Introduction: Toner Transfer for PCB : Flamethrower Style
If you are a Maker interested in electronics, chances are you are trying (or tried, or gave up trying) to make your own PCBs.
Going for professional PCB manufacturing may be a very good idea, especially if you are working on anything where reliability is not an option or if you need a lot of the same PCB. However, creating a working prototype (at least for me) usually takes more than one board and to tell you the truth, I'm not even close to be patient enough to wait for my boards to come back from the plant.
Now, I'm one of those unlucky guys who bought a Brother laser printer before getting interested in etching. You will find many comments on the web saying how it is difficult to melt the toner from those printers to transfer it to a copper plate.
It is all true.
Don't get me wrong : it is a very good printer. It was just not meant to be used to etch circuits.
I have tried many things : hot plates, laminators, steam iron... In the end, I probably should have given up and resigned myself to buying a cheap second-hand HP printer... But I really got mad one evening after a very time-consuming, elaborate and finally disappointing etching. I just imagined having a flamethrower to heat up that stupid steam iron... And got this idea of using a propane torch and push the melting to the limits of what the paper can endure.
Step 1: Some Background Informations...
Flash point, also called autoignition temperature, is the lowest temperature at which a substance will spontaneously ignite. For paper, it is between 218-246 Celsius (424-475 F), depending on local conditions. You should aim for a little under that if you don't want any trouble.
Propane : A by-product of natural gas processing, C3H8 combustion will release 2219 kj/mol, with a flame reaching up to 1430 Celsius. More than enough, see previous point and add to it the following piece of knowledge : Brother toner should melt at 120 Celsius.
Extinguisher : An active fire protection device used to extinguish or control small fires, often in emergency situations.
Step 2: What Do You Need?
You don't need a lot of stuff :
One solid flat piece of steel. I used a 5mm galvanized thing that I found at my local home center. It was in the "electrical stuff" aisle, but I don't have any idea what it should be used for. Don't use anything to thin, especially if made of aluminum (foil, soda can, etc) because while it is a good heat conductor, it will warp and oxidize.
You will need two metal clamps;
A flat piece of wood to clamp on the steel plate;
Some absorbent and spongy paper towels;
A propane torch;
A fire extinguisher;
Thick welding gloves;
And a bucket of water.
Of course, you will need your usual laser printer, with the paper you usually use for the transfer, some blank copper boards and your favorite etchant. This being said, I'm not going to detail how to use the printer for the toner transfer method nor discuss what is the best etchant, as this is not the purpose of this Instructable.
If you really want to know, I use the very toxic and non-staining sodium persulfate. I also use the vinegar / salt / hydrogen peroxide mix. I started with the muriatic acid / hydrogen peroxide mix of death, but it was eating away my traces and my lungs way to quickly to my liking. I never used ferric chloride.
With any etchant, follow the instructions, work with plenty of aeration, wear gloves and goggles and keep pets, kids and significant other away.
Step 3: Safety First
Yep, those should be "Best Friends Forever". And please notice that I'm working outside, on cement slabs, far from anything that could catch fire. This being said, yes of course it is dangerous. You make stuff at your own risks, such is life.
If you are a young Maker, go ask your parents before doing anything like using a propane torch. Better, let them take all the risks. If everything goes wrong, you will survive and likely post an update or a warning for the rest of us.
If you don't have an extinguisher, stop reading right here and get one. And if you want to do something brilliant, get one that you can use against electrical fires : one day, you will want to try making a capacitor bank, a Tesla coil or an induction oven...
Of course, if you don't have a propane torch, you should also stop reading and get one... Did you noticed that mine is "NC" and needs the trigger to be constantly pressed for the torch to work? Nice safety feature. If anything goes wrong, I throw it away and get that extinguisher working!
Step 4: Print Your Circuit and Prep Some Copper
I use 120g HP Premium Glossy Presentation Paper. It is cheap and available. Two important qualities for the Makers.
For the copper board, I used the cheapest, warped, recycled board I could find. My idea was to test this technique in the worst possible conditions. I'm just anxious to try it now with some really good quality boards!
The board was rinsed with acetone to remove all the old toner from previous transfer mishaps using the steam iron technique, then lightly sanded to remove oxidation and some rebellious toner.
Step 5: Place Your Printed Paper Against the Metal Plate
Just place the piece of paper with the toner up, unless you want to try etching a 5mm thick galvanized steel plate.
Maybe it is difficult to see, but this plate was far from being perfectly flat. I use my Dremmel to remove most of the bumps. My job was suboptimal to say the least, so I tried to use the flattest spot on the plate.
Step 6: Place the Copper Side Against the Toner
On top of the toner, the copper side... You don't need any tape : the pressure will hold everything in place and beside, the thickness of the tape, while being small, will be enough to make the pressure uneven, with undesirable results.
Step 7: Place the Paper Towel on the Fiberglass Side
Now, the little secret I gladly share with you...
Take a good piece of paper towel, fold it as a small cushion and use it as a pad between the fiberglass and the piece of wood. That will spread the pressure, flatten the PCB and will dramatically improve the results.
Like to paper on which you printed your circuit, the flash point of this paper towel is quite high, more than enough here.
Step 8: Squeeze Everything
I used metal clamp, and don't be shy to give it a good squeeze. Remember that the more pressure you put on the back of that PCB, the nicer the transfer will be.
Do I really have to tell you that those metal clamps will be scorching hot after the torching?
Do I really have to tell you not to use plastic clamps?
Step 9: Burn Baby, Burn!
Sorry, no action shot. It is quite difficult to hold the propane torch and take a picture when wearing welding gloves. Use your imagination to picture me with a sadistic grin carefully and equally heating the metal plate.
You will have to experiment a little bit to the best duration for the best results, as the plate thickness, the paper thickness, the ambient temperature and your propane torch will likely be different than mine. To give you an idea, I get pretty decent result with in less than a minute.
If you see smoke, it is likely too late, unless the flame just touched the wood.
You want a paper that will be very lightly roasted. No even caramelized.
Keep the extinguisher close by, you never know. It is unlikely that you will have the time to do anything if the propane torch explodes, but your neighbors will have something to use to make sure you will be looking great in that coffin.
Just kidding... but you get the idea.
Step 10: Soak PCB in Water
Take the burning hot piece of PCB (with the welding gloves of course) and dump it in the bucked of water.
When you think you waited enough, wait a little bit more.
You will notice that the soaked paper will start lifting from the board. Pull it very gently.
Some paper will stay on the toner : drop back the piece in the bucket and wait.
Repeat the process until most of the paper is removed. Be especially careful to look and remove all paper residues from thermal pads or from between close traces.
You can use a small toothpick or a soft toothbrush. Using the soft pulp of your fingers under the water is usually safe, but use your nails carefully if you don't want to scratch away the toner.
Step 11: Final Results
On the top, you have the Flamethrower transfer. On the bottom, the usual steam Iron transfer. For the comparison, I took the best iron transfer I ever made for this circuit. You will notice that even if the Flamethrower is not perfect, the lettering and the trace edges are much more defined.
I call it a success, considering that :
- I melted the toner in less than a minute with the propane torch compared to a full half-hour of misery, pressing the iron against the board, praying not to smudge anything;
- I scrapped at least 5 circuits with the iron (and had to use acetone to remove the toner and sandpaper to condition the copper again) while I got 5 successes in a row with 5 different circuits using the torch.
By the way, you probably noticed that my copper board are now shinning like the armors in Excalibur... This is not witchcraft, so don't try using my own torch to burn me alive!
I just tinned the copper with some Liquid Tin. If you drop your freshly etched PCBs in the solution (before they oxidize), they will be nicely covered with an easy-to-solder matte tin plating. To get the nice shiny finish, I polished the boards with a metal brush spinning like crazy on my Dremmel. Use gloves, a mask and goggles to do that, as the boards will heat up and the brush will throw tiny metal bits everywhere.
Step 12: What Can Go Wrong?
The circuit on the left was done without the folded absorbent paper, so the pressure from the piece of wood was not equally distributed. On a warped piece of PCB, it means some transfer issues. Also, when the PCB was cut, I forgot to sand the sides. That resulted in a minute elevation on one side that prevented a good transfer.
The one in the middle is close to perfection. Pressure was equally distributed on the entire surface, temperature was good and the edges being sanded and far from the circuit, no issues are visible.
On the right, this is what happens when you put too much heat.
Interestingly, the substance gluing the copper on the fiberglass board oozed through the metal (it looks like that), imprisoning some copper droplets.
Even after hours in the etchant, there was an intact spot, right over where the fiberglass showed signs of melting on the back (and visible through the PCB).
If you smell burnt paper or if you paper looks caramelized, you are likely to end up with this, and removing the paper will be quite difficult, even after a long swim in the water bucket.
Did you noticed that I said that I left the right circuit in the etchant for hours? Notice how the toner survived well this long soak! Usually, if I left a PCB done using the steam iron method in the etchant for longer periods, the traces would start lifting. This is very annoying on large circuits with different trace sizes.
Step 13: Conclusion
In the end, it took me longer to write this Instructable than to do my PCBs. This technique is much faster and easier than the usual steam iron method, and will give very detailed transfers. However, it is not the safest technique.
This being said, etching your own PCBs comes with other well known hazards : toxic acids, volatile alcohols, toxic dusts, Dremmel injuries, madness when nothing works... So adding some fire hazard is unlikely to frighten the real Maker.
However, stay prudent and enjoy etching.