PCBs’ Green Evolution

The humble printed circuit board continues to change to meet new demands.

Power is nothing without control. It’s not a quote by a famous politician or social commentator, or even Mark Twain. It’s an advertising slogan for car tires. But it’s also an apt description of the opportunities for our industry that are now happening as part of the green energy transition.

Electrification is one of today’s dominant megatrends. The “old way” of releasing energy from traditional fuels by explosions and burning is giving way to alternatives like electromagnetic and photovoltaic conversion, as well as chemical processes inside batteries and fuel cells. Taking the utmost care of every joule is critical to maximize the harvest from the scarce ambient energy sources and to minimize waste throughout the conversion system, distribution infrastructure, storage and – ultimately – the load.

Exercising that care demands control. This is where more power electronics are being employed to ensure efficient and precise conversion as we accelerate the pace of electrification; changing traditional mechanical, hydraulic, and fossil-fueled tools and vehicles that we have all become accustomed to using into electrical equivalents that can be powered from clean and sustainable energy. Replacing conventional boilers with electric heat pumps for heating buildings is one example.

The pace of electrification in the automotive industry is another. Automotive electrification has been going on for most of the past three decades, offloading crank-driven loads from the engine, saving weight, reducing cost, and improving reliability. Electrification also enables the latest software-defined features for safety, infotainment and driver assistance. The ultimate step is the change to electric traction, bringing yet more power electronics into the drivetrains of every new vehicle on the road.

I noted recently figures from TrendForce Global Automotive Reports showed that plug-in hybrid electric vehicle (PHEV) sales are vastly outstripping battery electric vehicles (BEVs), growing more than 10 times faster in the first quarter of this year at 48% versus 4%. PHEVs deliver some advantages over BEVs, such as freedom from range anxiety, despite having a battery that is not only significantly smaller and lighter, but also less expensive and easier to replace at its end of life. On the other hand, they are more electrically complex, placing greater demands on the electronics industry to step up and deliver solutions.

Of course, this also brings valuable opportunities for component suppliers, including PCBs. A modern PHEV is reckoned to contain over 1 sq. m. of printed circuit board in total; that’s more than double the quantity in a typical conventional vehicle after over 30 years spent electrifying auxiliary loads and adding smart features and infotainment. This is evidence that the PCB, our favorite component, has a leading role in making the green energy revolution happen.

New techniques are needed for managing the high power levels coming into and out of the circuits built on these substrates, and to dissipate the heat associated with the various loss elements. Technologies collectively known as metal in board (MiB) can extend the PCB designer’s toolkit, enabling greatly increased electrical and thermal power-handling capability. With these, we can build boards capable of carrying current as high as 1000A and raising power density beyond 50W/cm².

On the other hand, techniques like pedestals, inlays, encapsulated bus bars, and embedded wires and strips can be difficult to combine with some conventional processes and may demand specialist knowhow. MiB elements need to be designed into the PCB at an early stage, which increases opportunities for PCB designers to add value at the system design level, including completing all power and thermal calculations to select the right technology and optimize the selected materials and dimensions.

In addition to embedding metal, embedding silicon components such as power semiconductors promises to further enhance thermal performance and therefore add to the PCB’s power capabilities. Embedding components in drilled or fabricated recesses in the PCB surface makes sense from several perspectives, including reducing the number of parts to be surface mounted – thereby streamlining final assembly. In addition, reliability and ruggedness can be improved.

We have been working toward embedding passive components for more than 20 years. Now, as markets focus intently on power density and efficiency, emerging techniques can put power semiconductors such as inverter bridges inside the PCB to reduce thermal resistance and save switching losses by lowering overall inductance in the system, in addition to reducing system complexity, enhancing reliability, and simplifying surface-mount assembly.

In addition, new thermally conductive resins and resin-coated foils, generically known as bond-ply materials, are entering the market. Increasing the thermal conductivity of non-IMS substrates makes these a great fit with embedded semiconductors and MiB, as well as lighting, power conversion, motor drives, and high-performance computing like cloud AI accelerators. As glassless systems, these materials come without Dk issues and are used in low-loss applications.

Away from the search for greater power, other interesting developments could make tomorrow’s PCBs more benign toward the environment. New plant-based substrate materials to replace fiberglass now enable biodegradable PCBs to mitigate e-waste problems, enhancing recyclability and reducing landfill.

While the PCB’s underlying technical role – to support the connectivity between the different elements of the system – remains consistent, its properties continue to adapt and evolve to satisfy the changing priorities of our time.

Alun Morgan is technology ambassador at Ventec International Group (venteclaminates.com); alun.morgan@ventec-europe.com. His column runs monthly.