Metal fusion bonding – With means to juxtapose and bond plural workpieces – Wire lead bonder
Reexamination Certificate
2000-04-03
2001-02-06
Ryan, Patrick (Department: 1725)
Metal fusion bonding
With means to juxtapose and bond plural workpieces
Wire lead bonder
C228S025000, C228S033000, C228S049100, C219S085180
Reexamination Certificate
active
06182882
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to wire bonders and a method of wire bonding.
2. Brief Description of the Prior Art
In the fabrication of semiconductor devices, one of the generally required procedures is that of bonding wire between a pair of wire bonding locations, these wire bond location usually involving bond pads on a semiconductor chip and lead fingers of a lead frame. This procedure is generally accomplished by providing a ball bond onto the bond pad of the semiconductor chip and a stitch bond onto the lead finger of the lead frame, both of which are provided, at least in part, using ultrasonic or thermosonic heating techniques.
With the increasing demand for lower temperature thermosonic bonding processes, the stitch bonds become increasingly critical from the standpoint of reliability. Due to the inherent motion of ultrasonic energy being parallel to the axis of the ultrasonic transducer which provides the ultrasonic energy, wires bonded in a direction normal to the axis of the ultrasonic transducer have relatively high stitch flare area (meaning that the stitch bond spreads out on the surface to which the bond is being made) and have relatively high tensile strength as compared with stitch bonds formed wherein the ultrasonic energy moves in a direction parallel to the wire bonding direction, such bonds displaying relatively low tensile strength and having a relatively smaller stitch area.
To compensate for this known effect, in the prior art, the ultrasonic power bond force and bond time are programmed to vary, depending upon the wire angle or position with respect to the axis of the ultrasonic transducer. However, this approach fails to provide the optimum solution since the direction of the ultrasonic energy still remains the same, namely normal or with a component normal to the direction of the ultrasonic energy.
SUMMARY OF THE INVENTION
In accordance with the present invention, the above described problem of the prior art is minimized and there is provided a bonding method and apparatus which can provide bonds with required tensile strength regardless of the direction of travel of the capillary through which the ultrasonic energy is provided relative to the direction in which the stitch bond is made.
Briefly, the above is accomplished by positioning the transducers at right angles to each other and at a 45 degree angle relative to the x and y axes, with the x and y axes lying in the plane of the surface to which the stitch bond is to be made. This allows half of the array of wires to be normal to each transducer and addresses the above discussed limitation of the prior art and current wire bonders. This approach also provides more flexibility for low pitch lead frames by allowing the bond heads to be capable of being closer to each other without mechanical interference.
More specifically, a plurality of lead frames, each with a semiconductor chip thereon, move along a conveyor in an “x-axis” direction wherein the “y-axis” and “x-axis” both lie essentially in the same plane as that of the lead frame and chip. The “z-axis” is normal to the x and y axes. A pair of bonding capillaries which are each movable in each of the x, y and z axes, are positioned to deliver ultrasonic energy therethrough to wires to be stitch bonded in standard manner. Each of the capillaries is mounted to make an angle of substantially 45 degrees with each of the x and y axes. The angle made between the axis of each capillary and the z-axis can be from 0 to 90 degrees and is preferably about 45 degrees with the axes of the capillaries preferably extending in opposite directions such that the mouths of the capillaries through which wire is ejected face toward each other. This provides flexibility for tight pitch lead frames, flexibility for “stud bumping” on the wafer level and flexibility to optimize the capabilities of the transducers.
REFERENCES:
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patent: 5537737 (1996-07-01), Kamakura et al.
patent: 5544804 (1996-08-01), Test et al.
patent: 5702049 (1997-12-01), Biggs et al.
patent: 5735449 (1998-04-01), Magni
patent: 5944249 (1999-08-01), Macabitas et al.
patent: 6-69290 (1994-04-01), None
Hortaleza Edgardo R.
Subido Willmar E.
Brady III Wade James
Cooke Colleen
Ryan Patrick
Telecky , Jr. Frederick J.
Texas Instruments Incorporated
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