PCB Best Practices
This page is continuously updated for best practices for PCB designing. Note that some of these practices are industry standard, while others are defined in the OPEnS lab. If there are some questions / topics that are not covered in this documentation, reach out for help so it can be answered and documented.
- Modified Adafruit Feather M0 Library
- I2C Connections
- Labelling
- Ordering PCBs
- Planes
- Right Angle Traces
- Tolerances
Our lab commonly uses the Adafruit Feather footprint when designing PCBs to easily connect a Feather to the circuit. However, the problem that commonly occurs is the spacing between the two headers is incorrect-- preventing the Feather from being connected. Our solution to this: a modified Feather M0 library. Instructions on how to install it are listed on the GitHub repo. Installing this library will automatically label the pinouts for the Feather layout and space the headers accurately, avoiding any errors in spacing and labelling that may occur.
In the OPEnS lab, I2C wire connections are color coded yellow and white, SCL and SDA respectively, to easily recognize wire connections. When creating PCBs, the I2C connection ports are as followed: VCC, GND, SCL, SDA.
It's a good practice to label the components and important pins on a PCB so that anyone is able to tell what component goes where. Here's an example of what the Dendrometer Hub PCB looks like. The PCB has the LTE board label as well as a powerbooster and solar charger. Important pins are labelled such as 5V and 3V, GND, Tx and Rx, etc.
Another example of using labels is labelling pins on connectors. The Dendrometer PCB connects different sensors with JST connectors. When projects are taken outside of the lab into the field or with the stakeholder, it can be hard to identify which wire goes to which pin. Labelling helps with building and troubleshooting. The screenshot below shows how the Dendrometer labels each JST pin so it's easy to identify which wire is associated with which connection.
In order to create labels, use the text tool, type the labels you want, and place them to where they should be. Make sure the layer they are on is tPlace or bPlace (depending on if the text should be on the top or bottom) as it will put the text on the silk screen. To view what the text looks like, click the green "Manufacturing" button on the right side and adjust the text size and position accordingly.
We have two main locations where we order PCBs: OSHPARK and PCBWAY. PCBWAY is normally cheaper per board, but higher shipping. OSHPARK is in Portland but their board is $5 per square inch and takes around 2 weeks to receive. To order from OSHPARK, you will need the .sch and .brd files. To order from PCBWAY, you will need the .sch, .brd, and gerber files. Refer to this guide to generate the gerber files. First and foremost, you will need to ask Dr. Udell for approval for the board and for ordering.
Afterward you will want to email both Dr. Udell and Cara with the following:
- Number of boards
- Manufacturing location (OSHPARK or PCBWAY)
- What type of shipping
- The required files (.sch, .brd, and/or gerber files)
- A nice thank you!
The last thing you will need to do is order any parts / components that your board needs by adding it to the OPEnS shopping list. The spreadsheet is in the shared Google Drive named "OPENS shopping list." Follow the previous orders for the proper formatting.
It is a common practice to ground the front and/or back plane of the PCB. This reduces the amount of traces on the board and simplifies the routing process. It also ensures that each connection is consistent (i.e. if a GND plane is used, the GND signal is constant for all connections). In order to do this, follow the Build Electronic Circuit guide. Some designs have power planes instead as it is another common connection-- which is done the same way as making a ground plane. Other designs have both a power and a ground plane (one on the front and one on the back side).
Our lab commonly uses the ground plane, but a power plane may be appropriate depending on the project.
It's a good rule of thumb to avoid right angle traces on your PCB. In the lab, our signals are not usually high enough to cause concern but normally for high speed signals, right angle traces may be problematic and cause the transmission delay.
When making traces on your PCB, the thickness of your trace is important to carry the appropriate amount of power and current. For our purposes, power and ground traces can be around 0.3 mm and any signal traces can be around 0.2 mm. If you are going to make the traces larger, make sure that there is a good amount of space between the different traces on your board to avoid any problems. In special cases, these trace widths may not be enough. If that's the case, use the trace width calculator to calculate what trace width your PCB may need.