As the others have said, to date, you shouldn't do it. The reasons are few but good ones.
The 'substrate' isn't one that lends itself well for screwing in the backerboard. (Usually, the substrate is particle board or very thin plywood.) If you DON'T use a backerboard, you'll have to tile directly onto the top of the formica. Forget that - It's too 'bouncy' for tile. (You need a backerboard to make it stiffer.) Also, sometimes, the formica isn't glued in places to the substrate any more. So, when you go to tile over it, you have 'bumps' or 'hills', and the tile won't sit properly.
Really, it's easy for me to say, but I'd do it the RIGHT way. If you don't, you may end up doing it again at a MUCH more cost, and you'll be asking us if there's a way you can 'salvage' the tile.