^(?=.*[A-Z])(?=.*[0-9])[A-Za-z0-9]+$
должен сделать.
^ # start of string
(?=.*[A-Z]) # assert that there is at least one capital letter ahead
(?=.*[0-9]) # assert that there is at least one digit ahead
[A-Za-z0-9]+ # match any number of allowed characters
# Use {8,} instead of + to require a minimum length of 8 characters.
$ # end of string