Abstract:
The present disclosure suggests various microelectronic component assembly designs and methods for manufacturing microelectronic component assemblies. In one particular implementation, a microelectronic component assembly includes a microelectronic component mounted to a substrate. The substrate carries a plurality of bond pads at a location substantially coplanar with a terminal surface of the microelectronic component. This enables a smaller package to be produced by moving the bond pads laterally inwardly toward the periphery of the microelectronic component.

Description:
TECHNICAL FIELD  
       [0001]     The present invention relates to microelectronic component assemblies and methods of manufacturing microelectronic component assemblies. In particular, aspects of the invention relate to microelectronic component assemblies that include wire bonds. Certain embodiments of the invention are advantageous for packaged microelectronic component assemblies.  
       BACKGROUND  
       [0002]     Semiconductor chips or dies typically are manufactured from a semiconductor material such as silicon, germanium, or gallium/arsenide. An integrated circuit or other active feature(s) is incorporated in the die adjacent one surface, often referred to as the “active surface,” of the die. The active surface typically also includes input and output terminals to facilitate electrical connection of the die with another microelectronic component.  
         [0003]     Since semiconductor dies can be degraded by exposure to moisture and other chemical attack, most dies are encapsulated in a package that protects the dies from the surrounding environment. The packages typically include leads or other connection points that allow the encapsulated die to be electrically coupled to another electronic component, e.g., a printed circuit board. One common package design includes a semiconductor die attached to a small circuit board, e.g., via a die attach adhesive. Some or all of the terminals of the semiconductor die then may be connected electrically to a first set of contacts of the board, e.g., by wire bonding. The connected board and die may then be encapsulated in a mold compound to complete the packaged microelectronic component assembly. A second set of contacts carried on an outer surface of the board remain exposed; these exposed contacts are electrically connected to the first contacts, allowing the features of the semiconductor die to be electrically accessed.  
         [0004]      FIG. 1  schematically illustrates a conventional packaged microelectronic component assembly  10 . This microelectronic component assembly  10  includes a semiconductor die  20  having a front surface  22 , which bears an array of terminals  24 , and a back surface  26 . This semiconductor die  20  is mounted to a front side  42  of a circuit board  40 , e.g., by attaching the back surface  26  of the die  20  to the circuit board front side  42  with a die attach paste  35 .  
         [0005]     The microelectronic component assembly  10  also includes a plurality of bond wires  50  that extend from individual terminals  24  of the die  20  to bond pads  44  arranged on the front side  42  of the board  40 . Typically, these bond wires  50  are attached using wire-bonding machines that spool a length of wire through a capillary. As suggested in  FIG. 1 , these capillaries C feed a length of wire  50  through a narrow distal passage. Typically, a molten ball is formed at a protruding end of the wire  50  and the capillary C pushes this molten ball against one of the bond pads  44 , thereby attaching the terminal end of the wire  50  to the board  40 , as shown. Thereafter, the capillary C spools out a length of the wire  50 , presses the wire against one of the terminals  24  on the die  20 , and bonds the wire to the terminal  24 , e.g., by ultrasonic or thermosonic welding.  
         [0006]     The capillaries C commonly used in the field have precisely shaped ends to insure good bonding of the wire to the bond pads  44  of circuit boards  40  and the terminals  24  of dies  20 . Most capillaries C also taper outwardly moving away from this tip. As shown in  FIG. 1 , the capillary C will thus have an appreciable width W that must fit between the bond wire  50  in the capillary C and the top corner of the die  20 . This width W will depend, in part, on the height H of the front surface  22  of the die  20  from the front side  42  of the circuit board  40 . For one common type of semiconductor die, the height H is usually on the order of 100 μm. In such circumstances, the distance D between the edge of the die  20  and the bond pad  44  is over 0.2 mm, typically 0.5 mm or more, to accommodate the width W of the capillary C without unduly risking damage to the die  20 . Conventional designs such as those shown in  FIG. 1  often include bond pads  44  on opposing sides of the die  20 . Hence, the same space D must be provided on both sides of the die  20 , adding an additional 0.4 millimeters or more, typically at least 1 millimeter, to the lateral dimension of the final diced and packaged microelectronic component.  
         [0007]     Market pressures to reduce the size of electronic devices, e.g., mobile telephones and hand-held computing devices, place a premium on the space or “real estate” available for mounting microelectronic components on a printed circuit board or the like. Similar density pressures also impact manufacturers of computers and other larger-scale electronic devices. An extra half of a millimeter per package  10 , for example, can significantly add to the dimensions of an array of packaged memory chips, for example. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]      FIG. 1  is a schematic cross-sectional view of a conventional packaged microelectronic component assembly at one stage of manufacture.  
         [0009]      FIG. 2  is a schematic top view of a substrate including a plurality of microelectronic component assemblies in accordance with one embodiment of the invention.  
         [0010]      FIG. 3  is a schematic cross-sectional view of one of the microelectronic component assemblies of  FIG. 2  taken along line  3 - 3  in  FIG. 2 .  
         [0011]      FIG. 4  is a schematic isolation perspective view of a portion of  FIG. 3 .  
         [0012]      FIG. 5  is a schematic top view of a substrate including a plurality of microelectronic component assemblies in accordance with another embodiment of the invention.  
         [0013]      FIG. 6  is a schematic cross-sectional view of one of the microelectronic component assemblies of  FIG. 5  taken along line  6 - 6  in  FIG. 5 .  
         [0014]      FIG. 7  is a schematic cross-sectional view of a microelectronic component assembly in accordance with an additional embodiment of the invention.  
         [0015]      FIG. 8  is a schematic cross-sectional view of a microelectronic component assembly in accordance with one more embodiment of the invention.  
         [0016]      FIG. 9  is a schematic cross-sectional view of a packaged microelectronic component assembly incorporating the microelectronic component assembly of  FIGS. 2-4 . 
     
    
     DETAILED DESCRIPTION  
       [0000]     A. Overview  
         [0017]     Various embodiments of the present invention provide various microelectronic component assemblies and methods for forming microelectronic component assemblies. The terms “microelectronic component” and “microelectronic component assembly” may encompass a variety of articles of manufacture, including, e.g., SIMM, DRAM, flash-memory, ASICs, processors, flip chips, ball grid array (BGA) chips, or any of a variety of other types of microelectronic devices or components therefor.  
         [0018]     One embodiment provides a microelectronic component assembly that includes a microelectronic component substrate having a mounting surface. The microelectronic component is mounted to the mounting surface. The microelectronic component has a terminal surface spaced outwardly from the mounting surface, first and second terminals carried adjacent the terminal surface, and a periphery including first and second sides. A first support is carried by the substrate adjacent the first side of the microelectronic component periphery and a second support is carried by the substrate adjacent the second side of the microelectronic component periphery. The second support is spaced from the first support. A first bond pad surface is supported by the first support outwardly from the mounting surface and proximate the microelectronic component terminal surface. A second bond pad surface is supported by the second support outwardly from the mounting surface proximate the microelectronic component terminal surface. A first bond wire electrically couples the first terminal to the first bond pad surface and a second bond wire electrically couples the second terminal to the second bond pad surface. In select embodiments, the first support is spaced less than 0.2 millimeters, e.g., 0.05 millimeters or less, from the first side of the microelectronic component periphery.  
         [0019]     Another embodiment of the invention provides a microelectronic component substrate that includes a body, a first support, and a second support. The body carries a circuit and has a front surface. A portion of the front surface defines a microelectronic component mounting surface having a periphery and sized to support a microelectronic component. The first support is carried by the body proximate a first side of the mounting surface periphery. The first support supports a first bond pad surface at a position spaced outwardly from the mounting surface. The first bond pad surface is electrically coupled to the circuit of the body. The second support is carried by the body at a location spaced from the first contact support and proximate a second side of the mounting surface periphery. The second contact support supports a second bond pad surface at a position spaced outwardly from the mounting surface. The second bond pad surface is electrically coupled to the circuit of the body.  
         [0020]     A method of assembling a microelectronic component assembly in accordance with still another embodiment of the invention involves juxtaposing a confronting surface of a microelectronic component with a mounting surface of a substrate, wherein the microelectronic component is positioned between a first support carried by the substrate and a second support carried by the substrate. The confronting surface of the microelectronic component is attached to the mounting surface of the substrate, thus positioning a terminal surface of the microelectronic component outwardly from the mounting surface. A first bond wire is attached to a first terminal that is carried by the microelectronic component adjacent its terminal surface and to a first bond pad surface carried by the first support at a location proximate a plane of the terminal surface. A second bond wire is attached to a second terminal that is carried by the microelectronic component adjacent its terminal surface and to a second bond pad surface carried by the second support at a location proximate the plane of the terminal surface.  
         [0021]     For ease of understanding, the following discussion is subdivided into two areas of emphasis. The first section discusses microelectronic component assemblies in accordance with selected embodiments of the invention. The second section outlines methods in accordance with other embodiments of the invention.  
         [0000]     B. Microelectronic Component Assemblies Having Elevated Wire Bond Pads  
         [0022]      FIGS. 2-8  schematically illustrate microelectronic component assemblies in accordance with selected embodiments of the invention. These microelectronic component assemblies also may be referred to herein as subassemblies, primarily because they are unlikely to be sold commercially in this state and instead represent an intermediate stage in the manufacture of a commercial device, e.g., the packaged microelectronic component assembly  105  of  FIG. 9 .  
         [0023]      FIGS. 2-4  show a microelectronic component subassembly  100  that includes a microelectronic component  120  and a substrate  140 . The microelectronic component  120  has a terminal surface  122  and a back surface  126 . The terminal surface  122  carries an array of terminals  124  that are electrically connected to an integrated circuit  125 . In the illustrated embodiment, the terminals  124  are arranged to extend along opposed, longitudinally extending sides of the microelectronic component  120 . The terminals need not be so arranged, though. For example, the terminals  124  may be aligned along or adjacent a longitudinal midline of the microelectronic component  120 .  
         [0024]     The microelectronic component  120  may comprise a single microelectronic component or a subassembly of separate microelectronic components. In the embodiment shown in  FIGS. 2-4 , the microelectronic component  120  is typified as a single semiconductor die that includes an integrated circuit  125  (shown schematically in  FIGS. 3 and 4 ). In one particular implementation, the microelectronic component  120  comprises a memory element, e.g., SIMM, DRAM, or flash memory. In other implementations, the microelectronic component  120  may comprise an ASIC or a processor, for example.  
         [0025]     The substrate  140  may include circuitry  145  (shown schematically in  FIGS. 3 and 4 ) and a front surface  142  that carries one or more microelectronic components  120 . In the illustrated embodiment, a plurality of microelectronic components  120  is mounted in an array on the substrate  140 . The substrate front surface  142  includes a microelectronic component mounting surface  144  for each microelectronic component  120 . This mounting surface  144  is sized to closely receive a microelectronic component and may be thought of as having a periphery (shown in dashed lines in  FIG. 2 ) with dimensions close to the dimensions of the microelectronic component  120  mounted thereon.  
         [0026]     The substrate  140  also includes a plurality of supports  150  that extend outwardly from adjacent areas of the front surface  142  of the substrate  140 . As shown in  FIG. 3 , these supports  150  may have a height h s  outwardly from the substrate mounting surface  144  that is about the same as the height h m  of the terminal surface  122  of the microelectronic component  120  from the mounting surface  144 . This second height h m  may include the thickness of both the microelectronic component  120  and the adhesive  135  used to attach the microelectronic component  120  to the mounting surface  144 . In one embodiment, the height h s  of each support  150  is approximately the same as the height h m  of the adjacent microelectronic component terminal surface  122 , both measured outwardly from the mounting surface  144 . As a consequence, the upper ends of each of the supports  150  may generally coincide with the plane P ( FIG. 3 ) of the adjacent component terminal surface  122 .  
         [0027]     In the embodiment of  FIGS. 2-4 , each of the supports  150  comprises a pillar that carries adjacent its outward end a bond pad  152  having a bond pad surface. These pillars  150  are typified in the drawings as rectilinear, e.g., substantially square, in cross-section, but any suitable cross-sectional shape could be used instead. As shown schematically in  FIG. 4 , the bond pads  152  carried by the supports  150  may be electrically coupled to the circuit  145  of the substrate  140 . In one embodiment, the bond pads are formed using conventional wafer-level metal patterning techniques such as those used to create integrated circuits and electrical terminals of semiconductor dies.  
         [0028]     The supports  150  may be positioned proximate the component mounting surface  144  of the substrate  140  in an array. The arrangement of the supports  150  within the array will depend on the locations of the terminals  124  of the microelectronic components  120 . In the embodiments shown in  FIGS. 2-4 , the terminals  124  may be positioned in a pair of rows that extend longitudinally adjacent opposite sides of the microelectronic component periphery. The supports  150  are similarly arranged in a pair of generally parallel, spaced-apart rows. One of these rows may extend longitudinally adjacent one side of the microelectronic component  120  and the other row of supports  150  may extend longitudinally along an opposite side of the microelectronic component  120 . As a consequence, each microelectronic component  120  is positioned between parallel rows of pillars associated with that component&#39;s mounting surface  144 .  
         [0029]     The supports  150  are spaced a distance d from the adjacent side of the microelectronic component periphery. As explained above, the distance D between the circuit board contacts  44  and the die terminals  24  in conventional microelectronic component assemblies  10  is at least 0.2 mm, typically 0.5 mm or greater. This distance D is necessary to accommodate the width W of the tip of the capillary C used to form the wire bond. Given the vertical proximity of the bond pad  152  and the component terminal surface  122  in the design of  FIGS. 2-4 , the distance d need not be large enough to accommodate the width W of the outwardly tapering portion of the capillary C. Hence, the distance d between the supports  150  and the adjacent side of the microelectronic component  120  can be less than that typically achievable in the conventional design of  FIG. 1 . In one embodiment, the distance d in  FIGS. 3 and 4  is less than 0.2 mm, e.g., about 0.05 mm or less.  
         [0030]     The conventional design of  FIG. 1  employing a distance D of about 0.2 mm will add about 0.4 mm to the overall lateral dimension of the microelectronic component assembly  10  from the outer edge of one circuit board contact  44  to the outer edge of a contact  44  on the other side of the die  20 . Embodiments of the invention may reduce this additional lateral width below 0.4 mm. For example, a distance d of about 0.05 mm or less will reduce the width of the microelectronic component assembly  100  by at least about 0.3 mm when compared to the design of  FIG. 1 . For example, two times a distance D in  FIG. 1  of about 0.2 mm is 0.4 mm, whereas two times a distance d in  FIGS. 3 and 4  of about 0.05 mm is only about 0.1 mm. Saving 0.3 mm in the width of each microelectronic component can save valuable real estate in electronic devices. If a semiconductor wafer is used as the substrate, this may also allow more microelectronic component assemblies to be produced using a single wafer.  
         [0031]     Any of a variety of common microelectronic component substrate materials may be used to form the substrate  140 . For example, the substrate may comprise a semiconductor device. In  FIG. 2 , the substrate  140  is typified as a semiconductor wafer having a plurality of microelectronic component mounting surfaces  144  arranged in an array, as noted above. In this embodiment, the supports  150  may be formed using photolithographic and etching techniques conventional in semiconductor wafer processing, for example. Briefly, this could involve depositing a photosensitive mask, selectively illuminating the mask, and selectively etching the mask to leave an area of the mask on each of the bond pads  152 . A conventional chemical or plasma etch, e.g., an anisotropic chemical etch, may be used to remove material from the exposed areas of the substrate until the supports  150  have the desired height h m  ( FIG. 4 ). Thereafter, the photomask may be removed, leaving the illustrated structure.  
         [0032]     In other embodiments, the substrate  140  may be flexible or rigid and have any desired configuration. For example, the substrate  140  may be formed of materials commonly used in microelectronic substrates such as ceramic, silicon, glass, or combinations thereof. Alternatively, the substrate  140  may be formed from an organic material. For example, the substrate  140  may have a laminate structure such as that found in BT resin, FR-4, FR-5, ceramic, and polyimide printed circuit boards. In one embodiment, the substrate  140  may be formed of a first ply or set of plies that define a first thickness t ( FIG. 3 ) and a second ply or set of plies that have a thickness equal to the height h s  of the support pillars  150 .  
         [0033]     The substrate  140  may be attached to the microelectronic component  120  by means of an adhesive  135 . In the microelectronic component assembly  100  of  FIGS. 3 and 4 , the back surface  126  of the microelectronic component  120  is attached to the mounting surface  144  of the substrate  140  with a conventional die attach paste as the adhesive  135 . Die attach pastes are commercially available from a variety of sources and often comprise a thermoplastic resin or a curable epoxy. In other embodiments, the adhesive may comprise a die attach tape, e.g., a polyimide film such as KAPTON, or any other suitable adhesive.  
         [0034]     As illustrated in  FIGS. 2 and 3 , bond wires  160  may be used to electrically couple the terminals  124  of the microelectronic components  120  with the bond pads  152  of the adjacent supports  150 .  FIGS. 2 and 3  illustrate the microelectronic component assembly  100  at a stage of manufacture in which some of the bond wires  160  have been attached, but additional bond wires would be attached when the microelectronic component assembly  100  is completed. For example, the terminals  124  of the microelectronic component  120  in  FIG. 3  can be connected to the adjacent bond pads  152  by additional bond wires (not shown).  
         [0035]      FIGS. 5 and 6  schematically illustrate a microelectronic component assembly  200  in accordance with an alternative embodiment of the invention. Some elements of this design may be analogous to elements in the embodiment of  FIGS. 2-4  and like reference numbers are used in both drawings to indicate analogous structures.  
         [0036]     The microelectronic component assembly  200  of  FIGS. 5 and 6  comprises a substrate  240  having a front surface  242  that includes a plurality of microelectronic component mounting surfaces  244  arranged in an array. Each of the mounting surfaces  244  may be sized to receive a microelectronic component  120 , which may be substantially the same as the microelectronic component  120  of  FIGS. 2-4 .  
         [0037]     One difference between the microelectronic component assembly  200  of  FIGS. 5 and 6  and the microelectronic component assembly  100  of  FIGS. 2-4  lies in the nature of the supports. In  FIGS. 2-4 , the supports  150  comprise a series of individual pillars, each of which may support as few as one bond pad  152 . In the design of  FIGS. 5 and 6 , however, each of the supports  250  is sized to support two or more bond pads  252 . Each support  250  comprises an elongate member that extends along a length of a side of the periphery of the microelectronic component  120 . For each microelectronic component  120  and its associated mounting surface  244 , one support  250  extends along a length of one side of the microelectronic component  120  or mounting surface  244  and another support  250  extends along a length of another side of the microelectronic component  120  or mounting surface  244 . The substrate  240  and its supports  250  may be formed of similar materials and using similar techniques to those discussed above in connection with the support  140  of  FIGS. 2-4 .  
         [0038]     In the illustrated embodiment, the two supports  250  associated with a single microelectronic component  120  may be generally parallel to one another and extend along opposite sides of the microelectronic component  120 . In other embodiments, the first and second supports  250  may extend along adjacent sides of the microelectronic component  120 . These supports  250  may be separate from and spaced from one another, or they may be joined to form a more continuous structure. In one embodiment (not shown), a support  250  extends along each peripheral side of each of the microelectronic components  120 , essentially bounding all four sides of the mounting surface  244  for each microelectronic component  120 . In one particular implementation, these supports are joined to form a peripheral wall-like structure that completely encloses the mounting surface  244 .  
         [0039]      FIG. 7  illustrates another embodiment of the invention. Again, aspects of this design may be similar to aspects of the microelectronic component assembly  100  of  FIGS. 2-4  and like reference numbers are used to identify analogous structures in both embodiments. The microelectronic component assembly  300  of  FIG. 7  includes a microelectronic component  120  mounted to a mounting surface (not separately illustrated) of the substrate  340 .  
         [0040]     In  FIGS. 2-6 , the supports  150  and  250  may be formed integrally with, and be a part of, the substrate  140 . The bond pads  152  carried by these supports  150  typically are formed of a different material than the bulk of the support  150 . In  FIG. 7 , the support  350  and the bond pad surface  352  are integrally formed. In particular, the support comprises a pillar  350  of conductive material, e.g., a metal, carried on a contact  348  of the substrate. The entire pillar  350  may function as a bond pad and the bond wire (not shown) may be connected directly to the outer surface  352  of the pillar  350 . The contact  348  is coupled to the circuit  345  of the substrate  340 , thereby connecting the bond wire to the circuit  345 . The pillars may be formed in a variety of ways, e.g., by applying a metal layer having the desired thickness and using conventional photomask and etch techniques to define the supports  350 .  
         [0041]      FIG. 8  schematically illustrates a microelectronic component assembly  400  in still another embodiment of the invention. Like reference numbers are used in  FIGS. 7 and 8  to indicate analogous structures. One difference between the microelectronic component assemblies  300  and  400  lies in the structure of the supports  350  and  450 . In contract to the substantially integrally formed support  350  of  FIG. 7 , the support  450  of  FIG. 8  comprises a number of separate conductive elements  354  stacked atop one another. In one design, these conductive elements  354  comprise so-called “stud bumps” formed by forming a molten ball at the end of a bonding wire and pressing the bonding wire against a surface, much as discussed above. Instead of spooling out a length of wire and bonding the opposite end to a microelectronic component terminal  124 , the wire is cut off adjacent the now-squashed metal ball. (This technique of forming a stud bump is known in the art.) A series of these bumps may be stacked atop one another relatively quickly by the capillary C to build a support  450  of the desired height.  
         [0042]     The outer surface of the outer conductive element  454  provides a bond pad surface  452  to which a bond wire may be bonded. This bond pad surface  452  may be substantially coplanar with the plane P of the microelectronic component terminal surface  122 . Achieving precise alignment of the bond pad surface  452  and the plane P is not necessary. In one embodiment, any difference in alignment between the bond pad surface and the plane P is no greater than the average thickness of two conductive element  454 , and preferably no greater than the average thickness of one conductive element  454 .  
         [0043]      FIG. 9  schematically illustrates the microelectronic component assembly  100  of  FIGS. 2-4  incorporated in a packaged microelectronic component  105 . In addition to the microelectronic component assembly  100 , this packaged component  105  includes a dielectric matrix  170  that covers at least the bond wires  160  and the bond pad surfaces ( 152  in  FIGS. 3 and 4 ) of the supports  150 . In the illustrated embodiment, the dielectric matrix  170  also covers and substantially encapsulates the front surface  142  of the substrate  140  and the microelectronic component  120 .  
         [0044]     The dielectric matrix  170  may be formed of any material that will provide suitable protection for the elements within the matrix  170 . It is anticipated that most conventional, commercially available microelectronic packaging encapsulants may be useful as the dielectric matrix  170 . Such encapsulants typically comprise a dielectric thermosetting plastic that can be heated to flow under pressure into a mold cavity of a transfer mold. In other embodiments, the dielectric matrix  170  may comprise a more flowable dielectric resin that can be applied by wicking under capillary action instead of delivered under pressure in a transfer mold.  
         [0000]     C. Methods of Manufacturing Microelectronic Component Assemblies  
         [0045]     As noted above, other embodiments of the invention provide methods of manufacturing microelectronic component assemblies. In the following discussion, reference is made to the particular microelectronic component assembly  100  shown in  FIGS. 2-4 . It should be understood, though, that reference to this particular microelectronic component assembly is solely for purposes of illustration and that the method outlined below is not limited to any particular microelectronic component assembly shown in the drawings or discussed in detail above.  
         [0046]     One method of the invention includes juxtaposing the confronting surface  126  of a microelectronic component  120  with a mounting surface  144  of the substrate  140 . In so doing, the microelectronic component  120  is positioned between two of the supports  150  carried by the substrate. The confronting surface  126  may be attached to the mounting surface  144  in any desired fashion, e.g., using a die attach paste  135  or a die attach tape.  
         [0047]     When so mounted, the terminal surface  122  of the microelectronic component  120  is spaced outwardly from the mounting surface  144 . The plane P of the terminal surface  122  is desirably proximate the location of each of the bond pads  152  of the supports  150 ; in one embodiment, the surfaces of the bond pads  152  are substantially coplanar with this plane P.  
         [0048]     A bond wire  160  may be used to couple at least one of the terminals  124  of the microelectronic component  120  to at least one of the bond pads  152 . In the illustrated embodiment, a separate bond wire couples each of the terminals  124  to a different one of the bond pads  152 . To form the microelectronic component package  105  of  FIG. 9 , the dielectric matrix  170  may be applied to the microelectronic component assembly  100 . If a number of microelectronic component assemblies  100  are formed at the same time (as illustrated in  FIG. 2 ), the matrix  170  may be applied to the front surface  142  of substrate  140  prior to dicing the substrate to produce separate packages  105 .  
         [0049]     The above-detailed descriptions of embodiments of the invention are not intended to be exhaustive or to limit the invention to the precise form disclosed above. While specific embodiments of, and examples for, the invention are described above for illustrative purposes, various equivalent modifications are possible within the scope of the invention, as those skilled in the relevant art will recognize. For example, whereas steps are presented in a given order, alternative embodiments may perform steps in a different order. The various embodiments described herein can be combined to provide further embodiments. In general, the terms used in the following claims should not be construed to limit the invention to the specific embodiments disclosed in the specification, unless the above-detailed description explicitly defines such terms.