Abstract:
A component tray system comprises a component tray having pockets, such as a standard JEDEC tray, and a thermoformed sheet removably attached to either a top or a bottom surface of the tray. The sheet includes thermoformed protrusions for altering at least the depth of the pockets. During manufacture of components, first components of a first size, such as bare substrates, are loaded into the pockets in the tray and held securely in place by the protrusions of the sheet. After a manufacturing operation, the first components are transformed into second components, larger than the first components. The sheet is removed so that these larger second components can be accommodated in the pockets. This arrangement provides that a single tray can be used throughout a manufacturing process, yet can be adapted to snugly accommodate components of varying sizes throughout.

Description:
BACKGROUND TO THE INVENTION  
       [0001]    Trays made from injection moulding are commonplace in the Integrated Circuit (IC) and semiconductor industries for transporting sensitive components. These trays are covered by various industry standards, such as JEDEC, EIAJ, EIA and others. 
         [0002]    The trays are manufactured using injection moulding in various polymers, for example, PPO, PPE, PP, PC, PSU, PES, PAS and ABS. The polymers are usually filled to provide strength and conductivity. Various materials are often used such as talc, carbon fibre, carbon powder, metal fibre and the other usual polymer fillers. 
         [0003]    The most common use of the trays is in transporting and protecting the components through the stages of assembly, test and distribution. Each tray contains pockets, each pocket designed to accept a component. The component sits securely in the pocket, with as little free movement as possible. Within each tray, the pockets are arranged in a rectangular matrix and with a regular pitch, according to the standard, in order to facilitate robot pick and place operations. A tray will typically be able to hold between 1 and 2,500 components, depending on the size of the component and the pitch of the rectangular matrix. New trays are often designed for every requirement, e.g. component size and type. 
         [0004]    Each tray has features defining pockets on both the top and bottom surfaces. In this way a single tray can securely hold a component in X and Y planes, to present the component for inspection or processing, in a “live bug” or “dead bug” orientation, depending on which side of the tray is used to hold the component. 
         [0005]    Each tray is designed so as to be static dissipative or conductive. They conduct electrically to a certain specification and will dissipate static charges, thereby protecting the components stored within the pockets from the adverse effects of any static charges. 
         [0006]    So far, the component trays have been discussed individually. When used in combination, two similar trays can provide enhanced transport protection by creating a 3D enclosure surrounding the component. The pocket on the bottom side of the first tray cooperates with the pocket on the facing top side of the second tray, each pocket thus being one half of the whole pocket or 3D enclosure surrounding the component. To avoid ambiguity, the whole pocket defined by the cooperative pockets of the top and bottom surfaces of adjacent trays will hereafter be referred to as the 3D enclosure. Two trays, in a stacked pair, thus provide transport protection in both horizontal and vertical planes. 
         [0007]    When designing these injection moulded trays, the size of the pocket must conform as closely as possible to the size of the component it is designed to carry. In this way, the free movement of the component is reduced in both horizontal and vertical directions, preventing damage to the component. However, in order to accommodate manufacturing tolerances both of the components and the trays, the pockets are designed to be slightly larger than the components they are designed to carry. There should be free play between the component and the pocket inner walls. The oversized pockets are sized in such a way that the component does not fall from any seating ledges that may be present in the pocket due to too wide a gap and is not prevented from fully going down into the pocket. In general, all pocket designs incorporate a taper or draft angle on the walls (whether by intention or by way of the injection molding process). The molding process necessitates a usual draft taper of 5 degrees, and anything larger than that is intentional design. The wall taper ensures that the component automatically self-aligns or self-centers, and/or falls squarely into the central portion of the pocket and onto the seating ledges, where provided. 
         [0008]    Typically, one tray is designed to fit one specific type or size of component. Some trays however, are designed to protect multiple types and sizes of component. As the tray system through the 3D enclosures provides 3-dimensional protection, to protect multiple components compromises must be made. These include an inefficient use of available space, too much free movement of the component within the pockets or 3D enclosures thus affording less protection to the component, or a loss of rigidity of the tray, again decreasing the afforded protection. 
         [0009]    In some cases, the size of the component will vary during different stages of production as they progress down the assembly line process, from the addition or assembly of sub-components and materials that add to or subtract from the initial component. The tray must be able to adequately protect the largest size of component during production, however must also provide adequate protection during smaller phases. Manufacturing multiple trays for each stage is not only cost intensive but also space consuming and inconvenient in terms of having to use separate trays for each stage. 
         [0010]    Various solutions have been proposed to counteract this issue, each with inherent downfalls. One method, as described in U.S. Pat. No. 6,612,442, is to manufacture the trays using a thermoforming process, rather than injection moulding. The trays provide storage and cost savings over injection moulded trays, however suffer from a lack of rigidity inherent in thermoformed products. 
         [0011]    An injection moulded peripheral frame can be used to provide a modicum of rigidity, as is also described in U.S. Pat. No. 5,547,082. These solutions suffer from a tendency for the pockets to lose their shape. By using a peripheral, featureless frame, the thermoformed sheet is not held securely and the sheet can ‘sag’, moving away from the sheet&#39;s restraining points. Protection for the components is thus compromised during transport and use, especially when the tray is used singly and not as a stacked pair. 
         [0012]    Other solutions, such as US 2005/0072714 and US 2005/0072715, use a featureless injection moulded base tray as mentioned above, but use an injection moulded insert to provide the various pocket sizes required to house the component. Although these inserts provide a removable method of altering the pocket size for the intended purpose, they are expensive to produce, slow to design and manufacture and require a large amount of storage space. 
         [0013]    Other methods of transporting components can be used such as tubes and carrier tape and reel, but these do not provide the protection and easy accessibility of the conventional tray system. 
       SUMMARY OF THE INVENTION 
       [0014]    According to a first aspect of the present invention, there is provided a component tray system, the system comprising:
       a tray having one or more pockets, the or each pocket adapted to receive at least one component; and,   a removable, thermoformed sheet adapted to cooperate with said tray to reduce at least the depth of said one or more pockets.       
 
         [0017]    This provides the portability and security of a standard or common component tray system but is capable of easily receiving a plurality of different sized components for each purpose required. With the addition or removal of the thermoformed sheet, the dimensions of the or each pocket for receiving the components can be altered, thereby providing a carrier for components of differing sizes without compromising transport protection. 
         [0018]    Moreover, the costs of providing this uncompromised transport protection are reduced when compared with manufacturing a new tray with the alternative pocket dimensions. The time associated with manufacturing and inserting a replacement sheet is also markedly reduced. 
         [0019]    Typically, the tray has a top surface and a bottom surface. The pockets may be defined on either or both of the top and bottom surfaces, in which case the thermoformed sheet is adapted to cooperate with the respective top or bottom surface. 
         [0020]    The component tray system may further comprise a second thermoformed sheet adapted to cooperate with the other of the top surface or the bottom surface. Alternatively, the thermoformed sheet may be adapted to cooperate with both the top and bottom surfaces. 
         [0021]    In one embodiment, the thermoformed sheet is conformal, so as to conform with the tray—typically with the top and/or bottom surface, as discussed immediately above. In this way, the rigidity of the sheet is reinforced by the tray and the sheet is held securely to the tray. 
         [0022]    Preferably, the thermoformed sheet includes protrusions, such as bumps, studs, bosses, stand-offs, platforms or spikes to vary the profile of the sheet, thus to reduce at least the depth of said one or more pockets. These protrusions negate any potential problems caused by inaccuracy in the manufacturing process and more control over the size of the pockets is possible than simply varying the thickness of the thermoform sheet. In addition, the protrusions may also reduce the width of said one or more pockets. Optionally, the protrusions are positioned so as to contact only non-fragile portions of the at least one component when, in use, the tray is moved. In this way, the essential, sensitive portions of the component are thus left untouched and are therefore afforded greater protection. 
         [0023]    The thermoformed sheet may include indented portions, such as channels, and/or apertures, such as slots or holes. These indented portions and/or apertures can cooperate with pocket-defining features of the tray, in order to only vary the dimensions in one or two directions. The indented portions and/or apertures can also cooperate with the electrical contact surface portions of the components to avoid contact between the sheet and those delicate portions. 
         [0024]    The thermoformed sheet may be retained in registration with the tray by cooperative interengagement of tray features with corresponding features on the sheet. In one embodiment, the cooperative interengagement comprises a snap-fit, such as between pocket-defining features of the tray and corresponding cooperative apertures in the sheet. In another embodiment, the cooperative interengagement comprises a snug fit, such as through frictional interference between pocket-defining features of the tray and the protrusions of the sheet. 
         [0025]    The thickness of the sheet is typically between 0.2 mm and 1.0 mm, which are envisaged to be the effective limits for acceptably accurate thermoforming of the sheet. Preferably, the sheet thickness is between 0.2 mm and 0.8 mm, which reduced upper limit is applicable where it is required to form protrusion features, and is also a practical limit on the thickness of sheet that can be fitted to a tray. More preferably, the sheet thickness is 0.3 mm, which enables good formation of protrusion features with good dimensional stability and at a low cost. In general, thermoform process variations increase with sheet thickness. Also, thin sheets are less expensive than thicker sheets. 
         [0026]    According to another aspect of the invention, there is provided a method of manufacturing components, the method comprising the steps of:
       providing a first tray having one or more pockets on a first side thereof;   providing a second tray having a first side and a second side, the second side facing the first side of the first tray;   inserting at least one first component having a first size into the or each pocket on the first side of the first tray;   attaching a removable, thermoformed sheet to the second side of the second tray;   stacking the second tray on top of the first tray such that the thermoformed sheet is in registration with said first tray thereby reducing at least the depth of said one or more pockets, the at least one first component being retained snugly there within by virtue of the sheet;   performing a manufacturing operation on said at least one first component; and removing said thermoformed sheet.       
 
         [0033]    In one embodiment, the manufacturing operation simply comprises moving the stacked trays from one location to another, the first components being retained snugly within the pockets during the movement. 
         [0034]    However, the method preferably further includes a step of removing the second tray from the first tray prior to performing the manufacturing operation, which enables the manufacturing operation to result in the production of a second component having a second size, greater than said first size. Also, it enables the sheet to be removed from the second tray. 
         [0035]    Typically, the manufacturing operation is carried out on the first components in situ in the pockets. The sheet may be removed during or after the manufacturing operation has been performed on said at least one first component. The sheet may be removed, either by hand or by a removal mechanism, to effectively increase the pocket size, ready to receive the larger second components formed in the manufacturing operation. In an alternative manufacturing operation, the components would be removed from the pockets with a pick-and-place technique. 
         [0036]    The at least one first component may be inserted in either a “live bug” orientation or a “dead bug” orientation. 
         [0037]    Typically, the first and second trays are identical to one another. In this way, a single tray design can function both to form the pockets and to retain the thermoformed sheet. Also, multiple trays can be stacked on top of one another. 
         [0038]    In one embodiment, the sheet is attached before the insertion of the at least one first component. In this way, the sheet is attached to the top surface of a tray and the first components can be inserted into the reduced sized pockets. This avoids registration problems that might occur if the first components are instead loosely inserted into the full size pockets with the sheet then being overlaid to reduce the pocket size. 
         [0039]    A supplementary sheet may be attached to the first side of the first tray before the insertion of the at least one first component. Thus, the first components would be nestled between two sheets, providing enhanced protection and more flexibility in accommodating different sized components during their manufacturing stages. 
         [0040]    The method may further include a step of inverting the stacked first and second trays. This might be beneficial if it is required to perform a manufacturing operation with the components in, say, a “live bug” orientation where they have been inserted in a “dead bug” configuration, or vice versa. Inversion might also be required in order to remove the or each sheet from the trays without having to remove the components from their respective pockets. 
         [0041]    The tray and sheet required in the method may together comprise the component tray system of the first aspect of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0042]    An example of the present invention will now be described in detail with reference to the accompanying drawings, in which: 
           [0043]      FIG. 1  shows a top perspective view of an exemplary prior art component tray conforming to the JEDEC standard; 
           [0044]      FIG. 2  is a bottom perspective view of the tray of  FIG. 1 ; 
           [0045]      FIG. 3  shows an area of detail of  FIG. 1 ; 
           [0046]      FIG. 4  shows an area of detail of  FIG. 2 ; 
           [0047]      FIG. 5  is a top plan view of the tray of  FIGS. 1 to 4 ; 
           [0048]      FIG. 6  is a side elevation view of the tray of  FIG. 5 ; 
           [0049]      FIG. 7  is a bottom plan view of the tray of  FIGS. 1 to 4 ; 
           [0050]      FIG. 8  is a cross-sectional view, formed along the diagonal of a storage pocket formed by two successive trays, showing a ball grid array (BGA) integrated circuit chip secured therein; 
           [0051]      FIG. 9  shows an alternative tray and an associated thermoformed sheet, together comprising a component tray system in accordance with the invention; 
           [0052]      FIG. 10  shows an area of detail of the assembled component tray system, in which the thermoformed sheet is rendered transparent except for protrusion features; 
           [0053]      FIGS. 11   a - d  show alternative protrusion features for the sheet; 
           [0054]      FIG. 12  is an enlarged perspective view illustrating a snap-fit interengagement between the tray and the sheet; 
           [0055]      FIG. 13  corresponds to  FIG. 12 , but from another angle; 
           [0056]      FIG. 14  shows the assembled component tray system, including features from an overlying tray; 
           [0057]      FIG. 15  is a cross-sectional view of a stack of assembled component tray systems; 
           [0058]      FIGS. 16   a  and  16   b  show by comparison, the difference in pocket depth achieved respectively without and with the use of the sheet; 
           [0059]      FIG. 17  is a perspective view of an alternative tray and sheet combination, showing sliding capture features; and 
           [0060]      FIGS. 18   a  and  18   b  are detail views of the sliding capture features of  FIG. 17 . 
       
    
    
     DETAILED DESCRIPTION 
       [0061]    Referring now to the drawings in detail wherein like numerals refer to like elements throughout the several views, one sees that  FIG. 1  is a top perspective view of a known tray  10  suitable for use in the present invention.  FIG. 2  is a bottom perspective view of the same tray  10 .  FIG. 5  is a top plan view of the tray  10  of the present invention and  FIG. 7  is a bottom plan view of the tray  10  of the present invention. Tray  10  conforms to the standards of JEDEC and hence is bounded by long sides  12 ,  16  and short sides  14 ,  18  with interior structure provided by planar floor  20 . 
         [0062]    Sides  12 ,  14 ,  16 ,  18  are bounded by downwardly extending peripheral skirt  22  which further includes upper indentation  24  for receiving the peripheral skirt  22  of an upwardly adjacent tray thereby allowing the trays  10  to be stacked. Flanges  26 ,  28  are provided on short sides  14 ,  18  offset from one another in accordance with JEDEC standards to provide indication of the front and back of the tray. Additionally, as shown on  FIGS. 5 and 7 , the upper interior surface of sides  12 ,  14 ,  16 ,  18  include respective tab pairs  13 ,  15 ,  17 ,  19  for receiving the respective corresponding tabs  21 ,  23 ,  25 ,  27  on the lower interior surface of sides  12 ,  14 ,  16 ,  18  of a successive identical upper tray  10 , thereby aligning successive trays  10  in a stacked configuration. 
         [0063]    As noted, the entire peripheral structure, including peripheral skirt  22 , upper indentation  24  and flanges  26 ,  28 , is made in accordance with JEDEC standards to provide for standardized automated handling of tray  10 . 
         [0064]    Corner  30  is formed at the intersection of sides  12 ,  14 . Corner  32  is formed at the intersection of sides  14 ,  16 . Corner  34  is formed at the intersection of sides  16 ,  18 . Corner  36  is formed at the intersection of sides  12 ,  18 . L-shaped support elements  40  are formed on the upper surface or side ( FIGS. 1 ,  3  and  5 ) inwardly adjacent from corners  30 ,  32 ,  34 ,  36 , T-shaped support elements  44  are formed inwardly adjacent from sides  12 ,  14 ,  16 ,  18  on the upper surface of tray  10 , and X-shaped support elements  46  are formed on the upper surface in the interior of tray  10  thereby defining storage pockets  101 - 121  (see  FIG. 5 ) which are configured in rows and columns within the rectangular shape of tray  10 , which could likewise be provided in a square or other shape. 
         [0065]    Some of the storage pockets, such as those shown at  109 ,  111 ,  113  may include a solid planar floor  20  thereby forming vacuum storage pockets to permit vacuum operated equipment to couple to the tray  10  whereas the remaining storage pockets have a substantial portion of planar floor  20  removed as described below. Additionally, support elements  40 ,  44 ,  46  typically have bevelled upper (in the configuration or orientation of  FIGS. 1 and 3 ) surfaces. 
         [0066]    As shown in  FIGS. 2 ,  4  and  7 , the lower surface or side  20   b  of tray  10  includes L-shaped support elements  52  inwardly adjacent from corners  30 ,  32 ,  34 ,  36 . As best seen in  FIG. 4 , L-shaped support elements  52  include legs  54 ,  56  oriented perpendicular to each other, meeting at apex  58 , with an outer portion of legs  54 ,  56  removed adjacent to apex  58  in order to allow the corresponding L-shaped support element  40  from the upper surface of a downwardly successive tray  10  to seat on L-shaped support element  52 . Additionally, the inner portion of legs  54 ,  56  have a reduced height, and ledge  59  of this reduced height is formed along the interior of L-shaped support element  52 . T-shaped support elements  60  are formed inwardly adjacent from sides  12 ,  14 ,  16 ,  18  on the lower surface  20   b  of tray  10 . T-shaped support elements  60  are formed from collinear head segments  62 ,  64  which are parallel to the immediately adjacent side of the tray and further formed from segment  66  which is perpendicular to the head segments  62 ,  64 . A portion of the interior of segment  66  immediately adjacent to the intersection  68  of segments  62 ,  64 ,  66  is removed thereby forming slot  67 . Similarly, an outer portion of the collinear head segments  62 ,  64  immediately adjacent to the intersection  68  is removed in order, along with slot  67 , to form a seat to receive the corresponding T-shaped support element  44  from the upper surface of a downwardly successive tray  10 . Additionally, the inner portion of segments  62 ,  64 ,  66  have a reduced height, and ledge  69  of this reduced height is formed on both sides of segment  66  and along the interior of segments  62 ,  64 . 
         [0067]    X-shaped support elements  70  are formed from four segments  71 ,  72 ,  73 ,  74  at successive right angles to each other, joining at centre  75 . The interior of each four segments  71 ,  72 ,  73 ,  74  is removed thereby forming slots in order to form a seat to receive the corresponding X-shaped element  46  from an upper surface of a downwardly successive tray  10 . Additionally, the inner portion of segments  71 ,  72 ,  73 ,  74  have a reduced height, and ledge  77  of this reduced height is formed along both sides of segments  71 ,  72 ,  73 ,  74 . Typically, ledges  59 ,  69  and  77  are of equal height. 
         [0068]    Support elements  52 ,  60 ,  70  typically include bevelled upper (in the configuration or orientation of  FIGS. 2 and 4 ) surfaces and are formed directly below respective support elements  40 ,  44 ,  46 . Together, the L-, T- and X-shaped elements  52 ,  60 ,  70  of the bottom surface  20   b  define storage pockets  101 ′- 121 ′ (see  FIG. 7 ). When successive trays  10  are stacked, the storage pockets  101 - 121  defined by the L-, T- and X-shaped elements of the top surface  20   b  of a tray  10  are in registration with the storage pockets  101 ′- 121 ′ defined by the L-, T- and X-shaped elements of the bottom surface  20   b  of an adjacent tray  10 , to together define 3D enclosures. 
         [0069]    As shown in  FIGS. 1 ,  3 , and  5 , the upper surface or side  20   b  of tray  10  (which forms the lower surface of the storage pockets  101 - 121 ) includes, in each storage pocket other than vacuum storage pockets  109 ,  111 ,  113 , apertures  202 . 
         [0070]    As shown in  FIG. 8 , a component  1000  (here an integrated circuit chip) is captured between successive trays  10  in the 3D enclosure. In some trays  10 , a pedestal  210 , which may be comprised of rotationally segmented segments  212 ,  214 ,  216 ,  218 , each forming approximately a quarter circle, arises from the centre of each storage pocket on the upper surface  20   b  of the tray  10 . Pedestal  210  supports the component  1000  while being sufficiently spaced from the various support elements to allow spherical balls  1002  of the IC chip  1000  to point downwardly without being contacted by pedestal  210  or any other portion. The edges of component  1000  are likewise captured between the corresponding support elements of the successive trays  10 . 
         [0071]    An alternative tray  10  is illustrated in  FIGS. 9  onwards, in which there are twelve pockets on each of the top and bottom surfaces  20   a,    20   b.  The pockets  101 - 112  on the top surface  20   b  are each defined by L-shaped elements  40  at the corners of each pocket. The pockets  101 ′- 112 ′ on the bottom surface  20   b  are each defined by buttress-like projections  90  extending partially along each side of the respective pockets. Each buttress  90  includes, at a mid-point and projecting outwardly of the associated pocket  101 ′- 112 ′, a wedge  92  which tapers from a thin end  93  intersecting with the buttress at a point at least part way up the buttress  90 , to a thick end  95  near the bottom of the buttress  90  (as viewed in  FIGS. 10 ,  12  and  13 ). The wedge  92  overlies an aperture  96  through the tray  10 . Together, each wedge  92  and associated aperture  96  comprise a snap-fit feature. At the distal end of each buttress  90 , a ledge  94  is formed facing the associated pocket. 
         [0072]    A removable, thermoformed sheet  400  is adapted to cooperate with the tray  10  to reduce at least the depth of the pockets. The sheet  400  is generally planar and comprises a thin sheet of conformal material. The thickness of the sheet is between 0.2 mm and 1.0 mm, which are considered to be practical limits for acceptably accurate thermoforming. Preferably, the sheet thickness is between 0.2 mm and 0.8 mm, which reduced upper limit corresponds to the fact that it becomes impractical to connect the thicker sheets to a tray  10 . 
         [0073]    The thermoformed sheet  400  includes protrusions  402 , such as bumps, studs, bosses, stand-offs, platforms or spikes to vary the profile of the sheet, for a purpose described below. 
         [0074]    The thermoformed sheet  400  also includes slots  404  arranged in a regular array, so as to be in registration with the buttresses  90  of the associated tray  10 , as shown in  FIG. 10 . The thermoformed sheet  400  is attached to the bottom surface  20   b  of the tray  10  and retained in registration with the tray  10  by a snap-fit between the snap-fit features  90 - 96  on the tray and the corresponding slots  404  through the sheet  400 , as shown in  FIGS. 12 and 13 . As the sheet  400  is urged into the tray  10 , it resiliently deforms when passing the wedges  92  from the thin ends  93  to the thick ends  95  thereof, snapping back to an unstressed state on passing the bottom edges of the wedges  92  and entering the apertures  96 , to be retained by those bottom edges. This process can be reversed to remove the sheet  400  from the tray  10 , the conformal nature of the sheet allowing it to deform to pass back past the thick ends  95  of the wedges  92 . 
         [0075]    Of course, alternative arrangements are possible, provided that cooperative interengagement of tray features with corresponding features on the sheet  400  enable both accurate registration of the sheet  400  with the tray  10  and removability of the sheet from the tray. For example, the sheet  400  may be retained on the tray by a snug fit, such as through frictional interference between the pocket-defining features of the tray  10  and the protrusions  402  of the sheet  400 , or through frictional interference between the pocket-defining features of the tray  10  and the slots  404  in the sheet  400 , in which case the slots are arranged to be a snug fit on the pocket-defining features, such as by the pitching of the pockets on the tray being larger than the pitching of the slots/holes in the sheet. Additionally or alternatively, the frictional interference may be between other studs or protrusions (not shown) on the tray  10  and corresponding holes (not shown) in the sheet  400 . 
         [0076]    Another way to secure the sheet  400  to the tray  10  would be through the use of a sliding lock feature, as shown in  FIGS. 17 and 18 , where the sheet  400   b  provided with slots  406  would slide over corresponding capture features  408  on the tray  10 . The slots  406  are each sized and positioned to pass over the respective capture feature  408  when the sheet is pressed toward the tray. Once received over the capture features  408 , the sheet is slid in the direction of the slots  406  such that a first end of each slot is received in a facing rebate  410  in the respective capture feature  408 . Here, there is no interference fit, just a snug fit. 
         [0077]    The protrusions  402  are arranged in a regular array, so as to be in registration with the pockets  101 ′- 112 ′ of the associated tray  10 , thus to reduce at least the depth of those pockets. In some embodiments, the protrusions  402  additionally reduce the width of the pockets  101 ′- 112 ′. As illustrated, particularly in  FIGS. 10 and 14  (in which the sheet  400  is rendered transparent except for the protrusions  402  so as to show only the protrusions  402  in position in registration with each respective pocket), each pocket has associated therewith four protrusions  402 , one at each corner. Various alternative protrusions  402   a - d  are shown in  FIGS. 11   a - d.  This arrangement has the advantage of the protrusions  402  being positioned so as to contact only the corner edges  1004  of the component  1000  within the pocket when, in use, the tray  10  is moved, which portions tend not to be fragile. Also, the shape and configuration of the protrusions  402  can be selected to enhance frictional interference with the pocket defining features of the tray, particularly the L-shaped elements  40 . 
         [0078]    Most preferably, the sheet thickness is 0.3 mm, which enables good formation of protrusion features  402  with good dimensional stability and at a low cost. In general, thermoform process variations increase with sheet thickness. Also, thin sheets are less expensive than thicker sheets. 
         [0079]    The tray  10  and sheet  400  together comprise a component tray system for use in a method of manufacturing components  1000 . According to the method, a thermoformed sheet  400  is attached to the bottom surface  20   b  of a tray  10  as described above, thereby reducing at least the depth of the pockets  101 ′- 112 ′ of the tray  10 . First components  1000   a,  such as bare substrates, having a first size are inserted into the pockets  101 - 112  on the top side  20   b  of an underlying tray  10 , in a “live bug” orientation. Once loaded with the first components, the tray  10  with the sheet  400  attached to its bottom surface  20   b  can be stacked on top of the underlying tray  10 , as shown in  FIG. 15 . The facing pockets  101 ′- 112 ′ and  101 - 112  of the respective trays define respective 3D enclosures in which the first components  1000   b  are retained snugly by virtue of the reduced depth pockets  101 ′- 112 ′ due to the presence of the sheet  400  and, particularly, the protrusions  402 . 
         [0080]    This reduced depth is shown in  FIGS. 16   a  and b, where  FIG. 16   a  shows the first component  1000   b  in the large 3D enclosure formed by original sized pockets. Since the 3D enclosure is designed to accommodate larger components, the z-axis spacing h 1  between the first component  1000   b  and the ledges  94  of the buttresses  90  is relatively large and would not hold the first component snugly within the enclosure. The reduced z-axis spacing h 2  provided by the protrusions  402  on the sheet  400  is shown in  FIG. 16   b . This reduced spacing h 2  is effective to retain the first component snugly within the 3D enclosure. 
         [0081]    After loading, the stacked trays  10  can be moved to another location. 
         [0082]    There, the first components  1000   b  within the pockets  101 - 112  of a particular tray  10  are exposed in a “live bug” configuration by the removal of the overlying tray or trays  10 , and a manufacturing operation is performed on the first components  1000   b  to produce respective second components (not shown) having a second size, greater than said first size. In a typical manufacturing operation, the first components  1000   b  would be removed from the pockets  101 - 112  with a pick-and-place technique, for remote processing. However, the manufacturing operation could take place with the first components  1000   b  in situ in the pockets. 
         [0083]    In order to accommodate the larger second components, the or each thermoformed sheet  400  is removed from the bottom surface  20   b  of the overlying tray  10 , thus restoring the pockets  101 ′- 112 ′ and the associated 3D enclosures to their original dimensions, as defined by the tray features. Thus, the overlying tray  10  can once again be stacked on top of the tray  10  containing the processed, second components. 
         [0084]    The manufacturing operation might alternatively take place with the first components  1000   b  in a “dead bug” orientation, whereby the stacked trays  10  are first inverted before the first components  1000   b  within the pockets  101 ′- 112 ′ of a particular tray  10  are exposed in the “dead bug” configuration by the removal of the overlying tray or trays  10 , which were previously the underlying trays. The sheet  400  can then be removed from the tray  10  in which the components  1000   b  are exposed by replacing the overlying tray or trays, inverting the stacked trays, removing the overlying tray (i.e. the one to which the sheet  400  is attached), and replacing the sheetless tray as with the “live bug” method. 
         [0085]    In one embodiment, the sheet  400  is attached to the top surface  20   b  of a tray rather than to the bottom surface  20   b  of an overlying tray. In this instance, the sheet attachment must occur before the insertion of the first components  1000   b  into the pockets  101 - 112 . In this way, the dimensions of the pockets  101 - 112  are reduced and the first components  1000   b  can be inserted into the reduced sized pockets  101 - 112 . This is especially advantageous where the sheet  400  is for altering the width of the pockets  101 - 112  as well as their depth, because this addresses registration problems that might occur if the first components  1000   b  are instead loosely inserted into the full size pockets  101 - 112  with the sheet  400  then being overlaid to reduce the pocket size (by the stacking of an overlying tray  10 ). 
         [0086]    Alternatively, the components  1000   b  may be inserted into the pockets  101 ′- 112 ′ of an inverted tray  10  before an inverted overlying tray having the sheet attached is stacked on top. 
         [0087]    Where the sheet  400  is attached to the bottom surface  20   b  of an overlying tray, it can be removed at any time during or after the manufacturing operation, irrespective of whether the components  1000  are within the pockets  101 - 112  at the time. The sheet  400  is removed either by hand or by a removal mechanism. On the other hand, where the sheet  400  is attached to the top surface  20   b  of a tray, it is necessary for the first components  1000   b  to be removed from the pockets  101 - 112  before the sheet  400  can be removed. Alternatively, the trays  10  could be inverted before the manufacturing operation, so that the first components  1000   b  are instead retained in the pockets  101 ′- 112 ′ of the overlying tray  10  (which is now underlying), freeing the sheet  400  for removal and exposing the first components  1000   a.    
         [0088]    The thermoformed sheet  400  may further include indented portions, such as channels, and/or further apertures, such as slots or holes (not shown), so as to avoid contact between the sheet and portions of the components  1000 , particularly fragile portions. 
         [0089]    Although it is preferable to include protrusions  402 , the depth of the pockets can alternatively just be altered by providing a relatively thick conformal sheet. 
         [0090]    Whereas just first and second components have been described, further intermediate stages of processing can be envisaged, and additional sheets having features tailored to those intermediate components could also be provided. 
         [0091]    Moreover, the facing pockets  101 - 112  in the top surface  20   b  can also be fitted with a thermoformed sheet to alter the internal dimensions of those facing pockets. The sheet may be a continuation of the sheet  400  that is attached to the bottom surface  20   b  of that tray, or might be a second sheet. 
         [0092]    Although the foregoing description has been made with reference to a particular tray  10  complying with the JEDEC standard, it will be understood that the tray  10  may take a different configuration, such as a having a different number of pockets, the pockets being of a different shape, or the internal features defining the pockets taking a different form. In particular, it should be understood that the invention applies to any non-standard trays that are adapted to convey, protect and transport electronic and electric components. Moreover, the invention is not limited to application with JEDEC trays, and could equally be applied to trays complying with other known standards, as discussed in the introductory portion. 
         [0093]    The sheet  400  may not affect the depth and/or width of all pockets, but may be tailored instead to alter the dimensions of a selected pocket or pockets.