Abstract:
Systems for organizing substrates in deposition chambers of material deposition apparatuses are disclosed. Such a system may be configured to organize a large number of substrates (e.g., electronic device subassemblies, such as circuit boards with semiconductor devices and other components secured thereto; partially assembled electronic devices; fully assembled electronic devices; etc.) in a manner that will enable concurrent deposition of material onto all of the substrates of the plurality. The system may be configured to optimize an efficiency with which the substrates are packed into the deposition chamber.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    A claim for the benefit of priority to the Feb. 18, 2014 filing date of U.S. Provisional Patent Application 61/941,350, titled TRAYS FOR ORIENTING SUBSTRATES DURING MATERIAL APPLICATION PROCESSES (“the ′350 Provisional Application”), is hereby made pursuant to 35 U.S.C. §119(e). A claim for the benefit of priority to the Aug. 24, 2014 filing date of U.S. Provisional Patent Application 62/041,083, titled RACKS FOR MATERIAL DEPOSITION APPARATUSES (“the ′083 Provisional Application”), is also made pursuant to 35 U.S.C. §119(e). The entire disclosures of the ′350 Provisional Application and the ′083 Provisional Application are hereby incorporated herein. 
     
    
     TECHNICAL FIELD 
       [0002]    This disclosure relates generally to systems for introducing substrates into apparatuses that apply materials to the substrates, or “material application apparatuses,” and, more specifically, to systems for simultaneously introducing pluralities of identical substrates into material application apparatuses. Even more specifically, this disclosure relates to systems for orienting a plurality of substrates non-horizontally to enable material to be applied to exposed surfaces of the substrates. 
       SUMMARY 
       [0003]    In one aspect, a system is disclosed that is configured to orient a plurality of substrates non-horizontally as a material is applied to the substrates. A substrate support system according to this disclosure, which is also referred to herein as a “system” and as a “tray,” is configured to be used in a deposition chamber of a material deposition apparatus, such as a deposition chamber of an apparatus for depositing protective coatings (e.g., moisture-resistant materials, such as poly(p-xylylene), or parylene; etc.) onto substrates. The system is configured to organize a plurality of substrates (e.g., electronic device subassemblies, such as circuit boards with semiconductor devices and other components secured thereto; partially assembled electronic devices; fully assembled electronic devices; etc.) in a manner that will enable concurrent deposition of material onto all of the substrates of the plurality. The system may be configured to optimize an efficiency with which the substrates are packed into the deposition chamber. 
         [0004]    In some embodiments, such a system may include a frame and a plurality of positioners. The frame may be configured to receive the positioners in a plurality of different arrangements, which may enable customization of the system for use with a particular type of substrate. In a specific embodiment, the positioners may comprise elongated positioners, and the frame may be configured to orient the elongated positioners substantially parallel to one another. The frame may have a primary orientation (e.g., horizontal, etc.), and the positioners may be configured to orient substrates transverse (e.g., non-horizontally, etc.) to the primary orientation of the frame. 
         [0005]    A frame may have dimensions (e.g., a width, a height, etc.) that enable it to be positioned within a chamber of an apparatus for applying material to one or more substrates. In some embodiments, the frame may be configured to be placed directly within the chamber of the material application apparatus. In other embodiments, the frame may be configured to be assembled with a tray, a rack or another apparatus that, in turn, is configured to be placed within the chamber or to be assembled with another apparatus (e.g., a cart, etc.) that is configured to be placed within the chamber. See, e.g., U.S. Patent Application Publication 2013/0286567 of Sorenson et al. and U.S. Patent Application Publication 2013/0251889 of Cox et al., the entire disclosures of both of which are hereby incorporated herein. 
         [0006]    The frame may be configured in a manner that enables the selective arrangement of positioners over the frame. Thus, the frame may include engagement elements that engage corresponding features of positioners of the system. In some embodiments, the engagement elements of the frame and the corresponding features of the positioners may releasably engage one another. In other embodiments, the engagement elements of the frame and the corresponding features of the positioners may permanently engage one another. 
         [0007]    A positioner may include a plurality of protruding elements, with receptacles defined between each pair of adjacent protruding elements. In some embodiments, the distance across such a receptacle, or the distance between adjacent protruding elements of a positioner may be the same as or substantially the same as the thickness of a portion of a substrate to be positioned within the receptacle. Thus, the adjacent protruding elements may engage that portion of the substrate by way of an interference fit; i.e., by contacting opposite sides of the portion of the substrate in such a way that the adjacent protruding elements securely hold the portion of the substrate in place within the receptacle. A positioner with adjacent protruding elements that are positioned in such a way is referred to herein as “a retaining positioner.” 
         [0008]    In other embodiments of positioners, the distance adjacent protruding elements are spaced apart from one another may exceed the thickness of a portion of a substrate to be positioned between the adjacent protruding elements. Protruding elements that are spaced apart from one another in such a way may hold a portion of a substrate located therebetween in a non-horizontal orientation without engaging the portion of the substrate located between the adjacent protruding elements. Such an arrangement may also prevent adjacent substrates from contacting one another. In embodiments where adjacent protruding elements are spaced a sufficient distance apart from one another, material may be applied to the portion of the substrate located between the adjacent protruding elements. A positioner with protruding elements that do not engage a substrate is referred to herein as a “receiving positioner.” 
         [0009]    A set of positioners may be arranged in a manner that enables a plurality of substrates to be arranged adjacent to one another in a series (e.g., in a column, etc.). In some embodiments, such a set may include two or more positioners that are spaced apart a sufficient distance to support the substrates in non-horizontal orientations (e.g., in partially upright orientations, in upright orientations, in substantially vertical orientations, in vertical orientations, etc.). The distance(s) that adjacent positioners are spaced apart from each other may be defined by the frame (e.g., by engagement elements of the frame that engage complementarily configured features of the positioners, etc.). The two or more positioners of a set may be the same (e.g., all retaining positioners, all receiving positioners, etc.) or a plurality of different types of positioners may be used together. 
         [0010]    The positioners may be configured to orient substrates in a manner that optimizes the application of material to the substrates. Without limitation, the positioners may be configured to orient substrates in such a way that minimizes obstruction of the flow of material through a chamber, or even in a manner that enhances the way material flows through the chamber. The positioners may orient substrates to maximize the area of the surface of each substrate that is exposed to the material to be applied thereto. Of course, positioners that are configured to provide other advantageous substrate arrangements are also within the scope of the disclosed subject matter. 
         [0011]    In other embodiments, a system for organizing substrates may include a stamped sheet of a bendable material (e.g., steel, aluminum, etc.), in which a plurality of positioners are stamped, and selected positioners may be bent into upright orientations. Of course, other positioners may lie flat, and remain unused. All of the positioners of such an embodiment of a system for organizing substrates may be identical to one another. Alternatively, the system may include positioners with two or more different configurations. Selection of the positioners that are bent to upright orientations may be based upon the sizes and/or shapes substrates that are to be introduced into the deposition chamber of a material deposition apparatus, the desired density of and spacing between the substrates and/or any of a variety of other factors. 
         [0012]    Less customizable embodiments of systems for organizing substrates within deposition chambers are also disclosed, in which the relative positions of positioners are fixed or substantially fixed relative to one another. The positioners of such a system may be welded, soldered, bolted or otherwise fixed in place relative to one another. 
         [0013]    In other embodiments, a system that organizes substrates within a deposition chamber may be configured to hang the substrates in a vertically integrated manner to place the substrates in close proximity to one another. Such a system may also be customizable. 
         [0014]    Other aspects of the disclosed subject matter include methods that relate to the disclosed systems. As a few non-limiting examples, methods for arranging positioners on a frame to define a system for carrying a plurality of substrates, methods for using such a system to organize substrates, methods for introducing substrates into an apparatus for used applying material the substrates and methods for applying material to a plurality of substrates are disclosed. 
         [0015]    Other aspects, as well as features and advantages of various aspects, of the disclosed subject matter will become apparent to those of ordinary skill in the art though consideration of the ensuing description, the accompanying drawings and the appended claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]    In the drawings: 
           [0017]      FIGS. 1-3  are perspective views of an embodiment of a system that includes a frame and a plurality of positioners organized on the frame, with  FIGS. 1 ,  2  and  3  showing the positioners in different spacing arrangements; 
           [0018]      FIG. 4  provides an end view of an embodiment of elongated member of the frame shown in  FIGS. 1-3 ; 
           [0019]      FIG. 4A  illustrates another embodiment of an end of a frame that may be used in a system for supporting substrates; 
           [0020]      FIG. 5  shows an embodiment of system carrying a plurality of substrates, all of the same type; 
           [0021]      FIGS. 6 and 7  are partial orthogonal views of another embodiment of a system for organizing substrates, in which the substrates may hang under force of gravity; 
           [0022]      FIGS. 8 and 9  illustrate an embodiment of a base of the system shown in  FIGS. 6 and 7 ; 
           [0023]      FIGS. 10 and 11  depict an embodiment of a carrier of the system shown in  FIGS. 6 and 7 ; 
           [0024]      FIGS. 12-14  show an embodiment of a system with a pair of positioners whose positions are fixed relative to one another; 
           [0025]      FIGS. 15 and 16  illustrate an embodiment of a system that includes a main body with positioners that are configured to be selectively lifted and bent into upright positions for use in supporting substrates; and 
           [0026]      FIGS. 17-20  illustrate various embodiments of racks with which systems for organizing substrates may be assembled before a rack and the systems carried thereby are introduced into a deposition chamber of a material deposition apparatus. 
       
    
    
     DETAILED DESCRIPTION 
       [0027]      FIGS. 1-5  depict an embodiment of a system  10  for orienting a plurality of substrates  60  ( FIG. 5 ) for the application of a material, such as a protective coating (e.g., a poly(p-xylylene) (i.e., parylene), etc.) thereto. The system  10  includes a frame  20  and a plurality of positioners  40 ,  50 . 
         [0028]    In  FIGS. 1-3 , the frame  20  includes (or consists essentially of or consists of) elongated members  22 ,  24 ,  26 ,  28  that are secured to one another in a manner that defines the lateral extent, or outer periphery of the system  10 . Thus, material may pass through the illustrated embodiment of the frame  20 . Alternatively a frame may include a planar member, which may include one or more apertures to enable material to pass therethrough, or which may be substantially solid or even solid. 
         [0029]    In addition, as shown in  FIGS. 4 and 4A , the frame  20  or, more specifically, the elongated elements  22  and  26  of the embodiment of frame  20  shown in  FIGS. 1-3 , may include engagement elements  21 ,  21 ′. In the embodiment shown in  FIG. 4 , the engagement elements  21  may comprise notches that receive corresponding features (e.g., the bottom edges, complementarily configured notches, etc.) of a positioner  40 ,  50  ( FIG. 1 ). The engagement elements  21  may enable the elongated elements  22  and  26  and the positioners  40 ,  50  to be assembled in a variety of different ways, including the arrangements shown in  FIGS. 1-3  and in any of a variety of other ways that will become apparent to those of ordinary skill in the art from this disclosure. 
         [0030]    In the embodiment depicted by  FIG. 4A , the engagement elements  21 ′ comprise slots in the elongated elements  22  and  26 . These slots may be configured to receive the ends  41 ,  51  or features on the ends  41 ,  51  (e.g., tabs, etc.) of the positioners  40 ,  50 . The number and positions of the engagement elements  21 ′ may provide for wide variety in the manner in which the positioners  40 ,  50  are organized relative to the elongated elements  22  and  26 . 
         [0031]    Of course, other embodiments of engagement elements are also within the scope of this disclosure. 
         [0032]    With returned reference to  FIG. 1 , a frame  20  may be configured to receive a plurality of sets  30  of positioners  40 ,  50 . More specifically,  FIG. 1  depicts an embodiment in which each set  30  includes four positioners  40 ,  50 , with each positioner  40 ,  50  comprising an elongated element and all of the positioners  40 ,  50  being arranged parallel to one another. The two outermost positioners  40  comprise receiving positioners and, thus, including protruding elements  42  that are spaced apart from one another sufficient distances to define receiving receptacles  44  that will receive portions of substrates without engaging the substrates. A pair of retaining positioners  50  is located between the receiving positioners  40  of the set  30 . Retaining receptacles  54  are defined between adjacent protruding elements  52  of each retaining positioner  50 . The protruding elements  52  that define each retaining receptacle  54  are spaced apart a distance that will enable the retaining receptacle  54  to receive a portion of a substrate that is to be held in place by the system  10 , while opposed surfaces of the adjacent pair of protruding elements  52  engage surfaces of the portion of the substrate located therebetween to hold the substrate in a non-horizontal orientation. 
         [0033]    In  FIGS. 2 and 3 , arrangements of the system  10  that differ slightly from the arrangement shown in  FIG. 1  are shown. In  FIG. 2 , each receiving positioner  40  and the adjacent retaining positioner  50  of each set  30  are spaced apart a distance that is slightly greater than the spacing between the receiving positioners  40  and their corresponding retaining positioners  50  in the arrangement depicted by  FIG. 1 . That spacing is even greater in  FIG. 3 . The different spacing enables the system  10  to accommodate substrates of different dimensions. Without limitation, the arrangement depicted by  FIG. 1  may accommodate relatively short substrates, while the arrangement depicted by  FIG. 2  may accommodate medium length substrates and the arrangement shown in  FIG. 3  may accommodate long substrates. 
         [0034]    Of course, other arrangements of positioners  40 ,  50 , are also within the scope of this disclosure. As an example, a single retaining positioner  50  may be placed between two receiving positioners  40 . As another example, retaining positioners  50  may be placed at the outside locations of a set  30 , with one or more receiving positioners  40  placed therebetween. In other optional arrangements, a retaining positioner  50  may be placed on one side of a set  30 , while a receiving positioner  40  may be located at the opposite side of the set  30 . In other arrangements, a set  30  may include only receiving positioners  40  or only retaining positioners  50 . 
         [0035]      FIG. 5  illustrates an embodiment of a system  10  in which three sets  30  of positioners  40 ,  50  are arranged to hold a plurality of elongated substrates  60  in upright orientations. As illustrated, adjacent substrates  60  are lined up in a spaced-apart fashion, with each set  30  of positioners  40 ,  50  organizing a plurality of substrates  60  in series; three adjacent columns in the depicted embodiment. The substrates depicted by  FIG. 5  are electronic device subassemblies that include components carried by elongated, flexible substrates that have not yet been assembled with housings, input/output features (e.g., display screens, buttons, etc.) or the like. 
         [0036]    Turning now to  FIGS. 6-11 , an embodiment of a system  110  is shown that is configured to hang substrates  160  in a vertically integrated manner to position the substrates in close proximity to one another when the system  110  and the substrates  160  are placed within a deposition chamber of a material deposition apparatus. 
         [0037]      FIGS. 6 and 7  illustrate an embodiment of a system  110  that is configured to carry a plurality of substrates  160 . The system  110  includes an embodiment of a frame that is referred to herein as a “base  120 ” and an embodiment of positioner that is referred to herein as a “carrier  130 .” The carrier  130  is configured to hang the substrates  160 . More specifically, the carrier  130  may include a plurality of hanging posts  134 , which may be configured to be received by apertures, slots, recesses or other features of the substrates  160  and to enable the substrates  160  to hang under force of gravity. The carrier  130  may also include a plurality of support posts  135 , each of which may be configured to receive or otherwise engage another portion of a substrate  160  to prevent the substrate  160  from swinging as it hangs from one or more hanging posts  134 . 
         [0038]    The system  110  may be configured to carry the substrates  160  so that substantially all of their surfaces are exposed (e.g., other than those portions of the substrates  160  that contact a hanging post  134 , a support post  135  or another portion of the system  110 , etc.). In some embodiments, the system  110  may be configured to organize substrates  160  in such a way that they are placed adjacent to one another, or juxtaposed, in parallel relation to one another. 
         [0039]      FIGS. 8 and 9  show an embodiment of the base  120  of the system  110  shown in  FIGS. 6 and 7 . The base  120  may be configured to be positioned on a tray or a rack that may be positioned within a deposition chamber of a material deposition apparatus, such as an apparatus that is configured to deposit parylene or other materials onto one or more substrates  160  ( FIGS. 6 and 7 ). In the illustrated embodiment, the base  120  includes a central member  122  and feet  128  at opposite sides or ends of the central member  122 . The central member  122  may be configured to support one or more carriers  130  of the system  110 , while the feet  128  may be configured to elevate the central member  122  and any carrier(s)  130  ( FIGS. 6 and 7 ) thereon to a height above a surface on which the feet  128  rest to enable substrates  160  ( FIGS. 6 and 7 ) to hang freely. 
         [0040]    In the specific embodiment depicted by  FIGS. 8 and 9 , the central member  122  of the base  120  may comprise an elongated member with a pair of spaced apart side elements  123 . In addition, one or more transverse elements  124  may extend across a width of the central member  122 , or transverse to a length of the central member  122 . The embodiment of base  120  depicted by  FIGS. 8 and 9  includes a central member  122  with four transverse elements  124 . 
         [0041]    The side elements  123  and any transverse elements  124  of the central member  122  of the base  120  may define one or more receptacles  126  in the central member  122 . Each receptacle  126  may be configured to receive and a carrier  130  ( FIGS. 6 ,  7 ,  10  and  11 ) or a portion thereof, and to support the carrier  130  and any substrates  160  ( FIGS. 6 and 7 ) hanging therefrom. As illustrated by  FIGS. 6 and 7 , the receptacles  126  may receive a majority of a carrier  130 . In some embodiments, the receptacle(s)  126  may be configured to receive any of a variety of different configurations of carriers  130 ; e.g., carriers  130  that are configured to arrange substrates  160  in different ways or carriers  130  that are configured to hold different configurations of substrates  160 . 
         [0042]      FIGS. 10 and 11  illustrate an embodiment of a carrier  130  that may be used with the base  120  shown in  FIGS. 8 and 9 . The carrier  130  may include two side elements  131  and  133  that meet at a central location  132 . The central location  132  and the side elements  131  and  133  may extend along the length of the carrier  130 . The side elements  131  and  133  may be configured to rest upon side edges of a receptacle  126  ( FIGS. 8 and 9 ) of the base  120  of the system  110 . The side elements  131  and  133  may diverge from one another, or be arranged relative to one another, at the central location  132 , at an angle of less than 180°. The angle at which the side elements  131  and  133  are arranged may enable substrates  160  ( FIGS. 6 and 7 ) to be placed in a deposition chamber of a material deposition apparatus with a desired packing efficiency (e.g., number of substrates per volume, etc.). In some embodiments, the carrier  130  may be configured in such a way that the angle between its side elements  131  and  133  may be adjusted. 
         [0043]    The hanging posts  134  and the support posts  135  protrude from outer edges of the side elements  131  and  133  of the carrier  130 . Each hanging post  134  may be configured to be received by an aperture in a substrate  160  ( FIGS. 6 and 7 ) and may, therefore, carry the substrate  160 , such as a circuit board or a subassembly of an electronic device, without contacting any of its major surfaces (e.g., its top surface, its bottom surface, etc.). The support posts  135  may be similarly configured, and may merely make contact with a small portion, or point, of an edge of a substrate  160 . 
         [0044]    In embodiments of the system  110  where the base  120  ( FIGS. 6-9 ) includes one or more transverse elements  124  ( FIGS. 6-9 ), the carrier  130  may include a corresponding number of transverse slots  136 . Each transverse slot  136  may be configured to receive a transverse element of the base  120 , as shown in  FIGS. 6 and 7 . Accordingly, each transverse slot  136  may extend across the central location  132  of the carrier  130 , and into central portions of each side element  131  and  133  of the carrier  130 . The transverse slots  136  of the carrier  130  and the transverse elements  124  of the base  120  may be configured to cooperate with one another in a manner that enables proper positioning of the carrier  130  relative to the base  120  and/or in a manner that stabilizes the carrier  130  and any substrates  160  ( FIGS. 6 and 7 ) hanging therefrom. 
         [0045]    Another embodiment of system  210  for organizing substrates  260  is depicted by  FIGS. 12-14 . The system  210  shown in  FIGS. 12-14  is configured to orient a plurality of substrates  160  in upright orientations. The system  210  includes a base  220  with a pair of positioners, which are referred to as “side elements  222 ,” that may be oriented parallel to one another and at least one cross member  221  extending between the side elements  222  to hold the side elements  222  in place relative to one another. 
         [0046]    Each side element  222  may include a plurality of notches  225  defined in its upper edge  223 . The notches  225  may extend downward into an upper portion  224  of the side elements  222 . Each notch  225  may be configured to hold a corresponding portion of a substrate  260  in a manner that will enable the substrate  260  to be oriented in a non-horizontal or upright orientation while making minimal contact with the substrate  260 . 
         [0047]    Each corresponding pair of notches  225  (e.g., notches  225  that are aligned, side-to-side, etc.) may define a slot  226 . Each slot  226  is (and the notches  225  that define that slot  226  are) configured to receive an edge of a substrate  260 , such as the circuit board of an electronic subassembly, and to collectively support the substrate  260 . The slots  226  may be configured, positioned and oriented to arrange the substrates  260  in a desired manner. As illustrated by  FIGS. 12-14 , the slots  226  may be configured, positioned and oriented to arranged the substrates  260  in upright orientations, parallel and adjacent to one another. In addition, since the notches  225  are configured to establish minimal contact with the surfaces of the substrate  260 , the slots  226  may enable exposure of substantially all surfaces of the substrate  260 . 
         [0048]      FIGS. 15 and 16  illustrate an embodiment of system  310  for arranging or organizing substrates (not shown) onto which a material is to be deposited. In  FIG. 15 , the system  310  is in a flat orientation. As illustrated, the system  310  includes a main body  320  with a plurality of positioners  332 ,  334  that have been cut, or punched, from the main body  320 . All of the positioners  332 ,  334  of the system  320  may have the same configuration as one another or, as illustrated, the system may include two or more different configurations of positioners  332 ,  334 . 
         [0049]    The material from which the system  310  is formed may enable the positioners  332 ,  334  to be selectively lifted, or bent, to raised orientations, as shown in  FIG. 16 . Without limitation, the system may be formed from a metal or a metal alloy (e.g., a steel, etc.). Selection of the positioners  332 ,  334  that are to be lifted may be based on the size(s) and/or configuration(s) of substrates that are to be supported (e.g., in non-horizontal or at least partially upright orientations, etc.), the desired spacing between adjacent substrates, the orientations in which the substrates are to be supported and/or any of a variety of other factors. 
         [0050]    A system for organizing substrates according to this disclosure may be made from any of a variety of suitable materials. As indicated previously, a bendable material, such as a metal or a metal alloy may be used to form some embodiments of systems, or at least some of the elements thereof. 
         [0051]    The material from which a system or its elements is formed may comprise an electrostatic discharge or electrostatic dissipative (ESD) material. ESD materials are configured not to collect static electricity and, therefore, may prevent the potentially damaging discharge of static electricity onto or into the substrates that they may carry. Thus, the use of ESD materials in systems according to this disclosure may prevent damage to sensitive electronic devices and their components. Examples of ESD materials include, but are not limited to, a variety of plastics. 
         [0052]    In some embodiments, the material(s) from which the elements of a system of this disclosure are formed may enable the system to be made inexpensively. As an example, the embodiment of system  10  illustrated by  FIGS. 1-5  and described in reference to those drawings may comprise elements (e.g., elongated members  22 ,  24 ,  26 ,  28 ; positioners  40 ,  50 ) that are made by injection molding processes. The use of plastics to form these elements may enable them to be snapped together in a desired arrangement. Such a disposable system may be used once or a few times (e.g., until material build-up becomes undesirably thick, etc.), and then discarded. 
         [0053]    In other embodiments, a system according to this disclosure may be made from a material that is more suited for permanent use. Such a material may withstand repeated cycles of use (e.g., material deposition, etc.) and cleaning (e.g., removal of material buildup by mechanical processes and/or chemical processes, etc.), as well as preventative maintenance on the system or any of its elements. 
         [0054]    As indicated previously herein, a system according to this disclosure (e.g., system  10 ,  110 ,  210 ,  310 , etc.) may be introduced directly into a deposition chamber of a material deposition apparatus, or it may be assembled with a rack.  FIGS. 17-20  illustrate various non-limiting embodiments of racks. 
         [0055]    The rack  500  of  FIG. 17  includes a frame  510  with a base  512  and a plurality of upright elements  514  that extend vertically from the base  512 . Adjacent pairs of upright elements  514  form ends  516  of the frame  510 . Horizontal elements  518  extend across each end  516  of the frame  510 , from one upright element  514   a  to the other upright element  514   b  at that end  516 . Each horizontal element  518  may extend laterally toward an interior of the frame  510 , which may enable that horizontal element  518  to support an edge of a system, or a tray, for arranging a plurality of substrates. Accordingly, a corresponding pair of horizontal elements  518 , which may be located on opposite ends  516  of the frame  510 , may be configured to completely support a tray that has been introduced in a horizontal orientation or in a somewhat horizontal orientation between the ends  516  of the frame  10 . In the depicted embodiment, the frame  510  includes a plurality of corresponding pairs of horizontal elements  518 ; which may enable a plurality of trays to be stacked on and carried by the frame  510 . 
         [0056]    In addition to the frame  510 , the rack  500  shown in  FIG. 17  includes a pair of axles  520  associated with the base  512  of the frame  510  and wheels  522  at the ends of the axles  520 . 
         [0057]    The rack  500 ′ shown in  FIG. 18  is configured similarly to the rack  500  of  FIG. 17 , but lacks axles  520  and wheels  522 . 
         [0058]      FIG. 19  illustrates an embodiment of a rack  500 ″ that includes a frame  510 ″ with a base  512 ″ and upright elements  514 ″ that define ends  516 ″ of the frame  510 ″. In addition, the frame  510 ″ includes a plurality of intermediate upright elements  515 ″, which may be positioned between the upright elements  514 ″ and are positioned between the ends  516 ″ of the frame  510 ″. One or more groups  517 ″ of intermediate upright elements  515 ″ may be arranged linearly and, in some embodiments, each group  517 ″ may be oriented parallel to an end  516 ″ of the frame  510 ″. 
         [0059]    Each group  517 ″ of intermediate upright elements  515 ″ may carry a plurality of horizontal elements  518 ″, and these horizontal elements  518 ″ may extend laterally from both sides of the intermediate upright elements  515 ″. Each horizontal element  518 ″ may be positioned at an elevation along the upright elements  515 ″ that corresponds to an elevation of an opposed horizontal element  518 ″ on an adjacent end  516 ″ of the frame  510 ″ or on an adjacent group  517 ″ of intermediate upright elements  515 ″ of the frame  510 ″. Such an arrangement may enable a corresponding pair of horizontal elements  518 ″ to support a tray. In addition, such an arrangement may enable two or more trays to be supported at a same elevation of the frame  510 ″. 
         [0060]      FIG. 20  depicts an embodiment of rack  500 ′″ with a frame  510 ′″ that includes a base  512 ′″ and a plurality of upright elements  514 ′″, or posts, that extend upwardly from opposite sides of the base  512 ′″ and that define ends  516 ′″ of the frame  510 ′″. In the depicted embodiment, each end  516 ′″ includes a series of upright elements  514 ′″. Corresponding pairs  517 ′″ of upright elements  514 ′″ are located on opposite ends  516 ′″ of the frame  510 ′″ from one another. Each corresponding pair  517 ′″ of upright elements  514 ′″ may be configured for assembly with one or more rails  530 ′″ of the rack  500 ′″. 
         [0061]    Each rail  530 ′″ may comprise an elongated element with an aperture  534 ′″ adjacent to each of its ends  531 ′″. Each aperture  534 ′″ may be configured to receive an upright element  514 ′″. At opposite sides of each aperture  534 ′″, and on opposite sides  532 ′″ of the rail  530 ″, the rail  530 ′″ may include tabs  536 ′″ that are oriented to engage the upright element  514 ′″ that extends through each aperture  534 ′″ in a manner that will maintain a vertical position of the rail  530 ′″ along the height of the vertical element  514 ′″ under the weight of the rail  530 ′″ and under the weights of any substrates (not shown) that are at least partially carried by the rail  530 ′″. At intermediate locations  537 ′″, each rail  530 ′″ may include a plurality of substrate engagement features  538 ′″, which may be configured to receive an edge of a substrate (e.g., a printed circuit board, etc.). In some embodiments, a substrate may be held in place simply by positioning two rails  530 ′″ apart from one another by a distance that is slightly less than a corresponding dimension across the substrate, in which case opposite edges of the substrate may abut against and be held in place between the sides  532 ′″ of the adjacent rails  530 ′″. 
         [0062]    Such an embodiment of cart  500 ′″ allows for customization in the heights at which rails  530 ′″ may be positioned, the vertical spacing between two adjacent rails  530 ′″ and the lateral spacing between two adjacent rails  530 ′″. Thus, the height and/or width of each receptacle of the cart  500 ′″ may be customized. 
         [0063]    Although the foregoing disclosure provides many specifics, these should not be construed as limiting the scope of any of the ensuing claims. Other embodiments may be devised which do not depart from the scopes of the claims. Features from different embodiments may be employed in combination. The scope of each claim is, therefore, indicated and limited only by its plain language and the full scope of available legal equivalents to its elements.