Moly mask construction and process

A method of manufacturing a metal TMoly mask for a tin-rich cap of 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 4 mils thick and said photoresist is approximately 12 microns tick;
• exposing and developing said photoresist to have a first opening on a first side of said molybdenum foil sheet and a second opening on a second side of said molybdenum foil sheet, wherein said first opening has a first diameter of approximately 7 mils and said second opening has a second diameter of approximately 11 mils;
• 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 third diameter of approximately 10 mils adjacent to said first opening, a fourth diameter of approximately 14 mils adjacent to said second opening 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 both said first opening and said second 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.

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 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;
• periodically adjusting a chemistry of said etchant spray to avoid a reduction in etchant activity;
• 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, said using of said etchant spray with said pressure of approximately 5 psi, and said adjusting of said chemistry ensures that after said time period said unsupported edge survives.

A method of manufacturing a metal TMoly mask for a tin-rich cap of 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 4 mils thick and said photoresist is approximately 12 microns thick;
• exposing and developing said photoresist to have a first opening on a first side of said molybdenum foil sheet and a second opening on a second side of said molybdenum foil sheet, wherein said first opening has a first diameter of approximately 7 mils and said second opening has a second diameter of approximately 11 mils;
• and
• simultaneously etching both sides of said molybdenum foil for a time period sufficient to produce a via through said molybdenum foil sheet such that said via has a third diameter of approximately 10 mils adjacent to said first opening, a fourth diameter of approximately 14 mils adjacent to said second opening and a knife-edge of 0.2 mils,
• wherein said etching comprises:
• using an etchant spray with a pressure of approximately 5 psi;
• periodically adjusting a chemistry of said etchant spray to avoid a reduction in etchant activity;
• and
• undercutting said photoresist adjacent to both said first opening and said second opening to form an unsupported edge of said photoresist, and
• wherein said depositing of said photoresist that is approximately 12 microns thick, said using of said etchant spray with said pressure of approximately 5 psi, and said adjusting of said chemistry ensures that after said time period said unsupported edge survives.