Why Do TIMs Break Down at High Voltages? - Chomerics Division | Parker US
Blog: Top 5 Questions and Answers on Thermal Interface innovations for Consumer Electronics

Thermal interface materials (TIMs) are commonly used to eliminate air gaps present when an electronic component and its heat dissipating component (heat sink, vapor chamber, cooling pipe, etc.) are mated together. TIMs are typically comprised of two major constituents; the polymer binder, which allows for the TIM to be soft and conformable (necessary to displace air during the assembly process), and the ceramic filler particles, which provide the TIM with a high level of thermal conductivity. While both the polymer binder and the ceramic filler particles are typically electrically insulating, if the TIM is subjected to a high enough voltage differential, electrical current can still short its way through. This phenomenon is known as electrical breakdown, and the voltage at which this breakdown occurs is referred to as the breakdown voltage.

Causes of Electrical Breakdown in TIMs

There are four ways that electrical breakdown can occur within an electrically insulating material. While only one of these causes is commonly seen in TIMs, it’s important to understand the mechanisms that contribute to all four scenarios. 

Less Common Causes of Electrical Breakdown

The less common causes of electrical breakdown are:

  1. Polarization of the electron clouds surrounding the atoms within a material. This is only important in situations where the TIM would be exposed to extremely high frequencies (PHz and higher) and is not usually the cause of electrical breakdown within a TIM.
  2. Movement of ionic charges within a materials’ composition. This is also not often seen in TIMs as they are generally compromised of covalently bonded materials without ionic charges.
  3. Alignment of dipoles within a materials’ composition. Most TIMs are comprised of non-polar materials which do not feature dipoles; therefore, this is also not a prevalent cause for electrical breakdown within a TIM.

Primary Cause of Electrical Breakdown: Space Charge

The primary cause of electrical breakdown within TIMs is space charge, or the movement of charge carriers that are trapped within the material. There are two sources of space charge that you’ll often find within a TIM. Firstly, space charge can be introduced by impurities within the raw ceramic particles, which is often a byproduct of the processing that occurs when ceramics are mined, extracted, and broken down into the small particles used within TIMs. To reduce the effect of space charge on the breakdown voltage of an otherwise electrically insulating material, it is paramount that the highest purity of ceramic particles are used to manufacture a TIM. At Parker Chomerics, we have instituted robust supplier selection and raw material inspection processes to ensure the lowest possible chance for the presence of impurities within our materials.

The second source of space charge is humidity. Water is both a polar molecule and contains concentrations of ionic charges (OH- and H3O+). If the TIM is used in a high-humidity environment, over time you would expect to see a reduction in the breakdown voltage due to the permeation of moisture, and therefore charge carriers, into the material. 

Enhancing Resistance to Electrical Breakdown

Fortunately, Parker Chomerics can manufacture our TIMs in a manner that boosts their resistance to electrical breakdown and increase their breakdown voltage. The most popular way to do this is to use a dielectric carrier on the material to provide an extra layer of electrical insulation. Our THERM-A-GAP PAD 30PN and THERM-A-GAP PAD 80KT are two very popular configurations of these materials perfectly suited for applications with exposure to high-voltages and require electrical insulation.

Reach out today for a free sample of either of these materials. 

THERM-A-GAP PAD 30PN

Blog Post contributed by KJ Sterling, Global Automotive Market Manager, Chomerics Division.

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