As PCBs increasingly shrink in size, their capabilities, power and importance continue to grow.
Space travel, the consumer electronics boom and many ground-breaking (and life-saving) medical devices are quite simply unimaginable without the humble PCB.
Let’s review how we got here – and where we might be going – with a short history of the PCB.
Before the development of PCBs, circuits were wired point-to-point on a chassis.
This was usually made from a sheet metal frame with a wooden bottom. Insulators connected the components to the chassis and their leads were connected by soldering.
They worked – but they also left a lot to be desired. They were large, bulky, heavy and relatively fragile, not to mention being incredibly labour-intensive and costly to produce.
Early innovators point to the way forward
At the turn of the 20th century a number of innovations began to pave the way for the PCB – but it would take 36 years for these to coalesce into the PCB as we know and love it.
In 1903 Albert Hanson filed a British patent for a device described as a flat, foil conductor on an insulating board with multiple layers and the next year Thomas Edison experimented with various chemical methods to plate conductors onto linen paper.
By 1913 Arthur Berry was busy in the UK filing a patent that described a print-and-etch method while, across the pond, Max Shoop obtained a US patent for flame-spraying metal onto a board through a patterned mask.
We were getting closer – but there was still no cigar.
The first real breakthrough moment must be awarded to Charles Ducas.
He applied to the US Patent Office in 1927 to protect his method of electroplating circuit patterns. The process he used placed an electronic path directly onto an insulated surface. Copper wires were not yet available for these printed wire circuits, so the first almost-recognisable PCB was made from brass wires.
The music printing industry creates the first PCB
Closely resembling a PCB, Ducas’ electroplated circuits were only intended to be used as a flat heating coil. There was no actual electrical connectivity between board and components, but it was only going to be a matter of time until this was realised.
And it was realised by an Austrian engineer on the run from the Nazis. Working in the English music printing industry, Paul Eisler developed his PCBs partly while in jail as an illegal alien.
It was in 1936 that Eisler first produced a PCB as part of a radio. Eisler’s dream was to use the printing process to allow electronic circuits to be laid onto an insulating base in high volumes. At the time, the hand-soldered circuit wires were error-prone and not easily scalable.
The demands of war led to the PCB’s wider adoption
It wasn’t until 1943 that Eisler’s dream became a reality. In 1943 the USA began using his technology on the scale he envisioned to manufacture proximity fuses for use in World War II.
After the war, in 1948, the US military released their innovations into commercial use and the stage was set for a much wider adoption of PCBs.
Despite this, printed circuits did not become commonplace in consumer electronics until the mid-1950s. It was in the baby boomer years that the auto-assembly process developed by the United States Army Signal Corps allowed for much faster creation of PCBs.
This process was developed by Moe Abramson and Stanislaus F. Danko in 1949. It used component leads inserted into a copper foil interconnection pattern and dip soldering to speed things up.
This concept, complemented by board lamination and etching techniques, remains the standard PCB fabrication process used today. It solved once and for all the time-consuming demands and high costs of through-hole construction, which required holes to be drilled through the PCB for the wires of every component.
Multilayer PCBs and Surface Mount Technology
The rise in popularity of multilayer PCBs with more than two, and especially with more than four, copper planes was concurrent with the adoption of Surface Mount technology (SMT).
This began in the 1960s but it wasn’t until the 1980s that it was fully adopted as standard.
SMT was developed by IBM, and the densely packed components it allowed found their first practical use in the Saturn rocket boosters.
Throughout the 1970s, the circuitry and overall size of the boards were shrinking in size.
Components were mechanically redesigned to be soldered directly onto the PCB surface – and hot air soldering methods helped achieve this.
As components became smaller, they were increasingly placed on both sides of the board, allowing for much smaller PCB assemblies with higher circuit densities.
Surface mounting lends itself well to a high degree of automation, reducing labour costs and greatly increasing production rates.
Gerber and EDA in the 1980s
Despite these developments, many PCBs were still being drawn by hand with a light board and stencils until the 1980s.
The arrival of computers and EDA software, such as Protel and Eagle, was about to completely change the design and manufacture of PCBs.
Today designs are saved as Gerber text files and these coordinates are fed directly into the manufacturing machinery.
The HDI era of the 1990s
In 1995 we saw the first use of micro-via technology in PCB production, introducing the era of High Density Interconnect (HDI) PCBs.
HDI technology allowed for a denser design on the PCB and significantly smaller components. As a result, components can be closer and the paths between them shorter.
This is achieved through the use of blind (or buried) vias or microvias, which offers enhanced reliability and lower costs, especially for multilayer PCBs. HDI technology is particularly favoured for computer, mobile phones, medical and military equipment.
And into the future
Which brings us bang up to date.
But why stop there?
The incredible advances of the last 80 years show no signs of slowing.
In fact, the opposite: Moore’s law is far from being repealed, despite what you may have heard.
Here’s just a few of the forthcoming PCB features that will drive new capabilities and developments.
- Recent advances in 3D printing, using liquid inks that contains electronic functionalities, are leading to several applications for PCB manufacture.
- The increased use of integrated circuit chips to deliver millions of tiny resistors, capacitors, and transistors fabricated on a semiconductor wafer.
- The space-saving benefits and electrical performance benefits offered by package on package (POP) and embedded component techniques
- Greater environmental awareness is spearheading research into the possibility of adopting PCBs made from paper
- As medical technology look to create an endless feedback loop between patient, doctor and device flexible circuitry for wearables looks set to drive innovation
- Photonics and PCB are inching closer and herald efficiency, miniaturisation and flexibility on a scale previously unimaginable, as photons, rather than electrons, are used to route electrical signals.
- Wave technology may even replace the need for a physical medium to connect components – these are copper-less PCBs for a wireless age