Beagleboard:PCB Design Guide
The rules below are provided publicly with the intention of helping basic PCB designs to be cost-effective, manufacturer-friendly and user-friendly. These rules are made as generic as possible and DO NOT guarantee your design will work. They also DO NOT reflect our manufacturing capability in any way.
- Always keep your board size to a minimum. Larger boards cost more.
- Always keep standard board shapes like rectangles or squares if shape is not important for your PCB. Non-standard PCB shape may increase the fab cost.
- Avoid internal cutouts if they are not required. Internal cutouts will introduce more cost at fab shop.
- Go with 2 or 4 layers for simple design. Only go higher if required by your design.
- Standard PCBs have 0.062" thickness and are made of FR4 material. Use these unless you have a different reason.
- Each LED needs to be labeled with its function. This will be useful when using and troubleshooting. Examples: Power, User, CPU Activity, etc.
- Each button/switch needs to be labeled with its function. Sometimes it is useful to label the switch state as well. Examples: Power, Reset, Boot, etc.
- Each connector/header needs to be labeled with its function even for connectors with obvious functionalities. Examples: HDMI, Ethernet, Expansion, Serial, Input, etc.
- Pin 1 of each header needs to have a square pad. This is standard and will be helpful in assembly and troubleshooting.
- Include any information that you think can help manufacturing, using, or troubleshooting your board. Examples:
- For any part that has polarity, ensure the correct orientation is clear on its footprint. Examples: LED and diode require diode symbol markings; polarized capacitor and batteries require positive marking.
- It is very helpful to label pin numbers in intervals especially for connectors/headers with high number of positions. It will save some time from counting all the pins. Examples: 5, 10, 15.
- Adding signal name for each pin can be helpful if space allows and the number of position of that connector/header is not too high.
- Other parts (i.e. ICs) may also need its pin 1 to be labeled.
- Polarity markings should be visible even after the parts are mounted for inspecting purposes.
- Use standard reference designators for standard parts. See below for common designators:
|Connectors/Ports||P1, P2, etc|
|Headers||J1, J2, etc|
|ICs||U1, U2, etc|
|Switches/Buttons||SW1, SW2, S1, S2, etc|
|LEDs||D1, D2, etc|
- Avoid using trace width that is smaller than 10 mils.
- General power traces need to be at least 20 mils in width. You can use the chart below for Power Trace Width vs Amp
|Power Trace Current vs Trace Width For 1oz Copper|
|Temp Rise||10 C||20 C||30 C|
|Width (mil)||Max Current (A)|
- Keep a minimum of 10 mils between traces.
- Keep a minimum of 10 mils from copper to PCB edge for outer layers and 15 mils for inner layers.
- It is recommended to add ground pour especially for two layer boards. It usually makes it easier for routing. It can also reduce electrical noise and provide additional heat sinking.
- Minimize the number of vias. Avoid using blind vias or buried vias as they will introduce much more cost to your PCB.
- Add useful information to the board as silkscreen. Examples: it is useful to add voltage limits to an input voltage connector (i.e. 2.5V-5V) to avoid connecting wrong voltage to the board.
- If possible put all parts or at least through-hole parts on one side of the PCB. This will reduce the assembly cost
- Add fiducials to your board. Fiducials are used by pick-and-place machine to accurately locate the circuit pattern.
- Use 1mm diameter fiducials with good contrast. Use fiducials on both sides if both have SMT parts.
- It is recommended to use three fiducials. Place them as far apart as possible near the corners.