pcbetching
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pcbetching [2015-11-09 18:49] – [Developing] Fix typo miek | pcbetching [2022-07-22 22:12] (current) – [Flux] MirZa | ||
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====== PCB Etching ====== | ====== PCB Etching ====== | ||
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- | This is currently a rough guide to the equipment we have for DIY PCB etching and how to use it. | ||
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===== Equipment ==== | ===== Equipment ==== | ||
* [[http:// | * [[http:// | ||
- | * [[http:// | ||
* [[http:// | * [[http:// | ||
- | * [[http:// | ||
- | ===== Exposure | + | ==== Safety |
- | Print your design **mirrored** | + | There is currently no access control |
- | Place the printed design toner side up in the UV exposure box, peel off the protective cover from the PCB laminate and place it copper side down over your design. | + | UV exposer: currently it is unknown if this will switch on without |
- | Close the box and expose for ~10 minutes. After exposure the design | + | Flux spray: use in the workshop, over a bin, with the ventilation on max. Wear eye protection. |
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+ | Sodium carbonate (" | ||
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+ | Sodium hydroxide (" | ||
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+ | Ferric chloride (etchant): Moderately corrosive, strong skin and eye irritant, toxic if consumed, toxic vapours. Wear gloves. Wear eye protection. Open a window and/or switch on the air filter. Can be reused for months or even years, so you shouldn' | ||
+ | |||
+ | ===== Design and Trace File Prep ===== | ||
+ | |||
+ | There are a few approaches to this process. These instructions will assume you're using KiCad and FlatCam (both open source) for PCB design and file manipulation. | ||
+ | |||
+ | Make sure to design your board with nice thick traces - start with at least 0.8mm and then try going smaller once you've got the hang of the masking and etching process. If you can fit everything onto a single-sided board, you might be able to use the laser cutter for cutting and drilling; if not, you'll need to use the CNC (both options are detailed below). | ||
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+ | The first thing to create is your trace file. In KiCad, go to File - Plot. Set "Plot format" | ||
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+ | Open your plot file in your vector editing programme of choice and invert the colours (assuming you're using negative photoresist film - see notes under " | ||
+ | |||
+ | ===== Cutting (CNC) ===== | ||
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+ | The CNC is a bit tougher to get going on than the laser, but it opens up a lot more options, most notably two-sided boards. | ||
+ | |||
+ | Start by going back to KiCad' | ||
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+ | Now click " | ||
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+ | Open up FlatCam and use File - Open Gerber to load your edge cuts and File - Open Excellon to load your drill plot. | ||
+ | |||
+ | //Tip: at each stage of the FlatCam process below you can save your settings for next time by going to Options - Transfer options - Object to Application.// | ||
+ | |||
+ | It's a good idea to go into the " | ||
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+ | Double-click the drill plot in the layer list. You can skip over all the CNC settings here, just enter your tool size under "Mill Holes" (a 0.8mm bit is usually good) and click " | ||
+ | |||
+ | Now go back to the " | ||
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+ | Back in the " | ||
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+ | Double-click the new " | ||
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+ | From here, pop the SD card in the CNC laptop, load it into LinuxCNC, and proceed with the usual CNC process. | ||
+ | |||
+ | ===== Cutting (Laser Cutter) ===== | ||
+ | |||
+ | Another way to cut your board, which you may find simpler, is with one of the laser cutters. This is subject to two major restrictions: | ||
+ | |||
+ | Start by going back to KiCad' | ||
+ | |||
+ | Now click " | ||
+ | |||
+ | Open up FlatCam and use File - Open Gerber to load in each of the three files you just created. Combine these using Edit - Join Geometry and export the newly created " | ||
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+ | You should be able to improt this SVG directly into LaserCut 5.3, but it may take some cleanup in Inkscape/ | ||
+ | |||
+ | Place your workpiece in the laser cutter copper side DOWN. Cut settings may need some experimenting to get right. The aim is to cut all the way through the substrate without hitting the copper hard enough to cause lots of sparks. My best results have come from using the big laser with speed 25, power 60, corner power 50 on 1.5mm board. However, some boards are much tougher than others so your mileage can and will vary - try cutting out a small circle as a test for new stock. | ||
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+ | If you're sure you've got usable laser settings, download and run your cuts. Give it a couple of minutes before you open the lid, vapourised FR1/2 isn't as bad as FR4 but it's still unpleasant. | ||
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+ | {{:: | ||
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+ | Take the workpiece out and pop your board out of it. You'll need to snap the copper layer along the lines you've cut in the substrate, which should be tough but doable. You may need to flex the board a bit, or even use scissors or a guillotine on the edge lines. You can leave the through-holes for now, although you may find it useful to drill out a couple to help you align the trace design in the exposure step. | ||
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+ | {{: | ||
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+ | ===== Exposure ===== | ||
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+ | Currently (as of January 2022) the lab has NEGATIVE photoresist, | ||
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+ | The best option for creating your UV mask is to print it onto some heavy tracing paper on the laser printer in G1. You may need to print and overlay two copies. | ||
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+ | {{: | ||
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+ | You can also cut your trace pattern into a scrap bit of very thin plywood or black acrylic. | ||
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+ | {{: | ||
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+ | Either way, once you have your mask ready, grab the laminator, some sellotape, and a pair of scissors from G1. | ||
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+ | Cut a piece slightly larger than your board from the roll of photoresist film kept wrapped in a black bag in the cabinet in G14. PUT THE ROLL BACK IN THE BAG - it's UV sensitive. | ||
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+ | Peel off the backing (this is incredibly annoying to do - a couple of pieces of sellotape on either side of the corner can help peel the layers apart) and apply the blue film to your board. Try to squeeze any bubbles or wrinkles out to the sides, then run the board through the laminator. The laminator should be set on the largest thickness setting (2x125MIC), and it helps to run it through two or three times to improve the bond. | ||
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+ | Put your mask and film-coated board together in a sort of deadly yet exciting chemical sandwich. Align as best you can and add some sellotape to hold everything together. | ||
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+ | {{: | ||
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+ | Place your sandwich in the UV exposure box (aka the PCB panini press). | ||
==== Developing ==== | ==== Developing ==== | ||
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This step removes any photoresist that has been exposed to UV light in the previous step. | This step removes any photoresist that has been exposed to UV light in the previous step. | ||
- | Place your PCB in the ' | + | Make a solution of about 500ml water and 20g washing soda crystals (sodium carbonate decahydrate). There is a handy 3D-printed scoop to help you get the right amount |
- | Once developed, your design | + | Immerse the PCB in the solution for a few seconds, then remove it. You should |
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+ | {{: | ||
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+ | If you're having trouble getting the unwanted film to come off, your board is overexposed. If your traces/pads are coming off too, it's underexposed. Either way, strip the film off using the instructions below and try again. Most likely you need to increase or decrease the time in the UV box. | ||
==== Etching ==== | ==== Etching ==== | ||
- | Plug in and turn on the etch tank, give it some time to warm up. | + | Plug in and turn on the etch tank and give it some time to warm up. |
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+ | Put your PCB in the tank, using the net hanging from the lid to hold it so you can get it back out easily. | ||
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+ | {{: | ||
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+ | Check on it after a couple of minutes, by which time all copper to be removed should turn a dull pink. " | ||
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+ | Your board is finished when all the unwanted copper is gone. This usually takes about 10 minutes. Start checking it every minute or two after it's been in for 10, and take it out when the unwanted copper has all dissolved leaving just the substrate underneath. If you hit 15 minutes, your board may be underdeveloped. | ||
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+ | Once it's finished etching, turn off the etch tank and rinse the board with lots of water before touching it. | ||
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+ | ===== Stripping ===== | ||
+ | |||
+ | This step removes the rest of the photoresist from the board. Pour some drain cleaner into a tray and soak your board in it for 15-30 minutes, agitating and scraping it every few minutes with the toothbrush. | ||
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+ | {{: | ||
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+ | Once all blue photoresist has been removed, you should see your copper traces. Rinse your board off with lots of water and pop out the remaining through holes, using a .5mm drill bit if needed. | ||
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+ | Note: pure caustic soda will do the stripping job faster than regular commercial drain cleaner, hopefully we will be getting some in soon and this section can be updated. | ||
+ | |||
+ | ===== Final checks ===== | ||
+ | Inspect your board for any broken traces or traces/pads that haven' | ||
+ | |||
+ | Where two traces/pads have merged, you can remove some of the copper with a knife, sharp pair of tweezers, etc. | ||
- | Put your PCB in it, it takes somewhere around 5 minutes to etch. It's finished when all the unwanted copper is gone. If left too long then you'll start getting rough edges and/or breaks in small tracks. | + | Where a trace has been broken, apply a solder bridge to reconnect |
- | Once etched, remove the board and rinse with lots of water before touching | + | ===== Protective coating ===== |
+ | Bare copper traces oxidise very quickly without any protection. | ||
+ | Give your new board a spray with the can of clear varnish after soldering and leave to dry for a couple of hours. | ||
+ | Mask off any buttons or mechanical components with masking tape so they do not get stuck. | ||
- | ==== Stripping ==== | + | Another option is to use tinning solution before soldering. |
- | This step removes the rest of the photoresist from the board. Apply a few drops of methylated spirit to the board and allow it to coat it, wait a few seconds, rinse (or rub gently). | + | Congratulations, you made a PCB!! |
pcbetching.txt · Last modified: 2022-07-22 22:12 by MirZa