Immersive engineering hammer reqiured to make copper plate

IC2 definitely doesn't force that either way, so it could be a couple of things:

1. You're looking at a plate from Immersive Engineering rather than an IC2 one, thus it won't appear to be possible to make using a Forge Hammer
2. One of the mods you have is trying to unify recipes but doesn't do a great job at it so removes the IC2 recipes but doesn't add replacement versions of IE plates using the Forge Hammer
3. The recipes have been unified some other way, such as a modpack's custom Minetweaker scripts

It's hard to say which one of those it is (or whether it's even something else), the best test is to try something like a lead ingot and a forge hammer and see if it makes a lead plate or not. If it does then the recipes are probably fine and it's just the mod's plate you're looking at the recipe for. If it's not then chances are the recipe has been tinkered by another source, which can't really be determined past looking at the modlist for any mods that sound like they might.

From what I know, it's a bug in unidict. I bugged SnowShock about it and he said, that it'll be fixed in the next update of the FTB packs.