For many years I owned a small boat which gave me hours of fun on the water, but there are a few critical rules that have to be obeyed. One of those rules is that you MUST install the drain plug before putting your boat in the water. It’s a lot cheaper to go for a swim intentionally, rather than unexpectedly in order to retrieve your new boat.
Everyone knows that rules are there for our protection. But sometimes, whether accidentally or on purpose, the rules get bypassed. Circuit board designs also have rules that need to be followed. Fortunately, modern PCB design software is teaming up with Design Rule Checking routines, or DRC’s. Now, we as designers just need to use them.
Rules are there to help keep designs from sinking.
No matter the size and complexity of your circuit board design, it should be subjected to design rule checking. Some argue that certain designs are too simple to invest time on DRC’s. However, even the simplest designs can cause big problems from unexpected design violations that slip through the cracks. DRC’s ensure that the designs’ integrity is good before it is sent off for manufacturing. Circuit board design DRC’s change from tool-to-tool in name and description, so here are some of the more common elements that board design software should check your layouts for:
Board Technology Rules: Your layout tools should give you the ability to check the validity of the different physical parameters of your design, such as correctly defined physical layers that are not duplicated.
Footprints: Your layout tools should also give you the ability to check the footprints that you are using on your design, whether individually or in a batch mode.
Components: You can use layout tools to check whether or not your components are correctly setup for the appropriate footprints. Components should also be checked for the correct spacing and locations, and whether they are positioned correctly on or off the grid and within the expected contours of the board.
Nets: You can set up design rules to check for clearances of electrical objects on your board (pins, vias, traces, fills and planes), as well as other electrical constraints.
Hi-Speed: If you are doing design work with hi-speed constraints such as matched lengths, diff pairs, and from-to net rules, your layout tools should be able to check those as well.
Let’s not forget about the schematic side of the design either. DRC’s are often associated only with circuit board layout, but rule checking your schematic is equally important. Your schematic editor’s rule checking can tell you if your project has good design integrity, and whether or not there are problems on individual sheets or with symbols. You can verify if there are any net connection problems, and how well the schematic is connected to the physical layout. Ideally, you’ll also be able to check for updated library parts as well as any rules or constraints that need to be forward annotated to the layout.
Use DRCs to catch simple errors.
Put those DRC’s to work
The moral of the story is, all of these Design Rule Checks will not help you if you don’t use them. Sometimes it’s tempting to bypass complex DRC settings and only use the minimum or default setups to get by. Yes, some errors will be caught but simple errors can go undetected. For example, a component on the backside of the board being placed too close to a sensitive part. A missed violation like this could, at the very least, cause a delay in the project schedule, or at worst, allow a batch of bad boards to be built. This leads to cost overruns, broken schedules, and even loss of employment.
Have you ever put a boat in water without re-installing the drain plug? If you have, then you know how fast that boat will sink. In PCB designs, our work can sink just as fast if you don't use DRC’s. But you can avoid an unexpected swim in the deep dark waters of missed schedules and bad board builds by making sure to use your design tool’s DRC’s to their fullest extent. Advanced PCB design software, like Altium Designer, can help you keep your designs above water.
Would you like some more ideas on how to better protect your design by using advanced DRC’s? Talk to an expert at Altium.
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