When I was a teenager I was hiking with a group of people along the Washington State coast. We were somewhere that we probably shouldn’t have been, scrambling around the side of a cliff that extended down into the ocean without any safety equipment. At one point I began to lose my balance, and I knew that I was going to fall 25 feet into the deep water that was being churned up by the tide below us. But in the next instant, before I even had a chance to panic, the guy behind me grabbed my arm and restored my balance. He had seen my difficulty and gave me the help I needed to escape my predicament.
Although not as dramatic, there have been plenty of other times in my life where unexpected help has been there when I needed it. At work I have had many questions about PCB design throughout my career and I am truly grateful for those who have stepped in with different tips and tricks to help me. Now it’s time to pay it forward, so here are some of my top PCB layout tips that I have found to be extremely useful. Hopefully they will be of some help to you as well.
The Importance of a Complete Schematic Tops the PCB Layout Tips List
It is not at all unusual for those doing PCB layout to gloss over the importance of having a good schematic ready before they begin placing and routing components. It’s very easy to simply dismiss attention to detail in the schematic because you expect it to be taken care of later.
Because of this kind of thinking, design checks aren’t run, parts aren’t validated, and basic drafting tasks like cleaning up text to make it more readable aren’t followed. It may seem like you are saving yourself time by jumping straight into PCB layout, but often the opposite is true.
What you may find out is that those missed design checks would have caught some nets that were incorrectly connected. Now your layout has traces that need to be ripped up, or at worst, parts have to be completely replaced to accommodate the corrections. Remember those parts that weren’t validated? Now you may be spending time replacing parts that may not fit the way the original parts did, and you are forced to do more work.
That messy drafting, well, someone has to clean it up before it can be sent out, and that someone often ends up being you. So do yourself a favor and make sure that the schematic is ready before you actually start layout.
Make sure to be ready for layout to avoid redesigns of dense routing later
Find Out as Much Information as Possible Before You Start Layout
Jump starting a PCB layout before having all the board data at hand usually causes more problems than it’s worth. You may find yourself in a position where you have to rip up and modify portions of your design in order to accommodate a change that should have been done before you started your work. Here are a few items that you should verify first:
Board Layer Stackup: Make sure that the board layer stackup has been finalized before you start. Having to add or delete board layers can be a very painful process which sometimes results in redoing the entire layout.
Board Dimensions: Having to move carefully placed components because your board outline needs a cut-out in it that you didn’t know about can cost you a lot of time. Check first to save yourself a lot of trouble later on.
Keepout Zones: These zones could be for a number of different reasons including mechanical, thermal, height, or sensitive circuitry. If you don’t understand these requirements before you start layout, there’s a good chance that you will have to make unexpected changes later on.
Critical Placement & Routing: Nothing is worse than finding out that you’ve placed a component out of place for the signal path. It is very discouraging to have to redo the entire placement and routing just for one small chip component that won’t fit.
Check first before you start, and you will hopefully save yourself a lot of grief later on. And do yourself a favor by giving yourself some extra room in your placement for modifications, if at all possible. Design changes are inevitable, just make sure that when you have to account for the time you spent on redesigning the board that it is because of an official change. Having to admit to your boss that three days of redesign is because you jumped the gun and started before you were ready is not a conversation that you want to have.
Don’t rush through final manufacturing files, and blow a great design like this
Don’t Neglect the Final Manufacturing Output Files
Once the layout is complete, you are ready to get the board built. Everything that you’ve done so far now boils down to this final task. It is amazing though how many designers will rush through this process. It certainly can be tedious to create drawings and documentation when it is a lot more fun placing and routing components, but it has to be done.
Managing supply chain information and component sourcing, generating assembly drawings and Gerber files, and compiling board information in standardized file formats are simple but pivotal features of the production process. Don’t forget that your PCB manufacturer or fabricator are just emails or phone calls away—including their voice in your design process can save headaches as you’re trying to meet their specifications at the end of a long design process.
Remember that you are building a circuit board and the board will only be as successful as the manufacturing documentation that you create. So give yourself plenty of time, don’t rush the process, double check all of your work, and make sure that you send out a full and complete documentation package.
You can also help yourself by using PCB design tools that are built to help designers like you and me get our job done as quickly and efficiently as possible. OrCAD PCB Designer is a powerful set of design tools giving you the ability to lay out your PCB design with speed and accuracy.
If you’re looking to learn more about how Cadence has the solution for you, talk to us and our team of experts.