What Are Thermal Interface Materials?
The simplest explanation is that thermal interface materials (also knowns as TIMs) are used to draw heat from a heat producing component, then transfer that heat to a either a heat sink, or a case. Even more simply put, they get the heat out. Thermal interface materials have been used for decades, and the technology has rapidly developed as electronic designs have gotten smaller and hotter.
What was once accomplished by grease, mica and fans – is now accomplished with thin pads and cure in place liquid materials. These materials can range in thickness from 1.25mm to 6.5mm in pad form, while liquid dispensed based options are theoretically able to be as thin as .025mm and as thick as you want them to be. While both of those extremes are nearly impossible in practice, it does showcase the versatility of TIMs in liquid dispensed form.
Chemistry
The majority of thermal interface materials used today are silicone based, but there are several silicone-free thermal interface options. These options include polyurethane, polyester, graphite and some forms of phase change materials. Chemistries can make for wildly different behaviors, and this is explored in much greater depth here.
There are two main reasons for silicone dominating this space:
- Its soft. This can make or break performance. Because thermal cycling will create CTE (coefficient of thermal expansion) mismatch between the heat producing component and whatever its interfacing to, the material needs to be able to move with the components, in order to avoid exerting stress and damaging components or even breaking solder joints.
- Heat resistance. Silicones can handle heat well in excess of 200 C and keep their performance
Today, thermal interface materials are used in virtually all electronic segments. From smartphones to aerospace, they’ve become a necessity to design engineers that have heat to get rid of. Usually, the first go around is unforeseen, resulting in a very thick pad, or partial redesign. This is because its not always obvious that thermal relief will be needed. This is one of the reasons for such a wide array of shapes, sizes and use cases.
Thermal Fillers
Most thermal materials on the market are going to utilize fillers to work the magic of heat transfer. These fillers are most commonly made of alumina oxide, but can be made of other compounds like boron nitride on the high end and standard silica on the lower end. Thermal fillers range widely in quality and construct. More reliable suppliers will use higher grade fillers that not only transfer heat more effectively but suspend themselves in the carrier media more effectively.
Thermal Grease
Thermal grease has been around for decades and is used broadly in all applications. Grease is a favorite of DIY computer builders and can be seen in almost every YouTube instructional video on the subject. The reason it is largely avoided in industrial and professional application is simple. It doesn’t last. But Remember our old friend CTE mismatch? Well, that action does an excellent job of pumping thermal grease right out of the interface. Grease also tends to dry out over time as well – again rendering is use ineffective, especially in long term use.
But it can be alluring. It is always going to be much cheaper than most pad, and liquid dispensed option. Its also highly available. You can easily buy it in relative bulk from many online retailers. But this must be stressed. Thermal grease is not reliable for long-term end-product use.
Conclusion
Thermal interface materials are polymeric pads or liquids that are used to draw heat from heat-producing components and draw it to a heat sink or case. In many cases, they can alleviate the need for fans or heat pipes.
TIMs are used ubiquitously in electronics from virtually all industries. If you’d like to learn more about them, we invite you to read the rest of our learning articles. If you want some more in depth help, reach out and we’d be happy to connect you with the right supplier for your needs, or even consult on your thermal interface material needs.