Printed circuit boards have a wide array of uses in present technology. Their continued development have allowed supercomputers to be made in astonishingly small form factors. An example of this are today’s smartphones that are equipped with complicated components exponentially more powerful than desktop computers a decade ago. But PCBs were not always compact. Half a century ago, their production were still in their infantile stages.
The First Printed Circuits
At the dawn of the 20th century, the earliest concepts of functioning printed circuitry were burgeoning. There was Albert Hanson’s idea of laminated foil conductors on an insulating board. There was Thomas Edison’s ploy of printing graphite pastes to linen paper, which he got from a concept by Robert Sprague.
In 1925, Charles Ducas filed a patent at the US Patent Office for an easier way of printing circuit boards. He proposed directly mounting metal conductors onto the insulation material instead of earlier cumbersome processes of manually etching the boards. He traced a stencil on the insulation material where the conductors were to be placed, then applied conductive paste on the material. The lines were then reinforced to mount the metal conductors, in the process greatly simplifying the production process.
This was followed by a patent application of Francis Hartmann, also from the United States. This was for a subtracting method that greatly resembles modern circuit board etching processes. On the other side of the world, Samuel Charles Ryder from Australia proposed in 1927 to spray the substrate material with conductive paint. What all of these proposed processes had in common was the elimination of the use of copper wires in developing products.
Dr. Paul Eisler from Austria essentially made one of the biggest contributions in the development of printed circuit boards. After fleeing from Nazi-crazed Austria, Eisler proposed the use of a copper covered sheet as the primary material in manufacturing circuit boards. To achieve this, Eisler proposed that a circuit pattern be printed or etched into the copper covered material. After printing, the non-circuit areas of the base board will be stripped of the copper sheath, essentially resembling today’s printed circuit boards. Even better is his suggestion of drilling “eyelets” through the board so that connections for conductors on both sides can be established. Today this is a standard in circuit board manufacture and is called a “via”.
After the war, further innovation was contributed though this time by the US National Bureau of Standards. Instead of Eisler’s technique, the USNBS innovated the use of a ceramic substrate instead of the copper covered base. The printed copper circuit patterns were replaced by silver paste conductors, while graphite resistors controlled the flow of the electric current.
Consumer Use and Beyond
The postwar period saw the advent of double sided boards which replaced use of single sided boards on consumer electronics. The double sided boards allowed smaller printed circuit board footprints and was easier and cheaper to produce. In the mid-50’s Motorola reintroduced the use of copper plating on boards instead of the silver paste conductors. It was cheaper to produce, too. Further innovation took place in 1964 when the fully additive process was introduced. Instead of a copper-clad base material, copper was selectively plated into the substrate, further reducing production costs.
Further production processes were introduced in the 1970’s like CNC drilling, wet film resist, photo film lamination, and solder masking. The next evolution in the production process of PCBs came in the 1980’s. Surface mount technology replaced the through-hole technology as the industry standard. The new process mounts components directly onto the substrate of the circuit boards instead of through-hole technology where electronic components had to be manually embedded into the holes in a circuit board. This also led to smaller printed circuit boards and more complex designs, like multi-layered and flexi-rigid board designs.