Diamond Heat Sink Submounts for Large Unmanned Aerial Vehicles (UAVs): Applications and Specifications

I. Applications (Long-Endurance / Heavy-Lift Large UAVs, including High-Altitude Long Endurance, HALE)

Positioning: Packaging-level thermal spreader bonded to the backside of GaN/SiC power chips. It mitigates hotspot burnout under high-altitude low-pressure environments with minimal forced convection. Core benefits: weight reduction, higher power density, extended flight endurance, and improved high-temperature reliability.

1. Motor Electronic Speed Controllers (ESCs) – Primary ApplicationGaN/SiC power MOSFETs and power transistors inside ESCs. At high altitudes, rarefied air renders air cooling ineffective, resulting in extremely high localized heat flux on chips. Diamond heat sinks rapidly spread heat laterally to lower junction temperature and enable sustained high-power output of ESCs. With equivalent cooling performance, diamond submounts achieve over 70% weight reduction compared with copper substrates, directly increasing payload and flight time while mitigating delamination failure risks induced by repeated thermal cycling.

2. Onboard RF Power Amplifiers (Communication / Radar)GaN power amplifiers for airborne video links, data links and synthetic aperture radar (SAR). Hotspots are highly concentrated in high-frequency devices. Diamond heat sinks reduce thermal resistance to stabilize long-range communication and suppress gain drift caused by elevated temperatures.

3. LiDARThermal management for laser emitter chips. Laser diodes constitute the main heat source of LiDAR. Diamond heat sinks stabilize laser wavelength and output power to enhance the stability of long-range detection.

4. Airborne DC-DC Fast Charging Power ModulesHeat dissipation for high-power power conversion chips. Capable of withstanding heat flux exceeding 1 kW/cm² to prevent thermal breakdown of power devices during fast charging.

UAV-Specific Environmental Advantages: Low coefficient of thermal expansion (CTE) suited for wide thermal cycling from -55 °C to +125 °C at high altitude; electrically insulating with no leakage risk; vibration-resistant for severe airborne vibration conditions.

II. Product Specifications (Aerospace-Grade Polycrystalline CVD Diamond Heat Sink Submounts)

• Thermal conductivity: 1600–2000 W/m·K (at room temperature); high-grade samples reach 2000–2200 W/m·K

• Thickness: 200 μm / 300 μm / 500 μm; 300 μm is the mainstream choice balancing thermal spreading and weight saving

• Dimensions: small square pieces 5×5 mm, 8×8 mm, 10×10 mm; custom dicing available per bare die size, with edge chamfering to prevent chipping

• Surface polishing: double-sided CMP, Ra＜5 nm

• Metallization: Ti/Pt/Au (standard); pre-deposited AuSn solder layer optional for eutectic bonding

• Resistivity: ＞10¹³ Ω·cm, electrically insulating to prevent device leakage

• CTE (Coefficient of Thermal Expansion): ≈1.0 ppm/K, matched with SiC/GaN to minimize thermal cycling stress

• Operating temperature range: -60 °C ~ 150 °C, compliant with aerospace UAV environmental requirements

• Thickness tolerance: ±0.03 mm; low warpage to guarantee bonding yield

III. Selection Guidelines

1. Polycrystalline CVD diamond heat sink submounts are preferred; lower cost than single crystal and suitable for mass airborne sampling. Single crystal is mainly deployed for high-end radar power amplifiers.

2. The top priorities for high-altitude UAVs are low thermal resistance, lightweight design and thermal cycling reliability; maximum thermal conductivity is not blindly pursued.

3. Stack-up structure: Die → Solder → Diamond heat sink submount → AlN substrate / microchannel cold plate. This is a back-end packaging solution with mature processes and no modifications required to chip epitaxy.

Key Term Glossary

• HALE = High-Altitude Long Endurance

• ESC = Electronic Speed Controller

• SAR = Synthetic Aperture Radar 

• coefficient of thermal expansion (CTE)