glass is an advanced composite manufacturing technology that coats glass substrates with liquid silicone rubber through precision injection molding. This technology combines the excellent optical properties of glass (high light transmittance, high hardness, chemical resistance) with LSR's flexibility, sealing performance, biocompatibility, and impact protection capabilities.

Compared with traditional thermoset silicone compression molding or adhesive bonding, LSR Overmolding on Glass uses integrated injection molding, offering advantages such as no interfacial adhesive layer, no yellowing or aging, high dimensional accuracy, and high automation. This technology shows tremendous application potential in smartphone camera modules, AR/VR optical devices, medical examination windows, automotive LiDAR protective covers, and smart home touch panels.

II. Core Process Principles and Technical Challenges

2.1 Interface Bonding Mechanism of LSR and Glass

Glass surfaces mainly consist of silica (SiO₂), exhibiting hydrophilicity and high surface energy (approx. 70-80 mN/m), but poor chemical compatibility with LSR. Reliable bonding requires overcoming the following challenges:

Insufficient Chemical Bonding: The silanol groups (Si-OH) on the glass surface lack direct reactivity with vinyl or hydride groups in LSR molecular chains. Silane coupling agents must be used as "molecular bridges" to establish covalent bonds.

Severe Thermal Expansion Mismatch: Soda-lime glass has a CTE of about 8-9×10⁻⁶/°C, borosilicate glass about 3-4×10⁻⁶/°C, while LSR REACHes 250-300×10⁻⁶/°C - a difference of 30-70 times.

2.2 Key Technical Challenges and Engineering Solutions

Challenge 1: Glass Breakage Risk Control

Glass is a typical brittle material with low tensile strength (approx. 30-70 MPa), extremely sensitive to stress concentration. Engineering solutions include: optimized gate design, multi-stage injection strategy, mold temperature gradient control, annealing process, and use of strengthened glass (e.g., Corning Gorilla Glass).

Challenge 2: Optical Interface Quality Control

Control strategies: vacuum-assisted injection (vacuum ≤-0.095 MPa), ultra-clean environment (Class 1000 cleanroom), high-transparency LSR (>92% transmittance), surface treatment optimization (oxygen plasma activation), and online optical inspection (AOI).

Challenge 3: Precision Alignment and Thin Layer Uniformity

Optical devices typically require LSR coating thickness of 0.2-0.5mm with deviation <±0.05mm. Achieved through CCD vision alignment system (±0.02mm accuracy), laser thickness closed-loop control, and flow simulation optimized gate layout.

III. Typical Applications and Technical Cases

3.1 Smartphone Camera Protection Window

Integrated LSR sealing ring molding for rear camera module glass cover, achieving IP68 waterproofing. Key parameters: LSR coating width 0.8-1.2mm, compression set<10%.

3.2 AR/VR Glasses Optical Sealing

Precision sealing around AR waveguide edge, LSR coating thickness 0.15-0.25mm, transmittance maintained >90%, refractive index matching reduces interface reflection loss.

3.3 Medical Ultrasound Diagnostic Window

Glass window between medical ultrasound probe housing and piezoelectric crystal is sealed through integrated LSR encapsulation.

3.4 Automotive LiDAR Protective Cover

LSR edge sealing for vehicle LiDAR sensor glass cover, temperature range -40°C to 125°C, AEC-Q200 automotive grade certified.

IV. Material Selection and Process Optimization

4.1 LSR Material Recommendations

Smartphone Camera Window: Wacker LR 7663, Shore A 20-30, >92% transmittance
AR/VR Waveguide Seal: Momentive 7-4030, Shore A 10-20, >90% transmittance
Medical Ultrasound Window: Wacker LR 5040, Shore A 30-40, USP Class VI
Automotive LiDAR Cover: Momentive 7-4050, Shore A 40-50, 200°C resistance
General Optical Packaging: Dow Corning SE 1700, Shore A 20-40 adjustable

4.2 Glass Substrate Selection

Soda-lime Glass: Low-cost consumer electronics
Borosilicate Glass: Medical, automotive
Aluminosilicate Glass: High-end phones, AR/VR
Quartz Glass: UV optics, lasers

4.3 Key Process Parameters

Mold Temperature (Glass Zone): 80-100°C
Mold Temperature (LSR Zone): 120-130°C
Injection Pressure: 80-120MPa
Injection Speed: 20-50mm/s
Holding Time: 8-12s
Cooling Time: 15-25s
Vacuum Degree: ≤-0.095MPa

V. Quality Inspection and Reliability Verification

Online Inspection: AOI, laser thickness measurement, transmittance testing
Offline Sampling: Peel strength test, drop test, weathering test (QUV 1000h), temperature cycling (-40°C to 125°C/1000 cycles), humidity test (85°C/85%RH/1000h)
Reliability Certification: ISO 10993 medical grade, AEC-Q200 automotive grade, IP68 consumer electronics

VI. Future Development Trends

Ultra-thin and lightweight (coating breakthrough 0.1mm), intelligent process monitoring (digital twin + machine learning), multi-functional integrated packaging (anti-reflection + hydrophobic + shielding), environmental sustainability (bio-based LSR, solvent-free treatment), new glass material applications (ultra-thin glass, glass-ceramics, photonic crystal glass).

Keywords: LSR Overmolding on Glass