IXYS Power Semiconductor Thermal Design Guide
This technical reference document provides detailed information about ixys product specifications, characteristics, and performance parameters. Use this information to support your design and analysis activities.
Electrical characteristics are specified over the operating temperature range unless otherwise noted. Parameters are guaranteed by design, testing, or statistical analysis. Typical values is the most likely parametric norm at 25°C.
Thermal characteristics require careful attention during system design. The junction-to-ambient thermal resistance depends on the mounting configuration, PCB copper area, and airflow conditions. Use thermal simulation tools to predict operating temperatures under actual conditions.
Reliability data is based on accelerated life testing and field failure analysis. Mean time between failures (MTBF) calculations follow industry-standard methodologies. Contact BeiLuo for detailed reliability reports and qualification data.
💡 FAE Insights
Professional Insight
Thermal design is often the limiting factor in power electronics performance.
⚠️ Common Pitfalls
- ✗ Using datasheet Rds(on) at 25°C for loss calculations
- ✗ Insufficient heatsink for continuous operation
- ✗ Poor TIM application creating hot spots
- ✗ Ignoring altitude effects
📋 Customer Cases
Power Supply OEM
Electronics
Challenge
MOSFETs overheating in compact enclosure
Solution
Redesigned with larger heatsink and improved airflow
Customer Feedback
"LiTong's thermal analysis identified the root cause and helped optimize our design."
Results
Reduced junction temperature by 35°C, improved reliability
Frequently Asked Questions
1. How do I calculate the required heatsink size?
Calculate required heatsink thermal resistance: (1) Determine total power dissipation P = Pconduction + Pswitching; (2) Determine maximum allowable junction temperature Tj_max (typically 150°C or 175°C); (3) Determine maximum ambient temperature Ta_max; (4) Calculate required Rth(s-a) = (Tj_max - Ta_max)/P - Rth(j-c) - Rth(c-s). Example: P=50W, Tj_max=150°C, Ta_max=50°C, Rth(j-c)=0.5°C/W, Rth(c-s)=0.2°C/W. Rth(s-a) = (150-50)/50 - 0.5 - 0.2 = 2 - 0.7 = 1.3°C/W. Select heatsink with Rth(s-a) ≤ 1.3°C/W under your airflow conditions.
2. What thermal interface material should I use?
Thermal interface material (TIM) selection depends on application: (1) Thermal grease - best thermal performance (0.1-0.3°C·cm²/W), requires careful application; (2) Thermal pads - easier assembly, good for production (0.3-0.8°C·cm²/W), various thicknesses available; (3) Phase change materials - combine benefits of grease and pads; (4) Graphite sheets - excellent for high power density. For TO-220 and TO-247 packages, thermal resistance Rth(c-s) typically 0.2-0.5°C/W with good TIM. Apply thin, uniform layer of grease or use appropriate thickness pad. Replace TIM if removing and reattaching device.
3. How does altitude affect thermal performance?
Altitude affects air density and cooling effectiveness: (1) Natural convection - reduces approximately 10% per 1000m altitude increase due to lower air density; (2) Forced air cooling - less affected but still degrades at high altitude; (3) Thermal resistance increases with altitude, requiring larger heatsinks or increased airflow. At 3000m altitude, natural convection cooling is reduced by ~30%. Solutions: (1) Increase heatsink size by 20-30%; (2) Increase airflow for forced cooling; (3) Use liquid cooling for high-altitude applications. IXYS devices operate at full rating up to 2000m; derate above this altitude or improve cooling.