Abstract:
A leadframe structure ( 100 ) for an electronic package is provided, wherein the leadframe structure ( 100 ) comprises a die-pad ( 103 ), a barrier area ( 114 ), and a bonding area ( 111 ), wherein the barrier area ( 114 ) is arranged between the die-pad ( 103 ) and the bonding area ( 111 ), and wherein the barrier area ( 111 ) is adapted to electrically connect the die-pad ( 103 ) and the bonding area ( 111 ), and is further constructed in such a way that delamination growth between the leadframe structure ( 100 ) and a moulding compound fixable to the leadframe structure ( 100 ) is reduced.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates to a leadframe structure for electronic packages. 
         [0002]    Moreover, the invention relates to a method of bonding electrical connection, in particular bondwires to a leadframe structure. 
         [0003]    Further, the invention relates to an electronic package. 
       BACKGROUND OF THE INVENTION 
       [0004]    In the field of electronic packages, in particular in case that a plastic body encapsulates the chip of the electronic package, carriers or lead frames are widely used. For example, such a lead frame is a metal frame that includes the leads of a plastic encapsulated dual-in-line plastic package. In particular, electronic packages are featured with connection leads penetrating the plastic body surface. Electronic connection from chips of the electronic package to those leads is done by gold (Au) or aluminum (Al) bondwires. In many cases the bondwire is attached to the lead by thermocompression bonding. The inner part is encapsulated by mould compound (EMC). The lead frame holds the leads in place prior to encapsulation and is cut away after encapsulation. 
         [0005]    A known problem is the risk of wire bond breakage from the die-pad. Such a wire bond, also referred to as “downbond” is usually made to create an electrical connection from the die surface to the die-pad, which generally forms an electrical ground. Such a downbond has a high risk to come loose from the die-pad when it is used in the final application or during reliability tests. 
         [0006]    The die-pad on which the downbond is placed is usually silver-plated to allow wirebonding. The silver-plated surface has a poor adhesion to the moulded compound as used in semiconductor packaging. The die is generally glued on the die-pad, which is a part of the leadframe. The glue-fillet has bad adhesion to the moulding compound, so that during temperature cycling thermo-mechanical stress will cause delamination between moulding compound and leadframe on those locations where adhesion is inferior. The forces driving this delamination increase as the delaminated area grows bigger. The gap height in the delaminated area increases for larger delaminated areas. The delamination and a corresponding gap at the location of the downbond may crack or tear off the bondwire from the die-pad. This will result in electrical failure or performance out of electrical specification. 
       OBJECT AND SUMMARY OF THE INVENTION 
       [0007]    It is an object of the invention to provide a leadframe structure for electronic packages, a method of bonding an electrical connection, and an electronic package, which are less prone to failure or may have increased reliability. 
         [0008]    In order to achieve the object defined above a leadframe structure for electronic packages, a method of bonding an electrical connection, and an electronic package according to the independent claims are provided. 
         [0009]    According to an exemplary embodiment a leadframe structure for an electronic package is provided, wherein the leadframe structure comprises a die-pad, a barrier area, and a bonding area, wherein the barrier area is arranged between the die-pad and the bonding area, and wherein the barrier area is adapted to electrically connect the die-pad and the bonding area, and is further constructed in such a way that delamination growth between the leadframe structure and a moulding compound fixable to the leadframe structure is reduced. 
         [0010]    According to another exemplary embodiment of the leadframe structure the barrier area is formed by a barrier structure that has a width smaller than the bonding area. In particular, the barrier structure may be formed by a barrier structure having a length which is at least two times the width of the barrier structure. Specifically, the length may be more than four times the width. 
         [0011]    A metallic conductor or metallic track, e.g. the same material as the material of the die-pad and/or the bonding area, may form the barrier. The width may be measured transversal or lateral to the direction leading from the die-pad to the bonding area. That is, a longitudinal direction of the barrier structure or barrier area may be defined in particular substantially from a contact point of the barrier area and the die-pad and a contact point of the barrier area and the bonding area. Consequently, a width may be defined transversal and in particular perpendicular to that longitudinal direction. By providing a barrier structure having a greater length than width a long and narrow metal connection between die-pad and bonding area or downbond area may be provided which may act as an efficient barrier for growth of delamination. 
         [0012]    According to an exemplary embodiment a method of bonding an electrical connection onto a leadframe structure is provided, wherein the method comprises providing a leadframe structure according to an exemplary embodiment, and bonding an electrical connection onto the bonding area. In particular, the electrical connection may be a bondwire. 
         [0013]    According to an exemplary embodiment an electronic package comprises a leadframe structure according to an exemplary embodiment, and a die, wherein the die is attached to the die-pad, and wherein the die is further electrically contacted to the bonding area. In particular, the electronic package may further comprise a moulding compound, wherein the moulding compound is formed in such a way that it at least partially covers the leadframe structure and the die. The electronic package may comprise a Quad Flat Package, a Dual In-Line package, or a Small Outline package. 
         [0014]    The term “die-pad” may particularly denote an electrically conductive pad which may be adapted to be attached to a die or that a die is bondable to the die-pad. For example, the die may be glued to the die-pad. The die-pad may be electrically connected to ground. 
         [0015]    The term “bonding area” may particularly denote a pad or contact area which is adapted to be bonded to a bondwire or that a bondwire is bondable to the bonding area. Such a bonding area may in particular be connected or connectable to ground. In principle, such a bonding area may also form a terminal further electrical or electronic components may be attached to. 
         [0016]    By providing a barrier area between the bonding area and the die-pad it may be possible to reduce a risk of delamination between a moulding compound and the die pad which delamination would cause a risk of a breaking of bondwires. In particular, it may be possible to stop a delamination which starts at the glue-fillet and which possibly would grow along the interface between the die-pad and the moulding compound and which possibly depends on thermomechanical forces. Thus, the barrier area may form a barrier for the growth of a gap or delamination. In particular, the delamination may grow up to the edge of the die-pad but may not easily grow along the barrier area. 
         [0017]    It may be seen as a gist of an exemplary embodiment that a barrier area electrically connect a die-pad and a bonding area of a leadframe structure. The barrier area is adapted to decrease the probability for a delamination of a moulding compound and the die-pad. 
         [0018]    Next, further exemplary embodiments of the leadframe structure for electronic packages are described. However, these embodiments also apply to the method of bonding an electrical connection, and the electronic package. 
         [0019]    According to another exemplary embodiment of the leadframe structure the bonding area is formed by a fused lead. In particular, the fused lead may be formed by a dummy fused lead. 
         [0020]    The term “dummy fused lead” may particularly denote fused leads that are not connected to external ground, i.e. do not extend to the boundary of the leadframe structure. In other words an area between the dummy fused lead and the boundary of the leadframe structure is free of an electrical connection. Thus, the dummy fused leads may be connected to ground via the die-pad but may not have an own external connection to ground. 
         [0021]    According to another exemplary embodiment the leadframe structure further comprises a clamping area, which is adapted in such a way that the clamping area is clampable during a bonding step. In particular, the clamping area may be formed in the region of the bonding areas, for example in such a way that the clamping supports the bonding areas during a bonding process. For example, the clamping area may be arranged around the die-pad and may be usable to mechanically support the leads during wirebonding. In general, the leads are clamped close to the leadtips, where wirebonding usually takes place, to possibly avoid bending of the lead, which bending may act as a spring, due to the force and movements of the wirebond capillary. 
         [0022]    Next, further exemplary embodiments of the method of bonding an electrical connection are described. However, these embodiments also apply to the leadframe structure for electronic packages, and the electronic package. 
         [0023]    According to another exemplary embodiment the method further comprises attaching a die onto the die-pad, and bonding the electrical connection to a terminal of the die. Thus, an electrically conductive connection between a terminal of the die and ground may be established via the bonding wire, the bounding area and the barrier area. 
         [0024]    According to another exemplary embodiment the method further comprises clamping a clamping structure to a clamping area of the leadframe structure. In particular, the clamping structure may be clamped to the clamping area before the electrical connection is bonded onto the bonding area. 
         [0025]    The aspects and exemplary embodiments defined above and further aspects of the invention are apparent from the examples of embodiment to be described hereinafter and are explained with reference to these examples of embodiment. Features described in connection with an exemplary embodiment or an exemplary aspect may be combined with other exemplary embodiments or exemplary aspects. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0026]    The invention will be described in more detail hereinafter with reference to examples of embodiment but to which the invention is not limited. 
           [0027]      FIG. 1  schematically illustrates a leadframe structure. 
           [0028]      FIG. 2  schematically illustrates a detail of the leadframe structure shown in  FIG. 1 . 
           [0029]      FIG. 3  schematically illustrates growing of a delamination. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0030]    The illustration in the drawing is schematically. In different drawings, similar or identical elements are provided with the same reference signs. 
         [0031]    In the following, referring to  FIGS. 1 to 3 , a leadframe structure  100  and an electronic package is described. 
         [0032]      FIG. 1  schematically shows a top view of a leadframe structure  100  having attached two chips or dies  101  and  102  to it. The dies  101  and  102  are attached, e.g. glued, to die-pads  103  and  104 , respectively. The dies  101  and  102  comprise a plurality of terminals  105 , which are connected to a plurality of bonding areas  106  by respective bonding wires  107 . Some of the plurality of bonding areas are formed as fused leads, i.e. are connected to the die-pad and thus to ground. In particular, some of the fused leads  108 ,  109  and  110  are connected to external ground as well. Preferably, also corner leads are arranged in the corners of the leadframe structure that are used for mechanically supporting the leadframe itself. Some of the fused leads are formed as dummy fused leads  111 ,  112 , and  113 , i.e. fused leads which are not connected to external ground. These dummy fused leads  111 ,  112 , and  113  are connected to the die-pads by barrier areas  114 ,  115 , and  116 , respectively. Furthermore, a clamping area  117  is schematically indicated in  FIG. 1 , which supports the leadframe and the bonding areas during bonding of the bonding wires. 
         [0033]      FIG. 2A  schematically shows a top view of a detail of a leadframe structure  200 . A die  201  is attached to a die-pad  203  of the leadframe structure  200 . The die  201  comprises a plurality of terminals  205 , which are connected to a plurality of bonding areas  206  by respective bonding wires  207 . Some of the plurality of bonding areas are formed as fused leads, i.e. are connected to the die-pad and thus to ground. In particular, a dummy fused lead  211  is depicted in greater detail in  FIG. 2A . The bonding area  218  of the fused link  211  is contacted to the die-pad  203  by a barrier area  219  which is relative small and stout. 
         [0034]      FIG. 2B  schematically shows a top view of a detail of a leadframe structure  250 . A die  251  is attached to a die-pad  253  of the leadframe structure  250 . The die  251  comprises a plurality of terminals  255 , which are connected to a plurality of bonding areas  256  by respective bonding wires  257 . Some of the plurality of bonding areas are formed as fused leads, i.e. are connected to the die-pad and thus to ground. In particular, a dummy fused lead  261  is depicted in greater detail in  FIG. 2B . The bonding area  268  of the fused link  261  is contacted to the die-pad  253  by a barrier area  269 . Compared to the barrier area  218  shown in  FIG. 2A  the barrier area shown in  FIG. 2B  is longer and narrower, i.e. may be called an elongated barrier area. The longer a shape of the barrier area  269  may ease that the fused leads may be supportable by a clamping area  267  during the bonding of bonding wires. 
         [0035]      FIG. 3  schematically illustrates growing of a delamination. In particular,  FIG. 3  schematically shows a top view of a detail of a leadframe structure  300 . A die  301  is attached to a die-pad  303  of the leadframe structure  300 . The die  301  comprises a plurality of terminals  305 , which can be connected to a plurality of bonding areas  306  by bonding wires. In  FIG. 3A  one bonding area is formed as a fused lead  311 , i.e. is connected to the die-pad and thus to ground. The bonding area  318  of the fused link  311  is contacted to the die-pad  303  by a barrier area  319  which is, as shown in  FIG. 2B , long and narrow. Furthermore, a clamping area  317  is schematically indicated in  FIG. 3 , which supports the leadframe and the bonding areas during bonding of the bonding wires. In  FIG. 3A  a situation is shown in which the delamination process starts from the edge of the die  301 . The delamination is schematically indicated by the dots  320 . In  FIG. 3B  the situation of delamination growth is schematically depicted, i.e. the delamination process  320  is proceeded further up to the edge of the die-pad  303 . In particular, the long and narrow barrier area acts as an efficient barrier for the growth of the delamination. 
         [0036]    Finally, it should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be capable of designing many alternative embodiments without departing from the scope of the invention as defined by the appended claims. In the claims, any reference signs placed in parentheses shall not be construed as limiting the claims. The word “comprising” and “comprises”, and the like, does not exclude the presence of elements or steps other than those listed in any claim or the specification as a whole. The singular reference of an element does not exclude the plural reference of such elements and vice-versa. In a device claim enumerating several means, several of these means may be embodied by one and the same item of software or hardware. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.