First, the structure and types of metal-based copper clad laminate
Metal-based copper clad laminate is generally composed of three parts: metal substrate, insulating dielectric layer and conductive layer (generally copper foil), that is, one or both surfaces of the treated metal substrate are covered with insulating dielectric layer and copper foil, which are compounded by hot pressing. Because the structure, composition and performance of metal-based copper clad laminate are different, it can be divided into many kinds.
According to the structure of metal substrate, there are three common types: metal substrate, coated metal substrate and metal core substrate. The metal substrate is a metal plate (aluminum, copper, iron, molybdenum, etc.) as the base material, and its substrate is covered with an insulating dielectric layer and a conductive layer (copper foil); Type-A coated metal substrate is a bottom substrate which is formed by coating a layer of glaze on the six sides of the metal plate and sintering it. On this substrate, the conductor circuit pattern is made by screen leakage and sintering. Generally, the metal core substrate is made of copper and aluminum, and its surface is coated with a layer of organic polymer insulating medium, or it is compounded on a prepreg or PET film, and covered with a conductive foil (some of which directly form conductive patterns with additive process), as shown in Figure 5-1. Among them, metal substrate is the most common and the most used one.
Metal substrates can be divided into:
1 aluminum-based copper clad laminate; 3 copper-based copper clad laminate;
2 iron-based copper clad laminate; Molybdenum-based copper clad laminate.
From the characteristics of metal-based copper clad laminate, it can be divided into:
General-purpose metal-based copper clad laminate; 3 High heat-resistant metal-based copper clad laminate;
2 flame retardant metal-based copper clad laminate; 4 high thermal conductivity metal-based copper clad laminate;
5 ultra-high thermal conductivity metal-based copper clad laminate; 7 multilayer metal-based copper clad laminate.
6. High frequency and microwave type metal-based copper clad laminate;
Second, the main characteristics of metal-based copper clad laminate
1 Excellent heat dissipation performance
Metal-based copper clad laminate has excellent heat dissipation performance, which is the most prominent feature of this kind of sheet. The PCB made of it can prevent the working temperature of components and substrates loaded on the PCB from rising, and can also quickly dissipate the heat generated by power amplifier components, high-power components, large circuit power switches and other components. Among different metal substrates, copper has the best heat dissipation, and its thermal conductivity is higher than other metal substrates. Copper is not widely used because of its high density (8.9g/cm3), high price, easy oxidation, and inconsistent with the trend of lightweight substrate materials. It is only used when manufacturing ultra-high heat dissipation substrates. Although the heat dissipation of aluminum plate is worse than that of copper plate, it is much better than that of iron plate, and it has low density, light weight (2.7g/cm3), oxidation resistance and low price. Therefore, it is the most widely used and used composite plate in metal-based copper clad laminate.
The heat dissipation of metal-based copper clad laminate mainly depends on the metal type of the metal base material, but it is also related to its insulating layer thickness and thermal conductivity. In order to improve the thermal conductivity of metal-based copper clad laminate, it is necessary to add thermal conductive filler into the insulation layer. The thinner the insulation layer, the higher the thermal conductivity of the metal substrate, but the thinner the insulation layer, the lower the pressure resistance of the plate. Therefore, when users choose metal-based copper clad laminate, they should comprehensively consider the thermal conductivity, voltage resistance, insulation and so on.
2 Good machining performance.
Metal-based copper clad laminate has high mechanical strength and toughness, which is much better than rigid resin-based copper clad laminate and ceramic substrate. Therefore, a large-area printed board can be manufactured on a metal substrate. Heavy components can be mounted on such substrates. In addition, the metal substrate also has good flatness. It can be used for assembly processing such as hammering and riveting on the substrate. On the manufactured PCB, the non-wiring part can also be machined in aspects of bending and twisting.
3 Excellent dimensional stability
For all kinds of copper clad laminates, there is the problem of thermal expansion (dimensional stability), especially the thermal expansion in the thickness direction (Z axis), which affects the quality of metallized holes and circuits. The main reason is that the linear expansion coefficient of the board is different, for example, the linear expansion coefficient of copper is 17×10-6/℃ and that of epoxy glass fiber cloth substrate is (110~140)x10-6/℃. There is a big difference between the two, which is easy to cause the difference of the substrate’s thermal expansion, resulting in the fracture or destruction of copper lines and metallized holes. The linear expansion coefficients of iron and aluminum substrates are 40×10-6/℃ and 50×10-6/℃ respectively. It is much smaller than the general resin substrate, but closer to the linear expansion coefficient of copper, which is beneficial to ensure the quality and reliability of printed circuit.
4 Electromagnetic shielding
In order to ensure the performance of electronic circuits, some components in electronic products need to prevent the radiation and interference of electromagnetic waves, and metal substrates can act as shielding plates to shield electromagnetic waves.
5 Electromagnetic characteristics
The base material of iron-based copper clad laminate is made of alloy of iron elements with magnetic properties (such as silicon steel plate, low-carbon steel plate, galvanized cold-rolled steel plate, etc.), which is used in small precision motors such as tape recorders (VTR), floppy disk drives (FDD), servo motors, etc. This kind of metal-based copper clad laminate not only plays the role of PCB, but also plays the role of stator base plate of small motor.