A PCB (Printed Circuit Board) for the KMA28
This is my first attempt to use a self made PCB for my audio panel. To make PCB's, all you need is: A computer) preferably a CAD program), a laser printer, copper clad board (Conrad), etchant, a clothes iron and some glossy photo paper. You can buy special film for making PCB's, but it seems that photo quality glossy paper for inkjet printers gives good results.
The lay-out I designed for my audio panel is not exactly as the lay-out of the real KMA28. I also added indicators/leds (6 on the right side of the panel) to have the squawkbox3.0 indicators for on-line flying. More info on this: http://squawkbox.ca/doc/sdk/fsuipc.php
I used a CAD program to first place the components (first picture). The
second picture also shows the contacts (I used different layers in my CAD
program). It is easy if you use the standard grid of 2,54 mm.
Above: Position/ lay-out of the components
After placing the components I tried to optimize the wiring. I used different colours/layers for switches/ leds/ ground etc.
Wiring/PCB structure (not last version)
some of the components
Copy the design on the copper board
Use a laser printer to print the image on the glossy side of the photo paper. Clean the copper clad board with very fine wet sandpaper. Dry the board thoroughly. Make sure that the board is clean and free from fingerprints.
Place the photo paper face down on the copper clad board. Use masking tape to hold the paper in position. Don't use vinyl tape. Place the board on a flat surface. You will be using a very hot iron, so don't use the dining room table.
Use a hot clothes iron to transfer the track pattern from the paper to the copper board. Don't be afraid to use lots of heat and pressure.
Allow the board to cool. Don't be tempted to lift the paper. Put the board in a container full of warm soapy water. After about twenty minutes the paper will begin to dissolve and disintegrate.
Carefully remove the paper from the copper board. Rinse under a cold tap to remove paper residue (not last version).
You may need to touch up any broken tracks with an etch resist pen (I bought one at Conrad: Edding 780).
Etching the board
Etchant is just a polite word for a very strong acid that can desolve copper metal. Etchants are quite safe to use, provided appropriate care and handling is observed. So please be very careful).
This paragraph is not meant as an etching instruction, it is just an overview. If you want to etch yourself, do research and prepare thoroughly.
Etching is where the excess copper is removed to leave the individual tracks or traces as they are sometimes called. There is a lot of info on the web regarding etching (search for : Etch PCB, e.g.: http://www.headwize.com/projects/garbz2_prj.php, 5 Bears Engineering - PCB Creation, Thomas Gootee’s Easy PCB Creation or Printed Circuit Techniques)
There are 2 popular etchants: Ammonium Persulfate and Ferric Chloride. Both are effective.
I use Ammonium Persulfate ((NH4)2S2O8) ; etch temperature approx. 40-50°C.
Ammonium Persulfate comes as a white, crystalline powder which dissolves readily in water. Mixing the solution is easy and when mixed with water appears to be a water clear, colourless, odourless solution
During the etching process, the solution will turn a turquoise blue and precipitate a turquoise crystalline powder (especially at lower temperatures). This blue precipitate can solidify in the bottom of the etching tank or tray and can be extremely difficult to get rid of. If this water-clear solution gets on your clothing, it will appear to be just a "wet spot", but when you wash your clothes the area contaminated will literally dissolve, leaving huge holes. Use of gloves and apron are mandatory due to the damaging properties this etchant has to clothing.
Above: etching in progress, Copper is removing.
All copper removed (above), remove the etch resist with some acetone (result below).
Dry the board. Use a 0.8 or 1.0 mm drill to make the holes for component leads.
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