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Laser Deposition of Gold Bumps for TAB Packaging of Chips

IP.com Disclosure Number: IPCOM000039939D
Original Publication Date: 1987-Aug-01
Included in the Prior Art Database: 2005-Feb-01
Document File: 2 page(s) / 23K

Publishing Venue

IBM

Related People

Baum, TH: AUTHOR [+3]

Abstract

The low-end packaging of chips can be accomplished by Tape Automated Bonding (TAB), in which chip-to-package interconnections are formed simultaneously and reliably. This technique currently involves the placement of gold bumps (1 mil in thickness) on the I/O pads of the chip before bonding. The gold bumps are formed by electroplating which requires: a) electrically connecting all the I/O pads on the chip by deposition of a conductive gold layer; b) photoresist application and processing; c) a wet process for the plating of the gold bump. Alternatively, the bumps can be produced on the copper fingers (or beams) on the TAB tape by subtractive etching of a thick copper finger to form the bump. In this case, copper is the bump.

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Laser Deposition of Gold Bumps for TAB Packaging of Chips

The low-end packaging of chips can be accomplished by Tape Automated Bonding (TAB), in which chip-to-package interconnections are formed simultaneously and reliably. This technique currently involves the placement of gold bumps (1 mil in thickness) on the I/O pads of the chip before bonding. The gold bumps are formed by electroplating which requires: a) electrically connecting all the I/O pads on the chip by deposition of a conductive gold layer;
b) photoresist application and processing; c) a wet process for the plating of the gold bump. Alternatively, the bumps can be produced on the copper fingers (or beams) on the TAB tape by subtractive etching of a thick copper finger to form the bump. In this case, copper is the bump. Since copper is harder than gold, these bumps can cause chip cracking during thermocompression bonding of the bumps and the chip pads. Gold bumps can be formed on either the chip or the tape by laser chemical vapor deposition. This process can deposit gold on both conducting and non-conducting surfaces, and eliminates the need for blanket gold deposition. The laser process for gold deposition is a localized one, and thus avoids the complication of resist application, processing and masking steps. Since it is a dry process, it will minimize the contamination of chips from solvents and plating solutions. Since gold can be directly written with a laser, the process is useful for bumping i...