====== PCB making ======

Making PCB is not that hard.

After having tried various methods I picked up the one explained hereafter.
It might not be the best for everybody, but it does not require a lot of equipment and it is relatively cheap.

===== Materials needed =====

  * A photoresist PCB board (check out ebay, I got 20 of them for $45) ;
  * A software that can print your PCB artwork ;
  * A inkjet printer ;
  * A sheet of tracing paper ;
  * An UV exposure box (learn [[projects:finished:uvbox|here]] about how to make one) ;
  * Some Sodium Hydroxide (you can buy it at your local DIY store) ;
  * Some Aceton (DIY store as well) ;
  * Some Hydrogen peroxide (130 volume) (that one is a bit more difficult to buy, try drug stores if your DIY store don't sell it) ;
  * Some Hydrochloric acid (DIY store) ;
  * medical cotton (optionnal) ;
  * Water ;
  * Several boxes in which your PCB can fit ;
  * Gloves (if you don't want your skin to become white after touching some of the chemicals ...).

===== How to proceed =====

==== Printing the artwork ====

You will need to print your PCB artwork on the tracing paper with the highest ink volume you can ask your printer for.
That parameter can often be found in the printer parameters wizard available before you confirm the printing of your artwork.
Wait for the ink to dry (several minutes) and take care of not scratching the tracing paper, otherwise you might end having damaged/merged tracks.

==== Exposure ====

Put the tracing paper in the exposure box with a piece of PCB on it (sensitive layer facing the UV tubes of course ...).
Turn on the UV exposure box and wait for the exposure to end. The exposure time varies depending the material the sensitive layer is made of.
This value if ofen indicated on the PCB package, but it also depends on your UV exposure box design.
You may have to try several times with various timings on small PCB bits to estimate the best timing (mine is 1'45).
At the end of exposure, turn off the UV tubes but keep the board inside the box, so that it won't be deteriorated by ambient light.

==== Developing ====

To obtain developing liquid you have to mix a small amount of Sodium Hydroxide with water.
I use proportions of 80mL of Sodium Hydroxide for liter of water, adding more will speed up the process but might deteriorate your PCB.
**Remember to always pour the Sodium Hydroxide first.** I found out that this liquid cant be kept for long for later use easily as
it quicly starts to loose its efficiency so you may just make enough to cover the board.
**This liquid is a base so be careful**.

Put your exposed PCB board in the liquid. The sensible layer may change color, this is normal.
Wait for the tracks to appear (usually 5-7 seconds). Once the sensitive layer starts to "dissolve"
in the liquid wash your board in water carefully (avoid damaging the tracks that did appear).
Take care of not letting the board develop for too long or it will damage the tracks.
The color of the tracks must be clearly darker than the rest of the board.

==== Etching ====

That step must be achieved outdoors. Mix together 2 volumes of Hydrogen peroxide with 1 volume of Hydrochloric acid and
1 volume of water (don't make too much since that mix is not usable for long).
Pour it in a box the size of your PCB (**don't use the one used for developing**, since this mix is mainly acid it could react with the remaining Sodium Hydroxide).

Put your board in the mix and wait. The liquid will turn green, and bubbles will appear.
The reaction is quite quick, it rarely takes more than 3 minutes so keep an eye on the process.

Once it is finished, clean the board with water and use Aceton to remove the remaining sensible layer on the tracks.

==== (Optional) Tracks plating ====

To avoid tracks corrosion you can protect it with solder. You just have to put a small layer of
plumber acid paste (you can buy it at a DIY store) on the board, and then you put some solder on
the end of your soldering tip and coat the tracks with it. Clean the board with water and soap.

This is not needed but useful if you plan to use SMD components of if your board may be used in a humid environment.

==== Chemicals disposal ====

The best way to dispose of the chemicals created in the process is the give them to a specialized company,
but it may cost you some money.

Another way is to mix the two liquids (developing liquid and etching liquid) together (**do it outdoors !!!**).
Since one is acid and the other one is a base the will nearly "neutralize" each other.
This reaction will produce heat, bubbles and the liquid may change color.
After a while you can dilute the liquid in a large quantity of water and dispose of it (it is quite a good weedkiller ...).