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Homebrew PCBs via Toner Transfer By Alex Sum Here’s a method for the hobbyist to produce near-professional PCBs at home with consistent results. The equipment and materials required are readily available, reasonably priced and well within the capabilities of the average constructor. T he most popular way to build SILICON CHIP electronic projects is from a kit. However, not every project is available as a kit. While project components are generally readily available from component retailers, the PCB is not. Only recently has SILICON CHIP started selling PCBs and for the most part, they are mainly for recent projects. And this doesn’t help the home constructor who wants to design his own PCB. toner, so as long as you can print out a black inkjet copy AND your laser photocopier can handle film (many can’t!) you may still be in business. One other point to watch with both printers and copiers is that some do not give a true 1:1 print or copy. Obviously if the print or copy is distorted (in either direction) it may be useless for this process. Required resources You will need the following: Obviously, you need the PCB artwork. If it’s a SILICON Here’s a method of producing near-commercial quality CHIP project, download it from the SILICON CHIP website PCBs in either single or double-sided format using an image (www.siliconchip.com.au). If you are designing your own, you’ll need some CAD from a laser printer (note – inkjet printers are NOT suitable). The toner from the laser printer is transferred to a blank software for designing PCBs. This is freely available (eg, Autotrax, KiCAD, Eagle, etc), so printed circuit board and used with the method I describe below, as a resist for standard etchants. you can easily make PCBs for your Laser printer toner is mostly own projects as well as SILICON plastic particles that when fused CHIP projects. makes good etchant resist. There Access to a laser printer with are plenty of articles on the web 600 dpi resolution (or a laser explaining the theory behind photocopier). this method and I will not repeat Toner transfer film called them here. “Press ‘n’ Peel PCB film”. It’s If you don’t have a laser printer available from both Altronics (Cat but do have access to a laser Fig.1: a typical PCB artwork downloaded from No. H0770) and Jaycar (Cat No. photocopier, this can usually be the SILICON CHIP website as a PDF. It has been HG9980) as well as other sources. used – laser photocopier toner is printed “mirror image” so that it can be used This film has a special coating that not too different to laser printer with the Toner Transfer method. So what to do? 76  Silicon Chip siliconchip.com.au Fig.2: print the Universal Regulator PCB artwork first onto bond paper, then onto Press’n’Peel film. The arrow helps identify the top side of the paper before printing and also the direction of paper travel through the printer. Fig.3: you can cut blank PCB using a hacksaw and then remove any burrs with a file but I prefer to do it with a router. I made this one and it does the job superbly, with a nice clean cut and no burrs! allows printing the PCB track pattern onto the film with a laser printer and then transferring it to the copper surface of a blank PCB. A cheap A4 laminator (the ones that have synthetic rubber rollers, eg, the GBC brand or similar that retails for under $50.00). This provides both the heat and the pressure to transfer the Press ‘n’ Peel film image to the blank PCB. Incidentally, just last month Aldi stores had an A4 laminator on sale for just $16.99 . . . Suitable etchant and a suitable disposable plastic container to etch in. Ferric chloride etchant is arguably easier to use as it can work at room temperature (and may produce better results). But it is also much messier; ammonium persulphate is much cleaner but requires heating to be effective. the artwork. The example at left is the Universal Regulator Board (SILICON CHIP March 2011). The PDF file was downloaded from SILICON CHIP website by selecting “Downloads” then the month and finally the project. As downloaded, this file has the PCB pattern looking at the board from the solder side. Since we have to print this image onto Press ‘n’ Peel film and then transfer it onto copper side, we need to print it in mirror image. We also need to ensure that a positive image is printed – that is, the areas of copper are printed black and the areas between tracks (and the holes) are left white. Most graphics programs will allow you to print a mirror image – that is, as if you are looking through the PCB from the component side (some call it “flipped”). I use Photoshop Elements (a reduced, and much cheaper, version of Adobe Photoshop) to convert the file to mirror image. There are also plenty of downloads on the ’net which will also do this for you. Fig.1 shows this mirrored image. If you design your own PCB, you should be able to export Steps Artwork printout The first step in making a PCB is to obtain or produce A low-cost commercial laminator provides not only the heat but the pressure needed to transfer the laser printer toner from the Press’n’Peel film to the PCB so it can be etched in the normal way. It may take many passes through the laminator for the toner transfer process to occur. siliconchip.com.au February 2012  77 Fig.4: arguably 95% of the success of toner transfer lies in how well you have prepared the blank PCB. It needs to be scrupulously clean and once it has been done, make sure that there are no fingerprints or dust on the surface. Fig.5: the Press’n’Peel laid over the cleaned, blank PCB ready for transfer. We don’t waste much PCB or film – there’s no need to make the board much larger than about 5mm all around. the track pattern in mirror image (eg, Autotrax outputs the bottom layer in mirror image by default). Now you are in a position to print the track pattern onto “Press ‘n’ Peel” film. First, print out a copy of the track pattern from your laser printer onto standard A4 (bond) paper. The reason for this is you don’t want to waste a full sheet of Press-n-Peel, so you need to know where on the paper the image will be printed. I normally take one sheet of A4 paper and mark on it the top side and direction of paper feed (many printers “flip” the paper as it passes through). I then place this sheet into the manual feed tray of my laser printer and print the PCB image. This is also a good check that the printed size is right, that it is a positive image and that the blacks are black and there is no toner in what should be white or clear. Next, cut a piece of “Press ‘n’ Peel” film slightly larger than the actual size of the final PCB (say 3-4mm larger on all sides). Now carefully place this film with the dull side up onto the copy of the printed pattern and with 3M Scotch tape (which is usually unaffected by the heat of the printer) carefully stick the leading edge onto the paper. Place the paper into the manual feed tray again, noting your markings, and print another copy. You should now have the track pattern printed on the “Press ‘n’ Peel” film as shown in Fig.2. Ensure that the Press’n’Peel film image has no blemishes or missing toner where you want it. piece of 450x300x12mm melamine board with the router mounted upside down at the centre. I use a length of aluminium angle as an adjustable fence. I cut two 7mm wide parallel slots near the left and right edges and with the aid of 6.3mm bolts and wing nuts, I can set the distance of the fence from the router bit. I use a 3.175mm straight bit, so for clearance the diameter of the hole in the centre of the router table can be 6.35mm. Most small routers designed for edge trimming do not come with speed control. To cut blank PCB, you need to slow the speed right down. I use the SILICON CHIP (February 2009) motor speed controller to set the required speed. I set the router up to cut a depth of just under 1mm and cut the PCB with two passes. This results in minimum breakage of the router bit. I start cutting with the copper side up then flip the board over for the second pass. I use this same setup to cut rectangular holes in ABS boxes for my projects. Never throw away offcuts of PCB material, even small bits – you never know when you might want to make a board just that size! After you cut the blank PCB to size, prepare the copper surface. This step is vital; in order for the toner to adhere properly, you need a very clean matt finish on the copper surface like the one shown in Fig.4. I first clean the copper surface with isopropyl alcohol, then scrub the copper surface in random circular motion with a ScotchBrite scourer under running tap water until I get a fine matt finish. A really tarnished board can usually be cleaned with Ajax or similar and Scotchbrite but might need a bit of elbow grease. I use a clean paper tower to wipe the board dry and from now on, I wear a clean cotton glove whenever I need to handle the board, as oil from skin can stop the toner transfer from working properly. Once clean, always hold the board by the edges and do not touch the copper surface. And immediately before use, blow the surface of the board with clean air (either an air duster or filtered compressed air) to ensure there are no dust particles on it, nor minute paper particles from the paper towels. Either may affect toner transfer. Blank PCB preparation Blank PCB material is available from component retailers in various sizes. I find it more economical to purchase the larger size, 300x300mm (Altronics H0755, Jaycar HP9510). If sourcing it elsewhere and there is a choice, always choose fiberglass PCB over the older phenolic (or SRBP) type. Not only is it better electrically, it’s less brittle. Phenolic PCB material has a habit of splitting or shattering. Cut it to size as required, around 5mm larger than the final size on all sides (for double-sided board, 6-9mm larger on all sides). You can use a fine hacksaw (32 TPI) blade but it’s a slow process. Instead, I use a small router fitted to a homemade router table like the one shown in Fig.3. This setup consists of a 78  Silicon Chip Toner transfer via laminator Place the printed “Press ‘n’ Peel” film print side down siliconchip.com.au Fig.6: here’s the PCB with the artwork transferred via Press’n’Peel film and the laminator to form a resist. You might notice a couple of blemishes on the board, such as the highlighted scratch top left . . . Fig.7: any blemishes can be repaired with a standard permanent marker pen. If in doubt, touch it up! We’ve also used a marker pen to mask off most of the blank copper area around the board; it saves both etchant and time. onto the copper surface of the board. Try to centre the film so that there is bare copper showing on all four edges, then stick the leading edge to the blank PCB with Scotch tape as show in Fig.5. I sometimes add another piece of Scotch tape on the side as well to keep the film flat on the board. Allow the laminator to warm up to correct temperature. Most laminators switch on when just warm enough for laminating but leaving it a bit longer may result in a higher temperature (which you want). Pass the board, leading edge first, with film side up through the laminator as shown in the photo overleaf. The number of passes required depends on board size and ambient temperature and usually is in the order of 25 to 45 passes. The rollers on the laminator provide pressure and heat for the toner transfer process. Once the copper surface reaches the toner melting temperature, the transfer will take place. You have to experiment and start with, say, 30 passes and increase or decrease the number as required. After a while you will be able to work out what is the optimum number of passes for the various size boards. The board gets very hot after 10 passes or so, therefore you will need to wear cotton gloves to handle it. Using a laminator, I find that the maximum width of the board you can use without jamming is about 100mm. There is no restriction on the length. After the board has gone through the required number of passes, allow it to cool down to room temperature. You can now peel off the film and check the board. Sometimes fine dust particles can get between the film and copper surface and will result in tiny holes or tears, especially on the large fill areas as shown in Fig.6. You can fix this easily with a fine “permanent” marker pen (not a whiteboard pen). I also paint the excess border area of the copper surface with permanent marker (to save etchant and etching time), because that area will be trimmed off later (see Fig.7). of practice to get right and even then results can be patchy. If you don’t have a laminator . . . Second choice would be a domestic iron, set to non-steam (it’s probably a good idea to empty the water out anyway). Using the hottest setting (usually linen), slowly and methodically iron the toner onto the PCB. This takes a fair bit siliconchip.com.au Etching and drilling You are now ready to etch the board. I use a disposable rectangular plastic container to hold the etchant. My preferred etchant is ferric chloride solution (Altronics H0800). You can use ammonium persulphate (Altronics H0802, Jaycar NC4254) if you prefer. Unfortunately, it is more difficult to obtain Ferric Chloride because it cannot be sent through the post, even as powder. Ammonium persulphate, in crystal or powder form, can be mailed. The major reason I prefer ferric chloride to ammonium persulphate is I find much better edge contrast with ferric chloride. Fig.9 shows two identical boards one etched with ferric chloride, the other with ammonium persulphate, under 40 times magnification. Poor edge contrast with ammonium persulphate is due to bubbles forming during the etch process and eroding the resist. Another advantage of ferric chloride solution etchant is that it will work at room temperature. However the etching process will be quicker if a warm solution (say 30°C+) is used. Ammonium persulphate will NOT work at room temperature – it must be used at a temperature of 50-80°C (preferably the higher end of the range) so the powder needs to be mixed with hot water immediately prior to etching. I drill a small hole at the corner of the board and tie a piece of fishing line to it. This allows me to agitate the board when submerged in the etchant (agitation keeps fresh etchant flowing over the copper areas, a “must” to minimise etching time). Usually etching should take between 10 and 25 minutes to complete. Frequent checking will prevent over-etching and undercutting tracks. During the etching process, you should wear protective clothing and eyewear. Ferric chloride stains are impossible to remove so handle with due care. Fig.8 shows an etched board with toner still covering the track pattern and ready for drilling. The etched board should be thoroughly cleaned under running water to remove all traces of etchant. Re-using etchant Despite what many references and websites might say, February 2012  79 Fig.8: and here’s the result after about 15 minutes or so in the etchant. We generally use a flat tray and slosh the etchant over the board by rocking back and forth. Don’t spill ferric chloride – you’ll never get the stains out! Fig.10: if you wish, the same process can be used to transfer a component overlay to the top side of the PC board – how professional is that? Remember that the carbon tracks laid down might affect circuit performance. etchant can be used again and again. You will know when it is spent because etching times start to blow out significantly. When this happens, the etchant has absorbed as much copper as it readily can and is too weak to be useful. Used ferric chloride solution should be stored in a sealed bottle (definitely NOT any form of drink or food bottle), clearly marked as used etchant. Ammonium persulphate can be stored and re-used but as mentioned earlier, needs to be reheated to 80 C+ otherwise it won’t etch. That creates something of a problem because you can’t heat it in any sort of metal container on the stove! A friend who also etches PCBs but prefers ammonium persulphate has an old microwave oven in the workshop solely to heat up ammonium persulphate solution (OK, maybe it does heat the occasional cup of coffee). He rescued it from a council clean-up and repaired it so it cost nothing (it was, as expected, only a high voltage diode that had failed!). If and when it fails from corrosion (almost inevitable when heating etchant), he’ll throw it out and find another. time!), you end up with copper sulphate crystals that can be disposed of quite easily (eg, place in a plastic bag, wrap in newspaper and place in the garbage bin). Etchant disposal Drilling For small holes (0.6 to 1.5 mm), I use a 12V drill with a pin vice chuck. For larger holes I use a small drill press. Small HSS (high speed steel) drill bits are available in hobby shops and component suppliers. Do not remove the toner until you are ready for soldering, as the toner will protect the tracks and pads from oxidation. You can use fine steel wool to rub off the toner later when you are ready to solder. Most PCBs are designed with component holes of 0.8mm with larger component lead diameters of 1.0 or even 1.2mm. Mounting holes, screw holes for component tabs etc are generally 3mm. Fibreglass PCBs, though much preferred over the older phenolic type, unfortunately blunt drills much faster so you need to keep a few spares on hand. Component overlay I use the same toner transfer process to put a component Do not pour spent etchant down the drain. Even if you overlay on the component side of the board. I print the top think it’s lost all of its “oomph” it can – and will – attack overlay in mirror image onto “Press ‘n’ Peel” film, then use any metal drain fittings it finds. Given enough time and the same method as above to transfer it to the component enough etchant, you will be up for a costly plumbing repair. side of the board. It is likely to take more passes because the Neither should you pour it out on the ground – it is very fibreglass side of the board will not get anywhere near as likely to poison the soil. hot as the copper side. I mix spent ferric chloride Fig.10 shows the composolution with cement and nent side of the board with dispose of it when the cethe component overlay . ment dries. An alternative Since Autotrax uses very in many areas is councilfine line width for top overlay arranged paint and chemical print out, it is difficult to have collections. 100% complete toner transSpent ammonium perfer. However, there is enough sulphate solution is easier detail to show component to get rid of as it becomes a Fig.9: the reason I prefer ferric chloride etchant, Here is a orientation and values. Eagle 40x magnification of the same section of two boards, the bright blue copper sulphate one on the left etched with ferric chloride and the one on should do a better job and solution. will be my preferred CAD the right with ammonium persulphate. The right board If you let all the water shows clear signs of undercutting and less precise edges tool when I finish converting evaporate (it takes some (even though it may well be usable). my Autotrax custom library. 80  Silicon Chip siliconchip.com.au Fig.11: double-sided board are possible with this system; the only major difficulty is accurate alignment of the two sides. We use the “pins through the board” method and normally make the pads a little larger to compensate. A quick spray of circuit board lacquer (Altronics T3086, Jaycar NA1002) will give extra protection for the component overlay. Double-sided boards Fig.12: speaking of pins through the board, here’s the opposite side artwork being positioned as close as possible. board is ready for you to do the toner transfer. If you are designing your own double-sided board, you may want to make the pads larger (say 20% bigger) as the film alignment method described above may not be 100% accurate. Commercially made double-sided boards have platedthrough holes to electrically connect the top and bottom layers where required (they’re called “vias” in PCB-talk); this homemade version obviously does not have these. Therefore, when the board is finished, you will need to solder some lengths of tinned copper wire between the top and bottom layers for the pads which need to connect to each other. In some cases component leads also need to be soldered to both top and bottom layers. With some care, you should be able to produce doublesided boards as well. You need extra care when preparing the copper surface to make sure there is no contamination of the surfaces. You will need to print both top and bottom layers onto “Press ‘n’ Peel” film and cut the blank PCB bigger on all sides, which enables easier alignment of the two pieces of film. You will also need to print out a copy of the drill guide (or drill drawing) onto tracing paper. Place this guide on the blank PCB and tape down with scotch tape as show in Fig.13. Finishing the board Drill two 0.65mm diameter holes diagonally opposite near the corners. Make sure the drill is at right angles with the Clean and trim the board to its final size when you are board (use a drill press if you have one) and use very fine about ready to solder in the components. First trim it with sand paper to remove any burrs from the two holes. a fine hacksaw then finish off and de-burr with a suitable You can then prepare the copper surfaces for toner transfer. file. It helps to have the PCB clamped in a vise between I also make tiny scratches at the corners of the top layer so two pieces of timber as you cut it. that I can identify it for placing the correct film later. Clean the toner off the board with fine steel wool and Align the top layer film with toner side facing down onto then wipe the board with isopropyl alcohol. Apply a the top layer and use pins to quick spray of circuit board position it over the two holes lacquer and allow the board drilled earlier. to dry. Circuit board lacSecure the leading edge of quer protects the tracks and the film with Scotch tape as pads from oxidation and it shown in Fig.11. You can now contains solder flux to aid use a small pin and punch a soldering. tiny hole in the centre of the Conclusion corresponding pads on the bottom layer film. Turn the This method enables the board over and use the two hobbyist to produce protopins to get the bottom layer type quantity PCBs at home film into the correct position with ease. as shown in Fig.12. After some practice, you Once in position, you can will be able to make nearsecure the leading edge of the Fig.13 not all drill positions are shown on a double-sided professional-quality boards. film with tape. board so a printout of drill positions and sizes is made and In fact I make a PCB for all After the film is secure, pull taped to the board before drilling. That way you don’t have my projects, no matter how out the two pins and the blank to keep flipping the board over to get drill positions! simple. SC siliconchip.com.au February 2012  81