Patent Document

CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a divisional of application Ser. No. 10/788,990, filed Feb. 27, 2004, now U.S. Pat. No. 7,057,297, issued Jun. 6, 2006. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to flexible substrates and, more specifically, to tape-based substrates that include copper layers. In particular, the present invention relates to tape-based substrates with mold gates that are configured so as to require only a single copper layer. 
     2. Background of Related Art 
     Numerous semiconductor packaging methodologies have found widespread use. Among those that have been commonly used is the so-called “board-on-chip” arrangement of a substrate relative to a semiconductor die. As its name implies, a substrate, or “board,” which provides a connection pattern of input and output elements (e.g., contacts, leads, or other electrodes) is positioned on a semiconductor die. Typically, the substrate is positioned on the bond pad (i.e., input/output electrode) bearing surface, or “active” surface, of the semiconductor die. 
     In order to provide the desired connection pattern, a substrate typically includes a planar dielectric member, electrical contacts on the die-facing side of the substrate, conductive traces that extend laterally along the dielectric planar member, and redistributed contact pads, or “terminals,” that are exposed at the opposite surface of the substrate. A substrate may also include conductive vias that extend through at least a portion of the thickness of the substrate to connect contacts to corresponding conductive traces. 
     In addition, to facilitate the formation of a molded protective structure, or “package,” around the substrate-semiconductor die assembly, the substrate may also include a mold gate. A mold gate is a feature on the substrate which is configured to communicate with a mold runner through which liquid packaging material is introduced into a mold cavity and to direct the liquid packaging material to desired locations in a desired fashion. 
     Conventionally, when the substrate of a semiconductor device assembly is a so-called “two-layer flex” or “adhesiveless flex” tape-based substrate, or, more simply, a “tape substrate”  1 , it will include a flexible dielectric film  2  (e.g., polyimide) and a layer of conductive traces  6 , which are typically etched from a conductive (e.g., copper) film that was laminated to the polymeric film, that are carried upon a surface of the flexible dielectric film  2 , as shown in  FIG. 1A . At least one side, or surface  3 , of tape substrate  1  carries conductive traces  6 . Packaging, or encapsulating, material is typically introduced over surfaces of the tape substrate  1  and a semiconductor die thereon from the opposite side, or surface  4 , of the tape substrate  1 . As a result, the mold gate  5  is positioned on the opposite side, or surface  4 , of the tape substrate  1  from that which carries the conductive traces  6 . 
     Alternatively, as shown in  FIG. 1B , when the substrate of a semiconductor device assembly is a so-called “three-layer flex” or “adhesive flex” tape substrate  1 ′, it will include a flexible dielectric film  2 , adhesive material  7  on at least one surface  3  of tape substrate  1 ′, and conductive traces  6  that are secured to surface  3  by way of adhesive material  7 . 
     As the dielectric film  2  is flexible, the mold gates  5  of tape substrates  1 ,  1 ′ are typically formed by laminating an additional material layer to the surface  4  of the tape substrate  1 ,  1 ′ which is opposite from the conductive trace-bearing surface  3  of the tape substrate  1 ,  1 ′. This additional material layer may be used to form the mold gate  5  itself, or to support a mold gate  5  which has been formed in the flexible dielectric film  2 . Of course, the requirement that two material layers be laminated onto a flexible dielectric film  2  and, thus, separately patterned, undesirably increases the cost of fabricating the tape substrate  1 ,  1 ′. Moreover, the use of an additional material layer to form a mold gate  5  may undesirably increase the thickness of the tape substrate  1 ,  1 ′, which is counter to the trend toward semiconductor device packages of ever-decreasing dimensions. 
     Further, conventional tape-automated bonding (TAB) substrates, which include flexible dielectric films by which conductive traces and contacts, or terminals, are carried, are typically formed by mechanically punching the flexible dielectric film, laminating or adhesively securing a conductive film to a single surface of the flexible dielectric film, then patterning the conductive film to form conductive traces, contacts, and other conductive features. Because conventional tape substrates require that two conductive films be positioned on opposite surfaces of the flexible dielectric films thereof, many TAB substrate manufacturers are unable or unwilling to fabricate tape substrates. 
     Accordingly, there is a need for a mold gate configuration and mold gate fabrication methods which do not contribute to the thickness of a tape substrate of which the mold gate is a part or to the cost of fabricating the tape substrate. 
     SUMMARY OF THE INVENTION 
     The present invention, in an exemplary embodiment, includes a tape substrate with a flexible dielectric layer and a single conductive layer. A mold gate, which communicates with a surface of the flexible dielectric layer located opposite from that by which the single conductive layer is carried, is formed in the flexible dielectric layer. A support element of the mold gate, which has been formed from the single conductive layer, reinforces the mold gate. 
     In another embodiment, the present invention includes a mold gate for a tape substrate. The mold gate includes an aperture formed within a flexible dielectric film of the tape substrate. The mold gate also includes a support element that overlies at least a portion of the aperture and is formed from a single layer of conductive material, from which conductive traces of the tape substrate are also formed. Mold gates that incorporate teachings of the present invention may be used in conventional semiconductor device mold encapsulation processes. 
     The present invention also includes, in another embodiment, methods for forming the mold gate in a tape substrate. Such a method includes patterning a flexible dielectric film to include an aperture that communicates with an outer boundary of a tape substrate of which the flexible dielectric film is or is to be a part. A conductive film that is formed on or laminated to the polyimide film is patterned to form conductive structures, such as conductive traces, as well as to form the remaining support element of the mold gate. 
     In addition, in a further embodiment, methods for fabricating tape substrates are within the scope of the present invention. Such methods include, without being limited to the exemplary order given herein, providing a flexible dielectric film, forming desired features, including a mold gate, in the flexible dielectric layer, laminating a conductive film to a desired surface of the flexible dielectric film, and patterning the conductive film to form a support element of the mold gate, as well as conductive traces. 
     Systems and methods for assembling and encapsulating semiconductor device assemblies which include the tape substrates of the present invention are also within the scope of the invention. 
     Other features and advantages of the present invention will become apparent to those of ordinary skill in the art through consideration of the ensuing description, the accompanying drawings, and the appended claims. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       In the drawings, which depict various features of exemplary embodiments of the present invention: 
         FIGS. 1A and 1B  are perspective views of conventional tape substrates; 
         FIG. 2  is a perspective view of a tape substrate which includes a mold gate according to the present invention; 
         FIG. 3  is a side view of the tape substrate, including the mold gate thereof, shown in  FIG. 2 ; 
         FIGS. 4–7  are top views of exemplary configurations of mold gates according to the present invention; 
         FIGS. 8–13  are cross-sectional representations of a flexible dielectric film with a conductive layer laminated to a surface thereof depicting exemplary processing thereof to fabricate a tape substrate according to the present invention; 
         FIG. 14  is a schematic representation of a flexible dielectric film on which a plurality of tape substrates have been fabricated; 
         FIG. 15  is a side view of an exemplary mold gate that has been formed by the process shown in  FIGS. 8–14 ; 
         FIGS. 16–19  are cross-sectional representations of a flexible dielectric film which illustrate another example of processing that may be employed to fabricate a tape substrate of the present invention; 
         FIG. 20  is a side view of a mold gate that has been formed by the process shown in  FIGS. 16–19  and  11 – 14 ; 
         FIG. 21  depicts a strip including a plurality of tape substrates to which semiconductor dice have been secured and electrically connected; 
         FIGS. 22 and 22A  show the strip of  FIG. 21  with package structures formed over each tape substrate-semiconductor die assembly; and 
         FIGS. 23 and 24  schematically depict a process for degating a packaged semiconductor device that includes a tape substrate according to the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A tape substrate  10  that incorporates teachings of the present invention is shown in  FIGS. 2 and 3 . Tape substrate  10  includes a flexible dielectric film  20 , conductive traces  34  that are carried by a surface  22  of the flexible dielectric film  20 , and a mold gate  40 . Mold gate  40  includes an aperture  42  formed in the flexible dielectric film  20  and a support element  44 , which is substantially coplanar with, but electrically isolated from, conductive traces  34 . 
     As shown, flexible dielectric film  20  is a substantially planar member which includes oppositely facing first and second surfaces  22  and  24 , respectively. Flexible dielectric film  20  may be formed from any material which is suitable for use in so-called “carrier substrates,” which are configured to carry conductive traces and other conductive structures, as well as electronic components, such as semiconductor devices, that include input/output elements that communicate with the conductive structures. By way of example only, flexible dielectric film  20  may be formed from polyimide (e.g., 50 μm thick polyimide), which has gained wide acceptance in the semiconductor device industry for use as a carrier substrate material. 
     Conductive traces  34  may be secured to surface  22  nonadhesively (e.g., by lamination of the material thereof to surface  22 ), as in an adhesiveless flex substrate, or with a layer of adhesive material between conductive traces  34  and surface  22 , as in an adhesive flex substrate. 
     Aperture  42  of mold gate  40  is located adjacent to the location of an outer boundary  12  (e.g., at or outside of outer boundary  12 ) ( FIG. 21 ) of tape substrate  10 . In addition, aperture  42  opens to both surface  22  and surface  24  of flexible dielectric film  20 . Support element  44  of mold gate  40  partially overlies and is secured to surface  22 , which is the same surface by which conductive traces  34  are carried. Support element  44  is positioned so as to cover at least a portion of aperture  42  and forms a base of mold gate  40 . The end of aperture  42  that opens to surface  24  remains uncovered so as to facilitate the introduction of liquid packaging material into aperture  42  and, thus, onto surface  24  of flexible dielectric film  20 . 
       FIGS. 4–7  depict exemplary configurations of mold gates according to the present invention. 
     Mold gate  40 ′ of  FIG. 4  has a rectangular configuration. Mold gate  40 ″, shown in  FIG. 5 , includes an enlarged opening  45 ″ and a smaller interior  46 ″, both of which are rectangular in shape. As shown, interior  46 ″ may have a smaller width or a smaller height than opening  45 ″. 
       FIG. 6  illustrates a mold gate  40 ′″ with a Y shape, the opening  45 ′″ thereof comprising a single channel, while the interior  46 ′″ thereof, which is connected to opening  45 ′″ at a junction  47 ′″, includes two channels  46   a ′″ and  46   b ′″, between which a diversion dam  48 ′″, or tap, which prevents packaging material from flowing onto bond wires or other intermediate conductive elements, is located. 
     Mold gate  40 ′″ of  FIG. 7  includes an opening  45 ′″ which is rectangular in shape and which is narrower than the interior  46 ′″ thereof. The width of interior  46 ′″ tapers outwardly from its junction  47 ′″ with opening  45 ′″, imparting interior  46 ′″ with a somewhat triangular shape. Of course, other gate configurations are also within the scope of the present invention. 
     Turning now to  FIGS. 8–14 , an exemplary process for forming tape substrate  10  is depicted. The process, which is shown in  FIGS. 8–14 , may be used to form tape substrate  10  from either a two-layer (adhesiveless flex) tape or a three-layer (adhesive flex) tape. 
     In  FIG. 8 , a flexible dielectric film  20  is provided with a conductive film  30  (e.g., an 18 μm thick copper film) laminated to a surface  22  thereof. Flexible dielectric film  20  may have dimensions that facilitate the fabrication of a plurality of strips  100  of multiple tape substrates  10  thereon ( FIG. 14 ). 
     As shown in  FIG. 9 , masks  120 ,  130 , such as photomasks, may be formed on one or both of surface  24  of flexible dielectric film  20  and an exposed surface  32  of conductive film  30 , respectively. Mask  120  may include apertures  122  which are located and configured so as to expose regions of flexible dielectric film  20  within which apertures  42  of mold gate  40  ( FIGS. 2 and 3 ) are to be formed. Mask  130  may likewise include apertures  132  which are located and configured to expose regions of conductive film  30  that are to be removed, such as those areas located between conductive traces  34  ( FIGS. 2 and 3 ), as well as areas that are located laterally adjacent to the position where support element  44  of mold gate  40  is to be formed. 
       FIG. 10  depicts patterning of flexible dielectric film  20  through mask  120 . In particular, an etchant or other chemical or mixture of chemicals (e.g., in a liquid or plasma state) that will remove the material of flexible dielectric film  20  at a faster rate than it will remove the material of conductive film  30  is permitted to contact regions of flexible dielectric film  20  that are exposed through apertures  122  of mask  120 . The results are an aperture  42  of a mold gate  40  ( FIGS. 2 and 3 ), as well as other features, such as vias, slots, or other apertures. 
       FIG. 11  illustrates patterning of conductive film  30  through mask  130  to form conductive traces  34  and support element  44  of mold gate  40  ( FIGS. 2 and 3 ). For example, an etchant or mixture of etchants (e.g., wet or dry, isotropic or anisotropic) suitable for removing the material of conductive film  30  at a faster rate than it removes the material of flexible dielectric film  20  may be permitted to contact regions of conductive film  30  that are exposed through apertures  132  of mask  130 . 
     Following patterning of flexible dielectric film  20  and conductive film  30 , masks  120  and  130  may be removed, or “stripped,” as known in the art. 
     Thereafter, additional conductive features (not shown), may be formed by known processes. For example, the surfaces or sidewalls  43  of aperture  42  may be coated with a thin layer  49  of material (e.g., gold, platinum, palladium, nickel, silver, etc.) that will reduce or prevent adhesion of a packaging, or encapsulant, material to the material of flexible dielectric film  20 . As desired, some or all of the conductive structures that are carried by flexible dielectric film  20  may also be plated with desired materials (e.g., a barrier layer, such as nickel, or a noble layer, such as gold), as known in the art (e.g., by use of electrolytic, electroless, or immersion plating processes), as shown in  FIG. 12 . 
     A solder mask  140  may then be applied or formed, as shown in  FIG. 13 , over one or both of surfaces  24  and  22  to facilitate the subsequent formation of solder balls or other conductive structures at desired locations of each tape substrate  10 , i.e., those locations of tape substrate  10  that are exposed through apertures  142  of solder mask  140 . Solder mask  140  (e.g., an AUS5 solder mask having a thickness of about 15 μm to about 35 μm) may be applied to or formed on surface  24 ,  22  by known processes. 
     If it is desired that a diversion dam (e.g., diversion dam  48 ′″ of  FIG. 6 ) be included in a mold gate  40 , but the diversion dam was not formed while aperture  42  of mold gate  40  was being formed, diversion dam  48 ′″ may be formed during the application or formation of solder mask  140 . Diversion dam  48 ′″ may be formed or applied over the same surface  22 ,  24  of flexible dielectric film  20  as that over which solder mask  140  is formed or applied, or over the opposite surface  24 ,  22  of flexible dielectric film  20 . 
     Finally, as shown in  FIG. 14 , flexible dielectric film  20  may be singulated into a plurality of strips  100  of tape substrates  10 , as known in the art. By way of example, known die cutting, or “mechanical punching,” techniques may be used to form strips  100  from flexible dielectric film  20 . Additionally, various features of strips  100 , including, without limitation, transport apertures, or sprocket holes  102 , thereof, may be formed either concurrently with or separately in time from the singulation of strips  100  from flexible dielectric film  20 . 
     An exemplary mold gate  40  that may be formed by the process depicted in  FIGS. 8–13  is shown in  FIG. 15 . As shown, aperture  42  of mold gate  40  includes sidewalls  43  which are tapered. Such tapering may be obtained by use of isotropic etch processes to form aperture  42  in flexible dielectric film  20 . Of course, if anisotropic etch processes are employed, sidewalls  43 ′ which are oriented substantially perpendicular to a plane of flexible dielectric film  20 , such as those depicted in  FIG. 20 , may be formed. 
     With reference to  FIGS. 16–19 , as well as with returned reference to  FIGS. 11–14 , another exemplary embodiment of a process for fabricating a mold gate  40 , as well as a tape substrate  10  which includes mold gate  40 , is illustrated. The process shown in  FIGS. 16–19  may be used to form tape substrates  10  from three-layer (adhesive flex) tapes, as conductive film  30  may be secured to flexible dielectric film  20  following the formation of an aperture  42  of mold gate  40  ( FIGS. 2 and 3 ) therethrough. 
       FIG. 16  depicts a flexible dielectric film  20  with both oppositely facing surfaces  22  and  24  thereof being exposed. 
     As shown in  FIG. 17 , flexible dielectric film  20  may be patterned, such as by known die cutting, or “mechanical punching,” techniques, to form vias, slots, other apertures, an aperture  42  of a mold gate  40  ( FIGS. 2 and 3 ), or other features therein. In the depicted example, each of these features, including aperture  42 , extends substantially through the thickness of flexible dielectric film  20 . 
     Next, as shown in  FIG. 18 , a conductive film  30 , such as a foil that comprises any conductive material that is suitable for use as the conductive traces of a carrier substrate (e.g., copper, aluminum, etc.), is laminated to surface  22  of flexible dielectric film  20 . For example, conductive film  30  may be secured to surface  22  with a quantity of adhesive material  29 , which may be applied to either surface  22  or to a surface  31  of conductive film  30  by known processes (e.g., by spraying, use of a roller, etc.). 
     Once conductive film  30  has been secured to flexible dielectric film  20 , a mask  130 , such as a photomask, may be applied to or formed over the exposed surface  32  of conductive film  30 , as shown in  FIG. 19 . Regions of conductive film  30  that are to be removed during patterning thereof are exposed through apertures  132  of mask  130 . 
     Process then continues as shown in and described with reference to  FIGS. 11–14 , wherein conductive film  30  is patterned (e.g., by etching) through mask  130  ( FIG. 11 ), conductive features, such as conductive traces  34  and support element  44  (see  FIGS. 2 and 3 ) are plated ( FIG. 12 ), solder masks  140  are formed over surface  24  or surface  22  ( FIG. 13 ), and strips  100  including multiple tape substrates  10  and their corresponding mold gates  40  are singulated from flexible dielectric film  20  ( FIG. 14 ). 
     The result of such processes is the mold gate  40  shown in  FIG. 20 , which includes an aperture  42  with sidewalls  43 ′ that are oriented substantially perpendicular to a plane of flexible dielectric film  20 . 
     As the inventive processes described herein require that only one surface of a flexible dielectric film  20  have a conductive film  30  ( FIGS. 8 and 18 ) laminated thereto, and since the die cutting processes that are typically employed by TAB substrate manufacturers may be used to form aperture  42  of mold gate  40 , manufacturers of conventional TAB substrates are equipped to fabricate tape substrates  10  that incorporate teachings of the present invention. 
     Once strips  100  of tape substrates  10  according to the present invention have been formed, semiconductor dice  15  may be secured and electrically connected thereto, as known in the art and shown in  FIGS. 21 and 22 , to form semiconductor device assemblies  18 . In addition, conductive structures  16  ( FIG. 22 ), such as balls, bumps, pillars, or columns of conductive material (e.g., solder, another metal or metal alloy, conductive or conductor-filled elastomer, a dielectric film with anisotropically, or “z-axis,” conductive elements therein, etc.) may be secured to contact pads  11  ( FIG. 22 ) of tape substrates  10 . Such processes may be effected as tape substrates  10  remain a part of a strip  100 . 
     Thereafter, as illustrated in  FIGS. 22 and 22A , molded package structures  62  may be formed around semiconductor device assemblies  18  that have been formed on each strip  100 . In forming molded package structures  62 , each semiconductor device assembly  18  may be disposed within a cavity of a mold (not shown), with mold gate  40  of each assembly in alignment with a corresponding mold runner, which is a channel that extends between and communicates with a source of mold material, or “pot,” and the mold cavity within which the assembly is located. Of course, in order to effect such alignment, the mold may have to be specifically configured for use with strips  100  that bear tape substrates  10  according to the invention. A liquid packaging, or encapsulant, material is then introduced through each mold runner, into its corresponding mold cavity, through mold gate  40 , and over the surfaces of tape substrate  10  and the semiconductor device that has been assembled therewith. 
       FIGS. 23 and 24  depict an exemplary process that may be used to remove a sprue  64  (see also  FIG. 22A ), which is the resin from the mold runner that remains within a mold gate  40 , as well as the support element  44  of mold gate  40 , once the material of sprue  64  has sufficiently cured and prior to trimming portions of flexible dielectric film  20  that remain outside of a package structure  62  that has been molded over a tape substrate  10  ( FIGS. 2 and 3 ) and a semiconductor die (not shown) secured and electrically connected thereto to form a packaged semiconductor device  60 . 
     In  FIG. 23 , a strip  100  bearing a plurality of packaged semiconductor devices  60  (only one shown for clarity) is positioned within a degator  110 . More specifically, strip  100  is positioned beneath an upper degator  112 , or the upper degator  112  is positioned over strip  100 , with sprues  64  being received within corresponding slots  114  of upper degator  112 . Strip  100  is also positioned beneath a lower degator  115 , or lower degator  115  is positioned beneath strip  100 , such that an extendable punch  116  is located beneath each mold gate  40  and sprue  64 . 
     As shown in  FIG. 24 , once strip  100  has been positioned within degator  110 , each punch is extended toward and biased against support element  44  of its corresponding gate. As pressure is applied to support element  44 , support element  44  and the sprue  64  resting thereon are forced through aperture  42  of mold gate  40  and into slot  114  of upper degator  112 . Additionally, sprue  64  is broken free from the remainder of package structure  62 . Of course, surfaces  43  of aperture  42  may be lined with a layer  49  ( FIG. 12 ) of adhesion-reducing material, which effectively reduces the amount of force that need be applied to support element  44  to remove sprue  64  from aperture  42 . 
     Once a first packaged semiconductor device  60  of strip  100  has been degated in this fashion, strip  100  may be moved (e.g., by indexing the same) to position another packaged semiconductor device  60  at the appropriate location between upper degator  112  and lower degator  115 . 
     When all of the packaged semiconductor devices  60  on strip  100  have been degated, the semiconductor device packages  60  may then be separated from one another, as known in the art. 
     Although the foregoing description contains many specifics, these should not be construed as limiting the scope of the present invention, but merely as providing illustrations of some of the presently preferred embodiments. Similarly, other embodiments of the invention may be devised which do not depart from the spirit or scope of the present invention. Moreover, features from different embodiments of the invention may be employed in combination. The scope of the invention is, therefore, indicated and limited only by the appended claims and their legal equivalents, rather than by the foregoing description. All additions, deletions, and modifications to the invention, as disclosed herein, which fall within the meaning and scope of the claims are to be embraced thereby.

Technology Category: 5