After much patient effort and wasting many dozens of PCB s , i finally learnt the art of making pcbs the right way.
Here are the steps , so that you don’t have to undergo the grind that i had to :
1) Clean your PCB thoroughly.
Rub it vigorously with sandpaper both vertically and horizontally.
Then using some steel wool and a dish washing soap (such as Vim) , clean the PCB thoroughly.
Then dry the PCB using some tissues. Immediately after this , clean the PCB one final time using tissues and acetone. I have found that although alcohol works too , the success rate is much higher with acetone.
All this is done so that the PCB is clean and free of any dust or grease which repels toner. Make sure that you never touch the PCB directly during any point of time. The thin film of oil on your hands will stick to the PCB and will prevent the toner from adhering properly.
Also do not leave the PCB for more than 10 minutes after cleaning. Dust may resettle on it. I learnt this the hard way. Remember that every step is important and the PCB will almost definitely not come out right even if you miss a single step.
A word of caution : Do not use the steel wool that you used for any other purpose. Copper particles aren’t too good for health.
2) Preparing for Toner Transfer
This involves printing out your circuit design (though a Laser printer ONLY) on an OHP sheet and then taping it on a PCB and ironing on top of it. This will cause the toner to melt and get transferred onto the PCB. This is the most delicate and most crucial part in PCB making.
a) Design and print out your circuit using a software such as EAGLE or Express PCB on an OHP sheet using a Laser printer. I personally prefer ExpressPCB. Remember that your design will be inverted when it is transferred onto the PCB.
b) Cut the design to the appropriate size and lay it down on the PCB such that the cutout holds to the PCB by means of a ” Suction Lock “.
Then tape it to the PCB , making sure that there are no air gaps ( this is extremely crucial). I have found that the tape that works best is Painters Tape which is available at any hardware store. It is best if you can get tape of width ~ 1 inch ( shown in the pic on left).
3) The actual Toner Transfer
Using an electric Iron set to it highest setting (with the water removed ,please) press on the PCB with the largest force that you can muster for around 20 seconds.
If have taped the cutout properly , then the cutout should neither wrinkle nor blacken due to the heat. Using the tip of the Iron , carefully run over the traces a few times to fix them in place.
After doing this , once again press on the PCB for around 10 seconds. Make sure that at no point of time the traces get smudged or merge together.
At this point you must be able to visually see that the toner has melted. If you feel that the toner has not melted completely in a few places , then feel free to run them over using the tip of the Iron.
Now immediately take the PCB and dunk it in a container full of tap water. This will cause the toner to become solid and stick to the PCB. Leave in the water for atleast 15-20 seconds.
Then remove it from the water and slowly peel off the tape and remove the cutout. Atleast 95% of the toner must have transferred to the PCB.
here is a video which i made to show you how exactly it is done :
However , note from the video that a single pad hasn’t transferred from the sheet to the PCB.
To fix this , just use a permanent marker (blue or black) and just draw over the place where the pad should be several times (this is very important) . The permanent marker will act just like the missing toner.
4) The final part – Etching the PCB
This involves dunking the PCB in a tub full of a chemical that can dissolve copper. Some typical example are ferric chloride , ammonium persulfate , and a mixture of HCL and 3H% H2O2.
Ferric Chloride is most commonly available in india. To prepare the etchant using HCL and H2O2 , refer this link. Ammonium persulfate is said to be better than FeCl2 as the soultion is clear and hence you can overlook the etching process.
The etchant prepared from HCL and H2O2 is faster than FeCl2 , but unfortunately it also dissolves permanent marker ink. So , there is no chance of making any corrections on PCBs after you perform toner transfer. This is the primary reason why i am sticking with FeCl2.
Warning : If you are using FeCl2 , let me tell you that it stains anything , including skin upon contact. The stains are nearly impossible to remove. If you get FeCl2 on your skin , wash it off immediately using water.
Ferric chloride is available in the form of dry (and rather messy) power. The instructions say to dissolve 500g of the powder in 1 liter of water. I have found that dissolving around 700g makes a more potent solution.
After you prepare the , dunk the PCB in it and leave it for a while. At room temperature and with no heating or agitation , it takes around 4 hours to complete. With heating , it (reportedly) reduces to 1 hour. I have never tried heating myself so i really dont know much.
UPDATE : I bought a new 500g FeCl2 pack and dissolved it in 500ml of water ( The recommended amount is 1 liter). And i heated it by placing the container full of FeCl2 in another tub full of hot water. Amazingly , it finished etching in just 10-15 mins!!
I don’t know what had such a major impact on the etching time ; Was it the heating or was it the more concentrated solution??
Use ONLY PLASTIC TWEEZERS to remove the PCB from the etching solution. After it is done , clean the PCB thoroughly with water and soap. To remove the the toner , use either sandpaper or acetone.
And voila…You’re done…
Note : Always remember to sand the PCB once before soldering , as the oxidized copper will repel solder.