Thermal Design and Heatsink Selection Guide
Thermal Design Fundamentals
Proper thermal design is essential for reliable operation of power modules. This guide covers the fundamentals of thermal management including heat transfer mechanisms, thermal resistance networks, and temperature limitations.
Power Loss Calculation
Accurate power loss calculation is the foundation of thermal design. Calculate conduction losses based on voltage drop and current, and switching losses based on switching energy and frequency. Consider temperature effects on parameters.
Heatsink Selection
Heatsink selection involves determining the required thermal resistance based on power dissipation, ambient temperature, and maximum allowable junction temperature. Consider heatsink material, fin geometry, and airflow for forced convection designs.
Thermal Interface Materials
Thermal interface materials (TIM) fill microscopic air gaps between module and heatsink. Select TIM based on thermal conductivity, thickness, compliance, and long-term reliability. Proper application is critical for performance.
Cooling System Design
Cooling system options include natural convection, forced air, and liquid cooling. Select based on power level, ambient conditions, and system constraints. Design for worst-case conditions with appropriate safety margins.
Temperature Monitoring and Protection
Implement temperature monitoring using NTC thermistors integrated in modules. Use temperature data for protection, thermal management, and diagnostics. Plan for overtemperature protection with appropriate thresholds.
💡 FAE Insights
📋 Customer Cases
Power Electronics
Solution
Discovered poor TIM application and uneven mounting pressure; redesigned mounting
Results
Junction temperature reduced by 25°C, resolved thermal issues
Frequently Asked Questions
1. How do I calculate the required heatsink thermal resistance?
Calculate required heatsink thermal resistance using: RthSA = (Tj_max - Ta) / Ploss - RthJC - RthCS, where: Tj_max = maximum junction temperature (125-150°C for IGBT, 150-175°C for SiC), Ta = ambient temperature, Ploss = total power dissipation, RthJC = junction-to-case thermal resistance (from datasheet), RthCS = case-to-heatsink thermal resistance (typically 0.1-0.3K/W with TIM). Example: GD100HFL120C2S at 100A, 175W loss, Tj_max=125°C, Ta=40°C, RthJC=0.35K/W, RthCS=0.1K/W: RthSA = (125-40)/175 - 0.35 - 0.1 = 0.486 - 0.45 = 0.036K/W. This requires excellent cooling (liquid cooling or very large forced air heatsink). For practical designs, limit Tj to 100-110°C for long-term reliability.
2. What type of thermal interface material should I use?
TIM selection for Starpower modules: (1) Thermal grease (paste): Best thermal performance (0.05-0.1K·cm²/W), requires proper application (thin, uniform layer). Best for high-performance applications. (2) Phase change materials: Good performance (0.1-0.2K·cm²/W), easy application, reliable long-term. Good balance of performance and ease. (3) Thermal pads: Moderate performance (0.2-0.5K·cm²/W), easiest application, good for production. (4) Gap fillers: For uneven surfaces or large gaps. For Starpower modules, we recommend: High-performance applications - thermal grease (e.g., Shin-Etsu X-23-7762). General industrial - phase change (e.g., Honeywell PCM45F). Production environments - high-performance pad (thermal conductivity >5W/mK). Apply TIM per manufacturer guidelines - typically 0.1-0.2mm thickness.
3. How do I design a liquid cooling system for high-power modules?
Liquid cooling design for Starpower high-power modules: (1) Cold plate design: Use copper or aluminum with optimized channel geometry. Target thermal resistance <0.05K/W. (2) Flow rate: Typically 2-4 L/min per kW of heat dissipation. Higher flow improves heat transfer but increases pump power. (3) Coolant: Deionized water with corrosion inhibitors, or glycol/water mix for freeze protection. (4) Temperature rise: Design for 5-10°C temperature rise through cold plate. (5) Pressure drop: Balance between heat transfer and pump requirements; typically 0.2-0.5 bar. (6) Materials: Ensure compatibility between cold plate material and coolant; avoid galvanic corrosion. (7) Monitoring: Implement flow and temperature monitoring for protection. Example: 500W module with 0.05K/W cold plate, 25°C inlet: Tcase = 25 + 500 × 0.05 = 50°C, Tj = 50 + 500 × 0.35 = 225°C (too high). Need better cooling or lower power.
4. What mounting torque should I use for Starpower modules?
Mounting torque for Starpower modules: (1) 34mm modules: 2.5-3.0 N·m (22-27 lbf·in). Use M4 screws. (2) 62mm modules: 4.0-5.0 N·m (35-44 lbf·in). Use M5 screws. (3) EasyPACK/EasyPIM: 0.8-1.2 N·m (7-10.5 lbf·in). Use M3 screws. (4) General guidelines: Use torque wrench for consistent mounting. Apply torque in stages (50%, then 100%). Use proper thread engagement (1.5x screw diameter minimum). Use washers to distribute load. Follow cross-pattern for multiple screws. Overtorquing can damage module package or strip threads. Undertorquing results in high thermal resistance. Retorque after thermal cycling (24 hours operation). Starpower provides detailed mounting instructions in datasheets. Use specified torque for optimal thermal performance and reliability.