2The History of Printed Circuit Boards

Before PCBs became the common component used in electronic circuits, point to point construction was used. This meant some extremely bulky and unreliable designs that required large sockets and regular replacement. The first PCBs appeared in the 1920s. These PCBs were basically made from Bakelite and thin pieces of wood. The process consisted on drill holes in the material rivets of flat brass wires were made. These PCBs were mostly used in the fabrication of early tube style radios and gramophones at the time.

Dr. Paul Eisler in Austria began making the first real operational printed circuit boards in 1943 and the first double sided PCB’s with plated through holes was produced in 1947. By the 50's and early 60's laminates using different types of resins mixed with all sorts of different materials were being introduced but the PCBs were still single sided. The wiring would be printed on one side and the electrical components would be on the other.

The first multilayer PCBs were produced commercially also in the 60´s. In the next decade hot air soldering methods began to be used. Moreover, aqueous developed LPIs (liquid photo imageable masks) were introduced for screen processes, making it the global industry standard. This new fabrication process allowed to important reductions on the size of the PCBs. Gerber Scientific introduces RS-274-D as a machine-based format for vector photoplotters. This standard open ASCII vector format was used by the PCB industry software to describe the printed circuit board images: copper layers, solder masks and legends.

This size reduction continued along the 1980s and 1990s when surface mount parts where introduced along with the increase of the quality of the product. In 1986, the RS-274X released as an enhancement to RS-274-D data format as an extended version [3]. This new version supports embedded aperture information relieving the need for external aperture definition files.

Rigid-flex and flexible PCB options became more affordable because of the use of multi-layer circuit boards to effectively meet the needs of rapidly growing technology. Moreover, in the late 1990s HDI (High Density Interconnect) PCBs were developed by using micro-via technology.

A via or VIA (Latin for path or way, also known as vertical interconnect access) is an electrical connection between layers in a physical electronic circuit that goes through the plane of one or more adjacent layers.

The HDI technology allows shorter traces on the board by reducing the amount of time it takes an electrical signal to travel between components. Moreover, smaller vias between devices help to reduce the overall capacitance in the circuit, which reduces the rise time for the signal. On the other hand, the overall inductance is also reduced with the high-density design offered by HDI, lowering the effect on neighbouring leads and pins.

A side benefit to the reduction in overall capacitance has led to a reduction in required voltage in HDI devices. In turn, this drop in voltage not only means that smaller batteries are required, but also that heat generation is reduced; meaning heat dissipation is less problematic. The elimination of large heat sinks or cooling fans in many HDI applications has contributed to the development of mobile and wearable electronics.

HDI: High Density Interconnect, printed circuit board with a higher wiring density per unit area than conventional PCBs. They have finer lines and spaces (≤ 100 µm), smaller vias (≤ 150 µm), and capture pads (≤ 400 µm), and a very high connection pad density.

Nowadays, the PCB industry is still evolving further. The PCBs are expected to evolve according to user behaviour following miniaturization trends.