# Printed Circuit Board Layout

 It is a course of Electronic engineering
• Level 1
• Term 1

## Syllabus

This course will cover basic printed circuit board layout practices for low frequency designs.

• What is a PCB and why do we use them.
• Physical PCB construction. How are boards built, and how does this affect design.
• PCB Workflow. Good practices for going about designing a PCB
• Schematic practices
• Parts placement
• Routing
• Common pitfalls

## Lecture plan

• What is a PCB and why do we use them.
• Physical PCB construction. How are boards built, and how does this affect design.
• PCB Workflow. Good practices for going about designing a PCB
• Schematic practices
• Any board design begins with a schematic. For simple designs the schematic may not be drawn, but for anything beyond the most basic boards it is good practice to draw the schematic out before beginning layout.
• A schematic is the ideal representation of a circuit.
• Footprint generation
• Nearly all PCBs will use some components that must be soldered to the board. Each of these components must have a footprint. Most PCB layout software comes with a library of parts, but you will often need to make new footprints for parts not in the library.
• Parts placement
• Once you have all of the footprints created, the next step is to lay out the parts on your board. The general order to follow for parts placement is:
• Mechanically defined components. Any components that must be in a particular place for mechanical reasons. Most commonly connectors, LEDs and mounting holes.
• Large components. Any large components and high pin count components. Careful placement of these will make routing much easier.
• Crystals and bypass capacitors. These should be placed near the integrated circuit that requires them. Unlike a schematic, on the PCB the length of the trace will affect circuit performance.
• Remaining components.
• Routing
• This is the bulk of the layout process. Here all of the connections that are shown on the schematic must be made in the copper on the board. Unlike on the schematic, lines may not cross (this would cause a short). However, most circuit boards have more than 1 layer and traces can be connected through the board by vias. Vias are copper plated holes that travel through the pcb.
• Trace width is dependent on the current carried by the trace, the manufacturing process used, and the thickness of the copper used. For certain high speed signals the thickness is chosen to create a specific impedance.
• Routing guidelines (needs to be added)
• Copper Planes
• PCB Construction Options (Explanation of different (optional) features on pcb boards and reasons for choosing)
• Number of copper layers. (1,2...2n)
• Soldermask (protective coating over board to prevent accidental shorts)
• Silkscreen
• Copper thickness
• Minimum trace width/ spacing
• Laminate material (FR4 etc)
• Board thickness
• Available hole sizes
• Plated vs unplated holes
• Common pitfalls
• From Layout to production
• Gerber files
• Labs
• From schematic to PCB
• Parts placement and routing
• Making footprints

• Glossary
• Via: A copper plated hole through a circuit board.
• Footprint: A representation of the layout data for a particular component. Footprints can be moved about on top of a layout.
• Copper Thickness: The copper thickness of a PCB is measured in ounces per square meter (often referred to as simply ounces). 1 ${\displaystyle {\frac {oz}{m^{2}}}}$  corresponds to approximately 1.4 mils (.0014").