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The Difference between Aluminum PCB and FR4 PCB

by: Nov 13,2023 1227 Views 0 Comments Posted in PCB Basic Information

Aluminum PCB FR4 PCB

With the continuous development of electronic technology, the application of PCBs has become increasingly widespread. PCBs are integral components of electronic devices, playing crucial roles in various applications. Among them, Aluminum PCB and FR4 PCB (Glass Fiber Reinforced Epoxy Resin PCB) are two common types of PCBs with significant differences in terms of materials, performance, and applications. Copper-based PCBs have better thermal conductivity than aluminum-based PCBs. This article will explore the key differences between Aluminum PCB and FR4 PCB.

Materials

The name of Aluminum PCB already reveals its key material - aluminum. It typically exists in the form of an aluminum substrate, giving the PCB excellent thermal conductivity. An insulating layer is usually coated on the aluminum substrate to isolate the circuit.

In contrast, FR4 PCB uses a material made of glass fiber-reinforced epoxy resin, which has excellent mechanical strength but relatively poor thermal conductivity. The "FR" in FR4 stands for Flame Retardant, meeting the requirements of UL 94V-0.

Thermal Conductivity

Aluminum PCB stands out as a choice for thermal conductivity. Aluminum is an excellent thermal conductor, making Aluminum PCBs very useful in applications that require high heat conduction and dissipation. For example, LED lighting requires efficient heat conduction because LED light-emitting components generate heat. Aluminum PCBs can effectively transfer and dissipate this heat, helping improve the performance and lifespan of LEDs. In contrast, FR4 PCB has relatively poor thermal conductivity and is typically not suitable for applications that require efficient heat dissipation. This is because FR4 mainly consists of glass fiber-reinforced epoxy resin, which is not a good thermal conductor.

Coefficient of Thermal Expansion

Due to the issue of thermal expansion in general FR-4, especially in the thickness direction of the board, the quality of metalized holes and circuit lines can be affected. The main reason is that there is a significant difference in the coefficient of thermal expansion in the thickness direction of the board: the coefficient of thermal expansion of copper is 17×10^-6 cm/cm℃, while FR-4 board is 110×10^-6 cm/cm℃, which is a big difference and is prone to differences in thermal expansion of the base material, leading to breaks in copper lines and metalized holes, causing damage and affecting product reliability.

The coefficient of thermal expansion of aluminum substrates is 50×10^-6 cm/cm℃, which is smaller than that of the typical FR-4 board and closer to the coefficient of thermal expansion of copper foil. This is advantageous in ensuring the quality and reliability of printed circuit boards. Therefore, if you want to reduce the Coefficient of Thermal Expansion (CTR) for your application, aluminum substrates are the preferred choice.

Laminating Layers

In terms of layering, aluminum PCBs strictly have three layers, while FR4 PCBs can be single-layer, double-layer, or multi-layer. The three lamination layers of an aluminum PCB include the aluminum substrate, copper conductive layer, and dielectric layer, making it a suitable choice for applications exposed to high temperatures.

Mechanical Strength and Rigidity

Due to its metal core base, aluminum PCBs exhibit greater mechanical strength and rigidity compared to FR4. For applications that require PCBs with a large capacity to accommodate multiple electrical components, aluminum PCBs are a better alternative. The aluminum substrate layer in the PCB provides exceptional strength to the components.

Thickness

One aspect where FR4 PCBs surpass aluminum substrates is board thickness. FR4 PCBs offer thick PCBs, with thickness varying due to multi-layer lamination. However, the thickness range of aluminum PCBs is relatively lower due to the thickness of the dielectric or the backing metal layer. The credit goes to the backing plate, as the thickest component in aluminum PCBs is used for additional heat dissipation.

Applications

Different PCB types are suitable for different applications. Aluminum PCBs are typically used in applications that require high thermal conductivity and electrical conductivity. Apart from LED lighting, they find extensive use in power modules, high-power RF applications, automotive electronics, and more. FR4 PCBs are generally used in common electronic circuits, especially in applications that do not require high thermal conductivity. The mechanical strength and electrical insulation properties of FR4 PCBs make them suitable for many common electronic devices. In some special cases, a high TG FR4 (High Glass Transition Temperature FR4) is available, which has a higher glass transition temperature, enabling it to remain stable at higher temperatures. This makes it more suitable for applications with specific temperature requirements.

In summary, the differences between aluminum PCBs and FR4 PCBs are significant in terms of materials, thermal conductivity, coefficient of thermal expansion, layering, mechanical strength and rigidity, thickness, and applications. Choosing the right PCB type for a specific application is crucial as it directly impacts the performance and stability of electronic devices. Aluminum PCBs are suitable for applications that require high thermal conductivity and electrical conductivity, while FR4 PCBs are suitable for general electronic circuits. Understanding these differences can help engineers and designers make informed choices to meet the needs of their projects.

Additionally, if you require PCBs with different thicknesses, FR4 PCBs are the best choice. However, if you want to select PCBs with strong electromagnetic shielding and heat dissipation capabilities, then opt for aluminum PCBs.

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