Even if you aren’t a basketball fan, the 37 foot buzzer beating shot taken by Damian Lillard of the Portland Trail Blazers to win the 2019 first round series against the Oklahoma City Thunder was nothing less than amazing.
But where a lot of players might get swept up in the moment and ride the wave of accolades, Lillard was refreshingly real and down to earth about his abilities. He made it very clear in the post-game interview that he owes his performance to the training and conditioning he put in during the summer. He went on to say, “when you cheat yourself, you fail in those moments.” He certainly proved that night with his 50 total points and amazing game-winning shot that he was well prepared for what he had to do.
Preparation is the cornerstone of success and that is certainly true in PCB design too. Improvement and growth will come with experience, and being prepared first will enable you to leverage that experience into success. To help you be prepared, here are some basic PCB layout design steps to get started with.
Starting With Good Source Material is the First of Your PCB Layout Design Steps
No matter what task you set out to do, you need to start with good source material if you want to be successful. Just as a master carpenter doesn’t rough in a wall with a toy hammer and plastic nails, you shouldn’t try to design a circuit board without good materials either. The first thing to do then is to make sure that your CAD library parts and the schematic are ready to go:
Symbols: Although it is an accepted practice to work with “placeholder” parts, it can make your design very difficult to work with if your schematic symbols aren’t correct. Make sure that you symbols have the correct pins, part numbers, and component attributes.
PCB Footprints: When you get to layout you will need correct component size and shapes, pin locations and numbering, and land patterns sizes. Without this data you could be faced with unexpected redesign time to correct them later.
Schematic Placement and Connectivity: Components should be placed in an orderly fashion with readable text so that you can clearly see what you are working with. Nets should be neatly routed with clearly defined net names and pin numbers.
Next, gather as many of the board details together before you start:
Size and Shape: Having to change the size or shape of the board mid-design can really hurt your productivity.
Layer Stackup: Work with the manufacturer in determining the correct layer stackup before you start. Having to add, delete, or repurpose layers to your board in mid-design can cause serious delays.
Holes and Zones: The last thing you want after carefully placing your components is to rip them all up because you didn’t know about a mounting hole or keepout zone in the middle of the board. Make sure that you have all of this mechanical information before you start.
Finally, make sure you know who the manufacturer will be and acquaint yourself with their fabrication and assembly requirements. You don’t want to be forced into redesigns because the board can’t be built the way you laid it out.
The first steps in successful design are making sure your schematic and library parts are ready
Place and Route the PCB Layout
Now it is time to place and route the board. Although you obviously can’t route any traces until you place the parts, a good part placement does depend on how the traces will eventually be routed. Yup, it’s the old chicken and the egg question as to which came first. With that in mind then, here are some component placement considerations:
Place your components according to their schematic signal paths. That small terminating resistor may fit perfectly next to the driver, but it needs to go at the end of the signal path, not the beginning.
Place components to keep signal routing lengths as short as possible unless you have signals with specific length requirements.
Decoupling capacitors should be as close as possible to the device pins that they are tied to in the schematic.
Be mindful of all mechanical constraints so that you don’t have parts poking out of the device enclosure.
Place your components according to manufacturing, test, and thermal constraints.
Another aspect of place and route is planning out your power delivery network. You need to make sure that all components get good power coverage while at the same time ensuring that your signal routing will have an adequate return path on a continual ground plane. It can get a little tricky trying to balance all of these needs, so take the time to make it right so it doesn’t become a problem later on.
Interestingly enough, if your component placement and power delivery network is set up correctly, your routing often isn’t as difficult as it might seem. That isn’t to say that routing is easy, far from it. But a lot of the difficulty in routing is planning it out in the layout. Now it is time to “hook ‘em up.”
Take the time to carefully route the escape patterns for your BGA’s and other fine pitch devices. Use your design rules and constraints to their fullest extent so that your nets have the correct width, spacing, length, and topologies built into them. And lastly, make sure to run your design rule checks and clean up any errors.
By going through each step of the design, you will soon be routing boards like this
Your PCB Will Only Be as Good as Your Manufacturing Documentation
The last steps in finishing your PCB layout is in creating and sending out the manufacturing documentation. Depending on what you are designing and who is building it, you could be creating a variety of different documentation including:
Fabrication and assembly drawings.
Bill of Materials reports.
XY location files for automated assembly machines.
XY location files for testing.
These are just a sampling of what you may be required to create, it will all depend on your specific needs.
The critical thing is to put in as much effort into the manufacturing documentation as you do into the rest of the design. It is very tempting for PCB designers to relax and “phone in” the final deliverables of a job, and that will only result in confusion on the part of the manufacturer, and delayed or bad board builds. So take your time, and do it right.
There is another step that is crucial to your PCB layout success, and that is using the best PCB design tools for the job. You don’t want to be spending your valuable time trying to learn cumbersome and limited software, instead you need design tools that will help you to get the job done quickly and efficiently. The PCB design tools from Cadence have the capabilities you need to get you through all of the steps that we’ve listed here. OrCAD PCB Designer is a feature rich set of design tools that will help you to do it right.
If you’re looking to learn more about how Cadence has the solution for you, talk to us and our team of experts.
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