Aluminum PCB: A Type of Low-Cost Metal Substrate

Do you still remember when you were a child, your parents used to buy shoes one size larger to save money? Do you recall your youth when you bought expensive brands just to satisfy your vanity? Looking back, it seems quite foolish. Believe me, the right choice is always the best one.

In the construction of printed circuit boards, a key consideration is the choice of PCB substrate material. This requires matching project costs with circuit requirements. For instance, in high-frequency environments, materials like Teflon, Rogers, and Arlon are used, while price-sensitive projects often opt for FR4 or CEM-3. In high-power applications, metal substrates are preferred. Among metal substrates, aluminum PCB have become the top choice for many projects due to their excellent heat dissipation performance and higher cost-effectiveness.

aluminium pcb

Introduction to Aluminum PCB

Aluminum PCB, also known as aluminum-clad PCB or aluminum core PCB, is a type of circuit board that uses aluminum as the substrate material. In the same size and thickness, aluminum is lighter than other metal materials, and when compared to non-metallic materials, it is also more reliable in resisting physical impacts and vibrations. In terms of circuit performance, it acts as an excellent conductor and provides electromagnetic shielding capabilities. Additionally, its higher dielectric coefficient helps prevent issues like electrical breakdown in high-voltage applications.

These advantages mentioned above are secondary, as the primary reason designers choose aluminum PCB as the construction material for their projects is its outstanding thermal performance. In applications such as spotlights, the working principle involves resistive heating, and significant current is used to operate the device. This poses challenges for heat dissipation and thermal resistance in the entire electronic system.

black high power spotlight

As a metal material, aluminum is an excellent thermal conductor with a thermal conductivity of 237 W/m⋅K, which is several tens to hundreds of times higher than conventional materials. This property allows it to more effectively transfer heat from heat-generating components to the air. Furthermore, aluminum PCB exhibits excellent dimensional stability in high-temperature environments, meaning it does not change its structural shape and dimensions when exposed to temperature and humidity variations. When the circuit temperature rises from 130 degrees to 140 degrees, the size change of the aluminum PCB is approximately 2.5% to 3.0%.

However, despite the numerous advantages of Aluminum based PCB, some drawbacks need to be observed.

Aluminum PCB is typically composed of thin copper foils and aluminum substrates, with the circuit pattern on the copper layer and the dielectric layer between the aluminum substrate and the copper traces acting as an insulating layer. Aluminum, being an active metal, is susceptible to chemical corrosion. If an etching process is used, strict control over the etching solution’s temperature, time, and concentration is necessary to avoid over-etching, which could lead to the failure of delicate traces. During mechanical processing, its inherent rigidity makes it prone to burrs during drilling, potentially causing short-circuit problems. When applying solder resist printing, the softer nature of the aluminum substrate compared to copper traces may result in the delamination or peeling of the solder resist layer during the printing process. After manufacturing, aluminum PCB requires cleaning, drying, and proper storage in a dark and dry environment to prevent discoloration or darkening due to moisture.

To address these challenges, here are some recommendations to improve the manufacturing process of aluminum PCB:

  • Consider laser drilling instead of CNC drilling.
  • Ensure timely cleaning after etching.
  • Store in an environment with temperatures between 12-40°C and humidity levels below 75% RH.
  • Avoid immediate use upon receipt.
PropertyParameter
Cladding thickness10 to 500 µm
Total thickness0.2 to 10 mm
Surface finishMatte, bright, or brushed
Tensile strength300 to 400 MPa
Yield strength200 to 300 MPa
Elongation10 to 20%
Electrical conductivity90 to 95% of pure copper
Thermal conductivity90 to 95% of pure copper

Based on the above characteristics and advantages, aluminum PCB is used in many fields such as automobiles, aviation, cooling projects, etc. Among them, the most popular one is the use of aluminum PCB in LED.

Aluminum Core PCB Structure

Copper Foil

Also known as traces, despite being an aluminum PCB, copper foil is still used as the trace material. Firstly, copper has much higher electrical conductivity than aluminum, which greatly assists in signal transmission and energy conservation. Secondly, in terms of chemical properties, copper is more stable, thus avoiding chemical corrosion and enhancing circuit reliability. For copper foil design, designers need to determine the copper thickness and width based on the specific project requirements. Typically, in the aluminum circuit board, the thickness of copper foil ranges from 1oz (35μm) to 3oz (105μm).

Substrate Layer

The substrate layer is a primary component of aluminum PCB, typically made of aluminum 6061 or 5052. It provides the board with mechanical support, electrical grounding, and other functions. Being a metal material, it is more conducive to dispersing and dissipating the heat generated by electronic components. Additionally, due to the difficulty of constructing multiple layers, it has certain limitations for complex projects.

Misconceptions

The dielectric layer is a very common part of circuit boards. However, the purpose of an aluminum-based PCB is to enhance thermal conductivity, and the presence of a dielectric layer can reduce its heat dissipation capabilities. Therefore, dielectric layers are typically not present in aluminum PCB, as their design focus is on heat dissipation rather than insulation.

Types of Aluminum PCB Board

Single Layer & Double Layer

On a single-layer aluminum PCB, the circuit traces are directly printed on the surface of the metal aluminum. This design is suitable for relatively simple circuit layouts where components can be directly connected to the traces on the aluminum substrate. In contrast, double-layer aluminum PCB have two layers of traces, typically located on the top and bottom surfaces of the metal aluminum. It can meet the requirements of most applications that necessitate aluminum-based boards.

Four-Layer

This is not very common but does indeed exist. For most manufacturers, a 4-layer aluminum PCB represents the limit of their production capabilities. Its structure is roughly as follows:

  • Top Layer: Located at the very top of the PCB for circuit layout and component connections.
  • Inner Layers 1 and 2: These two inner copper layers can be used as signal layers, power planes, or ground planes according to the project’s design requirements. Unlike conventional multilayer PCB, aluminum PCB’s inner layers typically do not require insulating materials for separation since aluminum itself is conductive and does not need electrical isolation like insulating materials.
  • Bottom Layer: The bottom layer serves the same purpose as the top layer, facilitating circuit layout and component connections.

Flexible Aluminum PCB

Bendable flexible aluminum PCB

This may seem to challenge our understanding, but flexible aluminum-based PCBs do indeed exist. Firstly, in material selection, they use aluminum foils with flexibility to allow bending without damaging the circuit. Secondly, physical grooves are created to enhance their bending capability, similar to semi flex PCB. Lastly, to ensure feasibility, components are only placed on one layer of the board.

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