Inevitability of Equipment Service
Temperature control algorithm to expedite testing
Simple automation of thermal testing saves time and money
Today we will briefly discuss the trade offs of heat transfer via conduction versus convection in regards to thermal testing.
How tightly to clamp devices to a heatsink or Thermal Platform?
It is true that the more tightly you can clamp two surfaces together the better the heat transfer. This is especially important if you are looking to transfer large amounts of heat from one device to another.
How to choose an appropriate temperature sensor for thermal test:
Selection criteria of an appropriate temperature sensor for a given application can be detailed but it often does not need to be that complicated. Two main points we are going to address today are sensor size and speed of response. Prior discussions covered thermocouple v. RTD and in the future we will likely cover more of the environmental issues of temperature sensors such as temperature range and resistance to moisture or other abuse.
Topics: How to use thermal platforms
Why use anything?
Good thermal conductivity is important to the dissipation of unwanted heat from active power components and also important to the application of thermal platforms for testing electronics.
Perfectly flat, parallel and particle free surfaces might show better thermal conductivity directly pressed together, however some of the real-world realities generally prevent that best-case best performance. Here are a few reasons to use thermal grease:
- Metal surfaces that appear to the eye to be perfectly flat, free of voids and parallel are usually are not.
- Electronics likes cleanliness, not all products can be built in clean rooms. A small unseen particle between two surfaces can easily prevent them from mating properly
- Keeping even pressure on two surfaces is not always as easy as it might seem. Keeping an appropriate amount of pressure on the two surfaces is important to transfer heat. Grease fills voids caused by uneven clamping pressure.
Thermal grease to the rescue?
So - given that close enough to perfect flatness, cleanlieness and parallelness is hard to achieve, thermal grease has been used for decades to improve the thermal conductivity between two metal surfaces. Much has been said lately in the world of competitive computing & overclockers about heat transfer thermal grease. Generally the most important point is less is better. there are articles and stories reporting varying levels of improvement in heat transfer from different grades of thermal transfer grease. In general, what I have seen says that the quality of the grease can make some difference and the high end stuff is expensive but generally far from proprtionally better. One youtube video even sugested Nutella, the food product worked about as well as many thermal transfer product. Well I'd say don't try that but is interesting that it could work at all, even as a short term solution. I am pretty sure over time it would shrink and prove corrosive to metals to mention a few. Properly applied thermal compound should have little risk of making a mess over the rest of the electronics or in general. This is also a good time to note that often electrical conductivity doesn't matter that much but depending on the application, some thermal compounds are specified to be electrically conductive and some are requires to be insulating. clearly you wouldnt want unwanted electrical conductivity on a circuit assembly.
Silpads to the rescue from messy grease.
Silpads and similar products are pretty much what the name says, silicone based pads used in lieu of grease and designed to be either electrically conductive or not based on the application. They compress siightly to fill in voids and are often reusable providing faster, more repeatable results. Silpads are a good solution for many heat transfer requirements. Due to their generally thicker nature, they are generally slightly less thermally conductive than a very thin layer of thermal compound. When it is important to maintain electrical isolation, they are often better than other alternatives.
Topics: High Performance Thermal Testing
Thermal Platforms are a great alternative to a temperature chambers for accessible benchtop thermal testing. Keeping a few key points in mind will help make testing go as effectively as possible.
- Good surface-to-surface contact
- Protect the component from air currents with a cover
- Sense the temperature at the surface to optimize thermal performance and confirm low gradient results
- Use the best coolant for the application
Topics: How to use thermal platforms