Catch heat at the board before it turns into a full-time job.

Heat sneaks up fast in today’s electronics. Higher power density, smaller form factors and long-life reliability expectations all collide, requiring better thermal design. The teams that come out on top with this challenge are the ones who solve heat at the PCB level rather than trying to fix it later with a bigger heat sink or more airflow.

PCB products designed for this level of thermal management generally fall into two categories. The first is metal-base, often called IMS or insulated metal substrate. The second is metal-core. In both variations, the technology turns the familiar idea of a printed circuit board into an active part of the thermal system, rather than expecting FR-4 to carry the load. FR-4 is an excellent structural and electrical material, but it is not a thermal material.

IMS and metal-core types are often referred to interchangeably, and while they share many common traits, there are a few distinct differences worth understanding before choosing one over the other. With MC PCBs, for instance, the heat has a direct path into a metal substrate, such as aluminum or copper. This puts the thermal solution right beneath the components that generate the temperature rise. By permitting the PCB to act as a direct heat distributor, designs become more compact, more predictable, and often lower cost overall. It also buys a lot of reliability margin, especially in LED lighting, power electronics and automotive systems, where junction temperature directly translates to product life.

The fundamental advantage of a metal-base PCB comes down to thermal conductivity. FR-4 stays around 0.3 - 0.5W/m·K, which is enough for structural integrity and electrical insulation, but not for heat. Aluminum substrates typically offer 1 - 4W/m·K, while copper can reach anywhere from 3 to around 14W/m·K, depending on the grade and the dielectrics paired with it (Figure 1).

Figure 1. Thermal characteristics of some printed circuit materials.

When a copper circuitry layer is bonded to a thermally conductive dielectric over a metal-base, heat flows vertically, not just laterally (Figure 2). It travels from component pads into copper and then directly into the plate of the metal that can be bolted to a chassis. The improvements are noticeable: lower junction temperatures, increased stability under load and the ability to maintain performance in harsh environments. There is a reason LED manufacturers embraced aluminum-base PCBs early: without them, failures due to thermal stress would be a major issue.

Figure 2. Representation of a metal-base PCB construction.

Aluminum is the most common choice because it is affordable, lightweight and of sufficient quality for the majority of moderate-power applications. Copper is used when designs push into demanding current density, tight packaging, or high shock and vibration. The big differentiator between the two is not just thermal conductivity but manufacturability. Copper can survive drill and plating operations, which means it supports plated through-holes and even multilayer routing. Aluminum simply can’t handle the thermal stress of plated through-hole (PTH) fabrication without compromising reliability. Therefore, when a metal-base PCB with more than one routing layer or interconnects passing through the structure is needed, copper is where the design usually ends up.

The simplest and most cost-effective metal-base designs are single-sided (Figure 3). All components sit on one surface directly above the metal plate, and heat flows straight downward with almost nothing to get in the way. You still have copper planes to help spread heat laterally, but the real value comes from the short, direct conduction path to the base.

Figure 3. Examples of IMS builds.

There are plenty of situations, however, where that routing simplicity isn’t enough. Power conversion is a great example. You may have to bring signals around the board or support more elaborate circuitry. In those cases, the construction changes from aluminum-based designs to copper-core builds.

Once a copper core is introduced, plated through holes become a reliable option. Those vias can be intentionally tied into the metal-core when the goal is to spread heat more broadly, or they can be electrically isolated from the core when the design requires the interconnect to remain independent. This flexibility permits metal-base solutions to stretch into multilayer territory without giving up their thermal advantage.

As power devices shrink and technologies like GaN and SiC push current density through the roof, thermal engineering must evolve with them. Many modern designs are incorporating high-density interconnect (HDI) features into metal-base structures, such as laser-drilled microvias and thinner dielectrics that place heat-conduction paths closer to the active junction.

Another technique that is becoming standard in demanding power modules is the use of copper pedestals (Figure 4). A solid slug of copper is positioned directly beneath a hotspot, almost acting as a direct bridge to the metal foundation. The result is a dramatic reduction in thermal resistance for devices like IGBTs, Mosfets and high-power LEDs. This is the approach taken when even a small increase in junction temperature would cause performance degradation or shorten service life.

Figure 4. Copper pedestals involve a solid slug of copper positioned directly beneath a hotspot to reduce thermal resistance.

A misconception is that metal-base PCBs automatically represent a premium cost solution. In many cases, the opposite is true. When the PCB takes responsibility for heat spreading, other thermal hardware becomes unnecessary or can be reduced. Instead of installing oversized heatsinks or stacking up thermal interface materials, the heat goes directly into the chassis, with fewer components in the way. That cuts assembly cost and weight. These factors matter more than ever today.

Copper-core multilayers still sit at the higher end of the price spectrum, and aluminum-base single-sided designs are typically an affordable step above FR-4. The key is evaluating them not in isolation but against the total system cost. In many applications, the ROI isn’t just measurable, it’s immediate.

Metal-base PCBs are a powerful tool for power and thermal engineers when heat must be managed at the source. They keep designs smaller, improve reliability and solve thermal problems early and efficiently. They also give mechanical teams more freedom because less bulky cooling hardware means more room to innovate and more confidence that temperature won’t be the weak link.

They don’t eliminate the need for fans, heatsinks or proper airflow design. But they make each of those strategies more effective because the PCB is no longer simply a structural element. It becomes one of the primary heat-handling features of the entire assembly.

When the stakes are thermal, and they always are, starting the solution on the board is often the smartest move you can make.

Jeffrey Beauchamp is director of technology & engineering at NCAB Group USA (ncabgroup.com); This email address is being protected from spambots. You need JavaScript enabled to view it.. He started his career in the PCB industry in 2003 at PD Circuit, now part of NCAB Group, and works with PCB customers to provide optimal solutions. His column runs quarterly.