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--- pcbetching [2022-01-15 14:52] – jtdburton
+++ pcbetching [2022-07-22 22:12] (current) – [Flux] MirZa
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 ====== PCB Etching ======
-This is currently a rough guide to the equipment we have for DIY PCB etching and how to use it.
 ===== Equipment ====
   * [[http://www.megauk.com/uv_exposure_units.php|LV202E UV Exposure Unit]]
@@ Line 19: / Line 16: @@
 Sodium hydroxide ("drain cleaner"/photonegative stripper): Highly caustic. Wear gloves. Can be flushed down the drain (it's drain cleaner).
-Ferric chloride (etchant): Wear gloves. Wear eye protection. Touch it and die. Can be reused for months or even years, so you shouldn't need to dispose of it; if you do, there's a tub under the sink for the used stuff. DO NOT flush down the drain. DO NOT. You will kill hundreds of marine invertebrates who are just trying to have a nice day, and when the giant shrimp overlords arise, you will be their first sacrifice.
+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't need to dispose of it; if you do, there's a tub under the sink for the used stuff. DO NOT flush down the drain.
-===== Design/file prep =====
+===== Design and Trace File Prep =====
-Prepare your design using your PCB software of choice (KiCad is a good open-source option). Start with nice thick traces (at least 0.8mm) and then try going smaller once you've got the hang of the masking and etching process.
+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.
-Export one file with your cuts and another with your circuit traces. If you're making a double-sided board, you'll need one trace image for each side, but double-sided boards are trickier right now (see notes under "Cutting" below). Note that KiCad doesn't actually export all through-holes on the "edge cuts" setting. You might find it easier to export a single image with your copper traces and "print board edges on all pages" ticked, then separate the traces/pads from the holes in Inkscape/Illustrator/etc.
+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).
-===== Cutting =====
+The first thing to create is your trace file. In KiCad, go to File - Plot. Set "Plot format" to "SVG". Select your copper layers ("F.Cu", "B.Cu", or both). Tick "Plot Edge.Cuts on all layers" (this is to help you align the mask to your cut board), make sure "Drill marks" is set to "None", and click Plot.
-With the CNC router not really in working order at the moment, the best way to cut your board is with one of the laser cutters. This is subject to two major restrictions: use FR1 or FR2 boards ONLY (FR4 vapourises into some VERY nasty stuff), and use only single-sided boards (you can't laser through copper).
+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 "Exposure" below). In Illustrator, the easiest way to do this is to create a white filled rectangle slightly larger than your board, put it behind your traces, and then select all and click "Edit" - "Edit Colours" - "Invert Colours".
-Use your image editing software of choice to prepare your cut file for lasering. It needs to be a vector with all shapes as outlines and no fill, and it needs to be mirrored either in your image editor or once you import it into the LaserCut software.
+===== Cutting (CNC)  =====
-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 35, power 60, corner power 50 on 1.5mm board.
+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.
-Run the 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.
+Start by going back to KiCad's Plot dialogue. Make sure "Edge.Cuts" is the only layer selected. Select the Gerber plot format and click Plot.
+Now click "Generate Drill Files...". Select "Excellon" as your file format here, and tick "PTH and NPTH in single file". Make sure the "Absolute" and "Millimetres" options are selected and click "Generate Drill File".
+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 "Options" tab at the left here and make sure "mm" is selected as FlatCam defaults to inches.
+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 "Generate Geometry".
+Now go back to the "Project" tab and double-click the edge cuts layer. Enter the same tool size under "Board cutout" and set your Gap size to something reasonable. This setting creates either two or four gaps in the edge cut so your board doesn't come completely free of the stock. Four 3mm gaps is a good starting point.
+Back in the "Project" tab again, you'll have new .drl_mill and .gbr_cutout layers. Select both of these and go to Edit - Join Geometry. You'll see a new "Combo" layer. Double-click this and enter your CNC settings. Typical values will be around -1.6mm cut Z (this is the thickness of your board), 2mm travel Z, 200mm/min feed rate, and 10,000 RPM spindle speed. Click "Generate".
+Double-click the new "Combo_cnc" layer and enter "M30" in the "Append to G-Code" box (this is an "end of program" signal, and LinuxCNC won't process a file without it). Click "Export G-Code". Grab the SD card from the CNC laptop and save your gcode file on there with the file extension .ngc.
+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: use FR1 or FR2 boards ONLY (FR4 vapourises into some VERY nasty stuff), and use only single-sided boards (you can't laser through copper). Instructions for cutting a board with the CNC router will be added here eventually, but the file prep steps are similar so you may be able to figure it out for yourself.
+Start by going back to KiCad's Plot dialogue. Make sure "Edge.Cuts" is the only layer selected. Select the Gerber plot format and click Plot.
+Now click "Generate Drill Files...". Select "Gerber X2" as your file format here, and click "Generate Drill File". This will create two files, one for plated and one for non-plated through holes.
+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 "Combo" layer as an SVG.
+You should be able to improt this SVG directly into LaserCut 5.3, but it may take some cleanup in Inkscape/Illustrator first.
+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.
+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.
 {{::20220114_183346.jpg?400|}}
-Take the workpiece out and pop your board out of it. What you're doing here is snapping the copper layer along the lines you've cut in the substrate, it'll be tough but doable. You may need to flex the board a bit. You can leave the through-holes for now, although you may find it useful to punch out any mounting holes to help you align the trace design in the exposure step. Note that you'll lose some copper around the edges of whatever you pop out, so only do this in non-critical areas of your board.
+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.
 {{:20220115_113716.jpg?400|}}
-===== Exposure ====
+===== Exposure =====
 Currently (as of January 2022) the lab has NEGATIVE photoresist, which means the copper will be removed from the areas of your board NOT exposed to UV light.
-In the past the recommendation has been to use transparencies run off the laser printer for UV masking. This does not actually work very well because the "black" areas do not come out fully opaque. Tracing paper may work - as of this writing we don't have any. One good way to produce a UV mask in the absence of proper printables is to laser-cut your trace pattern into a scrap bit of very thin plywood or black acrylic.
+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.
+{{:20220118_211802.jpg?400|}}
+You can also cut your trace pattern into a scrap bit of very thin plywood or black acrylic.
 {{:20220115_112643.jpg?400|}}
+Either way, once you have your mask ready, grab the laminator, some sellotape, and a pair of scissors from G1.
 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.
-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 in G1 to seal it. 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.
+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.
-Put your mask and film-coated board together in a sort of deadly yet exciting chemical sandwich. Align as best you can using the mounting holes you hopefully punched out earlier, and add some sellotape to hold everything together.
+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.
 {{:20220115_125318.jpg?400|}}
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 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 of washing soda.
-Immerse the PCB in the solution for a few seconds, then remove it. You should now be able to easily peel off the transparent film on the front. Return the board to the solution and start gently brushing it with the paintbrush. You should notice bits of the blue mask coming off. Once all the copper you want to remove is exposed (this should take about 30-60 seconds), remove from the solution and rinse with plenty of water.
+Immerse the PCB in the solution for a few seconds, then remove it. You should now be able to easily peel off the transparent film on the front. Return the board to the solution and start gently brushing it with the paintbrush. You should notice bits of the blue mask coming off. Although it might look like all the unwanted copper is exposed after a minute or so, it actually takes about three minutes for the film to fully develop. After that time has passed, remove from the solution and rinse with plenty of water.
 {{:20220115_121125.jpg?400|}}
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 Where a trace has been broken, apply a solder bridge to reconnect it.
-===== Flux =====
+===== Protective coating =====
-Give your new board a spray with the can of flux. This will both prevent the copper traces from oxidising and make soldering to the board easier. Applies just like spraypaint - use back-and-forth motions from 20-30cm away.
+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.
+Another option is to use tinning solution before soldering.
-Leave to dry for a couple of hours. Congratulations, you made a PCB!!
+Congratulations, you made a PCB!!