The Complexity of Printed Circuit Board Design
Printed circuit boards or PCBs are the foundation of modern electronics. They do more than simply provide electrical connections between components. Some incorporate an internal ground plane for signal isolation, preventing capacitive coupling between adjacent conductors. The ground plane also helps to dissipate heat. Printed circuit boards may be rigid or flexible, with the flexible versions found in many automobiles and digital cameras.
Early electronics used point to point wiring that had to be installed by a skilled soldering technician, but the concept of a printed circuit began with Thomas Edison. He experimented with paper as a substrate, however the idea never went to production.
Early printed circuit boards were single-sided. The conductors were printed on one side while components were mounted on the opposite one. Component leads went through holes in the board and were soldered to the conductors. Double sided boards were slightly more complex, with conductors printed on both sides and connected with plated-through holes called vias.
Multi-layer PCB boards
Multi-layer boards are the current standard in electronics, though the older single and double-sided versions are still in use for simple circuitry. A multi-layer board is a sandwich comprised of thin, stacked printed circuits with vias connecting the various layers. Design complexity requires the use of Electronic Design Automation (EDA) also known as Electronic Computer Assisted Design (ECAD). Older designs were often drawn by hand, but the level of complexity in modern electronic requires computer assistance. Another benefit of this approach is the capability to test circuits in a virtual environment before any prototypes are built.
Components on multi-layer boards
Components on multi-layer boards may be surface mounted or through-hole types. It’s not unusual to find both on a single board. Parts may be soldered into the board with hot air, ovens, or wave soldering techniques, all of them performed by automated machinery. When subsequent testing reveals a defect, the board is routed to a soldering technician for repair.
Solder replacements
Due to environmental concerns, traditional tin-lead solder is being slowly replaced by lead-free solder composed of tin and silver. This is rapidly overtaking consumer electronics, but the reliability and longevity of lead-free solder is not yet known for use in critical medical, aerospace, and military applications. Conductive epoxy is another lead-free connective material that may replace solder. It includes silver with a conventional epoxy and offers the advantage of room temperature or low temperature oven curing.
The theoretical limit for component miniaturization is determined by the wavelength of the light used to etch the circuits. The masks must include conductors at least one wavelength wide so the etching process will work. Printed circuit boards face the same limits, and as their density and complexity increase, new manufacturing and repair techniques will require advanced automation rather than human intervention.
Philip King
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