Abstract:
Provided is a tray transfer apparatus having a transfer plate arranged and configured to support a tray containing a number of semiconductor devices in an array of pockets. The tray transfer apparatus further includes a driving means arranged and configured for the movement and positioning of the transfer plate. The transfer plate is provided with a plurality of tray holders that may be selectively engaged to support a tray and with detecting means corresponding to the array of pockets provided in a supported tray. In instances in which one or more of the detecting means sense the presence of more than one semiconductor device in a corresponding pocket of a supported tray, the tray transfer apparatus will generate an alarm signal and/or suspend operation so that corrective measures may be taken.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   This U.S. non-provisional application claims priority under 35 U.S.C. § 119 to Korean Patent Application No. 2003-36411 filed Jun. 5, 2003, the contents of which are incorporated herein, in its entirety, by reference. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a semiconductor manufacturing apparatus and, in particular, to an improved tray transfer unit and an automatic test handler including such a tray transfer unit. 
   2. Description of the Related Art 
   After being sawed from a wafer, semiconductor devices are typically placed in trays during certain points during their manufacture to reduce the likelihood of damage and to increase the ease with which the semiconductor devices may be handled. The semiconductor devices are typically removed from a tray for processing and discharged to the same or a different tray after processing in a manner that maintains the order in which they are arranged in the original tray. The semiconductor devices are also typically transferred between processing equipment as they are arranged in a tray. 
   The semiconductor devices are typically transferred between processing equipment by an operator, and are then transferred within the processing equipment using a tray transfer unit. The tray transfer unit is installed in a loading part or an unloading part of the processing equipment to load or unload the trays containing the semiconductor devices. The tray transfer unit may be incorporated in an automatic test handler used in a test process so that trays containing the semiconductor devices to be tested can be loaded and those devices that have been tested can be unloaded automatically. A conventional automatic test handler with a tray transfer unit is described below. 
     FIG. 1  is a plan view of a conventional automatic test handler.  FIG. 2  is a front view of the conventional automatic test handler. As illustrated in  FIGS. 1 and 2 , the conventional automatic test handler  300  comprises a tester (not shown) for testing the semiconductor devices, a first chamber  353  for establishing the temperature condition for test typically by heating or cooling the semiconductor devices to one or more temperatures as much as 50° C. or more above or below room temperature, a second chamber  355  for restoring the tested semiconductor devices to a temperature much closer to room temperature and a pick and place device  370  for transferring the semiconductor devices. The conventional automatic test handler  300  further comprises a plurality of tray stockers  311  having supply trays  21  and receiving trays  22 , a tray transfer unit  320  for transferring the supply tray  21 , grippers  341  for supporting the supply trays  21  and a control unit  380  for controlling the overall operation. 
   The loaded supply trays  21  containing a number of semiconductor devices are loaded in the tray stocker  311 . A supply tray  21  is then transferred to the gripper  341  by the tray transfer unit  320 . The semiconductor devices in the supply tray  21  may then be temporarily placed in a buffer  385  and finally placed onto a test tray  31  provided on a conveyor belt  357  by the pick and place device  370 . The test tray  31  is moved into the first chamber  353  to establish the test temperature(s) for the semiconductor devices in the test tray  31 . The test tray  31  is then transferred to the tester in which semiconductor devices in the test tray  31  are determined to pass or fail predetermined functional and/or parametric test processes. 
   After the test process is completed, the test tray  31  having the tested semiconductor devices is transferred to the second chamber  355  where the tested semiconductor devices are typically restored to a normal temperature of about 25° C. The semiconductor devices are then transferred by the pick and place device  370  through the buffer  385  and returned to open pockets on a supply tray  21  or a receiving tray  22  supported by a gripper  341  and may be sorted according to the test results. The trays, once loaded with tested and sorted semiconductor devices, are then transferred to the tray stocker  311  for unloading. 
   The conventional automatic test handler may automatically load or unload the semiconductor devices, thereby reducing the test time and eliminating the need for additional operator involvement, which may lead to increased productivity. The conventional automatic test handler, however, has disadvantages. For example, a so-called double device fault may occur during the test process. A double device fault refers to a fault where two or more semiconductor devices are placed in a single pocket or receptacle of the tray. A double device fault may result from the malfunction of an adsorption component, e.g., a vacuum adsorptive pad or a vacuum pump, or from the malfunction of a component used to detect the adsorption of the semiconductor device, e.g., a sensor. 
   If such a fault is caused by the malfunction of a component related to vacuum, it may be that a vacuum adsorptive force was not properly applied through the vacuum adsorptive pad or was improperly released. In such instances, the semiconductor device may not be adsorbed for loading or unloading, or may be released prematurely during transfer. 
   If the fault is caused by the malfunction of a component used to detect the adsorption, the adsorption of the semiconductor device by the vacuum adsorptive pad may not be detected accurately and may generate erroneous loading data. Errors in loading data may be transmitted to the control unit of the automatic test handler. As a result of the erroneous data, the control unit may attempt to load another semiconductor device in a pocket already containing a semiconductor device that has not been properly recognized or acknowledged by the control unit. 
   In order to prevent a double device fault, the components related to vacuum adsorption or detection of adsorption should be replaced or repaired before the durability of the components is exceeded either as a result of forced or natural deterioration or through faults generated by other causes. However, the durability of the components is affected by the environment, rendering it difficult to measure or estimate the durability of the component with sufficient accuracy to ensure that corrective maintenance is performed in a timely manner. Further, if faults are the result of causes other than exceeding component durability, the repair or replacement of such components may not be required. 
   For the above reasons, it has proven difficult to eliminate double device faults completely thereby making it necessary to detect a double device fault when it occurs so that corrective action may be taken. 
   SUMMARY OF THE INVENTION 
   The present invention is directed to an improved tray transfer unit, and an automatic test handler including such a tray transfer unit, which may detect double device faults in a manner that reduces product damage resulting from such faults. 
   A tray transfer unit comprises a transfer plate having tray holders. The tray holder supports the tray. Detecting means corresponding to each pocket of the tray are located and operated to detect a stack of semiconductor devices in a pocket. A detecting substrate comprises circuit wires and an input/output terminal. The circuit wires electrically connect the detecting means in parallel with the input/output terminal being connected to the circuit wires. 
   When a stack of at least two semiconductor devices are detected in a particular pocket of the tray, the detecting means will generate output signals from the detecting substrate through the input/output terminals. The output signals may activate one or more warning signals such as a flashing lamp or buzzer to alert an operator and/or may stop the operation of equipment so that corrective measures may be taken. 
   The detecting means may include a detecting switch such as a push-button switch having a mechanical contact mode. Push-button switches offer the advantages of a simple structure, easy installation, excellent durability and competitive price. The push-button switches may be mounted on the transfer plate so that a portion of the switch protrudes from the bottom of the transfer plate. The push-button switches may preferably perform a switching operation by pushing the button without changing the thickness of the transfer plate. 
   The detecting means may be fixed to the detecting substrate by soldering or may be configured to allow the detecting means to be easily detached from or connected to the detecting substrate. The tray holder comprises rotation axes located at the edges of the transfer plate, a catch finger rotatably connected to the rotation axis and a driving cylinder permitting application of rotation force to the catch finger. The detecting substrate may further comprise a connector connected to the input/output terminal. 
   The tray transfer unit may further comprise a control substrate for supplying power to the detecting substrate and for outputting control signals according to the switching operation of the detecting switches. The control substrate may include a flashing circuit for outputting flash signals and may include a NE555 circuit as a control chip and/or an AC/DC rectifier. 
   An automatic test handler of the present invention may comprise stockers having loaded trays and empty trays. A tray transfer unit may include a transfer plate, detecting switches, a detecting substrate and a driving means. The transfer plate may include a plurality of tray holders for supporting the tray. The detecting switches may be positioned to correspond to each pocket of the tray and operated to detect a stack of semiconductor devices in any of the pockets. 
   The detecting substrate will typically include circuit wirings and an input/output terminal. The circuit wiring may be configured to connect the detecting switches in a parallel configuration with the input/output terminal connected to the circuit wires. The driving means may be operated to move the transfer plate. A tester is operated to electrically test the semiconductor devices received in the test tray. 
   A first chamber may be operated to establish one or more predetermined test temperature condition(s) for the semiconductor devices. A second chamber may be operated to restore the tested semiconductor devices to the normal temperature. A pick and place device may be included to transfer the semiconductor devices between trays. A control unit may be operated to control the stockers, the tester, the tray transfer units, the pick and place devices and the first and second chambers. 
   The detecting substrate and the detecting switches may be installed in the tray transfer unit. The control unit may output test stop signals according to the detecting signals received from the detecting substrate. The automatic test handler may also include an alarm means which operates in response to the detecting signals generated by the detecting substrate. The alarm means may include a warning lamp and/or buzzer. The automatic test handler may also include a control substrate for supplying power to the detecting substrate and outputting control signals for flashing a warning lamp according to operation of the detecting switch. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other objects, features and advantages of the present invention will be readily understood with reference to the following detailed description thereof provided in conjunction with the accompanying drawings, wherein like reference numerals designate like structural elements, and in which: 
       FIG. 1  is a plan view of a conventional automatic test handler; 
       FIG. 2  is a front view of the conventional automatic test handler; 
       FIG. 3  is a perspective view of a tray transfer unit in accordance with an exemplary embodiment of the present invention; 
       FIG. 4  is an exploded perspective view of a transfer plate, a detecting switch and a detecting substrate of  FIG. 3 ; 
       FIG. 5  is a partially exploded perspective view of the transfer plate of  FIG. 4 ; 
       FIG. 6  is a bottom perspective view of the transfer plate of  FIG. 4  with a portion of the detecting switches protruding through the installation holes; 
       FIG. 7  is a bottom perspective view illustrating the connection of the detecting switches to the detecting substrate of  FIG. 4 ; 
       FIG. 8  is a perspective view of the connection of a transfer plate, a detecting substrate and a driving cylinder of  FIG. 3 ; 
       FIG. 9  is a partial cross-section view illustrating the operation of the detecting switch in accordance with an exemplary embodiment of the present invention; 
       FIG. 10  is a circuit diagram view of a control substrate of the tray transfer unit in accordance with an exemplary embodiment of the present invention; 
       FIG. 11  is a perspective view of an automatic test handler in accordance with an exemplary embodiment of the present invention; 
       FIG. 12  is a rear view of the automatic test handler in accordance with an exemplary embodiment of the present invention; and 
       FIG. 13  is a perspective view of a tray stocker and a catch finger of the automatic test handler in accordance with an exemplary embodiment of the present invention. 
     These drawings are representative of certain exemplary configurations of the invention and should not be construed as excluding alternative configurations, arrangements and materials. Similarly, the drawings are not to scale and the relative size and position of certain elements may have been modified to improve clarity. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Exemplary embodiments of the present invention will be described below with reference to the accompanying drawings. 
   Referring to  FIGS. 3 through 9 , a tray transfer unit  100  comprises a transfer plate  110 , detecting switches  130 , a detecting substrate  140  and a driving unit including both a vertical driving unit  151  and a horizontal driving unit  161 . The transfer plate  110  supports a tray containing semiconductor devices placed in an array of pockets provided on the tray. The driving units  151  and  161  may be utilized to transfer and position the transfer plate  110  relative to a tray that is intended for transfer. 
   The transfer plate  110  has connection holes  112  located at the edges thereof, as shown in  FIG. 5 . Tray holders  120  are formed at the connection holes  112  for supporting the tray. A series of installation holes  113  are provided on the transfer plate  110  at locations corresponding to each pocket  25  of the tray  21  that will be transferred by the transfer plate. The installation holes  113  provided in the transfer plate  110  allow for the installation of detecting switches  130  as described in more detail below. 
   The tray holder  120  comprises rotation bearings  121 , catch fingers  122 , connection bars  124  and driving bars  125 . The rotation bearings  121  or other rotatable members are rotatably inserted into the connection holes  112 . The catch fingers  122  are fixed to the rotation bearings  121  at the bottom portion of the transfer plate  110 . The connection bars  124  are connected between the rotation bearings  121  and the driving bars  125 . The installation holes  113  may be varied in size and shape depending on the type of the detecting switches  130  utilized. The installation holes  113  may be formed as a series of recesses having a predetermined size and depth with a penetrating hole provided in each recess. 
   The detecting switches  130  may be inserted as detecting means through the installation hole  113  of the transfer plate  110 , as shown in  FIGS. 4 and 6 . The detecting switches  130  may be push-button switches having a mechanical contact mode. As illustrated in  FIG. 4 , the detecting switches  130  may have a switch body  131 , which may be flexible, four leads  133  formed in one surface of the switch body  131  and a contact button  135  protruding from the surface opposite the leads. The leads  133  may be arranged internally in pairs that are electrically connected to each other when the contact button  135  is depressed and initiates a switching operation by the detecting switch  130 . 
   Each of the contact buttons  135  typically protrudes a predetermined distance from the bottom of the transfer plate  110 , as shown in  FIGS. 6 and 9 . The extent of protrusion is such that a contact button  135  is depressed when at least two semiconductor devices  10  are located in the corresponding pocket  25  of the tray  21  while the tray is supported against the transfer plate by the catch fingers  122  of the tray holders  120 . 
   The detecting substrate  140  may be provided on and attached to the upper portion of the transfer plate  110 . The detecting substrate  140  has the detecting switches  130  mounted in a configuration corresponding to the installation holes  113 , each of which correspond to a pocket  25  of the tray  21 . The leads  133  of the detecting switch  130  may be connected to the detecting substrate  140  by pin insertion into pin receptacles provided on the detecting substrate. The detecting substrate  140  may incorporate circuit wires  143  that connect the detecting switches  130  in a parallel configuration. An input/output terminal  145  for external connection may be connected to the circuit wires. A protection paper  149  or other protective covering may be provided on the upper portion of the detecting substrate  140  for protection from environmental or mechanical damage. 
   The transfer plate  110  may be connected to the vertical driving unit  151  and the horizontal driving unit  161  to provide for vertical and horizontal movement. The vertical driving unit  151  comprises a fixing plate  152  to which the transfer plate  110  is fixed, a first bracket  153  connected to the fixing plate  152 , a first screw  154  penetrating the first bracket  153  perpendicular to the ground and screw-connected to the first bracket  153 , a first motor  155  transmitting rotary force to the first screw  154 , a first base plate  157  to which the first screw  154  is fixed and a first guide rail  158  connected to the first bracket  153  for guiding the vertical movement of the transfer plate  110 . 
   The horizontal driving unit  161  comprises a second bracket  163  to which the first base plate  157  is fixed, a second screw  164  penetrating the second bracket  163  parallel to the ground and screw-connected to the second bracket  163 , a second motor  165  transmitting rotary force to the second screw  164 , a second base plate  167  to which the second screw  164  is fixed and a second guide rail  168  guiding the horizontal movement of the transfer plate  110 . The first and second motors  153  and  163  may be stepper motors. 
   Referring to  FIG. 8 , the fixing plate  152  has a catch finger driving cylinder  127  for moving the driving bar  125  of the transfer plate  110  forward or backward. The catch finger driving cylinder  127  transmits the driving force to the driving bar  125 , the movement of the driving bar causing the catch finger  122  to rotate. The catch finger driving cylinder  127  may incorporate a pneumatic cylinder. 
   In operation, the horizontal driving unit  161  may be used to position the transfer plate  110  above a target tray  21 . The vertical driving unit  151  may be used to lower the transfer plate  110  to a position adjacent a target tray  21 . Then, the catch finger driving cylinder  127  drives the catch finger driving plate  128 , which causes the driving bar  125  to move. The movement of the driving bar  125  causes the connection bar  124  to move, thereby rotating the rotation bearings  121  and the attached catch fingers  122  to support the bottom surface of the target tray  21 . 
   Once the target tray  21  is secured to the transfer plate  110 , the vertical driving unit  151  can be used to elevate the transfer plate  110  and the attached tray  21  and the horizontal driving unit  161  can be used to shift the transfer plate  110  to a desired horizontal position. Once in the desired horizontal position, the vertical driving unit  151  can be used to lower the transfer plate  110  to a desired vertical position, the catch finger driving cylinder  127  can be used to move the driving bar  125 , thereby rotating the rotation bearings  121  and catch fingers  122  to release the tray  21 . 
   If at least two semiconductor devices  10  are received in any one of the pockets  25  of the tray  21 , the contact button  135  associated with such a pocket will be depressed and activate detecting switch  130 . The resulting detecting signals are outputted through the input/output terminals  145  of the detecting substrate  140 . Because the detecting switches  130  are arranged in a parallel configuration, when any one of the detecting switches  130  is activated, a detecting signal is generated. The detecting signal is transmitted to the control unit of the equipment incorporating the tray transfer unit  100  of the present invention. When a fault is detected, the control unit may stop the operation of the equipment and/or operate the alarm sound or lamp, allowing the operator to take prompt corrective measures. 
   As described above, the control unit of the equipment will preferably alert the operator if a fault is detected in the tray transfer unit. However, if it would be difficult to modify the equipment construction in this manner, a separate control substrate may be installed to trigger an alarm upon the detection of a double device fault and/or stop the operation of the equipment. 
     FIG. 10  is a circuit diagram view of an exemplary control substrate suitable for use in the tray transfer unit in accordance with an exemplary embodiment of the present invention. As illustrated in  FIG. 10 , the control substrate  170  includes a rectifier  173  for changing the alternating current input voltage of the detecting substrate ( 140  of  FIG. 4 ) to direct current and a control chip  179  for generating alarm signals according to the input voltage from the rectifier  173 . 
   The control substrate  170  is connected to the detecting substrate ( 140  of  FIG. 4 ). A first terminal of a first connector  171  is connected to a second terminal of the rectifier  173 . A second terminal of the first connector  171  is connected to a third terminal of the rectifier  173 . The first terminal of the rectifier  173  is connected to a power terminal Vcc of a NE555 device which may be utilized as control chip  179 . The rectifier  173  may comprise a bridge diode for converting the AC voltage provided from the first connector  171 , e.g., an input alternating current voltage of 24V, to direct current. 
   The control chip  179  may be configured to generate periodic output signals. For example, the illustrated 8-pin NE555 device comprises one flip flop, one output transistor, two comparators and three resistors. A first pin is a ground terminal and a sixth pin is a power terminal. A second pin is a trigger, a third pin is an output terminal, a fourth pin is a reset terminal, a fifth pin is a control voltage terminal, a eighth pin is a threshold terminal and a seventh pin a discharge terminal. The sixth pin, Vcc, is disconnected from the seventh pin, CHG. 
   An electrolytic condenser  175  and a Zener diode  176  may be located between the rectifier  173  and the control chip  179 . In such an arrangement, the electrolytic condenser  175  filters the input voltage to stabilize the voltage and the Zener diode  176  protects the control chip  179  from overvoltage conditions. 
   The trigger terminal (pin  2 ) of the control chip  179  may be connected to the third connector  181  and also to an alarm lamp line. The output terminal (pin  3 ) of the control chip  179  may be connected to the second terminal of a magnetic switch  187  through a PNP transistor  185 . From the connection line after PNP transistor  185  the third output terminal diverges and is connected to both a fifth terminal of the magnetic switch  187  and the output of the rectifier  173  through a diode  186 . The first terminal of the magnetic switch  187  is connected to the third terminal of the rectifier  173 . The third terminal of the magnetic switch  187  is connected to the second terminal of the second connector  191 . The first terminal of the second connector  191  is connected to the connection line of the first connector  171  and the rectifier  173 . The second connector  191  is connected to the control line of the test handler. The magnetic switch  187  operates according to the output of the control chip  179  to control the control line of the test handler, consequently controlling the operation of the test handler. 
   When a double device fault is detected from the detecting substrate ( 140  of  FIG. 4 ) by the control substrate  170 , alternating current is input from the first connector  171 , converted to direct current by rectifier  173 , and then input into the control chip  179 . The magnetic switch  187  operates according to the output of the control chip  179  to control the alarms and/or the test handler operation. Therefore, when a double device fault occurs, the alarm lamp flashes and/or the test handler stops so that the operator can take corrective measures. The control substrate  170  or its equivalent may be incorporated in the circuit substrate of the control unit of the test handler or may be provided as a separate control unit. 
     FIG. 11  is a perspective view of an automatic test handler in accordance with an exemplary embodiment of the present invention.  FIG. 12  is a rear view of the automatic test handler in accordance with an exemplary embodiment of the present invention.  FIG. 13  is a perspective view of a tray stocker and a catch finger of the automatic test handler in accordance with an exemplary embodiment of the present invention. 
   Referring to  FIGS. 11 through 13 , an automatic test handler  200  comprises a tester  251  for testing semiconductor devices, a first chamber  253  for establishing the test temperature condition(s) for the semiconductor devices, a second chamber  255  for restoring the tested semiconductor devices to the normal temperature, a pick and place device  270  for transferring the semiconductor devices, a plurality of tray stockers  211  for receiving loaded trays  21  and empty trays  22  and grippers  241  for supporting the trays. The automatic test handler  200  further comprises a tray transfer unit  100  having a detecting substrate  140  for detecting the tray transfer and double device faults and a control unit  280  for controlling the overall operation. 
   The tray stocker  211  is installed on the upper portion of a cabinet  205 . Vertical guide pins  215  are provided in the tray stocker  211  for maintaining the orientation of the tray  21  and guiding its vertical movement. The tray stocker  211  is divided by supports  217  and may include a moving means (not shown) for automatically moving the tray stocker forward and backward to simplify loading trays into the tray stocker. The supply, i.e., initially full, trays  21  containing semiconductor devices and receiving, i.e., initially empty, trays  22  may be loaded into the tray stocker  211  and an automatic test process initiated. After the test process has been completed, the receiving trays containing the sorted semiconductor devices may be removed from the tray stocker  211  and transferred to a subsequent processing step. 
   The tray transfer unit  100  may be installed on the upper portion of the tray stocker  211 . As described above, the tray transfer unit  100  comprises a transfer plate  110 , detecting switches  130  and a detecting substrate  140 . The tray transfer unit  100  is connected to the control unit  280  to initiate an alarm in response to a double device fault and control the overall operation of the automatic test handler. 
   The tester  251  is installed on the upper portion of the cabinet  205 . The tester  251  is connected to the semiconductor devices received in the test tray  31  to perform one or more electrical tests according to a predetermined series of input and output test signals. The first chamber  253  may be used to establish the temperature condition(s) for test, e.g., one or more temperatures between about −30° C. and 125° C. The second chamber  255  may be used to restore the tested semiconductor devices to approximately normal room temperature. The test tray  31  is conveyed by the conveyor belt(s)  290 . 
   The pick and place device  270  may include both a loader pick and place device  270   a  and an unloader pick and place device  270   b . The pick and place device  270  absorbs or “picks” the semiconductor devices from a supply tray by applying a vacuum to a surface of the semiconductor devices and lifting the semiconductor device from the pocket in which it was held. Once “picked” or removed from the supply tray, the semiconductor device may be moved to and deposited or “placed” in a pocket provided in a receiving tray, a test tray  31  or a buffer  285 . 
   The pick and place device  270  may be configured to provide controlled movement in the x, y and z directions in order to provide the range of motion necessary to complete the desired transfers. As illustrated in  FIGS. 11 and 12 , the movement of the pick and place device  270  may be guided by a Y-axis support  271  and a X-axis support  273  to a position above a tray. Movement along a Z-axis, i.e., vertical, may then be initiated to position the absorbers in proximity to the pockets provided on the tray to remove semiconductor devices from or place semiconductor devices in the pockets according to the instructions received from the controller. 
   The gripper  241  is operated to support the tray  21  transferred by the tray transfer unit  100 . An insertion portion  241   a  (not identified) is formed on the upper surface in the middle of the cabinet  205 . The gripper moves upward and downward by a gripper moving means for insertion and detachment to/from the insertion portion  241   a . The gripper moving means includes a guide rail  243  for guiding the gripper  241  and a pneumatic cylinder to which one end of a rod  245  is fixed. 
   A buffer  285  may be installed between the test tray  31  and the gripper  241  for temporarily holding the semiconductor devices. The buffer may be utilized to adjust the adsorption position of the semiconductor device during the transfer between the test tray  31  and the trays  21  and/or trays  22 . 
   A control unit  280  is connected to at least the components related to loading/unloading and tray transfer operations and may be used to control the overall operation of the automatic test handler. For example, the control unit may be used to receive, store and/or evaluate the test data relating to semiconductor devices under test through a General Purpose Interface Bus (GPIB) and/or monitor and automatically control the temperature of the first chamber  253 . 
   Although the exemplary embodiments of the present invention have been described in detail hereinabove, it should be understood that many variations and/or modifications of the basic inventive concepts herein taught, which may appear to those skilled in the art, will still fall within the spirit and scope of the present invention as defined in the appended claims.