Why would a circuit board with aluminum?
The advantages and disadvantages of the ceramic PCB circuit board were introduced above. One of the disadvantages is that the ceramic substrate is too expensive and fragile. Ordinary glass fiber PCB has poor heat dissipation performance, ceramic PCB is relatively stable, and it is not easy to deform under high temperature and humidity environment, but the price is relatively expensive, and it is often used in high-end products. If my product is not so high-end, such as large-area high-power LED light board, Aluminum 2.0W LED board is relatively cheap, but it needs very good heat dissipation performance. Is there a PCB substrate with cheap material and good heat dissipation? ?
The answer is yes. That is the aluminum substrate PCB that this article will introduce. Everyone knows that aluminum is a metal and has conductivity. How can it be used as a PCB material?
This is because the aluminum substrate is composed of three layers: copper foil, insulating layer and metal aluminum. Since there is an insulating layer, can the metal layer be made of other materials besides aluminum? Such as copper plate, stainless steel, iron plate, silicon steel plate, etc. What kind of material is used for the metal substrate, in addition to considering the heat dissipation performance, but also consider the thermal expansion coefficient, thermal conductivity, strength, hardness, weight, surface condition and cost of the metal substrate.
Under normal circumstances, considering the cost and technical performance, aluminum plate is an ideal choice. Available aluminum plates are 6061, 5052, 1060, etc. If there are higher thermal conductivity, mechanical properties, electrical properties and other special performance requirements, copper plates, stainless steel plates, iron plates and silicon steel plates can also be used.
Commonly used in LED lighting products, such as 1 layer LED Based Night Lamp, it has both front and back sides. The white side is soldered with LED pins, and the other side is in the natural color of aluminum. Generally, it will contact the heat-conducting part after applying thermal paste. Mainly used in LED lamps and audio equipment, power supply equipment, etc., the main advantages are fast heat conduction and good heat dissipation performance.
Compared with the traditional FR-4, the aluminum substrate can minimize the thermal resistance, so that the aluminum substrate has excellent thermal conductivity; compared with the ceramic substrate, its mechanical properties are extremely good.
In addition to good heat dissipation performance, aluminum substrates also have the following advantages:
Comply with RoHS environmental protection requirements
More suitable for SMT process
Higher current carrying capacity
Extremely effective treatment of thermal diffusion in the circuit design scheme, thereby reducing the operating temperature of the module, prolonging the service life, and improving the 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; optimize the combination of power circuits and control circuits;
Replace fragile ceramic substrates to obtain better mechanical durability.
Compared with the ordinary FR-4 PCB board, the aluminum substrate has the biggest advantage that it can carry higher current. Like FR-4 PCB, the circuit layer uses copper foil as the wire for connection. Compared with the traditional FR4 PCB, the aluminum substrate can carry higher current with the same thickness and the same line width.
The core technology of the aluminum substrate is the insulating material in the middle, which mainly functions as adhesion, insulation and heat conduction. The insulating layer of the aluminum substrate is the largest thermal barrier in the power module structure. The better the thermal conductivity of the insulating layer, the better the diffusion of the heat generated during the operation of the Electronic Components, and the more helpful it is to reduce the operating temperature of the device, so as to increase the power load of the module, reduce the volume, extend the life, and increase the power output, etc. Purpose. While satisfying good thermal conductivity, it must also have high-voltage insulation capability.
The difference with FR-4 sheet
Heat dissipation
The biggest difference between aluminum-based copper clad laminates and conventional FR-4 copper clad laminates lies in heat dissipation. Compared with aluminum-based copper clad laminates with a thickness of 1.5mm, the former has a thermal resistance of 20~22 ℃, and the latter has a thermal resistance of 1.0~2.0. ℃, the latter is much smaller.
Thermal expansion coefficient
Because the general FR-4 has the problem of thermal expansion, that is, high temperature will cause the thickness and flatness of the plate to change, especially the thermal expansion in the thickness direction of the plate, which affects the quality of the metallized holes and circuits. The main reason for this is that the thermal expansion coefficient of the raw material of the board is different: the thermal expansion coefficient of copper is 17×106cm/cm℃, and the base material of FR-4 board is 110×106cm/cm℃. There is a big difference between the two, which is easy to cause thermal expansion. effect. The thermal expansion coefficient of the aluminum substrate is 50×106cm/cm°C, which is smaller than the general FR-4 board and closer to the thermal expansion coefficient of copper foil. This helps to ensure the quality and reliability of the printed circuit board.
The main purpose
FR-4 board is suitable for general circuit design and general electronic products. The aluminum substrate is suitable for circuits with special requirements. Such as: thick film hybrid integrated circuit (high frequency mixing pressure plate), heat dissipation of power circuit, heat dissipation and cooling of components in the circuit, large-scale substrates that ceramic substrates are difficult to handle, and circuits whose reliability cannot be solved by using ordinary heat sinks.
Machinability
Aluminum substrate has high mechanical strength and toughness, which is better than FR-4 board. For this reason, large-area printed boards can be manufactured on aluminum substrates, and electronic components with heavy weights can be installed on such substrates.
Electrical performance
From the comparison between the aluminum substrate and the FR-4 board, due to the high heat dissipation of the metal substrate, the wire fusing current has a significant increase, which shows the high heat dissipation characteristics of the aluminum substrate from another angle. 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 voltage resistance). 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 general conditions, the withstand voltage value of the aluminum substrate is determined by the thickness of the insulating layer. The withstand voltage value of the aluminum substrate is generally about 500v. If you need to test the withstand voltage value of the aluminum substrate of the LED fluorescent lamp, only It is sufficient to perform a high-voltage test on the input port shell. The UL and CE certification value should be 2500V, and the 3C certification value should be 3750V.
Classification of aluminum substrates
Aluminum-based copper clad laminates are divided into three categories:
General-purpose aluminum-based copper clad laminate, the insulating layer is composed of epoxy glass cloth bonding sheet;
High heat dissipation aluminum-based copper clad laminate, the insulating layer is made of epoxy resin or other resin with high thermal conductivity;
Aluminum-based copper-clad laminates for high-frequency circuits, the insulating layer is made of polyolefin resin or polyimide resin glass cloth bonding sheet.
The main purpose
Lighting products, high-power LED lighting products.
Audio equipment, preamplifier, power amplifier, etc.
Power equipment, DC/AC converters, rectifier bridges, solid state relays, etc.
Communication products, high-frequency amplifiers, filter appliances, and transmission circuits.
