Homemade PCB

It is possible to make quality PCBs at home for very little money, here is how I do it.

My first project was to make a UV exposure box. I used two under-counter slimline tubes lights and replaced the tubes with UV tubes. I built a plywood case based on a piece of glass that I had salvaged from an old document scanner. The dimensions were slightly too small and I had to make holes in the sides of the plywood case for the light power leads. I lined the inside of the case with tin foil and cut a thick piece of old card to seal the top (so I didn’t damage my eyesight).IMG_20161111_125923399_HDR.jpg

My first project was a PCB timer as can be seen on the side of the case in the photo above. It runs off 12v and energises the relay to switch power to the UV tubes.

Single Sided Board

I produce the artwork using Cadsoft’s fantastic Eagle PCB software and save it as a PDF (inverting the top layer). Next I print the artwork on a good quality laserprinter, which for me means a walk to my local library with a USB stick and spending 10p on an A4 printout. I make sure I have two images with a decent margin (say 1″) around the edge of both.

starburst_pcb

At home a pour a small amount of vegetable oil onto the paper and work it in carefully with a finger. I then press the artwork between kitchen paper in a heavy catalogue and leave it overnight to remove the excess oil. The oil makes the paper translucent to UV.

Whilst this is happening I often prep my pre-sensitised PCB by marking it out and cutting it with a fine hacksaw (usually over a waste bin to catch the dust and wear a dust mask ! ).

I cut the artwork leaving a large border if possible, lay one on the other and line up the images before stapling them together. Doubling upm the images makes for a really opaque to the UV (eg the areas we want to leave as copper).

Out of direct sunlight I remove the black protective film off the PCB and put it copper side down onto the toner side of the artwork – this way there is no microscopic gap that can cause the UV to undercut the image. This is also why the top layer/only layer is reversed.

Now let’s have some unknowns to deal with. The age of the board, type of photoresist, board temperature, tube strengths, paper thickness etc. You can do some tests on scrap pieces of board at this stage…in fact I recommend it initially rather than ruin your larger piece of PCB.

I clean the glass with a weak bleach solution and polish dry. Place the artwork (toner up and photo sensitive side down) onto the glass, place the thick card on top and then place a weight on that. I’ve used a container of fabric conditioner as I don’t know what else it would be useful for.

Now for my board variety and tube strength I find that 4 minutes is about right to soften the photoresist. When the time is up I quickly take the board and immerse it into a weak but fresh and warm solution of Sodium Hydroxide. (About 1 teaspoon into 1 L of water). This is where things may go wrong and where many people prefer to buy the proper developer solution but remember this is PCBs on a tight budget, so we’ll keep trying.

With a gloved hand, immerse the PCB into the solution and use a cheap old, soft bristled brush to wipe the copper. You should start to see the photo resist floating off where the UV light has attacked it. If the solution is too strong or hot there will be a few seconds between this happening and the rest of the photoresist being removed. If this happens that board is scrap (save it as you can coat it with photoresist yourself at a later date). If the solution is too weak or cold this can take a long time. There is also something else that can happen and that is that it looks like the photoresist has been removed but in reality there is still a very thin protective layer over the areas you want to remove the copper from….at this stage it is really hard to see if this is the case.

Once this is done I drill a hanging hole into one of the waste areas of the board and use a stainless steel brickwork wall tie/any other stainless wire to suspend the PCB into some hot Ferric Chloride solution. I heat the FeCl3 in a square Ikea vase into which I have placed an aquarium heater tube and an aquarium air pump. I also keep moving the board. I do this outside as the fumes from hot FeCl3 will seriously attach anything in the shed/kitchen and are also probably not good for health. I keep the whole lot in an old crate to catch the inevitable splashes and drips.

img_20161111_132526255

The Dirty Part – wear gloves or get yellow fingers !

I lower the board in and almost immediately take it out for a look. If the photoresist was successfully removed, those areas will be taking on a dull pink colour almost immediately. (If this isn’t the case theer may be a very thin-film of photoresist left behind in these areas. Wash the board and try dipping it in the NaOH for a bit longer/brushing while doing so). If the board was developed properly about 5 minutes in the FeCl3 and the board will be done, rinse it in a plastic bowl of fresh water to stop any chemical reactions.

Job done !

img_20161111_140601419

The SOIC PIC15F1509 for my Christmas Starburst

Double Sided Boards

I can also make these cheaply and of good quality for home projects. Using Eagle PCB software I print the top layer inverted and the bottom layer as normal. I do two images of each side and again oil the paper. When dry I cut the images out and double them up to make a better darker image. I then align the two sides and staple them together to make a ‘pocket’. After cutting the board I usually drill the hanging hole while the plastic film still protects the board from getting scratched (not as important when doing single side).

When ready I remove the photoresist protective film and place the PCB into the artwork pocket. I use a small piece of tape to secure the PCB into the pocket. I expose one side to the UV for ~4 minutes and then carefully flip the package and expose the other side.

Then develop and etch as before.

Sometime one side is really good and the other isn’t – this is a bit disappointing and often down to the developer stage rather than the etching. The edges of the board etch quicker than the centres so fine detail can sometimes be lost around the edge.

Most importantly – keep trying, make notes and perfect your technique based on what you can use cheaply.

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3 thoughts on “Homemade PCB

  1. Pingback: Christmas Lights Done the Hard Way | Hackaday

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