Why Use Metal PCB?
Metal PCB is the circuit board made by metal core laminates, which gets widely used in LED equipment. Metal PCB is difficult to produce than FR-4 PCB, sometimes more expensive.
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.
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.
The metal PCB can effectively solve the heat dissipation problem, thereby alleviating the thermal expansion and contraction, and improving the durability and reliability of the electronic equipment.
3. Dimensional Stability
Metal PCB is much more stable than conventional PCB in dimension. For example, the aluminum core metal PCB, heated from 30°C to 140~150°C, the size change is 2.5~3.0%.
4. Other Reasons
- iron core metal PCB has a shielding effect
- replaces the brittle ceramic substrate
- good for surface mounting
- replaces components such as heat sink, improves product heat resistance and physical properties
- reduces production cost and labor
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.
Structure and Types of Metal PCB
The currently typical metal PCBs on the market consist of three types: Aluminum core PCB, Copper core PCB, and Iron core PCB, among which Aluminum core PCBs are the most common. The typical structure of a metal PCB is as follows.
1. Metal Base
Provided by raw material suppliers, such as Arlon, Bergquist, DENKA, Panasonic, Laird, KinWong, Ventec, etc. PS Electronics uses reliable metal materials from top suppliers.
- Aluminum: 6061T6, 5052H34, R-0710, R-0771
- Copper: C1100, C1220
- Iron: SUS430…
2. Dielectric Layer
The dielectric layer is placed on an anodized, insulated metal base and laminated together with a copper foil on the surface. It acts as an insulating layer and is usually 50~200um. If it is too thick, can act as an insulator to prevent short-circuiting with the metal base, but it will affect the heat dissipation. If it is too thin, can dissipate heat well, but it is easy to cause the short-circuit.
3. Copper Layer
The back of the copper foil is chemically oxidized and the surface is galvanized and brass plated to increase the peel strength. The copper weight is usually 0.5/1.0oz.
Applications of Metal PCB
- Communication: voltage regulator, regulator, DC-AC adapter
- Electronic Control: relays, transistor bases, components in various circuits to cool down
- Switch, Microwave: heat sink, semiconductor device insulation heat conduction, motor controller
- Automotive: igniters, voltage regulators, automatic safety, control systems, lighting conversion systems
- Computer: power supply unit, floppy disk drive, motherboard
- Home appliances: input-output amplifiers, audio, power balance amplification, and more.