Hao is visiting Boston and working on controlling a 5 DOF robotic arm together with DGonz (detailed development on his blog) in MITERS, and when we try to make a double sided PCB boards with etching, we come up with a new method to do registration perfectly.
As you can see, the front and back side of the board aligned up very well.
The new method is simple. We didn't took picture of the process, so here's the simple text instruction:
1 Put both front and back side on same image, aligned up.
2 Move front and back side closer, with an isolation a little bit larger than the thickness of the board. Draw a line with width as same as the thickness of the board on the center of isolation. Print the pattern on a piece of gloss paper.
3 fold the two sides of gloss paper together, make sure grey line perfectly aligned up with both ends of board.
4 put the board into laminator.
If you can't understand the text (which is very possible due to Hao's English level), I might publish a tutorial after I do this workshop in toorcamp.