Thermal: what purchasers need to know

Example of Brushless Fan
COPAL – F310R DC brushless fan

Digi-Key’s manager applications engineering and tech support, Dany Haikin, guides readers through the world of thermal management.

Thermal management is the unsung hero of electronics, keeping devices cool and working properly. For purchasing professionals, identifying different types of thermal products, understanding of how they work and recognizing considerations for lead times can help them source the best solution.

Designing a thermal solution is not something purchasing professionals can typically do alone. Engineers should be involved because it requires a different approach than sourcing standard electronic components.

One way to divide different types of thermal products is by active cooling and passive cooling. Active cooling uses power to provide cooling, like a fan or Peltier. Cooling technologies which don’t require power include grease, putty or thermal pads.

The most important consideration is how much space is available? For example, computers with large enclosures have plenty of space for a fan.

Faced with applications like wearables or mobile phones, space is a critical consideration. Big thermal solutions won’t work. Instead we need to utilize thermal pads, gels or grease. These are the types of solutions that can be used to mitigate space constraints. It’s also important to note the types of components and modules which generate heat, such as wireless RF modules and power supplies.

Heat dissipation
Heat generated by a component must be dissipated outside of the application. It’s not enough to absorb the heat, it needs to be transferred to something else, either
the case, another area or into the air.

Thermal management is all about taking heat out of the component and dissipating it in other places. If heat is absorbed by the component, rather than being removed, it will, in the best case, slow down performance and in the worst case, destroy the part.

In applications where space is available, heat sinks can be used. A heat sink is a metal or ceramic sink which is placed on the component. Heat sinks have fins or ribs which transfer heat from the component to air. The heatsink must be mounted tightly to the component. The component’s surface might seem smooth but is actually not. The surface between the heat sink and component needs to be filled with an intermediate material such as a flexible pad, gel or grease. Some heat sinks are supplied with the intermediate pad integrated to the base.

Just as important as the solution you choose, is when you choose it. The two most important technical parameters for a thermal pad, which is a popular solution, is how much heat they can dissipate and how fast they can do it. That is something which needs to be calculated before or during the design process. It then needs to be tested in the actual application, which is where engineers should be involved.

The next major parameter to consider is how flexible the pad needs to be. At this point, it’s also important to consider whether the application should use a pad or a gel. A gel can be either a grease or putty. One problem with grease is that maintenance can become problematic, dirty and messy if a greased component needs to be reworked or repaired. Also, in the long-term grease is not very reliable because sometimes it can lose its shape and doesn’t spread equally across the component’s surface. On the other hand, grease is much cheaper than other solutions.

A pad is better in most cases but it should be cut to fit the component’s shape. The custom nature of using a pad solution means it can cost more. Purchasing professionals should take all of these variables into account, plus the quality and additional time it takes the manufacturer to cut the pads.

For lead times, most manufacturers will quote a standard time scale of something like five to six-weeks, plus maybe one to two additional weeks for pre-cutting. Some manufacturers might quote up to 12-weeks because the material used is a combination of many raw materials and is thus dependent on other manufacturers. Thus, external issues can delay lead times.

For example, the Japanese earthquake which occurred some years ago ruined many of the glue factories. Glue is a key component of pads, so lead times extended to 16-weeks or longer. With Covid-19, some factories closed. However, due to its stock holding, Digi-Key’s lead time remained unaffected and the influence of the pandemic has been minimal. Ultimately, it depends on the application and how things compete on price.

For thermal management, component traceability is also an important consideration. Digi-Key only buys directly from manufacturers to ensure authenticity. This also helps buyers quickly isolate any potential issues with prototypes and get to the source of the problem faster.

Another reason traceability is important with thermal management is shelf life. With specialty thermal pads, grease or putties, it is important the distributor is paying attention to shelf life. Different pads, manufacturers and chemistries all have different shelf lives: sometimes it can be one-year, sometimes it can be five-years, others can be indefinite. Regardless, it must be taken into account by sourcing professionals during the purchasing process.

While sourcing thermal management solutions can be more complex than typical electronic components, it can be a really rewarding experience, providing new pathways for the engineering and purchasing teams to work together. Digi-Key offers thousands of different thermal management parts from stock for immediate shipment from more than 65 quality, name-brand manufacturers. As always, Digi-Key and its in-house team of engineers are available to provide 24/7 customer support for purchasing professionals who are making decisions on thermal management solutions.