Often, when making circuits, it can be nice to put your finished project on a printed circuit board(PCB). Making single sided boards is easy enough, but sometimes a circuit is too dense or complicated for all the traces to fit on one side. Enter double sided boards. They are actually much easier to make than one might think, provided that you don't rush through the process. In this instructable, I will show you how to make double sided PCBs easily, and somewhat quickly.
Step 1: Materials
Things you will need:
Strip of 2-sided copper-clad board. The size of this will depend on the size of your layout.
Paper. You don't need anything fancy. Just get basic gloss photo paper.
Tape. Scotch tape works fine.
Sponge. I use a potter's sponge (available cheaply at art supply stores), but any type of sponge will work.
Ferric Chloride. Available at most Radio Shacks.
Light Box. Optional, but very useful. If you don't have one, you can make one easily, or use a window on a sunny day.
Drill Press. You really don't want to use a hand held drill.
#60 Drill Bit.
Acetone. This will dissolve toner in a hurry.
Scotch Brite Pad. Buy a lot of these. They wear out.
Rubber Gloves. You really don't want to get ferric chloride on your skin.
Safety Glasses. Need I say more?
Step 2: Print Your Board
I won't tell you how to lay out a board. If you want to learn, SparkFun has a great tutorial.http://www.sparkfun.com/commerce/tutorial_info.php?tutorials_id=109
Put your photo paper in to a laser printer. Most printers have a setting for the density of the toner. Turn that all the way up, and print your boards. Check to make sure they printed correctly, things are mirrored correctly, etc.
Step 3: Cut and Register Board Layers
Cut out your two layers. Leave at least 1/4" around the board on three sides. Leaving the other side longer is good.
Now, turn on the light box. Place the bottom layer facing up, and the top layer facing down. Line them up so that all the pads are aligned evenly. Then tape around the edges and draw a box outlining the board dimensions.
Take the two pieces of paper off the light box, and tape them down to a piece of copper board. Now, drill the registration holes. You should drill at least three holes in an asymmetric pattern around the edge of the box. The holes should go through the paper and the board. Un-tape the paper and board.
Step 4: Toner Transfer
It's time to transfer the image off the paper, and onto the board. This requires a clean board. As you can see, mine was pretty oxidized. Use a scotch brite pad to scrub it clean. Do not use steel wool. It will wreak havoc on your board. Once it's nice and shiny, rinse it off and blot with a clean cloth. Don't touch it. the oils from your skin will interfere with the transfer. Let it dry completely.
Find the side of the board that has holes that match the ones on your copper board. Line it up so that all the holes are aligned. The light table is helpful when doing this. Once aligned, tape two sides so it won't move. Heat up the iron. Put it on the hottest setting. Then iron over the paper, pushing down hard. You have to push down really hard. Do this in 30 second bursts for five to six minutes. When you're done ironing, run the board under cold water until it's cool. then peel off the paper. Rub it with your finders until there's no paper left on the board. That should be easy, as usually not much sticks.
Step 5: Etching
I use the sponge method of etching. It's not really that difficult, and is much faster than tank etching. It also has the nice benefit of allowing you to etch one side at a time. You'll want to use a utility sink, and a tub.
Before you do anything, put on your safety glasses and gloves.
Soak your sponge with water. Then squeeze it out. Do that four times. Then, put your sponge into the tub, and pour about a tablespoon of ferric chloride into it. Begin to wipe the board with the sponge. Don't scrub, just wipe. The copper should start disappearing very quickly. Keep going until you have etched a satisfactory portion of your board. Then rinse the board under running water until all the ferric chloride is gone. Wash out the sponge, making sure to use lots of water. Such a small amount of ferric chloride diluted with so much water is OK to put down your drain. Get rid of your gloves, or wash them off and reuse them if you like.
Step 6: Repeat
Repeat steps 4 and 5 again to do the other side of the board. That's it for etching. Now all that remains is to drill the board, cut it out, and get rid of the toner.
Step 7: Drilling
This is probably the simplest part. Put the #60 bit in the chuck of your drill press, and make sure it's centered. Then drill. Make sure that you go slowly so you don't blow out the pads on the bottom. It is also a good idea to have a piece of smooth wood underneath to drill into. I use a piece of 1 1/2" MDF.
Step 8: Finishing Up
All that remains is to cut the board, sand the edges, and get rid of the toner.
Cutting is easy, just be careful, wear safety glasses, and don't cut the traces or pads.
Sand the edges to smooth them out. 120 grit sandpaper works well.
Take some acetone, and wipe down the board. The toner should be no more.
And that's it! You're done!
This is my first instructable, so please feel free to tell me what you think.