Abstract:
A device comprising a circuit, a lead having a first end connected to the circuit and having a second end, and a deformable structure connected to the second end of the lead. The invention may be embodied on a circuit board, so that the circuit board includes a substrate and a deformable structure connected to said substrate. Also disclosed is a device comprising a circuit having an active side and a non-active side, a package enclosing the active side of the circuit and not enclosing a portion of the non-active side of the circuit, and a lead having a first end connected to the active side of the circuit via a lead-over-chip connection, and having a second end extending from the package. Also disclosed is a device comprising a circuit and a lead formed from a flexible conductor, with the lead having a first end connected to the circuit.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
         [0001]    Not Applicable.  
         STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT  
         [0002]    Not Applicable.  
         BACKGROUND OF THE INVENTION  
         [0003]    1. Field of the Invention  
           [0004]    The present invention is directed to a device that can be made smaller and with improved electrical characteristics than prior art devices and, more particularly, to a semiconductor device that can be made with a package that allows for greater device densities on circuit boards, shorter lead lengths, more tolerance to non-uniformities, and improved cooling.  
           [0005]    2. Description of the Background  
           [0006]    Electronic products typically contain a large number of electrical devices organized on one or more substrates, also known as circuit boards. The efficient packaging of those devices is an important factor in the product&#39;s performance. One way to improve performance is to increase the density of electrical devices on the substrate. For example, density may be increased by decreasing the size of the devices, thereby increasing the number of devices that can be placed on a given substrate.  
           [0007]    One way to increase device density is to use vertical packaging, which places devices perpendicular to the substrate. Vertical packaging allows for many more devices to be placed on a substrate because vertically oriented devices have smaller footprints than horizontally oriented devices. However, vertical packaging is subject to package instability (i.e. tipping over), particularly during processing steps involving poor adhesion between the device and the substrate, such as solder reflow. That instability is caused, in part, by non-uniformities in both the substrate and device. As a result, vertical packaging requires additional steps to create more uniform devices and substrates, and to stabilize the devices during some processing steps.  
           [0008]    Conventional devices and substrates also suffer from other problems caused by non-uniformities. For example, bending of device leads and poor contact between the device and substrate may result if the device and substrate are not uniform. Such problems require that device leads be lengthened to allow for greater flexibility to compensate for the non-uniformities. Longer leads, however, may result in the lead bending and possibly creating a short between conductors on the substrate. In addition, longer leads may cause detrimental electrical characteristics, such as increased resistance, increased capacitance, and decreased speed. Furthermore, longer leads tend to increase instability problems when there is poor adhesion between the device and the substrate.  
           [0009]    Thus, a need exists for an improved device to allow for increased device densities without the deficiencies of the prior art.  
         BRIEF SUMMARY OF THE INVENTION  
         [0010]    The present invention is direct to a device comprising a circuit, a lead having a first end connected to the circuit and having a second end, and a deformable structure connected to the second end of the lead. The invention may be embodied on a circuit board, so that the circuit board includes a substrate and a deformable structure connected to said substrate.  
           [0011]    The present invention is also directed to a device comprising a circuit having an active side and a non-active side, a package enclosing the active side of the circuit and not enclosing a portion of the non-active side of the circuit, and a lead having a first end connected to the active side of the circuit via a lead-over-chip connection, and having a second end extending from the package.  
           [0012]    The present invention is also directed to a device comprising a circuit and a lead formed from a flexible conductor, with the lead having a first end connected to the circuit.  
           [0013]    The present invention solves the shortcomings of the prior art by providing for higher device densities, shorter lead lengths, and more tolerance of non-uniformities, such as those in devices and substrates. Those and other advantages and benefits of the present invention will become apparent from the description of the invention provided hereinbelow. 
       
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING  
       [0014]    For the present invention to be clearly understood and readily practiced, the present invention will be described in conjunction with the following figures wherein:  
         [0015]    [0015]FIG. 1 is a perspective view of a circuit board including a substrate, a device, and a deformable structure between the circuit and conductive paths on the substrate;  
         [0016]    [0016]FIG. 2 is a cross sectional view along line II-II of the circuit board illustrated in FIG. 1;  
         [0017]    [0017]FIG. 3 is a perspective view of a circuit board including deformable structures in elongated form on the substrate;  
         [0018]    [0018]FIG. 4 is a cross-sectional view of a device including a deformable structure attached to leads of the device;  
         [0019]    [0019]FIG. 5 is a perspective view of a device including an integrated circuit partially enclosed in a package;  
         [0020]    [0020]FIG. 6 is a cross-sectional view along line VI-VI of the device illustrated in FIG. 5;  
         [0021]    [0021]FIG. 7 is a perspective view of a device including leads formed from tab-tape;  
         [0022]    [0022]FIG. 8 is a cross-sectional view along line VIII-VIII of the device illustrated in FIG. 7; and  
         [0023]    [0023]FIG. 9 is a cross-sectional view of a device including leads formed from multiple layered tab-tape. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0024]    It is to be understood that the description of the invention has been simplified to illustrate aspects that are relevant for a clear understanding of the present invention, while eliminating, for the purpose of clarity, other elements. Those of ordinary skill in the art will recognize that other elements may be desired and/or required.  
         [0025]    [0025]FIG. 1 is a perspective view of a circuit board  10  including a substrate  12 , such as a circuit board, having conductive paths  14  for transmitting signals, a device  16  having leads  18  for transmitting signals to and from the device  16 , and a deformable structure  20  connecting the substrate  12  to the device  16 .  
         [0026]    The device  16  may be an integrated circuit, a discrete component, or any other device that is connected to a substrate. In one embodiment of the present invention, the device  16  is a memory device. In that embodiment, the device may be dynamic memory or static memory. The leads  18  of the device  16  may be for surface mount connection to the substrate  12 .  
         [0027]    The deformable structures  20  connect the substrate  12  to the device  16 . In the present embodiment, the deformable structures  20  connect the conductive paths  14  of the substrate  12  to the leads  18  of the device  16 . The deformable structures  20  may be connected to the substrate  12  and the device  16  with conductive or non-conductive adhesives. Alternatively, the deformable structures  20  may themselves be adhesive so that additional adhesive is not required.  
         [0028]    The deformable structures  20  may be of a number of types and shapes. For example, the deformable structure may be of a structure for connecting a single lead  18  to a single conductive path  14 , as illustrated in FIG. 1. In that embodiment, the deformable structures  20  may be located at discrete locations on the substrate  12 , such as at places where leads  18  connect to conductive paths  14 . Alternatively, a single deformable structures  20  may connect several leads  18  to several conductive paths  14 , as described in more detail hereinbelow with respect to FIGS. 3 and 4. The deformable structures  20  may be placed at each location on the substrate  12  where the leads  18  connect to the conductive paths  14 . Alternatively, the deformable structures  20  may be selectively placed at locations where non-uniformities are likely to exist. Thus, there may be as few as one deformable structure  20 , or as many deformable structures  20  as there are leads  18 .  
         [0029]    The deformable structures  20  may be compressed between the leads  18  and the substrate  12 . That ability to be compressed compensates for non-uniformities that may exist, such as in the substrate  12 , the conductive paths  14 , the device  16 , and the leads  18 . That compensation reduces or eliminates bending of the leads  18  and poor contact between the leads  18  and the conductive paths  14  that would otherwise be caused by the non-uniformities. Furthermore, the deformable structures  20  eliminate the need to lengthen the leads  18 , thereby allowing for shorter leads  16 , shorter signal paths, and increased performance. Shortening the leads  18  also reduces or eliminates the risk of surface mount leads rubbing the bottom of the device  16  or rubbing the substrate  12 , thereby reducing the risk of short circuits.  
         [0030]    The deformable structures  20  may be any of several different materials. For example, the deformable structures  20  may be a polymer, such as silicone. The deformable structures  20  may also be resilient, such as when formed from elastomers, although the deformable structures  20  do not necessarily have to be resilient. The deformable structure  20  may be conductive or non-conductive, depending on the particular application.  
         [0031]    [0031]FIG. 2 is a cross sectional view along line II-II of the circuit board illustrated in FIG. 1. A conductor  24  may be disposed over the deformable structure  20  and in contact with both the leads  18  and the conductive paths  14 . The conductor  24  may be, for example, a conductive adhesive or a conductive tape used to secure the leads  18  to the deformable structures  20 . The conductor  24  may be applied on individual deformable structures to provide an electrical connection between one lead  18  and one conductive path  14 . Alternatively, the conductor  24  may be applied across several deformable structures  20  where an electrical connection is desired between several leads and/or several conductive paths  14   
         [0032]    The conductor  24  may be eliminated if connection between the leads  18  and the conductive paths  14  are not desired, such as if the leads  18  are only needed to support the device  16 . The conductor  24  may also be eliminated if the deformable structures  20  are conductive. In one embodiment, the deformable structures  20  are both conductive and adhesive, thereby eliminating the need for additional adhesives and conductors, but still providing electrical connection between the leads  18  and the conductive paths  14 .  
         [0033]    [0033]FIG. 3 is a perspective view of a circuit board  10  including deformable structures  20  in elongated form on the substrate  12 . The deformable structures  20  may extend over part or all of the substrate  12 . The deformable structures  20  may be non-conductive so that any one of the deformable structures  20  may contact several conductive paths  14  and several leads  18  but not cause a short circuit. In that embodiment, conductors  24  may be used to electrically connect individual leads  18  to individual conductive paths  14 , as discussed hereinabove.  
         [0034]    [0034]FIG. 4 is a cross-sectional view of a device  16  including deformable structures  20  attached to the leads  18 . In that embodiment, the deformable structures  20  may be attached to the leads  18  of the device  16  prior to connecting the device  16  to the substrate  12 . As described hereinabove, the deformable structures  20  may be adhesives, or adhesives may be used to attach the deformable structures  20  to the leads  18 .  
         [0035]    [0035]FIG. 5 is a perspective view of a device  16  including an integrated circuit  30  partially enclosed by a package  32 , and leads  18  extending from the package  32 . The device  16  may be, for example, an application specific integrated circuit or a memory device. The device  16  illustrated in FIG. 5, as well as the devices  16  described herein below with respect to FIGS.  6 - 9 , may be used with or without the deformable structures  20 . If the device  16  is used without the deformable structures  20 , it may be applied directly to flex tape or conductive traces on a substrate  12 .  
         [0036]    [0036]FIG. 6 is a cross-sectional view along line VI-VI of the device  16  illustrated in FIG. 5. The integrated circuit  30  has an active area  38  including electrically conductive connections to logic gates in the integrated circuit  30 . The integrated circuit  30  also includes a non-active area  40  which does not contain electrically conductive connections to logic gates forming the integrated circuit  30 .  
         [0037]    The package  32  encloses the active area  38  of the integrated circuit  30 , as is conventionally done, but does not enclose a portion of the non-active area  40 . The non-enclosed portion of the non-active area  40  is exposed to ambient environment. Exposing a portion of the non-active area  40  of the integrated circuit  30  facilitates cooling of the integrated circuit  30 . In addition, exposing a portion of the integrated circuit  30  allows for a smaller profile of the device  16 , because the package  32  is thinner, thereby allowing for increased density of devices  16  on a circuit board.  
         [0038]    The leads  18  may be connected to the active area  38  of the integrated circuit  30  with lead bonds  44  in a lead-over-chip manner. A lead-over-chip design offer an advantage of making connections near the center of the integrated circuit  30 , as opposed to near the edge of the integrated circuit  30 . As a result, the edge of the active area  38  of the integrated circuit  30  may be engaged by the package  32  to more securely hold the integrated circuit  30 . Alternatively, the leads  18  may also be connected to the integrated circuit  30  using a design other than lead-over-chip. Two such examples are tab bonding and peripheral bond pads that provide for sufficient space near the edge of the integrated circuit  30  to allow for engagement by the package  32 . Furthermore, the integrated circuit  30  may be engaged by the package  32  at only the sides, without engaging the active area  38   
         [0039]    [0039]FIG. 7 is a perspective view of a device  16  including leads  18  formed from a flexible conductor adhesive, such as tab-tape. A portion of the leads  18  may be attached to the package  32  with the adhesive. For example, the leads  18  may be attached to the outside of the package  32  from a point where the leads  18  exit the package to a point where the leads  18  are to be attached to another structure, such as a substrate. The leads  18  in that embodiment may be used with the deformable structures  20  described hereinabove, and may also be used with exposed integrated circuit  30  described hereinabove.  
         [0040]    [0040]FIG. 8 is a cross-sectional view along line VIII-VIII of the device  16  illustrated in FIG. 6. A spacer  50  may be used so that the leads  18  are away from the package  32 , thereby reducing the risk of the package  32  contacting the substrate  12 . The spacer  50  may be made of the same materials as the deformable structure  20  described hereinabove with respect to FIGS.  1 - 4 , so that the spacer  50  compensates for non-uniformities, such as on the substrate  12 . The spacer  50  may also be a dielectric so as to insulate signals on the leads  18 .  
         [0041]    [0041]FIG. 9 is a cross-sectional view of a device  16  having leads  18  formed from multiple layers of tab-tape. That embodiment allows for increased lead density. An additional spacer  52  may be placed between leads  18  to prevent a short between the leads  18 . The spacer  52  may be made of the same materials as the deformable structure  20  discussed hereinabove with respect to FIGS.  1 - 4 , so that the spacer  52  compensates for non-uniformities, such as on the substrate  12 . The spacer  52  may be a dielectric so as to insulate signals on the leads  18 .  
         [0042]    The nature of the present invention and its preferred embodiments as described herein allows the present invention to overcome many of the difficulties of increasing the density of packages on a substrate. The present invention can be used with or without a vertical packaging design, allowing for an increase in density through its method of adjustment to non-uniformities. In addition, when adjusting to non-uniformities on a substrate via the method explained herein, there is a significant decrease in the risk that the lead from an integrated circuit package will bend, break, or make poor contact with the substrate at the interconnect point. The present invention thereby ensures improved electrical performance of IC packages.  
         [0043]    The present invention as described herein may be used with or without L shaped leads. When the present invention is used with L shaped leads, the risk that the base of such leads will rub the bottom of the package, even when the exposed portion of the L is minimized, is greatly reduced. The present invention also provides for the use of new, varied lead types, such as tape leads. These tape leads may be used in an over/under configuration, enhancing the number of interconnect points available within the area covered by the IC package on the substrate. The use of non-standard lead configurations connected via an LOC method enables the exposure of one face of a die within the package, greatly enhancing thermal properties.  
         [0044]    The present invention has been described in connection with the preferred embodiments thereof. Those of ordinary skill in the art will recognize that many modifications and variations may be employed. For example, the embodiments illustrated in FIGS.  5 - 9  may be used either with or without the deformable structures  20  described with respect to FIGS.  1 - 4 . All such modifications and variations are intended to be covered by the foregoing description and the following claims.