Wonderboard installation

I am installing porcelain ceramic floor tile in bathroom. House is 40 years old. Sub flooring in good shape consists of 5/8" plywood mounted on 1x6 boards layed over joists. Since the base looks very sound, I am using 1/4' wonderboard as a backer for the tile. My question is: I plan to use modified thinset and then use 1 5/8 screws 6-8 inches apart. Is it necessary that I mesh tape all the seams? I am a bit nervous about creating "humps" at the tape seams and cause cracking pressure on the tiles. With a solid screwed in procedure is it ok to simply fill in the seams with thin set and smooth to the surface ...I plan to do that at wall edges.

Nope, you need to tape the seams, but you don't have to do it in advance...you can do it when you lay the tile. That helps prevent speed bumps. Go over to www.johnbridge.com and use their deflection calculator to verify your joists are strong enough. You probaby have enough subfloor, but you need to verify the joists. Make sure to follow the instructions and put the thinset under the wonderboard, too. This is very important to fill any minor imperfections with the thinset so the wonderboard is fully supported. That site can help out.

Thanks Jim. I think I will opt for the tape while tiling method to avert the speed bumps.