Diamond vs. Copper: A Technical Comparison for High-Power Electronics
By Appsilon Newsroom
As power densities climb, copper hits its physical limits. We compare synthetic diamond (2100 W/mK) against copper (400 W/mK) for thermal management in high-power electronics — and explain when engineers should switch.
## Why thermal management is now the bottleneck In high-power electronics — RF amplifiers, laser diodes, power modules, and next-generation GaN and SiC devices — performance is increasingly limited not by the transistor, but by how fast heat can be pulled away from the junction. Every additional degree at the junction reduces efficiency, shortens device lifetime, and caps the power you can safely push. For decades, copper has been the default heat spreader. But as power densities rise, copper is reaching its physical ceiling. Synthetic diamond, with a thermal conductivity roughly five times higher, is rapidly becoming the material of choice for the most demanding thermal challenges. ## The headline numbers | Property | Synthetic Diamond | Copper | | --- | --- | --- | | Thermal conductivity | **2100 W/mK** | 400 W/mK | | Coefficient of thermal expansion (CTE) | ~1.0 ppm/K | ~16.5 ppm/K | | Electrical behaviour | Electrical insulator | Conductor | | Density | 3.5 g/cm³ | 8.96 g/cm³ | Appsilon's CVD diamond delivers thermal conductivity above **2000 W/mK**, with our highest-grade material reaching **2100 W/mK** — more than five times that of copper. ## What the numbers mean in practice **1. Heat spreading.** A diamond heat spreader moves heat away from a hotspot far faster than copper, flattening the thermal profile across a die. For concentrated, high-flux heat sources this dramatically lowers peak junction temperature. **2. Thermal expansion match.** Copper's CTE (~16.5 ppm/K) is a poor match for semiconductors like GaN, SiC, and silicon, creating mechanical stress at every thermal cycle. Diamond's CTE (~1.0 ppm/K) sits far closer to these materials, improving reliability and reducing fatigue failures over the device lifetime. **3. Electrical isolation.** Because diamond is an electrical insulator while being an exceptional thermal conductor, it can sit directly in the electrical path as a submount without shorting the device — a combination copper simply cannot offer. **4. Weight.** At roughly 40% the density of copper, diamond delivers superior cooling at a fraction of the mass, which matters for aerospace, satellite, and portable RF systems. ## When should engineers switch from copper to diamond? Diamond is not a drop-in replacement for every heat sink. Copper remains cost-effective for bulk, low-flux cooling. Diamond earns its place when: - Heat flux is high and concentrated (RF/microwave power amplifiers, laser diode bars). - Junction temperature is the limiting factor on output power. - CTE mismatch with copper is causing reliability or lifetime problems. - Electrical isolation is required directly at the thermal interface. - Weight or volume is constrained. ## Appsilon's diamond for thermal management Appsilon Advanced Materials manufactures CVD and HPHT synthetic diamond engineered for thermal applications — heat spreaders, submounts, and thermal interface components — with conductivity exceeding 2000 W/mK. Our materials are produced to tight thickness, flatness, and surface-finish tolerances so they integrate directly into demanding electronic packages. If you are designing a high-power system and copper is no longer keeping the junction cool, our engineering team can help you evaluate diamond for your thermal stack. [Talk to our materials team](/#contact)
