Abstract:
A tray for handling and retaining a plurality of components, wherein the tray has a rigid body portion and an elastomeric contact layer. The contact layer has a planar upper surface for contacting and retaining the components, and may be formed from a thermoplastic material having a surface energy between 20 dyne/cm and 100 dyne/cm, a hardness of between about Shore A15 and Shore D75, and a surface electrical resistivity of between about 1×10 4  ohms/square and 1×10 12  ohms/square. The material for the contact layer may be urethane, polybutylene terephthalate, polyolefin, polyethylene terephthalate, styrenic block co-polymer, styrene-butadiene rubber, polyether block polyamide, or polypropylene/crosslinked EDPM rubber. The body portion may be formed from acrylonitrile-butadiene-styrene, polycarbonate, urethane, polyphenylene sulfide, polystyrene, polymethyl methacrylate, polyetherketone, polyetheretherketone, polyetherketoneketone, polyether imide, polysulfone, styrene acrylonitrile, polyethylene, polypropylene, fluoropolymer, polyolefin, or nylon. The body portion may have a peripheral border region and a downwardly projecting skirt portion to facilitate stacking of multiple trays. The contact layer may be divided into a grid portion defining a plurality of individual component receiving regions on the surface.

Description:
FIELD OF THE INVENTION  
         [0001]    This invention relates to trays for handling device, more particularly it relates to trays for handling semiconductor devices.  
         BACKGROUND OF THE INVENTION  
         [0002]    Processing of semi-conductor devices involves many processing steps. The devices are sensitive to physical and electrical damage, and must be handled carefully when being transported between processing steps. In addition, robots are often used to handle the devices during processing. These robots require precise positioning of the device to allow the robot to efficiently locate and engage the device. As a result, specialized trays have been developed to facilitate transport of the devices between processing steps.  
           [0003]    One type of previous chip tray, known as a film frame, generally has a frame portion surrounding a thin film. On the top surface of the thin film, a layer of adhesive is disposed. A plurality of devices may then be arranged at any desired locations on the adhesive, and the adhesive serves to secure the devices in place. An example of such a film frame carrier may be seen in U.S. Pat. No. 5,833,073, a copy of which is fully incorporated herein by reference.  
           [0004]    Other tray designs have been developed wherein physical structures, in the form of pockets, are used to secure a plurality of devices on the surface of the tray. An example of a pocketed matrix tray may be seen in U.S. Pat. No. 5,481,438. Some of these matrix tray designs, such as Japanese laid open patent application JP 05-335787, also include a multi-layer adhesive material in the bottom of the pockets for securing the devices in place.  
           [0005]    A problem with previous trays using typical adhesive materials is that such adhesives may attract contaminants in the form of particles that can damage the devices. These contaminants can be difficult to remove from the tray by washing without causing degradation of the adhesive. In addition, the adhesive itself may contain solvents or other undesirable chemicals that can contaminate the devices or the process. Also, the adhesive itself may undergo changes in response to environmental conditions, becoming either too tacky so as to interfere with the operation of the robotic device handling process, or not tacky enough so as not to properly secure the devices in place.  
           [0006]    Prior art matrix trays having pockets or other physical structures to retain the device may also present problems. Devices such as bare or leadless chips are not easily captured in a physical structure due to the lack of projections on the device. Also, the devices may become dislodged from the physical restraints during handling, leading to device damage or improper positioning for handling by a robot. Moreover, the necessity of forming additional structures on the tray surface leads to increased tray cost.  
           [0007]    Thus, there is still a need for an improved tray for handling semiconductor devices.  
         SUMMARY OF THE INVENTION  
         [0008]    The present invention is a chip tray for handling and retaining a plurality of components wherein the components are retained by adhesion between a surface of the components and a planar contact layer of the tray. The contact layer is formed from a relatively soft thermoplastic elastomer material having a moderate to high surface energy and that may have a surface electrical resistivity of between about 1×10 4  ohms/square and 1×10 12  ohms/square for purposes of electrostatic discharge (ESD) safety. The component is retained in place exclusively by adhesion with the thermoplastic contact layer and without other physical retaining structures or separate adhesives. The contact layer of the tray may be injection overmolded onto the rigid tray body portion, which is preferably formed from rigid thermoplastic material. The contact layer and the rigid body portion may be held together with a polar bond formed during the injection molding process. The relative amount of adhesion provided by the contact layer may be adjusted by intermixing or alloying the thermoplastic elastomer material with impact modifying polymers or blends of other thermoplastic elastomers. In addition, the relative amount of adhesion and the electrical properties of the contact layer may be modified by intermixing or alloying the thermoplastic elastomer with inherently static dissipative or conductive polymers, inorganic filler material such as carbon fiber, carbon powder, metallic, or ceramics, or organic filler material. In addition, small depressions or projections arranged randomly or in a regular matrixical pattern may be provided in the contact layer to alter the amount of surface area, and resultant amount of adhesion, available for contact with the components to be retained.  
           [0009]    Accordingly, the invention may be characterized in one aspect as a tray for handling and retaining a plurality of components including a rigid body portion and an elastomeric contact layer having a planar upper surface for contacting and retaining the components. The contact layer may be formed from a thermoplastic material having a surface energy between 20 dyne/cm and 100 dyne/cm and a hardness of between about Shore A15 and Shore D75. The contact layer may have a surface electrical resistivity of between about 1×10 4  ohms/square and 1×10 12  ohms/square. The contact layer may be formed from urethane, polybutylene terephthalate, polyolefin, polyethylene terephthalate, styrenic block co-polymer, styrene-butadiene rubber, polyether block polyamide, or polypropylene/crosslinked EDPM rubber. The body portion may be formed from acrylonitrile-butadiene-styrene, polycarbonate, urethane, polyphenylene sulfide, polystyrene, polymethyl methacrylate, polyetherketone, polyetheretherketone, polyetherketoneketone, polyether imide, polysulfone, rigid polyethylene, polypropylene, a fluoropolymer, polyolefin, nylon, polyamide, or any other suitable rigid polymer material. The body portion may have a peripheral border region and a downwardly projecting skirt portion or other structure to facilitate stacking of multiple trays. The contact layer may be divided into a grid portion defining a plurality of individual component receiving regions on the surface.  
           [0010]    The invention may also be characterized as a method of making a tray for handling and retaining a plurality of components. The method includes the steps of forming a rigid body portion from plastic material, and forming a component contact layer of thermoplastic elastomer on the upper surface of the body portion.  
           [0011]    The invention may also be characterized as a method for retaining a plurality of components on the surface of a chip tray.  
           [0012]    It is a feature and advantage of the invention that components are retained on the chip tray only by adhesion between a flat surface of the component with a thermoplastic elastomer contact layer of the tray and without any physical retaining structure or separate adhesive.  
           [0013]    It is another feature and advantage of the invention that components are retained in place on the tray with sufficient force so that the tray can be inverted and can be subjected to normal shipping and handling shocks without the components being dislodged.  
           [0014]    It is another feature and advantage of the invention that no lateral or vertical physical restraining structures are used to retain components in place on the tray, apart from the thermoplastic elastomer contact layer.  
           [0015]    It is another feature and advantage of the invention that no separate adhesive substance is used on the contact layer surface to adhere the components to the contact layer, thereby reducing the amount of process contamination from solvents and other undesirable chemicals.  
           [0016]    It is another feature and advantage of the invention that the tray contact layer and body portion may be ESD safe for the components retained.  
           [0017]    It is another feature and advantage of the invention that the tray is more easily recyclable than known chip trays.  
           [0018]    It is another feature and advantage of the invention is that a stack of chip trays according to the invention may be repositioned with the components retained in place, without the need for any lateral contact or constraint on the components, and without any contact with the top sides of the components.  
           [0019]    It is yet another feature and advantage of the invention that the relative amount of the adhesive force provided by the surface may be adjusted to suit an individual application by selection or modification of the materials used or by alteration of the surface geometry of the contact layer.  
           [0020]    Additional objects, advantages, and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0021]    [0021]FIG. 1 is a perspective view of a preferred embodiment of the tray of the present invention;  
         [0022]    [0022]FIG. 2 is a cross section of the tray shown in FIG. 1;  
         [0023]    [0023]FIG. 3 is a table listing the various materials that may be used for the contact layer and body of the tray;  
         [0024]    [0024]FIG. 4 is a cross sectional view of multiple trays in a stacked configuration and with small components arranged on the contact layers;  
         [0025]    [0025]FIG. 5A is an enlarged view of a portion of the view of FIG. 2;  
         [0026]    [0026]FIG. 5B is an alternative enlarged view of a portion of the view of FIG. 2;  
         [0027]    [0027]FIG. 5C is another alternative enlarged view of a portion of the view of FIG. 2;  
         [0028]    [0028]FIG. 5D is yet another alternative enlarged view of a portion of the view of FIG. 2;  
         [0029]    [0029]FIG. 5B is still another alternative enlarged view of a portion of the view of FIG. 2;  
         [0030]    [0030]FIG. 6 is a perspective view of the tray of the present invention with a grid for defining individual component retaining regions on the surface thereof; and  
         [0031]    [0031]FIG. 7 is a cross section of the view of FIG. 6. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0032]    The accompanying Figures depict embodiments of the matrix tray of the present invention, and features and components thereof. Any references to front and back, right and left, top and bottom, upper and lower, and horizontal and vertical are intended for convenience of description, not to limit the present invention or its components to any one positional or spacial orientation. Any dimensions specified in the attached Figures and this specification may vary with a potential design and the intended use of an embodiment of the invention without departing from the scope of the invention.  
         [0033]    As used herein, the term “about” means that dimensions, sizes, tolerances, formulations, parameters, shapes and other quantities and characteristics are not and need not be exact, but may be approximate and/or larger or smaller, as desired, reflecting tolerances, conversion factors, rounding off, measurement error and the like, and other factors known to those of skill in the art. In general, a dimension, size, formulation, parameter, shape or other quantity or characteristic is “about” or “approximate” whether or not expressly stated to be such.  
         [0034]    The present invention comprises a tray for handling semiconductor devices and other small components wherein the component has a surface area that can be placed into direct contact with a tray surface having a moderate to high surface energy. The tray is most suitable for components having no projections or leads, such as bare or leadless chips, but may also be used with devices having leads such Chip Scale Package (CSP) devices. The devices are retained on the tray without the use of a separate adhesive material, and without lateral or vertical physical restraints apart from the thermoplastic contact layer itself. In the invention, the upper surface of the tray comprises a continuous layer of relatively soft thermoplastic material having a moderate to high surface energy. The adhesion between the surface of the device and the surface of the tray retains the device during movement and normal handling of the tray while allowing the device to be easily lifted from the surface by a robotic handling apparatus. Further, the tray may be made ESD safe through the use of materials having a surface electrical resistivity of between about 1×10 4  ohms/square and 1×10 12  ohms/square for either or both the contact layer and the body portion.  
         [0035]    In FIGS. 1 and 2 there is shown a preferred embodiment of the device tray  100  of the present invention. Tray  100  has rigid body portion  110  oriented in a plane defined by the “x” and “y” axes as shown and having an upper surface overlain by a contact layer  120 . Body portion  110  preferably has a peripheral border region  112  projecting laterally outward beyond the edge  122  of contact layer  120 . A downwardly projecting skirt  114  may be provided on body portion  110 . The skirt  114  is positioned so as to engage the peripheral border region  112  of a tray located immediately below when multiple trays are stacked as shown in FIG. 4. As an alternative to skirt  114 , other structures such as downwardly projecting legs or posts may be used to facilitate stacking of multiple trays. Skirt  114  is of sufficient length so that any components  200  disposed on contact layer  120  do not contact any portion of a tray stacked immediately above.  
         [0036]    According to the invention, contact layer  120  is formed from a polymeric elastomer material having a moderate to high surface energy, a relatively soft surface, and that may be ESD safe. Although other polymers can be used, thermoplastics offer the general advantages of easier recyclability, greater purity with a smaller process contamination causing sol-fraction, and lower cost, and are hence preferred. Currently the preferred materials for contact layer  120  are relatively soft thermoplastic elastomers, including, for example, elastomeric variants of urethane (UR), polybutylene terephthalate (PBT), polyolefins (PO), polyethylene terephthalate (PET), styrenic block co-polymers (e.g. Kraton®), styrene-butadiene rubber, and nylon in the form of polyether block polyamide (PEBA). As an alternative, a thermoplastic vulcanizate material, such as polypropylene/crosslinked EDPM rubber, for example Santoprene® made by Advanced Elastomer Systems of Akron, Ohio, may be also used. The surface energy of the material is preferably 20 dyne/centimeter to 100 dyne/centimeter, more preferably between about 30 dyne/centimeter to 45 dyne/centimeter, and most preferably about 40 dyne/centimeter. The material preferably has a durometer hardness value of less than about Shore D75, and more than about Shore A15.  
         [0037]    It is preferred that contact layer  120  be ESD safe, having a surface electrical resistivity value of between about 1×10 4  ohms/square and 1×10 12  ohms/square. Inherently static dissipative polymers may be intermixed or alloyed with the contact layer material to achieve the desired surface electrical resistivity. Also, an inherently conductive polymer, such as doped polyaniline, polypyrrole, polythiophene, polyisothianaphthene, polyparaphenylene, polyparaphenylene vinylene, polyheptadiyne, or polyacetylene may be used as an alloying polymer. As an alternative, carbon fiber, carbon powder, metallic particulate, ceramic particulate, or other electrically conductive fillers may be added to the material. Organic filler materials may also be used to alter the surface resistivity of the material, such as for example, quaternary ammonium salts, sulfonium salts, alkyl sulfonates, alkyl sulfates, alkyl phosphates, ethanol amides, ethanol amines, or fatty amines. Of course any other method or material may be used for the purpose which provides the requisite electrical properties along with the desired physical properties of surface energy, relative hardness and purity.  
         [0038]    The amount of adhesion provided by contact layer  120  may be adjusted for particular applications wherein components with specific physical characteristics are to be retained. This adjustment may be accomplished by selecting or altering the material used for contact layer  120 , or through alterations to the geometry and dimensions of the surface itself. Generally, for example, the materials having surface energies at the higher end of the ranges will be more strongly retentive of components than materials at the lower end of the ranges. Also, materials with hardness values at the softer end of the range will typically be more strongly retentive of components than will the harder materials. Any of the alloying or filler materials discussed above may also be intermixed or alloyed with the base material for the purpose of altering the surface energy or relative hardness of the base material. The desired relative hardness properties may also be achieved using impact modifying polymers or blends of other thermoplastic elastomers as alloying agents. Generally, it is desired that surface layer  120  provide a degree of adhesion to a component per unit of component area at least greater than the corresponding gravitational force per unit area of the component, thus permitting retention of the component even when the tray is inverted. It is most preferred that the amount of adhesion be sufficient to retain the components under shock and vibration loads typically encountered during shipping and handling operations.  
         [0039]    The amount of adhesion may also be reduced by selectively altering the geometry and resulting amount of available component contact area of contact layer  120 . This may be accomplished by forming a multiplicity of regular depressions  180  or projections  182  in contact layer  120  as shown in greatly exaggerated fashion for clarity in FIG. 5C or  5 D, respectively. The depressions  180  or projections  182  may be arranged randomly or in a regular matrix pattern on contact layer  120 . The depressions  180  or projections  182  may be from about 0.000040 inch to 0.10 inch in depth or height respectively, and spaced from about 0.000040 inch to about 0.30 inch apart, as may be needed to achieve the desired amount of adhesion. The features may be formed on contact layer  120  by stamping with a mold machined with a negative impression of the desired features. Generally, the mold may be machined using known machining techniques. Photolithography may be used to machine the mold to form regular features at the smaller ends of the ranges. As an alternative, a mold having a fine, random distribution of features may be made by sandblasting, glass beading, or shotpeening the mold surface.  
         [0040]    It is currently most preferred that surface layer  120  be injection overmolded in a continuous layer onto body portion  110  as shown best in FIGS. 2 and 5A, using standard injection molding techniques. The two layers may also be mechanically fastened together, or may be secured by a combination of methods. Preferably, the materials for surface layer  120  and body portion  110  are selected so that a polar bond is formed during the injection molding process. In addition, mechanical bonding structures  160 , as shown best in FIG. 5B, may be provided on body portion  110  to enhance bonding efficacy. In addition, an intermediate or tie layer  170  may be used between the two materials to enhance bonding effectiveness as shown in FIG. 5E. It is preferred that thermoplastic polymers be used for body portion  110 , as well as for contact layer  120 , since thermoplastics tend to offer the general advantages of easier recyclability, greater purity with a smaller process contamination causing sol-fraction, and lower cost. Body portion  110  may be made ESD safe using the same materials and techniques as discussed for contact layer  120 . Suitable rigid thermosetting polymers may also be used for body portion  110 , but are less preferred.  
         [0041]    Body portion  110  provides rigidity and mechanical strength to the tray, and accordingly must be made from suitably rigid material and must have adequate thickness to withstand the mechanical loading anticipated during use and handling of the tray. Although any suitable polymer material having the desired qualities of rigidity, mechanical strength, and chemical compatibility may be used, some suitable polar polymer materials for body portion  110  are listed in the first column of the table found in FIG. 3. The listed “Group A” thermoplastic materials may be molded with any of the contact layer materials listed in the second column of the table without need for surface treatment of the body material, although surface treatment may be used to enhance bonding efficacy. The body materials listed in “Group B” are generally non-polar polymers, and require surface treatment in the form of corona, plasma, chemical, or flame treatment to achieve a proper polar bond with contact layer  120 . As an alternative, the materials in “Group B” may be bonded using a separate intermediate tie layer of mutually compatible material, such as Bynel® made by Du Pont Corporation or Tymor® made by Nichimen Corporation.  
         [0042]    Although it is not necessary for effective retention of components, it may be desirable to define individual component retaining regions  152  on contact layer  120 , as shown in FIGS. 6 and 7. A separate grid member  150  may be formed from suitable thermoplastic material and attached by any suitable method to contact layer  120  to define the component retaining regions  152 . The component retaining regions  152  may also be formed directly in the surface of contact layer  120  during the molding step, or by subsequent embossing.  
         [0043]    During use of the tray, individual components may be arranged anywhere on contact layer  120  with a significant portion of the surface area of the device in direct contact with contact layer  120 . The moderate to high surface energy and relative softness of contact layer  120  results in effective retention of the component on contact layer  120  by adhesion between the thermoplastic contact surface  120  and a surface of the device, but without the need for separate adhesives or other physical retaining structures. The ESD safe static dissipative properties of the materials for the contact surface, rigid body portion or both, provide electrical protection for the devices stored therein.  
         [0044]    The tray of the present invention is easily manufactured since the component contact layer  120  is formed in a single, monolithic piece, without the added complexity and cost of precision forming of physical retaining structures. In addition, the thermoplastic construction of the tray reduces the amount of process contamination contributed by the tray. Moreover, the thermoplastic components are more easily and completely recycled, for reduced environmental impact.  
         [0045]    The stacking features of the invention are best seen with reference to FIG. 4. In a stack of trays  101  as depicted in FIG. 4, each component  200  is in direct contact with, and is retained by contact surface  120 . When the trays  100  are stacked, downwardly projecting skirt  114  of each tray contacts and rests on peripheral border region  112  of the tray immediately below. Skirt  114  is of sufficient height so that bottom surface  126  of the tray is spaced apart from the components  200  below. Components  200  are retained in place only by adhesion with contact surface  120 . The components  200  are not vertically constrained by contact with bottom surface  126  of the tray immediately above. The stack of trays  101  may be repositioned and even inverted without causing the components  200  to be dislodged, and without the need for device contact with other trays or with other portions of the same tray.  
         [0046]    Although the description above contains many specificities, these should not be construed as limiting the scope of the invention but as merely providing illustrations of some of the presently preferred embodiments of the invention. Thus, the scope of the invention should be determined by the appended claims and their legal equivalents, rather than by the examples given.