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Make PCBs with Laser Engraver Making PCBs at home is an attractive option as you can go from a design to a board in less than an hour, thus reducing the time needed to go from a prototype to the final version. But most of the well-known methods are tricky and/or messy. This one is easy and reliable. You just need a laser engraver or cutter, which are surprisingly inexpensive! M aking your own PCBs is popular with many hobbyists. This has been fuelled in recent years by the widespread availability of low (or no) cost, easy-to-use PCB design software. While designing a PCB is now relatively easy, turning beautiful layouts on the screen into equally attractive, ready-to-use PCBs is a far more demanding challenge. Methods used by hobbyists range 36 Silicon Chip from hand-drawn PCBs using a spiritbased marker pen, photographic image methods using special photographic film or laser/ink-jet printed transparencies, UV light tables and photosensitive PCBs, schemes using domestic irons or heated roller laminators to heat-transfer laser printed artwork to bare PCB, and various CNC milling methods. Others with greater mechanical skills have modified an ink-jet or laser printer to print their layouts onto Australia’s electronics magazine blank PCB directly. Except for CNC milling, all of these methods also require chemical etching and subsequent cleaning, drilling and trimming to complete the PCB. Each approach has its advantages and disadvantages. Hand-drawing a PCB is only really suitable for the most basic designs, so we will only consider methods involving computer-aided design (CAD). These are summarised in the table opposite. siliconchip.com.au a Low-cost or Laser Cutter by Andrew Woodfield The photographic method usually involves printing a PCB layout onto transparent film with a laser printer. A blank PCB is covered by a photosensitive layer (or purchased complete with this photosensitive layer) and exposed to UV light passed through the layout artwork. The PCB is then developed to expose the copper to be etched, and the PCB etched in the usual manner. This method yields very high-quality PCBs. However, some of the chemicals and good light exposure equipment can be relatively costly. Larger PCBs may be difficult to make since these require an even light distribution across the layout film. The process is also fairly time-consuming. In recent years, the CNC method has become popular for PCB prototyping. A CNC milling machine with a V-shaped cutting tool cuts the layout onto a blank PCB. The process is fairly slow compared to other methods, and machine vibration and V-cutter wear can quickly lead to poor results. You need very flat blank PCBs, a flat milling bed and suitable clamps to get good results (see Fig.2). Plus it produces a lot of dust. Milled PCBs can also require considerable post-processing to produce adequate results. Tiny copper whiskers left by the V-cutters can be very time-consuming to locate. Recent improvements such as bedlevelling software and USB interfaces have made PCBs somewhat easier to make with this method, and the cost of small milling machines has reduced in recent years. Such CNC systems can give excellent results, and one significant advantage of this approach is the avoidance of chemicals in the production process. Other popular hobbyist methods include the heat transfer method or modified printers, both of which can give good results. However, the variability of domestic irons, temperatures and pressures can lead to mixed results for many (we’ve had many frustrating failures with this approach). Similarly, few have the time or ability to modify an ink-jet or laser printer to achieve the excellent results possible with direct printing to PCBs. In any case, many hobbyists have drifted away from making their own PCBs, the result of very low prices for small quantity ready-made PCBs from PCB manufacturers. The quality of the vast majority of these PCBs is very high. Method Equipment needed Setup Time & Cost Production Method Production Cost Post Production Photographic Pre-sensitised PCB, PCB developer, UV light box  Printing or exposure, spraying, developing, etching – Moderate Rinse clean, PCB drilling and trimming  Rinse clean, PCB drilling and trimming – Can be good with care Can be timeconsuming   Good Low (Noisy) Slow  Depends on etching chemicals  Heat transfer CNC milling Domestic iron or heat roller / laminator CNC milling machine with a flat bed and holding clips, cutting bits Moderate Low to moderate Printing, heat and pressure, chemical etching   CNC milling  High Modified printers Modified ink-jet or laser printer Commercial production    None Nil Laser engraver or cutter, spray paint  Laser Engraver siliconchip.com.au   Moderate (too difficult for many) Moderate Low to moderate  Moderate (V-cutters, mill bits, drill bits) Direct printing to PCB Low Chemical or hand clean, PCB drilling and trimming Third party  Nil  Low to moderate Paint, laser engraving, chemical etching  Low to moderate Quality & Resolution   High Good   Very good Chemical or hand clean, PCB drilling and trimming Australia’s electronics magazine  Good Environmental Impact Time to Make One PCB Depends on etching chemicals  OK  OK Vendordependent (Can be high) Depends on etching chemicals  OK   Slow (delivery)  OK December 2020  37 Fig.1: this is the sort of result that can easily be achieved using the laser engraving method. The only real defects that you could complain about here are the result of my lessthan-perfect drilling accuracy, which has nothing to do with the laser! The major disadvantages are the waiting time – anywhere from a few days to six weeks – and the potential for waste. If you only need one or two boards, the shipping costs can be much more than the cost of actually making the boards. And if design errors are subsequently discovered, you have to pay for another shipment and then wait all over again. Exploring other options In an effort to make reasonablequality prototype PCBs more quickly and easily, and to obtain better firsttime results from PCB vendors for larger quantities, I spent some time looking for a better solution. A laser engraver looked like a suit- Fig.2: milling a simple PCB with a hobby-level PC-controlled CNC mill. While this can undoubtedly produce usable results, without needing any chemicals, it’s a slow, noisy and dusty process and you need to do a lot of tweaking to set it up properly. Our attempts to do this in the past have been stymied by blank PCBs that were not perfectly flat. able candidate because these provide a very high degree of accuracy and reliably recreating an image transferred from a PC with little fuss. The problem was then how to use them with a blank copper-laminated PCB, as they are not really designed for working with metal. Laser cutters and engravers These come in a variety of sizes and powers. Chinese-made equipment dominates the low end of the market. The largest and most powerful types use glass-tube CO2-based laser cutters built into desktop fully enclosed cabinets with top-opening covers, fume extractor fans and hoses for water cooling. Fig.3: a highpower ‘K40’ cabinettype laser cutter. This is similar to the one we have at SILICON CHIP. Ours is bigger but also a bit more crudely constructed. One of the best things about these devices is how accurate they are, and how good the repeatability is. Once they are set up, they work very well indeed. 38 Silicon Chip Australia’s electronics magazine Laser power outputs claimed by vendors for these “K40-type” basic laser cutters range from 40W to over 100W (see Fig.3). The 40W lasers will cut through 6-8mm thick plywood, and they also work well with acrylic plastic sheets. These machines typically cost around $AU1000 including delivery, and often require another $200 or more spent for water pumps, vent pipes, repairs and additional items to make them safe and ready for use. More recently, solid-state laser engravers at much lower powers have appeared. Laser power ranges from 1W to 10W, and they are made in either a ‘square frame’ or ‘crane arm’ arrangement (see Figs.4 & 5). In this latter type, the stepper motor balances the weight of the laser at the far end of the arm. Both have a small controller board fitted to the outside edge of the frame or onto a vertical side panel. Both feature USB interfaces and are supplied complete with a small laptop-style power supply, Windowscompatible laser software, and, usually, a pair of safety glasses. A few sample scraps of thin plywood and acrylic for initial testing are also usually included. It was these latter inexpensive low power laser engravers that appeared to have the most potential for PCB prototyping. They offer a simple solution to optically ‘write’ the layout onto a blank PCB. Prices for engravers with 5W lasers are relatively attractive, at under $AU250 including delivery. This outsiliconchip.com.au Fig.4 (above): a low-cost ‘square-frame’ laser engraver. They typically use solid-state lasers in the range of 1-10W. 5W is a good figure to aim for if you want to make PCBs. Fig.5 (right): a low-cost ‘crane arm’ type laser engraver. It’s more compact and probably cheaper than the square-frame type, but may not offer quite the same speed or repeatability. put power was claimed to be suitable for cutting 1-2mm card or timber veneer. Of course, the larger and more expensive fully-enclosed laser cutters are also very suitable, and are more flexible devices. But if you only want it for making PCBs, it’s hard to justify that extra cost. Engraving copper with a laser Blank PCBs are made by bonding a thin copper layer onto one or both sides of a low-cost phenolic or highercost fibreglass panel. The most commonly used “1oz” (1 ounce) PCBs have a copper layer which is 1.4 mils (thousandths of an inch or thou) thick. In metric terms, that’s 36µm or 0.036mm. At first glance, it seems like it would be child’s play just to blast this ultrathin copper layer off the board using a laser. Unfortunately, the thermal and optical properties of the PCB’s copper layer make this impossible to achieve directly with sub-100W laser power outputs. Much of the laser energy is (dangerously) reflected and scattered by the bare copper. The energy that does heat the copper is efficiently dissipated by the thin copper layer on the PCB. Copper vapourisation is undoubtedly achievable with high-power 5kW and 10kW industrial lasers, but such equipment is well outside the price range of the average hobbyist. The solution to this is to employ a two-stage process. First, a layer is applied to the copper which can be accurately engraved by the inexpensive, low-power 5W laser. A subsequent standard chemical etching process can then remove the unwanted copper. A useful outcome of my effort was the ability to make PCBs during and after the COVID-19 lockdown, when siliconchip.com.au international PCB production stopped and shipping was halted. It turns out that a ‘suitable layer’ can consist of almost any type of spray paint. The cheaper the paint, it seems, the better the result. Of the various spray paints I have tried to date (six different brands), all were easy to apply and give good visual coverage of the copper. Usefully, as it turns out, the cheapest paint has the worst adhesion. Just one layer of paint is sufficient. When the paint layer is removed by the low-power laser, clean copper remains. In one set of tests, the paint was left to dry for the recommended minimum recoat time (one to two hours) and the laser still completely removed all residue. If, however, the painted PCB was left for several days, the paint bonded much better to the copper and this occasionally resulted in a residual layer which the laser did not remove. Tests also showed that darker paints gave better results than lighter colours. The low-power lasers very effectively removed colours such as black, dark grey, dark green and navy blue. White spray paint can be used, but the laser is noticeably less effective. Increased laser power or repeated engraving runs are required. Also, the level of reflected laser light increases significantly, which could potentially be dangerous. Incidentally, there was no practical difference found between gloss and matte paint. Once the laser hit them, the surface finish of both paint types was instantly removed. For completeness, standard plastic model enamel paints, the type that comes in tiny paint cans, were also tested. These were applied with a small modelling paintbrush. These paints appeared to have significantly better surface adhesion. Coupled with the variation in layer thickness Fig.6: a negative of my PCB layout, without any infill. By negative, I mean that the tracks are white and the blank space is black; the opposite of what you usually get when you export a PCB design from ECAD software. Fig.7: the same layout as Fig.6 but with infill. This ‘floods’ the unused area with copper, meaning that the laser and chemicals need to remove a lot less material from the blank PCB to give you a usable design. As a bonus, if you connect the infill area to ground, it might also perform better and radiate less EMI. Testing spray paint Australia’s electronics magazine December 2020  39 Fig.8: a blank PCB after I applied a single coat of cheap black spray paint. I leave them to dry for 1-2 hours before moving onto the laser etching stage. caused by a brush application, they were not as easy to use, although PCBs produced this way were (just) usable. Suggested procedure The following procedure was developed for use with a 5W laser engraver. It was operated on power levels between 60% with the cheapest paints and 80% for other paints; running this laser at full power (100%) appeared to ‘bake’ the paint onto the PCB. Using this 100% power level at higher writing speeds would also almost certainly give identical results to the 60% and 80% tests, as long as your engraver motors are reliable at these speeds. You will need to do some testing yourself for your paint and your laser to find the ideal settings. Laser power outputs as low as 2W will work, but may require repeated engraving passes. More expensive 7W, 10W and 15W solid-state laser modules are also likely to be successful, probably with much lower power settings. If you change the paint you use, these tests will almost certainly have to be repeated. Left-over PCB scraps are ideal for such tests. Here are the suggested steps for making the PCB: 1. Export the PCB layout in a suitable format from your PCB design software. 2. Prepare the blank PCB. 3. Load the layout into the laser engraver. 4. Check the layout is correct, ie, size/scale, inverted, mirrored. 5. Configure/check the laser engraver settings. 6. Place the blank PCB under the engraver and check the image borders. 7. Engrave the PCB. 40 Silicon Chip 8. Clean any residue from the PCB 9. Etch, drill, trim and clean the PCB. Now let’s expand on those steps. 1. Export the PCB layout When designing the layout, use the widest possible tracks, and set the diameter of all drilled holes to 20mil (0.5mm) or 25mil (0.635mm) diameter to act as centres for manual drilling later. These settings help to compensate for the limited beam focus of these cheap lasers, plus any undercutting during etching. Similarly, if possible, maximise the layer infill to retain most of the copper. My layout software calls this ‘automatic ground plane’ (or you could manually add a ground plane). This feature speeds up the laser engraving process and the subsequent etching, as less copper has to be removed and smaller amounts of the chemicals are consumed. The PCB layout must be exported as a negative and mirrored image. A negative image is necessary because the laser is turned on when the image is black and turned off when the image is clear or white. Most PCB design software exports an image assuming the coloured trace shows where the conducting copper will be left. Similarly, almost all PCB layout design software assumes you are looking down on the component side of the PCB. The mirror image is required because the laser engraver assumes the image it is burning is as seen from the solder side of the PCB. Figs.6 & 7 show what the required files look like. When infill is not used in the layout software, the result is like Fig.6. The black area to be removed by the laser is much greater than in Fig.7, where infill is used, so the result in Fig.7 is preferable. Most laser engravers can accept a wide variety of file types. JPG or BMP are usually the easiest to use. However, the laser engraver software does seem to ignore image dimensions and Fig.9: I downloaded the software for my laser engraver from the supplier’s website. It is very easy to use. Here, the PCB image to be engraved has been loaded, and initial settings can be confirmed or adjusted. Australia’s electronics magazine siliconchip.com.au scaling set in layout software so carefully check this just before engraving (see step 4). 2. Prepare the blank PCB Clean the PCB. Use a mildly abrasive white liquid kitchen surface cleaner and wash off any residue cleaner under the tap. The copper should be clean enough to etch immediately. Spray the copper side of the PCB with a single coat of your selected spray paint. All the copper should be covered evenly (see Fig.8). Allow to dry for the manufacturer’s minimum drying time; 1-2 hours is typical. 3. Load the layout into the laser engraver Manually locate the engraver’s laser in the correct location if necessary (see Step 6). Connect the USB cable to the computer and power up the engraver. Start the engraver software and load the image. An example screenshot for such software is shown in Fig.9. 4. Check the layout is correct Check (again) that the image shows the tracks as white against a black background, and the image is mirrored. Most laser engraver software also allows you to invert and mirror the image at this point. Check the image size reported in the laser engraver software matches what you are expecting. This may not match the edge-toedge PCB size used in the PCB layout program. If not, adjust the scaling. 5. Configure/check the laser engraver settings These will vary depending on the software supplied with the engraver. It will, almost certainly, allow configuration of the laser output power, the writing speed, the image resolution to be used for writing by the laser, and the time spent on each point. As a suggested starting configuration, the following are the author’s configuration: Mode: Line (or raster) mode This writes the image as a series of Laser safety Fig.10: checking placement of the surface to be engraved using the ‘range review’ mode. The visible laser dot races around the edges of the design, so you can verify that it’s the right size and it is correctly located on the PCB surface. ‘continuously-on’ lines rather than a sequence of laser ‘dots’ or ‘points’. Power: 80% Speed: 1000mm/minute Resolution: 10 dots/mm Engraving Time: 10ms These must be determined for your laser and your spray paint. Start with the default settings provided by the laser vendor or those shown here, which are for a 5W 410-480nm laser. To determine the best laser settings, I designed a small 30 x 30mm sample PCB layout for testing. I tested various power, speed and engraving time settings, one by one, to find the best result. In each case, the paint was applied to the bare PCB, and the laser engraver operated to engrave the layout. The result of each test was evaluated, the paint removed, and fresh paint applied for the next test. Mineral turpentine usually removes the paint quickly, with the occasional assistance of an abrasive stainless steel pad from the kitchen. I didn’t bother etching it until a satisfactory laser engraved result was obtained. So, if your engraved PCB from your first try with this method is not satisfactory, just scrub off the engraved paint, spray on a fresh coat, and have another try. This is a simple, quick and effective method without having to Lasers, especially those at the power levels discussed here, can be very dangerous. You must not look directly into the laser light at any time. Safety glasses with a suitable rating for the laser light MUST be worn during operation. I have seen some serious doubts expressed over the suitability of the safety glasses shipped with some of these laser engravers. Suitable safety glasses which meet accepted standards are available in most countries. While the price for these glasses may appear high, at around AU$150, they will prevent damage to your eyesight from accidental laser exposure. So they are worthwhile. siliconchip.com.au toss away a pile of poorly etched PCBs! 6. Checking the laser focus and borders If you are using an engraver which lacks an enclosure, now is the time to put on your laser safety glasses. Usually, the laser engraver will initialise with the loaded image centred at the current location of the laser. This is its location when the laser engraver’s power is turned on. Place the prepared blank PCB under the laser engraver. It is not necessary to fix the PCB in place but larger PCBs, say over 50mm in any dimension, may require the laser engraver to be firmly attached to the bench or table. This is an optical process and stepper motor vibration, if any, does not appear to move the PCB. However, your engraver may not be as obliging. Double-sided adhesive tape or pinboard tacks should be adequate in such cases. The laser module has a small latching pushbutton to start the laser in a ‘preview/low power’ mode. Turn on this low power switch. Check that the laser is correctly focused on the surface of the PCB. Then turn off the latching low power switch on the laser head. This step is essential. If you forget to do this, the laser will faithfully try to engrave your layout One possible supplier of such glasses in Australia is www.lasersafetyglasses.com.au Neither Silicon Chip nor the author have any association with this company. Each reader must confirm the suitability of any safety glasses purchased. Make sure they are suitable for the specific laser and the intended use. Otherwise, then you’re better off buying a fully enclosed laser engraver or cutter with a lid safety interlock switch, but those cost even more than the proper safety glasses. Australia’s electronics magazine December 2020  41 Fig.11: for your first few designs, or a particularly critical one, it’s a good idea to do a test print on cardboard to check for scaling accuracy, PCB dimensions and component clearances. Just make sure you run the laser at reduced power with cardboard; you aren’t trying to cut through it! during the next step with something like 1% of the normal laser power. That will not work very well. Next, check the layout is correctly located on the prepared PCB. Start the ‘Range Preview’ mode using the engraver software. The laser engraver will now show the boxed outline for the image it is about to write (see Fig.10). This outline is repeated continuously by the engraver, to allow manual adjustment of the PCB location. This is carried out at low power. Even so, wearing safety glasses is strongly recommended. Make sure all of the image falls in the correct location on the prepared PCB. Also, check (again!) that the image size is correct and in the right place. Stop the ‘Range Preview’ mode using the engraver software. It is sometimes useful to run a ‘test print’ to double-check the board dimensions before engraving a PCB. In this case, you can use a scrap of cardboard of similar thickness to the PCB and use a laser power setting of, say, 10%. This will burn the PCB layout onto the cardboard to allow final confirmation of measurements, component clearances and pad sizes before engraving the actual PCB. An example of this can be seen in Fig.11, a PCB for a VHF FM receiver. This was for a larger 120mm x 50mm board. 7. Engrave the PCB Start the laser engraving process using the vendor-supplied PC software. It usually has a large bright ‘Start’ icon on the screen for this purpose. You may wish to have a fan running during the engraving process to encourage good airflow around the laser engraver. The vapourised paint fumes are almost certainly harmful. This process is not one for the kitchen 42 Silicon Chip or bedroom – definitely head for the workshop or garage. Avoid looking into the laser light. It’s tempting to watch progress, but the laser light can cause significant damage to your eyesight. Protective glasses are vital, and even with these, avoidance is best. Be aware, too, that the very bright laser light can reflect off the etching paint and any walls and ceiling of the room being used. Reflected laser light may also be a hazard to those with sensitive skin. In any event, the engraver does not need any attention during the process. It will stop and turn off the laser when it is complete. A fan will often continue running on the laser module throughout and after the procedure. The vendors don’t mention this, but leaving it running for a minute afterwards to cool anything hot is probably a good idea. 8. Clean any residue from the PCB Once the process is complete, the software will turn off the laser and return it to the starting position. The power to the engraver can now be turned off. It’s now safe to pick up the board to see the result. You will likely see the surface covered with a clear outline of your layout submerged in a thin layer of fine grey or black dust (Fig.12). Lightly brush this dust off the surface of the PCB with a small 12mmwide paintbrush. Tapping the bristles directly downwards on the surface removes any ash-like powder from the surface. The PCB is now ready for etching (Fig.13). Note, though, that it’s possible that after brushing, there will be a faint near-transparent residual layer left after the laser etching. This only happened for me when using relatively expensive spray paint, when the paint was left to dry for several days, or when the laser power was too low, or the writing speed was too high. Using cheaper paint helps to avoid this problem, as do higher power levels or slower writing speeds. This thin layer can be hard to see. Careful continuity measurement across the layout of these exposed copper areas with an ohm-meter or a buzzer will show it to be a remarkably good etch-resist. Don’t use super-sharp pointed probes for this test; rounded ones are best. Just gently lay them on two separated engraved areas of the layout which are electrically connected. If your PCBs have this layer after engraving, and different settings fail to resolve it, don’t worry. It’s not difficult to remove. Bunch up a few paper tissues into a ball, and dampen these with a little mineral turpentine. Carefully, and lightly, wipe the surface of the PCB. One or two wipes is sufficient. Wait for the surface to dry and retest with your ohm-meter or buzzer. If Fig.12: you can just make out the slightly dusty engraved layout on the surface of this PCB. Australia’s electronics magazine siliconchip.com.au Fig.13: the layout is much more clear after carefully brushing the dust away. you are getting good conductivity, you are ready to proceed to etching. If not, try another careful wipe. The idea is to wipe off just this unwanted residual layer while leaving the etch-resistant painted layer unaffected. If you press too hard with the tissues or repeat it too many times, the paint may also be removed. Again, that’s not a huge problem. You just have to repeat the whole ‘clean-paint-engrave’ process. The PCB has not been damaged, and a new paint layer will allow you to have another try at the procedure. 9. Etch, drill, trim and clean the PCB The PCB can now be etched in the usual manner. I mix 20% hydrogen peroxide (H2O2) solution and 30% hydrochloric acid (HCl) solution in equal parts; just enough to cover the PCB. The etching usually takes one to two minutes. I use a small 12mm-wide foam pad brush with a timber handle to help wash the etchant across slower-to-etch areas. Other etchants can be used equally successfully and are arguably less dangerous. However, other etching chemicals may require heating (ammonium persulfate – (NH4)2S2O8) and/or take considerably longer (eg, ferric chloride – FeCl3). The paint appears equally impervious to any of these chemicals. Fig.14: the PCB after it has been chemically etched and the paint removed with mineral turpentine. sharp beam focus from these low-cost solid-state laser modules. The quality of these lasers varies, as you might expect. This method does support SMD layouts as well as a reasonable range of PCB sizes. The laser retains good focus and performance across the engraving span of the equipment purchased. The author has successfully produced over two dozen different PCBs over the past five months for a variety of projects with this method. It now takes about half a day, much of that time spent cleaning and painting the blank PCB, then waiting for it dry. The process of laser engraving, etching, cleaning, drilling and cutting to size averages about 1-2 hours per board depending on size and complexity. That time certainly beats the Results One of several PCBs made while this article was being prepared can be seen in Figs.1, 14 & 15. The resolution of the process is reasonably close to the best hobbyist or in-house photographic methods. It’s limited only by the ability to achieve a siliconchip.com.au Fig.15: the completed PCB, trimmed to size and drilled by hand. Australia’s electronics magazine delivery time for any of the low-cost PCB vendors. The process could be used to make double-sided PCBs, but I have not attempted that to date. There is no inherent reason why it should not be possible. Similarly, the procedure works with both fibreglass and very cheap phenolic PCBs. There was no sign of any temperature damage or heat marks on the phenolic material. The costs of this process are not as low as some other methods, such as the domestic iron thermal transfer approach. The cost of the laser engraver and safety glasses must be considered. But arguably, it will give more consistent results. The chemicals used are relatively cheap, but some can be difficult to obtain in some locations. You certainly can use this process to make your own boards for less than it would cost you to buy them (mainly because of delivery costs). Without a doubt, commercial manufacturers deliver excellent quality PCBs, but the wait is considerably longer. This laser-based approach also allows layout design errors to be identified quickly. Then, rather than throwing 5-10 commercial PCBs away, a single PCB is binned and another PCB is ready the next day. If you are looking for a better or faster solution for making prototype PCBs, you should try this method. It’s a very good cost-effective solution, and once you’ve figured out the parameters to use, it’s very straightforward to repeat. Just don’t forget those safety glasses! SC December 2020  43