Abstract:
A leadframe configuration for a semiconductor device has a die attach paddle with paddle support bars. In addition, clamp tabs extend outwardly from lesser supported locations of the paddle to underlie a conventional lead clamp. The clamp tabs are formed as an integral part of the paddle. Normal clamping during die attach and wire bonding operations prevents paddle movement and enhances integrity of the die bond and wire bonds.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of application Ser. No. 09/210,013, filed Dec. 11, 1998, now U.S. Pat. No. 6,162,662, issued Dec. 19, 2000, which is a divisional of application Ser. No. 09/028,133, filed Feb. 23, 1998, now U.S. Pat. No. 6,121,674, issued Sep. 19, 2000. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates generally to a semiconductor device assembly including a semiconductor die and leadframe. More particularly, the invention pertains to a leadframe with a mounting paddle to which a semiconductor die is bonded and with a plurality of leads of the leadframe connected to the bond pads on the die by wire bonding. 
     2. State of the Art 
     In the manufacture of semiconductor device assemblies, a single semiconductor die is most commonly incorporated into each sealed package. Many different package styles are used, including dual inline packages (DIP), zig-zag inline packages (ZIP), small outline J-bends (SOJ), thin small outline packages (TSOP), plastic leaded chip carriers (PLCC), small outline integrated circuits (SOIC), plastic quad flat packs (PQFP), and interdigitated leadframe (IDF). Some semiconductor device assemblies are connected to a substrate, such as a circuit board, prior to encapsulation. 
     The assembly of a semiconductor device and a leadframe and die ordinarily includes bonding of the die to a paddle of the leadframe, and wire bonding bond pads on the die to inner leads, i.e. lead fingers, of the leadframe. The inner leads, semiconductor die, and bond wires are then encapsulated, and extraneous parts of the leadframe excised. 
     In drawing FIG. 1, an exemplary PRIOR ART leadframe strip  10  is shown. The leadframe strip  10  comprises a thin metal foil. The leadframe strip  10  is configured for the mounting of a plurality of semiconductor dice, one on each die mount paddle  12 . The leadframe strip  10  also includes parallel spaced side rails  14 ,  16  formed with a pattern of registry holes  18  for handling by automatic machinery. In addition, the leadframe strip  10  includes an arrangement of inner leads  20  configured for attachment to the bond pads of a semiconductor die during a wire bonding step. Outer leads  22  will become the external leads of the completed semiconductor device package for connection to, e.g., a circuit board. The leads  20 ,  22  are connected to the side rails  14 ,  16  by dam bars  24 , and supported thereby. As shown, each of the die mount paddles  12  is connected to each of the side rails  14 ,  16  by a paddle support bar  26 ,  28 , respectively, extending transversely with respect to the centerline  30  of the leadframe strip  10 . 
     In an alternative arrangement, not shown, the paddle support bars  26 ,  28  extend parallel to centerline  30  from the die mount paddles  12  to dam bars  24  for support of the paddles. 
     In forming a semiconductor device package, semiconductor dice are typically bonded to the paddles of the leadframe strip with an adhesive polymer, such as epoxy or a thermoplastic, with soft solder, or with a gold-silicon eutectic layer. Generally, each paddle is slightly larger than the attached semiconductor die. The conductive bond pads of the semiconductor die are then wire bonded to the inner leads surrounding the semiconductor die, generally by the use of the well-known thermocompression bonding method, but sometimes by thermosonic or ultrasonic bonding methods. 
     During semiconductor die attach and wire bonding, the inner leads are typically clamped against a lower heater block or other flat member. The bonding tool itself is configured to compress the wire against the surface to which the wire is being bonded, i.e. bond pad or inner lead. Examples of such are found in U.S. Pat. No. 4,600,138 of Hill, U.S. Pat. No. 4,030,657 of Scheffer, U.S. Pat. No. 4,603,803 of Chan et al., U.S. Pat. No. 4,778,097 of Hauser, U.S. Pat. No. 5,148,959 of Cain et al., U.S. Pat. No. 5,217,154 of Elwood et al., U.S. Pat. No. 5,421,503 of Perlberg et al., and U.S. Pat. No. 5,445,306 of Huddleston. generally been found, however, that auxiliary clamping apparatus may improve the quality of “second bonding”, i.e., bonding of the wire to the inner leads. 
     Each inner lead being wire bonded may be clamped while being wire bonded only, or all leads may be simultaneously clamped. 
     Commercial wire bonding machines typically have an upper clamp member which includes a window for access to the semiconductor die, die paddle and inner end portions of the inner leads. The “frame” of the window acts as a narrow clamp which simultaneously holds down the inner leads surrounding the semiconductor die against the heater block. Alternatively, clamps are inserted through a window to hold the inner leads against the heater block. These “window” types of clamping arrangements are exemplified in U.S. Pat. No. 3,685,137 of Gardiner, U.S. Pat. No. 5,035,034 of Cotney, U.S. Pat. No. 5,322,207 of Fogal et al., U.S. Pat. No. 5,372,972 of Hayashi et al., U.S. Pat. No. 4,765,531, 5,238,174 and 5,307,978 of Ricketson et al., U.S. Pat. No. 5,082,165 of Ishizuka, and U.S. Pat. No. 5,264,002 of Egashira et al. 
     Various other types of prior art clamping apparatus and methods of clamping an inner lead or bond pad against a flat lower member are illustrated in U.S. Pat. No. 4,361,261 of Elles et al., U.S. Pat. No. 4,434,347 of Kurtz et al., U.S. Pat. No. 4,978,835 of Luijtjes et al., U.S. Pat. No. 5,193,733 of You, U.S. Pat. No. 5,197,652 of Yamazaki, U.S. Pat. No. 4,821,945 of Chase et al., and U.S. Pat. 5,647,528 of Ball et al. 
     U.S. Pat. No. 3,566,207 of Adams shows a leadframe in which the paddle support bars are clamped by “point” clamps. 
     A major source of package rejection is wire bond failure. Such failure has been attributed to overheating, underheating, chemical contamination, surface roughness, surface voids, oxide formation, presence of moisture, inadequate lead clamping, and other suspected causes. 
     While a wire bond “no-stick” may sometimes be detected and reworked on the spot, wire bond defects often do not become apparent until subsequent testing, or after the device has been encapsulated and/or has been in use. At this stage, the unit cost of the device itself is maximal. In addition, repair of a defective device may not be feasible. 
     On occasion, the die-to-paddle bond fails and may result in, e.g., shorting within the packaged device, wire bond breakage, loss of heat dissipation capability, and/or incomplete sealing of the package. 
     Even a relatively low frequency of defects in the wire bonds and in die-to-paddle bonds is extremely costly to the semiconductor industry. 
     It is therefore an object of the invention to provide a semiconductor device wherein the frequency of wire bond failures and die-to-paddle bond failures is reduced, the frequency of required wire bond rework is reduced, and the manufacturing cost is reduced. 
     BRIEF SUMMARY OF THE INVENTION 
     It has been generally assumed in the industry that the die mount paddle does not move during down-bonding of the semiconductor die, or during subsequent wire bonding. However, it has been discovered that significant movement sometimes may exist, and this movement contributes to poor semiconductor die-to-paddle bonding and can be a major cause of the observed failure, i.e., immediate “no-stick” or subsequent debonding of the wire bonds from the bond pads of the semiconductor die and/or from the metal inner leads. 
     In accordance with the invention, the pattern of paddle and leads on the leadframe is configured to provide a paddle with clampable tabs extending therefrom. The tabs extend outwardly from areas of the paddle which are otherwise largely unsupported or farthest from the paddle support bars. These tabs may be formed on the sides of the paddle along which there are few, if any, bond pads. Alternatively, the tabs may be on the same sides as the paddle support bars, particularly when the paddle support bars on the sides have few, if any, bond pads. Typically, the tabs are positioned on the long dimensions of the paddle. When the leadframe is clamped for die attach and wire bonding, a clamp member such as a circumscribing “window frame” simultaneously clamps the inner leads, paddle support bars and paddle tabs against a lower clamp member which may be a heater block. The paddle is thus more extensively supported and is much more resistant to flexing, bending, and lifting away from the lower clamp member during the bonding operations. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
     The invention is illustrated in the following figures, wherein the elements are not necessarily shown to scale: 
     FIG. 1 is a plan view of a prior art semiconductor leadframe strip; 
     FIG. 2 is a plan view of a wire-bonded semiconductor device having a leadframe of the invention; 
     FIG. 3 is a cross-sectional side view of a portion of a leadframe strip of the invention and a die bonded thereto, as taken along line  3 — 3  of FIG. 2; 
     FIG. 4 is a cross-sectional side view of a portion of another embodiment of a leadframe strip of the invention and a die bonded thereto, as taken along line  3 — 3  of FIG. 2; and 
     FIG. 5 is a plan view of a wire-bonded semiconductor device having another embodiment of a leadframe of the invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In the following discussion, the terms “upper” and “lower” are understood to include the inverse when referring to clamp members or leadframe levels of a bilevel leadframe. 
     As depicted in drawing FIGS. 2 and 3, a portion of an uncompleted exemplary semiconductor device  40  includes a semiconductor die  42  and a metal leadframe strip  44  to which the semiconductor die is attached. The final package outline  74  is shown with centerline  45 . The leadframe strip  44  includes inner leads  46 , outer leads  48 , and spacedapart side rails  50  and  52  for each of a plurality of leadframe panels  54 . The inner leads  46  and outer leads  48  are supported from the side rails  50 ,  52  by dam bars  76 . The outer leads  48  for the leadframe are only shown in part, but generally extend to a crossbar, not shown, or to the corresponding outer leads of the adjacent leadframe panels  54  of leadframe strip  44 . 
     The leadframe strip  44  also includes a die mount paddle  60  which is configured for the mounting of the back side  62  of semiconductor die  42  thereon, using an adhesive layer  104  such as polyimide, epoxy, polymeric tape, etc. The adhesive layer  104  may be electrically nonconductive or conductive, depending upon the particular use for which the device is designed. The die mount paddle  60  is connected at each end  56 ,  58  to one of the leadframe rails  50 ,  52  by paddle support bars  78  and  80 , and is supported thereby. 
     The semiconductor die  42  is illustrated as having an active surface  64  with a generally rectangular shape, although the semiconductor die may be of any shape. Bond pads  66  are arrayed adjacent the semiconductor die ends (edges)  68 ,  70  for conductive attachment to the inner leads  46  with thin wires  72 . The wire bonding process may be one of thermocompression, ultrasonics or thermosonics, for example. 
     In accordance with the invention, the die mount paddle  60  is formed with clamping tabs  90  on each non-supported side  82 ,  84 , i.e., the sides not having a paddle support bar  78 ,  80 . Each clamping tab  90  extends outwardly to underlie the upper clamp member  86  and may be clamped thereby to a lower clamp member, not shown, which underlies a major portion of the leadframe panel  54 . The clamping tabs  90  are shown with outer ends  88  not connected to inner leads  46 , side rails  50 ,  52 , or other parts of the leadframe panel  54 . Thus, the presence of the clamping tabs  90  does not affect the choice of conductive or nonconductive adhesive layer  104 . The clamping tabs  90  are configured to be totally encapsulated in the completed packaged device  40 . 
     Drawing FIG. 2 shows two clamping tabs  90  on each side  82 ,  84  of the die mount paddle  60 , the clamping tabs  90  extending outwardly and converging toward each other. The clamping surface  102  of the upper clamp member  86  intersects and exerts clamping force on the tab clamping areas  106  of the clamping tabs  90 . The clamping tabs  90  may take any reasonable shape which will make the die mount paddle  60  more rigid but not result in shorting to leads or wires, and will not hinder polymer passage during encapsulation. Thus, the spacing  108  between the clamping tabs  90  and adjacent inner leads  46  and the space  110  between the two clamping tabs  90  permit adequate flow of polymer. The clamping tabs are shown as having a width comparable to the outer leads  48 . 
     Preferably, the clamping tabs  90  are positioned so that there is no need for bond wires  72  to pass over the tabs. 
     As shown in the cross-sectional view of drawing FIG. 3, the inner leads  46  and die mount paddle  60  may be coplanar, and the upper clamp member  86  has a clamping surface  102  which surrounds wire-bonding access window  87  and compresses the inner leads  46 , die mount paddle  60  and, clamping tabs  90 , as well as the paddle support bars  78 ,  80  (not visible) against the flat surface  98  of the lower clamp member  96 , e.g., heater block. 
     An alternative configuration is shown in drawing FIG. 4, in which the die mount paddle  60  is depressed to a lower level  92  below an upper level  94  of the inner leads  46 . The paddle support bars (see bar  78 ) and the clamping tabs  90  are bent upwardly from the die  42  so that outer portions thereof underlie the clamping surface  102  of the upper clamp member  86  for firm clamping to the lower clamp member  96 , e.g., heater block. While a packaged semiconductor device may be made with this alternate configuration, the coplanar configuration of drawing FIG. 3 is generally preferred for ease of manufacture. 
     Drawing FIG. 5 depicts a variation, alternative embodiment, of the invention in which the clamping tabs  90  also act as paddle support bars. 
     As shown in drawing FIG. 5, a portion of an uncompleted exemplary semiconductor device  40  includes a semiconductor die  42  and a metal leadframe strip  44  to which the die  42  is attached. The final package outline  74  is shown with centerline  45 . The leadframe strip  44  includes inner leads  46 , outer leads  48 , and side rails  50  and  52 . The inner leads  46  and outer leads  48  are supported from the side rails  50 ,  52  by dam bars  76 . 
     The leadframe strip  44  also includes a die mount paddle  60  which is configured for the mounting of the semiconductor die  42  thereon, as previously described. 
     The semiconductor die  42  is illustrated as having an active surface  64  with a generally rectangular shape. Bond pads  66  are arrayed adjacent the die ends (edges)  68 ,  70  for conductive attachment to the inner leads  46  with thin wires  72 . The wire bonding process may be one of thermocompression, ultrasonics or thermosonics, for example. 
     In accordance with this embodiment of the invention, the die mount paddle  60  is formed with clamping tabs  90  on each of the sides  114 ,  116  having no (or few) bond pads  66 . In contrast to the version shown in drawing FIGS. 2-4, the ends  56 ,  58  of the die mount paddle  60  are not connected to the side rails  50 ,  52  by support bars. Each clamping tab  90  is integral with the die mount paddle  60  over a major portion of the side  114  or  116 . Each clamping tab  90  extends outwardly to underlie the upper clamp member  86  in tab clamping area  106  and may be clamped thereby to a lower clamp member, not shown, which underlies a major portion of the leadframe strip  44 . The clamping tabs  90  are shown with constricted outer ends  88  connected to dam bars  76  for supporting the die mount paddle  60  during die bond and wire bonding operations. Each clamping tab  90  is shown with apertures  112  therethrough whereby the flow of liquified polymer during device encapsulation is not deleteriously impeded. The clamping tabs  90  are configured to be totally encapsulated in the completed packaged device  40 . 
     The clamping tabs  90  may take any reasonable shape which will not result in shorting to leads or wires, and will not hinder polymer movement during encapsulation. Preferably, the clamping tabs  90  are positioned so that there is no need for bond wires  72  to pass over the tabs. 
     Following encapsulation, the tab ends  88  are severed, and the dam bars  76  removed to singulate the leads. 
     If desired, the die mount paddle  60  may be formed of a material different from the inner leads  46  and outer leads  48 . In the current state of the art, however, additional cost would be incurred. 
     A major advantage of the inclusion of clamping tabs  90  in the die mount paddle  60  is the prevention of paddle movement during die bonding and the subsequent wire bonding operations. The reduced movement permits more secure bonding of the semiconductor die  42  to the die mount paddle  60 . In addition, the first wire bond, i.e., to the bond pad  66 , as well as the second wire bond, i.e., to an inner lead  46 , are stronger. As a result, the device failure rate may be significantly reduced. 
     An additional advantage of the invention is the enhanced heat spread and dissipation through the clamping tabs. 
     It is apparent to those skilled in the art that various changes and modifications may be made to the leadframe configurations of the invention, devices formed therefrom and methods of making and practicing the invention as disclosed herein without departing from the spirit and scope of the invention as defined in the following claims.