Metal working – Method of mechanical manufacture – Electrical device making
Reexamination Certificate
2000-01-11
2003-12-30
Vo, Peter (Department: 3729)
Metal working
Method of mechanical manufacture
Electrical device making
C029S002100, C029S854000, C029S890100, C216S027000, C216S033000, C216S034000, C216S035000, C216S041000, C216S049000, C347S058000, C347S063000, C438S725000, C438S906000
Reexamination Certificate
active
06668445
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of TAB bonding, and, more particularly, to a method of attaching a beam of a flexible circuit to a bonding pad.
2. Description of the Related Art
Tape Automated Bonding (TAB) is used within the ink jet printer industry as a way of interconnecting a heater chip and a flexible circuit. The heater chip is a multi-layered device in which ink is heated in order to cause the ink to be jetted out of orifices or nozzles in the heater chip toward a print medium. The flexible circuit carries power to the heater chip in order to selectively energize the ink emitting nozzles. The bonding pads are patterned in a thin film process of fabricating the heater chip, which may include sputtering, chemical vapor deposition, etching and/or photolithography. The flexible circuit includes finger-like beams which are bonded or welded to the aluminum bonding pad on the heater chip. The bonding may be performed with ultrasonic, thermosonic or thermocompression bonding. A problem is that the TAB bond between the flexible circuit and the heater chip is known to fail due to poor bond strength. The poor bond strength can be attributed to many different factors, including contaminated bond pads or non-optimized bonding parameters. Since the TAB circuit is one of the most expensive parts within an ink jet print head, the scrap cost associated with TAB bond failure significantly increases the overall cost of the ink jet printhead.
What is needed in the art is an improved method of TAB bonding a flexible circuit to a bonding pad of a heater chip, such that higher bond strength and less bond failures are achieved.
SUMMARY OF THE INVENTION
The present invention provides a method of removing dirt or other contaminants from the surface of a bonding pad before TAB bonding is performed between the flexible circuit and the bonding pad of the heater chip.
The invention comprises, in one form thereof, a method of tape automated bonding a heater chip of an ink jet printer to a flexible circuit. The method includes the step of attaching an electrically conductive bonding pad to a first portion of a surface of the heater chip. A mask is applied to a second portion of the surface of the heater chip. An exposed surface of the bonding pad is chemical dry etched for a predetermined time period to thereby remove contaminants from the etched exposed surface. The chemical dry etching is terminated at an end of the predetermined time period such that substantially none of the bonding pad is removed. Lastly, the flexible circuit is electrically connected to the etched exposed surface.
An advantage of the present invention is that various contaminants are removed from the surface of the bonding pad which is to be TAB bonded to the flexible circuit, thereby resulting in higher bond strength and higher production yields.
Another advantage is that the cleaning process does not remove substantial amounts of material from the surface of the bonding pad, thereby leaving the bonding pad intact for TAB bonding.
BRIEF DESCRIPTION OF THE DRAWINGS
The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention will be better understood by reference to the following description of an embodiment of the invention taken in conjunction with the accompanying drawing, which is a side view of one embodiment of the method of the present invention, in which a heater chip is placed inside a reactive ion etching (RIE) chamber.
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Mrvos James Michael
Raulinaitis Michael
Sullivan Carl Edmond
Kim Paul
Lexmark International Inc.
Taylor & Aust P.C.
Vo Peter
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