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Is this the forum formerly known as the Electronics Forum? I sure hope so.
Some discussion in the Hammond Forum has come up recently about making PCBs. I thought I would post my technique here. I have been using and refining this since I was in high school; it's how we did thinks in electronics lab.
Materials Needed
- Ammonium Persulphate crystals
- Water
- Copper-clad PCB
- Drill press
- Tungsten-carbide PCB drill bit kit
- Laser Printer (or photocopier)
- Regular printer paper
- Access to a sink
- #000 steel wool
- Masking tape
- Iron
- Pyrex pie plate with resealable lid (never cook in again)
- Toaster oven (kitchen one is okay)
- Aquarium air pump
- PCB layout software
Layout with ExpressPCB
The software I use is http://expresspcb.com/ExpressPCBHtm/...d_software.htm .. This software can produce drawings for the fab facility that Express PCB uses, or it can "print preview". I haven't done this in a while, but IIRC the procedure is basically, lay the schematic you want to build out using ExpressSCH. Get happy with it. Then make a new PCB in ExpressPCB and link your schematic to it. Lay each part out on the screen, remember to use the netlist feature to insure that your layout matches your schematic. If you want to make a single-sided board (recommended), just use a double-sided board and only put components on one side. Then you can use a via and a trace on the other side help you jump over traces in your layout and keep things tidy. When it's time to build the board, just use a jumper wire on the back of the board in place of a trace. This also means you don't have to figure out how to plate vias...
Now that you have laid your PCB out in ExpressPCB, you need to get it out of there. Print just the copper on the back side of the board. I used some kind of print driver to give me a TIFF file, you could probably also print to PDF etc. Then I load the file up in Photoshop and get rid of the dots, by using "select by colour" or something like that. Then I can touch up the board in photoshop, write my name on it or whatever, turn it into a black and white (no grey!) image and flip it to make it a mirror-image. Also, make sure the image will print out at the correct size, you may need to play with Image->resize and a calculator. For best results, do not change the number of pixels, just alter the DPI. Next, I print the image out on my laser printer (MUST be laser). If your printer or print driver has settings for how much ink to use, set it as dark as it will go, you want as much ink on the paper as possible.
Make sure that whatever layout software you use that the copper lands have the holes for the pins in them, you will need this to guide your drill later.
Transfer etch-resist pattern to PCB
Pull the PCB out of the package and lightly "sand" the copper with #000 steel wool in criss-cross directions. Now you take your mirror-image of the copper, and tape it, face-down, to the copper side of the PCB. The ink will be transferred to the PCB and wherever the ink is, copper will stay. I like to use 1/16" copper-clad FR4 epoxy PCBs with 1 Oz copper coating, such as MG Chemicals #506. A 4x6" board costs $7.
Now, get your iron, and make sure there is NO water in it. Plug it and set it on the hottest temperature (wool/cotton/linen?) that it has. Make it gets really really hot. Now, iron the paper onto the PCB. Push down really hard, and iron until you scorch the paper light brown. Now, we go over to the sink and simply wash the paper off the PCB with cold water, leaving the ink behind. Use your thumbs to help. Don't worry about leaving paper hairs in the ink. Do worry about getting all of the paper off between traces, in copper land holes, etc.
If you somehow screwed up the iron-on process and there problematic traces, you can fix them with a Sharpie. Use lots of ink. Or an expensive etch-resist pen, your choice. :)
Making an etching tank
An etching tank is just a place to hold etchant. It will work faster, and you will get better results, if you have a way of agitating the tank and warming the etchant. I use a Pyrex pie plate (you can't use anything metal) to hold the etchant, and I warm it by sitting it on top of the toaster oven. Actually, a Black and Decker Toast-R-Oven. Put it on broil, sit the dish on top of (not inside) the oven and it will keep the etchant around 25-30C. That's plenty. A hot plate, anything like that will work.
A fish tank air pump can be used to agitate the solution. Rig the plastic hose up so that it makes bubbles that cross the PCB. Remember to put the pump above the tank so that tank doesn't drain into it.
You will want something to get the PCB out of the water that is not metal. You can drill a hole in the PCB and put a string in it, or you can use a couple of plastic forks..whatever. Even your hands will work if you wash them right after.
Etching the PCB
So, you mix up your etchant and put into the tank..you want a couple of inches of etchant in there. Measure the water you used and figure out how many crystals to use based on the container. Remember 1000mL of water (4 cups) weighs 1Kg (2.2 lbs). If you have a buddy with a "postage" scale that would come in handy. I used a balance made out of a piece of dowel and a ruler, with a measuring cup full of water for weight. Once you figure this out once, write it down. Crystals last a long long long and if the water evaporates, just add more water. You will notice after a dozen boards or so that etching is starting to get slow...that is when it is time to change the etchant.
The etchant I use is MG Chemicals #410. A 1Kg container will make about a hundred hobby boards. Maybe more, depends on your board layout (hint: large ground planes leave copper behind - the more copper you leave behind, the fresher your etchant will be)
Mix your etchant (see above), drop the board in. Turn on the heat and the bubbler and wait awhile, but not too long. The board is done when all the copper that is not under the ink is gone, but before the ink has been eaten through.
Drilling the PCB
Use tungsten carbide drill bits in a drill press. The bits are very delicate and do NOT like any lateral motion. They are also very sharp and will make quick work of your PCB. Remember, etch your boards so that the holes in the lands are already clear of copper. Lower the drill with your right hand and position the board with the other. Use a sharp, tungsten-carbide PCB drill bit, and use your hand on top of the PCB let it wobble a bit. As you lower the drill, the hole etched in the land will center the drill bit if you get your left-hand pressure just right.
I use a Mastercraft drill press..works really well, worth a couple of hundred bucks. You can get fake drill presses that work with your corded drill for $30. They work okay. A dremel drill press with a foot control work probably work well, too. A proper drill press is especially nice because the light and the shadow of the drill bit help to guide it, improving your accuracy. I've never tried one of those laser-guided jobbies.
Silk screen layer
Print the silk screen layer from Express PCB. Repeat the process we used for the copper side, but iron onto the bare side of the board this time. To line up the paper accurately, poke holes in two or three vias, and use the drill holes to line everything up. If you have paper hairs in the ink, you can lightly sand with #000 steel wool, or just colour them black with a Sharpie
Remove the resist
Steel wool until it is gone...
That's it. Now you are ready to stuff with components and solder! Some people like to tin PCBs...I generally don't bother.
Some discussion in the Hammond Forum has come up recently about making PCBs. I thought I would post my technique here. I have been using and refining this since I was in high school; it's how we did thinks in electronics lab.
Materials Needed
- Ammonium Persulphate crystals
- Water
- Copper-clad PCB
- Drill press
- Tungsten-carbide PCB drill bit kit
- Laser Printer (or photocopier)
- Regular printer paper
- Access to a sink
- #000 steel wool
- Masking tape
- Iron
- Pyrex pie plate with resealable lid (never cook in again)
- Toaster oven (kitchen one is okay)
- Aquarium air pump
- PCB layout software
Layout with ExpressPCB
The software I use is http://expresspcb.com/ExpressPCBHtm/...d_software.htm .. This software can produce drawings for the fab facility that Express PCB uses, or it can "print preview". I haven't done this in a while, but IIRC the procedure is basically, lay the schematic you want to build out using ExpressSCH. Get happy with it. Then make a new PCB in ExpressPCB and link your schematic to it. Lay each part out on the screen, remember to use the netlist feature to insure that your layout matches your schematic. If you want to make a single-sided board (recommended), just use a double-sided board and only put components on one side. Then you can use a via and a trace on the other side help you jump over traces in your layout and keep things tidy. When it's time to build the board, just use a jumper wire on the back of the board in place of a trace. This also means you don't have to figure out how to plate vias...
Now that you have laid your PCB out in ExpressPCB, you need to get it out of there. Print just the copper on the back side of the board. I used some kind of print driver to give me a TIFF file, you could probably also print to PDF etc. Then I load the file up in Photoshop and get rid of the dots, by using "select by colour" or something like that. Then I can touch up the board in photoshop, write my name on it or whatever, turn it into a black and white (no grey!) image and flip it to make it a mirror-image. Also, make sure the image will print out at the correct size, you may need to play with Image->resize and a calculator. For best results, do not change the number of pixels, just alter the DPI. Next, I print the image out on my laser printer (MUST be laser). If your printer or print driver has settings for how much ink to use, set it as dark as it will go, you want as much ink on the paper as possible.
Make sure that whatever layout software you use that the copper lands have the holes for the pins in them, you will need this to guide your drill later.
Transfer etch-resist pattern to PCB
Pull the PCB out of the package and lightly "sand" the copper with #000 steel wool in criss-cross directions. Now you take your mirror-image of the copper, and tape it, face-down, to the copper side of the PCB. The ink will be transferred to the PCB and wherever the ink is, copper will stay. I like to use 1/16" copper-clad FR4 epoxy PCBs with 1 Oz copper coating, such as MG Chemicals #506. A 4x6" board costs $7.
Now, get your iron, and make sure there is NO water in it. Plug it and set it on the hottest temperature (wool/cotton/linen?) that it has. Make it gets really really hot. Now, iron the paper onto the PCB. Push down really hard, and iron until you scorch the paper light brown. Now, we go over to the sink and simply wash the paper off the PCB with cold water, leaving the ink behind. Use your thumbs to help. Don't worry about leaving paper hairs in the ink. Do worry about getting all of the paper off between traces, in copper land holes, etc.
If you somehow screwed up the iron-on process and there problematic traces, you can fix them with a Sharpie. Use lots of ink. Or an expensive etch-resist pen, your choice. :)
Making an etching tank
An etching tank is just a place to hold etchant. It will work faster, and you will get better results, if you have a way of agitating the tank and warming the etchant. I use a Pyrex pie plate (you can't use anything metal) to hold the etchant, and I warm it by sitting it on top of the toaster oven. Actually, a Black and Decker Toast-R-Oven. Put it on broil, sit the dish on top of (not inside) the oven and it will keep the etchant around 25-30C. That's plenty. A hot plate, anything like that will work.
A fish tank air pump can be used to agitate the solution. Rig the plastic hose up so that it makes bubbles that cross the PCB. Remember to put the pump above the tank so that tank doesn't drain into it.
You will want something to get the PCB out of the water that is not metal. You can drill a hole in the PCB and put a string in it, or you can use a couple of plastic forks..whatever. Even your hands will work if you wash them right after.
Etching the PCB
So, you mix up your etchant and put into the tank..you want a couple of inches of etchant in there. Measure the water you used and figure out how many crystals to use based on the container. Remember 1000mL of water (4 cups) weighs 1Kg (2.2 lbs). If you have a buddy with a "postage" scale that would come in handy. I used a balance made out of a piece of dowel and a ruler, with a measuring cup full of water for weight. Once you figure this out once, write it down. Crystals last a long long long and if the water evaporates, just add more water. You will notice after a dozen boards or so that etching is starting to get slow...that is when it is time to change the etchant.
The etchant I use is MG Chemicals #410. A 1Kg container will make about a hundred hobby boards. Maybe more, depends on your board layout (hint: large ground planes leave copper behind - the more copper you leave behind, the fresher your etchant will be)
Mix your etchant (see above), drop the board in. Turn on the heat and the bubbler and wait awhile, but not too long. The board is done when all the copper that is not under the ink is gone, but before the ink has been eaten through.
Drilling the PCB
Use tungsten carbide drill bits in a drill press. The bits are very delicate and do NOT like any lateral motion. They are also very sharp and will make quick work of your PCB. Remember, etch your boards so that the holes in the lands are already clear of copper. Lower the drill with your right hand and position the board with the other. Use a sharp, tungsten-carbide PCB drill bit, and use your hand on top of the PCB let it wobble a bit. As you lower the drill, the hole etched in the land will center the drill bit if you get your left-hand pressure just right.
I use a Mastercraft drill press..works really well, worth a couple of hundred bucks. You can get fake drill presses that work with your corded drill for $30. They work okay. A dremel drill press with a foot control work probably work well, too. A proper drill press is especially nice because the light and the shadow of the drill bit help to guide it, improving your accuracy. I've never tried one of those laser-guided jobbies.
Silk screen layer
Print the silk screen layer from Express PCB. Repeat the process we used for the copper side, but iron onto the bare side of the board this time. To line up the paper accurately, poke holes in two or three vias, and use the drill holes to line everything up. If you have paper hairs in the ink, you can lightly sand with #000 steel wool, or just colour them black with a Sharpie
Remove the resist
Steel wool until it is gone...
That's it. Now you are ready to stuff with components and solder! Some people like to tin PCBs...I generally don't bother.
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