The evolution of PCB from a simple radio circuit with copper layers to the multi-layer flexible boards marks a path of tremendous progress.
Printed circuit board (PCB) was introduced as a replacement for bulky wiring circuits almost a century ago. Today, it’s the core of the electronics industry, supporting the latest designs like IoT, AI, and 5G. The evolution of PCB from a simple radio circuit with copper layers on either side of an insulating layer to the multi-layer flexible PCBs used in satellite and defense applications marks a path of tremendous progress.
Printed circuit boards were first built during the early 20th century, but became more prominent in 1925 when an American inventor Charles Ducas created an electrical path on an insulated surface. He also registered a patent for this “Printed wire” technique.
Paul Eisler, an Austrian engineer, made the first working PCB in 1943, replacing the large wiring of a radio tube. This PCB design involved the etching of a circuit on a copper foil that was bonded on a glass-reinforced, non-conductive substrate. The technique provided reliable results. So, the U.S. and British governments used PCBs to develop proximity fuse circuits in artillery shells and bombs during the World War II.
Figure 1 Electronics industry innovations during the World War II led to major advancements in PCB design. Source: Shutterstock
The U.S. military ramped up the production of PCBs using auto assembly methods. Double-sided circuits were designed with through-hole plating and copper-coated vias transmitted electrical signals across the board. Also, zinc plates were used in the PCB design with corrosion-resistant coatings to prevent degradation. Next, transistors significantly bolstered the PCB usage while also improving circuit reliability.
PCBs in the IC era
During the 1960s, the introduction of integrated circuits (ICs) revolutionized PCB development, as a single chip could replace multiple components. With the addition of ICs, the conductor layers increased in the PCB stack-up. This led to the usage of multi-layer PCBs. While the circuit size dramatically reduced, the difficulty of soldering connections increased as well.
A solder mask made from thin polymer material was introduced to simplify the soldering process, reducing the bridge formation between adjacent pins or discrete components. A photo-sensitive polymer coating was applied to the circuit, dried, and exposed to light for imaging. Going forward, this method became a standard procedure in the PCB fabrication process.
Next, surface-mount components became popular during the 1980s. The surface-mount technology (SMT), which enabled the automation of the assembly process, significantly improved the circuit performance by optimizing power consumption. Manufacturing costs also went down with SMT assembly methods as compared to the through-hole assembly technique.
Figure 2 The SMT technology was crucial in automating the PCB assembly. Source: Technotronix
Moreover, during the 1980s, designers were manually drawing the circuits using stencils. With the rise of computers, electronic design automation (EDA) methods were introduced. So, PCB designers quickly adapted to the computer-aided design methods, which helped them in drawing complex circuits easily with better efficiency. Also, the component manufacturers focused on building smaller components at lower costs to support the miniature PCB productions.
PCBs in the 1990s and beyond
As the PCB density and functionality increased, the scope of applications also expanded. In the 1990s, IC packaging technology ball-grid array (BGA) was invented. This package enabled the PCB functionality in the lower area of the component as well. The increased board complexity also led to the guidelines on design for testability (DFT). It was essential to control the quality of the PCB design. With these developments, the global PCB manufacturing industry reached new highs during the mid-1990s.
Figure 3 Design for testability or DFT manages major PCB considerations at the layout stage. Source: Technotronix
The layout routing techniques became stringent with the increased circuit complexities. Therefore, micro vias were introduced in the high-density PCB designs. As a result, flexible PCBs became common in applications that involved a range of motion. Next, every layer interconnection (ELIC) technique, one of the most complex types of high-density interconnect (HDI) PCBs, was developed in 2006, but was broadly used only in the early 2010s.
Then there were portable devices with extended capabilities, like tablets and smartphones, which grabbed a major market share during the 2010s. The automotive PCB market also grew during this time. Consequently, one of the biggest changes recorded during 2017 was the wider application of the substrate material in HDI PCBs to import the system-in-package (SiP) technology.
The above chronicle shows a huge progress in the PCB industry, starting from the choice of PCB substrate, the surface coating applied, drilling methods, and the overall fabrication process itself. Earlier, glass epoxy or paper phenolic substrates were used. Now, depending on the end application, PCB suppliers offer a wide range of substrates like polyimide, acrylic, epoxy adhesive, and polyethylene terephthalate (PET). For high-speed applications, rigid boards made of low-loss thermoset adhesives are used, while metal core substrates are used in LED applications for effective heat dissipation.
The future of PCBs
Apparently, the consumer market has expanded with the rising demand for devices like smartphones and smartwatches. Health monitoring and implantable devices are also becoming common in everyday life. Then there are safety devices like CCTV and fire alarms that rely on a tiny PCBs for effective operation. On the other hand, advanced applications in aerospace, telecommunication and military equipment are all using complex PCBs for reliable and robust performance.
At the same time, electronic waste from the PCB industry has raised environmental concerns. So, bio-degradable materials are evaluated as alternatives to the existing hazardous substance. That shows why technological innovations are critical for PCBs like the rest of the electronics industry. Case in point: developments in the automotive industry—electric cars and autonomous vehicles—are taking PCB designs to a whole new level.
Figure 4 The PCB industry has a history of innovations aligned with the larger trends in the electronics industry. Source: Technotronix
Then there are virtual reality (VR) and augmented reality (AR) devices that are influencing the flex PCB design to fit electronic devices into irregular shapes. So, PCBs themselves may be converted into active components in the future, reducing the count of components in the circuit design. For instance, the latest 3D printed electronics use an additive manufacturing process wherein a 3D PCB can be built.
A sneak peek at the history and evolution shows that PCBs have successfully adapted to the emerging technologies. Take the example of turnkey PCB assembly which has reduced the time required for PCB development. There will be more such advancements in the PCB industry in the future.
This article was originally published on EDN.
Ken G is a sales engineer at Technotronix.