When it comes to working with electronics and associated technology, one of the key principles or objectives along with producing high quality products in record time is to follow safety principles and keep the process as secure as possible. As fascinating and intricate as the process of designing and executing a printed circuit board or PCB design is, it is important to take the necessary precautions to ensure that you do not end up sparking a thermal event, especially when it comes to high power PCB.
Following are some of the best practices to follow and keep in mind when formulating the PCB design carrying high power or currents:
As a PCB designer, you must be aware that the longer your trace is, the higher resistance it carries. Your goal is to limit the loss of power and retain as much of it as possible within the tracks so that the reliability and longevity of your PCB can be maintained. One of the best practices in this regard is to keep the traces as short as possible if they are carrying high currents.
Using Heavy Copper
The default thickness of a standard printed circuit board is around 17.5 microns or 1 oz. per square foot. High power PCBs typically use heavier copper in order to reduce the trace width and still allow it to carry the same amount of current. A smaller trace width takes up less space on the board and makes it less crowded. Higher copper thickness can be anywhere between 35 to 50 microns or 3-4 oz. per square foot if operating at over 10 amps.
Another option you have at your disposal as opposed to using heavy copper thickness is to solder copper bus bars to the PCB pads for the high power and currents. While they may have similar width to the regular traces on your PCB, they have the capability to carry much higher currents as they tend to be much thicker.
In the case that you are using a number of individual electronic components that are high current and are likely to produce increased amounts of thermal energy, it is important to deliberate the position of these parts on the board. These high power components should not be mounted close to the board’s edge as that causes the accumulation of the heat over that region and raises the temperature significantly. Placing components like microcontrollers near the center of the package, however, allows the heat to be dissipated across the board in a diffuse manner and the resultant board temperature is relatively lower. If you are using multiple such high current components, it is wise to distribute them across the board instead of putting them all in one place to prevent heat concentration.
Part of the electrical energy derived from the power source is converted into other forms such as heat energy which is then dissipated into the surrounding environment. Boards that are carrying high amounts of current will inevitably produce high amounts of thermal energy as well.
A lot of the components that are used in electronic circuitry, including voltage references, regulators, amplifiers, and converters, are extremely sensitive to fluctuations in their immediate ambient. This means that if they detect significant thermal changes in their environment, it can alter the signal they are producing and open the board up to errors and reduced reliability of the device. That is why it is important to thermally isolate these sensitive components to protect them from the potentially harmful impacts of excessive thermal energy in the ambient.
Via stitching is a technique where multiple layers are connected with the help of vias to continue the same trace having the same width across the different layers. Thermal vias can also be used to direct the flow of heat energy within a package away from the sensitive components to maintain their integrity and performance.
The vias are able to absorb the heat produced by the high current passing through the circuit through basic conduction. Once the heat is transferred to the thermal vias, it can be transported to a thermal landing which is essentially a metal plate placed at the bottom of the board where there are no failure points and the critical components of the package are protected from the negative impact of the high power.
A trick often used to increase the current carrying capacity of a given package while also ensuring thermal isolation of sensitive components of the circuit board is to employ the use of polygon pours. These polygon pours associated with the power traces can be placed under the chip and connected to the board with the help of vias.
In the case that you are increasing the width of the traces on your PCB when using larger amounts of copper, you can accommodate them by creating space in the thickness of the board. Instead of expanding the horizontal surface, using thicker boards for the package allows you to place the traces within the thickness of the board and allow it to deal with the heat dissipation of the traces as well.
Eliminating Solder Mask
One way to enable a trace to carry higher amounts of current is to remove the solder mask from the board. Doing so exposes the underlying copper material which can then be supplemented with additional solders to increase the copper thickness and decrease the overall resistance in the current carrying components of the PCB. Now the PCB is able to accommodate a higher power carrying capacity without having to increase its trace width.
High power PCB designs and their use is becoming more and more common day by day. It is important for engineers to address the issues associated with high current carrying circuits and the dangers that come with poor thermal monitoring and management of these packages. Using some of the above mentioned techniques and practices, it is possible to design and execute a high current carrying printed circuit board in an effective and efficient manner.