PCB design guidelinesEIEF01 – Applied Mechatronics

fran.marquez@iea.lth.seLund, 10 September 2020

Stripboards (veroboards)- Bakelite board with

Copper (conductive) strips on one or both sides

- Matrix of holes- Multiple sizes (100 x 160

mm) possible to cut to measure

- Ideal for fast prototyping

PCB = Printed Circuit Board

1. Mechanically – support and hold all components in place, provide mechanical strength

2. Electrically – connect all components, distribute power / ground and signals

PCB design process

1. Define specifications, functionality, interfaces, power needs, environment (noise) etc

PCB design process

1. Define specifications, functionality, interfaces, power needs, environment (noise) etc

2. Identify components & version suitable for the job –preliminary list of materials

PCB design process

1. Define specifications, functionality, interfaces, power needs, environment (noise) etc

2. Identify components & version suitable for the job – list of materials

3. Create the schematic with all the components, all the connections, and if possible, simulate the circuit behaviour

PCB design process

1. Define specifications, functionality, interfaces, power needs, environment (noise) etc

2. Identify components & version suitable for the job – list of materials

3. Create the schematic with all the components, all the connections, and if possible, simulate the circuit behaviour

4. Move from the schematic to the PCB layout – components placement and routing of copper traces

PCB design process

1. Define specifications, functionality, interfaces, power needs, environment (noise) etc

2. Identify components & version suitable for the job – list of materials

3. Create the schematic with all the components, all the connections, and if possible, simulate the circuit behaviour

4. Move from the schematic to the PCB layout – components placement and routing of copper traces

5. Send the PCB design files for manufacturing

- The design information is stored in the (extended) GERBER files, one file per image layer. - RX-274 format used to define images- Excellon format used for holes- For a 2-layer board:

• Top layer• Bottom layer• Solder Stop Mask• Solder Stop Mask• Silk Top• Silk Bottom• Drill

https://www.ucamco.com/en/file-formats/gerber

Curiosities…

1. What’s the most common colour for PCBs?

2. Why?

3. What is a “mil”?

4. How many layers is it possible to have?

Good practice for routing a PCB…

1. Components placement

a. Arrange the components aiming for short and direct traces

b. Do not to mix technologies, but if you need to do so, try to group them: through-hole components always on top layer

c. Keep component orientation and group similar components together for easier manufacturing & debugging

Good practice for routing a PCB…

2. Power distribution inside the board

a. Symmetrical, centered solid Vcc and GND planes

b. Distribute power to components using “common rails” rather than daisy chaining

c. Avoid ground loops!

Good practice for routing a PCB…

3. How thick should copper traces be? IPC-2152, IPC-2221

Height

1 oz/ft2: 35 um

Rule of thumb

10 mil for low current (< 0.3 A)

Good practice for routing a PCB…

4. Decoupling capacitors

a. A set of 2 capacitors close to the main power supply connector of the board

1) Fast plastic capacitor (100 nF)

2) Slow “fat” electrolytic capacitor (1 – 10 uF)

b. 100nF per supply pin in a chip

Good practice for routing a PCB…

5. Avoid “peelables”!!

6. Avoid 90 deg angles!!

7. Use thermal reliefs

Curiosities…

1. What’s the most common colour for PCBs?

2. Why?

3. What is a “mil”?

4. How many layers is it possible to have? Over 100!!

0.001 inch = 0.0254 mm

Thank you for your attention!