Simulation Experts Save Electronics from Thermal Damage
Shawn Wasserman posted on February 13, 2017 |
Engineers might have good instincts, but they aren’t always right. This design assumed that the hard drives wouldn’t overheat. They did. Simulation can help engineers avoid these errors. (Images courtesy of QRC Technologies).

Engineers might have good instincts, but they aren’t always right. This design assumed that the hard drives wouldn’t overheat. They did. Simulation can help engineers avoid these errors. (Images courtesy of QRC Technologies).

We’ve all heard Donny from marketing come up with the bright idea that customers want smaller electronics. The problem is, how do the engineers, the real heroes of the design process, ensure those products don’t overheat with their ever-shrinking surface area?

 The smaller the space, the less options there are for cooling key components. It’s that simple. You can tell Donny all you like that it isn’t as easy as that shrink ray on TV. No mention of heat-cracking chips, hitting safety shutoffs or dropping data will get him to change his marketing-based product ideas. “I just can’t do it Captain” never worked with Kirk either; Scotty and you just have to figure it out.

This is the line that David McCall, senior mechanical engineer at QRC Technologies, walks. McCall designs enclosures for RF testing equipment that measure cellular band signals. Designing these enclosures using the SimScale simulation software to optimize the heat dissipation is a big part of his product design process. 

These RF testing tools can get hot, up to 50 °C (122 °F) hot when relying on passive cooling alone. This didn’t shape up too well with the initial designs from the QRC engineering team when they relied on gut intuition and rule-of-thumb engineering to cool the hard drives.

“It got so hot we had to put in an active cooling system,” said McCall. “It was getting so hot that the hard drives were dropping data. We assumed a thermal pad between the hard drive and board would be enough. It wasn’t. We had a good solution for the CPU, but the hard drives were at their limit. The controller chip was hitting the physical limit and was shutting down as a defensive strategy to ensure nothing got damaged.”

Much of the design behind cooling electronics comes from “common sense” science. It doesn’t take an engineer to see how the basic rules of heat dissipation work. The larger the surface area, the more heat you lose. Even your dog sprawled out in the shade understands this concept.

However, this rule of thumb gets jammed in a door when things get smaller; thermo and fluid dynamics make things complicated fast. To account for that, McCall and his team turned to SimScale for electronics thermal cooling simulations and physical testing.

Electronics Cooling Challenges

McCall and his team rearranged the internal layout of the device. The less air trapped inside acting as an insulator, the better it performed. This design isn’t perfect yet but it’s getting there. (Image courtesy of QRC Technologies.)

McCall and his team rearranged the internal layout of the device. The less air trapped inside acting as an insulator, the better it performed. This design isn’t perfect yet but it’s getting there. (Image courtesy of QRC Technologies.)

Okay, we get it, when cooling an electronic passively, the larger the surface area, the more heat you lose. Additionally, the more heat-conducting metal you have, the better. Additionally, the larger the mass of the heat sink, the longer it takes until it reaches its saturation temperature. But as previously stated, there is a point at which increasing the surface area can cause issues—for instance, too many fins.

“You could go with the fins, but you can also get them too close, where they don’t have any natural air flow,” explained McCall. “This is okay with active cooling but not with passive.”

McCall also notes the tradeoff—as these fins get closer together, they will also get smaller. And once they get too thin, they can fold over easier, reducing their effectiveness.

For those looking to create a rugged design with quick cool downs, this simply won’t do. You will want to make those fins as thick and far apart as possible.

So why not just make the case larger? It stands to reason that as the surface area of the case grows, the heat will dissipate faster. And to a certain extent, this is true, much to the chagrin of Donny from marketing. Unfortunately, this theory doesn’t always work when air flow is taken into consideration. So, score one for Donny?

“If you have a large case with a lot of wattage inside, then it will make it hotter anyway,” said McCall. “It’s also about what you have inside. We found that less air in the case helped us passively cool it. If you have air in there not moving, it’s a good insulator. If you are going to go with active cooling, however, you want to try and maximize the airflow so you don’t stagnate the air in the case.”

This was the case with the overheating hard drives. The team expected the power supply and CPU to be the major heat sources, so they designed them to have a heat sink that directly connected to the enclosure. The hard drives didn’t have this set up, but that heat had to go somewhere so it just stayed in the stagnate air within the housing.

“We designed some heat sinks with copper slugs and graphite to give these hard drives a heat path out to the enclosure,” noted McCall. “We went with copper and graphite for the internal piece, as the thermal conductivity is higher, especially for thinner pieces. This makes it lose more heat than just simply radiating into the enclosure.”

In other words, the solution was to ensure the heat can get to the product’s outer casing easier than it could traveling through the air. The enclosure then loses the heat to the outer environment from there. “The way to combat heat buildup is to get out of the enclosure,” confirmed McCall. “Get to the surface area and blow a fan on it or get a case to radiate it out into the environment.

So, a question you might be asking is why not have direct contact between the hot electronic part and the casing? The answer here is because of machine tolerances. You want them as close as possible to minimize the space between them, but if they touch, they can damage the electronics during manufacturing.

To combat this, engineers can use thermal pads. These pads ensure that the heat can be easily transferred between the chip and the enclosure while ensuring they don’t directly touch, risking damage. However, as with the hard drive example, these pads may not be enough, and a little copper and graphite will go a long way.

Other heat reduction suggestions from McCall include:

  • A stronger power supply—power supplies near their capacity will product more heat
  • Throttling the CPU so it doesn’t pull as much wattage, reducing the heat that bleeds off
  • Using heat pipes to move heat quickly 

However, for those looking to use heat pipes, they should be aware that they will still need to design the chip to have heat sinks. This is because the pipes won’t start working until the fluid inside reaches its vaporization point.

How to Reduce the Heat of Electronics with Simulation

“Always look at simulation and CAD as the first round of prototypes,” said McCall. “Thermal simulations act as the first line of defense to see if a chip will be too hot, or even break, if it has no path for the heat to get out.”

Using SimScale’s cloud-based simulation software, McCall and his team were able to test multiple variations of the RF tester quickly and accurately. The above comparison shows similar results between the vertical and horizontal fins. The team went with the horizontal fins because they are easier to machine. (Image courtesy of QRC Technologies.)
Using SimScale’s cloud-based simulation software, McCall and his team were able to test multiple variations of the RF tester quickly and accurately. The above comparison shows similar results between the vertical and horizontal fins. The team went with the horizontal fins because they are easier to machine. (Image courtesy of QRC Technologies.)

To perform these thermal simulations, McCall’s team used SimScale. SimScale is a browser-based simulation platform that allows engineers to perform their simulations in the cloud. The simulation platform works on a freemium licensing scheme in which engineers pay a monthly fee to use the platform to create private projects. Engineers will still be able to access this data after they cancel their subscription, but will only be able to make public projects until they restart the monthly fee.

“The reason we went with SimScale is because it doesn’t lock up resources locally,” said McCall. “I like the advantage of uploading the CAD into the cloud and running the simulation on someone else’s computer that we rent time on.” 

“This was also a lot more cost effective as opposed to getting a seat and having it sit there for three to four months,” McCall added. “We are a small company and might use a simulation for two solid weeks every six months—so you can’t borrow that from a friend.”

McCall has mostly stuck to the thermal side of SimScale’s simulation platform. However, he noted that these thermal functions were powerful and broad enough to meet his needs.

McCall warned that with all simulations, from any computer-aided engineering software, the results need be taken with a grain of salt until the model is verified. That is why McCall’s team still uses prototypes when designing products. The physical testing will never go away.

“You can simulate it all day, but you may not have set it up properly and it won’t go right,” said McCall. “You have to trust and verify. We will therefore get the first prototype up and then run it and compare the data with the simulation to validate it. We then rethink the simulation if needed. Next time you set up the simulation, you can then make something close to this configuration with added confidence.”

Good thing they verified the simulations, as even engineers make mistakes. McCall notes that a simple mistake such as forgetting to change the material properties on a part can have drastic effects on the results. It even happened to his team once. Thankfully, they caught it in time like any engineer worth their salt would.

McCall’s team used simulations to test the orientation of the fins on one of their product’s enclosures. They will often make several different CAD designs they think will improve performance and then run the simulations as a check. This will help them to avoid prototyping each of these designs since the simulation was already verified with the first prototype. This helps the team to find direction faster and cheaper.

“We spent about a week on four iterations of the design,” said McCall. “To build it would take three to four weeks and another one to two months to get the necessary parts and test it. So, simulation saved about four to six weeks.”

McCall also noted that this was a week well spent, as one of the permutations of the design performed worse than the original. Imagine if they went down that development path based on only a hunch?

Interested in SimScale? Try it out for free here.

SimScale has sponsored this post. It has provided no editorial input. Unless otherwise stated, all opinions are mine—Shawn Wasserman.

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