Lynn Settles's List: Magic of Electronics Resources

• • Foam box/container with a lid; Because ammonium persulphate requires  a temperature of 60~70'C in order to effectively operate, we need to prevent  heatloss from the system.

  • Good idea here to hold in the heat.

• For the crystals used in this article, they state to mix 400g of crystals  with 1500mL of hot water. Since that'd be an excessive amount of etchant for  this project we'll actually go with 40g of crystals and 150mL of hot water (note  that the ratio is the same). You could also use 80g of crystals with 300mL of  hot water. The crystals should fully dissolve to form your etchant solution  which will appear clear and colourless.

  • Students need to know how to work with ratios to adjust the amount of etchant they will make. A math lesson is in order.

• There are only a few secrets to making really good printed circuit boards. The  first is to get everything completely clean. The second is to use a good etch  resist
• • some black Sharpie® brand permanent markers (from a stationery store)  

  • Get the regular BLACK Sharpies, not the industrial quality ones.
• From this point on, only handle the board by its edges.

• Take a loop of masking tape and tape the board, copper side up, to a piece of  cardboard (eg. the back of a writing pad). Press it down flat (but don't touch  it with your bare fingers). Now you have a handy means of handling the board and  holding it still while you draw the traces on it.

  • This will be an easy way to handle the PCB after cleaning and preparing it. It's worth taking the time to do this step.
• Any power or ground traces that are next to the edge of the board should be  extended right to the edge of the board (especially if they will be handling  motor currents).
• Microwave on high for 20 to 30 seconds
• If you don't have a microwave, put the whole bottle of etchant in a sink full of  hot water for half an hour first. Open it occassionally to relieve the pressure.

• Place the tray on a table (on some newspaper), with a 1/8" x 1/4" strip of  balsa under the middle of it to act as a pivot for rocking it. Place the board  in the tray, copper side up. Rock the tray constantly while the board etches. It  will take about 20 minutes.

  • Using a circulating pump should keep us from having to do this step.

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• The toner transfer method relies on the fact that toner, being plastic based,  will form a protective coating on the copper which is resistant to the corrosion  of the etching agent. It is therefore important that the toner coverage is  consistent and will not stick to the paper more then the copper board.

  • Very important to remember. The image must transfer to the copper for this method to work well.
• acetone, nail polish remover

  • Easy to find at Walmart or hardware stores, even Lowe's.
• When applying the iron, apply it with as much pressure as possible
• After the board has been soaked, it is time to carefully peel off the paper
• scratch off the paper either rub it off with your thumb or use a toothbrush

• After drilling the board I carefully sand off the toner. The reason for  sanding as apposed to acetone is that any sharp parts left over from the  drilling process are also smoothed. Care must be taken not to damage fine traces  during sanding. Finally clean once more with acetone, meth, or PCB cleaner.

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