Characteristics Of Metal Core PCB
1.Heat dissipation
Conventional PCB substrates are generally hot undesirable conductors, The interlayer insulating material has a very slow heat emission. The internal heating of various electronic devices and power equipment can not be eliminated in time, result high speed components failure. But the metal core PCB has good heat dissipation. The metal core has high thermal capacity and high thermal conductivity, which can quickly dissipate the heat in the PCB. If the metal core is connected with the shell and the external radiator, the heat dissipation effect is better. Because the electronic equipment and communication system adopts metal core PCB, The fan in the equipment can be omitted, and the volume of the equipment is greatly reduced. The efficiency is improved, especially for the electronic equipment of closed chassis.
2.Thermal expansibility
Thermal expansion and contraction are the commonalities of matter, and the thermal expansion coefficients of different substances are different. PCB is a composite material made of resin, reinforced material and copper foil. The coefficient of thermal expansion is two opposite, in the direction of xY axis. The thermal expansion coefficient of PCB CTE is 13×10-6~ 18×10-6 /℃. In the direction of the thickness of the PCB (the direction of the Z axis) is 80×10-6～90×10-6/℃, and the CTE of copper is 16.8×10-6/℃, The CTE of the flake ceramic is 6×10-6/℃.From these data, it can be seen that the PCB metallized hole wall and the connected insulating substrate are quite different in the Z axis CTE. If the heat generated can not be eliminated in time, the thermal expansion and shrinkage will make the coating of the metallized hole wall crack or break. When the ceramic chip carrier is welded on PCB.Due to the difference between the device and the PCB material CTE, the fatigue failure of the solder joint will be caused by the long-term stress.
The thermal expansion rate of metal core PCB is small, and its size is much more stable with temperature than PCB of insulation material. Aluminum base PCB, aluminum sandwich PCB, the size change is only 2.5% to 3% from 30℃ to 140~150℃, It can meet the welding reliability requirements of ceramic chip carrier devices.
3.Magnetic shielding
Metal core PCB also has shielding effect, Especially the anti electromagnetic interference of CIC core plate is good, It can replace the radiator and other components, and effectively reduce the area of PCB. The effect of electromagnetic shielding, It can improve the electromagnetic compatibility of the products and reduce the production cost.
The use and characteristics of several common metal core substrates.
- Copper base: Good thermal conductivity, used for heat conduction and electromagnetic screen cutting, but with high quality and high price.
- Iron base: Anti electromagnetic interference, shielding performance is the best, but the heat dissipation is poor, the price is cheap.
- Aluminum base: The heat conduction is good, the quality is light, and the electromagnetic shielding is good
Commonly used metal core clad foil boards include aluminum core, iron core (including silicon steel plate), copper core and CIC.
The most commonly used aluminum base materials for making metal core PCB are LF, L4M and LY12. The tensile strength is 294N / mm and the elongation is 5%. Commonly used thickness is 1mm, 1.6mm, 2mm, 3.2mm four specifications. The common aluminum layer is is 140um used in communication power supply, with copper foil on top and bottom.
Copper base material
The tensile strength of copper based substrates usually ranges from 245 to 313.6N / mm2. The extension rate is 12%, Common thickness is 1mm, 1.6mm, 2mm, 2.36mm, 3.2mm five types.
Iron base material
The most common is cold rolled steel plate used in production. It belongs low carbon steel with two kinds of thickness of 1mm and 2.3mm. Or use phosphorus containing iron base thickness of 0.5mm, 0.8mm, 1.0mm three types.
Copper foil
The back of the copper foil is chemically oxidized, galvanized and brass plated. The aim is to increase the strength of anti peeling. The thickness of copper foil is usually 17.5um, 35um, 75um and 140um.