What Is a Thermal Pad Used For? Applications, Selection, and Best Practices

Overview: What Is a Thermal Pad?

A thermal pad is a soft, thermally conductive sheet placed between electronic components (like CPUs, MOSFETs, LEDs, or power ICs) and a heatsink or metal enclosure. Its main use is to fill micro-gaps and uneven surfaces, ensuring consistent heat transfer and reducing the risk of hotspots. Unlike liquid thermal paste, pads are solid at room temperature and are designed for quick, clean installation in both prototyping and production environments.

Thermal pads are available in varying thicknesses (usually 0.5mm to 5mm) and are made from silicone, graphite, or Phase Change Materials. They are commonly used in laptops, power supplies, LED modules, graphics cards, and automation control panels-applications found throughout South African industries and education labs.

Key Applications in South Africa

• Easily coupling single-board computers (e.g., Raspberry Pi, Arduino derivatives) to heatsinks or metal housings.
• Ensuring reliable thermal interface for industrial drives, automotive modules, and 3D printer control boards.
• Popular in tertiary engineering labs for rapid student prototyping-quick swaps and component changes are possible without messy residue.

How Do Thermal Pads Work?

Thermal pads compensate for microscopic surface imperfections between two mating parts. Without a pad, air gaps act as thermal insulators and reduce cooling performance. A pad provides an even, compressible layer that conforms to both surfaces and bridges these gaps, decreasing thermal resistance.

Thermal Pad Specifications & Standards

• Thermal Conductivity (W/mK): Higher values mean better heat transfer. 3-6 W/mK is common for most commercial pads.
• Thickness (mm): Choose based on the gap between surfaces-the pad should compress slightly for best contact.
• Operating Temperature: Most pads are safe up to 100-200 degreesC; always check datasheet if exposed to higher temperatures.
• Compressibility: Softer pads conform better but may have lower durability.
• Dielectric Strength: Important for pads used on exposed ICs or MOSFETs that need electrical isolation.

How to Choose a Thermal Pad: Step-by-Step

1. Measure the gap: Use calipers or stack-up drawings to estimate the space between component and heatsink.
2. Select thickness: Pad should compress by 25-50%, ensuring full contact but not excessive squish-out.
3. Check thermal conductivity: For power ICs or MOSFETs, 3-6 W/mK is usually enough. For high-brightness LEDs, consider 6+ W/mK.
4. Confirm dielectric strength: If used on exposed conductors, choose pads rated for the required voltage.
5. Cut to size: Most pads can be trimmed with scissors for odd shapes.

Example Calculation: Heatsinking a Raspberry Pi

Suppose you have a Raspberry Pi 4 with a CPU dissipating 5 W (watts) under load. You want to keep the temperature rise across the pad under 10 degreesC. How do you select a pad?

• CPU contact area: 15 x 15 mm (0.000225 m2)
• Pad thickness: 1 mm (0.001 m)
• Thermal conductivity: 6 W/mK

Temperature rise (ΔT) is calculated as:
T = (Power x Pad Thickness) / (Thermal Conductivity x Area)
Insert values:
T = (5 x 0.001) / (6 x 0.000225) ~ 3.7 degreesC

This pad keeps the CPU well within a 10 degreesC rise, confirming suitability.

Troubleshooting: Common Issues

• Pad too thick: Poor contact or board flex-try a firmer or thinner pad.
• Pad too thin: Doesn't bridge gap-hotspots, instability, or rapid thermal shutdown may result.
• Misalignment: Check pad placement carefully; even a small offset can increase thermal resistance.
• Dry-out or hardening: Over years, low-quality pads may lose compressibility; choose reputable suppliers and replace as needed during maintenance.

Where to Buy & Local Options

You can browse Thermal Management at Communica, including trusted brands and cut-to-size sheets in different profiles, right here in South Africa. Order for pickup at Samrand or main branches or request a VAT invoice/quote for educational orders.

Sources

• Bergquist Thermal Interface Materials Overview
• 3M: What Are Thermal Pads?
• Communica Thermal Management Range
• Electronics Cooling: Guide to Thermal Interface Materials
• Texas Instruments: Guide to Power Module Heatsinking