How to make professional looking PCBs at home
By Thanos
WARNING:: This method introduces the use of dangerous chemicals that are toxic.
First of all you have to construct a UV exposure chamber. To avoid all the extra effort an old scanner can be used. Unscrew the scanner lid and remove all the electronics.
Then place a sheet of aluminium on the bottom of the scanner to help reflect all the UV rays to the top.
For UV lamps you can use four PC mod "Ultra Bright Cold Cathode Light UV". Use the stickers that came with the lamps to mount them on the inside of the scanner
It might be necessary to cut a hole to pass thru the power cable and their switches.
You can place the Inverters inside the box next to the lamps too if there is enough space.
Then turn on all the switches and connect the power cables to a PSU power source. I used an computer PSU to power them but you can just connect them to a power line from inside your desktop computer.
Then give them power to ensure all lamps are working before closing back the lid.
You can use the bottom compartment of the scanner to place all the cables and switches leaving out only a power line.
The exposure chamber is ready!
Next is the preparation of the transparent sheets. You have to print your PCB layout on transparent sheets four times and put the aligned one on top of the other to ensure that no UV rays will pass thru the lines during bad quality of the laser printer. You have to print them on laser printer! Printing them on Inkjet transparent will not do. If the layout is small enough you can print it twice or four times on the same sheet and them cut it in pieces.
In the example below is a small PCB layout with the two of the four layers aligned. Notice how transparent is the black area on the single sheet!
Here is how an aligned four sheets layout looks. It may look thick but when pressed against the exposure chamber glass it will be flat.
Next step is the placement of the transparent layout sheet on the exposure chamber. (I turn on the lamps to be able to see the layout here, normally you turn it on after you placed on it the photosensitive PCB board after you remove its protection sticker.)
Then dim the lights of the room and remove the sticker of the PCB board, place it on the top of the transparent sheet and close the scanners lid.
Connect the power to the lamps and exposure for about 15 minutes.
Now the really dangerous stuff, chemical handling. Notice that in this phase you HAVE to wear protection gloves (latex gloves are ok to use) The chemicals are so strong that after handling for a while you will see the gloves changing color meaning they start to burn so be careful.
The chemicals you will use are:
Caustic Soda (for photograph development)
Perydrol (Caution this chemical removes the water from your skin, making it look white)
Hydrochloric Acid (you can get a bottle of 450ml that is sold on the supermarkets for cleaning that it has conciseness of 8-10%)
You have to make two solutions on two different tanks. One for development and one for etching.
The development solution consists of 1000ml of water and 10ml of Caustic Soda (or 1 & 1/2 spoon if you use a spoon to measure it as it in powder form). Just be sure to stir it good to melt evenly all the Caustic soda in the water.
The etching solution consists of 450ml of Hydrochloric Acid mixed with 50ml of Perydrol. Again stir it good (with a plastic stick, not metal cause it will destroy it).
Back to the procedure:
Now that it has passed 15 minutes that you exposed the PCB in UV rays remove it from the scanner (with the lights dimmed) and place it inside the development solution tank for about 2 minutes, you will know when it ready because the traces will start to appear.
Below is a sample board that it has developed but not etched yet. You can see the traces clearly on it. (Don't mind the center part cause I mistaken the amount of the water with more than 1000ml and when added later more caustic soda, the raw powder that fell on it, burned it instantly...That's way it need good stir when preparing the development solution).
After removing the board from the development tank wash it with water.
Then place it in the etching tank where you have to wait for about 20-30 minutes for all the metal to be removed around the traces. You will notice bubbles on the traces during the etching but this is normal.
After etching is done remove it and wash it again with plenty of water and its ready.
The traces still have its protective layer on them that provides also protection from oxidation so don't rub it until you are ready to solder. Then, unless you tin solder all the traces, you can spray it with protection silicone after you have done all the soldering of the parts to keep the traces in good condition.
That's all.