When evaluating thermally conductive silicone pads, hardware engineers and thermal solution designers typically focus on two core parameters at the same time: thermal performance and electrical insulation. In practice, a common misconception holds that a material capable of conducting heat must also conduct electricity. In fact, standard thermally conductive silicone pads are functional materials that conduct heat but not electricity. This article takes a closer look.

[Figure: TIF100-14 / 15 / 25 series thermally conductive silicone pads]

1. Thermal Conduction ≠ Electrical Conduction: The Basic Principle

Thermally conductive silicone pads are made from a silicone base into which non-metallic thermally conductive fillers such as aluminum oxide (alumina) and boron nitride are compounded. These fillers are responsible for transferring heat, but they contain no free electrons and therefore cannot conduct electric current.

The two product types can be distinguished by their filler systems:

As a result, the thermally conductive silicone pads used in everyday applications such as power supplies, graphics cards and motherboards are insulating by default, and will not short the chip to the metal housing.

2. How to Evaluate the Insulating Performance of Thermally Conductive Silicone Pads

The core parameter for evaluating insulating capability is breakdown voltage (dielectric strength), expressed in kV/mm: the voltage that one millimetre of the material can withstand without breakdown. For standard insulating thermally conductive silicone pads, breakdown voltage is generally ≥4 kV/mm, while some high-insulation grades reach 6~10 kV/mm, meeting the safety requirements for consumer electronics, industrial control, graphics cards and power supplies.

Key influencing factors to note:

Thickness: the thinner the pad, the lower the breakdown voltage it can withstand;

Surface condition: metal debris or dust on the surface will significantly reduce insulation effectiveness, so cleanliness must be maintained during assembly;

Pressure: assembly pressure likewise affects actual insulating performance.

In addition, the materials comply with RoHS and REACH environmental standards, do not readily carbonize under high-temperature operation, and maintain their insulating properties consistently.

3. Selection Notes: Applications Where Insulation Requires Particular Attention

1. Graphics cards and compute boards: between the chip and the metal base of the heatsink, heat must be conducted while chip pins must be prevented from shorting — insulating thermally conductive silicone pads should be the first choice;

2. Power supplies and inverters: at high-voltage/low-voltage isolation points, breakdown voltage parameters must be verified;

3. High-voltage applications: thermal conductivity must not be the only selection criterion — the insulation class must match the safety requirements of the complete system.

It should be emphasised that specifying a conductive silicone pad by mistake will directly short the circuit board and burn out components, causing major losses.

4. Summary

Standard thermally conductive silicone pads do not conduct electricity and offer good insulating performance. They conduct heat through ceramic fillers while also providing voltage isolation, meeting the dual requirements of heat dissipation and electrical isolation in electronic products.

It should be noted that a trade-off exists between thermal conductivity and insulating performance: the higher the thermal conductivity of a grade, the greater the filler loading, and breakdown voltage decreases slightly. Selection should therefore not pursue high thermal conductivity alone; device voltage and gap thickness must be matched together so that heat dissipation efficiency and electrical safety are balanced.