WO2020112635A1

WO2020112635A1 - Ultrasonic welding systems and methods of using the same

Info

Publication number: WO2020112635A1
Application number: PCT/US2019/063007
Authority: WO
Inventors: Theodore J. Copperthite; Hans H. VON TRESCKOW; Christopher R. LONGLEY; Siddharth D. KATARIA
Original assignee: Kulicke And Soffa Industries, Inc.
Priority date: 2018-11-28
Filing date: 2019-11-25
Publication date: 2020-06-04
Also published as: US11285561B2; JP7541806B2; US11958124B2; JP2022510882A; CN115971633A; CN113165102A; US20220143737A1; CN113165102B; EP3887085B1; EP4403292A2; US20200164460A1; EP3887085A1; US11504800B2; US20230043068A1; EP3887085A4

Abstract

An ultrasonic welding system is provided. The ultrasonic welding system includes a support structure for supporting a workpiece. The ultrasonic welding system also includes a weld head assembly including an ultrasonic converter carrying a sonotrode. The ultrasonic welding system also includes a z-axis motion system carrying the weld head assembly. The z-axis motion system includes (i) a z-axis forcer for moving the weld head assembly along a z-axis of the ultrasonic welding system, and (ii) a z-axis overtravel mechanism disposed between the z-axis forcer and the weld head assembly.

Description

ULTRASONIC WELDING SYSTEMS AND METHODS OF USING THE SAME

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This appl ication claims the benefit of U.S. Provisional Application No. 62/772, 113, filed November 28, 2019, the content of which is incorporated herei n by reference in its entirety.

FIELD

[0002] The invention relates to the ultrasonic welding systems, and more particularly, to improved systems and methods for performi ng ultrasonic welding operations.

BACKGROUND

[0003] Ultrasonic energy is widely used in forming interconnections between two or more materials. For examples, wire bonding machines (e.g ., ball bonding machines, wedge bonding machi nes, ribbon bonding machi nes, etc. ) are used to bond a wi re or ribbon to a bonding location. However, wire bonding utilizes relatively low levels of energy (e.g., bond force, ultrasonic energy, etc. ). Exemplary wire bonding machi nes are marketed by Kulicke and Soffa Industries, Inc. of Fort Washi ngton, Pennsylvania.

[0004] Certain applications involve joining of materials other than wire. Weldi ng has been considered for such applications. Ultrasonic welding is also a widely used technology. Ultrasonic welding may use an ultrasonic converter (e.g ., carryi ng a sonotrode) for converting electrical energy into mechanical movement/scrub (e.g ., linear movement/scrub, torsional movement/scrub, etc.) . However, existing ultrasonic welding technology and equipment is limited in its ability to provide solutions that can satisfy market demand in terms of cost, operational efficiency, flexi bi lity, portability, and related factors.

[0005] Thus, it would be desirable to i mprove ultrasonic welding technology to overcome existing barriers to potential markets.

SUMMARY

[0006] According to an exemplary embodiment of the invention, an ultrasonic welding system is provided . The ultrasonic welding system i ncludes a support structure for supporting a workpiece. The ultrasonic weldi ng system also includes a weld head assembly includi ng an ultrasonic converter carrying a sonotrode. The ultrasonic welding system also incl udes a z-axis motion system carrying the weld head assembly. The z-axis motion system includes (i) a z-axis forcer for movi ng the weld head assembly along a z-axis of the ultrasonic weldi ng system, and (i i) a z-axis overtravel mechanism disposed between the z-axis forcer and the weld head assembly.

[0007] According to yet another exemplary embodiment of the invention, an ultrasonic welding system is provided. The ultrasonic welding system includes a support structure for supporti ng a workpiece. The ultrasonic weldi ng system also includes a weld head assembly includi ng an ultrasonic converter carrying a sonotrode. The ultrasonic welding system further i ncludes a z-axis motion system carryi ng the weld head assembly. The z-axis motion system i ncludes (i) a z-axis forcer for moving the weld head assembly along a z-axis of the ultrasonic weldi ng system, the z-axis forcer incl uding a ball screw system for moving the weld head assembly along the z- axis of the ultrasonic weldi ng system, and (i i) a z-axis overtravel mechanism disposed between the z-axis forcer and the weld head assembly, the z-axis overtravel mechanism includi ng an inline spring. The ultrasonic welding system further includes : (a) a z-axis encoder for sensing motion of (i) a moveable portion of the z-axis forcer with respect to (ii) a stationary portion of the z-axis forcer along the z-axis of the ultrasonic welding system; and (b) an overtravel encoder for sensing motion of (i) the moveable portion of the z-axis forcer with respect to (ii) the weld head assembly along the z-axis of the ultrasonic welding system.

[0008] According to yet another exemplary embodiment of the invention, a method of ultrasonically welding a conductive terminal to a workpiece is provided. The method includes the steps of: (a) supporti ng a workpiece on a support structure of an ultrasonic welding system, a conductive termi nal being aligned with a conductive region of the workpiece; (b) providing a weld head assembly, includi ng an ultrasonic converter carrying a sonotrode, the weld head assembly being configured for motion along a z- axis of the ultrasonic weldi ng system using a z-axis forcer of a z-axis motion system of the ultrasonic welding system; (c) providing a z-axis overtravel mechanism disposed between the z-axis forcer and the weld head assembly, the z-axis forcer carrying the weld head assembly and the z-axis overtravel mechanism; (d) moving a moveable portion of the z-axis forcer downward along the z-axis of the ultrasonic welding system until a welding tip of the sonotrode is i n contact with the conductive termi nal ; (e) moving the moveable portion of the z-axis forcer further downward along the z-axis of the ultrasonic welding system to activate the z-axis overtravel mechanism after step (d) ; and (f) applying ultrasonic energy to the weldi ng ti p of the sonotrode to weld the conductive terminal to the conductive region of the workpiece.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] The invention is best understood from the fol lowi ng detai led description when read in connection with the accompanying drawings. It is emphasized that, according to common practice, the various features of the drawings are not to scale.

On the contrary, the dimensions of the various features are arbitrarily expanded or reduced for clarity. Included in the drawi ngs are the following figures:

[0010] FIG. 1A is a block diagram side view of an ultrasonic welding system in accordance with an exemplary embodiment of the invention;

[0011] FIG. IB is a block diagram side view of another ultrasonic welding system in accordance with an exemplary embodiment of the invention;

[0012] FIG. 2A is a block diagram side view of yet another ultrasonic weldi ng system in accordance with an exemplary embodiment of the invention;

[0013] FIG. 2B is a block diagram side view of yet another ultrasonic weldi ng system in accordance with an exemplary embodiment of the invention;

[0014] FIG. 3A is a block diagram side view of yet another ultrasonic weldi ng system in accordance with an exemplary embodiment of the invention;

[0015] FIG. 3B is a block diagram side view of yet another ultrasonic weldi ng system in accordance with an exemplary embodiment of the invention;

[0016] FIG. 4 is a block diagram side view of yet another ultrasonic welding system in accordance with an exemplary embodiment of the invention;

[0017] FIG. 5 is a block diagram side view of yet another ultrasonic welding system in accordance with an exemplary embodiment of the invention; and

[0018] FIGS. 6A - 6D are block diagram side views of the ultrasonic weldi ng system of FIG. 3A illustrating a method of ultrasonically welding a conductive terminal to a workpiece in accordance with an exemplary embodi ment of the i nvention.

DETAILED DESCRIPTION [0019] The content of International Patent Application No. PCT/US2018/025941, with a priority date of April 4, 2017, is incorporated herein by reference in its entirety.

[0020] In accordance with the invention, ultrasonic welding capability is provided in welding systems (and corresponding methods) that may achieve efficient volume production. Aspects of the invention relate to ultrasonic welding systems including z-axis motion systems having (i) a z-axis forcer for moving a weld head assembly along a z-axis of the ultrasonic welding system (e.g., linear motor driven forcers, ball/screw system driven forcers, pneumatic cylinder driven forcers, etc.), and (ii) a z-axis overtravel mechanism (e.g., inline spring based overtravel mechanisms, pneumatic cylinder based overtravel mechanisms, etc.). In certain embodiments of the invention, a secondary z-axis forcer (e.g., including a pneumatic cylinder, among other variations) may be incorporated to provide a variable force along the z-axis of the ultrasonic welding system.

[0021] Exemplary electro servo motor systems (e.g., ball/screw driven systems) are controlled along the z-axis to provide large bond/weld forces (e.g., greater than 1500 N) with a drive system rated at less than 1 kW continuous. For example, a ball screw may be used to generate a gear reduction and convert to linear motion, which then controls the compression of an inline spring (e.g., a stiff inline spring) included in a z-axis overtavel mechanism which generates the actual weld forces.

[0022] In a ball screw driven system, the ball screw pushes on the inline spring to generate the desired weld/bond forces. In such a system, two position feedback sensors (e.g., a z-axis encoder and an overtravel encoder) may be utilized to combine the signals to determine the desired deformation signal during welding. The z-axis position may be dynamically controlled during welding such that the z-axis maintains substantially constant bond/weld forces during the ultrasonic welding process.

[0023] In accordance with aspects of the invention, a separate overtravel mechanism is provided to minimize impact forces during welding operations.

[0024] Further, in accordance with aspects of the invention, the z-axis motor forces are all in line with each other (and the sonotrode) to minimize shifting during bond/weld force application.

[0025] In accordance with further aspects of the invention, a secondary forcer motor may be utilized that can fine-tune the bond/weld forces applied with the primary z-axis forcer. Such an approach al lows for precision force cal ibration plus fine force adj ustment capability via the additional forcer mounted to the overtravel mechanism.

[0026] Referri ng now to the drawi ngs, FIG. 1A il lustrates an ultrasonic welding system 100a. Ultrasonic welding system 100a i ncludes support structure 102 supporting workpiece 104. Workpiece includes a substrate 104a, and a conductive terminal 104b configured to be ultrasonically welded to a conductive region of substate 104a. Ultrasonic welding system 100a also includes weld head assembly 106 i ncluding an ultrasonic converter 106a, and a sonotrode 106b carried by ultrasonic converter 106a.

[0027] Ultrasonic welding system 100a also i ncludes a z-axis motion system 108a carrying weld head assembly 106. Z-axis motion system 108a includes (a) a z- axis forcer 110 for movi ng weld head assembly 106 along a z-axis of ultrasonic welding system 100a (see example x, y, z axis legend proximate FIG. 1A), and (b) a z-axis overtravel mechanism 112 disposed between z-axis forcer 110 and weld head assembly 106. Z-axis bearings are not shown in any of these diagrams (for si mpl icity and clarity), but may also be i n the mechanism for any implementation. Such z-axis beari ngs would constrai n moveable portion 110b to move in the z-direction with respect to stationary portion 110a .

[0028] In FIG. 1A, z-axis forcer 110 is a bal l screw driven forcer, and i ncludes (i) a stationary portion 110a (i .e., stationary in that it does not move with the moveable portion 110b), a moveable portion 110b (incl uding z-axis encoder l lOb l), and a motion system 110c. Motion system 110c drives moveable portion 110b with respect to stationary portion 110a . Motion system 110c i ncludes a rotary motor l lOcl, a threaded shaft 110c2, a ball assembly 110c3 for moving along threaded shaft 110c2, and mounts 110c4 for mounting threaded shaft 110c2 to stationary portion 110a . As wi ll be appreciated by those skil led in the art, rotary motor l lOcl rotates threaded shaft 110c2, thereby movi ng ball assembly 110c3. As ball assembly 110c3 carries moveable portion 110b, moveable portion 110b moves along with ball assembly 110c3. Of course, z-axis forcer 110 is i llustrated and described herei n as a simple ball screw driven forcer; however, it is understood that different screw driven forcers are contemplated .

[0029] In FIG. 1A, z-axis overtravel mechanism 112 incl udes (i) z-axis block 112a (coupled to weld head assembly 106, either di rectly or indirectly), inline spri ng 112b, overtravel encoder 112c, and z-axis alignment structure 112d (e.g ., one or more pins, flexures, bearings, etc. providi ng z-axis alignment such that motion of z-axis block 112a with respect to moveable portion 110b is substantially along the z-axis (and not the x-axis or y-axis)) .

[0030] Weld head assembly 106 (carried by z-axis motion system 108a) is also moveable along a plurality of substantially horizontal axes. In the example shown in FIG. 1A, weld head assembly 106 is configured to move along the x-axis and the y-axis of ultrasonic welding system 100a through the use of x-axis motion system 118 and y- axis motion system 116. More specifical ly, y-axis motion system 116 includes y-axis gantry 116a coupled to machine frame 114 via y-axis bearings 116b. X-axis motion system 118 is carried by y-axis motion system 116. X-axis motion system 118 i ncludes x-axis gantry 118a coupled to y-axis gantry 116a via x-axis beari ngs 118b. Stationary portion 110a is coupled to x-axis gantry 118a . It is noteworthy that for all

implementations of the invention, stationary portion 110a may be part of the same element/structure as x-axis gantry 118a; however, they are ill ustrated as separate elements conceptual ly.

[0031] Thus, i n the example ultrasonic weldi ng system 100a shown in FIG. 1A (and the other exemplary welding systems il lustrated and described herei n), the x-axis motion system is carried by the y-axis motion system, and the z-axis motion system (and the weld head assembly) is carried by the x-axis motion system. Of course, changes to these configurations are contemplated. For example, the y-axis motion system may be carried by the x-axis motion system, and the z-axis motion system (and the weld head assembly) is carried by the y-axis motion system.

[0032] FIG. IB i llustrates an ultrasonic welding system 100b. Ultrasonic welding system 100b incl udes a number of identical components/elements as compared to ultrasonic welding system 100a (illustrated and described with respect to FIG. 1A), including, for example : support structure 102, workpiece 104, weld head assembly 106, z-axis forcer 110, machine frame 114, y-axis motion system 116, and x-axis motion system 118. Thus, certain detai ls of such components/elements are not repeated with respect to FIG. IB.

[0033] Ultrasonic welding system 100b (of FIG. IB) differs from ultrasonic welding system 100a (of FIG. 1A) in that z-axis overtravel mechanism 132 (of FIG. IB) replaces z-axis overtravel mechanism 112 (of FIG. 1A) . Z-axis overtravel mechanism 132, along with z-axis forcer 110, is part of z-axis motion system 108b of ultrasonic welding system 100b. Z-axis overtravel mechanism 132 includes (i) z-axis block 132a (coupled to weld head assembly 106, either di rectly or indirectly), pneumatic cyl inder 132b, overtravel encoder 132c, and z-axis alignment structure 132d (e.g ., one or more pins, flexures, bearings, etc. providi ng z-axis alignment such that motion of z-axis block 112a with respect to moveable portion 110b is substantially along the z-axis (and not the x-axis or y-axis)) .

[0034] FIG. 2A i llustrates an ultrasonic welding system 200a . Ultrasonic welding system 200a incl udes a number of identical components/elements as compared to ultrasonic welding system 100a (illustrated and described with respect to FIG. 1A), including, for example : support structure 102, workpiece 104, weld head assembly 106, certain elements of z-axis forcer 110 (i .e., stationary portion 110a, moveable portion 110b), z-axis overtravel mechanism 112, machine frame 114, y-axis motion system 116, and x-axis motion system 118. Thus, certain details of such

components/elements are not repeated with respect to FIG. 2A.

[0035] Ultrasonic welding system 200a (of FIG. 2A) differs from ultrasonic welding system 100a (of FIG. 1A) in that z-axis motion system 210c of z-axis forcer 210 (of FIG. 2A) replaces z-axis motion system 110c of z-axis forcer 110 (of FIG. 1A) . Z-axis motion system 210c is part of z-axis forcer 210, which is part of z-axis motion system 208a of ultrasonic weldi ng system 200a . Z-axis motion system 210c i ncludes pneumatic cyli nder 210cl (coupled to stationary portion 110a, either directly or indirectly), and piston rod 210c2 (coupled to a piston in pneumatic cylinder 210cl, not shown for simplicity, and coupled to moveable portion 110b, either di rectly or indirectly) . Because piston rod 210c2 carries moveable portion 110b, moveable portion 110b moves along with piston rod 210c2.

[0036] FIG. 2B i llustrates an ultrasonic welding system 200b. Ultrasonic welding system 200b incl udes a number of identical components/elements as compared to respective ultrasonic welding systems 100a, 100b, 200a (i llustrated and described with respect to FIGS. 1A, IB and 2A), incl uding, for example : support structure 102, workpiece 104, weld head assembly 106, z-axis forcer 210, z-axis motion system 210c, machine frame 114, y-axis motion system 116, and x-axis motion system 118. Thus, certain details of such components/elements are not repeated with respect to FIG. 2B.

[0037] Ultrasonic welding system 200b (of FIG. 2B) differs from ultrasonic welding system 200a (of FIG. 2A) in that z-axis overtravel mechanism 132 (of FIG. 2B, previosuly descri bed with respect to FIG. IB) replaces z-axis overtravel mechanism 112 (of FIG. 2A) . Z-axis overtravel mechanism 132, along with z-axis forcer 210, is part of z-axis motion system 208b of ultrasonic weldi ng system 200b. Z-axis overtravel mechanism 132 includes (i) z-axis block 132a (coupled to weld head assembly 106, either di rectly or indi rectly), pnuematic cyl inder 132b, overtravel encoder 132c, and z- axis alignment structure 132d (e.g., one or more pi ns, flexures, bearings, etc. providing z-axis alignment such that motion of z-axis block 132a with respect to moveable portion 110b is substantially along the z-axis (and not the x-axis or y-axis)) .

[0038] FIG. 3A i llustrates an ultrasonic welding system 300a . Ultrasonic welding system 300a incl udes a number of identical components/elements as compared to ultrasonic welding system 100a (illustrated and described with respect to FIG. 1A), including, for example : support structure 102, workpiece 104, weld head assembly 106, certain elements of z-axis forcer 110 (i .e., stationary portion 110a, moveable portion 110b), z-axis overtravel mechanism 112, machine frame 114, y-axis motion system 116, and x-axis motion system 118. Thus, certain details of such

components/elements are not repeated with respect to FIG. 3A.

[0039] Ultrasonic welding system 300a (of FIG. 3A) differs from ultrasonic welding system 100a (of FIG. 1A) in that linear motor 310c of z-axis forcer 310 (of FIG. 3A) replaces z-axis motion system 110c of z-axis forcer 110 (of FIG. 1A) . Linear motor 310c is part of z-axis forcer 310, which is part of z-axis motion system 308a of ultrasonic welding system 300a. Li near motor 310c i ncludes stationary portion 310cl (coupled to stationary portion 110a, either directly or indirectly), and moveable portion 310c2 (coupled to a moveable portion 110b, either directly or indirectly) . As moveable portion 310c2 carries moveable portion 110b, moveable portion 110b moves along with moveable portion 310c2.

[0040] FIG. 3B i llustrates an ultrasonic welding system 300b. Ultrasonic welding system 300b incl udes a number of identical components/elements as compared to respective ultrasonic welding systems 100a, 100b, 300a (i llustrated and described with respect to FIGS. 1A, IB, and 3A), incl uding, for example : support structure 102, workpiece 104, weld head assembly 106, z-axis forcer 310, li near motor 310c, machine frame 114, y-axis motion system 116, and x-axis motion system 118. Thus, certain details of such components/elements are not repeated with respect to FIG. 3B.

[0041] Ultrasonic welding system 300b (of FIG. 3B) differs from ultrasonic welding system 300a (of FIG. 3A) in that z-axis overtravel mechanism 132 (of FIG. 3B) replaces z-axis overtravel mechanism 112 (of FIG. 3A) . Z-axis overtravel mechanism 132, along with z-axis forcer 310, is part of z-axis motion system 308b of ultrasonic welding system 300b. Z-axis overtravel mechanism 132 includes (i) z-axis block 132a (coupled to weld head assembly 106, either di rectly or indirectly), pnuematic cyl inder 132b, overtravel encoder 132c, and z-axis alignment structure 132d (e.g ., one or more pins, flexures, bearings, etc. providi ng z-axis alignment such that motion of z-axis block 112a with respect to moveable portion 110b is substantially along the z-axis (and not the x-axis or y-axis)) .

[0042] FIG. 4 i llustrates an ultrasonic weldi ng system lOOa l . Ultrasonic welding system lOOa l is substantial ly simi lar to ultrasonic weldi ng system 100a (i llustrated and described with respect to FIG. 1A), and incl udes a number of identical

components/elements as compared to ultrasonic welding system 100a . Thus, certain details of such components/elements are not repeated with respect to FIG. 4.

[0043] Ultrasonic welding system lOOa l (of FIG. 4) differs from ultrasonic welding system 100a (of FIG. 1A) in that z-axis motion system 108a l (of FIG. 4) includes a force detection mechanism 120 (e.g ., a load cel l 120) for detecti ng a z-axis force applied by ultrasonic welding system lOOa l along the z-axis of ultrasonic welding system lOOa l . In FIG. 4, force detection mechanism 120 is positioned between i nline spring 112b and moveable portion 110b. Alternative positions for force detection mechanism 120 are contemplated, for example: between i nli ne spring 112b and z-axis block 112a; between z-axis block 112a and ultrasonic converter 106a, among other positions - so long as the force measurement may be accomplished .

[0044] FIG. 5 i llustrates an ultrasonic weldi ng system 100a2. Ultrasonic welding system 100a2 is substantial ly simi lar to ultrasonic weldi ng system 100a (i llustrated and described with respect to FIG. 1A), and incl udes a number of identical

components/elements as compared to ultrasonic welding system 100a . Thus, certain details of such components/elements are not repeated with respect to FIG. 5.

[0045] Ultrasonic welding system 100a2 (of FIG. 5) differs from ultrasonic welding system 100a (of FIG. 1A) in that z-axis motion system 108a2 (of FIG. 5) includes a secondary z-axis forcer 122 (e.g., a pneumatic cyl inder 122 or other forcer) carried by moveable portion 110b of z-axis forcer 110. In FIG. 5, secondary z-axis forcer 122 provides a variable force along the z-axis of ultrasonic welding system 100a2.

[0046] FIGS. 6A-6D il lustrate an exemplary operation of an ultrasonic weldi ng system in accordance with certain exemplary embodi ments of the present invention. The operation illustrated in FIGS. 6A-6D is shown and descri bed with respect to ultrasonic welding system 300a (from FIG. 3A) . However, it is understood that the operation of FIGS. 6A-6D is equally applicable to any of the ultrasonic welding systems illustrated and descri bed herein (e.g., ultrasonic weldi ng system 100a, 100b, 200a, 200b, 300a, 300b, lOOa l, 100a2), or any other ultrasonic welding system within the scope of the invention.

[0047] Referri ng now to FIG. 6A, workpiece 104 is supported on support structure 102 of ultrasonic welding system 300a . Workpiece 104 includes conductive terminal 104b al igned with a conductive region of substrate 104a of workpiece 104. At FIG. 6A, weld head assembly 106 (i ncludi ng ultrasonic converter 106a carrying sonotrode 106b) is positioned above workpiece 104 prior to the ultrasonic welding of conductive terminal 104b to a conductive region of substrate 104a. Weld head assembly 106 is configured for motion along the z-axis of ultrasonic welding system 300a using z-axis forcer 310 of a z-axis motion system 308a . At FIG. 6B, weld head assembly 106 has been moved downward (through motion of moveable portion 110b of z-axis motion system 308a, where moveable portion 110b carries weld head assembly 106), along the z-axis, using z-axis forcer 310 such that a welding ti p of sonotrode 106b is in contact with conductive terminal 104b. At FIG. 6C, moveable portion 110b of the z-axis forcer 310 is moved further downward along the z-axis to activate z-axis overtravel mechanism 112. That is, inl ine spring 112b of z-axis overtravel mechanism 112 is compressed in FIG. 6C. In this position, with the desired level of bonding force now applied to conductive termi nal 104b via sonotrode 106b, ultrasonic energy is applied to the weldi ng ti p of sonotrode 106b to weld conductive terminal 104b to the conductive region of substrate 104a of workpiece 104. After the ultrasonic welding operation is complete, moveable portion 110b is raised such that sonotrode 106b is no longer in contact with conductive terminal 104b.

[0048] To il lustrate the movement of (i) moveable portion 110b of z-axis motion system 308a with respect to (ii) stationary portion 110a of z-axis motion system 308a, FIGS. 6A-6C incl ude markings Dl, D2, and D3. These markings, the corresponding heights/distances, and the relative components/elements used to delineate these markings are selected somewhat arbitrarily. But the markings ill ustrate the important poi nt of relative motion. In FIG. 6A, a height difference "Dl" is provided between an upper edge of stationary portion 110a and moveable portion 110b. In FIG. 6B, after lowering moveable portion 110b downward such that the welding tip of sonotrode 106b is i n contact with conductive terminal 104b, this height difference has i ncreased to "D2". In FIG. 6C, after further loweri ng of moveable portion 110b downward to activate z-axis overtravel mechanism 112 (thereby compressing inli ne spring 112b), this height difference has further i ncreased to "D3". Between FIGS. 6B and 6C, another variable height is shown (i .e., the height between a lower surface of moveable portion 110b and overtravel encoder 112c) corresponding to the spri ng gap. More specifically, in FIG. 6B, this height/gap is shown as "h i", but in FIG. 6C due to the further lowering of moveable portion 110b (and the correspondi ng spring compression of inl ine spring 112b) this height/gap has been reduced to "h2".

[0049] According to certain exemplary embodiments of the invention, during the ultrasonic welding operations, exemplary technical specifications incl ude: (i) the sonotrode bei ng configured to operate at a bond force of between 5-500 kg, or the sonotrode bei ng configured to operate at a bond force of between 5-300 kg, or the sonotrode bei ng configured to operate at a bond force of between 5- 100 kg; (i i) the sonotrode ti p motion amplitude bei ng between 5- 150 microns, or the sonotrode ti p motion amplitude being between 5- 120 microns, or the sonotrode ti p motion ampl itude being between 5-100 microns; (i ii) the sonotrode being configured to form an ultrasonic weld between a first portion of a workpiece and a second portion of a workpiece havi ng an area in a range between 1.5-30 mm²; or the sonotrode being configured to form an ultrasonic weld between a first portion of a workpiece and a second portion of a workpiece having an area in a range between 1.5-30 mm²; or the sonotrode bei ng configured to form an ultrasonic weld between a first portion of a workpiece and a second portion of a workpiece having an area in a range between 1.5- 16 mm²; and (iv) the sonotrode bei ng configured to operate at a frequency i n a range between 15-40 kHz, or the sonotrode bei ng configured to operate at a frequency in a range between 20-35 kHz, or the sonotrode bei ng configured to operate at a frequency in a range between 20-30 kHz. Exemplary thicknesses of the conductive contact of the contact element (the part of the workpiece being contacted by the sonotrode) incl ude: between 0.2-3 mm; 0.2- 1.5 mm, and 0.2- 1.2 mm.

[0050] In contrast to conventional wire or ribbon bonding machines (which utilize a continuous supply of wire such as from a spool), ultrasonic weldi ng machines typical ly are used to weld a first portion of a workpiece (e.g ., a conductive terminal) to a second portion of the workpiece. For example, the conductive terminal is a disti nct piece of material (as opposed to a portion of a wi re on a spool), and the terminal may be presented with (and/or al igned with) the second portion of the workpiece prior to being received at the welding area (e.g., the area below the weld head assembly) .

[0051] Various types of workpieces may be welded using the ultrasonic welding systems il lustrated and described herein (or other systems with the scope of the invention). Such workpieces may include a first portion of the workpiece (e.g., conductive terminal 104b illustrated and described herein) configured to be welded to a second portion of the workpiece (e.g., a conductive regsion of substrate 104a illustrated and described herein). Such workpieces may be particularly applicable to power modules. Of course, any other types of workpieces may be welded in accordance with the invention.

[0052] Exemplary conductive terminals may be copper terminals, terminals included as part of a copper busbars, or any other conductive terminals configured for use in the desired application. Exemplary substrates include a DBC (Direct Bonded Copper) assembly, copper plates, copper strips, or any other substrate configured for use in the desired application.

[0053] It will be appreciated that the term "power module" (sometimes referred to as a power electronic module), as used herein, relates to a module for containing one or more power components (e.g., power semiconductor devices). Example power components include MOSFETs, IGBTs, BJTs, thyristors, GTPs, and JFETs. Such a module also typically includes a power electronic substrate for carrying the power components. As compared to discrete power semiconductors, power modules tend to provide a higher power density.

[0054] The ultrasonic welding operations described herein may utilize (i) linear ultrasonic motion, (ii) torsional ultrasonic motion, (iii) a combination of linear and torsional ultrasonic motion, and (iv) other types of ultrasonic motion.

[0055] While not detailed herein, theta motion is contemplated as an option in connection with ultrasonic welding systems. As described herein, the weld head assembly may be moved along an x-axisd, a y-axis, and/or a z-axis. But additional motion may be provided about a theta axis. A theta motion system may be provided for the weld head assembly only, or the theta motion system may also carry certain elements of the z-axis motion system, etc.

[0056] Although the invention is illustrated and described herein with reference to specific embodiments, the invention is not intended to be limited to the details shown. Rather, various modifications may be made in the details within the scope and range of equivalents of the claims and without departing from the invention.

Claims

What is Claimed :

1. An ultrasonic welding system comprising : a support structure for supporting a workpiece; a weld head assembly including an ultrasonic converter carrying a sonotrode; and a z-axis motion system carrying the weld head assembly, the z-axis motion system including (i) a z-axis forcer for moving the weld head assembly along a z-axis of the ultrasonic welding system, and (ii) a z-axis overtravel mechanism disposed between the z-axis forcer and the weld head assembly.

2. The ultrasonic welding system of claim 1 wherein the z-axis forcer includes a linear motor for moving the weld head assembly along the z-axis of the ultrasonic welding system.

3. The ultrasonic welding system of claim 1 wherein the z-axis forcer includes a ball screw system for moving the weld head assembly along the z-axis of the ultrasonic welding system.

4. The ultrasonic welding system of claim 1 wherein the z-axis forcer includes a pneumatic cylinder for moving the weld head assembly along the z-axis of the ultrasonic welding system.

5. The ultrasonic welding system of claim 1 wherein the z-axis overtravel mechanism includes an inline spring.

6. The ultrasonic welding system of claim 1 wherein the z-axis overtravel mechanism includes a pneumatic cylinder.

7. The ultrasonic welding system of claim 6 wherein the pneumatic cylinder is a secondary z-axis forcer providing a variable force along the z-axis of the ultrasonic welding system.

8. The ultrasonic welding system of claim 1 further comprising an x-axis motion system for moving the weld head assembly along an x-axis of the ultrasonic welding system, and a y-axis motion system for moving the weld head assembly along a y-axis of the ultrasonic weldi ng system, wherein one of the x-axis motion system and the y- axis motion system carries the other of the x-axis motion system and the y-axis motion system.

9. The ultrasonic weldi ng system of claim 8 wherein the z-axis motion system is carried by the x-axis motion system and the y-axis motion system.

10. The ultrasonic weldi ng system of claim 1 further comprising a z-axis encoder for sensing motion of (i) a moveable portion of the z-axis forcer with respect to (ii) a stationary portion of the z-axis forcer along the z-axis of the ultrasonic welding system.

11. The ultrasonic weldi ng system of claim 1 further comprising an overtravel encoder for sensing motion of (i) a moveable portion of the z-axis forcer with respect to (ii) the weld head assembly along the z-axis of the ultrasonic weldi ng system.

12. The ultrasonic welding system of clai m 1 further comprisi ng a secondary z-axis forcer carried by a moveable portion of the z-axis forcer, the secondary z-axis forcer providing a variable force along the z-axis of the ultrasonic welding system.

13. The ultrasonic welding system of clai m 1 further comprisi ng a force detection mechanism for detecti ng a z-axis force appl ied by the ultrasonic welding system along the z-axis of the ultrasonic welding system.

14. The ultrasonic welding system of clai m 1 wherein the sonotrode is configured to operate during a welding operation at a bond force of between 5-500 kg, and with a sonotrode ti p motion amplitude of between 5-150 microns.

15. The ultrasonic welding system of clai m 1 wherein the sonotrode is configured to weld a first portion of the workpiece to a second portion of the workpiece using at least one of linear ultrasonic motion and torsional ultrasonic motion.

16. The ultrasonic welding system of clai m 1 further comprisi ng an input workpiece supply for providing the workpiece, and a material handli ng system for movi ng the workpiece from the i nput workpiece supply to the support structure.

17. The ultrasonic welding system of clai m 1 wherein the workpiece is selected from the group consisting of a power module, a lead frame and a battery module.

18. The ultrasonic welding system of clai m 1 wherein the workpiece includes a terminal, wherei n the sonotrode is configured to ultrasonically weld the termi nal to another portion of the workpiece.

19. The ultrasonic welding system of clai m 1 further comprisi ng a workpiece clamping system for clamping the workpiece to the support structure during ultrasonic welding by the sonotrode.

20. The ultrasonic welding system of clai m 1 further comprisi ng a workpiece assembly station configured to assemble the workpiece before ultrasonic welding of the workpiece by the sonotrode, the workpiece assembly station being configured to align a terminal of the workpiece with another portion of the workpiece.

21. The ultrasonic welding system of clai m 1 wherein the sonotrode is configured to form an ultrasonic weld between a terminal of the workpiece and another portion of the workpiece havi ng an area in a range between 1.5-30 mm².

22. The ultrasonic welding system of clai m 1 wherein the sonotrode is configured to operate at a frequency in a range between 15-40 kHz.

23. An ultrasonic welding system comprising : a support structure for supporting a workpiece; a weld head assembly includi ng an ultrasonic converter carrying a sonotrode; a z-axis motion system carrying the weld head assembly, the z-axis motion system incl uding (i) a z-axis forcer for moving the weld head assembly along a z-axis of the ultrasonic welding system, the z-axis forcer including a ball screw system for moving the weld head assembly along the z-axis of the ultrasonic welding system, and (ii) a z-axis overtravel mechanism disposed between the z-axis forcer and the weld head assembly, the z-axis overtravel mechanism including an inline spring ; a z-axis encoder for sensing motion of (i) a moveable portion of the z-axis forcer with respect to (ii) a stationary portion of the z-axis forcer along the z-axis of the ultrasonic welding system; and an overtravel encoder for sensi ng motion of (i) the moveable portion of the z- axis forcer with respect to (ii) the weld head assembly along the z-axis of the ultrasonic welding system.

24. A method of ultrasonical ly welding a conductive termi nal to a workpiece, the method comprising the steps of:

(a) supporting a workpiece on a support structure of an ultrasonic welding system, a conductive termi nal being aligned with a conductive region of the workpiece;

(b) providing a weld head assembly, incl udi ng an ultrasonic converter carryi ng a sonotrode, the weld head assembly being configured for motion along a z-axis of the ultrasonic welding system using a z-axis forcer of a z-axis motion system of the ultrasonic welding system;

(c) providing a z-axis overtravel mechanism disposed between the z-axis forcer and the weld head assembly, the z-axis forcer carrying the weld head assembly and the z-axis overtravel mechanism;

(d) moving a moveable portion of the z-axis forcer downward along the z-axis of the ultrasonic welding system unti l a welding tip of the sonotrode is i n contact with the conductive terminal ;

(e) movi ng the moveable portion of the z-axis forcer further downward along the z-axis of the ultrasonic welding system to activate the z-axis overtravel mechanism after step (d) ; and

(f) applying ultrasonic energy to the welding tip of the sonotrode to weld the conductive terminal to the conductive region of the workpiece.

25. The method of claim 24 wherei n step (e) includes applying a controlled weld force to the conductive terminal .

26. The method of claim 24 wherei n step (e) includes moving the moveable portion of the z-axis forcer further downward along the z-axis of the of the ultrasonic weldi ng system to compress a spring of the z-axis overtravel mechanism accordi ng to a predetermined compression profile to apply a controlled weld force to the conductive terminal .

27. The method of claim 24 wherei n step (e) includes moving the moveable portion of the z-axis forcer further downward along the z-axis of the of the ultrasonic weldi ng system to operate a pneumatic cyl inder of the z-axis overtravel mechanism to apply a controlled weld force to the conductive termi nal .

28. The method of claim 24 further comprising, after step (d) but before step (f), the step of (el) i ncreasing a z-axis force appl ied by the sonotrode to the conductive terminal using a secondary z-axis forcer carried by the moveable portion of the z-axis forcer, the secondary z-axis forcer configured to provide a variable force along the z- axis of the ultrasonic weldi ng system.

29. The method of claim 28 wherei n the secondary z-axis forcer i ncludes a pneumatic cyli nder.

30. The method of claim 28 wherei n the secondary z-axis forcer i ncludes an electric linear motor.