Altium Schematics and Footprints Guidelines

(Category: Altium) If you're looking at this right now, you have probably finished the design process of your PCB and picked out all the parts/components you need. If yes, it is highly recommended to make sure you also have schematics and footprints associated with every part before moving on with reading. If not, you should refer to The Art of PCB Design page before coming back.

PCB Terminology

• PCB: Printed Circuit Board.

Schematics Terminology

• Symbol: the representation of an electrical component in the schematic file.
• Net: Any wire that connects to a node. In Altium, the name of the net is the combination of the index of the block (chip) and the component it connects to.
• Tag: Yellow-colored arrow-shaped items in the schematics file. From a separate sheet, the input (inward pointing) tag imports the net defined by the name of the net indicated in the tag. There are also output and bidirectional tags.
• Harness: a group of nets connected to the same terminal. In GPIO/SPI/UART/I2C serial communication methods, the TX and RX data lines will often be grouped by a harness for clarity.

Footprints Terminology

• Footprint: the representation of an electrical component in the PCB file. It also indicates the location of an electrical component, and you will see it on the manufactured PCB.
• Trace: the copper wires that connect different electrical components on the PCB.
• Via: A hole in the PCB that electrically connects through the board. The copper conductive part is inside the PCB. This moves the copper track to another layer in the PCB and prevent two nets from overlapping on the same layer.
• Pads: metal regions needed to electrically connect components on the board with the inner traces and wirings.
• Surface-mount pads: pads that only exist on the surface of a layer. They do not cut through the board. Used for surface-mount devices/technology (SMD/SMT). Usually harder for soldering but required for most chips and smaller electrical components.
• Through-hole pads: pads that cut through the board. Used for through-hole technology (THT). Usually easier for soldering.

Altium Schematics (SchDoc)

• Designing the schematics means you will wire up the necessary electrical components that make your PCB board function electrically. You should refer to the datasheets of different parts to see the additional components you might need.
• The Altium schematic sheet of a completed board shows a block diagram with all the electrical components of the board. Each block represents a chip and has a detailed sheet associated with it.
• If you are confused about the functions of components shown in a schematic file, Khan Academy can be a great resource for understanding electrical components and what they are used for.
• When the schematic is done, Altium will generate a netlist and import it to the PCB document. You will see all the nets turned into tracks on the PCB, which size can be customized.
  • In the Schematic window, go to Design → Update PCB. You can see what parts in the schematic are not on the PCB (They should!). Once you have confirmed everything, click on Execute Changes to update the PCB file (PcbDoc).
  • To find where the schematic of a missing part is, use the Find tool (Ctrl + F) and type in the part name.

Altium Footprints & PCB (PcbDoc)

This is when we switch from designing the circuit to laying out the PCB itself, i.e. planning out the physical locations of each part and component.

Layers in Altium

• The PCB can have many copper layers that supply power to different components running on different voltages.
• The transparent function in Altium will show two sides of every layer at the same time, which can be confusing at first and will take time to get used to.
• By default, all components on the same page in the schematic document will be in the same “room,” and you can move all the components together in that room.
  • Rooms will allow a repeated circuit to be dealt with more quickly. For instance, if you want to have the same circuit repeated 10 times, having the circuit organized in a "room" will make editing the components easier.
  • If you don't find this convenient, you can disable this in Altium settings.

Wiring Guidelines

• Make wire traces/new vias/new layers to finish all connections.
• For higher power/voltage data/power lines, it is recommended to use thicker traces.
• Avoid 90° traces due to high likelihood of EMI (electromagnetic interference).
• No traces can go through a via.
• Make sure the via on one layer is not on top of a via in another layer (or else undesired electrical connections may occur).
• A mechanical hole for mounting certain big components (like battery holders) cannot interfere with any vias or traces, or else an electrical connection cannot be made.
• Select the layer you’re working on with tabs at the bottom of the window for easier selection of traces/components.

After all the checks are done, a 3D model will be generated, and all the information can be sent to a fabrication company.

Authors' Note

This page is written on January 18, 2024 by Sam Chen and Abelle Jayadinata based on the materials covered in the Winter 2024 Altium PCB Workshops hosted by Evelyn Nutt. We thank Evelyn Nutt and Ethan Brinser for their expertise and knowledge, which made the writing of this page possible.

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