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Removing Residual Polyamic Acid Salt Films From Chip Joining Solder Balls

IP.com Disclosure Number: IPCOM000059746D
Original Publication Date: 1986-Jan-01
Included in the Prior Art Database: 2005-Mar-08
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Linde, HG: AUTHOR

Abstract

Polyamic acid used in the final step of an integrated circuit (IC) fabrication process forms an undesirable lead polyamate salt (a barrier film) on the solder ball chip interconnect. A technique for the removal of this film from the surface of the solder ball is described. Polyamic acid is applied over an entire chip as the last step of an IC fabrication process. Lead polyamate salts are formed on the solder balls during this process step. When cured, these salts form stable encapsulating imide films which prevent wetting by the solder and inhibit chip joining to the substrate. The problem films form during the initial contact between the polyamic acid and the lead in the solder ball.

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Removing Residual Polyamic Acid Salt Films From Chip Joining Solder Balls

Polyamic acid used in the final step of an integrated circuit (IC) fabrication process forms an undesirable lead polyamate salt (a barrier film) on the solder ball chip interconnect. A technique for the removal of this film from the surface of the solder ball is described. Polyamic acid is applied over an entire chip as the last step of an IC fabrication process. Lead polyamate salts are formed on the solder balls during this process step. When cured, these salts form stable encapsulating imide films which prevent wetting by the solder and inhibit chip joining to the substrate. The problem films form during the initial contact between the polyamic acid and the lead in the solder ball. However, the uncured deposited polymer is permeable and permits removal of the problem film during the normal develop-etch process if a lead reactive octanoic acid reagent is used. Subsequent etching in the process removes the octanoic acid salt. PROCESS STEPS: 1) Polyamic acid is normally applied to the chip including the reflowed solder balls, causing a film of polyamic acid salt to to be formed over the the surfaces of the solder balls. 2) After baking to dry the polyamic acid, a photoresist layer is applied over the polyamic acid film and exposed in the solder ball chip interconnect regions. 3) A two step process follows which simultaneously develops the photoresist and etches the underlying polymer. A) Du...