Projects/PCB/PCB manufacturing

PCB Manufacturing Guide
This guide is designed to take you through, step by step, producing high quality, homemade, PCB boards. The guide assumes full access to the Reading Makerspace, and access to some interesting, or unusual equipment. When this is the case, however, a note is made of methods to do the job using more mundane methods. It should therefore still be useful to those of you reading who don't have access to RMS. It will just require a lot more effort on your part.

The guide assumes a novice, but competent, reader. There are still a lot of tips and tricks buried away in here, so it's worth a glance through before starting, even if you know the general method.

If your unsure about any of the steps, feel free to ask in the hackspace, on the google groups mailing list, or on IRC (Freenode, #reading-hackspace).

Lastly, this is all done at you own risk. PLEASE read ALL safety advice before starting and follow it!

Happy Hacking.

Paul

Designing

 * todo

Using Eagle PCB to design single or double sided PCBs

Element14 intro to Eagle Video on YouTube

Exporting

 * todo

Exporting tool paths for drilling and milling producing images for top and bottom pcbs from Eagle PCB

Design Transfer
There are 2 methods of getting your design off of the computer and on to the board. Toner Transfer is the simplest and cheapest, and is good for one off boards, with a simple, chunky design. Photo Lithography is more complex and finicky, but produces very high quality results. It also lends itself well to making several of the same design.

Both methods can be used for Double sided PCBs, but again, TT is the better one for this, unless you need the high detail of PL.

Toner Transfer Method
Toner Transfer makes use of the fact that Laser Printer Toner (Ink) is, in fact, a finely powdered plastic. This means it can be used to block the etching solution in the next stage. The hardest part is getting the toner on to the PCB board.

The first step to do is to print out your design onto Photo Paper from a laser printer. The design should be printed in black, at the darkest setting the printer can achieve. Check you have the board correctly mirrored from the previous step.

Double Sided
If you are making a double sided PCB, then you now have the fun and games of alignment. You need the drill hole on both sides of the board to line up with each other. This is quire fiddly, but doable.

To do it, print out both sides on separate pieces of photo paper. Next, place the 2 prints, toner side in, face to face. Hold them up to the light and align them via the hole marks. Then trim them both together to the same size as your board. Place the upper and lower designs on to the PCB, toner facing inwards, and use the corner of the PCB to align all 3 layers (lower design-PCB-Upper design). It can sometimes help to use a couple of small pieces of masking take to hold the pieces aligned.

Place the whole stack into the PCB press, and tighten the wing nuts. Be careful not to knock the alignment of the layers. The nuts should be finger tight+ 1/4 of a turn. This provides an even pressure on the board.

Single Sided
Single sided PCBs are a lot easier to make. Just print out the bottom design, as for the Double Sided, trim and align it with 1 corner of the board. Now place both paper and board into the PCB press and tighten.

Fixing
Take the whole PCB press, and place it inside the mini oven. The oven should be brought up to 200 degrees and held there for 10 minutes, to allow the heat to penetrate the metal. It should then be turned off, opened and allowed to cool to a safe temperature. PLEASE be careful not to burn yourself. Also make sure the oven is safe and monitored while on, and not a burn risk when cooling down again.

Once the PCB press as cooled down, open it up and remove the board+paper. The toner is now fused to the board, unfortunately, it's still fused to the paper as well. Place the board and paper into Warm soapy water. This will soak into the paper and begin to break it down. You can speed up the process a lot by gently rubbing the paper on the board. Rub from the inside out, to minimise the chances of damaging the tracks. Once most of the paper is removed, use a paper towel to rub the last bits off. You can rub reasonably hard, just be careful not to remove any of the black tracks.

Once the board looks clear of paper, remove it from the water and pat it dry with paper towel. Depending how tight your tracks are, there might be some paper/wax between the tracks. You can get rid of this by running a pin, or nail tip along it. Once it is dry it should crumble relatively easily. Give the board 1 final rinse and move on to etching.

Photo Lithography Method
This method requires a few more chemicals, as well as pre-sensitised board. The process is also UV sensitive, and so you need to proceed quickly from transfer to etching. The process does produce the finest boards possible at home though. The board resolution is only limited by the resolution of the printer used to print the design.

The first step is to take the design from the previous stage and print it onto either transparency or thick tracing paper. The tracing paper tends to give better results, but the transparency still works well, and are a lot cheaper and easier to obtain. As for the TT method, the design should be printed at the highest contrast settings available, and care should be taken on mirroring where necessary. A laser printer tends to give better results, but an inkjet should still work.

Once the design is printed, hold it up to the light and check for any pinpricks in the traces. If there are any, they can be repaired using a fine tipped, black, permanent marker. If you are doing a double sided PCB place the 2 designs face-to-face and align the prints. Use the paper trimmer to cut the designs to the size of the board.

Place the bottom transparency, with the design facing upwards onto the glass of the UV light box. Slide so that it is tight into the corner. Now take the PCB and peal off the protective sheet,to expose the UV sensitive coating. place this, face down, on top of the lower design, tight into the corner.

Close the UV box and turn it on. The time required depends on how opaque the sheet used is, as well as the board coating's sensitivity. Tracing paper tends to need about twice as long as transparencies. For the Maplins, pre-sensitised boards, this seems to be about 6 minutes for transparencies and 12 for tracing paper.

Once this is done open the box and remove the board and design. If you are doing a double sided board, replace the lower design with the upper one and repeat the above process with the other side of the board. Take care to align the upper and lower traces!

Once the board has been exposed, it needs to be dipped in developer solution. Follow the instructions on the bottle. This step requires some practice. If the developer is too strong or too hot, it will eat into the unexposed tracks, and so degrade the results. If it is too weak, it will not fully remove the protective coating. After a few minutes the design should become visible, wait till the copper is fully exposed before removing and rinsing the board. Keep the remaining developer for now, since it will be needed to clean the board after etching. The developer does not keep more than a day or so once made up however and needs to be disposed of properly. DO NOT pore it down the drain. There is a plastic bottle to pore the waste into. this needs to be disposed of periodically.

The board is now ready for etching.

Safety
WARNING!

Etching uses some nasty chemicals, it must always be done outside, away from cars and people. Take care not to inhale any fumes and ALWAYS wear gloves! Etchant of any sort should never be tipped down the drain. Not only can it damage the pipes, it is highly toxic to aquatic life and so should be disposed of properly. Please note, the etchant is acidic and will burn. In the event of etchant or other chemicals making contact with the skin, rinse immediately under a tap and seek medical advice. (Etchant, treat as HCL 'pool acid', PCB developer is NaOH based)

Background
Right, now the rant's over, the normal etching solution used in home PCB making is ferric chloride. This is cheap, e.g. Link to Maplin works well, but is short lived and needs disposing off properly. At the hackspace we use a Copper chloride based etchant. This is reusable, and in fact get stronger with use, not weaker! It does, however, require some finesse to keep it in top shape.

Usage wise, the solution should have been left in a usable state, if not, see here for details of how to make/recover the solution. All steps should be done wearing rubber gloves.

Usage
Place the Etching Bath on a safe, flat, stable place with good ventilation. Pour in enough of the green etchant to just cover the board. Larger boards might also require the air stone to agitate the solution. Take your board, with the design already transferred on to it (via either TT or PL) and place it in the PCB holder. Place the board and holder into the etching solution. The board should begin to bubble slightly as the board is eaten away by the etchant. Periodically lift the board from the solution and check to see how much exposed copper is left. If there is any left exposed, place it back into the etchant and repeat. this should take 5-10minutes depending on how strong the etchant is.

Once the board is clear of exposed copper, shake the excess off into the tank. Pat the board dry using a paper towel, then rinse clean under an outside tap, and dry.

Cleaning
If you used the TT method, you can now use Acetone to remove the toner layer. Apply it to a paper towel and rub the board. It will take a couple of passes to fully remove the toner.

If you used the PL method, place the board in the light box again, and fully expose on both sides. Now place it back into the developer solution. This will dissolve off the remaining coating. Rinse under water and wipe down with Acetone to finish it off. the developer solution needs to be disposed of properly.

Any spillages should be mopped up with paper towels, and any paper towels should be allowed to dry out, before being disposed of normally. All equipment need to be cleaned and packed away.

The etchant may also now need regenerating. Please follow the steps here to do this, if needed.

Solder Resist

 * todo

adding a solder resist layer to a pcb, as well as, potentially, a silkscreen layer

Drilling
Eagle's excellon.cam job produces nice drill output. However finding tools to convert that into easy to use g-code is surprisingly difficult (they are almost the same format after all). For one it tends to use a lot of tool changes to accurately match hole sizes, which is usually more detail then I need. I have been using this quick script [[Media:Drd2gcode.zip]] to drill them all using one tool.

Milling
I have had the most luck using Visolate. This creates efficient tool-paths based on the minimum isolation necessary, allowing much looser tolerances then trying to outline all the paths.

Visolate seems to be buggy when handling non-circular pads; Eagle's Drc shapes tab can easily replace them. The built-in gerb274x.cam job produces suitable input, and in Visolate clicking 'Fix Topology' and 'Make Toolpaths' is usually all that is needed. Simple 45° etching bits seem to work well, ensure the height is set to only just remove the copper.

If you need more traditional layouts then the is a UPL for eagle [here], it needs very carefully calibrating to your machine, but with perseverance can perfectly match any Eagle board. Install to your UPL folder, then in Eagle's board window: run pcb-gcode-setup

pcb-gcode also produces its matching drill files. Don't mix-n-match with others as they often do not use the same offsets.

Soldering Vias
how to proper do vias.
 * todo

Tinning
how to tin the board, to aid soldering and increase unsoldered lifespan
 * todo

Soldering Components

 * todo

how to solder the components to the board, both through hole and surface mount.

We have a Halogen oven which works quite well for SMD reflow soldering. There is also a project to build a RHS toaster reflow oven