WO2006118421A1 - Method of fabricating bonding wire and apparatus for strengthening bonding wire - Google Patents

Method of fabricating bonding wire and apparatus for strengthening bonding wire Download PDF

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Publication number
WO2006118421A1
WO2006118421A1 PCT/KR2006/001665 KR2006001665W WO2006118421A1 WO 2006118421 A1 WO2006118421 A1 WO 2006118421A1 KR 2006001665 W KR2006001665 W KR 2006001665W WO 2006118421 A1 WO2006118421 A1 WO 2006118421A1
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WIPO (PCT)
Prior art keywords
bonding wire
continuous casting
wire
motor
tensile strength
Prior art date
Application number
PCT/KR2006/001665
Other languages
French (fr)
Inventor
June-Sub Hwang
Jong-Soo Cho
Yong-Jin Park
Kyu-Hwan Oh
Suk-Hoon Kang
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Mk Electron Co., Ltd.
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Publication date
Application filed by Mk Electron Co., Ltd. filed Critical Mk Electron Co., Ltd.
Publication of WO2006118421A1 publication Critical patent/WO2006118421A1/en

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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
    • H04B10/25—Arrangements specific to fibre transmission
    • H04B10/2589—Bidirectional transmission
    • H04B10/25891—Transmission components
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L24/00—Arrangements for connecting or disconnecting semiconductor or solid-state bodies; Methods or apparatus related thereto
    • H01L24/01—Means for bonding being attached to, or being formed on, the surface to be connected, e.g. chip-to-package, die-attach, "first-level" interconnects; Manufacturing methods related thereto
    • H01L24/42—Wire connectors; Manufacturing methods related thereto
    • H01L24/43—Manufacturing methods
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21F—WORKING OR PROCESSING OF METAL WIRE
    • B21F99/00—Subject matter not provided for in other groups of this subclass
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D7/00—Modifying the physical properties of iron or steel by deformation
    • C21D7/02—Modifying the physical properties of iron or steel by deformation by cold working
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/06—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of rods or wires
    • C21D8/065—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of rods or wires of ferrous alloys
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
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    • H01L24/00—Arrangements for connecting or disconnecting semiconductor or solid-state bodies; Methods or apparatus related thereto
    • H01L24/01—Means for bonding being attached to, or being formed on, the surface to be connected, e.g. chip-to-package, die-attach, "first-level" interconnects; Manufacturing methods related thereto
    • H01L24/42—Wire connectors; Manufacturing methods related thereto
    • H01L24/44—Structure, shape, material or disposition of the wire connectors prior to the connecting process
    • H01L24/45—Structure, shape, material or disposition of the wire connectors prior to the connecting process of an individual wire connector
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    • H01L24/74—Apparatus for manufacturing arrangements for connecting or disconnecting semiconductor or solid-state bodies
    • H01L24/741—Apparatus for manufacturing means for bonding, e.g. connectors
    • H01L24/745—Apparatus for manufacturing wire connectors
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/52—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for wires; for strips ; for rods of unlimited length
    • C21D9/54—Furnaces for treating strips or wire
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    • H01L2224/451—Material with a principal constituent of the material being a metal or a metalloid, e.g. boron (B), silicon (Si), germanium (Ge), arsenic (As), antimony (Sb), tellurium (Te) and polonium (Po), and alloys thereof
    • H01L2224/45138—Material with a principal constituent of the material being a metal or a metalloid, e.g. boron (B), silicon (Si), germanium (Ge), arsenic (As), antimony (Sb), tellurium (Te) and polonium (Po), and alloys thereof the principal constituent melting at a temperature of greater than or equal to 950°C and less than 1550°C
    • H01L2224/45144—Gold (Au) as principal constituent
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    • H01L2224/01—Means for bonding being attached to, or being formed on, the surface to be connected, e.g. chip-to-package, die-attach, "first-level" interconnects; Manufacturing methods related thereto
    • H01L2224/42—Wire connectors; Manufacturing methods related thereto
    • H01L2224/44—Structure, shape, material or disposition of the wire connectors prior to the connecting process
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    • H01L2224/451—Material with a principal constituent of the material being a metal or a metalloid, e.g. boron (B), silicon (Si), germanium (Ge), arsenic (As), antimony (Sb), tellurium (Te) and polonium (Po), and alloys thereof
    • H01L2224/45138—Material with a principal constituent of the material being a metal or a metalloid, e.g. boron (B), silicon (Si), germanium (Ge), arsenic (As), antimony (Sb), tellurium (Te) and polonium (Po), and alloys thereof the principal constituent melting at a temperature of greater than or equal to 950°C and less than 1550°C
    • H01L2224/45147—Copper (Cu) as principal constituent
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
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    • H01L2224/01—Means for bonding being attached to, or being formed on, the surface to be connected, e.g. chip-to-package, die-attach, "first-level" interconnects; Manufacturing methods related thereto
    • H01L2224/42—Wire connectors; Manufacturing methods related thereto
    • H01L2224/44—Structure, shape, material or disposition of the wire connectors prior to the connecting process
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    • H01L2224/451—Material with a principal constituent of the material being a metal or a metalloid, e.g. boron (B), silicon (Si), germanium (Ge), arsenic (As), antimony (Sb), tellurium (Te) and polonium (Po), and alloys thereof
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    • H01L2224/45164—Palladium (Pd) as principal constituent
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    • H01L2224/42—Wire connectors; Manufacturing methods related thereto
    • H01L2224/47—Structure, shape, material or disposition of the wire connectors after the connecting process
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    • H01L2224/485—Material
    • H01L2224/48505—Material at the bonding interface
    • H01L2224/4851—Morphology of the connecting portion, e.g. grain size distribution
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    • H01L2924/0001—Technical content checked by a classifier
    • H01L2924/00014—Technical content checked by a classifier the subject-matter covered by the group, the symbol of which is combined with the symbol of this group, being disclosed without further technical details
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    • H01L2924/012—Semiconductor purity grades
    • H01L2924/01204—4N purity grades, i.e. 99.99%

Definitions

  • the present invention relates to a method for fabricating a bonding wire electrically connecting a semiconductor chip to an external lead part during packaging of a semiconductor device and an apparatus for strengthening the bonding wire, and more particularly, to a method of fabricating a bonding wire having a tensile strength appropriate for packaging a high integrated semiconductor device and an apparatus for strengthening the bonding wire.
  • a gap between wires of a semiconductor chip is reduced.
  • a number of pins of a bond pad is increased, a gap between pins is reduced, and a bonding wire is minute.
  • a bonding wire must have a high electric characteristic, an improved loop shape, an improved tensile strength, an improved vibration resistance, an improved bond pull strength/ball shear strength between the bonding wire and a bond pad/lead frame, and a prevention of chip crack.
  • a gold (Au) bonding wire having a purity of 99.9% or 99.99% is mainly used in consideration of electric characteristic and reliability.
  • the purity of the Au bonding wire is improved to reduce an electric resistance without an effect of impurity elements.
  • a mechanical tensile strength is reduced.
  • the reduction in the tensile strength is more serious due to the minute of the Au bonding wire.
  • the bonding wire is frequently broken.
  • a yield of the bonding wire is reduced.
  • a loop formed during bonding is sagged by the weak tensile strength, and mold sweeping occurs during sealing of the bonding wire.
  • adjacent loops contact each other to generate an electric short-circuit.
  • the present invention provides a method of fabricating a bonding wire having a high tensile strength and an apparatus for strengthening the bonding wire.
  • a method of fabricating a bonding wire including: fabricating a continuous casting bonding wire; twisting the continuous casting bonding wire so as to work harden the continuous casting bonding wire; reducing a cross-section of the continuous casting bonding wire work hardened to draw the continuous casting bonding wire to a bonding wire having a desired diameter through a drawing process; and annealing the bonding wire.
  • Drawing the continuous casting bonding wire to the bonding wire having the desired diameter may include: intermediate annealing the bonding wire.
  • the bonding wire may be a gold alloy wire, a copper alloy wire, or a palladium alloy wire.
  • Work hardening the continuous casting bonding wire may include: fixing an end of the continuous casting bonding wire; and connecting the other end of the continuous casting bonding wire to a motor so as to rotate the motor.
  • the work hardening the continuous casting bonding wire may include: connecting an end of the continuous casting bonding wire to a motor; connecting the other end of the continuous casting bonding wire to another motor; and rotating the motors.
  • the continuous casting bonding wire may be work hardened in a roll-to-roll way.
  • an apparatus for strengthening a bonding wire including: first and second fasteners inserted into both ends of a continuous casting bonding wire; a support part combined with the first fastener; and a motor combined with the second fastener.
  • the first and second fasteners, the support part, and the motor may be provided on a table.
  • a controller may be provided on the table to control a rotation direction of the motor and an RPM.
  • the apparatus may further include a motor instead of the support part.
  • the apparatus may be embodied in a roll-to-roll way in consideration of productivity.
  • twisting and work hardening the continuous casting bonding wire may be further included between the continuous casting bonding wire and the drawing bonding wire.
  • a metal crystal in a metal may be broken down so that a size of the metal crystal is finer, so as to improve a tensile strength of the bonding wire.
  • the work hardening may be performed using an external force together with or separately from a design of an alloy including an addition of impurities so as to overcome a limit of the bonding wire to the tensile strength. An electric characteristic may not be restricted.
  • FlG. 1 is a flowchart of a method of fabricating a bonding wire according to the present invention
  • FIGS. 2 through 4 are views illustrating apparatuses for strengthening a bonding wire, the apparatuses being used in work hardening of the method of fabricating the bonding wire according to the present invention
  • FlG. 5 is a view illustrating an electron back scattered diffraction (EBSD) of a bonding wire before and after the work hardening is applied to the method of fabricating the bonding wire according to the present invention
  • FlG. 6 is a view illustrating an EBSD of a continuous casting bonding wire when a processing speed of the continuous casting bonding wire is lOOmpm, 200mpm, 300mpm, and 400mpm;
  • FlG. 7 is a graph illustrating variations in a tensile strength with respect to the processing speed of the continuous casting bonding wire.
  • FlG. 8 is a view illustrating variations in the tensile strength with respect to a processing degree. Best Mode for Carrying Out the Invention
  • FlG. 1 is a flowchart of a method of fabricating a bonding wire according to the present invention.
  • a raw material is melted and then continuously cast to fabricate a continuous casting bonding wire.
  • the method of fabricating the bonding wire according to the present invention is not limited to a composition of the bonding wire and may be applied to fabricate various bonding wires such as an Au alloy wire, a copper (Cu) alloy wire, or a palladium (Pd) alloy wire.
  • a processing speed of the continuous casting may be a parameter determining a characteristic of a bonding wire, which will be described in detail in an experiment that will be described later.
  • the continuous casting bonding wire is twisted to be work hardened according to the spirit of the present invention.
  • twisting or torsion processing is performed.
  • a twisting pitch, a number of turns, or a ratio of a total length of a circumference depending on a twisting turn to a length of a bonding wire may be a parameter.
  • a metal crystal in a metal may be broken down to transform the metal crystal so that a size of the metal crystal is finer.
  • the size of the metal crystal is reduced to increase grain boundaries.
  • a tensile strength of a bonding wire can be improved.
  • work hardening may be performed using an external force together with or separately from a design of an alloy including an addition of impurities so as to overcome a limit of the bonding wire to the tensile strength.
  • FIGS. 2 through 4 are views illustrating apparatuses for strengthening a bonding wire, the apparatuses being used in the work hardening of the method of fabricating the bonding wire according to the present invention
  • an other end of the continuous casting bonding wire may be twisted to be work hardened.
  • the end of the bonding wire is fixed to a predetermined machinery, and then the other end of the bonding wire is connected to a motor. Next, the motor is rotated to twist only an end of the bonding wire.
  • an apparatus I for strengthening a bonding wire includes a support part 10 with which a first fastener 20 is combined on a table 1 and a motor 50 with which a second fastener 40 is combined.
  • a controller 2 is further provided on the table 1 to control a rotation direction of the motor 50 and an RPM.
  • a method of performing work hardening using the apparatus I will now be described.
  • An end of a continuous casting bonding wire 30 is inserted into the first fastener 20 so as to be fixed to the support 10.
  • the other end of the continuous casting bonding wire 30 is inserted into a second fastener 40.
  • the motor 50 combined with the second fastener 40 is rotated to twist the continuous cast bonding wire 30.
  • an axis is determined as a rotation axis and the other axis is determined as a stationary axis to twist the continuous casting bonding wire 30.
  • the stationary axis i.e., the support part 10
  • the stationary axis is gradually moved outward to apply a predetermined tensile strength to the continuous casting bonding wire 30 that may be twisted to be sagged so as to prevent the continuous casting bonding wire 30 from being sagged.
  • the work hardening may be performed using an apparatus II for strengthening a bonding wire shown in FlG. 3.
  • the apparatus II may further include a rotation axis instead of a stationary axis to insert both ends of a bonding wire into the rotation axis.
  • rotation axes are rotated in reverse directions to twist a continuous casting bonding wire 130.
  • the apparatus II includes a first motor 110 with which a first fastener 120 is combined on a table 11 and a second motor 150 with which a second fastener 140 is combined on the table 11. Controllers 12 and 13 may be further provided on the table 11 to control rotation directions of the first and second motors 110 and 150 and an RPM.
  • an apparatus for strengthening a bonding wire is constituted in a roll-to-roll way as shown in FlG. 4 to perform work hardening, the apparatus is advantageous in terms of productivity.
  • an apparatus HI for strengthening a bonding wire shown in FlG. 4 is based on a principle of the apparatus II.
  • a bare wire i.e., the continuous casting bonding wire 130, is continuously supplied to the second motor 150 using a rolling 160 so as to be twisted in consideration of productivity and process, and simultaneously gets out of the first motor 110 and is treated using a rolling 170.
  • the continuous casting bonding wire work hardened according to various methods as described above is drawn to a bonding wire having a desired diameter so as to reduce a cross-section thereof.
  • the continuous casting bonding wire is drawn to a bonding wire having a diameter of 25D.
  • the bonding wire may be intermediate annealed. As shown in the results of an experiment that will be described later, an error rate is high due to a short-circuit in a process not including intermediate annealing. A substantial tensile strength does not show a great difference. Thus, a process including intermediate annealing is stable and effective.
  • the bonding wire is annealed to remove a stress field inside the bonding wire and wire curl.
  • a continuous casting bonding wire is twisted to be work hardened. If the continuous casting bonding wire is twisted, a metal crystal inside a metal may be broken down so that a size of the metal crystal is finer. Thus, grain boundaries are increased to improve a tensile strength of the continuous casting bonding wire. Work hardening using an external force is used separately from a design of an alloy including an addition of impurities. Thus, a limit of the continuous casting bonding wire to the tensile strength can be overcome. An electric characteristic may not be restricted by the addition of the impurities.
  • a bonding wire was fabricated using the method of fabricating the bonding wire according to the present invention.
  • the Au alloy continuous casting bonding wire was twisted to be work hardened using an apparatus as shown in FIGS. 2 through 4.
  • the work hardening was performed by changing a ratio of a total length of a circumference formed a twisting rotation to a length of the Au alloy continuous casting bonding wire into 1 : 1, 1 : 2, 1 : 3, and 1 : 4.
  • a cross-section of the Au alloy continuous casting bonding wire was reduced to draw an Au alloy bonding wire having a diameter of 25D.
  • the Au alloy continuous casting bonding wire has a diameter of 3mm or 1.5mm, a portion of the bonding wire was intermediate annealed. The other portion of the Au alloy continuous casting bonding wire was not intermediate annealed.
  • the entire portion of the Au alloy bonding wire was intermediate annealed after drawing.
  • the Au alloy bonding wire, a Cu bonding wire and a Pd bonding wire were also fabricated according to the same method.
  • a necessary raw material was made, and then a continuous casting bonding wire having a diameter of 9.5mm was fabricated.
  • the continuous casting bonding wire was twisted to be work hardened using an apparatus as shown in FIGS. 2 through 4.
  • the continuous cast bonding wire was drawn to a bonding wire having a diameter of 25D.
  • the continuous casting bonding wire has a diameter of 1.5mm, the continuous casting bonding wire was intermediate annealed. After the bonding wire was drawn, the bonding wire was annealed.
  • Bonding wires were fabricated to be compared with bonding wires fabricating using such a method.
  • the bonding wires as comparison examples have the same compositions as the bonding wires of the present invention.
  • the bonding wires were fabricated as continuous casting bonding wires having a single diameter of 9.5mm and then drawn to bonding wires having a diameter 25D without being work hardened.
  • the bonding wires have a diameter of 1.5mm during drawing, the bonding wires were intermediate annealed. After drawing, the bonding wires were annealed as in the method of fabricating the bonding wire according to the present invention.
  • Table 1 shows conditions of fabricating the bonding wires according to embodiments of the present invention and the bonding wires as the comparison examples. [43] Table 1
  • FIG. 5 is a view illustrating an EBSD of a bonding wire before and after work hardening is applied.
  • the EBSD maps a direction of a crystal affecting a tensile strength to detect a directionality of a crystal of a metal so as to measure a tensile strength.
  • a blue color (a dark portion of portions marked with black and white) that is direction ⁇ 111> occupies a greater area than a red color (a bright portion of the portions marked with black and white) that is direction ⁇ 100>, and a size of the crystal is reduced.
  • a tensile strength of a grain boundary of the direction ⁇ 111> is greater than a tensile strength of a grain boundary of the direction ⁇ 100> in the metal.
  • a modulus of the grain boundary of the direction ⁇ 111> is 115GPa
  • a modulus of the grain boundary of the direction ⁇ 100> is 42GPa.
  • An improvement of the tensile strength may be checked from an increase in an area of a portion showing the direction ⁇ 111> after the work hardening is applied.
  • a breakdown of the crystal of the metal caused by the work hardening and the denser structure of the crystal can be checked from the reduction in the sized of the crystal.
  • the Au alloy bonding wire was work hardened but not intermediate annealed.
  • the Au alloy bonding wire was intermediate annealed.
  • Table 2 the tensile strength does now show a great difference depending on whether intermediate annealing is performed. However, an error rate is high due to a short- circuit in a process not including intermediate annealing. Thus, a process including intermediate annealing is stable and effective.
  • the tensile strength in the comparison 1) is about 250MPa. In a case of the Cu alloy bonding wire according to the embodiment 1) of the present invention, a minimum value of the tensile strength is greater than 310MPa. In a case of the Pd alloy bonding wire, the tensile strength in the comparison 1) is about 260MPa. However, in a case of the Cu alloy bonding wire according to the embodiment 1) of the present invention, a minimum value of the tensile strength is greater than 310MPa.
  • Pd alloy bonding wire fabricated according to the method of present invention including work hardening have considerably improved tensile strength values compared to the comparison examples not performing work hardening.
  • Mold sweeping was measured. As shown in Table 2, in the case of the Au alloy bonding wire of the comparison examples 1) through 5), mold sweeping is 11%. In the case of the Au alloy bonding wire according to the embodiments 1) through 32) of the present invention, mold sweeping is 3.3% or less. Thus, in the present invention, mold sweeping is remarkably inhibited by the increase in the tensile strength.
  • FIG. 6 is a view illustrating an EBSD when the processing speed is lOOmpm
  • FIG. 7 is a graph illustrating variations in the tensile strength with respect to the processing speed.
  • a diameter of a continuous casting bonding wire immediately before work hardening was changed to 3mm, 7mm, and 9.5mm.
  • the continuous casting bonding wire was work hardened until a ratio of a total length of a circumference depending on twisting rotation to a length of the continuous casting bonding wire was 1:3.
  • the continuous casting bonding wire was drawn to a bonding wire having a diameter of 25D. Variations in the tensile strength with respect to the processing degree (a diameter degree of the continuous casting bonding wire immediately before work hardening) were measured.
  • FIG. 8 is a view illustrating variations in the tensile strength with respect to the processing degree. 9.5mm.
  • the tensile strength is 301.67MPa. The tensile strength is the highest in this case.
  • a tensile strength of the bonding wire can be improved by using work hardening, a bonding wire strengthening apparatus, and a strengthening process using torsion during the a design of an alloy.
  • the strengthening process according to the present invention does not use alloying using an addition of impurities. Thus, an electric characteristic is not restricted by the addition of the impurities.
  • a tensile strength of a bonding wire according to the present invention is improved by about 30% compared to a bonding wire fabricating according to an existing process.
  • a bonding capability, an electric characteristic, and a physical characteristic of the bonding wire according to the present invention are improved compared to the bonding wire fabricated according to the existing process. If a drawing speed is increased to increase productivity, a short-circuit that may occur in a drawing process can be solved.
  • a snake wire, a leaning wire, and a weak tensile strength such as sagging occurring during bonding of a wire can be solved.
  • the bonding wire has a strong resistance against mold sweeping occurring during sealing after bonding of the wire.

Abstract

Provided a method of fabricating a bonding wire and an apparatus for strengthening the bonding wire. The method includes: fabricating a continuous casting bonding wire; twisting the continuous casting bonding wire so as to work harden the continuous casting bonding wire; reducing a cross-section of the continuous casting bonding wire work hardened to draw the continuous casting bonding wire to a bonding wire having a desired diameter through a drawing process; and annealing the bonding wire.

Description

Description
METHOD OF FABRICATING BONDING WIRE AND APPARATUS FOR STRENGTHENING BONDING WIRE
Technical Field
[1] This application claims the benefit of Korean Patent Application No.
10-2005-0037071, filed on May 3, 2005, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.
[2] The present invention relates to a method for fabricating a bonding wire electrically connecting a semiconductor chip to an external lead part during packaging of a semiconductor device and an apparatus for strengthening the bonding wire, and more particularly, to a method of fabricating a bonding wire having a tensile strength appropriate for packaging a high integrated semiconductor device and an apparatus for strengthening the bonding wire. Background Art
[3] As semiconductor devices are high integrated and compact, a gap between wires of a semiconductor chip is reduced. In addition, a number of pins of a bond pad is increased, a gap between pins is reduced, and a bonding wire is minute. During bonding, a bonding wire must have a high electric characteristic, an improved loop shape, an improved tensile strength, an improved vibration resistance, an improved bond pull strength/ball shear strength between the bonding wire and a bond pad/lead frame, and a prevention of chip crack.
[4] Conventionally, a gold (Au) bonding wire having a purity of 99.9% or 99.99% is mainly used in consideration of electric characteristic and reliability. Thus, the purity of the Au bonding wire is improved to reduce an electric resistance without an effect of impurity elements. However, as the Au bonding wire has a high purity, a mechanical tensile strength is reduced. The reduction in the tensile strength is more serious due to the minute of the Au bonding wire. Thus, when the bonding wire is pulled, the bonding wire is frequently broken. As a result, a yield of the bonding wire is reduced. In addition, a loop formed during bonding is sagged by the weak tensile strength, and mold sweeping occurs during sealing of the bonding wire. Thus, adjacent loops contact each other to generate an electric short-circuit.
[5] Alloying methods have been suggested to increase a tensile strength of a bonding wire. The alloying methods cannot overcome a limit to the tensile strength of the bonding wire and have a limit to an electric characteristic caused by the addition of impurities. Disclosure of Invention Technical Problem
[6] The present invention provides a method of fabricating a bonding wire having a high tensile strength and an apparatus for strengthening the bonding wire.
Technical Solution
[7] According to an aspect of the present invention, there is provided a method of fabricating a bonding wire, including: fabricating a continuous casting bonding wire; twisting the continuous casting bonding wire so as to work harden the continuous casting bonding wire; reducing a cross-section of the continuous casting bonding wire work hardened to draw the continuous casting bonding wire to a bonding wire having a desired diameter through a drawing process; and annealing the bonding wire.
[8] Drawing the continuous casting bonding wire to the bonding wire having the desired diameter may include: intermediate annealing the bonding wire. The bonding wire may be a gold alloy wire, a copper alloy wire, or a palladium alloy wire.
[9] Work hardening the continuous casting bonding wire may include: fixing an end of the continuous casting bonding wire; and connecting the other end of the continuous casting bonding wire to a motor so as to rotate the motor. Alternatively, the work hardening the continuous casting bonding wire may include: connecting an end of the continuous casting bonding wire to a motor; connecting the other end of the continuous casting bonding wire to another motor; and rotating the motors. The continuous casting bonding wire may be work hardened in a roll-to-roll way.
[10] According to another aspect of the present invention, there is provided an apparatus for strengthening a bonding wire, including: first and second fasteners inserted into both ends of a continuous casting bonding wire; a support part combined with the first fastener; and a motor combined with the second fastener. Here, the first and second fasteners, the support part, and the motor may be provided on a table. A controller may be provided on the table to control a rotation direction of the motor and an RPM. Alternatively, the apparatus may further include a motor instead of the support part. The apparatus may be embodied in a roll-to-roll way in consideration of productivity.
[11] In the present invention, twisting and work hardening the continuous casting bonding wire may be further included between the continuous casting bonding wire and the drawing bonding wire. Thus, a metal crystal in a metal may be broken down so that a size of the metal crystal is finer, so as to improve a tensile strength of the bonding wire. The work hardening may be performed using an external force together with or separately from a design of an alloy including an addition of impurities so as to overcome a limit of the bonding wire to the tensile strength. An electric characteristic may not be restricted. Brief Description of the Drawings [12] The above and other features and advantages of the present invention will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings in which:
[13] FlG. 1 is a flowchart of a method of fabricating a bonding wire according to the present invention;
[14] FIGS. 2 through 4 are views illustrating apparatuses for strengthening a bonding wire, the apparatuses being used in work hardening of the method of fabricating the bonding wire according to the present invention;
[15] FlG. 5 is a view illustrating an electron back scattered diffraction (EBSD) of a bonding wire before and after the work hardening is applied to the method of fabricating the bonding wire according to the present invention;
[16] FlG. 6 is a view illustrating an EBSD of a continuous casting bonding wire when a processing speed of the continuous casting bonding wire is lOOmpm, 200mpm, 300mpm, and 400mpm;
[17] FlG. 7 is a graph illustrating variations in a tensile strength with respect to the processing speed of the continuous casting bonding wire; and
[18] FlG. 8 is a view illustrating variations in the tensile strength with respect to a processing degree. Best Mode for Carrying Out the Invention
[19] The present invention will be described more fully hereinafter with reference to the accompanying drawings in which preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. In the drawings, the forms of elements are exaggerated for clarity. To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures.
[20] FlG. 1 is a flowchart of a method of fabricating a bonding wire according to the present invention. Referring to FlG. 1, in operation Sl, a raw material is melted and then continuously cast to fabricate a continuous casting bonding wire. The method of fabricating the bonding wire according to the present invention is not limited to a composition of the bonding wire and may be applied to fabricate various bonding wires such as an Au alloy wire, a copper (Cu) alloy wire, or a palladium (Pd) alloy wire. Here, a processing speed of the continuous casting may be a parameter determining a characteristic of a bonding wire, which will be described in detail in an experiment that will be described later. [21] In operation S2, the continuous casting bonding wire is twisted to be work hardened according to the spirit of the present invention. In other words, twisting or torsion processing is performed. Here, a twisting pitch, a number of turns, or a ratio of a total length of a circumference depending on a twisting turn to a length of a bonding wire may be a parameter.
[22] If the continuous bonding wire is twisted, a metal crystal in a metal may be broken down to transform the metal crystal so that a size of the metal crystal is finer. Thus, the size of the metal crystal is reduced to increase grain boundaries. As a result, a tensile strength of a bonding wire can be improved. In the present invention, work hardening may be performed using an external force together with or separately from a design of an alloy including an addition of impurities so as to overcome a limit of the bonding wire to the tensile strength.
[23] As will be described below, the work hardening using torsion may be performed using various methods and various apparatuses. FIGS. 2 through 4 are views illustrating apparatuses for strengthening a bonding wire, the apparatuses being used in the work hardening of the method of fabricating the bonding wire according to the present invention
[24] After an end of the continuous casting bonding wire is fixed, an other end of the continuous casting bonding wire may be twisted to be work hardened. For example, the end of the bonding wire is fixed to a predetermined machinery, and then the other end of the bonding wire is connected to a motor. Next, the motor is rotated to twist only an end of the bonding wire.
[25] Referring to FlG. 2, an apparatus I for strengthening a bonding wire includes a support part 10 with which a first fastener 20 is combined on a table 1 and a motor 50 with which a second fastener 40 is combined. A controller 2 is further provided on the table 1 to control a rotation direction of the motor 50 and an RPM.
[26] A method of performing work hardening using the apparatus I will now be described. An end of a continuous casting bonding wire 30 is inserted into the first fastener 20 so as to be fixed to the support 10. The other end of the continuous casting bonding wire 30 is inserted into a second fastener 40. The motor 50 combined with the second fastener 40 is rotated to twist the continuous cast bonding wire 30. In other words, an axis is determined as a rotation axis and the other axis is determined as a stationary axis to twist the continuous casting bonding wire 30. Here, the stationary axis, i.e., the support part 10, is gradually moved outward to apply a predetermined tensile strength to the continuous casting bonding wire 30 that may be twisted to be sagged so as to prevent the continuous casting bonding wire 30 from being sagged.
[27] The work hardening may be performed using an apparatus II for strengthening a bonding wire shown in FlG. 3. Unlike the apparatus I shown in FlG. 2, the apparatus II may further include a rotation axis instead of a stationary axis to insert both ends of a bonding wire into the rotation axis. Next, rotation axes are rotated in reverse directions to twist a continuous casting bonding wire 130.
[28] Referring to FlG. 3, the apparatus II includes a first motor 110 with which a first fastener 120 is combined on a table 11 and a second motor 150 with which a second fastener 140 is combined on the table 11. Controllers 12 and 13 may be further provided on the table 11 to control rotation directions of the first and second motors 110 and 150 and an RPM.
[29] A method of performing work hardening using the apparatus II will now be described. An end of the continuous casting bonding wire 130 is inserted into the first fastener 120, and an other end of the continuous casting bonding wire 130 is inserted into the second fastener 140. The first and second motors 110 and 150 are rotated in reverse directions to twist the continuous casting bonding wire 130.
[30] Here, if an apparatus for strengthening a bonding wire is constituted in a roll-to-roll way as shown in FlG. 4 to perform work hardening, the apparatus is advantageous in terms of productivity. In other words, an apparatus HI for strengthening a bonding wire shown in FlG. 4 is based on a principle of the apparatus II. However, a bare wire, i.e., the continuous casting bonding wire 130, is continuously supplied to the second motor 150 using a rolling 160 so as to be twisted in consideration of productivity and process, and simultaneously gets out of the first motor 110 and is treated using a rolling 170.
[31] In operation S3, The continuous casting bonding wire work hardened according to various methods as described above is drawn to a bonding wire having a desired diameter so as to reduce a cross-section thereof. For example, the continuous casting bonding wire is drawn to a bonding wire having a diameter of 25D. In operation S3, the bonding wire may be intermediate annealed. As shown in the results of an experiment that will be described later, an error rate is high due to a short-circuit in a process not including intermediate annealing. A substantial tensile strength does not show a great difference. Thus, a process including intermediate annealing is stable and effective.
[32] In operation S4, the bonding wire is annealed to remove a stress field inside the bonding wire and wire curl.
[33] As described above, according to the present invention, a continuous casting bonding wire is twisted to be work hardened. If the continuous casting bonding wire is twisted, a metal crystal inside a metal may be broken down so that a size of the metal crystal is finer. Thus, grain boundaries are increased to improve a tensile strength of the continuous casting bonding wire. Work hardening using an external force is used separately from a design of an alloy including an addition of impurities. Thus, a limit of the continuous casting bonding wire to the tensile strength can be overcome. An electric characteristic may not be restricted by the addition of the impurities.
[34] (Experiment)
[35] Results of an experiment performed on a bonding wire fabricated using the method of fabricating the bonding wire according to the present invention will now be described in detail. However, the experiment is only provided to more easily understand the present invention. The present invention is not limited to the experiment.
[36] Fabricating Bonding Wire
[37] A bonding wire was fabricated using the method of fabricating the bonding wire according to the present invention.
[38] Be of under lOppm and Ca of under 50ppm were added to Au having a purity of
99.99% to fabricate an Au alloy continuous casting bonding wire having a diameter of 3mm, 5mm, 7mm, 9.5mm, 10.5mm, 12.5mm, 13mm, and 15mm. Here, a processing speed (a continuous casting speed) was changed from lOOmpm to 400mpm in the unit of lOOmpm.
[39] Next, the Au alloy continuous casting bonding wire was twisted to be work hardened using an apparatus as shown in FIGS. 2 through 4. The work hardening was performed by changing a ratio of a total length of a circumference formed a twisting rotation to a length of the Au alloy continuous casting bonding wire into 1 : 1, 1 : 2, 1 : 3, and 1 : 4. A cross-section of the Au alloy continuous casting bonding wire was reduced to draw an Au alloy bonding wire having a diameter of 25D. When the Au alloy continuous casting bonding wire has a diameter of 3mm or 1.5mm, a portion of the bonding wire was intermediate annealed. The other portion of the Au alloy continuous casting bonding wire was not intermediate annealed. Here, the entire portion of the Au alloy bonding wire was intermediate annealed after drawing.
[40] Besides, the Au alloy bonding wire, a Cu bonding wire and a Pd bonding wire were also fabricated according to the same method. In other words, a necessary raw material was made, and then a continuous casting bonding wire having a diameter of 9.5mm was fabricated. The continuous casting bonding wire was twisted to be work hardened using an apparatus as shown in FIGS. 2 through 4. The continuous cast bonding wire was drawn to a bonding wire having a diameter of 25D. When the continuous casting bonding wire has a diameter of 1.5mm, the continuous casting bonding wire was intermediate annealed. After the bonding wire was drawn, the bonding wire was annealed.
[41] Bonding wires were fabricated to be compared with bonding wires fabricating using such a method. The bonding wires as comparison examples have the same compositions as the bonding wires of the present invention. However, the bonding wires were fabricated as continuous casting bonding wires having a single diameter of 9.5mm and then drawn to bonding wires having a diameter 25D without being work hardened. When the bonding wires have a diameter of 1.5mm during drawing, the bonding wires were intermediate annealed. After drawing, the bonding wires were annealed as in the method of fabricating the bonding wire according to the present invention.
[42] Table 1 below shows conditions of fabricating the bonding wires according to embodiments of the present invention and the bonding wires as the comparison examples. [43] Table 1
Figure imgf000008_0001
Figure imgf000009_0001
Figure imgf000010_0001
[44] [45] Experiment Result 1 [46] Tensile strengths, electric resistances, sagging, and mold sweeping were measured with respect to the bonding wires according to the present invention and the bonding wires as the comparison examples. Table 2 below shows these.
[47] Table 2 [Table 2]
Figure imgf000010_0002
Figure imgf000011_0001
Figure imgf000012_0001
[48] [49] (1) Tensile Strength [50] In a case of the Au alloy bonding wire, a maximum value of the tensile strength was about 255MPa in the comparison examples 1) through 5). However, in a case of the Au gold alloy bonding wire according to the present invention, a minimum value of the tensile strength was greater than 300MPa in the embodiments 1) through 32). Thus, in the present invention, the tensile strength was improved by about 30% compared to the existing tensile strength. A significant difference among torsion apparatuses, i.e., the apparatuses I, π, and HI, does not occur.
[51] FIG. 5 is a view illustrating an EBSD of a bonding wire before and after work hardening is applied. In general, the EBSD maps a direction of a crystal affecting a tensile strength to detect a directionality of a crystal of a metal so as to measure a tensile strength. Referring to FIG. 5, after the work hardening is applied, a blue color (a dark portion of portions marked with black and white) that is direction <111> occupies a greater area than a red color (a bright portion of the portions marked with black and white) that is direction <100>, and a size of the crystal is reduced. A tensile strength of a grain boundary of the direction <111> is greater than a tensile strength of a grain boundary of the direction <100> in the metal. For example, in Au, a modulus of the grain boundary of the direction <111> is 115GPa, and a modulus of the grain boundary of the direction <100> is 42GPa.
[52] An improvement of the tensile strength may be checked from an increase in an area of a portion showing the direction <111> after the work hardening is applied. A breakdown of the crystal of the metal caused by the work hardening and the denser structure of the crystal can be checked from the reduction in the sized of the crystal.
[53] In the embodiments 1) through 8) and 17) through 24, the Au alloy bonding wire was work hardened but not intermediate annealed. In the embodiments 9) through 16) and 25) through 32), the Au alloy bonding wire was intermediate annealed. As shown in Table 2, the tensile strength does now show a great difference depending on whether intermediate annealing is performed. However, an error rate is high due to a short- circuit in a process not including intermediate annealing. Thus, a process including intermediate annealing is stable and effective.
[54] In a case of the Cu alloy bonding wire, the tensile strength in the comparison 1) is about 250MPa. In a case of the Cu alloy bonding wire according to the embodiment 1) of the present invention, a minimum value of the tensile strength is greater than 310MPa. In a case of the Pd alloy bonding wire, the tensile strength in the comparison 1) is about 260MPa. However, in a case of the Cu alloy bonding wire according to the embodiment 1) of the present invention, a minimum value of the tensile strength is greater than 310MPa.
[55] As described above, the Au alloy bonding wire, the Cu alloy bonding wire, and the
Pd alloy bonding wire fabricated according to the method of present invention including work hardening have considerably improved tensile strength values compared to the comparison examples not performing work hardening.
[56] (2) Electric Resistance
[57] In general, if a grain boundary in a material is increased, an electric resistance is increased. According to work hardening of the present invention, a metal crystal in a metal of a continuous casting bonding wire is broken down, and thus a size of the metal crystal is finer. As a result, the grain boundary is increased. Due to this, an experiment on an increase in the electric resistance of the bonding wire fabricated according to the present invention was performed. Referring to Table 2, there is no significant difference between the Au alloy bonding wires of the comparison examples 1) through 5) and the embodiments 1) through 32) of the present invention. Thus, in the present invention, a grain boundary inside the bonding wire is increased to improve a tensile strength. However, the electric resistance is not increased by the increase in the grain boundary. Therefore, in the present invention, a limit of the bonding wire to the tensile strength can be overcome by using work hardening using an external force, and an electric characteristic is not restricted.
[58] (3) Sagging
[59] Sagging was measured. As shown in Table 2, in the case of the Au alloy bonding wire of the comparison examples 1) through 5), sagging is 3000ppm or more. However, in the case of the Au alloy bonding wire according to the embodiments 1) through 32) of the present invention, sagging is 15ppm or less. In more serious cases, sagging is Oppm. Thus, in the present invention, sagging is remarkably inhibited by an increase in the tensile strength.
[60] (4) Mold Sweeping
[61] Mold sweeping was measured. As shown in Table 2, in the case of the Au alloy bonding wire of the comparison examples 1) through 5), mold sweeping is 11%. In the case of the Au alloy bonding wire according to the embodiments 1) through 32) of the present invention, mold sweeping is 3.3% or less. Thus, in the present invention, mold sweeping is remarkably inhibited by the increase in the tensile strength.
[62] Experiment Result 2
[63] (1) Effect of Processing Speed (Continuous Casting Speed)
[64] As previously described, to observe an effect of a processing speed, the processing s peed was changed from lOOmpm to 400mpm in the unit of lOOmpm during fabricating of an Au alloy continuous casting bonding wire.
[65] FIG. 6 is a view illustrating an EBSD when the processing speed is lOOmpm,
200mpm, 300mpm, and 400mpm. Referring to FIG. 6, as the processing speed is increased from lOOmpm to 400mpm, a blue color (a dark portion when being marked with black and white) that is directionality in which the tensile strength is increased is gradually increased.
[66] FIG. 7 is a graph illustrating variations in the tensile strength with respect to the processing speed.
[67] (2) Variations in Tensile Strength with respect to Processing Degree and EBSD
Results
[68] As previously described, in the present experiment, a diameter of a continuous casting bonding wire immediately before work hardening was changed to 3mm, 7mm, and 9.5mm. Next, the continuous casting bonding wire was work hardened until a ratio of a total length of a circumference depending on twisting rotation to a length of the continuous casting bonding wire was 1:3. Thereafter, the continuous casting bonding wire was drawn to a bonding wire having a diameter of 25D. Variations in the tensile strength with respect to the processing degree (a diameter degree of the continuous casting bonding wire immediately before work hardening) were measured.
[69] FIG. 8 is a view illustrating variations in the tensile strength with respect to the processing degree. 9.5mm. When work hardening is performed using a continuous casting bonding wire having a diameter of 9.5mm, the tensile strength is 301.67MPa. The tensile strength is the highest in this case.
[70] As described above, in a method of fabricating a bonding wire and an apparatus for strengthening the bonding wire, a tensile strength of the bonding wire can be improved by using work hardening, a bonding wire strengthening apparatus, and a strengthening process using torsion during the a design of an alloy. The strengthening process according to the present invention does not use alloying using an addition of impurities. Thus, an electric characteristic is not restricted by the addition of the impurities.
[71] As shown from the results of an experiment, a tensile strength of a bonding wire according to the present invention is improved by about 30% compared to a bonding wire fabricating according to an existing process. As the results of a bonding test based on this, a bonding capability, an electric characteristic, and a physical characteristic of the bonding wire according to the present invention are improved compared to the bonding wire fabricated according to the existing process. If a drawing speed is increased to increase productivity, a short-circuit that may occur in a drawing process can be solved.
[72] Also, a snake wire, a leaning wire, and a weak tensile strength such as sagging occurring during bonding of a wire can be solved. In addition, the bonding wire has a strong resistance against mold sweeping occurring during sealing after bonding of the wire.
[73] While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims.

Claims

Claims
[1] A method of fabricating a bonding wire, comprising: fabricating a continuous casting bonding wire; twisting the continuous casting bonding wire so as to work harden the continuous casting bonding wire; reducing a cross-section of the continuous casting bonding wire work hardened to draw the continuous casting bonding wire to a bonding wire having a desired diameter through a drawing process; and annealing the bonding wire. [2] The method of claim 1, wherein drawing the continuous casting bonding wire to the bonding wire having the desired diameter comprises: intermediate annealing the bonding wire. [3] The method of claim 1, wherein the bonding wire is one of a gold alloy wire, a copper alloy wire, and a palladium alloy wire. [4] The method of claim 1, wherein work hardening the continuous casting bonding wire comprises: fixing an end of the continuous casting bonding wire; and connecting the other end of the continuous casting bonding wire to a motor so as to rotate the motor. [5] The method of claim 1, wherein work hardening the continuous casting bonding wire comprises: connecting an end of the continuous casting bonding wire to a motor; connecting the other end of the continuous casting bonding wire to another motor; and rotating the motors. [6] The method of claim 5, wherein the continuous casting bonding wire is work hardened in a roll-to-roll way. [7] An apparatus for strengthening a bonding wire, comprising: first and second fasteners inserted into both ends of a continuous casting bonding wire; a support part combined with the first fastener; and a motor combined with the second fastener. [8] An apparatus for strengthening a bonding wire, comprising: first and second fasteners inserted into both ends of a continuous casting bonding wire; a first motor combined with the first fastener; and a second motor combined with the second fastener. [9] The apparatus of claim 8, wherein the continuous casting bonging wire is processed from the first motor to the second motor in a roll-to-roll way.
PCT/KR2006/001665 2005-05-03 2006-05-03 Method of fabricating bonding wire and apparatus for strengthening bonding wire WO2006118421A1 (en)

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Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS6364332A (en) * 1986-09-05 1988-03-22 Toshiba Corp Fine bonding wire for semiconductor device
JPH11135541A (en) * 1997-10-29 1999-05-21 Nec Kyushu Ltd Wire for wire bonding
KR100273702B1 (en) * 1995-08-23 2000-11-15 사토 케이지 Process for preparing gold alloy wire for bonding
KR20010073501A (en) * 2000-01-17 2001-08-01 강도원 A alloy of bonding wire for high stretch using for semiconductor packaging

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS6364332A (en) * 1986-09-05 1988-03-22 Toshiba Corp Fine bonding wire for semiconductor device
KR100273702B1 (en) * 1995-08-23 2000-11-15 사토 케이지 Process for preparing gold alloy wire for bonding
JPH11135541A (en) * 1997-10-29 1999-05-21 Nec Kyushu Ltd Wire for wire bonding
KR20010073501A (en) * 2000-01-17 2001-08-01 강도원 A alloy of bonding wire for high stretch using for semiconductor packaging

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