Thin wafers have become a basic need for a wide variety of new microelectronic products. Thinner die are being required to fit into thinner packages. Wafers that have been thinned using a final wet etch process on the backside have less stress compared with standard mechanical backgrinding. Isotropic wet etching of silicon is typically done with a mixture of nitric and hydrofluoric acids along with the addition of chemicals to adjust for viscosity and surface wettability for single wafer spin processing. As the silicon is etched and incorporated in the etching solution the etch rate will decrease with time. This variation has been modeled. The focus of this paper is to compare the process control techniques for maintaining a consistent etch rate as a function of time and wafers processed. The models allow for either the time to be extended, chemicals to be replenished or a combination of these. Results will be presented including the cost of ownership for each scenario.