Translating the Curve: A Practical Guide to Reading TIM Supplier Datasheets
A Thermal Interface Material (TIM) datasheet is your primary tool for selection, but it can be a mix of essential data, standardized specs, and marketing flair. Knowing what to look for—and what questions to ask—transforms this document from a sales piece into an engineering blueprint. Let’s dissect a typical datasheet.
Section 1: The Headline Numbers – Proceed with Caution
- Thermal Conductivity (k): This is the most prominent number, but never make a decision based on this alone. Always check the test method and conditions (e.g., “ASTM D5470, @ 50 psi, 50°C”). A high k-value achieved at 200 psi on a polished surface may be irrelevant to your low-pressure, rough-surface application.
- Thermal Impedance (θ): This is a far more valuable metric than k alone, as it includes contact resistance. A lower θ is better. Ensure it is specified at a relevant pressure and temperature (e.g., “0.15 °C·cm²/W @ 20 psi, 75°C”).
Section 2: The Graphical Gold – Performance Under Pressure
The most informative part of a good datasheet is the Thermal Impedance vs. Applied Pressure curve. This reveals:
- Pressure Sensitivity: Does the performance improve dramatically with more pressure? If your assembly has low clamping force, a TIM that only works well at high pressure is a poor choice.
- Comparative Performance: Overlay curves from different suppliers to see which material performs best across your specific pressure range.
Section 3: The Reliability Snapshot
Look for summarized results from key tests:
- Thermal Cycling: e.g., “-40°C to +125°C, 500 cycles. Δθ < 10%”. This indicates long-term stability.
- High-Temperature Aging: e.g., “150°C, 1000 hours. No cracking or delamination.”
- Outgassing Data: Critical for vacuum or optical applications. Look for low %TML (Total Mass Loss) and %CVCM (Collected Volatile Condensable Materials).
Section 4: Material Composition & Properties
- Polymer Base: Silicone, acrylate, polyolefin? This affects chemical compatibility and temperature range.
- Filler Type: Alumina (Al2O3) is common and cost-effective. Boron Nitride (BN) offers higher performance. Aluminum (Al) or graphite fillers are conductive.
- Fire Rating: UL 94 V-0 is standard for many electronics.
- Dielectric Strength: Important for insulating applications.
A datasheet is a starting point for conversation, not the end. Use it to formulate specific questions for your supplier: “Can you provide the full impedance curve?” or “What is the peel adhesion strength to anodized aluminum?”
