Issue link: https://iconnect007.uberflip.com/i/1114420
48 DESIGN007 MAGAZINE I MAY 2019 routing between the lines instead of crossing over them as well. But you might be surprised how many people refuse to use the full poten- tial of their DRCs to protect themselves, and in some cases, refuse to use them at all. When online design rule checking first ap- peared in PCB design tools many, many years ago, there were a lot of problems associat- ed with them. At first, they only had a few (if that many) clearance settings, and those didn't always work as they should. I remember be- ing warned of clearance errors on some tools that actually weren't errors at all; the tools just weren't reporting them correctly. This would happen more often if you were using oddly an - gled traces on too fine of a grid. It was not unex- pected then that PCB designers back then were sometimes leery of using or relying on DRCs. Another problem during that time was PCB design was largely converting over from hand- taped designs to computer-aided design tools. If you aren't familiar with the process of hand-tap - ing a design, PCBs were laid out at two, four, or even 10 times the actual size working on a transparent grid over a light table. The designer would apply opaque tape and dots to create the traces and vias of the layout using the grid for a reference. The grid, plus the designer's experi - ence, was the only clearance checking available, and designers would maintain the correct trace to via spacing by eyeballing it. If something was too close together, an X-Acto knife would be used to trim the tape or dot down a bit. For PCB designers that were artists with tape and dots, the transition to CAD was sometimes difficult. To gain freedom with their work the way that they were used to, they would often disable the grids and online DRCs. Al- though this would give them a design environ- ment that they were more comfortable with, it would make a mess of the job because of all the DRC errors. I used to spend days repairing designs like these because I would first have to move all of the existing routing onto a grid to clean up the DRC errors. Once everything was back on a grid, it was a lot easier to edit the placement and routing for modifications. How- ever, many of these designs took a lot more ef- fort than I expected because when I did bump every trace and via to get the correct spacing, there was no longer enough room for all of the traces. Those were the times my mood would get really bad for a while. So, yes; it was understandable why design rules were ignored in the past, but that still didn't make it right. I know first-hand the cost of not using the available DRCs because of all the heroics that I had to go through to fix them. If turning off the DRCs wasn't the right thing to do back then, it certainly isn't these days either. Last fall, while driving I-5 from California to Oregon, I had the misfortune of getting caught up in the forest fire that ravaged the beautiful scenery of the Mount Shasta area (Figure 1). Shortly before I arrived there, the safety officials decided to close the freeway at a specific point due to concern that the fire was about to jump the road. If I had been just 10 minutes earlier, I probably would have beat the road closure, but as it was, I had to retrace my route and take the long way around Mt. Shasta to the east. I don't want to bore you with the details, but let's just say that four extra hours of slow, bum- per-to-bumper traffic on winding backroads without adequate rest areas was not fun. But my point is that someone made the right call when the fire exceeded specific safety rules that were created for the protection of the public. Although my extended detour wasn't fun, I was very happy with the safety those rules afforded. PCB Design Rules Just as traffic rules are intended to keep us safe and out of trouble on the road, PCB design rules are also intended to keep our designs When online design rule checking first appeared in PCB design tools many, many years ago, there were a lot of problems associated with them.