This should be moved to the connection thread either in the Germany forum or in the Lufthansa forum.
If this is on one ticket, it's usually no problem if plane is on time. Make sure agent checks your bags in the US to Berlin so that you don't have to recheck them in Frankfurt. This is possible in Europe!
Immigration has to be done in Frankfurt which will usually not take that long (not comparable to US standards) and customs for hand luggage is in Frankfurt as well (not a big deal either unless you are smuggling something

), customs for checked bags is in Berlin.
Have a safe trip.
Welcome to FT!