Sorry for not checking back to this thread..
When hinging the photo to the backer board, we use what is called T hinges. They go approximately 1/4 of the way in from each end of the top of the paper. Having any tape at the ends is one of the reasons for rippling as is taping all the way across the top.
By only hinging in 2 spots, the paper has more room for expansion and contraction.
When it is taped at the ends, the paper only has in towards the middle to expand causing ripples.
When it is taped all the way across the top, then the paper will ripple more severely at the top and taper down and away from the tape.