1、 Structure and types of metal base copper clad laminate
In PCB type, metal base copper clad plate is generally composed of three parts: metal substrate, insulating dielectrIC layer and conductive layer (generally copper foil). That is, one or both sides of the surface treated metal substrate are covered with insulating dielectric layer and copper foil, and then they are hot pressed and compounded. As the metal base copper clad laminate is different in its structure, composition and performance, it can be divided into many kinds.
According to the structure of metal substrate, there are three common types, namely metal substrate, coated substrate and metal core substrate. The metal substrate is made of metal plates (aluminum, copper, iron, molybdenum, etc.), which are covered with insulating dielectric layer and conductive layer (copper foil); The coated metal substrate is a substrate which is made of six surfaces of the metal plate covered with a layer of glaze and sintered into a whole, on which the conductor circuit diagram is made by leaking, sintering and wire mesh; The metal core substrate is generally made of copper and aluminum as the core materials, and its surface is coated with an organic polymer insulating dielectric layer, or it is compounded on a sEMI solidified sheet or in a PET film, and coated with a conductive foil (some directly form conductive patterns by addition), as shown in Figure 5-1. Among them, metal substrate is the most common and used one.
The metal substrate can be divided into:
1 Aluminum base copper clad plate; 3 Copper base copper clad plate;
2 Iron base copper clad plate; 4 Molybdenum based copper clad plate.
From the characteristics of metal base copper clad laminate, it can be divided into:
1 Universal metal base copper clad plate; 3 High heat resistance metal base copper clad plate
2 Flame retardant metal base copper clad plate; 4 High thermal conductivity metal base copper clad plate;
5 Ultra high thermal conductivity metal base copper clad plate; 7 Multilayer metal base copper clad plate.
6 high frequency and microwave type metal base copper clad laminate;
2、 Main characteristics of metal base copper clad laminate
1 Excellent heat dissipation performance
The metal based copper clad laminate has excellent heat dissipation performance, which is the most prominent feature of this type of plate. The PCB made of it can prevent the working temperature of the components loaded on the PCB and the substrate from rising, and can also rapidly dissipate the heat generated by PCB components such as power amplifier components, high-power components, and power switches of large circuits. Among different metal substrates, copper has the best heat dissipation, and its heat 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 inconformity with the development trend of lightweight substrate materials. It is only used when making ultra-high heat dissipation substrate. Although the heat dissipation of aluminum plate is worse than that of copper plate, it is much better than that of iron plate, with SMAll density, light weight (2.7g/cm3), oxidation resistance and low price. Therefore, it is the most widely used and most widely used composite plate among metal based copper clad plates.
The heat dissipation of metal based CCL mainly depends on the metal type of metal substrate, but also on its insulation thickness, thermal conductivity, etc. In order to improve the thermal conductivity of metal based copper clad laminate, thermal conductive filler should be added to the insulating 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 selecting metal base copper clad laminate, users should consider the heat conduction performance, voltage withstand performance, insulation performance, etc. of the plate comprehensively.
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, the manufacture of large area printed boards can be realized on the metal substrate. Components with large weight can be instalLED on such substrates. In addition, the metal substrate has good flatness. assembly and processing of hammering, riveting, etc. can be carried out on the base plate. On the PCB made of it, the non wiring part can also be machined in terms of bending, twisting, etc
3 Excellent dimensional stability
For all kinds of CCL, there is a problem of thermal expansion (dimensional stability), especially the thermal expansion in the thickness direction (Z-axis) of the board, which affects the quality of metallized holes and circuits. The main reason is that the linear expansion coefficient of plates is different. For example, the linear expansion coefficient of copper is 17x10-6/℃ and that of epoxy glass fiber cloth substrate is (110~140) x10-6/℃. The difference between the two is very large, which is easy to cause the difference in the thermal expansion of the substrate, resulting in the fracture or destruction of the copper circuit and the metallized hole. The linear expansion coefficients of iron and aluminum substrates are 40x10-6/℃ and 50x10-6/℃ respectively. It is much smaller than the general resin substrate, and closer to the linear expansion coefficient of copper, which is conducive to ensuring the quality and reliability of printed circuits.
4 Electromagnetic shielding
In order to ensure the performance of electronic circuits, some components in PCB electronic products need to prevent the radiation and interference of electromagnetic waves. The metal substrate can act as a shielding plate to shield electromagnetic waves.
5 Electromagnetic characteristics
The base plate material of iron base copper clad laminate is composed of iron series elements with magnetic properties (such as silicon steel plate, low carbon steel, galvanized cold rolled steel plate, etc.), which is used in small precision motors such as tape recorder (VTR), floppy disk driver (FDD), servo motor, etc. The metal base copper clad plate not only functions as a PCB, but also as a PCB base plate for small motor stator.