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Guides/PCB Fabrication: Difference between revisions
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There comes a time when an electronic circuit just needs something a bit more permanent to be built on. That's when you will want to build a PCB. | There comes a time when an electronic circuit just needs something a bit more permanent to be built on. That's when you will want to build a PCB. | ||
== Etching in the space == | == Design == | ||
Before you can make your PCB, you'll have to design it. You'll need to do this with some CAD software - there are a few out there, some are "free" and some are free software. | |||
These packages often have quite a steep learning curve, so you may need to invest some time into learning them for the first time. | |||
=== EAGLE CAD === | |||
[[File:Eagle screenshot.jpg]] | |||
[http://www.cadsoftusa.com/eagle-pcb-design-software/product-overview/?language=en EAGLE] is a low cost, hobbyist friendly bit of software that allows you to do schematic capture and PCB design. There is a freeware version, with some limitations on what you can do. You can also buy a fairly cheap [http://uk.farnell.com/cadsoft/lsr-1ss/eagle-pcb-tool-lsr-hobbyist-1user/dp/2067881?Ntt=eagle+hobbyist Hobbyist license] to lift some restrictions (e.g. more than 2 layers, slightly large board size, more schematic pages). | |||
There are a number of tutorials available on the [http://www.cadsoftusa.com/training/tutorials/ Cadsoft website] and also [http://www.youtube.com/watch?v=qG0O9LKH-_E&feature=share&list=PLB4C63828A483E756 youtube] | |||
SparkFun have a lot of [https://learn.sparkfun.com/tutorials/tags/eagle excellent EAGLE tutorials] which can help you get started. | |||
[[Project:PCB_Design_with_Eagle_CAD]] | |||
=== KiCad === | |||
[[File:Kicad pcbnew.png]] | |||
[http://www.kicad-pcb.org/ KiCad] is an EDA software suite for the creation of professional schematics and printed circuit boards up to 16 layers. KiCad runs on Windows, Linux and Apple OS X and is released under the open-source GNU GPL v2 free of charge. | |||
The particularly useful thing about KiCad is that it is entirely unlimited, and also free. This means you can design 4 layer boards without having to buy any (possibly restrictive) software licenses. It's extremely powerful, but somewhat unorthodox. | |||
There is a full [http://www.kicad-pcb.org/display/KICAD/Tutorials Getting Started guide] on the KiCad website, as well as various tutorials on [https://www.youtube.com/results?search_query=kicad+tutorials youtube] to help you get started. | |||
== Fabrication == | |||
Once you have finished your design, you'll want to actually make the board! | |||
=== Etching in the space === | |||
The space has some etching facilities, for which you can view the instructions here: [[Pcb_etching_instructions|PCB Etching Instructions]]. | The space has some etching facilities, for which you can view the instructions here: [[Pcb_etching_instructions|PCB Etching Instructions]]. | ||
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Be warned, though, there are no tinning, through hole plating, silk screening facilities. It's great to get you by for a quick turnaround prototype, but for anything more fancy, you'll probably want to send your design off to the professionals. | Be warned, though, there are no tinning, through hole plating, silk screening facilities. It's great to get you by for a quick turnaround prototype, but for anything more fancy, you'll probably want to send your design off to the professionals. | ||
== Fabrication | === Professional Fabrication === | ||
To get that lovely shiny looking PCB you're after, you can send off the design to a fabrication house to have it made for you. | |||
==== Processes ==== | |||
===== Copper Pour ===== | |||
This is the copper which makes up your circuit. The process starts with a copper clad board, which has a thickness of copper denoted by the weight of copper spread over a 1 ft square area (in Ounces). Typically this is 1 oz for external layers, and less for internal layers. | |||
1 oz equates to 1.37 mils (thousandsth of an inch) or 0.0347 mm [http://www.pcbuniverse.com/pcbu-tech-tips.php?a=4]. The width scales up rectiliniarly, so 2 oz is twice the width of 1 oz, etc. | |||
If your design has critical dimensions for your tracks, you might want to double check the thickness available to you before starting the layout. | |||
===== Soldermasks ===== | |||
Soldermasks are a coloured coating that goes over your board that prevents solder from flowing into bits that you don't want solder to flow. Traditionally, this is a darkish green colour (which is what primarily makes PCBs look so green!) - however there are a variety of different colours available. Some fab houses will do boards without soldermasks and silkscreen cheap (or maybe even free) - but bear in mind that a soldermask is important for components with a fine pitch (SMT, mainly) as it will prevent shorts between pins. | |||
===== Silkscreen ===== | |||
This is the (usually) marking you see on the boards with component identifiers and the like. This is purely decorative, and isn't usually applied as precisely as the other layers - so you may get slight registration errors. Silkscreen has to be applied over a soldermask - it will not adhere to exposed copper or board. | |||
===== Plated Through Holes ===== | |||
When you want to get a signal from one side of the board to another, you'll need a via. This is just a pad which is drilled through to both sides of the board, with an electrical connection between the pads. If you're etching a board yourself, you'll need to make this connection yourself using a small bit of wire, or a rivet. | |||
PCB fabrication houses provide a way of electroplaying the holes (plated-through holes (PTH) [http://en.wikipedia.org/wiki/Through-hole_technology] ) such that they make the connection without needing any extra processing [http://en.wikipedia.org/wiki/Via_(electronics)]. | |||
===== Finishing ===== | |||
Once the PCB has been etched and soldermask applied, a number of different finishing processes may be used to improve the quality of the board. | |||
'''Hot Air Solder Levelling''' [http://en.wikipedia.org/wiki/Hot_air_solder_leveling] involves the PCB being dipped into a solder bath - which wets the exposed copper with solder. You can get this in tin/lead or lead-free compositions. This provides a good solderable finish, but possibly not completely flat pads (especially for large areas). | |||
'''Immersion Silvering''' [http://en.wikipedia.org/wiki/IAg] [http://www.pcbtrain.co.uk/schematic/immersion-silver-pcb-finish/] [http://www.ami.ac.uk/courses/topics/0146_imag/index.html] involves depositing a thin layer of silver onto your PCBs contacts. This produces a much flatter result than HASL, and even better wetting. But it can be a bit more expensive. | |||
==== Gerber files ==== | |||
Most fabrication houses will accept "industry standard" [http://en.wikipedia.org/wiki/Gerber_format Gerber files]. You'll need to find out how to generate these in your CAD software, and what the specifications of the files are from your fabrication house. They'll normally require a standard subset of files (layers) for top and bottom copper, silkscreens, drills and holes. | |||
Once you've generated these files, you should load them into a gerber viewer (like [http://gerbv.sourceforge.net/ gerbv]) to check them before you send them off! | |||
==== Fab Houses ==== | |||
There are a number of places which can fabricate your board, here are some possibilities | There are a number of places which can fabricate your board, here are some possibilities | ||
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=== Comparisons === | ===== Comparisons ===== | ||
For some kind of reference for comparison, here is a table of quotes for a fairly standard small board: | For some kind of reference for comparison, here is a table of quotes for a fairly standard small board: | ||
