The advantages and disadvantages of ceramic PCB circuit boards have been described earlier, one of which is that ceramic substrates are too expensive and fragile. Ordinary glass fiber PCBs have poor heat dissipation, while ceramic PCBs are relatively stable and not prone to deformation in high temperature and humidity environments. However, they are relatively expensive and are commonly used in high-end products. If my product is not so high-end, such as a large area and high-power LED lamp board, which is relatively inexpensive, but requires very good heat dissipation performance, is there a PCB board that is cheap in material and has good heat dissipation?
The answer is yes. That is the aluminum substrate PCB to be introduced in this article. Everyone knows that aluminum is a metal with electrical conductivity. How can it be used as a PCB material?
Aluminum pcb composition
This is because the aluminum substrate consists of three layers of structure: copper foil, insulating layer, and metal aluminum. Since there is an insulating layer, can other materials be used for the metal layer besides aluminum? Such as copper plate, stainless steel, iron plate, silicon steel plate, etc. The material used for a metal substrate should not only consider the heat dissipation performance, but also consider the thermal expansion coefficient, thermal conductivity, strength, hardness, weight, surface condition, and cost of the metal substrate.
Generally speaking, considering cost and technical performance, aluminum plate is an ideal choice. Available aluminum plates include 606150521060, etc. Copper plate, stainless steel plate, iron plate, and silicon steel plate can also be used if there are requirements for higher thermal conductivity, mechanical properties, electrical properties, and other special properties.
Commonly used in LED lighting products, there are two sides, the white side is welded to the LED pins, and the other side presents the natural color of aluminum. Generally, it is coated with thermal conductive paste and comes into contact with the thermal conductive part. It is mainly used in LED lamps, audio equipment, power supply equipment, etc. Its main advantages are fast heat conduction and good heat dissipation performance.
Compared to the traditional FR-4, aluminum PCB can minimize thermal resistance and provide excellent thermal conductivity; Compared with ceramic substrates, its mechanical properties are extremely excellent.
The advantages of aluminum PCB
In addition to good heat dissipation performance, aluminum PCB also have the following advantages:
- Comply with RoHS environmental requirements
- More suitable for SMT process
- Higher current carrying capacity
- In the circuit design scheme, heat diffusion is treated extremely effectively, thereby reducing the operating temperature of the module, extending its service life, and improving power density and reliability;
- Reduce the assembly of heat sinks and other hardware (including thermal interface materials), reduce product volume, and reduce hardware and assembly costs; Optimizing the combination of power circuits and control circuits;
- Replace fragile ceramic substrates for better mechanical durability.
Compared to ordinary FR-4 plates, the biggest advantage of aluminum PCB is that they can carry higher currents. Like FR-4, the line layer is connected using copper foil as a conductor. Compared to traditional FR-4, the aluminum substrate can carry higher currents with the same thickness and line width.
The core technology of aluminum substrate is the insulating layer material in the middle, which mainly plays the functions of adhesion, insulation, and heat conduction. The aluminum substrate insulation layer is the largest thermal barrier in the power module structure. The better the thermal conductivity of the insulation layer, the more conducive it is to the diffusion of heat generated during device operation, and the more conducive it is to reducing the operating temperature of the device, thereby achieving the goals of increasing the power load of the module, reducing the volume, extending the life span, and improving power output. While satisfying good thermal conductivity, it also requires high voltage insulation.
Difference from FR-4 plate
Heat dissipation
The biggest difference between aluminum based copper clad plates and conventional FR-4 copper clad plates lies in their heat dissipation. Compared with aluminum based copper clad plates with a thickness of 1.5mm, the former has a thermal resistance of 20 to 22 ℃, while the latter has a thermal resistance of 1.0 to 2.0 ℃, which is much smaller.
Coefficient of thermal expansion
Due to the problem of thermal expansion in general FR-4, high temperatures can lead to changes in the thickness and flatness of the plate, especially the thermal expansion in the thickness direction of the plate, which affects the quality of the metallized holes and lines. This is mainly due to the difference in the thermal expansion coefficient of the raw material thickness direction of the plate: the thermal expansion coefficient of copper is 17 × 106cm/cm ℃, FR-4 plate substrate is 110 × 106cm/cm ℃, with a large difference between the two, prone to thermal expansion effects. The thermal expansion coefficient of the aluminum substrate is 50 × 106cm/cm ℃, smaller than ordinary FR-4 plates, and closer to the thermal expansion coefficient of copper foil. This is conducive to ensuring the quality and reliability of printed circuit boards.
FR-4 PCB Main uses
The FR-4 board is suitable for general circuit design and general electronic products. aluminum PCB are suitable for circuits with special requirements. For example, thick film hybrid integrated circuits, heat dissipation of power supply circuits, heat dissipation and cooling of components in circuits, large-scale substrates where ceramic substrates are not competent, and circuits where the use of ordinary heat sinks cannot solve reliability problems.
Machinability
The aluminum substrate has high mechanical strength and toughness, which is superior to the FR-4 plate. Therefore, the manufacturing of large area printed boards can be realized on aluminum PCB, and heavy components can be installed on such substrates.
Electrical performance
From the comparison between aluminum substrate and FR-4 plate, due to the high heat dissipation of metal substrate, there is a significant improvement in wire fusing current, which indicates the high heat dissipation characteristics of aluminum substrate from another perspective. The heat dissipation of its aluminum substrate is related to its insulating layer thickness and thermal conductivity. The thinner the insulating layer, the higher the thermal conductivity of the aluminum substrate (but the lower the withstand voltage performance). In order to ensure the performance of electronic circuits, some components in electronic products need to prevent electromagnetic wave radiation and interference. The aluminum substrate can act as a shielding plate to shield electromagnetic waves.
Insulation performance
Under normal conditions, the voltage withstand value of the aluminum substrate is determined by the thickness of the insulation layer. In aluminum PCB, the voltage withstand value is generally around 500v. If you need to test the voltage withstand value of the aluminum substrate for LED fluorescent lamps, you only need to perform a high-voltage test on the input port housing. The UL and CE certified value should be 2500 V, and the 3C certified value should be 3750 V.
Classification of aluminum PCB
Aluminum based copper clad panels are divided into three categories:
Universal aluminum based copper clad plate, with an insulating layer composed of epoxy glass cloth adhesive sheets;
High heat dissipation aluminum based copper clad plate, with an insulating layer composed of high thermal conductivity epoxy resin or other resins;
Aluminum based copper clad plate for high-frequency circuits, with an insulating layer composed of polyolefin resin or polyimide resin glass cloth adhesive sheets.
Aluminum PCB Main uses
Lighting products, high-power LED lighting products.
Audio equipment, preamplifiers, power amplifiers, etc.
Power supply equipment, DC/AC converters, rectifier bridges, solid-state relays, etc.
Communication products, high-frequency amplifiers, filter appliances, and transmission circuits.
