Welcome to FT, Aston Villa Fan!

1 1/2 hr should be enough for this connection though it could be tight if the incoming flight is late. If the two flights are on a single ticket they will put you on the next flight to BHX should you miss your connection.

You don't need to leave secure area (i.e. no passport control or customs) but you will have to go through one or two security screening (depending on where your flight arrives).

You may also want to check the FRA connection thread in the LH M&M forum.