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24 DESIGN007 MAGAZINE I JUNE 2021 Feature Article by Clyde Coombs In this issue of Design007 Magazine, we're taking time to reflect on the development of PCB technology since the first episode of Star Trek aired in 1966. I believe that it is instruc- tive to remember just how close Hewlett- Packard—and likely the entire industry—came to adopting eyelets instead of plated through- holes in the early 1960s. Except for the transistor, no other technical development of the 20th century has had such a profound impact on all aspects of daily life as the plated-through-hole (PTH) printed cir- cuit. In its role of interconnecting digital com- ponents reliably, cheaply, and universally, it makes possible all the wonders of modern life that utilize the transistor. at there was ever a controversy over the use of plated through-holes as an acceptable printed circuit interconnection process seems almost impossible to consider, let alone take seriously today. But in the late 1950s and early 1960s, the PTH was not just a controversial Hewlett-Packard's Adoption—and Controversy—of Plated Through-Holes Figure 1. Figure 1 above: The image shows a cross-section of a typical double-sided eyeleted PCB in the late 1950s. Each side of the board has been laminated with copper. The board has had etch resist printed on the copper with the silkscreen process, and then, typically, etched in ferric chloride. After the resist is removed, holes are drilled and the board is ready for the eye- let process. Eyelet machines were the same machines used to put eyelets in shoes. Eyelets were installed one at a time by positioning a hole in the board onto the anvil of the foot-activated eyelet machine. The machine would insert an eyelet as shown, shaped by the anvil to produce either a crimped form or—in the case of single-sided boards—a flared form to capture more solder on that side. The eyelet then provided the metal contact between the two sides of the board, and the significant metal barrel allowed the solder to provide electrical connection and physical support for the component lead. Image © I-Connect007

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