How to get the adhesive tape to stick good after screen replacement?

I use original adhesive tape to connect the screen and backside. But everytime I fix a phone it does not stick good enough. I use clamps for 12 hours to get good pressure and also use a heatgun to heat it up before I put the clamps on. Still I have many customers complaining about the sceeen or backside coming off. So I end up using glue. Any suggestions on how to get the adhesive tape to stick good?