Abstract:
A method of forming a wire interconnect structure includes the steps of: (a) forming a wire bond at a bonding location on a substrate using a wire bonding tool; (b) extending a length of wire, continuous with the wire bond, to another location; (c) pressing a portion of the length of wire against the other location using the wire bonding tool; (d) moving the wire bonding tool, and the pressed portion of the length of wire, to a position above the wire bond; and (e) separating the length of wire from a wire supply at the pressed portion, thereby providing a wire interconnect structure bonded to the bonding location.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 14/413,475, filed Jan. 8, 2015, which claims the benefit of PCT Application No. PCT/US2013/048860, filed Jul. 1, 2013, which claims the benefit of U.S. Provisional Application No. 61/672,449, filed Jul. 17, 2012, the contents of which are incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to semiconductor packaging, and more particularly, to improved methods of forming wire interconnect structures. 
     BACKGROUND OF THE INVENTION 
     A wire bonder (i.e., wire bonding machine) may form wire loops between respective locations to be electrically interconnected. Exemplary wire bonding techniques include ball bonding and wedge bonding. Steps in a ball bonding application include: bonding a free air ball to a first bond location (e.g., a die pad of a semiconductor die); extending a length of wire continuous with the bonded free air ball to a second bond location (e.g., a lead of a leadframe); and bonding the wire to the second bond location, thereby forming a wire loop between the first bond location and the second bond location. In forming the bonds between (a) the ends of the wire loop and (b) the bond sites (e.g., die pads, leads, etc.) varying types of bonding energy may be used including, for example, ultrasonic energy, thermosonic energy, thermo-compressive energy, amongst others. 
     Wire bonding machines have also been used to form wire contacts and interconnects having a free end for a number of years. For example, U.S. Pat. No. 5,476,211 to Khandros discloses forming such conductive contacts using ball bonding techniques. However, conventional techniques of forming such wire contacts and interconnects suffer from a lack of consistency (e.g., height consistency, shape consistency, etc.) and undesirable shapes of the wire contacts and interconnects. 
     Thus, it would be desirable to provide improved methods of forming wire interconnect structures. 
     SUMMARY OF THE INVENTION 
     According to an exemplary embodiment of the present invention, a method of forming a wire interconnect structure includes the steps of: (a) forming a wire bond at a bonding location on a substrate using a wire bonding tool; (b) extending a length of wire, continuous with the wire bond, to another location; (c) pressing a portion of the length of wire against the other location using the wire bonding tool; (d) moving the wire bonding tool, and the pressed portion of the length of wire, to a position above the wire bond; and (e) separating (e.g., stretching and tearing) the length of wire from a wire supply at the pressed portion, thereby providing a wire interconnect structure bonded to the bonding location. 
     According to another exemplary embodiment of the present invention, a method of forming a wire interconnect structure, the method comprising the steps of: (a) forming a ball bond at a bonding location on a substrate using a wire bonding tool; (b) extending a length of wire, continuous with the ball bond, to another location; (c) pressing a portion of the length of wire against the other location using the wire bonding tool to partially cut a portion of the length of wire; (d) moving the wire bonding tool, and the partially cut portion of the length of wire, to a position above the wire bond; (e) extending an additional length of wire from the wire bonding tool, and above the partially cut portion of the length of wire; and (f) separating the length of wire from a wire supply at the partially cut portion, thereby providing a wire interconnect structure bonded to the bonding location, the wire interconnect structure extending substantially vertical above the wire bond. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention is best understood from the following detailed 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 drawings are the following figures: 
         FIGS. 1A-1I  are block, side view diagrams illustrating formation of vertical wire interconnects in accordance with an exemplary embodiment of the present invention; and 
         FIG. 2  is a block, side view diagram illustrating formation of vertical wire interconnects on a substrate in accordance with another exemplary embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     As used herein, the term “interconnect structures” or “wire interconnect structures” are intended to refer to conductive structures that may be used to provide any type of electrical interconnection (e.g., a temporary interconnection as in a contact used for testing, a permanent interconnection as in a semiconductor package interconnect, etc.). 
       FIGS. 1A-1I  illustrate a method of forming one or more wire interconnect structures in accordance with an exemplary embodiment of the present invention. As illustrated in  FIG. 1A , free air ball  106  is seated at the tip of bonding tool  104  (e.g., wire bonding tool  104 ) with wire  110  extending upwardly through a bore, or the like, in wire bonding tool  104  and through open wire clamp  108 . Wire bonding tool  104  and wire clamp  108  are carried by a common bond head assembly (not shown) and as such, move together, for example, in a vertical Z axis. As will be understood by those skilled in the art, free air ball  106  is formed on an end of wire  110  that hangs below the tip of bonding tool  104  using an electronic flame-off device or the like (not shown). It will be understood that, many elements are omitted from the simplified views of  FIGS. 1A-1I  (e.g., an ultrasonic transducer carrying bonding tool  104 , etc.). 
     After free air ball  106  is formed, wire  110  is drawn upwards (e.g., using a vacuum control tensioner or the like) such that free air ball  106  is seated at the tip of bonding tool  104  as shown in  FIG. 1A . Wire bonding tool  104  and wire clamp  108  are positioned over substrate  100 . As will be appreciated by those skilled in the art, substrate  100  may be any type of element to which a wire interconnect may be bonded. Exemplary substrates include leadframes, semiconductor die, BGA (ball grid array) package elements, flip chip elements, package-on-package (POP) elements, etc. Bonding location  102  may be any type structure configured to receive a wire interconnect. For example, if substrate  100  is a semiconductor die then bonding location  102  may be a die pad. Other exemplary bonding locations include leads, circuits traces, etc. 
     As shown in  FIG. 1A , bonding tool  104  and wire clamp  108  are then moved downwardly, as at the arrows in a downward Z direction, towards bonding location  102  (e.g., along with other elements of the bond head assembly). As illustrated in  FIG. 1B , bonding tool  104  and wire clamp  108  are lowered and free air ball  106  contacts bonding location  102  and will form a ball bond using, for example, bonding force, ultrasonic energy, and heat (e.g., a heat block positioned below substrate  100 , not shown). As illustrated in  FIGS. 1C-1D , ball bond  112  has now been formed, and bonding tool  104  and wire clamp  108  (in an open position) are moved upwardly while extending a length of wire  114  from ball bond  112  towards another location  116 . Length of wire  114  is continuous with ball bond  112 . Length of wire  114  may be extended in a single step, or a plurality of steps and associated motions, as desired. The motions used to extend length of wire  114  may be similar to conventional looping motions used to extend a wire loop from a first bond location to a second bond location; however, the portion of wire  114  adjacent tip  120  of bonding tool  104  is not ultrasonically bonded/welded to another location  116 . Rather, a predetermined level of bond force (e.g., likely without ultrasonic energy), is applied to tip  120  of wire bonding tool  104  to press the portion of wire  114  against other location  116  (e.g., see  FIG. 1D ). In another example, rather than applying a predetermined amount of bonding force, wire bonding tool  104  is moved to a predetermined position such that a bond force is applied to press the portion of wire  114  against other location  116 . Regardless of whether the bond force is applied in a force controlled mode, a position controlled mode, or other mode of operation—this pressing may “deform,” or partially cut, pressed portion  118  of wire  114  beneath tip side  120   a  of bonding tool  104 , for example, shown as deformed/cut wire portion  118 . As provided above, deformed/cut wire portion  118  has not been bonded/welded to another location  116 . Rather, it may be temporarily stuck to another location  116  during the formation of deformed/cut wire portion  118 . 
     As illustrated in  FIG. 1E , wire bonding tool  104  and wire clamp  108  (e.g., in a closed position, but may be open if desired) have been raised to a position above ball bond  112  with wire  110 , having deformed/cut wire portion  118 , continuous with ball bond  112 . Such a position may be considered to be a top of loop (i.e., TOL) position in conventional wire looping terminology. 
     At  FIG. 1F  wire clamp  108  has been moved to an open position, and wire bonding tool  104  and open wire clamp  108  are being raised, as at the arrows in an upward Z direction, to pay out another portion of wire  114 ′ (e.g., a tail length of wire  114 ′) from wire bonding tool tip  120  that is continuous with deformed/cut wire portion  118 . For example, wire portion  114 ′ may become a wire tail for a subsequent free air ball. As more clearly shown in the enlarged portion of the circle below tip  120  of bonding tool  104  in  FIGS. 1E-1F , pressed wire portion  118  of wire  110  may be a partial cut in wire  110 , and separates wire portions  114 ,  114 ′. As illustrated in  FIG. 1G , wire clamp  108  is closed over an upper portion of wire  110  and, as illustrated in  FIG. 1H , wire bonding tool  104  and wire clamp  108  are then raised as at the arrows in an upward Z direction to separate wire  110  proximate deformed/cut wire portion  118  to form wire interconnect structure  122 . The enlarged portion of the circle below the tip of wire bonding tool  104  more clearly shows that wire interconnect structure  122  (separated from wire portion  114 ′) may have an upper tapered, or sharp, end  124 .  FIG. 1I  illustrates substrate  100  with other wire interconnect structures  122  formed on additional bonding locations  102  by the repeating of the method described above. As illustrated, wire interconnect structures  122  may be vertically erect, or substantially so. 
     As described above in connection with  FIG. 1D , a portion of wire  114  is pressed against another location  116 . In the embodiment of  FIGS. 1A-1H , another location  116  may be a portion of substrate  100  (e.g. a surface portion of substrate  100 , etc.). However, it may be appreciated by those skilled in the art that any location may be used for another location  116 . For example, as illustrated in  FIG. 2 , and according to another embodiment of the present invention, the pressing of wire portion  118  (for some, or all, of wire interconnect structures  122  to be formed on substrate  100 ) may occur at a location other than substrate  100  (e.g., on another substrate or structure), such as at another location/substrate  200  shown in  FIG. 2  that is not (directly) part of substrate  100 . 
     Wire interconnect structures formed in accordance with the present invention may have improved consistency in height and resultant wire tail lengths, as well as increased efficiency in production (e.g., an increase in unit per hour produced). 
     Wire interconnect structures formed in accordance with the present invention may be used, for example, as contact structures in probe cards, as interconnects between die in stacked die applications, as interconnects in flip chip applications, as interconnects in through silicon via or through mold via applications, as interconnects between packages in POP (package on package) applications, amongst others. 
     Although the present invention has been described primarily with respect to certain exemplary method steps in a predetermined order, it is not limited thereto. Certain of the steps may be rearranged or omitted, or additional steps may be added, within the scope of the present invention. 
     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.