Metal Core and Aluminium PCBs
What a Metal Core Board Is
A metal core board replaces the usual laminate with a metal base, usually aluminium, covered by a thin dielectric layer and the copper circuit. The metal base provides a thermal path that a normal laminate cannot, because the dielectric layer is far thinner and more conductive than FR-4, and the aluminium spreads the heat laterally and can be attached to a heatsink or to the enclosure. The result is a board that can carry a high power LED, a motor drive or a power supply with far less temperature rise than a conventional construction.
How the Heat Moves
The heat from a device passes through the solder joint, through the copper, through the thin dielectric and into the aluminium, which spreads it and passes it on. The dielectric is the controlling element: it is thin, but its thermal conductivity is much lower than the aluminium, so it still dominates the resistance. Its thickness and its conductivity therefore decide the board’s thermal performance, and a thinner or more conductive dielectric is worth more than a thicker aluminium base. The design should treat the dielectric as the interface that it is and specify it deliberately.
Where It Is Used
The applications are those where the heat has to leave a small area. An LED board is the classic case, where the junctions are hot and the light source is compact. A power supply or a motor drive uses a metal core to spread the heat from a switching device. An automotive module uses it for thermal and mechanical reasons together, since the metal base is also rigid and can be attached to a chassis. The construction is also used where a conventional board would need a heatsink and a thermal interface, because the board itself becomes the heatsink.
Design Rules That Differ
The rules differ from a conventional board in several ways. The dielectric’s breakdown voltage is lower than FR-4’s per unit thickness, so the isolation distances and the voltage rating have to be specified from the dielectric’s data rather than assumed. The circuit is usually single sided or double sided, because building a multilayer on a metal core is difficult and expensive, so the routing has to be planned accordingly. Thermal vias are not possible in the metal, so the thermal path is through the dielectric. The copper’s thickness is often heavier to spread the heat, which widens the minimum features. And the board cannot be drilled and plated in the same way, so the mechanical features are formed differently.
The Dielectric and Its Limits
The dielectric is a filled polymer, and its properties decide what the board can do. Its thermal conductivity, its thickness, its breakdown voltage and its temperature rating are the parameters to specify, and they trade against each other: a thinner layer conducts better but withstands less voltage. The dielectric’s adhesion to the aluminium and to the copper is critical, because a delamination breaks the thermal path and the isolation. Where the product will see thermal cycling, the adhesion should be qualified by test, since the aluminium expands far more than the copper and the dielectric has to accommodate the difference.
Mechanical and Assembly Considerations
An aluminium board is stiff and it is heavy, and it does not flex the way an FR-4 board does. The panel handling, the support during printing and placement and the depaneling all change, and the assembly equipment has to be able to handle the weight and the stiffness. Soldering is often done by reflow on a single side, and the thermal mass of the aluminium means the profile has to be longer or the board preheated more, because the metal absorbs heat. Where the board is attached to a heatsink, the interface and the mounting force matter as much as they do on a conventional assembly.
Cost and When to Use It
A metal core board is more expensive than a conventional one, and it is justified when the thermal performance is required rather than simply desirable. Where the heat can be managed by a copper plane, a thermal via array and a heatsink, a conventional board may be cheaper and adequate. Where the heat density is high, where the space is small or where the metal base also serves a mechanical function, the metal core is often the simpler solution because it removes the separate thermal interface. The decision should follow a thermal calculation and a comparison of the total cost rather than an assumption.
Aluminium versus Copper and Other Bases
Aluminium is the usual base because it is light, cheap and a good conductor, but it has limits: it cannot be soldered easily, it corrodes without a treatment and its expansion is high. A copper base conducts better and matches the copper circuit thermally, which suits a very high power density, at a much higher weight and cost. An iron or a steel base is used where mechanical strength or magnetic properties matter. The choice of base should follow the requirement, and the assembly process has to suit the material: an aluminium base is usually not soldered directly, so the connections are made through the dielectric to the copper circuit above it.
FAQ
What does a metal core board do? It provides a short thermal path from the components to a metal base that spreads and dissipates the heat.
What dominates the thermal resistance? The thin dielectric layer, so its thickness and conductivity matter more than the aluminium’s thickness.
Can a metal core board be multilayer? It is difficult and expensive, so the design is usually single or double sided.
Why are the isolation distances different? The dielectric’s breakdown voltage per unit thickness is lower than FR-4’s, so the voltage rating has to come from its data.
When is a conventional board better? When a copper plane, thermal vias and a heatsink can manage the heat at a lower total cost.
Conclusion
A metal core board is chosen for its thermal path, so specify the dielectric deliberately and design within the construction’s rules. Compare the total cost before deciding. Metal core construction belongs to PCB manufacturing, the thermal design is part of PCB design and layout, and the assembly of the board sits within PCB assembly. Metal core designs are first built during prototype PCB assembly in 2026.
