Metal Core PCB: Base Materials, Types and Properties

Not every board is built on FR-4. Where a design has to move serious amounts of heat, or where a circuit must be shielded and mechanically robust at the same time, a metal core PCB becomes the practical choice. The construction looks simple — a metal base, an insulating dielectric layer and a conductive layer, normally copper foil, bonded by hot pressing — but the variants and the trade-offs between them are more varied than the description suggests.

Base Structures

Three constructions are common, and the differences lie in how the metal is used.

A metal base board uses a metal plate — aluminium, copper, iron or molybdenum — as the substrate, with the dielectric layer and the copper foil applied over it. This is the most common and most widely used form.

A cladding type board coats a metal plate on all six faces with a glaze and sinters it into an integral base material, after which conductors are formed by screen printing and sintering. The structure is unusual, but it produces a particularly well-protected metal core.

A metal core substrate generally uses copper or aluminium as the core, coated with an organic polymer dielectric layer or composited into prepreg or a polyester film, with conductor foil on top. In some variants the conductor pattern is formed additively rather than etched from foil.

Classifications

By base metal, the family divides into aluminium-based, iron-based, copper-based and molybdenum-based copper-clad laminate.

By characteristic, it divides into general purpose, flame retardant, high heat resistance, high thermal conductivity, ultra-high thermal conductivity, high frequency and microwave, and multilayer metal base types. The last two categories are the ones that extend the material beyond simple heat spreading into applications where dielectric behaviour matters as much as conduction.

<img src="https://www.gopcba.com/wp-content/uploads/2026/08/word-image-24809-4.png" alt="metal core PCB with aluminium base plate” />

Heat Dissipation

Excellent heat removal is the defining property of the family, and the reason most designs consider it.

A board built on metal prevents the operating temperature of the components and the substrate from rising as far as it otherwise would, and it can move heat away quickly from power amplifier devices, high-power components and large-current switches. Those are the cases where heat is not a nuisance to be managed but the limiting factor on output.

The choice of metal determines much of the performance. Copper is the best conductor of the metals used, but its density is around 8.9 grams per cubic centimetre, it is expensive, it oxidises readily and it works against the industry’s general move toward lighter products. As a result it is reserved for boards with extreme dissipation requirements. Aluminium conducts less well than copper but far better than iron, and its advantages are decisive in practice: a density of about 2.7 grams per cubic centimetre, resistance to oxidation and a lower cost. It is therefore the most widely used metal base by a wide margin.

The metal is not the only variable. Dissipation also depends on the thickness of the insulating layer and on its thermal conductivity, which is why thermally conductive fillers are added to the dielectric. A thinner insulating layer conducts heat better, but a thinner layer withstands less voltage — so thermal conductivity, voltage withstand and insulation performance have to be weighed together rather than optimised one at a time. That trade-off is the central decision in specifying a metal core board, and it is the same tension that appears in any design where heat must pass through a dielectric, as discussed in this look at thermal management on dense boards.

Mechanical Working

Laminates on a metal base have high mechanical strength and toughness, and they outperform rigid resin laminates and ceramic substrates on both counts.

That strength has practical consequences. It allows very large boards to be produced on a metal base, and it allows heavy components to be mounted on one. The material also has good flatness, which matters for assembly, and it tolerates operations that would damage a resin board — hammering and riveting, for example. Non-circuit areas of a finished board can be bent and twisted as part of the mechanical integration.

Dimensional Stability

Every laminate has a thermal expansion problem, and the one that matters most is along the Z axis, through the thickness of the board, because that is the direction in which plated holes and the copper around them must stay intact.

The underlying issue is the difference in expansion between copper and the dielectric. Copper expands at about 17 parts per million per degree Celsius, while epoxy glass cloth laminate expands at 110 to 140. The gap is large, and when the board is heated the two move by different amounts, which can fracture conductors and plated holes.

A metal base changes that arithmetic. Iron expands at roughly 40 parts per million per degree and aluminium at about 50 — far lower than a resin laminate and much closer to copper. The mismatch is reduced, so the plated holes and conductors survive thermal excursions better, and the reliability of the finished board improves accordingly.

EMI Shielding

The last advantage is one that metal provides naturally. Components in an electronic product often need protection from radiated interference, and a metal base plate acts as a shield, blocking electromagnetic energy from crossing it.

That is not a substitute for good layout — the shielding is below the circuitry and does not address coupling between conductors on the same layer — but it removes a whole class of external coupling that would otherwise have to be handled with cans, gaskets and additional layers. In effect, the metal core makes the mechanical structure part of the electrical solution.

Choosing a Metal Core Board

Four questions decide the specification.

How much heat must be removed, and through what path? That determines the metal, the dielectric thickness and whether fillers are needed. What voltage must the dielectric withstand? That sets the minimum insulation thickness, which may override the thermal preference. How much does weight matter? That usually settles the choice between copper and aluminium. And does the product need the mechanical stiffness and shielding that the metal provides, or would a resin board with a heat sink achieve the same result more cheaply?

Where heavy copper is used for current rather than for heat, the constraints overlap but the design intent does not, and the process implications are set out in this discussion of heavy copper and HDI compatibility. Where the requirement is a dielectric that behaves predictably at frequency rather than a thermally conductive one, the comparison is with the materials described in this guide to laminate selection.

FAQ

Why is aluminium used more than copper as a metal base? Because copper, although it conducts heat better, is dense, costly and prone to oxidation. Aluminium offers most of the thermal benefit at a fraction of the weight and cost, so it is reserved for copper only where dissipation requirements are extreme.

Does a thinner insulating layer always give better thermal performance? It gives better conduction, but it also reduces the voltage the layer can withstand. The two requirements have to be balanced, which is why thermal conductivity, breakdown voltage and insulation performance are specified together.

Why does a metal base improve plated hole reliability? Because its expansion is far closer to that of copper than a resin laminate’s is. The smaller mismatch means less stress on the barrel and the conductors during thermal cycling, so they are less likely to crack.