thermal

**Thermal Interface Material** is **material between die and heatsink enabling efficient heat transfer while accommodating mechanical mismatch** — critical for temperature management. **Thermal Conductivity** k: air ~0.026; silicon ~150; copper ~400 W/mK. TIM goal: maximize k. **Thermal Resistance** R_th = L/(k·A); minimize thickness, maximize area, maximize k. **Types** phase-change (PCM): solid, melts slightly when compressed. Thermal grease: oil + particles. **Phase-Change Materials** excellent wetting; no pump-out. Preferred for reliability. **Thermal Grease** convenient; risk oil pump-out over thermal cycling. **Fillers** ceramic particles (alumina, BN, AlN) ~70 wt% increase k. **Bondline Thickness** typical 0.1-0.5 mm; thinner reduces resistance but harder to apply uniformly. **Pressure Dependence** resistance decreases with applied pressure (5-50 psi). Compliance needed. **Surface Finish** rough surfaces increase contact resistance (Ra ~0.4-0.8 μm ideal). **Compliance** TIM deforms accommodating CTE mismatch. Prevents die cracking. **Pump-Out** grease exudation over time; minimize via viscosity, particle structure. **Long-Term Stability** thermal properties degrade: oxidation, phase separation, hardening. **Testing** thermal cycling, pressure cycling, humidity validate reliability. **Cost** high-k TIM expensive; choose lowest-cost meeting requirements. **TIM optimization crucial for thermal management** of high-power packages.