Surely nothing could go wrong with making a simple dinner like heating an instant pizza in the oven. As hunger get the best of me, I forgot to put on the baking gloves and tried to remove the scalding tray. In an instant, the pain registered and rushed to place my finger under the rushing cold water from the tap. The singe mark on my finger lasted for a few weeks after, but the warning will stay with me until the next time I get too hungry.
In electronics, things can get pretty hot on your PCB and could bring a rude shock to unsuspecting technicians. Not only that, but the extreme temperature that goes beyond the operating range of components can mean a shorter lifespan for your product. The heat-producer itself will be defective, and the performance of surrounding parts can be negatively affected as well. With proper using and understanding of SMD heat sinks, you can save your designs (and your hands).
What Causes A PCB To Heat-Up and Need an SMD Heat Sink
Simple electronics like a digital calculator produces negligible heat. But when you are designing a high-end controller or a high-current power transistor circuit, it is inevitable that things get pretty hot on your PCB. For some components, like a voltage regulator, the rise of temperature as defined by its thermal resistance can be calculated by the value provided in the datasheet.
For example, the popular LM7805 in a TO-220 package will increase by 22°C at every 1 Watt of power dissipated without a heat sink. But that’s nothing compared to a power transistor, as some could even hit 100°C of increase per Watt dissipated. You’ll also find your microcontroller heating up when you’re turning on all its peripherals and running it at its maximum speed.
It doesn’t help when the demands on a smaller PCB size are increasing and causing heat to build up faster than it can dissipate. And when you are placing PCB in an outdoor enclosure, the heat often increase to twice the temperature. Of course, ventilation opening and exhaust fans do help in keeping the temperature down. But such approach is only as effective as the heat dissipation techniques implemented on the PCB itself.
Power transistors can get very hot, handle with care.
Designing for Effective Circuit Board Heat Distribution
The heat sink is an effective component to increase the efficiency when used correctly. Like other electronic components, they are available in surface mount packages. High-power SMD components usually have a thermal tab or pad where you would solder it against a heat spreading pattern on the PCB. An SMD heat sink is then soldered onto the other end of the copper to provide better dissipation.
Before you choose a heat sink for your high power component, there are two factors to take into consideration: the junction-to-case thermal resistance of the component, and the heat sink itself. You’ll want to ensure that the temperature of the component does not exceed its safety limit and the heat sink is not too hot to cause serious injury to the skin.
It’s important to calculate the total junction temperature by dividing the dissipated power with the sum of the thermal resistance of the device, PCB thermal dissipation area, and the heat sink itself. You can also get the temperature of the heat sink itself by multiplying the thermal resistance of the heat sink with the dissipated power. The right design will result in the heat sink being much cooler than the high power component by itself.
Make sure your heat sink can come to the rescue of your PCB.
It is a misconception to assume that using a heat sink will totally eliminate heat issues on your PCB. It merely prevents the accumulation of heat on one single point. You’ll still need to keep heat-sensitive components like sensors away from the heat sink. Proper airflow should also be part of the enclosure design to prevent the heat from eventually building-up.
An SMD heat sink is a great way to properly dissipate heat in high power components. As SMD heat sinks come in various sizes and shapes, you’ll want to ensure that the right footprint is created and that you have the proper PCB design software in place to use it. An intuitive tool for footprint creation in Altium’s CircuitStudio will be useful to guide you along.
If you’re still worried about your PCB getting burnt, then consider talking to the experts at Altium now.