PCB Thermal Design

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Jun 13, 2022|Product Innovations and Design

The majority of electronic devices emit considerable amounts of waste heat through the power components inside them. This heat build-up can cause severe damage to sensitive circuits such as microprocessors, RAM, and other essential parts. That’s why a PCB (printed circuit board) is needed to ensure high performance in these devices. Yet, What is a PCB? 

A printed circuit board is a laminated surface in which electronic components mount over a non-conductive material. The surface has conductive circuits printed over it that together help support electronic components.

A circuit board with a considerable thermal resistance will limit the effectiveness of its cooling system, thus increasing the risk of overheating (and even causing permanent damage). Making it all the more important to be wary of the PCB design tools.

Proper thermal design maintains a product’s life and performance with proper cooling. Thermal design is the necessity of incorporating thermal management elements and evaluating space, power, temperature, and resistance in a PCB. When electronic components operate, they release and transfer heat to resolve power loss.

Basic Principles of Thermal Design

One of the fundamental thermodynamic principles is that heat transfer can occur through thermal conductivity, radiation, and convection when there is a temperature difference between two zones. The rate at which these processes occur depends on the size of the temperature difference, the area of contact between the two objects, and their material thermal properties.

To ensure its reliability, valid thermodynamic design measures should be taken from the following four perspectives:

1- Natural Cooling, when it comes to natural cooling, the most effective way is to use passive methods like airflow, natural convection, and natural radiation. In this case, the device does not have any active cooling systems.

2- Active Cooling, when using active cooling, the device has an internal fan or blower that forces air over the component’s surface. This method is widespread in consumer products because it is inexpensive and easy to implement. 

3- Fluid Cooling uses liquid coolant to remove heat from the device. The liquid coolant is circulated by pumps and then flows through tubes or channels within the device. 

• Direct Fluid Cooling occurs when parts are immersed or in direct contact with the coolant.
• Indirect Fluid Cooling occurs when parts are not in direct contact with the coolant; however, a heat sink or heat exchanger is in direct contact with the cooling agent.

4- Evaporation cooling, this method involves the removal of heat by evaporating fluid into vapor form. This process requires a lot of energy and must be done carefully so that the vapor pressure remains low enough for the fluid to stay in a liquid state.

The thermal design measures can be carried out under different circumstances. Such as the realistic operating environment (temperature, relative humidity, atmospheric pressure, air pollution, wind speed, dust, etc.), thermal fluids inside the equipment, power density, total power consumption capacity, surface area, volume, and other special conditions, to ensure even temperature distribution and moderate temperature increase within the regulated limits.

Thermal Design Rules

Thermal design (not the same as pcb schematics)  is used for controlling the temperature of all electronic components assembled on a circuit board, which ensures the stability of electrical performance, reduces the basic failure rate of the product; and extends the life cycle of the component.

There are many rules in thermal design, but they are mainly based on the following four aspects:

1. Heat Transfer Resistance
2. Power Dissipation
3. Temperature Rise
4. Thermal Compliance

Electronic Components

The first factor that affects component failures is its operating temperature. When designing high-reliability systems, we should consider the maximum temperature and the failure rates of individual parts.

Component internal thermal resistance and environmental temperature should be considered for heat dissipation. Therefore, deratings, circuits that contain power components, and detailed guidelines should be applied.

Thermal Design Rules of PCBs

A PCB’s thermal design is closely related to the system’s reliability. To achieve good thermal design, you need to know how much heat each part generates? where the heat will go? how much heat can a PCB dissipate? and what kind of materials are used.

Heat transfer is affected by three factors:

1. Surface Area
2. Material Thickness
3. Conductivity

Surface area refers to the size of the surface area exposed to the ambient atmosphere. A larger surface area means more heat is dissipated.  

Components Assembly and PCB Layout

Assembling components in a way that minimizes both mechanical stress and current density helps improve heat dissipation. Also, the component layout must be done according to the flow characteristics of the coolant so that the flow of coolant through the board is optimized. Here are a few tips on how to assemble the PCB layout: 

1- Use the lengthwise component arrangement with the free convection air cooling method. 

2- Use the component lalongate arrangement with the forced air cooling method. 

3- The components on the board should be categorized and arranged according to their heat output and heat dissipation.

4- Sensitive components need to be placed in an area that has the lowest temperature. 

5- Components that require the most power and generate the most heat need to be placed where the most heat dissipation happens.

6- Power should be equally spread across the board so that there is no hot spot.

7- You need to consider airflow paths when designing a PCB; this is crucial to ensure the longevity of the device and its components.

8- When manufacturing electronic products, thermal assembly technology should be used to achieve sound heat transmission effects.

9- When connecting components with high heat dissipation and circuit boards, thermal resistance should be reduced as much as possible.

10- Shorten the pins of components when connecting them to both the board and each other.

Other Requirement

1. Avoid having the heat conduction path with air break
2. Add copper to the soldier paste to avoid local high temperature
3. Increase power density of PCBs by adding heat dissipation holes.

Thermal Analysis

What is Thermal Analysis in PCB design? It helps us understand the heat generated by various factors and the heat flow through the whole system. For example, if there is no airflow around a chip, it may create more heat than expected.

In summary, thermal design is an essential part of the entire system. The primary purpose of thermal design is to reduce the risk of overheating and damage caused by excessive temperatures. In addition, it can help improve the reliability of the system.

The Candor Copper Coin Tech Difference

When it comes to thermal design, Candor puts a “copper coin” heatsink right onto the board to increase the thermal management of localized areas which creates the best heat dissipation possible. This generates a direct contact to a heatsink, vastly improving overall heat dissipation. T-Coins can be implemented if the top side needs to be larger than the bottom, copper coins with mounting holes can be placed for direct heatsink access, and any copper coin can be directly connected by traces/images as they are plated over. It’s an efficient process that greatly mitigates overheating, excessive temperature damage, and overall system endurance.

Conclusion

With the development of technology, electronic products have increased continuously. As the demand for energy efficiency increases, the use of electronic devices becomes increasingly widespread. Due to its increasing popularity, the demand for new PCBs has been growing rapidly.