Guide to Material Selection and Application of Thermal Interface Sheets and Electromagnetic Shielding Materials for LiDAR

2026/09/28 0

As a high-precision automotive optoelectronic sensor, LiDAR integrates high-frequency optoelectronic chips, power drive devices and precision optical paths. It faces three major challenges: thermal management & temperature control, electromagnetic compatibility (EMC), and optical contamination prevention. The module features densely packed heat-generating components and severe high-frequency electromagnetic interference. In addition, optical lenses and photodetector chips are extremely sensitive to volatile impurities and oil adsorption. Therefore, thermal and electromagnetic shielding materials must meet automotive-grade reliability requirements, including low outgassing, low contamination, vibration resistance, and compatibility with high-frequency EMI suppression. The following presents detailed material selection, application scenarios and key technical points for these two categories of materials.

hermal Interface Sheets and Electromagnetic Shielding Materials for LiDAR

I. Dedicated Thermal Interface Sheets for LiDAR (Thermal Interface Materials, TIM)

Thermal interface sheets fill microscopic gaps between heat-generating components, heat sinks and metal housings in LiDAR to reduce contact thermal resistance. They rapidly dissipate heat from laser diodes, driver chips, receiver chips and power management devices, preventing ranging accuracy degradation, component ageing and thermal shutdown caused by excessive temperature. Different from thermal materials for consumer electronics, LiDAR thermal sheets have core requirements: low volatility, minimal oil bleed, no optical contamination, automotive weather resistance, high compression resilience and vibration resistance.

(I) Main Grades and Application Scenarios

Low-volatility, low-oil thermal silicone sheet (mainstream for mass production)

Fabricated with modified silicone matrix filled with high-thermal-conductivity alumina and aluminum nitride fillers, this is the most widely adopted thermal material for automotive LiDAR. Optimized formulations remove highly volatile D3/D4/D5 siloxane oligomers to drastically reduce oil bleed, preventing fogging of optical lenses and contamination-induced failure of photodetector chips.

Key parameters: thermal conductivity 1~10 W/mK; standard thickness 0.2~3.0 mm. It delivers excellent compression resilience and low-stress bonding to chips, avoiding component crushing under vibration. Compliant with UL94-V0 flammability rating and AEC-Q100 automotive qualification. Operating temperature: -40℃ to 125℃, suitable for automotive thermal cycling environments.

Application locations: bonding interfaces between VCSEL laser emitters, FPGA driver chips, TIA amplifier chips, LDO power regulators and housings/heat sinks. For thermal gap filling in all non-optical-path regions.

Silicone-free thermal pad (for optically sensitive zones)

Polyurethane/carbon fiber composite silicone-free substrate, containing zero silicone oil or siloxane molecules. It fundamentally eliminates contamination from silicone bleed-out. This dedicated thermal material is used for modules adjacent to short-range optical paths and optical windows, solving the industry pain point of optical-path contamination from trace volatiles of silicone sheets.

Key parameters: thermal conductivity 1~4 W/mK. Resistant to pump-out and ageing with stable resilience. No material failure or displacement under long-term automotive vibration. Total volatiles (TVOC, TML) are well below automotive specification limits.

Application locations: inner side of front optical windows, heat-generating components surrounding optical paths, around high-precision APD/SPAD photodetector chips; all thermal interfaces adjacent to precision optical assemblies.

Artificial graphite thermal film (for heat spreading)

Ultra-high in-plane thermal conductivity (1000~1800 W/mK), thin and flexible (thickness: 25~100 μm). Primarily used for full-area heat spreading on housings and PCB surfaces to eliminate hotspots. Through-plane thermal conductivity is low; only for planar heat spreading rather than gap filling.

Application locations: inner wall of LiDAR housing, full-PCB heat spreading, remote heat dissipation zones to assist homogenization of the overall temperature field.

Integrated thermal-conductive and wave-absorbing pad (for high-density integrated designs)

Combines thermal conduction and high-frequency electromagnetic wave absorption. Covers interference bands from 500 MHz to 40 GHz. It simultaneously provides component cooling and local EMI suppression, saving limited internal space for compact, highly integrated solid-state LiDAR.

Core selection rule: match the material’s resonant absorption peak to the actual interference frequency band of LiDAR. Material thickness shall follow quarter-wavelength theory strictly, to avoid simultaneous failure of heat dissipation and wave absorption due to mismatched parameters.

(II) Key Considerations for Thermal Sheet Application

Optical isolation principle: All silicone-containing thermal sheets must maintain a safe clearance from optical lenses, optical paths and photodetector chips. Direct contact with optical zones is prohibited. Only silicone-free thermal pads can be deployed near optical paths.
Thickness matching principle: Select thickness precisely based on assembly gaps. Optimal compression ratio is 20%~40%. Excessively small gaps cause squeeze-out; oversized gaps raise thermal resistance and lead to thermal failure.
Automotive reliability: Must pass AEC-Q automotive qualification and low-outgassing tests to prevent volatile release under high temperature & humidity and long-term contamination of optical systems.
Vibration compatibility: Prioritize high-resilience, low-stress grades. Prevent material fatigue, shifting or detachment under road vibration to sustain stable long-term thermal performance.

II. Electromagnetic Shielding Materials for LiDAR

High-frequency drive circuits and high-speed signal traces inside LiDAR generate high-frequency electromagnetic radiation. Meanwhile, external automotive electronics, radars and RF signals interfere with precision photodetection and ranging signals of LiDAR, resulting in point cloud distortion and ranging errors. Electromagnetic shielding materials isolate internal interference, block external stray waves and provide electromagnetic sealing of the cavity. Core requirements: high shielding effectiveness at high frequencies, thin lightweight construction, weather & vibration resistance, and zero impact on optical performance.

(I) Main Grades and Application Scenarios

Metal shielding can (board-level primary shielding)

Shielding cavities fabricated from 0.2 mm nickel silver, stainless steel or aluminum alloy. It is the mainstream shielding solution for core PCB circuits of LiDAR. It provides wideband shielding from DC up to tens of GHz with shielding effectiveness of 50~100 dB, meeting the safety certification requirement of minimum 60 dB isolation for automotive sensors.

Application locations: above TIA amplifier circuits, APD/SPAD analog photodetection circuits and high-speed signal processing chips. It isolates high-frequency crosstalk inside PCB and external electromagnetic interference, protecting high-precision weak-signal acquisition circuits.

Conductive foam / conductive fabric (cavity gap shielding)

Polyurethane foam core clad with highly conductive nickel-copper plating. Flexible and compressible, suitable for assembly seams of LiDAR housings, wire harness interfaces and gaps between shielding cans, solving cavity electromagnetic leakage. Good resilience ensures sustained shielding sealing at gaps under vibration.

Key parameters: shielding band 10 MHz~18 GHz, shielding effectiveness 40~80 dB. Resists high/low temperature and oxidation for harsh automotive environments.

High-frequency wave-absorbing material (stray wave suppression)

Flexible thin wave-absorbing sheets optimized for the primary 2 GHz~6 GHz interference band of LiDAR. Unlike reflective shielding materials, it converts stray electromagnetic waves into heat, eliminating secondary interference caused by reflection from shields and mitigating high-frequency resonance and crosstalk.

Application locations: empty areas inside the cavity, beneath high-speed signal traces, inner surface of shielding cans. Suppress internally reflected stray electromagnetic waves and improve signal purity.

Optically transparent conductive coating (window electromagnetic shielding)

ITO (Indium Tin Oxide) transparent coating deposited on LiDAR optical windows. It delivers high optical transmittance together with electromagnetic shielding. It does not interfere with 905 nm /1550 nm laser transmit/receive, while blocking external high-frequency electromagnetic waves from entering the cavity through the window.

Application locations: front and rear optical lenses and transparent windows of LiDAR; the only viable electromagnetic shielding solution for optical windows.

(II) Key Considerations for Electromagnetic Shielding Material Application

High-frequency priority: LiDAR interference is dominated by GHz-band signals. Low-frequency shielding materials shall not be used. High-frequency high-shielding-effectiveness grades must be selected to avoid shielding failure at high frequencies.
Co-design of shielding and heat dissipation: Metal shielding cans shall reserve thermal paths or be paired with thermal sheets / thermal-conductive wave-absorbing materials. Avoid heat accumulation inside enclosed shielding cavities and conflicts between heat dissipation and EMC.
Zero optical interference: Only ITO transparent conductive coating can be used for optical windows. Opaque shielding materials or conductive foam must not block optical paths, to prevent transmittance degradation and laser TX/RX loss.
Full gap sealing: All assembly seams of housings, harnesses and shielding cans shall be fully covered with flexible shielding materials. Electromagnetic leakage mostly originates from gaps; partial gaps drastically degrade overall shielding effectiveness.
Avoid secondary interference: Wave-absorbing materials are preferred inside high-frequency cavities to reduce superposition of reflected electromagnetic waves from metal shields, preventing signal distortion and excessive noise in point clouds.

III. General Principles for Coordinated Material Selection

Optical path zone: Silicone-free thermal pad + ITO transparent shielding coating. Prevent silicone contamination, light obstruction and electromagnetic intrusion to preserve optical precision.
Core chip zone: Low-volatility silicone thermal sheet + metal shielding can + local wave-absorbing material. Balances efficient heat dissipation, high-frequency shielding and stray-wave suppression.
Cavity seam zone: Conductive foam + thin graphite thermal film. Achieves electromagnetic sealing and overall heat spreading, compatible with automotive vibration.
Highly integrated compact models: Prefer integrated thermal-conductive wave-absorbing pads to simplify structure, save space and resolve heat dissipation and EMC concurrently.