Manufacturing PCB’s in a small scale is often expensive, time consuming and inconvenient for the hobby engineer. Setting time aside to design a PCB, sending the design off to be manufactured and the getting it back to realise its the wrong size or worse that a pin is in the wrong place is often a costly process.
I have for a number of years been building PCB’s at home using various bits of software and manufacturing techniques. These boards were very simple and usually designed to convert DC to DC power from batteries or other sources into another voltage – usually to power a 3rd party circuit or in a pinch my iPhone.
My tried and traditional method of PCB manufacture has been to design the part using Adobe Illustrator, flip the board and print it onto ‘PCB’ toner transfer paper, iron the transfer onto a copper clad board and then etch the board using PCB etchant.
While this has worked great, it has a number of limitations; the level of detail I can work with on illustrator isn’t quite setup for PCB designing, everything is a manual process, the iron on transfer often didn’t work (well) completely and so I had to use a pen to fill in the gaps – making for a messy PCB.
Attending a MakerFair in Brighton (South Coast of England) in the summer, I got chatting to a number of people who represented ‘Build Brighton’ – http://www.buildbrighton.com
Seeing the quality of the PCB’s they had designed and made using gloss paper and a laminator inspired my to change my process.
Deciding to start from the beginning I have throw away all the old processes that didn’t work and refreshed them with new.
PCB Design software:
I evaluated a number of bits of PCB software, the list including:
- OsmondPCB (Mac only)
I finally settled on FreePCB, I was looking for something that would allow me to build without needing a schematic first. With the software it was very easy to define a PCB board size / shape and then add parts from a pre-defined library. If the part you needed didnt exist, it was very easy to add the part to your own custom library and then import it to your design.
Its worth noting that FreePCB allows the use of multiple layers per board – this is something new to me and I am keen to find a project that will allow me to build a circuit board with both top and bottom tracks & components.
Once I had a basic grasp of FreePCB, I began the redesign of my latest project dubbed ‘BeeSafe’; you can read more on that here http://www.mathewjenkinson.co.uk/beesafe-pcb-initial-thoughts-and-feedback/
Using predefined parts, I was able to define the board size (adjusted to the same size as the Raspberry Pi) move the GPIO cable to a more suitable location, place LED’s and switches and locate the 3xAxis accelerometer. The process itself was straight forward and easy to follow, I was able to adjust the track sizes and route all the connections with ease.
As the board itself was now positioned the right way around, I did not have to flip the image. Exporting to a super high resolution tiff file means that the image coming out from the printer was super crisp. The paper used in the printer is super high quality gloss paper, it has a plastic feel to the coated sheet and the toner doesn’t bleed or blur.
To transfer the image to the PCB board is a two step process. One part cleaning and one part heat. Its important to ensure that the copper clad board is 100% clean and free from oils and finger prints as this will reduce the contact the toner has with the board and ultimately effect the end result.
To clean the board, I start with dish soap and a coarse sponge. Scrubbing the board to remove grime, oils and finger prints gets the top layer off and a final buff is done using steel wool, which brings the board up in a nice shine – removing the copper oxide layer.
From here I need to apply heat. Using a laminator and a laminator pouch I run the board through the laminator flipping and turning the board to ensure constant heat distribution along the surfaces. The end goal being that the toner melts off the gloss paper and adheres to the surface of the (now clean) PCB. I have found that that using a laminator pouch acts to prevent the paper + PCB from slipping and keeps the overall temperature stable for longer.
*NB* After a weekend of making PCB’s I can confirm there is a SIGNIFICANT difference between toner transfer with and without a lamination pouch. With the pouch returns a near 100% transfer of toner and pattern while without can be incredibly hit and miss.
Once the board has cooled and can be handled, I cut it from the plastic surround and then submerge it in water to help dissolve the paper. This doesn’t usually take long as the paper is thin and soon falls off the board.
The next step is etching. This is a chemical milling process where the board is submersed in a liquid solution that will dissolve away the copper, any part covered by the toner will be protected and after 20 mins or so (depending on the strength of solution, temp etc) the board will be finished and can be removed from the solution. NB – do not tip the waste down the sink / toilet as it is still quite toxic and may corrode your pipes!
While the toner is still attached to the board, I drill the holes. I have found that the drill travels less and tends to protect the track below.
Finally you need to remove the toner from the board, this can be done in a number of ways. Nail polish works well, as does a quick scrub under a hot tap with a brillo pad.
The final step is to solder your components and test your board!