Abstract
An investigation to develop a better understanding of the fundamentals behind the operation of spray‐etching processes revealed several interesting phenomena that explain some of the difficulties encountered during operation. Higher spray pressures are required for the top sides than for the bottom sides in order to achieve equal amounts of etching on each side of the boards being processed. This is due to additional mass‐transfer limitations that are created when puddles of liquid collect on the top side of the boards. Another phenomenon observed was an increase in the etch angle, resulting in more vertical sidewalls, as the extent of etch undercut increases. Based on these experimental observations, a dynamic model for the spray‐etching process is developed.