Adjust the Layout of Components on PCB
The layout of a PCB can be very important so I always lay the components out as they are in the circuit diagram to begin with. Instead of circuit symbols I draw the component pins. The drawing is made with a pencil on 1/4″ squared paper. The compnents are then “shuffled around” with a pencil/eraser to get a compact layout. Each square of the paper represents 0.1″ so resistor leads are spaced 4 squares appart for horizontal mounting or one square if mounted vertically. Draw lines between tracks and try various compinations that don’t require tracks crossing. The drawing should be viewed from the top component side of the board.
Remove each component and mark the holes in the stripboard with an eraseable felt-tip marker. Clamp the stripboard over the copperclad board and a sheet of flat wood to form a sandwich with the copper clad board in the middle and the copper side DOWN. Drill through all the holes marked with the felt tip pen, and the copper-clad board will be drilled with perfectly regemented 1mm holes for your components. On the copper side of the copper-clad board, join the dots with a DALO or other etch-resist pen. Clean off the stripboard and re-use it for the next project. The PCB is etched in the normal way.
RF PCBs can be made very simply when they are to be used for VHF Power Amp’s up to 10 watts or so. These boards nearly always have square or rectangular pads for the RF conductors. Measure and mark the copper where you want the track to be and stick SELLOTAPE (UK), DUREX (Australia) SCOTCH TAPE (rest of the world) where you want the copper to be. Make certain that there are no air-bubbles under the tape. Using a sharp knife (or scalpel) and ruler, cut around the tracks and remove unwanted tape. This will leave you with tape on the copper in the positions you want the tracks. Use a DALO pen if you need to add the odd thin track. Etch the PCB as usual.
Put the copper-clad board in the oven, pre-heated to 120 degrees Celcius and drop a small lump of candle wax in the centre. Remove the board and allow it to cool whilst keeping it horizontal. The wax is a good etch-resist, so just scrape away the wax where you do NOT want the copper to be. A flat modelling chizel-knife (Xacto etc) is ideal for this. You can use a ruler and felt-tip pen on the wax without damaging the wax surface. Etch the PCB as usual.
Expose the PCB in a custom made printing frame. Build up a sandwich of (top to bottom) glass, artwork, copper-clad board and a bit of chip-board (wood). The artwork must be inky-side down. The copper-clad board must be sensitive side up. Expose for 2 HOURS 10cm from an 18 watt DAYLIGHT flourescent tube. You will have a even and uniform exposure if you position the tube over one side of the board for 1 hour, then the other side for the other hour. If you have access to a UV light box with two 8-watt tubes then 5 – 6 minutes is all that you will normally need.
Whatever method you have used to create your artwork on the copper foil, you must now etch it. Place the board with resist in a vertical tank filled with etchant solution (normally 1/2 Kg Ferric Chloride to 1 liter of water). The board should be totally emersed and vertical. This will ensure that bubbles are allowed to rise and the sedement is allowed to fall. I usually support my boards using plastic clothes pegs (clothes pins). My etching tank is a stout plastic bag in a wooden former. The front of my tank is replaced with perspex sheet so that I can see the board etching. You could of course use a plastic “tupperware” type of bowl, but you will need constant agitation or to float the board on the surface of the etchant. Etching is complete when all the unwanted copper is dissolved. Wash the board thoroughly after etching is complete.
When you first put the board in the tank the copper will turn a dark colour where it is exposed. If bits of WANTED copper turn dark then the board may be removed, washed and touched up with a DALO pen. If UNWANTED copper stays nice and shiny then the board may be removed, washed, and carefully scraped free of the grease or resist where it should not be.
The board will normally etch within 15 minutes, less if the etchant is warm during etching. Save etchant for re-use on the next PC board in a tightly stoppered bottle. When the etchant is almost exhausted the etching time is increased. If etching takes longer than two hours then adding a little salt to the etchant will speed it up a little.
Mix together 1-part Hydrochloric Acid (HCl), 1-part Hydrogen Peroxide (H2O2) and four parts of water (H2O). Place the board in the solution copper-side up. Etching is completed when all the unwanted copper has been dissolved. This usually takes about 2 to 3 minutes. Small splashes of any of these liquids on clothing will cause holes to appear and will also burn skin. Wear rubber gloves and use photographic tongs to handle the boards. The fumes can also cause damage so use in a well ventillated area and a fan to take fumes away from you. Never try to store ready-mixed etchant – it gasses and blows bottles apart. If you should try this method you will find it is clean, cheap and quick but you have to be a little carefull with it.
