PTH drawing

We have been looking for the answer to this and realize that there is no single answer. The truth is that it is a line of inventions that together contributed to today’s PCB. Of course, there is endless material about this on the Internet, but we have tried to pinpoint an unambiguous answer.

Kopparremsor i papper

The oldest variants of printed circuit boards are not what can be considered “printed”, but can be worth mentioning anyway, because the principle is the same. A series of odd constructions with, among other things, a wooden laminate with brass rodsbolted on each side (1850), as well as paraffined paper (Pat. Albert Hansson 1903) with copper strips glued inside. The picture is from the patent application and the application included also a double-sided version.

Thomas Edison may well be considered one of the greatest inventors in history and stood for about 2500 inventions and 1093 patents. His good friend, Frank Sprauge (Sprauge Electric) asked him to come up with a proposal on how to simplify the interconnection of electrical devices and developed a method where he painted tracks with a polymer adhesive that was sprinkled with graphite powder. When the polymer hardened, remnants of the graphite were removed and a board was obtained which can be considered as a printed circuit board. However, not “printed”. (Paint polymer and coal. 1904).

In 1913, Arthur Berry applied for a patent showing a method of making circuits in which metal was etched away. He described the process of coating metal with a resist, before etching, as an improvement over cutting that could give fractures in sharp corners. Berry seems to be the first to describe etched circuits. The picture above shows his etched heating circuit for a later patent.

Charles Ducas described both etching and plated tracks. One version involved galvanic plating of a copper, silver or gold pattern through a contact mask. Heating allowed the conductor (usually a coil) to separate from the fusible bus plate and mask. Another Ducas process involves forming grooves in a dielectric such as wax and filling them with conductive paste which is galvanized. Conductive paste can also be printed or stenciled on a dielectric and then galvanized. Both sides of the dielectric layer can be used for circuits. In fact, Ducus goes on to describe multilayer circuits and a way of interconnecting layers, “Two or more panels can be placed on top of each other”. Charles Ducas was the first to invent the galvanic plating of copper in 1925. This is the first patent, but many different methods were then patented.

Paul Eisler, an Austrian who filed a patent application in England for what he called “photographic printing and etching of copper foil”. It was the first method of producing printed circuit boards as mass production at an economically defensible cost. The first patents were filed in 1943, but maybe the background to the applications dates back to 1936. The technology originated from the well-established printing industry, with the difference that Eisler worked with thin copper and etched all copper all the way down, to create insulation between conductors. In his patent, Eisler referred only to “as used in the printing industry” and did not specify which components the etching liquid consisted of. This became devastating when he later applied for a patent in the United States, which was based on the British patent. In addition to the fact that it was delayed by 4 years, there where competitors that he believed violated the patent. Consequently, he sues one of them (Bendix), but eventually loses the case on May 27, 1963. Much because of the vague description “as used in the printing industry”, which the court thought was far too universal to violate. The picture shows his “3 bulb radio” from 1942. Which is the first electronic product that uses a PCB.

During the Second World War and at the same time as Paul Eisler developed his radio with printed circuit boards, the British, together with the United States, developed the proximity fuse, which greatly increased the accuracy of artillery and air defense. The first use of printed circuit boards in mass production saw its light. Attempts had been made before, but the electronics could not bear the heavy g-force during firing of the grenade. The working variant, which was then mass-produced in the United States, was based on a double-sided printed circuit board (not plated trough) where the assembled PCB was encapsulated by wax. It is believed that printed circuit boards in particular were of crucial importance for function, reliability and the ability to quickly produce large volumes.

The breakthrough of radio (1930-1940) required industrial methods to be able to produce radios in large volumes quickly and cheaply. However, there was still a lot of electronics manufactured according to “point-to-point” method, where the components were soldered to each other without printed circuit boards. The picture above shows a Motorola VT-73 (VT-71) “Golden View” TV from 1948.

The 60’s gave us a couple of improvements that changed the printed circuit boards forever – namely Hazeltyne Corporation’s patent application from 1963 as the first method for through-plated holes in printed circuit boards and the development of surface-mounted components (SMT) by IBM. However, the surface assembly did not take full effect until the end of the 1980s. Both techniques were crucial to the packing density and are considered crucial for the great technological leap of the 60s. The picture shows a patent application from North American Aviation Inc. and refers to a later variant of hole plating. In 1967, RCA company applied for a patent for a “multilayer” PCB, then called BUM (Build up multi-layer). However, only much later does the multi-layer technology really take off.

Another technical solution that became a reality in the 60s, was the flexible printed circuit board. For several decades in the past, there were different solutions to this problem, with the big breakthrough happening when Du Pont apply for patent on its product “Kapton” (Polyimide). Due to its low weight, and ability to make compact electronics, it will be widely used in the aerospace industry. The crucial properties are low weight, high insulation capacity and stability under extreme temperatures (-269 to +400 C). The Apollo project used, for example, aluminum-coated Kapton as insulation on the lunar module (pictured). In recent years, however, it has been noticed that the material can be degraded under high temperature and humidity, and caused short circuits. Which had major consequences for the aviation industry, which was forced to costly modifications.

Quicksilver company releases 1978 its “Hot Air Solder Leveler” breakthrough machine. This replaced the old “fusion method” which was based on the Sn/Pb coating from the galvanic process being reflowed in either a “hot oil process” or an IR heater. The picture shows a reflowed PCB, with a time-typical wave pattern on the tracks. The HASL method solved many of the problems with reflowed PCB´s. Much because the solder mask was applied to the bare copper and the surface treatment added afterwards. HASL is today by far the most common surface treatment.

In the 1990s, “microvia” (the latter definition) was produced. The idea was developed throughout the 90s and is today absolutely crucial for the production of today’s smartphones, tablets and other ultra-compact electronics. Ibiden is a Japanese company that has granted hundreds of patents for PCBs and ICs. At the time, they were the world’s largest manufacturer of printed circuit boards and were leaders in the development of microvia. The surface treatment ENIG (Electroless Nickel Gold) also had its breakthrough during this time.

Who then was the inventor the PCB? And what conclusions can we make?

To save space, we have not taken up all the ideas and inventions during the 20th century concerning printed circuit boards and their manufacture. The methods are many and very similar. There is also no method that describes the whole process we use today as a single patent. It is simply the case that the method we use today is the result of 120 years of development. If we are to try to determine who can be considered to have contributed the most, we must first define “printed circuit boards”. In English it is quite easy. It is called “printed” circuits. Although Edison’s idea is early with leaders on a record that binds components together, our choice probably falls on Paul Eisler, because his idea is precisely “printed”. His method is also reductive and photo-transferred which is mainly the technology still in use. Unfortunately, he failed to defend his patent and fought for it for much of his life. Until he died he felt wronged by the American legal system. Although there are more small inventions that have led to today’s printed circuit boards, it is not for nothing that Paul Eisler is called “the father of PCB”.

For the nerd. Some special constructions that have made history.

What you see above is a cordwood PCB. An interesting design technique from the time before integrated circuits. The circuit consists of two circuit boards parallel to each other with components that hold them apart. This was at one time the most compact construction technology, used in everything from the late 50’s space technology to mainframe computers that filled entire rooms. For the nerd. Some special constructions that have made history.

Multiwire Board, is a PCB where copper wire is pre-insulated with a polyimide and wired by a machine that connects the terminals by “point-to-point” method. Because it allows cross-wires, the number of wires that can be in a layer increases significantly, and consequently a high-density board can be manufactured with a smaller number of layers than common PCBs. In addition, since the Multiwire Board uses copper wire with a uniform diameter, it has superior electrical properties, such as providing a stable characteristic impedance. Compared to a common printed circuit board, MWB has about 3 times greater packing density. Very exclusive and extremely expensive.

Wire wrap is an electronic component mounting technology that was invented for telephone switchboards and later adapted to construct circuit boards. The components were mounted on an insulating board and connected with an insulated metal wire between their terminals. The connections were wraped several turns around the uninsulated part of the terminal or a sleeve pin on the component. The wire wrap technology was able to produce devices that were more reliable than printed circuit boards. The connections were less likely to rupture due to vibrations or physical stress. And the lack of soldering prevented soldering errors such as corrosion, cold soldering, etc. The connection itself also has lower electrical resistance due to cold welding of the wire to the terminal. Wire wrap construction became popular around 1960, but its use has now fallen sharply. Today’s technology with surface-mounted components has made the technology much less useful than previous decades. The picture shows the “Apollo Guidance Computer”, (Raytheon 1966) which, with its short service life and strict requirements for reliability, was one of the early applications of wire wrap in computer manufacturing.