Compliant pins, waterproof connector designs, modular connectors, egg-crate shielding, air-dielectric designs – we can now look back on inventions like these and put them in perspective. It is interesting to see how a real understanding of the technology and the problem, as well as a vision toward the future, can lead connector design engineers, and now signal integrity engineers, to outside-the-box solutions that fundamentally improve connectors and change the industry in the process.
One of the most fundamental connector technologies, compliant press-fit, did not exist until the 1970s when Robert Knowles of Winchester invented the C-Press compliant pin and convinced Western Electric, the manufacturing arm for the great AT&T monopoly, to qualify this new technology. Up until then, backplane pins were either soldered or rigid square or rectangular pins were forced into plated through-holes. For this process to create a gas-tight joint, the hole tolerance had to be +/- 0.002″ (5%), which was very challenging, especially for large boards. The dominant technology at that time used large 0.040″-diameter holes with 0.025″ square pins.
Anyway, back to the importance of compliant pins. The C-Press pin was fantastic in service, but difficult to stamp. This pin contacted >70% of the diameter of the plated through-hole. The conservative operating companies tested these compliant pins to ensure they could last for 40 years through accelerated life testing. They learned that electrical performance was comparable to soldered pins and the compliance made these much easier to use in manufacturing, opening up PCB hole tolerances to +/- 0.003″ (7.5%).