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Productivity features not only save time-to-market, but they also curb frustration. One of the most common issues that managers and PCB designers face today is lack of time. Unlike money, time is a non-renewable resource. Once time has passed, it is gone forever. With that said, getting more work done, in the same period of time, by using the right tools results in higher profits. Add it all up and it equates to cost savings and improved productivity. Integrated software is the key to efficient PCB design.
One of the main details lacking in today’s PCB design software is the flow of impedance control from design capture through to board fabrication. If the impedance of all the required technologies, used in the design, is determined up-front at the time of capture, the engineer’s intent should be preserved and flow through to downstream tools. However, that scenario rarely happens. Many PCB designers simply select the trace width and spacing, that they typically use assuming all FR-4 is the same, and start routing, thinking that the fab shop can fix it later. This is due to their inability to define the requirements as they rely on their fab shop’s feedback, on impedance control, after completion of the Gerbers. This is analogous to shutting the gate once the horse has bolted.
I originally came up with the concept of an online impedance calculator way back in 1994 when I was working on the PCB layout and design for a new generation of SPARC 20 servers. We basically reformatted a Sun SPARC 20 pizza box motherboard to fit into a 5.25-inch drive slot. This was of course a tight exercise, but my idea was this: If I could physically fit all the required chips and connectors on the board, then it could be routed. This design required a 12-layer motherboard, and I used the IPC-317 “Design Guidelines for Electronic Packaging Utilizing High Speed Techniques” closed-loop equations to determine the signal layer impedance. The maximum CPU frequency was 200MHz, so there was plenty of margin.
To cut a long story short, after months of development, the project was completed and launched into the market. In 1995, the development team received an IEEE Engineering Excellence Award for the design. The server was subsequently licensed to a US company, jointly owned by Fujitsu and Sun Microsystems. Under license, the manufactured machine, a US-built SparcPlug Station, won the Best Performance category in the 1997 US AIM "Hot Iron" Awards.
To read this entire column, which appeared in the February 2017 issue of The PCB Design Magazine, click here.