Abstract:
A method of manufacturing a plurality of microelectronic packages including electrically and/or thermally conductive elements. The method includes providing a support structure having a plurality of protrusions and depressions extending outwardly from the support. A conductive element is then mated to the support structure in a male-to-female relationship. The depressions formed in the support structure and conductive element are used to house a microelectronic element such as a semiconductor chip. A substrate is provided so as to cover substantially each depression located in the conductive element. Leads interconnect contacts to the chip to terminals on the substrate. A curable encapsulant material may be deposited into the depression so as to protect and support the leads and the microelectronic element. Additionally, the curable encapsulant material forms part of the exterior of a single resulting chip package once the assembly is diced and cut into individual packages.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application claims benefit of U.S. Provisional Application No. 60/391,814 filed on Jun. 27, 2002, the disclosure of which is incorporated by reference herein. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    The present invention relates to methods of making microelectronic assemblies, such as semiconductor chip packages, including an electrically and/or thermally conductive element.  
           [0003]    Modern electronic devices utilize semiconductor chips, commonly referred to as “integrated circuits”, which incorporate numerous electronic elements. These chips are mounted on substrates that physically support the chips and electrically interconnect each chip with other elements of a circuit. The substrate may be a part of a chip package including terminals for interconnecting the chip with external circuit elements. The interconnection between the chip and its supporting substrate is commonly referred to as a “first level” interconnection. The interconnection between the substrate and the larger elements of the circuit is commonly referred to as a “second level” interconnection.  
           [0004]    A plurality of semiconductor chips may be assembled with a substantially continuous strip, as disclosed in certain embodiments of WO 94/03036, the disclosure of which is hereby incorporated by reference herein. The strip may have a plurality of sprocket holes for advancing the strip in a direction for assembly with semiconductor chips. The strip has leads connected to terminals on a surface of the strip that faces away from the chips. The strip includes apertures aligned with the leads. The strip is disposed on top of the chips so that the leads generally extend over the contacts of the chips. A bonding tool is utilized to bond each lead to a contact, by advancing the tool toward a lead and forcing the lead toward the contact on the chip. Heat and/or ultrasonic vibration is applied to the lead by the tool so as to bond the lead to the contact. Alternatively, a wafer incorporating a plurality of chips is assembled with a sheet incorporating a plurality of interposers. The wafer and sheet are severed to provide individual packages.  
           [0005]    After forming semiconductor chip packages, the individual packages may be assembled with an electrically or thermally conductive element. A thermal or electrical connection is formed between the element and external circuit elements for shielding or heat spreading. Assembling such individual elements, commonly known as “cans”, with each semiconductor chip is costly and time-consuming.  
           [0006]    Despite the foregoing improvements, further advancement in making microelectronic assemblies is desirable.  
         SUMMARY OF THE INVENTION  
         [0007]    The present invention addresses these needs.  
           [0008]    In a first aspect of the present application, a method of making a microelectronic package comprises providing a plurality of microelectronic packages, providing a support having a plurality of recesses, the support carrying a conductive element having a plurality of depressions, at least some of the depressions being disposed in a recess. The conductive element is assembled with the microelectronic packages. Most preferably, the support is removed after this assembly step, and the conductive element is severed between at least some of the depressions to form individual assemblies each including one or more microelectronic packages with a portion of the conductive element as a conductive shell or shield at least partially encompassing the package or packages. In assembling a plurality of packages with a conductive element and then severing the conductive element, a plurality of separate conductive elements need not be assembled with each package. The conductive element may comprise a thermally conductive element to form a thermal heat spreader, or the conductive element may comprise an electrically conductive element for forming shields, or both.  
           [0009]    The support may comprise a mandrel having a plurality of recesses corresponding to the depressions in the conductive element. The step of providing a support may comprise depositing a conductive material on a surface of the support. In preferred embodiments, the surface of the support comprises a material that does not adhere to the conductive material deposited thereon. The support, for example, may comprise molybdenum, steel, brass or chromium. The conductive material may comprise a material such as copper, nickel or gold.  
           [0010]    In certain preferred embodiments, each package comprises a semiconductor chip attached to a dielectric layer and has leads connected to the chip and to terminals on the dielectric layer. Bonding material as, for example, a solder, may be applied to the terminals on the package, for connection to external elements such as contact pads on a circuit board. The microelectronic package may also include one or more conductive planes that may be connected to other elements using bonding material. Further, bonding material may be applied to the conductive element before or after the severing step so that the shell formed from the conductive element also may be connected to the circuit board.  
           [0011]    In preferred embodiments, a flowable material is introduced in the depressions to encapsulate the elements of the packages disposed within the depressions. In embodiments in which the package includes leads, the flowable material is introduced so as to surround the leads. Desirably, the conductive element comprises a recession or hole that communicates between depressions. Such recession or hole is desirably arranged so that the flowable material can flow between adjacent depressions. For example, the side walls forming boundaries between adjacent depressions can be formed as a plurality of spaced pillars with gaps therebetween.  
           [0012]    The conductive element, in certain preferred embodiments, has protruding portions or bumps adjacent each depression so that the protruding portions are disposed adjacent each package when the conductive element is assembled with the microelectronic packages. In certain preferred embodiments, the packages comprise a tape or strip assembled with a plurality of semiconductor chips and the tape or strip has holes between each semiconductor chip. The holes may be shaped, sized and arranged to receive the bumps of the conductive elements.  
           [0013]    Yet another aspect of the invention provides microelectronic assemblies which desirably include a conductive element including a bottom wall and a plurality of side walls extending from said bottom wall so that said bottom wall and said side walls define a depression, said conductive element having one or more additional openings therein. The assembly; desirably includes a dielectric layer extending between the side walls, so that said dielectric layer and the conductive element substantially enclose an interior space within the depression. The one or more openings in the conductive element communicate with the interior space.  
           [0014]    A microelectronic element is disposed within the space. An encapsulant includes an interior portion at least partially filling the space and at least partially surrounding the microelectronic element, and an exterior portion being disposed outside of said interior space in contact with the conductive element, said portions of said encapsulant being connected to one another through said one or more openings in the conductive element. Stated another way, in this aspect of the invention, portions of the encapsulant are exposed at the exterior of the assembly, desirably along the side walls of the conductive element. For example, where the conductive element includes multiple pillars defining the side walls, portions of the encapsulant fill the gaps in the side walls so that these portions are exposed at the outside of the assembly. Thus, even where the conductive element does not provide a complete, continuous covering over the microelectronic element, the encapsulant fills the gaps. The encapsulant exposed at the exterior of the assembly may also serve to protect the conductive element from mechanical damage. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]    These and other features, aspects and advantages of the present invention will become better understood with regard to the following description, appended claims, and accompanying drawings where:  
         [0016]    [0016]FIG. 1 is a perspective view of a support used in a method in accordance with an embodiment of the invention;  
         [0017]    [0017]FIG. 2 is a perspective view of the support of FIG. 1 at a later stage in a method in accordance with the embodiment of FIG. 1;  
         [0018]    [0018]FIG. 3 is a bottom plan view of a microelectronic package used in a method in accordance with the embodiment of FIGS.  1 - 2 ;  
         [0019]    [0019]FIG. 4 is a cross-sectional view of the support of FIG. 2 engaged with the package of FIG. 3;  
         [0020]    [0020]FIG. 5 is view similar to FIG. 4 but depicting the support and package at a later stage in the method;  
         [0021]    [0021]FIG. 6 is a cross-sectional view of packages formed in the method of FIGS.  1 - 5 ;  
         [0022]    [0022]FIG. 6A is a cross-sectional view of packages formed in the method of FIGS.  1 - 5 .  
         [0023]    [0023]FIG. 6B is a bottom view of a package formed in the method of FIGS.  1 - 5 .  
         [0024]    [0024]FIG. 6C is a perspective view of a package formed in the method of FIGS.  1 - 5 .  
         [0025]    [0025]FIG. 6D is a cross-sectional view of an individual assembly formed in a method in accordance with a further embodiment of the invention.  
         [0026]    [0026]FIG. 7 is a cross-sectional view of an individual assembly formed in a method in accordance with a further embodiment of the present invention;  
         [0027]    [0027]FIG. 8 is a cross-sectional view of an individual assembly formed in a method in accordance with another embodiment of the invention;  
         [0028]    [0028]FIG. 9 is a cross-sectional view of an individual assembly formed in a method in accordance with yet another embodiment of the invention;  
         [0029]    [0029]FIG. 10 is a cross-sectional, partial view of a conductive element assembled with a plurality of packages in a method according to yet another embodiment of the present invention;  
         [0030]    [0030]FIG. 11 is the cross-sectional view of the assembly of FIG. 10 at a later stage in the method; 
     
    
     DETAILED DESCRIPTION  
       [0031]    A method in accordance with one embodiment of the invention includes using a support  10 . Support  10  comprises an element having a first major surface  12  and a second major surface  14  facing oppositely from the first major surface  12 . Recesses  16  are formed in the first major surface  12  of the support  10 . The support has surface portions  11  surrounding each recess  16  and projecting upwardly from the bottom surface of the recess. In this embodiment, each surface portion  11  is in the form of a substantially continuous wall extending along one side of a recess or forming a division between two adjacent recesses. Each surface portion or wall  11  has outwardly-sloping surfaces extending from the top of the wall to the bottom surface of each adjacent recess, so that each wall widens toward the bottom of the recess whereas each recess widens toward the top or open side of the recess. Each surface portion or wall  11  has a set of spaced apart support protrusions or bumps  13  disposed along the length of the wall. Bumps  13  project upwardly from the top surface of the wall. Each support protrusion or bump  13  may have the shape of a pyramid, a cone, an elongate protruding element, or any other shape.  
         [0032]    The recesses  16  and other features of the support  10  may be formed by machining, by casting, by molding, or by providing a sheet and etching the first major surface  12  of the sheet to form the features discussed above. The support may comprise a metal or a polymer, and may be rigid or flexible.  
         [0033]    A conductive element  20  having depressions  22  is provided on the support  10 , as shown in FIG. 2, most preferably by forming the conductive element as a layer of conductive material overlying the top surface of the support so that the shape of conductive element  20  conforms to the shape of the support top surface  12 . Thus, the conductive element  20  has depressions  22  corresponding to the recesses in the support surface, each such depression having a bottom wall  57  and side walls  59  projecting upwardly from the bottom wall around the periphery of each depression. The side walls  59  correspond to walls  11  (FIG. 1) of the support, and form borders between adjacent depressions  22 . The side walls  59  have sloping wall portions  55 . Each side wall  59  has spaced-apart protruding portions or bumps  21  projecting upwardly from the top of the side wall. Bumps  21  correspond to the support protrusions or bumps  13 .  
         [0034]    The conductive element  20  may be formed on the support  10  by depositing a layer of conductive material on the first major surface  12  of the support. For example, metal may be deposited on the first major surface  12  until a layer of metal having depressions  22  is formed on the support  10 . Where the support is formed from an electrically conductive material, the metal can be electroplated directly on the support. Alternatively, where the support is formed from a nonconductive material, a thin conductive layer may be deposited on the support by sputtering, electroplating, evaporation or chemical vapor deposition, whereupon additional metal can be deposited on the conductive layer by electroplating.  
         [0035]    The conductive element  20  may also be formed by placing a metal sheet over the first major surface  12  and pressing the metal sheet against the recesses  16  so as to form the depressions  22  in the, recesses  16  of the support  10 . For example, the support  10  and metal sheet may be placed in a press having a compliant pad, such as a rubber sheet, on one side with the support  10  on the other side, and the metal sheet can be squeezed between the support  10  and the compliant pad. In another example, the metal sheet can be squeezed in a press between the support and a mating female die, i.e., a die having a shape substantially complementary to the shape of support top surface  12 .  
         [0036]    Desirably, the depressions  22  closely conform to the recesses  16  in the support  10  so that the support  10  can be engaged and moved and the conductive element  20  will be carried on the support  10 . Although the support  10 , recesses  16 , conductive element  20 , support protrusions  13 , protruding portions  21 , and depressions  22  have rectangular shapes in FIGS.  1 - 7 , these features may have any regular or irregular shape. The designations “top” and “bottom” are used for convenience and do not refer to any gravitational frame of reference.  
         [0037]    Preferably, the support  10  comprises a material, at least at the first major surface  12 , that does not adhere to the conductive element  20  formed on the support. In a preferred embodiment, the support comprises a metal, such as molybdenum, steel, or brass and has a coating of chromium. In embodiments including a coating on the support, the coating is preferably applied after the recesses and other features of the support surface  12  are formed.  
         [0038]    A plurality of microelectronic packages  24  is provided. Each of the packages  24  shown in FIGS. 3 and 4 comprises a microelectronic element  26 , such as a semiconductor chip and a region  33  of a dielectric layer  27 . As used herein, the term “microelectronic element” comprises a semiconductor chip, a printed circuit board, a wafer or stacked assembly incorporating a plurality of semiconductor chips, or any other microelectronic element. In the embodiment shown in FIG. 3, the dielectric layer regions  33  associated with numerous packages  24  are provided as parts of a unitary strip  27  of dielectric material. The strip  27  has a region  33  corresponding to each microelectronic element. Each region  33  has a plurality of leads  32  arranged with apertures  30 , also referred to herein as bond windows. The bond windows  30  provide access to the leads  32  so that they can be bonded to contacts  34  on the microelectronic element  26 . Terminal structures  36  on each region  33  of the strip  27 , as shown in FIG. 4, are connected to the leads  32 . The terminal structures are exposed at an outer surface of the dielectric layer or strip  27 , i.e., the surface facing away from microelectronic elements  26 . The terminal structures may be flush with the outer surface, recessed relative to the outer surface, or project from the outer surface. In the particular embodiment depicted in the drawings, terminal structures  36  lie on the inner surface of the dielectric layer (the surface facing toward microelectronic elements  26 ) and are exposed at the outer surface through holes in the dielectric layer aligned with the terminal structures. As further discussed below, the terminal structures will be used to provide connections to external circuitry, such as a printed circuit board or other microelectronic element. In the particular embodiment depicted, each package  24  includes a compliant layer  38  between the strip  27  and the microelectronic element  26  and the leads  32  are disposed between the strip and the compliant layer  38 . The compliant layer  38  is best seen in FIGS.  4 - 6 . During manufacture of the packages  24 , the leads and terminal structures on the dielectric elements shown in FIGS.  3 - 6  may be connected to microelectronic elements  26  using a lead-bonding process according to certain embodiments of International Patent Publication WO 94/03036, the disclosure of which is hereby incorporated by reference herein. In other embodiments, the terminal structures on the dielectric elements may be connected to microelectric elements  26  by wire-bonding.  
         [0039]    The strip  27  shown in FIGS.  3 - 6  also has a central hole  46  as shown in FIG. 6, in each region  33  and a thermally conductive plane as, for example, a metallic plane  48  is accessible through the central hole  46 .  
         [0040]    The strip  27  preferably includes holes  31  separating each region  33 , in between the individual packages  24 . The holes  31  are arranged in a pattern corresponding to the pattern of protruding portions or bumps  21  on conductive element  20 . Preferably, the holes  31  have a shape for engaging the protruding portions  21 .  
         [0041]    In the assembly method, the support  10  and conductive element  20  are juxtaposed with the plurality of microelectronic packages  24  so that the conductive element faces the packages  24  and each package  24  is aligned with a depression  22  in the conductive element  20 . The inner side of the dielectric layer, bearing the microelectronic elements faces toward conductive element  20 . The support  10  and packages  24  are moved in relation to one another so that a surface of each package  24  touches a surface of the conductive element  20  within a depression  22  and so that the protruding portions or bumps  21  of the conductive element are received in the holes  31  in the strip. In the embodiment shown, a rear surface of the microelectronic element or chip  26  is brought into contact with the bottom wall  57 . The holes  31  aid in registration of the plurality of packages with the conductive element. Moreover, the support  10  reinforces the conductive element during the assembly process so that the conductive element does not bend or otherwise distort during this step. This further aids in registration of the conductive element with the packages.  
         [0042]    The packages  24  may be oriented so that the rear surface of the microelectronic element  26  faces upwardly and the support  10  may be oriented so that the conductive element  20  faces downwardly toward the packages  24 , as shown in FIG. 5. However, the orientation of the support  10  and microelectronic element  26  relative to gravity is in no way essential to the invention. The packages may be assembled with the conductive element utilizing robotic equipment, computer controllers, optical systems, and any other equipment used in the microelectronic arts.  
         [0043]    As best appreciated with reference to FIG. 2, the conductive element  20  defines several rows  23  and columns  25  of depressions  22 . A strip  27  having a corresponding number of rows and columns of packages  24  is desirably used with the support  10  and conductive element  20 . In other embodiments, a plurality of strips  27 , may be assembled with the conductive element  20  so that a strip  27  corresponds to a row  23  of depressions  22 . In other embodiments, the conductive element  20  may comprise a single row of depressions  22  for assembly with a single strip  27 . In other embodiments, the strip may comprise a sheet incorporating packages  24  arranged in a two-dimensional array other than the specific array shown in FIG. 3.  
         [0044]    After assembly of the packages with the conductive element, a flowable material  40  is introduced into the space between the conductive element  20  and the dielectric component  27 , so that the leads  32  and the microelectronic element  26  are surrounded by the flowable material  40 . The flowable material may be inserted into depressions  22  via any open area of depression  22  not covered by strip  27 . For example, the bond windows  30  can be used for this purpose. In an alternate embodiment not shown, strip  27  may be provided with apertures remote from the bond windows for permitting introduction of flowable material  40  into depression  22 . The flowable material may be introduced into the various depressions  22  of conductive element  20  either simultaneously or sequentially. Merely by way of example, the flowable material may be introduced by conventional dispensing equipment using a needle (not shown) aligned with an opening in the strip at each depression. The flowable material also adheres the microelectronic element  26  to the conductive element  20 . In a further variant, a layer of a thermally-conductive material such as a grease, gel or curable adhesive composition loaded with a thermally-conductive filler may be provided between the rear surfaces of each microelectronic element and the bottom surface  57  of each depression. For example, the thermally-conductive material may be applied to the rear surfaces of the microelectronic elements or to the bottom surfaces of the depressions before assembling the packages with the conductive element.  
         [0045]    The support  10  is removed after the packages  24  are adhered to the conductive element  20 . The conductive element  20  releases from the support  10 , as the conductive element  20  is not adhered thereto. The fit of the conductive element  20  in the recesses  16  is overcome by the adhesion between the packages  24  and the conductive element  20 . The cured flowable material desirably contributes to the adhesion between the packages and the conductive element. The sloping wall portions  55  of the conductive element  20  may be arranged to facilitate the release of the conductive element  20  from the support  10 .  
         [0046]    Conductive features such as masses of an electrically conductive bonding material as, for example, a solder, may be added to the dielectric layer, in contact with the terminal structures, so that the packages  24  can be interconnected with external circuitry. As shown in FIG. 6, first conductive features  42  are added on the terminal structures  36 . Second conductive features  43  are placed in the central holes  46  in contact with the conductive planes  48 . Third conductive features  47  are disposed on the bumps or protruding portions  21  of the conductive element  20 .  
         [0047]    The packages  24  are diced into individual assemblies  50  by severing the conductive element  20  and strip  27 , at the middle of each wall  59  between adjacent depressions  22 , so that the strip and conductive element are severed along lines  35  shown in FIG. 3. After dicing, each assembly  50  includes a package  24 , with the microelectronic element  26  and with a portion  33  of the dielectric layer, together with an individual element  52  formed from a portion of the conductive element  20 . Thus, the conductive element  20  and strip  27  are severed along lines  35   a  cutting through rows of packages, and along lines  35   b  cutting through columns of packages, as best seen in FIG. 3. In this arrangement, the conductive element  20  is severed through the protruding portions or bumps  21 . Thus, each wall  59  provided in the original conductive element  20  is severed to leave one sloping wall portion  55  of the conductive element as a side wall along one side of the assembly, and each bump  21  of the conductive element is severed to form a tab  51  at an edge of such side wall or sloping wall portion  57 . Preferably, the process of placing the third conductive features  47  on the bumps and the severing process are conducted so that after the severing process, the third conductive features  47  remain on all of the bumps. For example, pairs of conductive features  47  may be added to each bump  21  and the each bump  21  may be severed between the conductive features  47  of the pair. Alternatively, the third conductive features may be provided as masses of solder covering the entire exposed surface of each bump  21 , and these masses may be severed into smaller masses when the conductive element is severed. In a further alternative, the conductive features may be added after the severing operation.  
         [0048]    The dicing or severing operating may be performed by utilizing a blade or a laser or any other means of cutting through the conductive element  20  and strip  27 . Preferably, the dicing or severing operation is performed after the support  10  has been removed. In an alternative, the support can be severed along with the conductive element and strip, so that a portion of the support remains in place on each assembly after the severing step. These portions of the support can be removed after severing. The step of adding the conductive features can be performed before or after the severing step, and before or after removing the support.  
         [0049]    Each finished assembly includes an individual element or electrically conductive shield  52  formed by a portion of the conductive element  20  having one depression  22 . The wall  57  which originally constituted the bottom wall of the depression forms a wall of the shield whereas sloping side walls  55  form walls of the shield projecting from wall  57  to the vicinity of the dielectric element  33 . Each wall  57  has a tabs  51  at its edge remote from wall  57 .  
         [0050]    In use, the finished assembly can be bonded to a circuit board. The first conductive elements or bonding material  42  serves to connect terminal structures  36  to contact pads of the circuit board. The third conductive element or bonding material  47  can connect tabs  51 , and hence the conductive shell, to a mating conductive feature on the circuit board. This connection can be used to carry a voltage such as ground potential to the shell, to conduct heat from the shell to the circuit board, or both. Thus, the individual element  52  comprises a heat spreader, or an electromagnetic shield for the package  24 . The second conductive element  43  can connect the metallic plate  48  to a mating metallic or other thermally conductive feature on the circuit board, and may also form an electrical ground or other electrical connection. These features of the finished assembly and its use with a circuit board may be in accordance with copending, commonly assigned U.S. patent application Ser. No. 10/210,160 and copending, commonly assigned PCT International Application U.S. Ser. No. 02/27,509, the disclosures of which are hereby incorporated by reference herein.  
         [0051]    In other embodiments, an adhesive  41  may be disposed on the surface of the conductive element  20  in the depressions  22 , on the package  24 , or both, before the microelectronic element  26  is brought into contact with the conductive element  20 . The adhesive may be thermally conductive, electrically conductive or both. In other preferred embodiments, the conductive element  20  is attached to another part of the microelectronic package  24 , such as the upper surface of the microelectronic element  26  or the dielectric layer  27 .  
         [0052]    The flowable material may comprise a curable dielectric material. In addition, certain embodiments of U.S. Pat. Nos. 6,329,224, 6,359,335, 6,232,152, and 5,776,796, the disclosures of which are hereby incorporated by reference herein, may be used. Desirably, the conductive element  20  comprises a recession or hole that communicates between depressions. Such recession or hole is desirably arranged so that the flowable material can flow between adjacent depressions.  
         [0053]    An example of such a recession of hole is used in the method shown in FIGS. 6A and 6B. In this method, support  10 ′ is provided with rows of projecting posts  79  projecting upwardly from a generally planar bottom surface  77 . Here again, the conductive element  20 ′ is provided as a layer of conductive material such as a metal closely overlying and conforming to support  10 ′, preferably by forming the conductive element on the support by the methods discussed above. Thus, the conductive element will include rows of spaced-apart protrusions or pillars  65  extending outwardly from a bottom wall  75 , each such pillar being hollow and substantially surrounding one post  79  of the support. The pillars are separated from one another by gaps or recessions  63 .  
         [0054]    Thus, the conductive element includes depressions  22 ′ surrounded by rows of projecting pillars  65 , each such depression having a bottom wall constituted by a portion of bottom wall  75 . The gaps or recessions  63  act as a bridge between adjacent depressions  22 ′ or a depression  22 ′ and the exterior of the assembly. In the assembly method, packages  24 ′ are assembled with the conductive element in substantially the same manner as discussed above. The pillars  65  desirably project through holes  31 ′ in the dielectric element in much the same manner as the bumps discussed above. The dielectric element includes conductive features similar to those discussed above, such as terminal structures  36 ′ exposed at an outer surface  68  of the dielectric layer (the surface facing away from support  10 ′ in FIG. 6A).  
         [0055]    In this method as well, a flowable material  40 ′ is introduced into depressions  22 ′ after assembling the packages to the conductive element, and desirably before removing support  10 ′. Before introducing flowable material  40 ′, a solder mask or coverlay  66  may be attached to outer surface  68  as taught in commonly-assigned U.S. Pat. No. 6,359,335, which is hereby incorporated by reference herein. Coverlay  66  seals the bond windows  30 ′ in the dielectric strip. The coverlay desirably also extends over the tips of pillars  65 , and seals the holes  30  in the dielectric layer which receive the pillars. In this condition, the various depressions  22 ′ communicate with one another through the gaps  63  between the pillars, but do not communicate with the outer surface of the dielectric element. A flowable material  40 ′ may be introduced between the dielectric strip  27 ′ and the conductive element  20 ′ as, for example, by injecting the dielectric material into the gaps between pillars at an edge of the assembly. The dielectric material can flow through all of the depressions  22 ′ and disperse through the entire assembly when it is introduced. However, the flowable material will not contaminate the conductive features exposed at the outer surface of the dielectric element. In this process, the flowable material  40 ′ will fill all of the depressions and will also fill the gaps  63  between the pillars.  
         [0056]    In an alternate embodiment, coverlay  66  may be provided with apertures remote from the terminal structures  36 ′, and flowable material may be introduced into one or more of the depressions  22 ′ through these apertures. Here again, the flowable material will pass from one depression to another via gaps or recessions  63 .  
         [0057]    As shown in FIG. 6B, the pillars  65  are spaced so that gaps or recessions  63  have a dimension d large enough to permit flowable material  40 ′ to permeate through, from one depression  24 ′ to another. However, dimension d is small enough not to permit electromagnetic radiation wavelengths at an operating frequency associated with the microelectronic elements  26 ′ from passing between adjacent pillars  65  during operation of the finished assemblies. Stated another way, the pillars are close enough to one another to form a Faraday shield effective to block electromagnetic radiation at an operating frequency used by the microelectronic element. To act as a Faraday shield, the dimension d of the gaps, and hence the distance between adjacent pillars, should be less than the wavelength of radiation at the operating frequency. Where the microelectronic element is a radio frequency power amplifier, the operating frequency may be taken as the carrier frequency of the signals which are to be amplified. Where the microelectronic element is a digital element such as a conventional digital semiconductor chip, the operating frequency may be taken as the clock frequency of the chip.  
         [0058]    Here again, after injection and curing of the flowable material, and desirably after removing the conductive element and strip from support  10 , the conductive element and dielectric strip are severed along severance planes extending between adjacent depressions  22 ′ to yield individual assemblies  50 ′ (FIG. 6C).  
         [0059]    As shown in FIG. 6C, each assembly  50 ′ includes a conductive shell or shield including a bottom wall  57 ′ formed from a portion of the original bottom wall  75  of the conductive element, and side walls  55 ′ projecting upwardly from the bottom wall  57 ′. Each side wall  55 ′ is formed by a plurality of conductive pillar portions  74 , formed from the conductive pillars  65  of the original conductive element. Regions of cured flowable material  72  are also present at the exterior surfaces of the sidewalls  55 ′, in the portions of the sidewalls corresponding to the gaps  63  between the posts in the original conductive element.  
         [0060]    In another embodiment of the invention, as shown in FIG. 6D, the conductive element  20 ″ is formed with raised portions or walls  59 ″ having substantially continuous side walls  55 ″ and having bumps or protrusions  21 ″ similar to the side walls and bumps of the conductive element discussed with reference to FIGS.  2 - 6 . However, at least one passageway  80  extends through each wall  59 ″ connecting adjacent depressions  22 ″. As seen in FIG. 6D, each passageway  80  includes a portion extending through one side wall  55 ″ of a hollow wall  59 ″ defining a wall space  81  open toward the rear surface of the conductive element, i.e., toward the top of the drawing in FIG. 6D. Each passageway  80  also includes a further portion extending through the opposite side wall of the same hollow wall  59 ″, so that the depressions  22 ″ communicate with one another through the wall space  81  within the wall. According to this embodiment, the support is removed before flowable material  40 ″ is introduced. Coverlay  66 ″ is applied to both the front surface  68  of the structure (the outer surface of the dielectric layer) and rear surface  69  of the structure (defined by the outwardly facing surfaces of the depression bottom walls  57 ″). Flowable material  40 ″ may be introduced into the structure either by apertures  82  in conductive element  20  or through pathways  80  in walls  59 ″ on the edges of the structure. In a further embodiment, flowable material  40 ″ may be introduced into the structure at more than one location simultaneously. Pathways  80 , similar to recessions  63  discussed above with reference to FIGS.  6 A- 6 B, enable flowable material  40 ″ to permeate from one depression  22 ″ to another.  
         [0061]    As previously mentioned coverlay  66 ″ on front surface  68  seals the bond windows and other openings in the dielectric layer. Additionally the coverlay  66 ″ on rear surface  69  of assembly  50  prevents flowable material passing through the wall spaces within the hollow walls  59 ″ from leaking onto the rear surface of the structure. The rear or outwardly-facing surfaces of depression bottom walls  57 ″ remain substantially free of the flowable material. In use of the completed assemblies, this surface may be connected to a heat sink or thermal spreader without an insulative material impeding the dissipation of heat from the chip.  
         [0062]    Preferably, pathways  80  are sized so as to permit flowable material  40 ″ to pass through the structure but are also sized so as not to permit wavelengths of electromagnetic radiation at an operating frequency to pass.  
         [0063]    In another embodiment of the invention, as shown in FIG. 7, a plurality of stacks  124  of microelectronic elements are assembled in the depressions  122  of a conductive element. The stack  124  may be assembled with a compliant layer  155 , or another pad of dielectric material and a dielectric layer  129 . The dielectric layer  129  may comprise a strip, as discussed above or may be provided in other forms. Contacts of the microelectronic elements  126   a  and  126   b  are connected to terminal structures  136  on the dielectric layer  129 . The dielectric layer  129  and conductive element are severed to form individual assemblies  150 , each having one or more stacks  124  disposed in a depression  122 .  
         [0064]    In another embodiment, the packages  224  each comprise a semiconductor chip with contacts that face away from the dielectric layer, as shown in FIG. 8. The conductive element  220  is assembled with the plurality of packages  224  so that the conductive element  220  overlies the surface of the chip having the contacts  234 . The contacts  234  may be attached to terminal structures  236  on the dielectric layer  229  using wire bonds  237 . The conductive element  220  is placed over the upper surface of the microelectronic element with enough clearance so as to avoid interfering with the wire bonds  237 . For example, the depression  222  in the conductive element  220  has a depth “x” greater than the height of the package  224  and wire bonds. In other embodiments, standoff is provided using a pad  255 , disposed on the microelectronic element and the conductive element  220  is attached to the pad. The dielectric layer  229  and conductive element  220  are severed to form individual assemblies  250  in substantially the same manner as discussed above.  
         [0065]    In another embodiment, a plurality of stacks  324  are disposed in depressions  422  of a conductive element, as shown in FIG. 9. The conductive element is assembled with the stack  324  so that contacts on a face of one of the microelectronic elements  326  faces the bottom  357  of the depression  322 . A pad  355  may be disposed between the microelectronic element  326   a  and the bottom  357 . Contacts on the microelectronic element  326   a  and microelectronic element  326   b  are connected to terminal structures  336  on a dielectric layer  329 .  
         [0066]    More than one device may be assembled in each depression of the conductive element. For example, the conductive element may be assembled with a strip carrying pairs of chips or devices so that the pair of chips or devices are both disposed in a depression. In another example, one or more devices are placed in each depression. Individual devices or packages may be placed in the depression using, for example, a pick and place machine.  
         [0067]    In a further embodiment of the invention, as shown in FIGS. 10 and 11, the conductive element is severed at some but not all of the protruding portions. Thus, each individual assembly resulting from the severing step includes two depressions and the devices disposed in those depressions. In this embodiment, the conductive element acts as a shield to prevent electromagnetic fields from one device from propagating to the adjacent die in the same assembly. A conductive element  420  is assembled with a plurality of packages  424 , as discussed above. The conductive element  420  and packages  424  may be assembled so that a single chip or other microelectronic element is disposed in a depression, or a plurality of microelectronic elements is disposed in each depression. In the embodiment shown, a pair of packages  424  are disposed in each depression  422 . A flowable material is introduced around the microelectronic elements. The conductive element  420  is severed along the walls  459  so that individual assemblies  450  having a pair of depressions  422  are formed. In other embodiments, more than a pair of depressions  422  are incorporated in the individual assemblies by selecting protruding portions  421  to sever. In other words, walls  459   a  along a selected dicing plane  435  (FIG. 10) are severed and walls  459   b  are not severed.  
         [0068]    In another embodiment of the present invention, the support and conductive element disclosed herein is used to form assemblies disclosed in certain embodiments of U.S. Provisional Application No. 60/315,408, filed Aug. 28, 2001, the disclosure of which is hereby incorporated by reference herein.  
         [0069]    These and other variations and combinations of the features discussed above can be utilized without departing from the invention. For example, a plurality of microelectronic elements may be directly assembled with a conductive element, without being packaged with a dielectric layer. The conductive element may be assembled with other types of packages, having configurations other than the packages discussed above. A microelectronic element in a flip-chip arrangement may be used. The packages may be assembled with the conductive element by placing packages into the depressions using robotic or pick and place equipment. Devices other than microelectronic elements may be assembled with the conductive element. Active dies, passive dies, elements of a circuit other than dies, may be assembled with the conductive element. Thus, the foregoing description of the preferred embodiments should be taken by way of illustration rather than by way of limitation of the invention as defined by the claims.