Historical evolution of PCBs

Figure 1. PCB with SMD technology

The history of the development of printed circuits is not as old as that of the industrial revolution, around 1950 is when the first electronic boards began to be commercialized, although at the beginning of 1900 it is when the first attempts of PCB designs arise. The human being had the need to have electrical equipment that would have a small size, before that begins the search to replace the complex and extensive cable connections with electronic components.

Figure 2. PCB with very old technology.

It was on March 2, 1925, when Charles Ducas presented for the first time a patent that included the creation of an electric path directly on an insulating surface. The US Patent Office received its proposal: to mount electric metal tanks in the form of conductors directly on the insulation material to simplify the construction of electrical appliances (Fjelstad, 2001). It was a revolutionary idea, since it could eliminate complex wiring and provide consistent results.

However, it was actually after the Second World War that Dr. Paul Eisler in Austria (born in Vienna from a Jewish family) started to make the first printed circuit boards that began to work, this was in 1943 Dr. Paul Eisler was the one who gave the main contribution to the development of modern printed circuit technology, his proposal was to use a sheet of insulating material coated with copper as the base material. The pattern of the printed circuit is applied to it, overlaid, so that the copper discovered is removed by chemical attack (R S Khandpur, 2005).

These ideas led to a reduction in weight, space and a mass production of the systems that led to a reduction in prices and, as a result, an application of this technique to all types of electrical / electronic systems. He also proposed a new generation of plates which contain conductors on both sides of the copper-clad base material, with connection between the conductors on both sides through holes (Through Hole technology).

Figure 3. PCB with THT technology.

Eisler’s work not only gave birth to a mass production method and assembly scheme, but also offered economy in weight and space, which is especially important in military equipment. It is no wonder that Dr. Eisler is often called the father of printed circuit board technology. However, he preferred the use of eyelets instead of the metallized hole technology, which, over time, became an essential process for the manufacture of double-sided and multilayer PCBs.

Towards the end of World War II, the National Institute of Standards and Technology (National Bureau of Standards NBS) of the United States began to use printed circuit technology in the creation of a proximity fuze (also called a VT Fuze), the which was vital to counteract the German air bomb V-1. Unlike Eisler’s printing and engraving technique, this technology uses a conductive silver paste and graphite resistances engraved onto the ceramic substrate. This technique is most commonly associated with today’s hybrid circuit technology. This was the technique that marked the beginning of the commercial use of printed circuits.

The era of the Second World War marked a fierce arms race which led to the commissioning of many investigations aimed at producing lethal weapons. The field of activity of the electronics was highly linked to the vile interests of the nations that desperately wanted to win the war by force, the United States and Great Britain united multiple efforts in the electronic advances.

Finally at the end of the Second World War many fascinating advances took place in the field of electronics and a great demand arose towards consumer products, such as radio and television equipment; Despite the obscure purposes of military equipment, the electronic industry could benefit from valuable research that led to the appearance of electronic components of small dimensions and powerful features. These developments resulted in the demand for reliable circuit boards as complexity increased.

After reaching the maximum density level, based on the manufacturing limitations for the moment, it was necessary to replace the individual side cards which were replaced by double lateral joints, which allowed the cables the possibility of crossing each other without the need for special additional bridges. This was achieved, finally, thanks to the use of the metallized holes.

The company Motorola also had an important participation in the evolution of the PCB, during the years 1953-1955 the company introduced the process of metallic copper coating to facilitate the interconnection between the two sides of a card, the investigations pointed out that this process It was more suitable for mass production. In the 1960s, the electrolytic method was introduced using activators (known as catalysts).

The end of the 1960s witnessed a phenomenal growth in the field of consumer electronics, which made it necessary to introduce automation in manufacturing and Testing to PCBs without assembling (bare board) and the assembled plates. Soon after, in the 1970s, the manufacture of printed circuit boards was firmly directed towards the development of: consumer electronic equipment (TV, radio, etc.), scientific equipment, medical equipment, equipment for aeronautics and space, defense and almost all branches of electronics, which later culminated in the personal computing industry. They also started new processes which would serve for the development of applications such as: photosensitive film lamination, solder masking, legend printing and CNC drilling (numerical control center), etc.

The size of the printed circuit boards was considerably reduced with the new manufacturing techniques such as: multilayers, flexible rigid boards, which started to use Blind and Burried vias to allow the connection through metallic holes. Another step that led to a great improvement in the manufacturing automation processes of PCBs is the SMT technique (source mounted-technology, surface mounting technique).

Figure 3. Wearable type PCB.

With the increasing complexity of integrated circuits, the use of outgoing terminals was more necessary. This type of packaging was very expensive and was replaced by a ceramic packaging with two rows of terminals, these are called integrated DIP (“Dual Inline Package”). They were created to facilitate the insertion of the components in the printed boards. This technology proved to be very reliable and easy to attach. In the decade of the 60 more SMT components appeared to satisfy the needs of the limited market of hybrid circuits. The substrates of the hybrid circuits are ceramic, so it is necessary to weld the components on the surface of the substrate. In the 70s, the growing European and Japanese electronic industry, strongly oriented to the consumer market, that is, to build serial electronics through production lines; was pushed to a reduction in costs. This type of products also required a miniaturization to adapt to the needs of the market. The first most widely used components were resistors and capacitors.

The Japanese quickly realized that manipulating a cylindrical or rectangular component without terminals is much easier than preforming, cutting and riveting terminals. In the late 70’s and early 80’s, the circuit industry had become very sophisticated and the integrated circuits very complex, greatly increasing its number of terminals, in many cases over 100. The use of DIP encapsulation became a charge due to the large amount of space required to accommodate these devices. The best solution was a plastic encapsulation, slightly thinner than the DIP type, with terminals on all four sides, usually called QP (“Quad Pack”). This encapsulation was the genesis for the BQFP (“Bumpered Quad Flat Pack”) of today.

The new developments in component technology, especially in the area of surface mount technology, resulted in a series of innovations in materials and processes for PCBs, leading to constant pressures for improvements in PCB technology in today’s world. all its aspects. The continuous tendency to the high functionality of integrated circuits (IC), components with greater quantities of input and output (I / O) pins, has led to higher demands for fine performance in PCBs, resulting in “interconnection structures High density (HDIS) “that are now manufactured by a large number of companies. High frequency electronic systems, with their high-speed operations, create a demand for PCBs with lower electrical losses. In addition, high operating voltages require PCBs with higher resistance for breaking voltages and high voltage tracks.

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