Why do we need to use metal PCB? from buzai232's blog

Why do we need to use metal PCB?

1. Heat Dissipation

At present, many double-sided and multi-layer PCBs are high density, high power boards, which are difficult to dissipate heat. Conventional substrates such as FR4 and CEM3 are poor conductors of heat, which are insulated between layers and heat cannot be dissipated, while local heating of electronics will result in high-temperature failure of the components. Insulated metal substrates possess a heat dissipation capacity 5-10 times than FR4, can solve this heat dissipation problem.To get more news about fr4 circuit board, you can visit pcbmake official website.
2. Thermal Expansion

The conventional printed circuit board consists of resin, reinforcing material (such as glass fiber) and copper foil. The thermal expansion coefficient (CTE) of the substrate is 80~90PPM/°C in the Z-axis direction, while the CTE of copper is 16.8PPM/°C, that means the metalized hole wall and the insulating wall of conventional PCB have a large difference in the CTE. If the generated heat cannot be eliminated in time, the metalized hole will be cracked by thermal expansion and contraction, resulting in unreliable electronic equipment.

SMT (Surface Mount Technology) makes this problem more prominent. Because the connection is achieved by direct soldering between the metal pad and SMD, the CTE difference of the ceramic chip (6PPM/°C) and FR4 substrate (13-18PPM/°C) probably cause connection fracture after a long time running.
Differences Between Metal PCB and FR4 PCB
Conductivity: FR4 has a low thermal conductivity, typically about 0.3W, while metal PCB has a higher thermal conductivity from 1.0W to 4.0W, the most common being about 1.0W.

PTH for Mount: Conventional boards typically requires PTHs to assemble DIP parts. But PTHs are not suitable for 1-sided metal PCBs, all of the components are surface mounted.

Heat Dissipation: Heat dissipation in FR4 PCB typically involves vias for heat transfer, which require longer drilling cycle, more extra processes. Metal PCB provide their own heat dissipation. Via drilling, deposition, and plating processes are eliminated.

Solder Mask: Conventional PCB solder mask is usually green/red/blue/white/black/Orange... Usually applied to the top and bottom. Metal PCB solder mask is almost entirely white for LED boards. Applied only to the top.

Thickness: Conventional PCB such as FR4 is available in a variety of thicknesses and can be selected using a variety of material combinations and layers. The thickness variation of the Metal PCB is limited by the thickness of the insulated metal substrate.

Machining Process: Metal PCB uses the same standard machining methods with FR4 PCB, except that V-groove must use diamond-coated saw blades for the added strain from cutting into metal.