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Design007-Nov2020

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82 DESIGN007 MAGAZINE I NOVEMBER 2020 Printed circuits have been in use in the man- ufacturing of electronic products for roughly 80 years. Early circuits were simple and often only required a single layer of circuits. The circuit patterns were typically screen printed or stenciled using conductive inks—hence the name "printed circuit" was quite apropos. And for those who have been paying attention to technological trends, the printing of connec- tive inks to make circuit patterns has seen a surge of recent interest in use to make a varia- tion of flexible circuits that market makers have labeled flex hybrid electronics (FHE). Thin copper foils were soon after applied to insulating laminates, and printing was again used to print the circuit pattern, only this time as an etch resist to protect the desired circuit pattern when subjected to an etchant. Holes were commonly drilled into the copper foil and substrate, where a connection to electronic component leads was desired, and solder was used to interconnect them. As electron- ics increased in complexity, a second layer of copper was laminated to the back side of the insulating material. And where an interconnec- tion between the top and bottom circuits was required, wires—often referred to as Z wires (Figure 1) —were pushed through those holes and the ends soldered to opposite sides. This was arguably the first form of PCB via. Enterprising and attentive engineers saw the potential of making such side-to-side inter- connection by using the equivalent of metal shoe eyelets, and a second-generation alter- native was introduced. Not long after, other engineers, seeing the limitations of one by one via formation, realized the potential benefit of using plating to make interconnection through A Brief History of Electrical Vias in PCBs Flexible Thinking by Joe Fjelstad, VERDANT ELECTRONICS Figure 1: Via types, including (A) Z-wire, (B) rivet, (C) plated via, (D) buried via, (E) blind via, (F) stacked via, and (G) staggered via.

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