The operational temperature of a PCB is very crucial. Higher power applications subjected to heat need PCBs that ensure heat dissipation. Too much heat can result in circuit failure or other issues. Also, the rapid development in the electronics industry raised concerns about heat dissipation.
Heat dissipation can affect the performance of high-power electronic devices. Therefore, the demand for metal clad PCBs increased. Metal clad boards are specifically fabricated to meet the demands of high power applications.
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Metal Clad PCB – What is it?
A metal clad PCB comprises three major parts. These parts are the copper foil, dielectric, and the base layer.
Copper foil
The copper foil is the top layer of the material. This layer will be finally processed into the electrical conductors. Most times its thickness is between 1oz and 4 oz. However, it can be greater than this.
Dielectric
This material is very important. The dielectric is the substance that isolates the aluminum base layer from the copper foil. Also, it ensures rapid transfer of heat between the two components. In addition, it allows the generated heat in the components to disperse to the heat sink. Therefore, it determines the thermal properties of the materials.
Base layer
The base layer is usually aluminum. Also, its thickness ranges from 1 mm to 3.2 mm. Aluminum is a good conductor of heat. Therefore, it is ideal for applications that involve rapid transfer of heat.
The Benefit of Metal Clad PCB
There are several benefits of utilizing metal clad PCB. Metal clad materials have more benefits than traditional materials like CEM and FR4. Also, these materials have the ability to dissipate heat. There is an unwanted side effect when current passes through an electrical system. This is because part of the electrical energy can convert into heat.
This might be unnecessary with some applications. However, when it comes to high power applications, it can have a costly effect. Also, there are many side effects of high temperature. Some of these effects are low-life span and high rate of failure.
FR4 features a low thermal conductivity. Therefore, the generated heat from the components is inefficiently transmitted via the PCB to the heat sink. However, the greatest heat sink will be ineffective if the PCB material serves as a thermal insulator between the heat sink and the heat source.
In this case, the dielectric plays a significant role. Dielectrics feature high thermal conductivity that ranges from 1 W/mK to 9W/mK. But, some materials can have better performance. With the aluminum base’s high thermal conductivity, there is a faster rate of heat transfer from the heat source to the sink.
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What is the Importance of the Dielectric in Metal Clad PCB?
The dielectric plays a crucial role in the metal clad PCB. Also, it is the major factor that differentiates the base materials used in metal clad PCB’s production. Also, the thermal properties of a substrate depend on the dielectric. The dielectric is the basic layer that determines the reliability of the final PCB.
The production of dielectrics includes different materials. Some of these materials include:
- Boron Nitride
- Ceramic
- Polymer
- Epoxy
- A combination of the materials above
A thermal substrate must feature low thermal impedance. This is a basic thermal property. Therefore, PCB manufacturers need dielectric that features great thermal conductivity. Also, a thin distribution of the dielectric over the aluminum base layer will result in low thermal impedance.
However, it is not ideal to make the dielectric layer too thin. A thinner dielectric layer will result in lower breakdown voltage of the substrate.
The Thermal Properties of Metal Clad PCB
A metal clad PCB features great thermal properties. These properties are explained below:
Thermal resistance
This property determines the thickness and conductivity of the metal clad PCB. Its measures of the material’s thickness area will change the thermal resistance’s value.
Thermal impedance
Thermal impedance measures a material’s ability to oppose heat flow. Therefore, this value must be very low from a PCB perspective. Lower thermal impedance results in faster heat flow via the PCB and to the heat sink.
The thermal conductivity of the material determines the value of thermal impedance. Therefore, it is an object property as the value will change in line with the material’s thickness.
Thermal conductivity
This determines a substrate’s ability to conduct heat. Thermal conductivity is always measured in W/mK. Also, it is a material property. This means that when the material’s dimension changes, it doesn’t change. For instance, the thermal conductivity of a 10cm of gold is the same as the thermal conductivity of a 100m of gold.
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Factors to Consider When Designing Thermal Circuit Boards
There are several factors to consider when designing a PCB. It is important that the design is ideal for the purpose of the final product. However, the design should be cost effective to minimize the effect on the total cost of the PCB.
Material selection
The metal clad PCB technology is based on heat removal from the final product. Also, heat removal ensures increased longevity. Therefore, you should consider the specifications the material must meet. There are ideal materials that meet the application requirements.
PCB size and shape
The base materials are available in different sizes. Therefore, the shape or size of the PCB design is very important. Rectangular/square designs are ideal for yield because of their tessellation.
Fabrication
The square/rectangular shapes are the most common process. This process is ideal for high and low volume. Also, it enables the best yield for each production panel as no spacing is needed between PCBs.
The application of the final product should determine the surface finish type. Also, the assembly method utilized for populating the boards will determine surface finish. Each surface finish type has its benefits and limitations. Therefore, this will determine if it meets your application’s requirement.
Conclusion
Metal clad PCBs have become so popular in different applications. With the rise in the LED lighting industry, there is high demand for metal clad boards. These boards are very ideal for high power applications. Also, these boards feature more benefits than FR4 boards.
