Classifications

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  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K3/00—Tools, devices or special appurtenances for soldering, e.g. brazing, or unsoldering, not specially adapted for particular methods
  • B23K3/06—Solder feeding devices; Solder melting pans
  • B23K3/0607—Solder feeding devices
  • B23K3/0623—Solder feeding devices for shaped solder piece feeding, e.g. preforms, bumps, balls, pellets, droplets
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  • B23K20/00—Non-electric welding by applying impact or other pressure, with or without the application of heat, e.g. cladding or plating
  • B23K20/002—Non-electric welding by applying impact or other pressure, with or without the application of heat, e.g. cladding or plating specially adapted for particular articles or work
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  • B23K2101/00—Articles made by soldering, welding or cutting
  • B23K2101/36—Electric or electronic devices
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  • H10W72/012—Manufacture or treatment of bump connectors, dummy bumps or thermal bumps
  • H10W72/01221—Manufacture or treatment of bump connectors, dummy bumps or thermal bumps using local deposition
  • H10W72/01225—Manufacture or treatment of bump connectors, dummy bumps or thermal bumps using local deposition in solid form, e.g. by using a powder or by stud bumping
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  • H10W72/071—Connecting or disconnecting
  • H10W72/075—Connecting or disconnecting of bond wires
  • H10W72/07511—Treating the bonding area before connecting, e.g. by applying flux or cleaning
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  • H10W72/071—Connecting or disconnecting
  • H10W72/075—Connecting or disconnecting of bond wires
  • H10W72/07531—Techniques
  • H10W72/07532—Compression bonding, e.g. thermocompression bonding
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  • H10W72/00—Interconnections or connectors in packages
  • H10W72/071—Connecting or disconnecting
  • H10W72/075—Connecting or disconnecting of bond wires
  • H10W72/07531—Techniques
  • H10W72/07532—Compression bonding, e.g. thermocompression bonding
  • H10W72/07533—Ultrasonic bonding, e.g. thermosonic bonding
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  • H10W72/00—Interconnections or connectors in packages
  • H10W72/20—Bump connectors, e.g. solder bumps or copper pillars; Dummy bumps; Thermal bumps
  • H10W72/251—Materials
  • H10W72/252—Materials comprising solid metals or solid metalloids, e.g. PbSn, Ag or Cu
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  • H10W72/00—Interconnections or connectors in packages
  • H10W72/20—Bump connectors, e.g. solder bumps or copper pillars; Dummy bumps; Thermal bumps
  • H10W72/251—Materials
  • H10W72/255—Materials of outermost layers of multilayered bumps, e.g. material of a coating
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  • H10W72/00—Interconnections or connectors in packages
  • H10W72/20—Bump connectors, e.g. solder bumps or copper pillars; Dummy bumps; Thermal bumps
  • H10W72/29—Bond pads specially adapted therefor
• • H—ELECTRICITY
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  • H10W72/00—Interconnections or connectors in packages
  • H10W72/50—Bond wires
  • H10W72/521—Structures or relative sizes of bond wires
  • H10W72/522—Multilayered bond wires, e.g. having a coating concentric around a core
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  • H10W72/00—Interconnections or connectors in packages
  • H10W72/50—Bond wires
  • H10W72/531—Shapes of wire connectors
  • H10W72/536—Shapes of wire connectors the connected ends being ball-shaped
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  • H10W72/00—Interconnections or connectors in packages
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  • H10W72/531—Shapes of wire connectors
  • H10W72/5363—Shapes of wire connectors the connected ends being wedge-shaped
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  • H10W72/00—Interconnections or connectors in packages
  • H10W72/50—Bond wires
  • H10W72/531—Shapes of wire connectors
  • H10W72/5366—Shapes of wire connectors the bond wires having kinks
• • H—ELECTRICITY
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  • H10W72/00—Interconnections or connectors in packages
  • H10W72/50—Bond wires
  • H10W72/541—Dispositions of bond wires
  • H10W72/5434—Dispositions of bond wires the connected ends being on auxiliary connecting means on bond pads, e.g. on other bond wires
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  • H10W72/551—Materials of bond wires
  • H10W72/552—Materials of bond wires comprising metals or metalloids, e.g. silver
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  • H10W72/50—Bond wires
  • H10W72/551—Materials of bond wires
  • H10W72/552—Materials of bond wires comprising metals or metalloids, e.g. silver
  • H10W72/5522—Materials of bond wires comprising metals or metalloids, e.g. silver comprising gold [Au]
• • H—ELECTRICITY
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  • H10W72/551—Materials of bond wires
  • H10W72/552—Materials of bond wires comprising metals or metalloids, e.g. silver
  • H10W72/5524—Materials of bond wires comprising metals or metalloids, e.g. silver comprising aluminium [Al]
• • H—ELECTRICITY
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  • H10W72/00—Interconnections or connectors in packages
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  • H10W72/551—Materials of bond wires
  • H10W72/552—Materials of bond wires comprising metals or metalloids, e.g. silver
  • H10W72/5525—Materials of bond wires comprising metals or metalloids, e.g. silver comprising copper [Cu]
• • H—ELECTRICITY
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  • H10W72/00—Interconnections or connectors in packages
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  • H10W72/551—Materials of bond wires
  • H10W72/555—Materials of bond wires of outermost layers of multilayered bond wires, e.g. material of a coating
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  • H10W—GENERIC PACKAGES, INTERCONNECTIONS, CONNECTORS OR OTHER CONSTRUCTIONAL DETAILS OF DEVICES COVERED BY CLASS H10
  • H10W90/00—Package configurations
  • H10W90/701—Package configurations characterised by the relative positions of pads or connectors relative to package parts
  • H10W90/751—Package configurations characterised by the relative positions of pads or connectors relative to package parts of bond wires
  • H10W90/756—Package configurations characterised by the relative positions of pads or connectors relative to package parts of bond wires between a chip and a stacked lead frame, conducting package substrate or heat sink
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10S228/00—Metal fusion bonding
  • Y10S228/904—Wire bonding

Definitions

• the present invention relates to conductive bumps and wire loops utilizing conductive bumps, and to improved methods of forming conductive bumps and wire loops.
• conductive bumps are formed for use in providing electrical interconnections.
• such bumps may be provided for: (1) use in flip-chip applications, (2) use as stand-off conductors, (3) wire looping applications, (4) test points for testing applications, amongst others.
• Such conductive bumps may be formed in varying techniques. One such technique is to form the conductive bumps using wire, such as on a wire bonding machine or a stud bumping machine.
• FIG. 1 illustrates an exemplary sequence of forming a conductive bump on a wire bonding machine or bumping machine.
• free air ball 100a is seated at the tip of bonding tool 102.
• free air ball 100a has been formed on an end of wire 100 that hangs below the tip of bonding tool 102 using an electronic flame-off device or the like.
• Wire clamp 104 is also shown at Step 1 in the open position.
• wire 100 is provided by a wire spool on the machine (not shown). Wire 100 extends from the wire spool through wire clamp 104 (and through other structures not shown) and through bonding tool 102.
• Step 2 After free air ball 100a is formed (prior to Step 1), wire 100 is drawn upwards (e.g., using a vacuum control tensioner or the like) such that free air ball 100a is seated at the tip of bonding tool 102 as shown at Step 1 of FIG. 1.
• bonding tool 102 (along with other elements of a bond head assembly including wire clamp 104) is lowered and free air ball 100a is bonded to bonding location 106 (e.g., a die pad of semiconductor die 106).
• bonding of free air ball 100a to bonding location 106 may utilize ultrasonic energy, thermosonic energy, thermocompressive energy, XY table scrub, combinations thereof, amongst other techniques.
• bonding tool 102 is raised to a desired height. This height may be referred to as a separation height (from viewing Step 3 of FIG. 1, one can see that bonding tool 102 has been raised such that bonded ball 100b is no longer seated in the tip of bonding tool 102).
• bonding tool 102 is moved in at least one horizontal direction (e.g., along the X axis or Y axis of the machine) to smooth the top surface of bonded ball 100b.
• bonding tool 102 is raised to another height (which may be referred to as the wire tail height), and then wire clamp 104 is closed. Then at Step 6, bonding tool 102 is raised to break the connection between bonded ball 100b (which may now be termed conductive bump 100c) and the remainder of wire 100.
• bonding tool 102 may be raised to an EFO height which is a position at which an electronic flame-off device forms a free air ball on wire tail lOOd of wire 100.
• Forming conductive bumps using such conventional techniques involves certain deficiencies.
• the connection between bonded ball 100b and the rest of the wire is weakened; however, in certain processes the connection may be weakened to the point where the connection breaks prematurely (that is, the connection may separate during the rise to tail height shown at Step 5 prior to the closing of clamp 104).
• the wire tail that is provided for the next free air ball that is, wire tail 10Od
• the smoothing in Step 4 may be reduced such that the connection is not excessively weakened; however, this reduction in smoothing may have deleterious effects in terms of the resultant bump surface.
• Yet another problem that may result is a long tail, where too much wire is on the wire tail.
• forming second bonds on a conventional bump involves certain challenges related to, for example, the compliant nature of the bump and the physical configuration of the top surface of the bump. These challenges tend to result in poorly formed second/stitch bonds and potential short tail conditions.
• a method of forming a conductive bump includes the steps of: (1) bonding a free air ball to a bonding location using a bonding tool to form a bonded ball; (2) raising the bonding tool to a desired height, with a wire clamp open, while paying out wire continuous with the bonded ball; (3) closing the wire clamp; (4) lowering the bonding tool to a smoothing height with the wire clamp still closed; (5) smoothing an upper surface of the bonded ball, with the wire clamp still closed, using the bonding tool; and (6) raising the bonding tool, with the wire clamp still closed, to separate the bonded ball from wire engaged with the bonding tool.
• a method of forming a wire loop includes the steps of: (1) forming a conductive bump on a bonding location, the step of forming the conductive bump being according to the present invention; (2) bonding a portion of wire to another bonding location using the bonding tool; (3) extending a length of wire from the bonded portion of wire to the conductive bump; and (4) bonding an end of the length of wire to the conductive bump.
• FIG. 1 is a series of diagrams illustrating a conventional approach of forming a conductive bump
• FIG. 2 is a series of diagrams illustrating a method of forming a conductive bump in accordance with an exemplary embodiment of the present invention
• FIGS. 3A-3B are side and top block diagram views of a conductive bump formed according to the technique of FIG. 1;
• FIGS. 3C-3D are side and top block diagram views of a conductive bump formed according to the inventive technique of FIG. 2;
• FIGS. 4A-4B are diagrams illustrating a method of forming a wire loop in accordance with an exemplary embodiment of the present invention.
• conductive bumps are formed.
• An upper surface of a conductive bump is smoothed, for example, using an XY smoothing motion of a bonding tool.
• the bonding tool is raised to a desired height (e.g., a tail height) with the wire clamp open. Then the wire clamp is closed and the bonding tool is lowered to perform the upper surface smoothing of the conductive bump. This process results in a slack length of wire between the top of the bonding tool and the bottom of the wire clamp.
• the bonding tool is raised to separate the conductive bump from the remainder of the wire.
• the slack length of wire now facilitates a desirable wire tail length, thereby substantially reducing the potential for shorts tails and associated problems.
• the wire clamp remains closed which substantially reduces the potential for (or even prevents) the wire from passing through the bonding tool creating a stoppage in the process (which may result in a short tail error).
• the wire tail is formed before the smoothing occurs.
• the wire tail will tend to be stronger as compared to conventional processes because no smoothing motion has occurred to weaken the wire tail, thereby reducing the potential for additional errors.
• FIG. 2 illustrates an exemplary sequence of forming a conductive bump on a wire bonding machine or bumping machine according to the present invention.
• free air ball 200a is seated at the tip of bonding tool 202.
• free air ball 200a has been formed on an end of wire 200 that hangs below the tip of bonding tool using an electronic flame-off device or the like.
• Wire clamp 204 is also shown at Step 1 in the open position.
• Step 2 After free air ball 200a is formed (prior to Step 1), wire 200 is drawn upwards (e.g., using a vacuum control tensioner or the like) such that free air ball 200a is seated at the tip of bonding tool 202 as shown at Step 1 of FIG. 2.
• bonding tool 202 (along with other elements of a bond head assembly including wire clamp 204) is lowered and free air ball 200a is bonded to bonding location 206 (e.g., a die pad of semiconductor die 206).
• bonding of free air ball 200a to bonding location 206 may utilize ultrasonic energy, thermosonic energy, thermocompressive energy, XY table scrub, combinations thereof, amongst other techniques.
• bonding tool 202 is raised to a desired height at Step 3.
• This height may be referred to as a tail height (from viewing Step 3 of FIG. 2 one can see that the tip of bonding tool is separated from bonded ball 200b at this height); however, it is understood that different heights may be selected. While the invention is not limited thereto, exemplary ranges for this height are between 5-20 mils and between 10-20 mils above the top of bonded free air ball 200b.
• wire clamp 204 is closed.
• bonding tool 202 is lowered to a desired height. This height may be referred to as a separation height (from viewing Step 5 of FIG.
• Step 2 one can see that the tool has been lowered such that the tip of bonding tool 202 is just barely in contact with an upper surface of bonded ball 200b. While the invention is not limited thereto, exemplary ranges for this height are between 0.1-2 mils and between 1-2 mils above the height of bonding tool 202 at Step 2.
• Step 5 by lowering bonding tool 202 with the wire clamp closed, a slack length of wire 20Oe has been provided below the bottom of wire clamp 204 and above bonding tool 202.
• bonding tool 202 is moved in at least one horizontal direction (e.g., along the X axis, the Y axis, both the X and Y axes, another horizontal direction, etc.) to smooth the top surface of bonded free air ball 200a.
• Such smoothing provides a desirable top surface for a conductive bump, and also weakens the connection between the bonded ball and the rest of the wire to assist in the separation therebetween.
• bonding tool 202 is raised to break the connection between bonded ball 200b (which may now be termed conductive bump 200c) and the remainder of wire 200.
• bonding tool 202 may be raised to an EFO height which is a position at which an electronic flame-off device forms a free air ball on wire tail 20Od of wire 200.
• ultrasonic energy or the like may also be applied to facilitate threading of slack length of wire 20Oe through the tip of bonding tool 202 to provide wire tail 20Od.
• the height of bonding tool 202 at Steps 5 and 6 is the same; however, it is understood that this height may be changed as desired from one step to the next to achieve the desired smoothing.
• the smoothing at Step 6 of FIG. 2 may vary considerably.
• the smoothing operation may consist of a single horizontal motion of bonding tool 202 across the top surface of bonded ball 200b as shown in FIG. 2.
• multiple motions e.g., back and forth, in different directions, etc.
• the smoothing motion may be completely horizontal as shown in Step 6, or may have both horizontal and vertical (e.g., upward or downward) components.
• the smoothed surface may be sloped in a given direction as is desired.
• the smoothing step of Step 6 may be combined with the lowering of bonding tool 202 of Step 5 into a single (e.g., simultaneous) motion. That is, the motion of bonding tool 202 may follow an angled path (e.g., downward and to the right as shown in FIG. 2) whereby the lowering of Step 5 and the smoothing of Step 6 are completed in a single motion.
• Conductive bump 100c includes lower surface 100c2 bonded to a bonding location (such as bonding location 106 in FIG. 1), and an upper surface lOOcl that has been smoothed (e.g., using Step 4 of FIG. 1).
• the area of upper surface lOOcl is significantly smaller than that of lower surface 100c2.
• the surface area of upper surface lOOcl may be between 50-80% of the surface area of lower surface 100c2.
• Conductive bump 200c includes lower surface 200c2 bonded to a bonding location (such as bonding location 206 in FIG. 2), and an upper surface 200cl that has been smoothed (e.g., using Step 6 of FIG. 2). As can be seen from looking at the top view of conductive bump 200c, upper surface 200cl occupies almost the same area as lower surface 100c2.
• upper surface 200cl may be between 80-98% of the surface area of lower surface 100c2, and pehaps even 90-98% of the surface area of lower surface 100c2.
• This increase in the relative surface area of the upper surface of a conductive bump in comparision to the lower surface of the bump is at least partially attributed to the increased horizontal smoothing that is enabled according to the present invention.
• the present invention may be used to form conductive bumps in a number of applications.
• the bumps may be used in connection with flip chip interconnections.
• Another exemplary application is conductive bumping associated with wafer testing of devices.
• Yet another exemplary use of the conductive bumps is as stand offs.
• the inventive conductive bumps may be used as a stand off in connection with stacked die wire bonding.
• the inventive conductive bumps may be used as a stand off in connection with stand-off stitch bonding (i.e., SSB bonding) such as illustrated in FIGS. 4A-4B.
• FIG. 4A illustrates conductive bump 400c which has been formed on bonding location 406a (e.g., die pad 406a of semiconductor die 406).
• Semiconductor die 406 is supported by substrate 408 (e.g., leadframe 408).
• substrate 408 e.g., leadframe 408.
• conductive bump 400c has been formed according to the method described in FIG. 2 or another method according to the present invention. It is desired to now electrically connect bonding location 408a (e.g., lead finger 408a of leadframe 408) to conductive bump 400c.
• FIG. 4B illustrates continuous wire loop 410 providing electrical interconnection between lead finger 408a and conductive bump 400c.
• bonded portion 410a (e.g., first bond 410a) is formed on lead finger 408a. Then, length of wire 410b (continuous with first bond 410a) is extended toward conductive bump 400c. Then, wire portion 410c is bonded (e.g., second bond 410c is formed as a stich bond) on conductive bump 400b. Thus, conductive bump 400b acts as a stand-off for wire loop 410.
• the bonding of wire portion 410c (e.g., second bond 410c) to conductive bump 400c may be a closed loop controlled process. For example, a z-position of the bonding tool may be monitored, wherein the ultrasonic energy applied during the bonding of wire portion 410c to conductive bump 400c is turned off upon the bonding tool reaching a predetermined z-position. More specifically, prior to the formation of second bond 410c on conductive bump 400c, the bonding tool descends toward conductive bump 400c.
• a reference position may be established (where the reference position may be, for example, the impact z-position, a z-position slightly above the impact position, the smoothing z-position, a z-position where ultrasonic energy is applied during second bond formation, a z-position at a predetermined time after impact between the bonding tool and the bump, amongst others). Then, the ultrasonic energy is applied to form second bond 410c, that is, to bond wire portion 410c to conductive bump 400c (where the ultrasonic energy may be turned on before impact, upon impact, upon the bonding tool reaching the reference position, etc.).
• the ultrasonic energy is turned off (or reduced, for example, by at least 50% of the energy level) (e.g., with or without a predetermined time delay) upon the bonding tool reaching the predetermined z-position such that the bonding tool does not drive too deep into conductive bump 400c.
• the predetermined z- position may be selected relative to a reference z-position. That is, after the bonding tool reaches the selected reference position, the z-position is monitored (e.g., using a z-axis encoder or other technique) to determine when the bonding tool reaches the predetermined position.
• a z-axis encoder or other technique e.g., other techniques of determining the predetermined z-position (and/or the reference z-position) are contemplated within the scope of the present invention.
• inventive technqiques disclosed herein are particularly applicable to copper wire bonding. Copper wire has certain physical properties that tend to exacerbate the potential for short tail errors using conventional bumping techniques. Thus, the present invention provides exceptional benefits to copper wire bumping and bonding processes. Of course, the inventive techniques are also applicable to other types of wire bonding including, for example, gold, aluminum, and Pd coated Cu wire bonding.

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• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Wire Bonding (AREA)
• Electric Connection Of Electric Components To Printed Circuits (AREA)

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• 2010
  • 2010-03-26 JP JP2012503531A patent/JP5567657B2/ja active Active
  • 2010-03-26 WO PCT/US2010/028824 patent/WO2010120473A2/en not_active Ceased
  • 2010-03-26 US US13/063,852 patent/US8152046B2/en active Active
  • 2010-03-26 KR KR1020117012537A patent/KR101641102B1/ko active Active
  • 2010-03-26 CN CN201080002737.7A patent/CN102187444B/zh active Active
  • 2010-04-01 TW TW099110100A patent/TWI511209B/zh active

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