Patent ID: 7115207

Claim:
A method of manufacturing a metal UMoly mask for an integrated circuit chip interconnect solder bump, said method comprising: depositing a photoresist on both sides of a molybdenum foil sheet, wherein said molybdenum foil sheet is approximately 8 mils thick and said photoresist is approximately 12 microns thick; exposing and developing said photoresist to have at least one opening having a first diameter of approximately 4 mil; and simultaneously etching both sides of said molybdenum foil sheet for a time period sufficient to produce a via through said molybdenum foil sheet such that said via has a second diameter of approximately 12 mils and a knife-edge of approximately 0.2 mils, wherein said etching comprises using an etchant spray with a pressure of approximately 5 psi and undercutting said photoresist adjacent to said at least one opening to form an unsupported edge of said photoresist, and wherein said depositing of said photoresist that is approximately 12 microns thick and said using of said etchant spray with said pressure of approximately 5 psi ensures that after said time period said unsupported edge survives.