Abstract:
A method and apparatus for assembling and packaging semiconductor die assemblies utilizes a coating element such as a wafer backside laminate formed on a backside of a semiconductor die. The coating element may be formed from a somewhat compressible and, optionally, resilient material, which seals against a surface of a mold cavity while the semiconductor die assembly is being encapsulated. In this manner, the coating element prevents encapsulant material from covering at least a portion of the backside of the semiconductor die to prevent encapsulant flashing over the backside and thus improve heat dissipation characteristics of the packaged semiconductor die during operation.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates generally to packaging of semiconductor dice and, more specifically, packaging of semiconductor dice to provide improved heat dissipation characteristics.  
           [0003]    2. State of the Art  
           [0004]    During operation, semiconductor devices typically generate large amounts of heat. The amount of heat that a semiconductor device generates is typically related, if not proportional to, the density of features of the semiconductor device. Heat reduces the reliability with which semiconductor devices, including processors and memory devices, operate. In addition, the exposure of semiconductor devices to elevated temperatures for prolonged periods of time may also decrease the useful lives thereof. Accordingly, the dissipation of heat from semiconductor devices has long been a concern in the semiconductor device industry.  
           [0005]    The reduced power requirements of state-of-the-art semiconductor dice have been useful for decreasing the amount of heat generated by such semiconductor dice. Nonetheless, as feature densities are ever-increasing, the temperatures generated by semiconductor dice with even reduced power requirements will also continue to increase. Thus, heat dissipation continues to be of concern, even with the low power requirements of state-of-the-art semiconductor dice.  
           [0006]    When a semiconductor die is encapsulated, or packaged, the most delicate regions thereof, such as the active surface that bears integrated circuitry and the bond wires that connect bond pads of the semiconductor die to corresponding leads of a lead frame or contacts of a carrier substrate, are covered with a dielectric protective material. In addition, other, more robust surfaces of the semiconductor die, such as the peripheral edges and backside thereof, are also covered with dielectric protective material. Unfortunately, many of the dielectric protective materials that are used to encapsulate semiconductor dice are not good heat conductors. As a result of the manner in which such dielectric protective materials have been used to coat semiconductor dice, a large amount of the heat generated by an encapsulated semiconductor die becomes trapped within or around the die.  
           [0007]    Several approaches have been taken to improve the rate at which heat is transferred and dissipated from packaged semiconductor devices. Conventionally, large surface area structures formed from materials that have good heat conductivity properties and, thus, which are able to “pull” or transfer heat away from a structure, such as a semiconductor die, contacted thereby have been used to dissipate heat from the package during operation of the semiconductor die or dice thereof. These large surface area structures are generally known in the art as “heat sinks.” Air circulation systems, which often include cooling fans, have also been used, typically in combination with heat sinks or other heat dissipation means. While heat sinks and air circulation systems may be useful for maintaining conventionally configured semiconductor dice at acceptable operational temperatures in some applications, heat sinks are typically fairly massive and the size thereof prevents further increases in the densities at which semiconductor devices are carried upon circuit boards, as is desired to maintain the trend for ever-decreasing electronic device sizes. In addition, heat sinks may also present locational problems between adjacent, superimposed circuit boards and for space-critical applications such as laptop and notebook computers, cell phones, personal digital assistants and the like.  
           [0008]    As an alternative to the use of space-consuming heat sinks, encapsulation processes have been modified to reduce the amount of dielectric protective material that covers the surfaces of semiconductor dice. Additionally, encapsulation techniques have been developed that protect the most delicate portions of a semiconductor die, while leaving other surfaces of the semiconductor die bare, thereby improving heat dissipation therefrom.  
           [0009]    One such technique is described in U.S. Pat. No. 5,604,376 to Hamburgen et al. (hereinafter “Hamburgen”), which describes a packaged semiconductor device in which a backside of a semiconductor die is exposed through an encapsulant to facilitate the dissipation and transfer of heat from the backside of the semiconductor die. The packaged semiconductor device of Hamburgen also includes leads to which bond pads of the semiconductor die are electrically connected. The assembly and packaging method described in Hamburgen includes temporarily securing a bare semiconductor die upon a pedestal by application of a vacuum through the pedestal to a backside of the semiconductor die. Leads are then electrically connected to corresponding bond pads of the semiconductor die by way of conventional wire bonding processes. Next, the assembly is positioned over a bottom half of a mold, with the backside of the semiconductor die resting upon a platform. Upon enclosing the semiconductor die and the bond wires within a cavity of the mold and as a molding compound is introduced into the cavity, a negative pressure is applied through an aperture in the platform to the backside of the semiconductor die, causing the backside of the semiconductor die to be pulled against the platform and purportedly preventing the molding compound from flowing onto the backside of the semiconductor die. This process may be somewhat undesirable for several reasons. For example, as the semiconductor die and the mold platform therefor are both rigid structures, any deviations in the planarity or mutual orientation of either the backside of the semiconductor die or the surface of the platform may permit molding compound to flow therebetween. Such planarity deviations, coupled with the force applied to the semiconductor die to temporarily secure the same to the mold platform, may also exert potentially damaging stresses on the semiconductor die during the encapsulation process.  
           [0010]    Another example of a packaged semiconductor device that includes a semiconductor die with an exposed backside is described in U.S. Pat. No. 6,348,729 to Li et al. (hereinafter “Li”). The packaged semiconductor device of Li is formed by attaching an adhesive-coated tape or film to a surface of a lead frame and securing a semiconductor die to the adhesive-coated tape or film, within a centrally located opening of the lead frame. Bond pads of the semiconductor die are then electrically connected with corresponding leads of the lead frame by forming or positioning intermediate conductive elements (e.g., bond wires) therebetween. Next, the semiconductor die, intermediate conductive elements, and regions of the leads that are located adjacent to the semiconductor die and above the tape or film are encapsulated. Finally, the tape or film is removed from the packaged semiconductor device structure (e.g., by peeling). Unfortunately, in addition to exposing the backside of the semiconductor die, surfaces of the leads are also somewhat undesirably exposed. Exposure of the bottom surfaces of the leads may increase the likelihood of electrical shorting between leads as the packaged semiconductor device is positioned upon a carrier substrate, such as a circuit board. Moreover, upon securing the packaged semiconductor device of Li to a carrier substrate, the backside of the semiconductor die thereof will be positioned adjacent or very closely to the carrier substrate, which may hinder the dissipation of heat from the backside of the semiconductor die, defeating the intent of exposing the backside.  
           [0011]    During the preliminary stages of semiconductor device fabrication processes, the backsides of silicon wafers and other bulk semiconductor substrates are typically adhered to a preformed dielectric protective film, such as a polyimide film. In addition to protecting the backsides of substrates during fabrication processes and as the substrates are being handled and transported from one fabrication process location to another, these dielectric protective films also retain the positions of the various semiconductor devices that have been fabricated on a particular semiconductor substrate following singulation of the semiconductor devices, which are, at this point, commonly referred to as “dice,” from one another. The dice may then be tested or otherwise evaluated, and operable, useful dice picked from the dielectric protective film for further testing, assembly, or packaging.  
           [0012]    The inventors are not aware of structures that facilitate heat dissipation from a backside of a semiconductor die through a molded encapsulant while reducing compressional stresses on the semiconductor die during encapsulation thereof and without undesirably increasing the size of the packaged semiconductor device or causing electrically conductive structures from being undesirably exposed through the encapsulant.  
         BRIEF SUMMARY OF THE INVENTION  
         [0013]    The present invention includes methods and apparatus for packaging semiconductor device assemblies in such a way as to facilitate the transfer of heat from the backsides of semiconductor dice thereof.  
           [0014]    One aspect of the present invention includes a coating element for use on a backside of a semiconductor die. The coating element is configured to seal against a surface of a mold cavity during packaging of a semiconductor device assembly of which the semiconductor die is a part to prevent packaging material from covering or “flashing” over the backside of the semiconductor die. The coating element may also protect the backside of the semiconductor die during encapsulation of at least portions of the semiconductor device assembly. Accordingly, the material of the coating element may be a somewhat compressible or compliant, and resilient, material which is configured to act as a sealant against an inside surface of a mold while packaging the semiconductor device assembly. The materials of the coating element may also be compressible and compliant, but not necessarily resilient so that it remains in a substantially compressed state after the encapsulation process. The material of the coating element may also be somewhat durable so that the coating element may protect the die during the assembly and encapsulation processes.  
           [0015]    The backside of a semiconductor die may receive a coating element prior to severing the semiconductor die from a common substrate upon which a plurality of semiconductor dice or other electronic components has been fabricated (e.g., at the wafer level), subsequent to singulating the semiconductor die from a wafer or other common substrate, or following assembly of the semiconductor die with a carrier therefor. The coating element may comprise a preformed, substantially planar element or a quantity of uncured material that will be cured and, optionally, patterned following application thereof to the backside of the semiconductor die. The coating element may be applied so as to cover substantially the entire backside of the semiconductor die or, in a variation, to cover only a portion of the backside of the semiconductor die at or proximate a lateral periphery thereof. In the case of applying coating elements onto semiconductor devices that have not yet been severed or singulated from a common substrate, the coating element may comprise a single member that substantially covers the backside of the common substrate and which is severed as the semiconductor devices that have been fabricated on the common substrate are singulated from one another, or separate coating elements may be formed on or secured to the backsides of each yet-to-be severed semiconductor device.  
           [0016]    A semiconductor device assembly according to the present invention includes one or more semiconductor dice and a carrier. The carrier and at least one semiconductor die are oriented in a substantially parallel manner relative to one another with the backside of the at least one semiconductor die in the assembly facing outward in such a way as to contact a surface of a mold cavity during encapsulation of the assembly. The carrier and each semiconductor die assembled therewith are electrically connected to one another by way of intermediate conductive elements, such as bond wires, thermocompression bonded leads, conductive tape-automated bonding (TAB) elements carried by a dielectric polymeric film, or the like, for electrical interconnection of the carrier to each semiconductor die thereon.  
           [0017]    In use of a coating element according to the present invention, a semiconductor device assembly including a semiconductor die with a coating element on a backside thereof may be positioned within a cavity of a mold. This may be done by placing a portion of the assembly in either a first cavity segment of a first mold section or a second cavity segment of a second mold section. In other words, the semiconductor device assembly may be positioned with the coating element adjacent a mold cavity surface of either mold section. As the first and second mold sections are assembled with one another, the semiconductor device assembly is enclosed within the cavity formed by the first and second cavity segments, with at least a portion of the carrier sitting between the first and second mold sections. With this arrangement, the coating element on the backside of a semiconductor die of the assembly may be positioned and sealed against the inside surface of a cavity half of one of the mold sections. Molten dielectric encapsulation material may then be introduced into the mold under pressure so that particular sensitive portions of the assembly, such as a lateral periphery and active surface of the semiconductor die and the intermediate conductive elements electrically interconnecting the die to the carrier, are encapsulated. The seal created against the surface of the mold cavity by the coating element on the backside of the semiconductor die prevents dielectric encapsulation material from flowing over or flashing onto and, thus, covering a substantial portion of the backside of the semiconductor die. By preventing the dielectric encapsulation material from covering the backside of the semiconductor die, heat may readily dissipate from the backside thereof. Further, the coating element provides a compressible surface on the backside of the semiconductor die to reduce potential stresses to the semiconductor die, such as stresses applied to the semiconductor die from the mold wall abutting the backside, during the encapsulation process.  
           [0018]    The inside surface or wall of a portion of a mold cavity segment may include a surface finish of enhanced smoothness relative to the finish of the remainder of the mold cavity surfaces. Such a finish may be effected by grinding, lapping or polishing and be at least sized, shaped and positioned on a portion of the inside surface of the mold cavity segment to correspond with the dimensions of the backside of the semiconductor die. During encapsulation of the assembly, the enhanced smoothness surface finish provides a surface that readily creates a seal with the coating element on the backside of the semiconductor die so that the encapsulation material cannot extrude between the backside of the die and the inside surface to form flash on the backside during the encapsulation of portions of the assembly.  
           [0019]    Following encapsulation, the packaged semiconductor device assembly may be mounted to higher-level packaging such as a circuit board for use in an electronic system, such as a computer system. In the electronic system, the circuit board electrically communicates with a processor, which electrically communicates with one or more input devices and output devices of the electronic system.  
           [0020]    Other features and advantages of the present invention will become apparent to those of skill in the art through a consideration of the ensuing description, the accompanying drawings and the appended claims.  
       
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS  
       [0021]    While the specification concludes with claims particularly pointing out and distinctly claiming that which is regarded as the present invention, the advantages of this invention may be ascertained from the following description of the invention when read in conjunction with the accompanying drawings, wherein:  
         [0022]    [0022]FIG. 1 illustrates a simplified side view of a wafer having a coating element disposed thereon, according to the present invention;  
         [0023]    [0023]FIG. 2 illustrates a simplified bottom view of a board-on-chip semiconductor assembly, depicting the coating element disposed over substantially an entire back surface of the semiconductor die, according to a first embodiment of the present invention;  
         [0024]    [0024]FIG. 2( a ) illustrates a simplified bottom view of a board-on-chip semiconductor assembly, depicting the coating element disposed proximate a periphery of the back surface of the semiconductor die, according to a variation of the first embodiment of the present invention;  
         [0025]    [0025]FIG. 3 illustrates a simplified cross-sectional side view taken along line  3 - 3  in FIG. 2, depicting the board-on-chip semiconductor assembly with bond wires extending between the semiconductor die and the carrier substrate, according to the first embodiment of the present invention;  
         [0026]    [0026]FIG. 3( a ) illustrates a simplified cross-sectional side view taken along line  3   a - 3   a  in FIG. 2( a ), depicting the board-on-chip semiconductor assembly with the coating element disposed proximate the periphery of the back surface of the semiconductor die, according to a variation of the first embodiment of the present invention;  
         [0027]    [0027]FIG. 4 illustrates a simplified cross-sectional side view of the board-on-chip semiconductor assembly in a mold, depicting a surface of the mold abutting a surface of the coating element, according to the first embodiment of the present invention;  
         [0028]    [0028]FIG. 4( a ) illustrates a simplified partial cross-sectional view of the mold in an unengaged position with the coating element on the semiconductor die, according to the present invention;  
         [0029]    [0029]FIG. 4( b ) illustrates a simplified partial cross-sectional view of the mold in an engaged position with the coating element on the semiconductor die, according to the present invention;  
         [0030]    [0030]FIG. 5 illustrates a simplified view of the inside surface of the mold, depicting a matte finish and a finely ground finish on the inside surface, according to the present invention;  
         [0031]    [0031]FIG. 6 illustrates a simplified cross-sectional view of a board-on-chip wire bonded semiconductor package, depicting the coating element exposed through the encapsulation material, according to a first embodiment of the present invention;  
         [0032]    [0032]FIG. 7 illustrates a simplified cross-sectional view of a board-on-chip flip-chip semiconductor package, depicting the coating element exposed through the encapsulation material, according to a second embodiment of the present invention;  
         [0033]    [0033]FIG. 8 illustrates a simplified cross-sectional view of a lead-on-chip semiconductor package, depicting the coating element exposed through the encapsulation material, according to a third embodiment of the present invention; and  
         [0034]    [0034]FIG. 9 illustrates a simplified block diagram of the semiconductor assembly of the present invention integrated in an electronic system. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0035]    Embodiments of the present invention will be hereinafter described with reference to the accompanying drawings. It would be understood that these illustrations are not to be taken as actual views of any specific apparatus or method of the present invention, but are merely exemplary, idealized representations employed to more clearly and fully depict the present invention than might otherwise be possible. Additionally, elements and features common between the drawing figures retain the same or similar reference numerals.  
         [0036]    [0036]FIG. 1 illustrates a side view of a wafer  100 . Wafer  100  includes multiple semiconductor dice  110  in a physically interconnected array of columns and rows (not shown), each semiconductor die  110  distinguished from others on wafer  100  by broken lines  118 , along which the semiconductor dice are separated or singulated, as by sawing or scribing. Wafer  100 , and each of the multiple semiconductor dice  110  thereof, includes an active surface  112  and a backside  114 . The wafer  100  is formed from a semiconducting material and is preferably formed from silicon, but may be formed from gallium arsenide, indium phosphide or any other known semiconducting material, the electrical conductivity and resistivity of which lie between those of a conductor and an insulator. Other bulk substrates, including partial wafers, as well as silicon-on-insulator (SOI) substrates (e.g., silicon-on-glass (SOG), silicon-on-ceramic (SOC), silicon-on-sapphire (SOS), etc.) are also within the scope of the present invention and included within the meaning of the term “wafer.” 
         [0037]    According to the present invention, wafer  100  may receive a coating element  150  formed on the backside  114  thereof. Coating element  150  is configured to be compressible or compliant so as to act as a sealant, which will be further described herein. Coating element  150  may be a coating element applied to the semiconductor dice  110  to reduce stresses thereto and/or prevent chipping of the backside  114  thereof during procedures of testing, general handling, singulation and encapsulation procedures. Coating element  150  may be configured to readily conduct and dissipate heat, wherein coating element  150  provides a surface that easily allows heat to dissipate from the semiconductor dice  110 . The coating element  150  may have a coefficient of thermal expansion (CTE) similar to that of the adjacent semiconductor or insulator (in the case of nonwafer bulk substrates) material.  
         [0038]    Coating element  150  may be applied to the backside  114  of each of the semiconductor dice  110  by flowing a polyimide material thereon (e.g., by known spin-on, screen printing, spray-on, or spreading processes). Such a technique may be especially desirable to employ at the wafer scale. If required, filler material, such as polysilicon, may be added to the polyimide material to adjust the coefficient of thermal expansion to substantially match the coefficient of thermal expansion of the backside  114  of the semiconductor die  110 . A photosensitive material such as is employed for etch masking may also be applied, exposed, and developed and undesired portions of the coating element  150  removed from the backsides  114  of semiconductor dice  110 , individually but preferably at the wafer scale. In the alternative, the coating element  150  may be already prepared as a preformed polyimide sheet or film, wherein the polyimide sheet or film may be adhesively attached to the backside  114  of the semiconductor die  110  using, for example, a pressure-sensitive adhesive. Such a structure may be termed a “wafer backside laminate.” As a further variation, a resin may be applied to a sheet, tape or film to form a composite coating element providing sufficient adherency to the wafer  100  or a semiconductor die  110  along with sufficient resiliency and compressibility. The resin may provide adhesion for the sheet, tape or film to the backsides  114  of semiconductor dice  110 .  
         [0039]    In whatever form, coating element  150  may be of sufficient thickness such that, in combination with a selected compressibility, it accommodates when compressed at least an average bondline deviation (the deviation between the semiconductor die surface and carrier substrate, such as an interposer, surface during die mount) of between about 20 and 30 μm to prevent flash over the backside  114  during encapsulation. Thus, for example and without limitation, an initial, resiliently compressible coating element thickness of between about 50 and 100 μm may be used to allow for and accommodate bondline deviation while still minimizing the height of the finished package and any thermal barrier to heat transfer from the backside  114  of semiconductor die  110 .  
         [0040]    The wafer  100  may be singulated along broken lines  118  to provide multiple semiconductor dice  110 . The coating element  150  may be disposed on the backside  114  of each of the semiconductor dice  110  prior to, or subsequent to, singulation thereof from the wafer  100 . In either case, each of the individual semiconductor dice  110  receives the coating element  150  prior to a die attach process wherein a semiconductor die  110  is secured to a carrier substrate such as an interposer or lead frame.  
         [0041]    [0041]FIG. 2 illustrates a bottom view of a board-on-chip (BOC) assembly subsequent to the die attach process. The singulated semiconductor die  110  having the coating element  150  formed on a backside  114  thereof may be attached to a carrier substrate  120 . Specifically, as shown, the semiconductor die  110  is attached with its active surface toward the carrier substrate  120  so that the coating element  150  is facing outward.  
         [0042]    [0042]FIG. 3 is a cross-sectional view taken along line- 3 - 3  in FIG. 2, illustrating the carrier substrate  120  and semiconductor die  110  and the interconnections therebetween. The carrier substrate  110  includes a first surface  122  and a second surface  124  with an opening  126  that may be centrally located in the carrier substrate  120  and extends between the first surface  122  and the second surface  124  on the carrier substrate  120 . Carrier substrate  120  may be any suitable carrier-type substrate known in the art, such as an interposer or printed circuit board. Carrier substrate  120  may also be made of any type of substrate material known in the art, such as bismaleimide triazine (BT) resin, ceramics, flexible polyimides, FR-4 or FR-5 materials, glass, insulator-coated silicon, or the like.  
         [0043]    The semiconductor die  110  includes an active surface  112  and a backside  114  with bond pads  116  formed on the active surface  112  thereof. The bond pads  116  may be centrally located and exposed on the active surface  112  of the semiconductor die  110  and interconnected with integrated circuitry (not shown) on the active surface  112  of the semiconductor die  110 . With this arrangement, the carrier substrate  120  may be secured to a peripheral region of the active surface  112  of the semiconductor die  110  so that the bond pads  116  may be exposed through the opening  126  of the carrier substrate  120 . The semiconductor die  110  may be attached to the carrier substrate  120  with one or more adhesive elements  130 . The adhesive element  130  may be any known adhesive structure, such as an adhesive decal, adhesive-coated tape, a liquid or gel adhesive material, or the like. Bond wires  132  or other intermediate conductive elements (e.g., conductive tape-automated bonding (TAB) conductive elements carried upon a dielectric polymer film, thermocompression-bonded leads, etc.) may then be formed or extended between the bond pads  116  on the active surface  112  of the semiconductor die  110  and their corresponding conductive pads  128  on the second surface  124  of the carrier substrate  120 , with bond wires  132  or other intermediate conductive elements extending through the opening  126 .  
         [0044]    As illustrated in FIGS. 2 and 3, the coating element  150  may substantially cover the entire backside  114  of the semiconductor die  110  and face outward from the assembled semiconductor die  110  and carrier substrate  120 .  
         [0045]    [0045]FIG. 2( a ) illustrates a variation of the coating element  150 . In this variation, coating element  150 ′ is disposed on the backside  114  and forms a frame proximate only a periphery  115  of the semiconductor die  110 . This variation provides that a central portion of the backside  114  of the semiconductor die  110  is left without the coating element  150 ′. In this alternative, it is contemplated that the coating element  150 ′ may be applied to the backside  114  utilizing a masking and patterning type process, as is well known in the art, using a positive or negative photoresist. Coating element  150 ′ may also be applied by use of a stencil, as is also known. The coating element  150 ′ may be applied to the backside  114  at a wafer level or to each semiconductor die  110  on an individual basis.  
         [0046]    Illustrated in FIG. 3( a ) is a cross-sectional bottom view taken along line  3   a - 3   a  in FIG. 2( a ), depicting the carrier substrate  120  and semiconductor die  110  with the coating element  150 ′ on the backside  114  of the semiconductor die  110  according to a variation of the first embodiment. In particular, the coating element  150 ′ is provided on the backside  114  proximate periphery  115  of the semiconductor die  110  so that a central portion of the backside  114  is left without the coating element  150 ′.  
         [0047]    Turning to FIG. 4, the board-on-chip assembly is positioned in a mold  140  preparatory to encapsulating the assembly in a transfer molding process. The term “transfer molding” is descriptive of an example of this process, as a filled polymer thermoplastic molding compound, in a liquid or molten state, is transferred under pressure to a plurality of remotely located mold cavities containing semiconductor device assemblies to be encapsulated. However, for purposes of simplicity, only one mold cavity  146  associated with the mold  140  is depicted in drawing FIG. 4. Pot molding processes, injection molding processes and other encapsulation techniques may also be used with, and benefit from, the present invention.  
         [0048]    The mold  140  includes a first mold section  142  and a second mold section  144 , each of which includes recesses that together form multiple mold cavities, such as the depicted mold cavity  146 . The mold cavity  146  is sized and configured to contain the semiconductor die  110  in the assembly and, specifically, an inside surface  148  of the mold  140  is configured with at least a portion located and oriented to abut with the coating element  150  on the backside  114  of the semiconductor die  110 . The mold cavity  146  is also sized and configured to contain, without contacting, the bond wires  132  or other intermediate conductive elements that electrically interconnect the semiconductor die  110  to the carrier substrate  120 . In this manner, the mold cavity  146  is filled with a dielectric encapsulation material  134  (FIG. 6), such as a molding compound introduced by transfer or injection molding, to coat, cover and protect at least a periphery of the semiconductor die  110 , the bond wires  132 , bond pads  116  and conductive pads  128 .  
         [0049]    Each mold cavity  146  in a transfer mold includes a gate and vent (not shown), as known in the art. The gate is used as an inlet for a thermoplastic dielectric encapsulation material  134  to flow into the mold cavity  146 . The vent, typically located at an opposite end of the mold cavity  146  from the gate, permits air or other gases in the mold cavity  146  to be displaced by the wave front of the dielectric encapsulation material and escape from the mold cavity  146  upon introduction of the dielectric encapsulation material  134  thereinto. After entry into the mold cavity  146 , the dielectric encapsulation material  134  solidifies and forms a part of the semiconductor device assembly.  
         [0050]    FIGS.  4 ( a ) and  4 ( b ) illustrate the semiconductor die  110  and an inside surface  148  of the mold  140  in an unengaged position and a fully engaged position, respectively. According to the present invention, the inside surface  148  of the mold  140  may include some regions with a relatively smoother, ground, lapped or polished finish  154  and other regions with a rougher, matte finish  156 . The area of the enhanced smoothness finish  154  is substantially sized and shaped to correspond with the backside  114  of the semiconductor die  110  and may be square shaped and centrally located within the matte finish  156  area, as depicted in FIG. 5, illustrating a top inside view of the central, bottom portion B and side portions S of the mold cavity segment of the first mold section  142 . The matte finish  156  area may comprise the raw, as cast or machined, inside surface  148  of the mold  140  without further grinding or polishing thereof. With respect to the enhanced smoothness finish  154  area, it exhibits a fine finish, such as a ground, lapped or polished finish, having a surface topography configured to facilitate a seal  158  between the coating element  150  and the inside surface  148  of the mold  140 . The seal  158  is provided by coating element  150  when the semiconductor die  110  is in the fully engaged position with the first mold section  142 , such as when the first and second mold sections  142  and  144  are assembled with one another. In this manner, seal  158  provided by the coating element  150  resiliently compressed between the semiconductor die  110  and the first mold section  142  in the fully engaged position is configured to prevent the encapsulation material  134  from flowing over, and flashing onto, the backside  114  of the semiconductor die  110 .  
         [0051]    It will be appreciated that, once the semiconductor die  110  has been removed from the mold cavity  146 , coating element  150  may remain in a substantially compressed state and thus have an outer surface substantially coplanar with that of the hardened dielectric encapsulation material  134  surrounding the coating element  150 . Alternatively, the coating element  150  may have sufficient resiliency so as to spring back to an uncompressed thickness or to regain at least a portion thereof, in which instance the outer surface of the coating element  150  may project slightly above the outer surface of the surrounding, hardened dielectric encapsulation material  134 .  
         [0052]    Turning to FIG. 6, a board-on-chip semiconductor package  160  having portions of the semiconductor die  110  and carrier substrate  120  and the electrical interconnections therebetween encapsulated by dielectric encapsulation material  134  is illustrated. A significant aspect of the present invention is exposure in the finished semiconductor device package of the relatively thin coating element  150  through the encapsulation material  134  on the backside  114  of the semiconductor die  110 . With this arrangement, heat may readily transfer through the substrate of semiconductor die  110  from the active surface  112  and dissipate from the backside  114  of the semiconductor die  110 . It is notable that coating element  150 , due to its relative thinness, is not a significant impediment to heat transfer from the semiconductor die  110  and thus need not be removed from backside  114  and remains as part of semiconductor package  160 . If desired, coating element  150  may be colored and may include graphics thereon to identify the manufacturer, part number, etc. Alternatively, coating element  150  may be formulated to be sensitive to heat or to specific wavelengths of electromagnetic radiation to facilitate marking, as by a laser, of the semiconductor package after fabrication as well as after various stages of testing. As shown at  170 , a plurality of discrete conductive elements in the form of solder bumps, conductive or conductor-filled epoxy pillars or columns or other suitable structures may be applied to or formed on carrier substrate  120  in communication with conductive traces (not shown) of carrier substrate  120  extending to conductive pads  128  to provide external electrical connections from semiconductor die  110  to higher-level packaging.  
         [0053]    [0053]FIG. 7 illustrates a second embodiment of a semiconductor package  260 . The semiconductor package  260  includes a flip-chip type assembly, wherein a semiconductor die  210  is attached facedown to a carrier substrate  220  with discrete conductive elements such as conductive bumps  232  therebetween. The semiconductor die  210  includes an active surface  212  and a backside  214 , wherein the backside  214  includes coating element  250  disposed thereon. The carrier substrate  220  includes a first surface  222  and a second surface  224 . The conductive bumps  232  electrically and mechanically interconnect the semiconductor die  210  to the carrier substrate  220  by being disposed between and bonded to bond pads  216  on the active surface  212  of the semiconductor die  210  and conductive pads  226  on the first surface  222  of the carrier substrate  220 . A dielectric encapsulation material  234  is introduced in a gap between the semiconductor die  210  and carrier substrate  220 , as well as around a periphery  211  of the semiconductor die  210 . Similar in fashion to the first embodiment, the backside  214  of the semiconductor die  210  having coating element  250  thereon is exposed through the encapsulation material  234 , thereby providing an outlet for heat to dissipate from the semiconductor die  210 . Further, the exposed coating element  250  seals to an inside surface of a mold (not shown) during the encapsulation process, in a manner similar to that described in the first embodiment.  
         [0054]    With respect to FIG. 8, a third embodiment of a semiconductor package  360  is illustrated. Semiconductor package  360  includes a leads-over-chip (LOC) type assembly, wherein there is a carrier  320 , or leads, attached to an active surface  312  of a semiconductor die  310  via adhesive tape  330  or the like. The carrier  320  includes a first surface  322  and a second surface  324  and is electrically interconnected to the semiconductor die  310  by bond wires  332  or other intermediate conductive elements extending from bond pads  316  on the active surface  312  of the semiconductor die  310  to conductive pads  338  on second surface  324  of the carrier  320 . The backside  314  of the semiconductor die  310  includes coating element  350  disposed thereon. With this arrangement, the leads-over-chip assembly may be encapsulated in a mold (not shown) with encapsulation material  334  to encapsulate portions of the semiconductor die  310 , the carrier  320  and the bond wires  332  and interconnections thereof. As in the previous embodiments, the coating element  350  is exposed through the encapsulation material  334 . Such an exposed coating element  350  may provide an outlet for heat to dissipate from the semiconductor die  310 . Other types of lead frame-type assemblies may be utilized in the present invention as long as the coating element  350  on the backside  314  of the semiconductor die  310  is exposed through the encapsulation material  334  to provide a heat dissipation outlet for the semiconductor package  360 .  
         [0055]    As illustrated in block diagram form in drawing FIG. 9, semiconductor packages  160 ,  260  and/or  360  may be mounted to a circuit board  410  in an electronic system  400 , such as a computer system. In the electronic system  400 , the circuit board  410  may be connected to a processor device  420  which communicates with an input device  430  and an output device  440 . The input device  430  may comprise a keyboard, mouse, joystick or any other type of electronic input device. The output device  440  may comprise a monitor, printer or storage device, such as a disk drive, or any other type of output device. The processor device  420  may be, but is not limited to, a microprocessor or a circuit card including hardware for processing instructions for the electronic system  400 . Additional structure for the electronic system  400  is readily apparent to those of ordinary skill in the art.  
         [0056]    While the present invention has been disclosed with reference to certain illustrated embodiments, those of ordinary skill in the art will recognize and appreciate that it is not so limited. Rather, additions, deletions and modifications to the illustrated embodiments may be made, and features and elements from one embodiment employed, as appropriate, in another. In addition, the coating element of the present invention may be applied between the die and a carrier substrate such as an interposer to accommodate bondline deviation and provide the necessary resiliency while leaving the backside of the die bare. Further, the coating element may be placed on the side of the carrier substrate opposite the semiconductor die for bondline deviation accommodation and to provide compressibility. The present invention and the scope thereof is defined by the following claims and equivalents of the elements, features and acts recited therein.