MakePCBInstructions
Contents
Making PCBs yourself
Overview
You print the PCB designs on overhead projector transparency sheets using a good laserprinter (inkjets aren't black enough).
You sandwich a photoresist-covered PCB blank between the sheets and expose it to ultraviolet light.
You put the PCB in a developer solution, which removes the photoresist wherever the UV light fell.
You put the PCB in ferric chloride solution, which dissolves away the copper where the resist has been removed.
You clean the resist off the resulting finished PCB with alcohol (or by re-exposing it).
You will need:
- Double-sided photo-resist PCB (for example from RS - part number 3970160)
- A UV lamp or UV lightbox (Maplins UV lamps part number L31AF)
- Ferric chloride (RS part number 551-277)
- PCB developer (RS part number 690-849)
- A dish or plastic tray in which to do the etching
- Some mugs/jam-jars to mix the chemicals
Safety
UV light will damage your eyes and skin. Keep it in a box, or don't be in the room when it's being used. A few seconds exposure while you're setting things up won't hurt.
PCB developer is sodium metasilicate, which is bad for you. Wear gloves, don't get it on your skin, in your eyes, or in your mouth. If you do (Dimwit! What did I just tell you?), wash it away with lots of water.
Ferric chloride is less harmful (though it still is a bit - keep wearing gloves, and wash away as before if you come into direct contact); also it will stain anything that even a minute quantity of it touches (including glass and plastic) bright orange. You may want to wear a lab coat, or some old clothes.
If you do use mugs to mix the chemicals, eschew drinking coffee from them subsequently...
What you are going to do
The example we will use is the Universal PCB that is used for both the RepRap motor controllers and the extruders. It is in the KiCad project file ~your-id/workspace/electronics/Universal-pcb/stepper-and-extruder.pro. The PCB looks like this in KiCad:
The red tracks are on the obverse (component) side, and the green ones are on the reverse. Here is what you are going to make:
Printing and taping up the designs
Postscript files for both sides of the board are in the files stepper-and-extruder-Copper.ps and stepper-and-extruder-Component.ps in ~your-id/workspace/electronics/Universal-pcb/. These files were created by KiCad, and you can get it to write them again, if you want; if you modify the design you'll need to re-write them, of course. Use the KiCad mirror check-box in its print options to ensure that the two files are printed such that the side of the print with the toner is the side that will be against the PCB when it is being exposed.
Print the files on overhead projector transparent sheets on a good-quality laserprinter (as mentioned above, inkjets don't produce a black enough print). The scale in the postscript files should be right, but check it as some print drivers rescale prints to fit them to their idea of a page. The simplest way to check is to hold the pins of an 18-pin DIP socket (which you'll need to put the PIC in) against the pads on the print where it will be located. The pins should fall exactly in the centres of the holes.
Cut about 2 cm off the long side of one of the prints. Put the two prints together toner-side to toner-side and get the circuits into registration. If you have a light-box this will help, but it is quite easy to do just resting them on a white sheet of paper. If (like mine) your close-up vision is blurred by the passing of the years, use a magnifier to check that things are exactly aligned.
Without breaking the alignment tape the cut sheet to the uncut one to make a hinge:
The tape, being clear, is not very clear... So here's what it looks like with the hinge unfolded:
-- Main.AdrianBowyer - 30 Dec 2006
