This is a different way of making a double sided PCB, having one feature in common with the previously presented option – it also relies on vinyl sticker. For this reason we’re going to call it double sided vinyl sticker PCB. As you will soon discover, I have used pins for synchronizing the two sides. It’s a little bit more complicated BUT it should provide more accuracy with aligning the two sides. For starters, let’s take a look at the schematic I have set in Sprint Layout 6.0:
The 8 holes from the right side will have to be perfectly overlapped because they will serve as communication path in between the top and the bottom of the copper board. Choosing the top respectively the bottom can be arbitrary. In order to avoid complications however, let’s agree that the first one is the bottom (the rear side). Naturally, the second one, from the bottom of the previous photo, is the top (the front side). On the top of the double sided vinyl sticker PCB we will attach the displays, facing us.
Important to specify, the two sides of the board are now mirrored. After finishing the project, the holes will overlap correctly. For a better understanding, follow the holes for +5V and Gnd – notice their disposal in this initial photo and see how they look in the end.
Making this double sided vinyl sticker pcb requires three different stages: bottom, synchronizing and top. We will use a double sided copper board. But since the sides will me projected individually, one after the other, we will need to entirely cover with vinyl sticker one side of the board while we etch the other one. Now let’s be more specific:
Double sided vinyl sticker PCB manufacturing stages
Begin by copying the bottom of the board in a new sheet and adjusting the dimensions for an approximate fitting of the draw. We do just the same with the top of the board. In the end, we should obtain two different drawings in two different sheets of Sprint Layout 6.0:
First, we print the border, the place where we will place the vinyl sticker foil, and we do it from the menu File/Print or Ctrl+P. We drag and drop the drawing towards the middle of the page and select on the left side only the options Targets and Board respectively layer 0:
From the Setup button we choose the maximum resolution for the printer. The idea is to use as much toner as possible. Click on the Print button and you should get the border on a regular A4 paper.
You can see in the first photo that we have already printed layer 0 and we are about to overlap the piece of vinyl on top of it. At the bottom of the photo it’s the Oracal 651 vinyl sticker foil. By using a sharp object or tip we will detach it from its support and stick it so that it will entirely cover layer 0. We will make no concession on this chapter – it is better to have more vinyl than too little. For this reason, we want to show you the risks of using too little of it.
In the second photo we have already cut the initial piece of vinyl in two parts. We have checked layer C2 and printed it on the vinyl. See that the drawing was already conceived in the mirror, therefore we don’t need to check the Mirror box prior to printing. If we happen to make a mistake with the mirroring, we will have no other option but to throw the double sided vinyl sticker PCB at the garbage. And because it’s a double sided pcb, making a mistake when projecting the second side is very likely.
Personally, I always project the schematic already mirrored. In this way I don’t have to use the Mirror printing option. But if you find this approach difficult, do whatever fits you best and make sure you use the mirroring function right when printing it. Because believe me, there is nothing more frustrating than an upside pcb!
Also important, we must pay attention to how we put the paper into the printer so that the second time to print precisely in the same place, only that on the vinyl. Ideally, test the process in advance while using any other type of material instead of the vinyl and make sure you understand how things work with multiple printings on the same paper.
After that, we repeat the printing for the top of the pcb as well, we are going to need it later.
The toner transfer
We take a piece of double sided PCB – meaning a board with copper on both sides – and cut it to a slightly larger dimension than the border – layer 0. We clean it thoroughly and use isopropyl alcohol to remove the grease from it. Then comes the part of the stoned (deburred) edges, that we cover with the right tool.
The crucial issue at this stage is that while you straighten the edges you must make sure you keep them at the same level with the board. Any irregularity can prevent the iron from applying equal pressure and heat on the double sided vinyl sticker PCB.
After the copper dries, we put the drawing of the bottom with the toner on one of the two sides of the copper board. We place the schematic by using the small crosses of guidance to fix it relatively parallel and start bending the paper from the laterals towards the mid, over the copper board just like in the photo from below:
We can see the vinyl foil right through the paper, which means that the copper side of the board is beneath it. We:
- put the assembly on a hard and heat resistant surface
- we moderately heat the iron – take the temperature used for ironing a regular shirt – and make a test on a piece of paper. If the paper doesn’t get a yellowish shade, we can shift to our double sided vinyl sticker PCB
- apply the iron with circular moves, at uniform pressure, on top of the assembly paper – vinyl foil – cooper board, for 30 to 50 seconds.
The vinyl sticker should produce a particular smell as it gets hot, only that it should make no smoke whatsoever. Anyway, in order to avoid any potential unpleasant experience, it is advisable to do this procedure in an open, well ventilated space. In this way, you will not inhale the resulted vapors – which, by the way, I have no idea if they are toxic or not.
When we finish with the ironing, we take the assembly to the sink – be careful not to touch the heated parts and get burned. The board should be cooled with cold water, first on the side with the copper layer and then on the side with vinyl. Verify if you have unplugged the iron – we don’t want any nasty experience from this category.
Now we detach the vinyl from the copper by pulling it upwards under an angle of maximum 90 degrees (even though 60 degrees would be better). If the toner transfer has some flaws, clean the copper with acetone and repeat the entire procedure – from printing to ironing until you get it right.
Double sided vinyl sticker PCB Etching
Now we prep a new piece of vinyl to cover the part on which there is no printing for now. We do this to protect the second part of the double sided vinyl sticker PCB and etch what we printed so far:
We take four little spacers made of double adhesive tape – we detach the paper from one side to stick them to the side of the PCB on which we have transferred the schematic. And we leave the paper on the other side, just like in the photo from below. We sink it into ferric chloride, shaking a little bit the pcb when introducing it. We do so in order to eliminate the potential air bubbles.
Please notice I have used a larger recipient with hot water and after that I placed the recipient with ferric chloride in it, so that the chloride will gradually get warmer as well.
I used to constantly shake the assembly at this stage of PCB etching to accelerate the process. However, I have noticed that by simply placing the board face down and letting some space in between the copper and the bottom, I no longer have to do so. It’s true that the process will take a little longer, but I can do anything else during all that time. The etching is made even, with very good results. After that, we use nitrocellulose thinner or acetone to remove the toner and we should obtain a board just like in the photos from below.
Synchronizing the two sides and making the toner transfer
The next step would be to create the holes. In this case we only have 8. We will be using a very sharp drill.
We detach the vinyl from the other side, the one that was protected from etching.
We prepare two pins and stick them in the two holes from the two ends of the row, on the vinyl sheet previously printed for the top side, just to make the holes in the vinyl as well. We remove the pins and introduce them through the holes of the double sided vinyl sticker PCB just like in this photo:
We turn upside down the board by also passing the pins through the printed vinyl while making sure that the toner from the vinyl will get in contact with the copper side of our double sided vinyl sticker PCB. We press them to perfectly overlap and as we keep it firmly with the hand, we bend the margins of the paper over the board:
We take out the pins without releasing the pressure from the assembly and we bend the left side of the paper as well, making sure that the paper will not move in relation to the PCB and we turn it upside down again. The purpose is to place it with the vinyl side on top and the already etched part on bottom. Be careful, the vinyl can barely be seen through the paper:
We put it in this position on the ironing surface and we press it with the iron for 30 to 50 seconds. Again with circular moves, just like we did the first time. The aluminum from the iron may leave some traces on the paper, as you can see below:
Take the paper from one corner – don’t worry, the board won’t fall off, it’s attached because of the pressure. Take it to the sink and repeat the process with cold water, first over the board and secondly over the sheet of paper. After that, detach the vinyl foil by pulling it up (a maximum angle of 90 degrees) and you should get something similar to the next photo. Again, if you are not satisfied with the results, you can clean the toner with acetone and repeat the process. If flaws are minor, you can always correct them with a permanent marker with a thin tip.
Very important: the holes must be centered right in the middle of the pads. If you missed this synchronization you must restart the process. Say that the holes are not perfectly centered but they are in an acceptable position – it should be fine for a small double sided vinyl sticker PCB. Larger projects however cannot accept this drawback because synchronization is essential.
When this is all over, we still need to etch this second schematic. Before we proceed, we must protect the part that was already finished, so we cover it with a vinyl foil. This measure will keep the copper traces from getting in contact with the ferric chloride and be etched:
Everything from this point will be the same with what we did for setting the first side of the copper board. In the end, after we do the second etching and we cut the extra sides of the board, we should obtain something like this:
Now we thoroughly polish both sides with sandpaper, cover them with a solution of rosin diluted in izopropyl or ethyl alcohol and solder it with a soldering tool of low power (30 W):
That’s how we got a double sided vinyl sticker PCB, well synchronized, with traces of 0.3 mm.
Be aware! The larger are the spaces with toner that must remain on the final board, the higher should be the resolution of the laser printer that you use – 1200 dpi minimum. And even so, some traces may need to be fixed with a permanent marker.