Heat can be produced on a circuit board due to certain components as well as the resistance inside the lines. If somehow PCB thermal resistance becomes large, such high temperatures might harm the board. Heat sinks and fans are options, but they are insufficient. Fans raise power consumption, and they also add weight to the PCB.
The best course of action is to create a thermal management strategy that takes thermal resistance as well as conductivity into account. To ensure that components function properly, this method should maintain the circuit board’s peak temperature nearer to the surrounding air temperature. Here, we’ve discussed PCB thermal resistance as well as how to optimize your designs for maximum heat dissipation.
Why Is PCB Thermal Resistance Significant and What Does It Mean?
Circuit board thermal conductivity is inversely proportional to PCB thermal resistance. It specifies how quickly or slowly the Circuit board materials let heat to dissipate from the source. It displays the pace at which heat moves from hot to cool areas of the PCB.
Thermal pads and thermal vias are two connections towards the copper planes, affect thermal resistance.
What Affects Your PCB Substrate’s Thermal Resistance?
The PCB’s copper components and the material properties of the substrate together define the heat resistance. Those two ought to help when establishing the board design’s thermal management approach.
The plan should demonstrate the following and aim to lower heat resistance:
- The ideal arrangement of electrical components
- Which components require cooling sinks or fans
- Position thermal vias optimally close to hot components
Techniques for Testing PCB Thermal Resistance
Thermal resistance may be determined in three different methods.
Thermal Conductivity Measurement
Utilizing thermal conductivity is the most common way to measure thermal resistance. Resistance would be the opposite of conductivity, making it simple to calculate heat conductivity.
Guarded Hot Plate Technique
It is quicker and simpler to test the heat resistance of a fully constructed yet unassembled board to use this approach since the circuit board substrates were two-dimensional.
When heat flows from the hot locations to cooler areas, the two Circuit board sides are measured to determine their respective temperatures. It is a straightforward method for determining thermal conductance, that can be utilized later to determine resistance and thermal conductivity.
Design to Reduce PCB Thermal Resistance
The three methods for reducing thermal resistance are as follows.
Employ High Thermal Conductivity Materials
Using materials that have high thermal conductivity is the most efficient technique to lower PCB thermal resistance. Hence, copper in the plane layers should be used on boards containing hot components to create quick-heat, low-resistance flow channels.
Instead, for high-speed or high-frequency boards, employ the internal power or ground plane layers. They will serve many functions as they additionally help with isolation and offer EMI shielding from the outside.
Place the copper pads beneath hot components
Copper pads placed beneath hot components help deflect heat out of the upper layer. Their internal ground planes, which is often linked to these pads by vias, protects the components.
For optimal heat transmission, solder the parts into the thermal pads if the component has a thermal paddle that is die-attached. It is important to remember, nevertheless, that too large or many vias might make it possible for the solder to flow through it during the board assembly.
Utilize Heavy Copper
Copper traces that are thicker or heavier may carry greater currents with little resistance. If the pcb must operate at high power, thicker copper would keep temperatures low since resistance raises temperature.
Alternate Substrate Materials to Boost Heat Dissipation
Using different substrate materials is another efficient method of lowering heat resistance. FR4 is a common type of substrate material. It has a conductivity of around 1.0 W/m-K, which is far lower than that of ceramic and metal.
This figure is comparable to the conductance of other laminates that are compatible with high frequencies, such as Rogers and Isola.
The increased thermal conductivity of ceramic and metal substrates, however, makes them more desirable for thermal control.
Ceramic
Ceramic materials have thermal conductivities ranging from 20 to 300 W/m (m-K). It is therefore perfect for positioning underneath or next to hot electronic systems. It may also do away with the requirement for large heat sinks or fans.
Ceramics also have the benefit of having a thermal expansion coefficient that is more similar to copper than the FR4. Consequently, it decreases stress on the thin copper vias and traces. Unfortunately, the substance is brittle and rapidly fractures.
Metal Cores
A typical aluminum metal substrate for metal-core PCBs has a thermal conductivity of 239 W/(m-K). You can attach this sheet to nearby ground planes to generate a second EFI shielding surface. This metal core offers greater mechanical durability and adaptability than ceramic, adding to superior conductivity. Metal-core PCBs are typically used in high-power LED systems since the diodes produce a lot of heat.
Suggestions for Managing PCB Thermal Resistance for Manufacturing
While choosing PCB substrates and components, take temperature coefficient into consideration
The trace and component thermal resistance is determined by the material characteristics and components of the board, as was previously mentioned. As a result, you should pick PCB substrates as well as components with good resistance and temperature specifications. For rapid heat transmission from LEDs, aluminum serves as a better material compared to FR4, for instance.
Provide High Power Component with Enough Room
Sparingly place the heat-generating parts on the circuit board. This allocation ought to reduce any hot spots that could lead to problems during the assembly reflow process.
Employ Thermal Vias to Improve Heat Dissipation
To dissipate heat from the components, most especially the high-power SMD components, use many vias. Since they transmit heat away from the board surface, heat source, as well as components more quickly than buried, blind, or micro vias, through-hole vias were preferable to those.
The Thermal Management Plan You Have
One crucial component of designing a board is to have improved efficient thermal conductivity is defining the stackup. The overall PCB thermal resistance as well as subsequent rate of heat transfer in the board will be influenced by the materials utilized in the stackup. Heat from the components which create a lot of heat can be transported using the placement of the copper conductors as well as the usage of heavier copper.
Several design decisions may need to be made according to the setting where the board would be deployed.
Ensure the necessary components don’t cause too much noise in surrounding circuits while using active cooling techniques.
Creating a Thermal Management Plan
Heat will be transported throughout the circuit board more efficiently with the careful placement of the via thermal resistance calculator, the use of active cooling mechanisms like fans, as well as the proper arrangement of the components. By positioning active components from the board’s edge and avoiding grouping them inside one area on the circuit board with a lot of them, you can assist avoid hot spots.
The temperature distribution ought to improve even while operating when employed with the via thermal resistance calculator as well as planes within internal layers.
The ideal thermal management plan for your Circuit board can be determined with the use of a thermal simulation program. Tracking power loss across your PCB might help you understand how the PDN behaves as heat source. You may get a picture as to how heat would move across your board as well as the ultimate temperature distribution by using this information combined with power ratings of each component values plus the measurements for the PCB thermal resistance.
Enhancing FR4 Thermal Resistance
The most popular PCB materials are called FR4 and are characterized by the epoxy laminate. This FR4 has a very poor thermal conductivity as a result of this fabrication approach.
Thermal vias are among the low-cost methods designers can increase FR4 thermal resistance. The two conducting layers are connected via plated through holes.
Designers are able to increase the FR4 thermal resistance by inserting PTH vias in the right places. When the source of heat is immediately normal to a thermal via and has a diameter of 0.6 mm, it has a PCB thermal resistance standing at 96.8 °C/W. The FR4 thermal resistance is significantly improved when the amount of thermal via is increased. For instance, the initial 270-mm2 board will have its thermal resistance drop to 12 °C/W, which is a significant improvement of approximately 60% from the initial value.
Since this area normal to a heat source shrinks for open vias, the thermal resistance produced by the former is higher than that from the filled vias.
Makers of metal-core PCBs produce their boards in various ways. Solder mask, copper circuit surface, thermally-conductive dielectric layer, as well as a metal core layer—typically an aluminum substrate—are all visible when a one-layer MCPCB is examined.
Conclusion
You can design the thermal management plan which can help in controlling heat transfer in the board by selecting the appropriate pcb substrate material as well as component options. The thermal management approach can shift heat away out of each source of heat and lower the temperature of the printed circuit board by strategically placing copper components, elements, as well as interior plane layers.
