Mentioning metal in printed circuit boards is understandable, but for those unfamiliar, the misconception that the entire board is metal is clearly mistaken. In modern electronics, the most widely used is the FR4 PCB, a glass fiber-reinforced epoxy resin composite, with metal representing the copper on the surface and within. So, what is a metal PCB?
Definition of Metal PCB
PCB is typically named based on its features, and Metal PCB is named so because it uses metals like aluminum, copper, or other metallic substrates. Therefore, it is also known as Metal Backed PCB, Metal Core PCB (MCPCB), or Metal Base PCB. Among these terms, Metal Core PCB is the most commonly used. Due to the challenges associated with multi-layering metal materials, most Metal Core PCB have a three-layer structure: a metal core, a dielectric layer, and a copper foil layer.
Metal Core PCB has garnered widespread attention due to its robust thermal management capabilities. In comparison to traditional FR-4 or polyimide PCB, metal materials excel in both thermal conductivity and heat dissipation. This makes it the preferred choice for high-power and high-temperature applications. It can effectively handle the heat generated by components on the PCB or from the surrounding environment, ensuring efficient heat dissipation without compromising functionality. The most common types of Metal Core PCB are Aluminum PCB and Copper PCB, with Aluminum being more cost-effective and Copper exhibiting excellent thermal conductivity.
Structure of Metal Core PCB
In reality, the structure of printed circuit boards is largely similar, with the main distinction lying in the choice of substrate material. Typically, PCB consists of outer layers (solder mask and silkscreen layers) and inner layers (substrate layer and copper layer). In this structure, the solder mask layer covers the copper traces and pads, and the circuit pattern is etched onto the copper layer. As for Metal Core PCB, the substrate is usually located at the bottom or in the middle.
While researching information about the structure of Metal Core PCB online, you may come across articles that frequently mention an insulation layer. However, in practical terms, Metal Core PCB may not necessarily require a traditional insulation layer, such as FR4. I consulted our company’s PCB engineer, and he explained to me that Metal Core PCB typically do not need an insulation layer similar to FR4.
Types of Metal Core PCB
Single Layer MCPCB
It has only one copper layer on a single side, separated by a dielectric layer. This type of MCPCB is commonly used in LED lights, where the aluminum on the other side of the PCB serves as a heatsink.
Double Layer MCPCB
It comprises a metal core on one side of the PCB and two copper layers separated by dielectric layers on the other side. The metal core is positioned at the bottom of the layer stack.
In contrast to the double layer MCPCB, the two copper layers of the double-sided MCPCB are positioned on opposite sides of the metal core. The metal core is situated in the middle of the layer stack, separated from the two copper layers by dielectric material.
This type features multiple copper layers, each separated by a thermally conductive dielectric material. At the bottom of the layer structure lies the metal core. Components can only be placed on one side of the PCB, namely the top side. However, even top metal-core PCB manufacturers encounter challenges in constructing additional layers due to the inherently difficult-to-process nature of metal materials.
This type of PCB incorporates a thin copper layer into its layer stack, serving as a conductive layer for thermal dissipation or grounding purposes.
Metal Core PCB Design
Before embarking on PCB design, the primary task is to clearly define the main purpose of the project. Metal-core printed circuit board is specifically designed for high-power and high-temperature applications. Although they can provide excellent heat dissipation, special attention still needs to be paid to thermal management during the design phase.
Firstly, choose a suitable substrate material based on project requirements, with a focus on material thermal conductivity, dielectric constant, and thickness. These factors contribute to efficient heat dissipation, and the dielectric layer should also provide good electrical insulation.
Secondly, in high-power applications, consider using thicker copper traces. This design can better carry current and provide additional heat dissipation performance. However, when laying out the circuits, be cautious to avoid close proximity between traces to reduce the risk of arc generation.
Regarding component placement, have a clear understanding of which components are heat-sensitive and which ones generate a significant amount of heat during operation. Additionally, consider adding heat dissipation holes on the metal-clad PCB or using heat pads and professional cooling solutions to achieve better physical cooling effects.
Alternative Solutions for Metal PCB
When dealing with advanced equipment projects, if the thermal performance requirements for the PCB are relatively low, one can consider using FR4 or other conventional materials as alternatives to metal-core PCB to reduce project costs and increase circuit density.
Typically, the heat sources generated by devices mainly come from the following three aspects:
- Environment: In some industrial fields, devices may need to operate continuously or be used for heating, resulting in an elevated operating temperature of the PCB.
- Component Operation: Internal components of the device generate heat during operation, similar to the heat generated when a computer is running. This heat is not only from the casing but is primarily the result of the components’ own operation.
- Circuits: When current passes through resistive conductors, electron collisions with atoms cause power loss, ultimately released in the form of heat, resulting in resistive heating.
To achieve the heat dissipation effect of metal-core PCB on traditional PCBs, some effective measures can be taken, such as:
- Physical Cooling: Use additional materials such as heat sinks and fans. Heat sinks are typically made of copper or aluminum fins attached to the heating components on the PCB. Fans can assist in dissipating heat by forcing air through the PCB surface or heat sinks.
- Design Optimization: Add features like heat dissipation holes, thermal pads, and copper planes for design optimization. More heat dissipation holes don’t necessarily mean better performance; an increase in heat dissipation holes may reduce the mechanical performance of the PCB. Thermal pads are designed to conform to irregular patterns on the PCB surface to ensure maximum surface contact for enhanced heat dissipation. Copper planes are large filled copper areas connected to a network, helping to disperse heat throughout the PCB to reduce temperature gradients.
- Liquid Cooling: Suitable for applications with higher heat dissipation requirements, such as computers and laptops. Coolants or refrigerants circulate through copper tubes in contact with the heat-generating components, helping to carry away heat and dissipate it through the copper board.
- Heat Pipes: They utilize the principle of phase change materials, absorbing heat through the solid-to-liquid conversion. Designers can embed heat pipes into the PCB or add them externally.
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