Modern electronics make use of high-power components, such as MOSFETS, high-performance processors, IGBTs, high-power LEDs, etc. There is a trend happening in the electronics industry to ensure that these components are smaller. However, this will lead to thermal hotspots creation. The high temperatures present at the PCB thermal management.
Whenever you are designing an electronic product, one important factor to look into is thermal performance. To fight heating issues, all PCB designers have to integrate techniques, which can reduce heating impact. This means that designers will have to learn those air cooling methods that are useful in different electronic devices. Also, they have to know the techniques that aid the internal reduction of heat dissipation.
What is Thermal Modeling and PCB Thermal Management?
Thermal modeling is an important tool, useful in conducting analysis of thermal failure. Furthermore, it allows designers to understand the different thermal issues that could happen to their circuit design. In addition, it also assists in selecting the right cooling methods as well as accurate techniques for PCB design.
Furthermore, PCB designers will be able to know the best positioning and design of the different components present in the layout, making use of appropriate modeling software. Also, with thermal modeling, the designer will be able to figure out these aspects efficiently. These include design of heat sinks, pattern of heat flow, and the air cooling methods that should serve active devices.
What are the Techniques for PCB Thermal Management in Reducing PCB Heating?
Identification of the high-current traces and thermal hotspots
In order to fabricate a PCB that is thermally stable, then you must study the thermal effects during the PCB design phase. The first-ever step for thermal design is the identification of hotspots. Thermal simulation or thermal modeling techniques are useful in finding hotspots. In addition, there must be current flow analysis with it. This is due to the fact that high current traces can lead to heat generation.
When the geometrical arrangement of high-current traces and components are properly done, then the distribution of heat can happen evenly. There is a need to route away high-current traces from components that are thermally sensitive like Op-amps and sensors.
Width of Traces and Copper Thickness
The width and thickness of the traces or copper pad plays a huge role in any PCB thermal design. Also, copper trace thickness has to be adequate so as to offer a low impedance path for any current that passes through it.
Also, this is due to the resistance of the vias accounts and copper traces for significant heat generation and power loss most especially when the current density they bear is high. This is why an appropriate trace width as well as thickness is highly recommended so as to ensure the reduction of heat generation.
The Pad Design
Pad thickness is just as important has the trace thickness. Here, the dissipation of heat is done directly to the topmost copper layer. This is why the topmost layer of the copper pad has to feature sufficient area and thickness in order to provide sufficient heat spreading.
Also, if your PCB design features heat sinks, they are normally mounted on top of the bottom part of the copper pad. Furthermore, the copper pads at the bottom have to have enough coverage in order to permit the best heat transfer into the heatsink.
With the support from the pads, the soldering of the component pins to the printed circuit board (PCB) happens. There is a direct connection of the component to the pad. This leads to a thermal resistance that is very low to the PCB. Furthermore, a welding pad, known as thermal pad, is also used on that circuit board. The pad can only be connected to the copper pour with the help of thin bridges.
The solder paste utilized in connecting the footprint of the component with your thermal pad has to be minimal. When the solder paste is too much beneath the thermal pads, it could cause the components to float on a molten solder pool during reflow. If this happens, there is a tendency for that component package to move. A good solution to this floating package issue is optimizing the volume of the solder paste.
Placement of the high power components into Printed circuit boards
To ensure more heat dissipation, then you must place high power components like microcontrollers and processors at the PCB’s center. When you mount a component of high power close to the board’s edge, then heat will be accumulated close to the edge, which then raises the local temperature.
However, if you place the device close to the board’s center, then heat will end up scattering all over the entire surface and in all possible directions. Therefore the PCB’s surface temperature will become lower and will dissipate easily.
In addition, ensure that your high-power components are placed away from any sensitive device. Also, ensure proper spacing in-between the high-power devices. Also place the components of high power evenly and across the PCB.
Integrated Cooling Methods
The integrated cooling measures or methods are useful in achieving higher coefficients for heat conductivity in contrast to traditional fan setups and external heat sink. The idea or concept here is the blowing of a cooling agent via dedicated vias to the processors’ bottom or BGAs, or other heating components.
The designer should determine the number or amount of vias. This depends on the mounted component’s thermal criteria. One via is first considered, then you can add more on-demand. This depends on the cooling fluid’s velocity, as well as the component’s surface area.
Other integrated cooling measures exist. For instance, the inboard type, where the heat exchanger is integrated in the board. Since you don’t need a cold plate or heat sink, there is a reduction in the steps for PCB assembly and the final product’s weight. However, the coolers need a high density for the thermal via around these cooling channels.
PCB Design for Thermal Vias
Thermal vias are known as copper barrels that conduct heat, which runs in-between the board’s top and bottom. These types of vias are great thermal conductors. They help in transferring heat away from electronic components that are critical. Furthermore, these vias are useful in facilitating quick dissipation of heat away from SMDs (surface mount devices).
Imagine the top area of the PCB has no space to house the cooling system, just like an indicator, integrated sensor, or backed boards having numerous components. One easy way of dissipating heat to a cooling system is through thermal vias (heat pipes of heat sink).
Thermal vias are useful for designers for heat transfer in-between the conductive layers. The designers will determine the amount of thermal vias present under the processors or the BGAs considering the surface area and range of heat dissipation. The below are the dimensions of a standard thermal via.
- Absence of via filling
- Standard thickness of the copper plating is 1 mil
- You place a diameter of 0.3 mm or 12 mil on a grid spacing of 0.64 mm or 25 mils
Heat Sink
This is known as a cooling method that helps in transferring dissipated heat from the components of the PCB into a specific cooling medium. The heat sink functions with the conduction principle. This states that the transfer of heat from a high thermal resistance area to a low thermal resistance area. Also, this heat flows from areas of high temperature to one with low temperature. Furthermore, there is a direct proportion of heat flow to the temperature difference.
Heat is drawn away from the printed circuit board with the help of the heat sink. It draws it to the fins, which offers a larger and wider surface area to ensure quicker heat dissipation. The designers will be able to choose a good heat sink for the design as a result of some factors. Take for instance, the material’s thermal resistivity, thermal interface material, the cooling fluid’s velocity in the sink, the spacing in-between the fins, the number of available fins, the type of mounting technique, etc.
Integration of heat pipe
The heat pipes are known as cooling devices that serve applications of higher temperatures like in avionics, satellites, and rockets. Most times, the heat pipes come in a cylindrical shape, which can convert it to any shape without stress.
Also, any heat that is dissipated from these devices is transferred into the liquid in the heat pipe, which vaporizes that liquid. This liquid then condensates at the condenser. Also, through capillary action, it returns the evaporator via the wick structure. This process makes sure that the heat that has been dissipated flows away from the printed circuit board (PCB).
Make sure that designers work with heat pipes covering the heat source entirely. Also, they should be able to bend with respect to the design requirements. Also, there are different working fluids for heat pipes available. This covers cryogens and liquid metals. The choice of working fluid has to do with the circuit’s temperature range and the chemical compatibility of the fluid with the wick of your heat pipe and the container.
Thicker PCB Boards
For devices that are smaller, cooling methods such as cooling fans, heat pipes, and heat sinks isn’t an option. For cases like this, the only way is increasing the board’s thermal conductivity and also spreading the heat generated. Also, thick boards having a larger surface area will be able to dissipate heat faster.
You can determine a PCB’s thermal conductivity based on the materials’ CTE (coefficient of thermal expansion) as well as its thickness. This is why designers have to be more focused when choosing a material for the layers of the PCB stackup.
Furthermore, when the CTE of different materials present in the layers are mismatched, when there is a continuous thermal cycling, there can be fatigue to aid in reducing the thermal conductivity. Also, copper plating in solder balls and vias are usually more vulnerable to any damage when the thermal cycling is high.
Cooling Fans
In our article, we have explained several methods for cooling including heat pipes, heat sinks, etc. These techniques use conduction to exchange heat which is not enough most times. This cooling fan makes use of the convective method of heat transfer, which provides the designer with a better and efficient method to get rid of heat from the components.
The efficiency of cooling fans has to do with the ability of pushing air from a device as well as how compatible placing the cooling fan is. There are things that a designer must consider. These include cost, noise, size, power requirement, operation, friction, etc, when choosing the fan.
However, the main purpose of the fan is to push a specific air volume. This means that capacity is a very important factor when it comes to selecting a cooling fan.
Soldering Concentration
A device joint’s soldering thickness must be ambient and even to help in reducing the accumulation of heat on component leads. When soldering close to the vias, there must be extra care. This is because the solder can overfill the hole causing bumps on the board’s bottom and this causes a reduction in the heat sink’s contact area.
The PCB designers can make use of one of these options in avoiding solder reflow. First, is decreasing the via’s diameter below 0.3mm. When the vias are smaller, the liquid solder present in the via has a surface tension that can fight against gravity.
Tenting is the second option. This is the process involving the covering of the via’s pad using a solder mask. This helps in preventing the flowing of the solder to the via.
Thermoelectric Coolers/ Peltier Heat Pump
Thermoelectric cooling makes use of the Peltier effect when cooling. This effect is known as the reverse of thermal steam generation. These devices help in cooling components to a sub-ambient temperature. TECs are useful in a scenario where the temperature of the component should remain at a specific level.
Conclusion
Here comes the end of our article on PCB thermal analysis. Please if you have any questions, contact us.
