High-power components are used in modern electronics, including MOSFETS, IGBTs, high-performance processors, high-power LEDs, and so on. Throughout the electronics sector, there’s a tendency toward making these components smaller. Thermal hotspots will be produced as a result, though. This PCB thermal design management is experiencing high temperatures.
Thermal performance is an essential consideration whenever you’re constructing any electronic product. Every PCB designer must incorporate methods that can lessen the impact of heating in order to combat heating difficulties. As a result, designers will need to study the air cooling techniques that are applicable to various electronic gadgets. Also, they must be familiar with the methods that reduce heat dissipation internally.
What are PCB Thermal Design Management and Thermal Modeling?
An effective tool for doing thermal failure analysis is thermal modeling. Also, it enables designers to comprehend the various thermal problems that could affect the circuit design. Also, it aids in picking the appropriate cooling strategies and precise PCB design procedures.
By using the proper modeling software, Circuit board designers will additionally be able to determine the ideal placement and layout for the various components that make up the layout. The designer has the ability to efficiently determine these aspects using thermal modeling as well. These include the layout of the heat sinks, the direction of the flow of heat, as well as the recommended air cooling techniques for active devices.
Methods for managing PCB Thermal Design to Lessen PCB Heating
Detection of the thermal hotspots and high-current traces
It is necessary to research the thermal impacts throughout the process of PCB design to be able to construct a PCB which is thermally stable. This detection of hotspots constitutes the initial step in thermal design. Techniques for thermal modeling or simulation are helpful in locating hotspots. The analysis of current flow is also required to go along with it. It occurs as a result of the possibility of heat development in the high current trace.
Heat can be distributed evenly whenever the geometrical organization of high-current components and traces are done correctly. High-current traces have to be routed from components that are thermally sensitive such as Op-amps and sensors.
Copper Thickness with Trace Width
In a PCB thermal design, the thickness and width of the copper pad or traces is quite important. Moreover, copper traces must have a suitable thickness to provide low impedance paths for the current flowing through them.
Moreover, the resistance of the copper traces and vias causes for significant power loss and heat generation, especially whenever the density of current supported is high. To guarantee the minimization of heat production, it is therefore strongly advised to use a suitable trace width and thickness.
Pad Design
The trace thickness is equally crucial as the pad thickness. Here, the heat is dissipated immediately to the first copper layer (topmost). Because of this, the uppermost copper pad layer needs to be big enough and thick enough to diffuse heat evenly.
Moreover, heat sinks are often put on the bottom portion of a copper pad if your circuit board design has them. Also, for the optimum heat transfer to the heatsink, these bottom copper pads must be sufficiently covered.
These component pins are soldered to the PCB with the assistance of the pads. The component and the pad are directly connected. The PCB experiences extremely little thermal resistance as a result. Also utilized on the circuit board is a welding pad called thermal pad. Only thin bridges are capable of joining the pad to a copper pour.
A minimum amount of solder paste must be used to join the component’s footprint to the thermal pad. During reflow, if there is too much solder paste underneath these thermal pads, the components may float on such a pool of molten solder. If this occurs, the component package has a propensity to move. Optimizing the solder paste’s volume is a smart way to address the floating package problem.
Placing the high-power components in PCBs
Place high-power components including processors and microcontrollers in the center of the PCB to guarantee better heat dissipation. When you place the high-power components close to the edge of the board, heat will build up there, raising its local temperature.
The heat would instead disperse over the entire surface and in all directions if the gadget is placed near to the midpoint of your circuit board. As a result, the surface temperature of the PCB will drop and evaporate quickly.
Moreover, make sure that every sensitive equipment is positioned away from all high-power components. Moreover, make sure these high-power gadgets are spaced properly apart. Also, distribute these high-power components equally across the Circuit board.
Techniques of Integrated Cooling
In comparison to conventional fan configurations as well as external heat sinks, integrated cooling techniques or procedures are helpful in achieving greater heat conductivity coefficients.
The notion or idea is to blow the cooling agent through designated vias into the BGAs or heating components, such as the bottom of the processors.
The quantity or number of vias should be decided by the designer. It’s dependent on the heat requirements of the installed component. Priority is given to one through; additional ones can be added if needed. This is dependent on both the surface area of the component and the velocity of the cooling fluid.
There are more built-in cooling techniques. Consider the inboard design, in which this heat exchanger has been built into the board. There are fewer stages involved in PCB construction and less weight in the finished product because a heat sink or cold plate is not required. Therefore, the thermal conductor around the coolers must be highly dense.
Thermal Vias PCB Design
The term “thermal vias” refers to such copper barrels which run between the bottom and top of the board and conduct heat. Vias of this kind are excellent thermal conductors. These aid in moving heat from crucial electronic components. Moreover, these vias help with the rapid heat dissipation away from the SMD (surface mount device).
Consider a PCB with no space for a cooling system at the top, similar to the indicator, backed boards, or integrated sensor with many components. Thermal vias are a simple means of transferring heat into the cooling system (heat pipe of the heat sink).
Designers can utilize thermal vias to transport heat between conductive layers. By taking into account the range as well as the surface area of the heat dissipation, the designers are going to select the number of thermal vias to be present beneath the CPUs or BGAs. The dimensions for a typical thermal passage are listed below.
- Not via filling
- The copper plating’s standard thickness is 1 mil.
- You arrange a 0.3 mm (12 mil) diameter on a 0.64 mm (25 mils) grid spacing.
Heat Sink
The heat sink can be referred to as the cooling technique that aids in transporting waste heat out from the PCB’s components into a particular cooling medium. This conduction principle describes the way a heat sink operates. According to this, heat can flow from a region with a thermal resistance that is high to an area with a thermal resistance that is low.
Moreover, the heat is transferred from hot spots to cold spots. Moreover, there’s a direct relationship between heat flow and temperature difference.
This heat sink assists in removing heat from the PCB. It pulls the heat into the fins, and then has a bigger surface area and therefore can dissipate heat more quickly. Several considerations will enable the designers that select a heat sink that suits the design. Consider factors like thermal resistivity of the material, thermal interface materials, velocity of the cooling fluid inside the sink, distance between the fins, quantity of accessible fins, kind of mounting techniques, etc.
Incorporating the heat pipe
Heat pipes are cooling systems used in high-temperature applications including avionics, spacecraft, and rockets. These heat pipes typically have cylindrical shapes that allow for stress-free transformation into any shape.
Also, whatever heat that escapes from these gadgets is transmitted to the liquid inside these heat pipes, thereby vaporizing it. At this condenser, the liquid will then condense. Moreover, this returns its evaporator through a wick structure through a capillary action. Using this procedure, the PCB is protected from the heat which has already been dissipated.
Make sure this heat source is completely covered by the heat pipes used by designers. Moreover, they ought to be flexible in light of the demands of the design.
Several working fluids on heat pipes are also available. Liquid metals and cryogens are covered by this. The working fluid choice depends on the temperature range of the circuit as well as the fluid’s chemical compatibility with the heat pipe’s wick as well as the containers.
Thicker Circuit Boards
Smaller equipment can’t use cooling techniques like heat pipes, cooling fans, or heat sinks. The only solution in situations like this is to improve the thermal conductivity of the board while also dispersing the heat produced. Moreover, thick boards with a wide surface area can dissipate heat more quickly.
Based on the materials’ CTE and thickness, you may calculate the thermal conductivity of a printed circuit board. Designers must therefore be more selective when deciding on the material for PCB stackup layers.
Furthermore, fatigue may occur as a result of constant thermal cycling and mismatched CTE of the various materials that comprise the layers, which can help lower thermal conductivity. Furthermore, when thermal cycling becomes significant, copper plating within the vias and solder balls are typically more susceptible to every damage.
Cooling Fans
We have covered a number of cooling techniques in this post, such as heat pipes and heat sinks. These methods rely on conduction for exchanging heat, and are known to be frequently insufficient. Convective heat transfer is used in this cooling fan, giving the creator a more effective and reliable technique for getting rid of any heat present on the components.
The effectiveness of these cooling fans depends on their capacity to push out air from the device and how well they fit in their intended location. A designer needs to take certain factors into account. While picking a fan, consider factors like cost, size, noise, operation, power requirement, friction, etc.
The fan’s primary function is to pump a certain amount of air, though. This means when choosing any cooling fan, the capacity becomes a crucial consideration.
Soldering Concentration
To aid in lowering the buildup of heat onto component leads, the soldering thickness of the device joint must be uniform and ambient. There has to be special caution taken when soldering near the vias. This is due to the possibility that the solder may overfill this hole, resulting in bumps present on the bottom of the board and a decrease in the contact area of the heat sink.
Any of these methods can be used by PCB designers to prevent solder reflow. Firstly, reduce the diameter of the via to less than 0.3mm. The smaller vias allow for liquid solder which has a strong enough surface tension to defy gravity.
The second choice is tenting. This procedure involves applying a solder mask to cover the pad of the via. This aids in preventing solder from leaking into the via.
Peltier Heat Pumps/Thermoelectric Coolers
This Peltier effect is utilized by thermoelectric cooling. This result is referred to as the opposite of thermal steam creation.
These tools aid in lowering component temperatures below the ambient level. When a component’s temperature needs to stay at a particular level, TECs can be helpful.
Conclusion
Here comes the end of our article on PCB thermal design. Thermal performance is an essential consideration whenever you’re constructing any electronic product. Every PCB designer must incorporate methods that can lessen the impact of heating in order to combat heating difficulties. Designers can utilize thermal vias to transport heat between conductive layers. By taking into account the range as well as the surface area of the heat dissipation, the designers are going to select the number of thermal vias to be present beneath the CPUs or BGAs.
