Metal core printed circuit boards or MCPCBs are a specialized type of printed circuit board that contains a thermally conductive metal layer as the core or base material. The metal core offers superior heat dissipation capabilities compared to traditional glass epoxy FR-4 circuit boards. This makes metal core PCB well-suited for applications that require the management of high thermal loads.
MCPCBs Provide Several Key Benefits:
- Excellent thermal performance – The metal core acts as a heat sink, conducting heat away from components mounted on the board and spreading it over the larger PCB area. This allows heat to dissipate rapidly and prevents components from overheating.
- Higher current capacity – The metal core also functions as a large conductive plane for carrying current. This provides lower electrical resistance and enables higher amperage capacity compared to regular PCBs.
- Reliability – By preventing overheating of components, MCPCBs improve system reliability and longevity. The metal core’s rigidity also provides mechanical strength.
- Lightweight – Aluminum is commonly used as the metal core, allowing substantial weight savings versus a traditional glass epoxy-based PCB of the same size.
MCPCBs are widely used in applications such as LED lighting, motor drives, power electronics, and automotive electronics. Any application where heat dissipation and electrical current demands are high can benefit from the unique properties of MCPCBs. They provide rugged and thermally optimized solutions for demanding electronic designs and environments.
What are the materials used?
Metal core PCB utilizes various metal and dielectric materials in their construction to achieve optimal thermal and electrical performance.
Types of metals used
The base metal used is typically a thin sheet of aluminum, copper, or alloys of aluminum and copper. Aluminum provides high thermal conductivity at a lower cost, while copper offers even better thermal performance. Some alloys balance conductivity and cost-effectiveness. The thickness of the metal base ranges from 0.4mm to 3mm.
The dielectric insulating layers on MCPCBs are made from resin systems like standard FR-4, polyimides, epoxy, Teflon, and ceramic-filled hydrocarbons. These ensure electrical isolation and bond the layers together. Polyimides and epoxies have high thermal stability for managing heat effectively.
The dielectric materials are bonded to the metal core through processes like high-pressure pressing and vacuuming. This removes air pockets and creates a solid bond. Additional plating and coating steps may be used to optimize adhesion. The laminated layers form a sturdy thermal core capable of conducting heat across the PCB.
MCPCBs provide superior thermal management compared to traditional FR4 PCBs. The metal core acts as a heat spreader, conducting heat efficiently across the board and away from heat-generating components. This allows metal core PCBs to operate at higher power levels without overheating.
Several factors contribute to the thermal performance of metal core PCBs:
Heat Dissipation Properties – The metal core layer, generally aluminum or copper, has a very high thermal conductivity. This allows heat to quickly spread from components into the metal core, which acts as a heat sink. The metal’s high thermal mass also enables it to absorb and dissipate large amounts of heat.
- Thermal Vias – Plated through holes called thermal vias conduct heat between the outer copper layers and the inner metal core. Thermal vias provide low thermal resistance paths for heat to flow into the metal core layer. More thermal vias can be included under hot components to further improve heat spreading.
- Dielectric Material – The dielectric insulating layer between the metal core and copper layers is chosen to have high thermal conductivity, maximizing heat transfer. Common materials used include ceramic, aluminum nitride, and silicon nitride. The dielectric thickness is minimized to reduce thermal resistance.
- Thermal Modeling – Thermal modeling tools like finite element analysis are used to simulate the PCB’s thermal performance. This enables the optimization of thermal via placement and dielectric material selection to achieve the required operating temperatures for components. The modeling considers factors like ambient temperature, airflow, and the placement of heat-generating components.
By providing an integrated heat spreader layer and optimizing the design for heat dissipation, metal core PCBs can effectively manage high thermal loads. This enables their use in LED lighting, power electronics, and other high-power applications. The superior thermal performance extends the life of PCB components by preventing overheating damage.
MCPCBs are designed to provide excellent electrical performance, especially for high-frequency applications. The metal core acts as a ground plane, providing a low-impedance return path that helps control impedance and reduces electrical noise.
Some key electrical benefits of MCPCBs:
- High-frequency operation – The metal core helps maintain signal integrity at high frequencies by controlling impedance and reducing radiated emission. Metal core PCBs can operate well into the GHz frequency range.
- Low noise – The metal core minimizes electrical noise by providing a continuous low-impedance reference plane. This helps reduce crosstalk between traces and shield-sensitive components.
- Controlled impedance – Impedance can be tightly controlled due to the metal core ground plane. The dielectric constant of the insulation layer is also consistent. This helps maintain signal quality for digital circuits.
- Shielding – The metal core shields circuits from EMI/RFI and avoids issues with electromagnetic compatibility (EMC).
- Current capacity – The metal baseplate can act as a heat spreader, allowing higher current levels without overheating.
A key aspect of designing a metal core PCB is the layer stack-up. The dielectric materials and copper weights need to be selected carefully to balance thermal dissipation and electrical performance. Some common stack-ups for metal core PCBs include:
- 4-layer board with 0.5 oz copper on the outer layers and 2 oz copper on the inner layers, dielectric thickness around 0.002″
- 6-layer board with 1 oz copper on the outer layers and 2 oz copper on the inner layers, dielectric thickness around 0.004″
- 8-layer board with 2 oz copper throughout, dielectric thickness around 0.008″
The higher layer count boards offer more potential for spreading heat but also increase cost. So the design should aim for the minimum number of layers needed.
Trace widths and clearances also require special attention with metal core PCBs. Since the board itself acts as a heat sink, the traces can handle higher current densities before overheating. This allows the use of narrower traces than typical PCBs. Clearances between traces and pads need to account for voltage and potential arcing. A minimum clearance of 0.003-0.005″ is common for high-voltage areas. Proper plane connections are also critical, tying the metal core to ground or power planes with multiple vias helps dissipate heat efficiently. Careful engineering of the layer stack-up and layout is essential to utilize the full benefits of a metal core printed circuit board.