PCB Fabrication
From Bob's Basement
Contents |
[edit] Introduction
Making your own PCBs is great for your own homebrew projects. Whilst there are many methods available to allow you place a layout on a PCB, the one we discuss here is perhaps the most popular for the electronics hobbyist capable of producing quality boards at relatively small cost.
[edit] Method Overview
Assuming we have already prepared the artwork and it is available on the computer, the first step is to print this onto a sheet of acetate (transparent film) using a laser printer. We then select a suitably sized piece of single-sided photo-resist PCB and in as much darkness as possible, remove the protective film and place our acetate artwork facing the correct orientation onto the exposed side of the photo-resist PCB. If possible, attach some tape on an empty part of the artwork to fix the acetate to the photo-resist PCB. We then place our photo-resist PCB along with the affixed acetate artwork upside down on a sheet of glass beneath which is a UV lamp. Turn on the lamp, avert your eyes from the light and turn it off after about 5 minutes. The UV creates a chemical change in the photo-resist coating on the areas which were exposed (i.e. between the solid tracks on the artwork).
The next stage requires the use of two chemicals to remove two layers of our copper clad (photo-resist) PCB. The first layer to be removed is the softened portions of the photo-resist. We use an NaOH (or similar) developer solution to achieve this and this is then followed (after rinsing) with a Ferric Chloride solution to etch away the exposed copper.
After final rising, this leaves us with a board comprising copper tracks representative of our original artwork.
[edit] Materials
- UV Light-Box
- Single-sided photo-resist PCB
- 1x Glass container and 1x Plastic container
- PCB Developer Solution
- PCB Etching Solution
- Transparencies (Acetate)
- Laser Printer
- Dremel Drill (0.8mm and 1.0mm bits)
[edit] Process
[edit] Producing The Artwork
This guide will be using the gEDA suite of tools. Have a look at the gEDA guide for more info on using the electronic schematic and PCB design tools. On Debian and friends, installation of gEDA can be done as
# apt-get install geda geda-utils pcb // untested
[edit] UV Exposure
In this step you will expose the photo etch PCB to UV light, which will remove the light sensitive etch resist ink when you develop it. The areas where the etch resist is developed away (areas not exposed to light) will not be protected from the Ferric chloride and the copper will be etched away.
- Print the PCB artwork on a transparency (tracing paper will do, and is substantially cheaper than acetate).
- Place the transparency onto the glass place, face down.
- Obtain the photo etch board and peel off the side you wish to etch onto. Ensure there are no pieces of dirt between the transparency and the board, or the image will be out of focus and inaccurate.
- Place the PCB onto the transparency, using whatever registration marks or holes you have arranged.
- Shut the lid or cover the UV light box, and turn on the light. The length of time to expose the PCB for depends on both the power of the bulb and the type of photo etch PCB, however a guideline is approximately 2 minutes.
[edit] Developing
In this stage you will remove the etch resist from the PCB.
- Pour enough developer into a plastic container to immerse the PCB.
- Take the PCB and place it into the developing solution.
- Leave the board for a few moments.
- Use a soft sponge or brush to wash away the dissolving etch resist.
- You will see the design becoming more clear. You want to continue washing away etch resist until you see a coppery shine on the background
TIP: If you see a defect in a track where the etch resist has been removed where it should not, you can patch this up using an etch resist pen.
[edit] Rinsing 1
- Place the board under a running cold tap and brush away the developing solution.
- Leave the board to dry in air on a drying rack before etching.
[edit] Etching
In this step you will remove the copper from the non-track areas of the PCB.
NOTE: The etching solution is 'corrosive', and really really shouldn't get spilt, especially on you. Use safety precautions like goggles, gloves and, preferably, a lab coat.
PS: This is all just theory at the moment as I (naxxtor) have not done this practically yet! Please check this over and remove this notice
- Ensure the PCB is fully dry.
- Pour enough etching solution into the 'glass' container to immerse the PCB.
- Gently lower the PCB into the etching solution with stainless steel tweezers.
- Leave for x ammount of time, and them remove.
[edit] Rinsing 2
This step we will rinse and dry the PCB, ready to drill.
- If a rinsing solution is recommended, use it to rinse the PCB - otherwise run under a tap for about a minute using stainless steel tweezers.
- Leave the PCB to dry on a rack, or use a hair drier to dry.
[edit] Final words
- Whilst both the developer and etchant can be reused multiple times, when the time does come to dispose of the chemicals be sure to dispose of them properly as they are both extremely hazardous.
- DO NOT reuse your containers for cooking or anything other than PCB fabrication.
- DO NOT stare at the UV lamp no matter how groovy it looks.
- Wear a face mask if you are trimming a large piece of PCB to fit your artwork as FR4 boards which contain glass will throw particulates in the air and you don't want to breathe these in.
- Ensure that any steps requiring the use of chemicals is performed in a well ventilated area otherwise your brain WILL go screwy.
[edit] Disclaimer
Bobs Basement bears no responsibility over accident of injury. Do it at your own risk.
