For the heat transfer, prep the board, and then transfer it to your working surface. Set the iron to its max temperature setting, and then pre-heat the PC board without the image. Leave it for a few seconds, then *carefully* place the image face down on the hot PC board; this will cause it to stick somewhat to the surface, which is exactly what you want.
The next step requires brute force: start ironing the PC board, pressing down hard and moving the iron all around the board. This is where the baking parchment becomes useful: by placing it on top of the image, the friction is greatly reduced, and thus putting pressure on the board won’t make it shift on your working surface. Use the edges of the iron to create a little more pressure over the image. The idea is to give it heat and press down, the more pressure the better. Don’t be afraid to really have at it! The good thing about this method in particular is that the image won’t smudge unless you overheat it and actually move the paper, but that has only happened to me once. (If my examples aren’t descriptive enough for you, here is the video that helped with some of the finer points).
The method that works best for me is to use the large surface of the iron for pressure, pressing down hard, then running over the image with the edges, repeating as many times as you feel comfortable with. The more time you spend on it, the higher the likelihood of success. This usually takes between 2-3 minutes.
Have the container of warm water nearby, as well as a tool that can touch a scalding hot PC board without causing you any harm. Move the PC board over(and this is the hard part), dunk it. I prefer to put the board in hot, because my theory (totally unproven, by the way) is that the ink should stick better to the copper surface, since it cools faster. The water should be hot so that it permeates the paper faster, which means that there is less chance that the image will stay on the paper. Once the whole piece becomes semitransparent, stick your hand in the container (aren’t you happy you didn’t use boiling water?) and peel away the top layers, which should reveal an image on the surface, which may or may not have patches of thin paper still stuck to it. Be careful, the PC board may still be hot. If any pieces of paper are left over, and with your fingers gently rub it away. If your circuit/image has small areas that can be bridged, it may not be enough to remove the paper with just your fingers; at which point it is time to crack out the ear buds and alcohol. This is kind of important: the alcohol will weaken the paper but not the print, so you can use it to clear out any stubborn bits from the image, making it clear and perfect for etching. So dip the earbud in the alcohol and (once again, gently) rub at the exposed pieces of paper that you want to remove.
That’s about the grand sum of things that can go wrong, but here are some honorable mentions that made getting to the first success a living nightmare. Trust me; these will screw up the project every single time:
The first go around I did not have an iron, instead opting for a heat press. The idea seemed good enough, and it may have actually worked if not for the fact that I was using transparent paper at the time. Several blogs will tell you that it’s a good idea since you can see where the image lands and that you can use the same method as the high gloss paper, but really you can’t. For one thing it’s plastic, so no amount of water is ever going to get it loose from a pc board. That other thing is that there is a fine line between the point where you may or may not plausibly get image transference, and what I call ‘the white out’ stage. The white out point is where enough heat is applied to degrade the plastic, causing it to melt and adhere itself to the board, thus making it nearly impossible to reclaim the board.
Next up is a tool I think could only be made by Satan himself, the ancient iron that I got a hold of. There is a reason I’m happy to be living in this time period, and it’s this iron. Back in the ‘good old days’, irons ran without any limiting mechanism and they had induction coils that ran as hot as the current would allow. These things burn like hell. The iron can burn through the paper, PC board and any underlying materials. This thing was a monster and I wisely decided to set it aside. Luckily, modern steam-free irons are very cheap.
After those disasters I’ve had a few minor hiccups here and there, but following the prescribed method works out a good portion of the time. I still get failures, but every time gets a little bit better.