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Interface materials are used to eliminate any air filled gaps (typically microscopic gaps) that may exist between the heat source and the intended heat sink. There are many different types of thermal interface materials (aks TIM’s). All applications have specific needs and selecting the most effective material will require some effort to choose the correct on. The following is a short list of the most common types and some of the pros and cons. Grease | Probably the most common thermal interface material for high performance applications. Pros - The lowest thermal resistance based on the typical thickness that you will use.
- Can be applied in very thin layers.
- Can be applied in any shape or pattern – circles, dots, squares etc.
Cons - Difficult to apply
- Cannot fill large gaps.
- Difficult to package and ship without contamination.
- Rework is challenging. Assembly house typically does not have the correct tools to reapply.
| Pads | Many types of materials will be lumped in this category. Pros - Typically easy to handle.
- Typically have an adhesive on one side to enable it to adhere to the heat sink during shipping and handling at the assembly site.
- Easy to handle and ship.
- Rework is easy.
- inexpensive
- Many suppliers
Cons - Typically not the best thermal performance.
| Phase Change
Materials (PCM) | Materials that are solid or waxy at room temperature and become more liquid at elevated temperatures. Pros - Excellent gap fillers – the material softens as the heat source rises in temperature causing the PCM to become less viscous filling all gaps.
- Easy to handle and ship.
Cons - Rework can be challenging. It is difficult to clean the heat source and the heat sink before reapplying.
- Material can migrate off the heat source and contaminate nearby components.
| Gap Fillers | Typically used to cover low wattage components where a nearby or overhead heatsink cannot attach. Pros - Good for covering large areas and large gaps.
Cons - Thermal performance is poor.
- Material needs to be compressed – the higher the compression the better the performance.
| Double Sided Tapes | Pros - Easy and inexpensive way to attach heat sink to heat source.
Cons - Thermal performance not great, but typically OK for low wattage BGA heat sinks.
- Heat sink must be small and light weight.
- Rework is difficult.
| Epoxies | Pros - Thermal performance not great, but typically adequate.
- Relatively easy to use at the assembly house (Contract Manufacturer).
Cons - Rework is very difficult. Typically cannot remove after hardening.
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Interface
