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| Member Modding Tips and Guides Here is where you can share your modding techniques and tips. New threads will be placed in an approval queue before posting to make sure that only legit guides are posted. |
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06-March-06, 08:41 AM
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| Apex Techie I  |  A guide to making PCBs by laser printer transfer I posted this picture not all that long ago, ‘cause I was fairly pleased with how the PCB had turned out. * * * **  There was some interest in a guide to doing this, so here we go. I’ll go through the process I’ve used from start to finish. I apologize for the less-than-stellar pictures. I don’t have a digital camera, so I had to use the one on my phone. The Circuit The goal in the beginning was just to create a fader for some LEDs so I could get ripple water effects behind a frosted window, or just fade between 2 LED colors to add some interest to my mods. I started in the usual place…Google, and after a little looking, I found Bill Bowden’s page. He’s got some good stuff on there, including this nice, versatile circuit for fading lamps or LEDs on off a 12V power source. http://ourworld.compuserve.com/homepages/Bill_Bowden/page6.htm#eyes2.gif Perfect. Having found the circuit I was going to work with, I had a choice. I could go out, buy a resist pen, and make a PCB (since I wanted my own board), or find some software to help me design the PCB. I really want to keep the controller as small as possible, so I found this software. www.expresspcb.com I’ll be writing this with my modified design. I put the first board together, and like many first runs, it didn’t work…it made a horrible snapping sound, and that was that. I figured what I’d made was too small for me to hand solder safely, and I hadn’t allowed enough room for some wires. The pictures from here on out are of my improved, second run at this circuit. To save production money, and because I now know I can print the traces small enough, I’ve chosen surface mount components for my transistors and op-amp IC. The Express PCB package comes with 2 programs, a schematic and a PCB designer. This ends up being very helpful. You lay out your schematic, make all the connections, and make sure everything is correctly labeled, then you can link this to your PCB design. My schematic looks like this:  Doing this allows you to make sure that all the connections you need to make have been made because the software will highlight all the pins a selected pin is suppose to be connected to. Double checking your circuit becomes a snap. Here’s an example tracing down the connections for pin 11 out of my 14 pin quad op amp:  The pins highlighted in blue all need to be connected. If you follow the traces here, you’ll see that I made allowances for a wire jumper to get all these joined…sometimes you need to do this if you’re working on a single sided board. The program comes with a decent library of built in components, or you can create new ones if you have the dimensions and know the pinning. I used a trace twice as wide as the default, because I wasn’t sure how small I was realistically going to be able to etch. It can be important to remember that you will be transferring a mirror image of your circuit. If you aren’t using surface mount components, this is not a problem, as you’ll be mounting them on the opposite side of the board, thus making the pattern correct. It you are using surface mounts, be sure to flip the components on their axis to get the pin mounts in the correct place. If you look at my example, pin 11 is highlighted. Normally this would be pin 4, but I’ve flipped my op amp IC left to right to position it correctly when the pattern is transferred. I’ve also left a lot more space on this pattern than I need to. I did this to account for my clumsy soldering. If you’re good or have a needle solder tip you can make your patterns very tight. Testing the circuit I ordered all my components online, since our only real electronics store here seems to be Fry’s, and they are not that well stocked. When I had everything, I hooked it all up on a testing breadboard, and made sure everything functioned as I wanted it to. No problems here…Bill’s circuit worked as advertised. I used regular, rather than surface mount components for breadboard testing. Some of what I needed is still on backorder, so the pictures at the end of this guide are not of the complete device...bits are missing. Making the PCB Another online search produced several possible ways to etch my PCB. I decided to go with a method using transfer paper from Pulsar (www.pulsar.gs). It was advertised as very fast, accurate, and easy. It’s a little pricy, but not bad. You will need: A laser printer A PCB (I used a single sided 1/32†thick CU since it seemed a good starter) An iron Pulsar transfer paper A hard surface to iron on Scotch tape Pulsar green TRF foil First,. Print out your PCB on to the transfer paper (PCB Express will print just the copper traces to scale). You have to use a laser printer…ink jet will not react with the transfer paper, only toner. Pulsar says you can also print to regular paper, then photocopy to the transfer paper. I set my printer on the darkest settings possible to get the best lines I could. I used Adobe Acrobat to make a 9 board per page printout so I would not waste the expensive paper. This is a good thing, as getting the transfer just right was harder than they indicated on Pulsar’s web site.  Cut your copper clad board to size (a little larger than your pattern) and clean it. To clean the board, I used a Scotch-Brite type plastic pad. The idea is to get all the oxidation off so you have a nice, shiny exposed copper surface. I used a 1/32 inch single sided board for this circuit. You can use thicker cladding (1/16 inch is standard) or double sided boards, but this is a simple circuit, and a simple guide. You can use these techniques to do double sided boards…just drill your through holes after printing the first side, line up the printout for the second side on these holes, and transfer the second side. Next, cut the pattern out of the transfer paper. Turn your iron up about ¾ of the way and let it warm up. The Pulsar website has a guide to calibrating your iron for the transfer. This is best done on an iron with an area without steam holes. I happened to have an old one and a newer one, and found that the older one works much better due to it having fewer steam holes…these will create areas that are not heated under pressure. To transfer the pattern to your board, place the pattern face down on the copper, and press down with the hot iron for 30 seconds. When I say “press hard†I mean put a lot of weight behind it. I used my kitchen countertop to do this because I figured it would be heat resistant enough to not be damaged, while being strong enough to support the pressure I was applying. If your iron has holes, you may want to shift the iron and repeat this to try to get rid of any cold places created by the lack of contact caused by the steam holes. It may be helpful to tape the pattern to the PCB so it doesn’t shift. Using a soft cloth beneath the board will also help prevent slippage. As the toner is softened by the hot iron, the paper may slide on the board. You don’t want this to happen, as it will smear your lines, and ruin the transfer. Use just a little tape, because too much tape will create a barrier that water can’t easily get under, and you’ll have trouble in the next step. If you do happen to smear your lines, you can just scrub the transfer off the board with your abrasive pad or remove the bad transfer with acetone, and start again…you won’t be wasting the board, just the transfer printout.  Let your board cool to room temperature (just takes a minute or so). Place the board and paper (should be stuck together at this point) into a shallow dish of water. Let it soak for about a minute, then remove the paper. It should come right off. It should also leave behind the PCB pattern on the copper board. Check your pattern and make sure it is a good transfer. You may be able to make some repairs with a resist pen if there are places the transfer didn’t stick completely. It’s up to you to decide if you’ve made a good enough transfer. If you are happy, proceed. If not, repeat the process until you get a good transfer. My best advice in getting a good transfer is to be very careful with the ironing. Do your best to not let the paper move while the iron is on it, and try to use a spot on the iron that has no holes for steam. It will probably take you a few tries to get a good transfer. Pulsar does sell a starter kit ($99 as of this writing) that includes a laminator they recommend that is suppose to give clean transfers all the time. I have not tried this with a laminator, but I can see how it would make the process much easier and quicker. A look at the first picture below shows that this needs some work with the resist pen to clean it up. The second picture is after some quick work with the pen.   Applying the TRF Foil The next step is to apply the green TRF foil to the board. This step could potentially be skipped, but doing it will make for a much cleaner etch. The foil will cover the transferred toner, and close any tiny holes and unevenness that might etch through. Place the PCB face up on a cushioned surface over a hard surface. Place the foil (dull side to the copper) over the PCB, and tape the whole group to your hard surface so it won’t move. I used a dish rag for the soft surface, and my kitchen counter again for my hard surface. The soft surface is to keep everything from sliding. Do your best to remove all wrinkles from the foil before you apply heat.  Using your iron again, on a low to medium setting, apply pressure for 20-30 seconds. To make sure you got everything, you can run the iron across the backside of the foil perpendicular to the length of the foil. You should be able to see the traces come through the foil.  Carefully peel back the foil from the board. If you see any black, pull the foil back over the board (so it’s lined up the same), and run the iron over that spot again. I’ve found that it’s not super critical to get the green covering absolutely every bit of black, but the more you cover, the better. If you did any repair with a resist pen, the foil will not stick to this. That’s OK…just make sure your repair work is nice and dark. Clean off any extra green or black with a que tip and some rubbing alcohol or turpentine (be careful not to mess up any of your traces if you do this.) It’s ok to leave a bit of extra green…as long as it isn’t going to short your traces. You can probably get this to etch away since it won’t be stuck to toner.  Etching and Tinning What you’ll need: Ferric Chloride solution (you can make this from powder or buy as solution). Liquid Tin (or some other tinning product) Plastic container for FeCl solution (do not use metal) Plastic tray to etch and tin in (do not use metal) Plastic container to store used tinning solution (do not use metal) Latex gloves Safety glasses Plastic bags Sponge Old clothes Paper towels The first thing you’ll need to do is mix up some FeCl solution if you’re starting with powder. There are some important things to remember when working with this chemical:
FeCl solution is generally very safe…the most hazardous part of the whole PCB process in making it from powder. A little care here is important. To mix FeCl from powder, follow the powder manufacturer’s instructions. Wear old clothes, as FeCl stains permanently. I use a plastic refrigerator water holder to store my solution because it’s safe to mix it in this, and it is easy to dispense the correct amount from the spigot. For my powder, I add a pint of water to the container, then gradually add my powder and mix. Enough heat is generated to cause the water to steam, so be careful. Make sure all the powder is dissolved. If you have premixed solution, you’re already good to go.  If you don’t have your old clothes on yet, get in them…that FeCl does stain. Place to PCB in your plastic tray, and put just enough FeCl solution in there to cover the board. Agitate the tray. I hand shake mine for a few minutes. Do it gently, you don’t want to splash the solution. You should be able to see the copper start to etch away where your green foil is not covering. For stubborn spots that don’t seem to be etching nicely, or to make sure you get everything out of the tiny pin holes for your components, run a sponge across the board in the solution…this should help remove any stubborn copper. Be careful doing this. On the board pictured in this guide, I scrubbed too hard with the sponge, and etched away some of my traces. The etching process should take a few minutes. If your solution turns very black, you may need to freshen it up. The whole etching process should take from a minute to 5 minutes on a 1/32 board…perhaps longer for thicker copper.   I just transfer my used FeCl back to my main container when the board is etched. You can reuse solution until it stops being effective. It should then be disposed of as hazardous waste. If you used a sponge, wring the solution out of it, and seal it in a plastic bag. Use paper towels for clean up as needed. Rinse your etched PCB in warm water to remove any remaining FeCl. You can then scrub the foil, toner, and any resist pen repairs off with your plastic scrub pad, or if you want to be more careful, wipe it all away with a paper towel wet with acetone. You want a clean, shiny, oxidation and toner free surface for the next step. You will want to tin the board. This will help keep the copper traces safe from oxidation. I use Liquid Tin to do this, but there are some other products out there as well (Pulsar recommends a silver powder, but it seems a bit expensive to me). Have your gloves and safety glasses on. Clean out your plastic tray, and put your etched, cleaned PCB back in it (copper side up.) Pour enough liquid tin the tray to just cover the board. Leave the board in the solution for 5 minutes (or whatever your liquid tin manufacturer’s instructions recommend.) Pour the spent tin solution into a container for later disposal (as hazardous waste), rinse off your PCB and clean everything up. You should have a fully tinned PCB at this point.  Repair As I mentioned before, I messed the board I was using for this example up a little. I was to rough with my sponge while etching, and etched away some of the traces. I also had some that were almost disconnected. This is not the end of the world…repairs can be made. The picture below shows the board after post-etch rinsing. You can pretty clearly see some of the places the traces were etched away. To fix very small gaps, I just joined and filled in the area with solder. For larger gaps, I used a conductive paint from a auto rear window defroster repair kit. I could have also used silver conductive paint or copper strip tape that is sold at electronics stores for this specific purpose.  Here’s the repaired board…not attractive, but it will work if you mess up like I did.  Drilling Holes For Your Components and Finishing You will need: A drill press Tungsten carbide micro drill bits Safety goggles/glasses The holes for your components will be very small. You will break bits very, very fast if you don’t use a drill press, or something to keep your drill very steady. If you don’t use tungsten carbide bits, PCB boards will dull your bits very quickly. Wear your safety glasses when drilling. I purchased this set of bits on Ebay for about $25.  Use the size bit that looks best for your holes. I generally use a 0.03†bit. Go slowly here…you will break fewer bits, and end up with more accurate holes. You’re working on a small scale, so a magnifier may be helpful here. Be careful with your hands. These tiny drill bits are sharp and dangerous. They will happily drill through flesh and bone if your get your fingers in the way. The drill bits may bind a bit when they poke through the bottom side of the board and cause it to pull up…if you go slowly, this will be minimized. If you don’t you increase your chances of damaging the board or breaking a drill bit. In the picture below, my finger is right next to the drill bit for scale…no forced perspective here.  Here’s the board once it was drilled.  Once you have all your holes, you can overcoat the board with a transparent paint if you want. This looks more professional, and provides an extra layer of oxidation resistance. The paint will burn away from where you solder, so it will not interfere with contact. First picture below is the painted side. The second picture is the backside. See how much more professional this looks?   Now, just solder your components on, and you’re done. If using surface mount components, pre-solder your pads, line up your component, then stick them to the pad with your iron. Fast is good here, because your components can be damaged by the heat of the soldering iron. There are plenty of guides out there that cover good soldering technique.   You should end up with a professional looking electronic component that is small enough to be useful for modding. I hope this guide has helped you. Feel free to mail me any questions via the PC Apex forums, or at grue@darkstarpc.com. | |
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