Fairchild Camera and Instrument Corp.

Fairchild Semiconductor Corporation

Mark D Dufour

John A Kurtz

Donald E Cousens

An apparatus is described for maintaining and delivering a slack reserve length of lead wire between a spool or other source and the wire bonding tool of a lead wire bonding machine. A slack chamber or wind chamber comprised of a housing enclosure, an inlet guide on one side for guiding lead wire into the slack chamber from a spool, an outlet guide on the other side for guiding lead wire out of the slack chamber towards the wire bonding tool maintains the reserve length of lead wire in untangled condition. A source of pressurized dry air or other gas directs a gaseous flow into the slack chamber so that the lead wire is maintained suspended in the gaseous flow in an offset configuration. Wire sensors are operatively positioned in the slack chamber for sensing the offset of lead wire in the wind stream. The wire sensors are coupled to sensor and control logic for controlling the delivery and feeding of lead wire from a spool into the slack chamber. The wire sensors define inner and outer limits of offset thereby maintaining the reserve length within a desired range. Additional elements for back-up control of the lead wire and for handling the spool are described.

Apparatus for feeding bonding wire

A lead wire bonding machine is described for ball bonding the end of a lead wire held in a bonding tool to a die pad of an integrated circuit chip and for wedge bonding a segment of the lead wire spaced from the ball bond to a lead frame finger during successive ball bond wedge bond cycles. The bonding machine includes a variable linear drive such as a solenoid or small linear motor coupled to the bonding head for applying the first bond force to the bonding tool during ball bonding and the second bond force to the bonding tool during wedge bonding. A control circuit coupled to the solenoid or other variable linear drive delivers a first current having a desired profile or amplitude wave envelope for applying the first bond force with a first force profile during ball bonding to die pads and by delivering a second current having a desired profile or amplitude wave form for applying the second bond force with a second force profile during wedge bonding to lead frame fingers. A wave form generator generates the wave form envelopes for achieving the desired force profile so that the bond force may be varied according to the force profile during bonding at a particular site. Thus, the bond force may be varied and modulated according to the welding requirements at different die pads or lead frame fingers and according to the composition of the constituent metals of the lead wire and bonding substrate.

Variation and control of bond force

An improved lead wire ball bonding machine for bonding wire leads between an integrated circuit chip and the lead frame on which the chip is mounted is provided with a bonding tool position sensor coupled to receive the Z-motion velocity waveform signal to the servo motor which drives the bonding head and bonding tool. This sensor detects the signal level and direction of change or polarity of the Z-motion velocity waveform signal for determining the location of the bonding head and bonding tool. The bonding tool position sensor is coupled and adjusted for generating a first output signal corresponding to a first location of the bonding head and bonding tool during motion downward to the die pad of an integrated circuit chip prior to contact by the bonding tool and lead wire for ball bonding. The position sensor also provides a second output signal corresponding to a second location of the bonding head and bonding tool during motion downward toward a lead frame finger prior to contact of the bonding tool and lead wire for wedge bonding. The first and second output signals from the sensor are coupled to the ultrasonic generator of the bonding machine for application of ultrasonic bonding energy to the bonding tool prior to contact thereby increasing the bonding surface area between the lead wire and substrate. According to an alternative embodiment, an electrical sensor is provided for electrically sensing initial contact of the bonding tool and lead wire with the die pad or lead frame finger for actuating the ultrasonic generator and applying ultrasonic bonding energy to the bonding tool substantially upon initial contact with minimal delay thereby also optimizing the bonding surface area of the ball bond and wedge bond. Both the apparatus and method for lead wire bonding with increased bonding surface area are described.

Lead wire bonding with increased bonding surface area

A method and circuits are described for sensing and detecting bond attempts and weld attempts during bonding and welding of lead wire. The method and circuitry are particularly applicable for detecting missed ball bonds and missed wedge bonds during bonding of lead wire between the die pad of a microcircuit chip and the lead frame on which the chip is mounted. A sensor (30) or sensing circuit (42) senses the different characteristic electrical condition of the lead wire (11) following a ball bond attempt and following a wedge bond attempt. A bond attempt indicator (45) indicates high resistance in the lead wire following a missed ball bond while weld attempt indicator (46) indicates low resistance in the lead wire (11) following a missed wedge bond. The lead wire (11) is isolated from uncontrolled contacts with ground potential while the lead wire is held in the bonding tool and bonding machine. Switching circuit (38) electrically switches and couples the lead wire to a controlled ground coupling (27), (52) during ball formation or to a ground isolating voltage source (28 ), (54) for delivering current to the lead wire and establishing a bond sensing and detecting mode following the ball bonding operating mode and wedge bonding operating mode of the bonding machine. The switching circuit (38) is actuated by a control signal (40) from the control signal circuitry of the bonding machine or from independent control circuitry. Time sequence circuitry may also be provided for the control signals.

Lead wire bond attempt detection

Apparatus for maintaining reserve bonding wire

A method, timing control circuit, and power supply are described for initiating arc discharge between the cover gas delivery shroud and lead wire held in the bonding tool of a lead wire bonding machine for melting and forming a ball at the end of the lead wire. An arc discharge timing control pulse controls duration of the arc discharge within an empirically determined time window between the shortest and longest durations of arc discharge which result in optimal ball formation of a substantially spherical ball at the end of the lead wire without necking of the lead wire above the formed ball. The timing control circuit also provides an initial cover gas movement delay before ball formation for displacing oxygen from the shield and the end of the lead wire, and a subsequent cooling delay for solidifying and cooling the formed ball in the cover gas stream prior to ball bonding. The timing control pulses are applied to the ball bonding machine and are also coupled to the transistor electronic switch of a relatively high voltage power supply circuit for applying the arc discharge voltage through a resistance to the shield and lead wire when the electronic switch is conducting. Optical coupling is used between the low voltage timing control circuit and high voltage power supply circuit for electrically isolating the two voltage levels. The duration of arc discharge is controlled to fall within the critical time window between longest and shortest durations of arc discharge which result in optimal ball formation. Initially, the lead wire tail length extending below the bonding tool is selected to provide a ball of specified size; the voltage is selected according to tail length to form the mass of tail length metal into a substantially spherical ball; and a neck of desired thickness is selected by adjusting the duration of the arc discharge timing control pulse within the time window.

Pulse-width control of bonding ball formation

Apparatus and method are described for rapid ball formation at the end of lead wire retained in the capillary wire holding tool of a ball bonding machine. A circuit is coupled between the cover gas shroud and lead wire for establishing controlled electrical discharge between the end of the bonding wire and the shroud, for melting and forming a ball. The circuit includes a DC power supply for delivering a positive polarity to the shroud and negative polarity to the lead wire for drawing a discharge of electrons from the end of the lead wire to the shroud. A capacitor is coupled in series with the DC power supply for receiving the electrical discharge. An impedance is also coupled in series for limiting the electrical discharge current. Charging of the capacitor limits and shapes the electrical arc discharge to a controlled pulse profile of short duration for rapid ball formation. An electronic gate is also used to control pulse duration. The rapid and controlled ball formation avoids necking or thinning of the lead wire which often occurs at the stem above the bonding ball.

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Portland, ME, United States of America

Mark D Dufour