I think people that advise to get PCB's from China don't understand that nothing beats something that is done by yourself.
Because:
1. It is deeply satisfying
2. As already told it allows a much faster process to get a working prototype.Obviously this is a real market since there are companies that make equipment's that allow having PCB's done in the office (at home).
Besides. The OP question imply that it is about something belonging to DIY area.
Here I am going to enumerate all the DIY methods of making PCB's that I am aware of.1. Toner transfer using a laser printed PCB pattern on a substrate (either paper - IKEA catalog works best
or vinyl).
The limitations of this method is that it require uniform heat/uniform pressure and good quality toner, in order to get the best results. And very good results can be obtained without much bother.
a) The transfer is done by applying heat. Some use an household iron but the best results (impeccable results for as low as 7 mils trace width, or less) is by using a laminator modified to allow the thickness of the PCB. When using heat, the used temperature depends of the kind of toner that is used. About 180°C for HP toner and more (up until 205°C) for Brother, Kyocera, Xerox printers.
Pay attention to how much toner you use when printing. It is desired to have as much as possible (set in the printer settings) but once you get to under 10mils traces you need to be careful because too much toner will be pushed to the sides and may create short-circuits.
a2) Some use professional toner transfer paper (like the one from Pulsar) but I never had the need to use it, not when the Ikea catalog sheets works so great (100% transfer when used with a HP LaserJet 1022 with original toner and transferred at 190°C using a laminator - I have this one:
https://www.aliexpress.com/item/32866074378.html).
b) Some do transfer the PCB pattern from the laser-printed paper using acetone. They wet the paper with acetone (or the PCB laminate, or both) and then the sheet of paper (vinyl) is pressed onto the PCB laminate until the acetone evaporate and the toner is transferred.
Due of limitations of how the laser printing is done, there may be a need for a post-process step involving a so-called "toner blackener" that will be sprayed over the printed PCB pattern to fuse together the toner and remove small spaces between dots. Here are used some commercial sprays (like Takter 330) or simply spraying "white spirit" solvent (stink) over the paper that holds the PCB pattern.
After transfer you need to remove the paper substrate (vinyl is removed much easier) by immersion in moderate-hot water (with a bit of soap). Clean the traces (especially between them) of the residual paper or it may create issues when etching.
After etching the toner can be removed by using acetone.
2. UV transferThis is the so-called professional way to make PCB's, it is the most involved and will take a lot of time (about 2 hours from start to the end results, etched PCB).
The limitations of this method are that you need a perfect printed mask, any imperfections are transferred to the PCB.
a) positive transfer - means that what you print on the film mask (the opaque regions) is what you get on the PCB laminate after UV exposure. All the UV sensitive stuff that is exposed to UV light will be softened and removed after the developing step.
b) negative transfer - using the negative photosensitive UV film found on Aliexpress, what you print and is opaque on the printed film will be removed after etching. This means that everything touched by the UV light will be hardened (will survive to the developing step) and all that is hidden from the light will be removed after the developing step.
The steps are:
- print (laser or inkjet) onto a transparent medium. If using laser, the heat will deform slightly the film if using acetate transparent sheet. Try to compensate when printing (Sprint Layout software has a nice GUI but it has issues when loading Gerber files generated by some software like Altium - the ground plane is covering everything). Some laser print on tracing paper but I found that sometime the toner will not stick correctly and leave some gaps which are annoying because then the PCB needs corrections.
If using inkjet, it require the usage of pigment ink (not dye inks) to get the required degree of opaqueness. Some print them in double and overlap them one over the other to increase de opacity. Some fill all the colors with black ink (I do that).
- clean the PCB laminate. I start by using fine sandpaper to promote better adhesion. After that use some Unilever CIF (household cleaning stuff, the one with bleach and crystals - works best) to remove the oxides and greases. Fingers have a lot of grease on them so if you know you can't do without, use gloves.
Also, when printing with the laser, it will benefit if using a toner density spray (like Takter 330 or the like) it increases a lot the opacity (no longer the need to print in double the pattern).
- laminate the photosensitive film if using the negative transfer. This can be done dry or wet. The dry method involved applying the UV-film sheet to a the PCB using a laminator set at about 108°C. Sometime the film is sticky (especially if old) and for larger PCB patterns the curvature (it come rolled) can get in the way because once it touch itself (after removing the thin layer that exposes the sticky side) it glue to itself and you need to repeat the process.
The wet method involves spraying a mist of distilled water (not too much) over the cleaned PCB laminate followed by applying the film by hand. It gives you some time to get it right, you can remove the already applied film a few times in order to make sure that there are no bubbles of air caught here and there. Then starting from the center with gentle moves, press the water out to the sides. Once the film is applied and there are no bubbles, put it through the laminator (108°C) a few times.
I find that it is better to do this laminating step a few more times after I decide I should be over.
When using positive transfer either you get pre-made PCB sensitized o UV laminates or you need to spray yourself the stuff onto a PCB laminate by using special sprays. This is messy and it also is hard to get a homogeneous layer which matter when doing the exposure.
- UV exposure - apply the printed film (UV mask) over the sensitized PCB laminate, the printed part should be oriented toward the PCB, toward the copper sheet. This way the mask is as close to the sensitive UV film and therefore minimize the light spread under the mask. When using the Chinese photosensitive film, it is better not to overexpose, it is actually better to slightly underexpose. When exposing using an A4 board covered with one of those 5 meter UV LED strip - Aliexpress/Ebay - I found that about 20 seconds exposure is OK.
I say slight underexposure because after exposure, you need to be patient and wait about 10 minutes for the polymerizing process to finish. Leave the exposed board covered for about 10 minutes until the next step and you are good to go.
- develop the exposed PCB - you may need to remove a thin sheet of plastic over the now exposed PCB if you used the negative photosensitive film. For the negative film a solution of 9 grams of sodium carbonate (warning: not the sodium bicarbonate you get in the kitchen) to 1 liter of water will do the trick. One can make sodium carbonate from sodium bicarbonate by heating it in the oven for a time. Look on the YouTube/Internet for the process (
https://www.youtube.com/watch?v=cpGEc-pLXN4).
For the positive film PCB's a 10g of sodium hidroxide (NaOH) to one liter of water should be enough. Others use the sodium metasilicate pentahydrate (About 100 grams to one liter of water from what I've read but I never used it).
Use a brush to speed up the process (if you are lazy like me and don't want to heat the solution to about 30°C as it is recommended) and brush continuously to remove the gunk that is forming when the photosensitive stuff is attacked by the developer solution) and exposing the lower layers.
When you see that all is developed insist for another minute or so to make sure that the transparent stuff that may still be there is removed. It is interesting how a very very thin layer can still protect the copper, of course it depends on the kind of etching solution you are using.
- etch the PCB board using chemical reagents
3. Direct laser printing You can use:
- A 3D printer with a laser head
- a CNC machine with a lser head
- dedicated laser cutter machine with a laser head, the ones without an enclosure
Make sure you have a UV sensitized PCB laminate. I will talk about one covered with negative photosensitive film (made like indicated above) but you can adapt this for the per-sensitized positive PCB laminates.
Make sure you use a laser head that is not too powerful. The more powerful Laser LED diodes do not have a round dot but a square or worse, a rectangle. The 400mW Laser diodes should be OK.
Create a GCode that will cover the areas that will have to be sensitized by the laser light (the traces, pads, regions etc).
This can be done by either:
- rasterize a picture (BMP, JPG, PNG) at real size of the PCB (check LightBurn software).
- make sure you focus the laser beam the best you can and get an idea of how wide is the beam dot
- vectorize the Gerber features using software like Vectric or FlatCAM (beta version has those features) using a suitable feedrate and the dot dimension as tool width
The steps:
- expose the PCB pattern on the PCB UV-sensitized laminate
- develop the PCB like above
- etch the PCB board using chemical reagents
Or:
- paint the PCB with normal black paint and let it dry
- use a more powerful laser beam to create isolation paths inside the paint by burning the paint where the laser beam touches the PCB laminated. It may need a slower feedrate to allow for cutting into the paint.
- etch the PCB using chemical reagents.
Note: this can be used to create soldermasks too.
4. Direct printing using a modified printer.This require to mechanically modify a printer such that the "paper" will travel in a linear way. Some modified a laser printer and made it to print toner directly on the PCB laminate.
Some others modified inkjet printers using a special ink that acted as a resist when etching (some yellow ink is reported to work).
There is also a UV ink that can be printed by Epson inkjet printers (they use a reusable head with piezo elements) and then can be hardened by UV exposure. This needs to be looked up as to how high the PH needs to be for removal of the stuff after etching
5. Use a
CNC machine (or 3D printer) to guide a marker with a suitable tip diameter and plot the PCB pattern onto a PCB laminate. The CNC GCode can be obtained from FlatCAM (using the so-called Paint functionality) or from the Inkscape GCode plugin.
6. Mechanical isolation (aka scratching). This is done by scratching the copper layer and creating islands of copper to act as traces and pads.
The limitations are that it creates dangerous dust of glass particles that are so fine that can cross the blood barrier in the lungs and get into the blood). It is also a very long (and boring) process but the results can be unexpectedly good. The up side is that it does not involve long steps and chemicals.
The most primitive way is to manually scratch the copper layer using a sharp tool (either a needle of a knife/cutter).
The advanced way is to use a CNC machine (3D printer) to actually go around and isolate each trace using special milling bits (V-bits or pyramid-shape bits or the most advanced and expensive spiral milling bits with diameters of 0.1mm or greater).
To get the GCode to guide the milling bit you can use the following software:
- venerable CopperCAM (paid software)
- Inkscape plugin
- AntFarm new software:
https://github.com/TheAntTeam/TheAntFarm- FlatCAM:
https://bitbucket.org/jpcgt/flatcam/downloads/PS:
When doing
chemical etching some do it using one of the following chemicals to remove the excess copper:
- ferric chloride - nasty stuff, stains anything it touches and in time it degrades. Needs a bit of temperature to accelerate the process and shaking (air bubble mixing) helps a lot.
- sodium persulphate, amonium persulphate - slow process, the stuff is not stable for long after it is mixed in water (it comes as a solid), only for a few days. Needs about 50°C temperature or the process is simply to slow.
- a mix of hydrochloric acid and peroxide (hydrogen peroxide) - fast process, needs to be slowed down if you have fine PCB features by diluting with water. I use (when in hurry) about 2 part hydrochoric acid, 2part peroxide (depending on how concentrated is the stuff, for 3% found in pharmacy use 2 parts) and 3 or more parts ordinary water.
You see if you need more peroxide if the copper is not turning to brown color immediately after immersion in the solution of the PCB laminate in the exposed copper areas. Add more peroxide.
If the copper is turning brown color but you don't see bubbles of gas developing then add more acid.
Slowly, do not splash. Use glasses or you might remain without eyesight, - some use nitric acid . Nasty stuff, I still have a healed mark of a small hole in my left arm from since I played with it. Nasty and toxic fumes, burns almost anything except aluminum.
-
BEST: use the copper chloride. Requires maintenance (hydrochloric acid and peroxide added from time to time) but you can basically use it forever and it is gentle with the underside etch.
Ok, I hope I covered everything. Took a while to write this huge post, I hope it will help someone.
