Board Design OVerview
All the chip selection and planning is done for your printed circuit board and the real fun is about to begin. It is time for schematic and eventually board layout! All the hard work and planning you have put in this far will make this a much easier process. For hobbyists and non-profits, there are many free options to create your schematic and layout. First, let's go over the process of how a printed circuit board gets made.
What type of board do I need?
Printed circuit boards come in various shapes, sizes, and materials. Two dimensions are called board size which is normally a length and width measurement such as 2 x 1 inches. This is fairly self explanatory. Thickness is a little more complicated since a thickness is normally given in mils (in the USA). 1 Mil is 1 thousandth of an inch. Standard boards come in various thicknesses such as 20, 31, 62, 93, 125 mil depending on who you use to create your boards.
In addition to thickness value, there are also layers. Layers are, as you would expect, stacked together to form the PCB thickness. Each layer uses copper to make connections and also has a substrate that the copper is mounted on for stability. The top layer of a PCB is shown in the picture has a bunch of traces connecting to vias which are holes that connect layers to each other. Layers and vias are very important to understand for layout.
The last characteristic of PCBs is the material of the substrate. Most common substrates are dielectrics. The cheapest (in general) and most common substrate is called FR-4. FR-4 is made of fiberglass epoxy resin. If there are no antennas or high frequency circuits on your board, the material and thickness of each layer have very little effect and do not have to be designed for.
What type of board do I need?
Printed circuit boards come in various shapes, sizes, and materials. Two dimensions are called board size which is normally a length and width measurement such as 2 x 1 inches. This is fairly self explanatory. Thickness is a little more complicated since a thickness is normally given in mils (in the USA). 1 Mil is 1 thousandth of an inch. Standard boards come in various thicknesses such as 20, 31, 62, 93, 125 mil depending on who you use to create your boards.
In addition to thickness value, there are also layers. Layers are, as you would expect, stacked together to form the PCB thickness. Each layer uses copper to make connections and also has a substrate that the copper is mounted on for stability. The top layer of a PCB is shown in the picture has a bunch of traces connecting to vias which are holes that connect layers to each other. Layers and vias are very important to understand for layout.
The last characteristic of PCBs is the material of the substrate. Most common substrates are dielectrics. The cheapest (in general) and most common substrate is called FR-4. FR-4 is made of fiberglass epoxy resin. If there are no antennas or high frequency circuits on your board, the material and thickness of each layer have very little effect and do not have to be designed for.
How to make a PCB:
1. Component import/creation - Each component chosen for your design must be imported into your software with a schematic symbol and a layout footprint. If there is no compatible component to import from the web, the symbol and footprint must be custom created by the user to be used during design.
2. Schematic Design - After all the components are created or imported, the schematic stage can begin. All the components should be added and connected as desired to create your schematic (using your spreadsheet will be excellent for this step).
3. Schematic Review - Time to a grab a smart friend to go over your schematic with you and ensure that every pin is hooked up correctly and every chip is connected as wanted.
4. Layout Design - Although most of the engineering is done by this step, the artist in you better come out to create a beautiful layout and more importantly a SMALL layout. Keep your chips close together for small overall board.
5. Layout Review - After finishing the layout, run design rule check (DRC) to ensure no errors were made. Then, grab your smart friend again to, painstakingly, go through each pad and how it is connected to avoid any mistakes. Be smart and check the "show stoppers" first.
6. Gerber Generation / Fabrication - Once you gain final approval by your buddy and you have looked at the board enough times to believe everything is correct, it is time for submission to a fabrication house (PCB manufacturer). The fab house will check your layout again for tolerances of their equipment to make sure they can produce what you expect of them. Check what files they require for fabrication (normally Gerbers).
1. Component import/creation - Each component chosen for your design must be imported into your software with a schematic symbol and a layout footprint. If there is no compatible component to import from the web, the symbol and footprint must be custom created by the user to be used during design.
2. Schematic Design - After all the components are created or imported, the schematic stage can begin. All the components should be added and connected as desired to create your schematic (using your spreadsheet will be excellent for this step).
3. Schematic Review - Time to a grab a smart friend to go over your schematic with you and ensure that every pin is hooked up correctly and every chip is connected as wanted.
4. Layout Design - Although most of the engineering is done by this step, the artist in you better come out to create a beautiful layout and more importantly a SMALL layout. Keep your chips close together for small overall board.
5. Layout Review - After finishing the layout, run design rule check (DRC) to ensure no errors were made. Then, grab your smart friend again to, painstakingly, go through each pad and how it is connected to avoid any mistakes. Be smart and check the "show stoppers" first.
6. Gerber Generation / Fabrication - Once you gain final approval by your buddy and you have looked at the board enough times to believe everything is correct, it is time for submission to a fabrication house (PCB manufacturer). The fab house will check your layout again for tolerances of their equipment to make sure they can produce what you expect of them. Check what files they require for fabrication (normally Gerbers).