Bleed and Feed Method of Controlling Aqueous Photoresist
Original Publication Date: 1981-Jun-01
Included in the Prior Art Database: 2005-Feb-11
In processing printed circuit boards using an aqueous-type photoresist, the standard practice is to fill the machine sumps with fresh (no resist loading) solutions which are then used until depleted and then replaced. The disadvantage of this system is that the processing speeds must be continually reduced as the solution strength weakens, since the rate of attack on the photoresist will not be constant. Problems that may arise are insufficient developing, causing "scumming", and incomplete stripping, causing traces of resist or adhesion promoters to remain on the panel surface.