Aluminium PCB Thickness: How to Choose

The Three Thicknesses on an Aluminium Board

Every metal core board has three layers, and each has its own thickness. The copper foil carries the circuit, typically one ounce, two ounces or heavier where current is high. The dielectric layer bonds the copper to the base and provides the electrical isolation, usually between 0.075 and 0.15 millimetres. And the aluminium base provides the mechanical support and spreads the heat, most often between 0.5 and 3.0 millimetres.

When someone asks about the thickness of an aluminium board they almost always mean the base, and that is the number that is easiest to see and hardest to change later. The copper and the dielectric are specified by the circuit, but the base thickness is chosen by the mechanical and thermal engineer, and the choice affects the cost, the weight and the stiffness of the whole product.

Standard Base Thicknesses

• 0.5 millimetres. The thinnest standard base, used for ultra-light LED strips and backlight modules where weight and profile matter more than stiffness.
• 1.0 millimetre. The balance point for cost and performance, common in general LED modules and consumer lighting.
• 1.2 millimetres. A common choice for LED light bars and driver boards, giving a little more stiffness than 1.0 without a large cost step.
• 1.6 millimetres. The industry standard for power work, equivalent in thickness to the usual FR-4 board and strong enough for most LED and power supply applications.
• 2.0 to 3.0 millimetres. Structural bases for automotive electronics, industrial control and outdoor lighting, used where the board itself has to carry a load or resist vibration.

What Base Thickness Does for Heat

The base is a heat spreader, not a heat sink. Its job is to take the heat from the small area where the components sit and spread it over the whole board before it is transferred to the air or to the metal housing behind it. A thicker base spreads the heat over a larger area and reduces the peak temperature, and the effect is significant: moving from a thin base to a 1.6 millimetre base in a typical LED design can drop the junction temperature enough to extend the life of the emitter by a third or more.

The base thickness is not the only variable. The dielectric layer is in the path between the copper and the aluminium, and its thermal conductivity, commonly between 1 and 12 watts per metre kelvin depending on the grade, has at least as much influence as the base thickness. A thin board with a high conductivity dielectric can outperform a thick board with a poor one, and the price of the high conductivity dielectric is usually lower than the price of the extra aluminium.

Two design rules follow. Do not treat the base as a substitute for spreading the heat in the copper first, because the copper is the closer conductor and the dielectric is the bottleneck. And do not choose the base thickness before deciding the dielectric grade; the two are chosen together from the watts that have to move.

What Base Thickness Does for Strength

Stiffness rises with the cube of the thickness, so the difference between a thin base and a standard one is much larger than the numbers suggest. A 1.6 millimetre base is roughly three times as stiff as a 0.5 millimetre base of the same outline, and it deflects far less under its own weight. That matters in four situations.

Long, narrow LED boards. A light bar over 300 millimetres long will sag and flex with a thin base, and the solder joints on the emitters will fatigue as it moves.

Heavy components. Transformers, inductors, large capacitors and connectors soldered to a thin base create local stress that the copper cannot absorb.

Vibration and shock. Automotive, motor drive and outdoor products see continuous vibration, and a stiff base keeps the strain away from the joints.

Mechanical fixing. Screw fixings, standoffs and clips load the board locally, and a thin base distorts around the fixing.

A practical example is an outdoor floodlight that was first built on a 0.8 millimetre base. It warped with temperature, the solder joints cracked and the optical alignment drifted. Moving to 1.6 millimetres removed the warping, cut the joint stress substantially and stabilised the beam. The extra aluminium cost less than the field failures.

How Thickness Affects the Rest of the Design

The base thickness changes more than the temperature. It sets the maximum board size the plant can handle without excessive bowing, it affects how the board is routed or punched, and it changes the thermal mass the reflow oven has to heat. A thick base takes longer to reach soldering temperature and holds it longer, so the reflow profile has to be adjusted, and the assembly process for a 3 millimetre base looks more like heavy metal soldering than ordinary surface mount work.

A thicker base also limits the use of some processes. Punching and forming need more force and different tooling, and a very thick base is cut with a router or a saw instead. The dielectric withstand voltage is set by the dielectric layer rather than the base, so the isolation does not improve with base thickness.

Recommended Thickness by Application

• LED lighting: 1.0 to 1.6 millimetres covers most designs, with the thinner end for low power strips and the thicker end for high power fixtures.
• Power supplies, drivers and motor control: 1.6 to 3.0 millimetres, driven by the thermal load and the weight of the magnetic components.
• Automotive and new energy: 2.0 millimetres and above, for vibration and thermal cycling.
• Consumer electronics: 1.0 millimetre, which balances cost and structure.

Our notes on energy PCBA describe how these boards are used in power conversion, and the assembly consequences are set out in our notes on PCB assembly.

What Thickness Costs

Indicative unit prices for a standard aluminium board, before tooling and with ordinary quantities, run roughly as follows.

• 0.5 millimetre base: 0.35 to 0.55 US dollars per board.
• 1.0 millimetre base: 0.45 to 0.80 dollars.
• 1.6 millimetre base: 0.50 to 1.20 dollars.
• 2.0 to 3.0 millimetre base: 0.90 to 1.90 dollars.

Upgrading the dielectric to a high conductivity grade of 8 to 12 watts per metre kelvin adds roughly 20 to 60 percent to the board price, which is often the cheaper way to improve the thermal performance of a design that is running hot. The aluminium itself is not the dominant cost at these thicknesses; the processing, the dielectric and the finish are.

Mistakes to Avoid

Choosing the base on cost alone. The saving on a thinner base is a fraction of the cost of a failed fixture or a returned lighting product.

Specifying the aluminium without the dielectric. The dielectric sets the thermal resistance and the voltage rating, and a specification that names only the base thickness is incomplete.

Ignoring the environment. Vibration, thermal cycling and humidity invert the ranking of two designs that look equal on a bench.

Soldering heavy parts to a thin base. The mechanical load has to be carried by the base or by the housing, not by the solder joint.

Forgetting the assembly profile. A heavy base needs its own reflow profile, and our notes on PCB design and layout cover the thermal design that goes with it.

Specifying an Aluminium Board

A complete specification names the aluminium alloy and temper, the base thickness and its tolerance, the dielectric grade with its thermal conductivity and its breakdown voltage, the copper weight, the board size, the finish and the mechanical requirements such as screw holes and the outline process. Our notes on PCB manufacturing describe how the board is built to that specification, and our notes on quality management describe the checks that confirm it was.

FAQ

What is the most common aluminium PCB thickness? 1.6 millimetres for power and LED work, with 1.0 millimetre used where weight and cost matter more than stiffness.

Does a thicker base always run cooler? It spreads heat over a larger area, which lowers the peak temperature, but the dielectric layer is the real bottleneck. Improving the dielectric often helps more than adding aluminium.

How thin can an aluminium board be? 0.5 millimetres is the usual practical minimum for a standard construction, and thinner boards exist but are fragile and need mechanical support.

Can base thickness be changed after the design is released? The base thickness is a mechanical and thermal parameter, so changing it changes the mounting, the weight and the reflow profile. It is easier to decide it with the enclosure design.

Conclusion

Aluminium PCB thickness is a mechanical and thermal decision rather than an electrical one. Choose the base from the stiffness the product needs and the area over which the heat must spread, choose the dielectric from the watts crossing it, and remember that stiffness rises with the cube of thickness while heat spreading rises much more slowly. Specify all three layers, and the board will behave the way the thermal model promised.