Greetings, fellow electronics hobbyists!
In this instructable I am going to describe a very cheap and precise way of manufacturing PCBs at home.
Unlike toner transfer, this method allows you to produce tracks as thin as 0.016" and is very useful when making two-sided boards(...and it does not require any special skills or superpowers).
Money-wise it is a bit more demanding than toner transfer, but is definitely more affordable than buying high-precision CNC mill.
Step 1: Gathering Tools and Materials
Small paychecks and a bit of dedication make you do wonders with tight budget, so most of the tools I use are either repurposed or bought on junkyard sales.
So, let's start with tools:
- Laminator (no modifications required)
Got mine for free from the office closing sale (broken, required minor wiring fixes).
Cheapest letter-sized laminator goes for ~$14.00-25.00 on eBay and it is good for up to 1.5mm thick boards
- Laser or inkjet printer (required for photomask printing).
I've fixed up my cousin's old Brother DCP-7010R just for that purpose.
Used inkjet in mint condition will cost you around $15-$20
- UV lamp. Got a few 9W Philips bulbs at the same sale for $0.50 apiece (broken counterfeit currency detectors). Alternatively you can use sunlight, but you have to experiment with exposure timings.
New bulbs cost somewhere between $1.75-$3.00 depending on brand and power rating.
Also you may consider used acrylic nail curing machines: it's a perfect exposure box for small prototypes.
- Two plastic tubs (small depth, but big enough to fit your PCB prototype)
- One larger tub for rinsing
- Soft paint brush or something similar. ($0.20)
I have an old keyboard duster, which sucked at cleaning keyboards, but does really good job in a chemical bath
- Scalpel, scissors, XActo knife or box cutter
- Small rotary tool
- Fine sandpaper
Minimal sum for everything on this list is ~$31,00
If you are completely broke, you can skip laminator and UV light bulb (use sunlight), but you'll need two very clean square pieces of glass to make an exposure frame and a stack of books or something heavy to attach photoresist to PCB surface.
In my case the total amount spent on tools was under $10 (most expensive tools were free [e.g. broken]), but if you have some extra cash, you can add few other useful things like a fish tank pump and some tubing for etching container, enclosed exposure box with a timer, small reflow [e.g. toaster] oven etc. Basically with $100 in your pocket: the sky's your limit.
Also remember, that all this is a one-time purchase and can be used in variety of other ways, like actually printing , laminating stuff or making toasts :)
- Photoresist dry film (~$4.00 per 300x1000mm sheet, or as low as $2.50 for a 6"x8" sheet).
- Printing film (clear). My local distributor has 2 kinds: one for inkjet printers(rougher surface to prevent smudging) and for laser printers(smooth). They cost around $0.40 per sheet. Some people have successfully used regular paper, which was chemically cured or treated with cooking oil to provide transparency.
Some people still do it by hand with a sharpie marker =)
- Photoresist developer (~$1.00 per small 20g pack). Can be substituted with sodium carbonate (used in various cleaning solutions, fabric softeners etc.)
- Sodium persulfate (~$1.00 per 100g pack). I strongly recommend to forget about Ferric Chloride.
- Copper-clad board. I am using 1mm thick FR4 with 35 micron copper layer($1.50 for a 100x150mm single-sided piece or $2.50 for two-sided)
- Rubber or plastic gloves
- Rubbing alcohol or Isopropyl (for cleaning the PCB surface and removing soldering flux at the end)
- Soft cloth or paper towels
A minimal sum needed for materials is less than $7.00. If you have extra cash, then you should buy materials and chemicals in bulk - it will save you money in the long run.
All chemicals can be used more than once, so instead of discarding everything after first use just pour it into a glass or plastic bottle for the next time.
CAUTION: Both photo-developing and etching solutions are active chemicals. Use caution while working with them and if you get exposed (eyes or skin), then quickly rinse the exposed place with water.
Step 2: Board Layout
First thing you need to do is to create a layout for your PCB from a schematic.
My tool of choice is Eagle CAD, because it is very easy to work with.
Once you have a ready-to-make layout, you need to create a negative photomask for printing. There are few ways of doing this.
The quickest way is to use a built-in CAM processor and use PS_INVERTED setting to make a PostScript rendering of your layout and then print it. To work with PostScript files I am using gswin (Ghost Script for Windows) with gsview (*.ps viewer extension with the ability to export to raster formats like PNG).
If you want to adjust the position/sizing of the mask you have to use GSView to export rasterized image to whatever format you like and then edit in whatever graphics editor you use.
The only bad thing about this approach is that GSView rasterization supports 600dpi max and even though this number seems reasonably high, it actually produces pixelated artifacts on round corners and has some sizing problems (I had to adjust height/width proportion by the factor of 1.05 ... 1.10 most of the time).
Alternatively you can print your layout to PDF file and edit it in Inkscape . I've attached a quick video on how to do it.
Once complete - print it on paper first. Make sure that sizing is proper by matching critical parts(ICs, sockets, pin headers etc.) with printed holes and pads, and only then you can print the photomask on film.
Next on our agenda: developing and etching.
Step 3: Developing and Etching
This process requires preliminary preparation and accurate timing. It helps to have a stopwatch or a cell phone laying around.
It is nice to have a dark envelope/box for your PCB, if your work space is limited (like mine). This will allow you to clean up the desk/workbench and prepare chemicals after your PCB is exposed to UV light.
Also most people do this a bit differently, but I found some tricks that work better for me and can save you lots of time in the process.
- It is hard to work in complete darkness, so here's what you can do:
Close your blinds during the day or use warm LED lighting during the evening to prevent accidental UV exposure of photoresist film
- Cut your layout from photomask film to the size of PCB
- Cut the same size of photoresist film
- Scrub the copper clad board with sandpaper, wash it and clean the surface with rubbing alcohol
- Don't forget to wash your hands!!!
- Use a small piece of adhesive tape to peel the inner layer of protective film from photoresist
- Attach the peeled side of photoresist to your PCB and run it through the laminator a few times (while it is not very hot)
- Put the PCB into the dark place and wait for laminator to warm up completely
- Attach the photomask facing toner down so it can stick to the surface of photoresist film. This trick eliminates the use of glass panels and clamps for UV exposure, also providing much better and faster results
- Run the PCB with photomask through the laminator until it is firmly attached (usually 3-4 runs is enough)
Then we get to exposure. Once again, put your PCB into the dark place, turn on the UV lamp and allow it to warm up for at least 5 minutes.
Then put the PCB under the UV light and allow it to expose for no more than 3 minutes (80-90 sec if you use sunlight, more than 9W bulb or multiple bulbs in an exposure box). The distance between the UV source and PCB also matters. Since I have only 1 lamp, I try to keep it ~15cm away to provide more or less uniform exposure.
One last time, hide the PCB in a dark place, clear out the work space and start preparing chemicals.
First, make a developer solution and a rinsing bath. Photoresist developer has to be dissolved in warm water in the following proportions: 20g of developer per 0.5L of water. Rinsing bath is just regular tap water(temperature does not matter).
Remove the photomask and the top protective film from PCB, submerge the board in developer solution for 60-90 seconds, while GENTLY stroking the surface of the board with soft brush. Once you see the unexposed part dissolve, rinse it with water. If some parts did not come off (usually due to slight overexposure) you can repeat the procedure for 30 more seconds.
Once done we can get to etching. For this you'll need a solution of sodium persulphate (100g for 0.5L of water at 40-45C). Put your PCB in there for ~15-20 minutes and wait for it to etch completely. It helps if you mix the solution occasionally and keep the temperature at 40C during the entire process.
When etching is done, rinse the almost-ready PCB with water and put it in developer solution again to remove the remaining photoresist layer. Rinse and air-dry the board afterwards.
This is pretty much the same process, except you'll need a positive printout of solder mask layer.
Cut another piece of photoresist film to the size of PCB and run it through the laminator. Then attach the solder mask printout aligned with pads and vias on PCB and run it through the laminator again.
For small power circuits with large tracks and pads you can skip the printing part and simply use a sharpie to cover solder mask areas by hand (draw on top of protective film)
Expose it to UV light for 90 seconds, develop it until all unexposed places dissolve or peel, and then rinse it with water.
To provide better sticking - put it in the oven for about 10-15 minutes at 200C and then, just to make sure, expose it to UV light for about an hour or so (you can use direct sunlight exposure to not bother with the lamp).
If you want to make a two-sided board you should do the second side separately at least for the first dozen times ))
Seal layer 2 with some adhesive tape to protect it during the etching process and when the first side is done, do the following:
1) Select 2 or more control points on your PCB layout. It could be corners or through-holes preferably placed as far from each other as possible
2) Drill a small hole at each point for alignment
3) Repeat the photo-developing process for side 2, while using holes for photomask alignment.
Step 4: Finishing Touches
If you are using through-the-hole components - it is time to drill!
Use the rotary tool with appropriate drill bits. Try not to damage copper layer or solder mask during this process.
Once done, you can start the final assembly.
If you have an SMD design, you can make a cheap stencil out of soda can by using an awesome method perfected by this guy
For 2-sided boards I am using regular jumpers soldered at both sides to connect layers together, or trying to match junction points with through-the-hole component placement pads. A more expensive solution is a conductive glue or a homemade electroplating tank, but we'll get to that some other day.
The end results will vary, but once you get used to your lab setup and develop proper sense of timings - you'll get much better at it.
After the first 4-5 semi-successful trials I got my process length down to approximately 1 hour.
--------------------The only thing I haven't had a chance to make is a proper silkscreen layer [YET]---------------------
Just tried the crayon on hot copper surface - it worked!
After curing process I've used my rework station to keep target spots hot (@230C) and applied regular white crayon. Wax pencils should work too, if you want to get creative with colors.
If you have any questions/ideas/suggestions you can always send me a message.
You can also find more of my projects either on my profile page, or by visiting my website at http://mygeekblog.net
Once again, thank you for your time, comments and feedback.
Good luck in your projects!