Abstract:
A system including a shuttle movable along a shuttle path, the shuttle being operable to support a sheet; a pick-up assembly including a yoke and a detection plate located above the shuttle path, the detection plate being freely supported by the yoke and movable in a vertical direction relative to the yoke with an upper limit and a lower limit defined by the yoke, wherein the yoke is operable to pick and place the sheet, and wherein the detection plate is used to detect the presence of a piece of debris on a surface of the sheet or a surface of the shuttle; and a cleaning device located adjacent to the pick-up assembly and above the shuttle path, wherein the cleaning device is operable to remove the piece of debris located on the surface of the sheet or the surface of the shuttle.

Description:
BACKGROUND 
       [0001]    1. Field of the Invention 
         [0002]    This invention relates to a system for detecting particulate contaminants associated with ceramic sheets during processing in the manufacture of integrated circuits. 
         [0003]    2. Background of Invention 
         [0004]    In the manufacture of integrated circuits, unfired ceramic sheets (hereinafter “green sheets”) are subjected to a variety of processing techniques, such as blanking, punching, screening with a conductive paste, and stacking into multilayer modules. The green sheets are generally flexible and soft until fired. They have a propensity to carry with them particulate contaminants, typically ceramic debris, which tend to adhere to their soft surfaces. These contaminants may be carried with the green sheets from station to station since handling is generally by vacuum pick-up or Bernouilli techniques. Thus, at those stations where debris is likely to be created, such as in blanking and punching of the green sheet material, it is difficult to eliminate all contaminants when the sheets are moved to the next processing station. 
         [0005]    The existence of these contaminants is especially severe during processing to screen a conductive paste pattern on the green sheet. During this process step, a thin mask may be placed over the green sheet wafer for the purpose of screening a highly complex and fine pattern of conductive lines. The presence of such contaminants has a twofold effect. First, they may cause dents in the mask during screening resulting in the destruction of the mask and poor dimensional control of the screened pattern. In the formation of integrated circuits, layers of green sheets may be stacked to define a multi-layer ceramic module. Alignment from layer to layer is crucial and the existence of a dent caused by a particle may destroy the conductive alignment in the mask which is used to screen conductive paste on that respective green sheet. As a result, the damaged mask must be discarded. 
         [0006]    Secondly, the presence of a contaminant inhibits effective screening of the conductive pattern. In the absence of a test to determine whether particles are present, screening takes place and it is only in subsequent quality control steps that the accuracy of the screening procedure is determined. Should the screening be defective, the sheets are generally unusable. Thus, in addition to destroying the mask, defective green sheets are produced. 
       SUMMARY 
       [0007]    According to one embodiment of the present invention, a system is provided. The system may include a shuttle movable along a shuttle path, the shuttle being operable to support a sheet; a pick-up assembly including a yoke and a detection plate located above the shuttle path, the detection plate being freely supported by the yoke and movable in a vertical direction relative to the yoke with an upper limit and a lower limit defined by the yoke, wherein the yoke is operable to pick and place the sheet, and wherein the detection plate is used to detect the presence of a piece of debris on a surface of the sheet or a surface of the shuttle; and a cleaning device located adjacent to the pick-up assembly and above the shuttle path, wherein the cleaning device is operable to remove the piece of debris located on the surface of the sheet or the surface of the shuttle. 
         [0008]    According to another exemplary embodiment, a method is provided. The method may include cleaning a shuttle by moving the shuttle along a shuttle path below a cleaning assembly; placing a sheet on the shuttle using a pick-up assembly comprising a detection plate; the detection plate being freely supported by a yoke and movable in a vertical direction relative to the yoke with an upper limit and a lower limit defined by the yoke; cleaning the sheet by moving the shuttle with the sheet along the shuttle path below the cleaning assembly; and checking for debris by lowering the pick-up assembly and resting the detection plate on the sheet. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0009]    The following detailed description, given by way of example and not intend to limit the invention solely thereto, will best be appreciated in conjunction with the accompanying drawings, in which: 
           [0010]      FIG. 1  illustrates a pick-up head assembly and a nest assembly according to one embodiment. 
           [0011]      FIG. 2  illustrates the sensor set position of the pick-up head assembly according to one embodiment. 
           [0012]      FIG. 3  illustrates debris detection using the pick-up head assembly according to one embodiment. 
           [0013]      FIG. 4  illustrates a cleaning device according to one embodiment. 
           [0014]      FIG. 4A  illustrates a cleaning device according to one embodiment. 
           [0015]      FIG. 5  illustrates a cross-sectional view of  FIG. 4 . 
           [0016]      FIGS. 6A-6G  illustrate the steps of a method of cleaning and detecting debris according to one embodiment. 
           [0017]      FIG. 6A  illustrates moving a shuttle from the input station to the load station and raising the detection plate according to one embodiment. 
           [0018]      FIG. 6B  illustrates picking up a greet sheet according to one embodiment. 
           [0019]      FIG. 6C  illustrates moving the shuttle from the load station back to the input station and cleaning the nest assembly as it moves under the cleaning device from the screen station to the load station according to one embodiment. 
           [0020]      FIG. 6D  illustrates depositing the green sheet on the nest assembly at the load station according to one embodiment. 
           [0021]      FIG. 6E  illustrates cleaning the surface of the green sheet as the nest assembly moves from the load station to the screen station and back the load station while passing under the cleaning device according to one embodiment. 
           [0022]      FIG. 6F  illustrates a debris detection sequence without the presence of debris according to one embodiment. 
           [0023]      FIG. 6G  illustrates a debris detection sequence with the presence of debris according to one embodiment. 
       
    
    
       [0024]    The drawings are not necessarily to scale. The drawings are merely schematic representations, not intended to portray specific parameters of the invention. The drawings are intended to depict only typical embodiments of the invention. In the drawings, like numbering represents like elements. 
       DETAILED DESCRIPTION 
       [0025]    Detailed embodiments of the claimed structures and methods are disclosed herein; however, it can be understood that the disclosed embodiments are merely illustrative of the claimed structures and methods that may be embodied in various forms. This invention may, however, be embodied in many different forms and should not be construed as limited to the exemplary embodiments set forth herein. Rather, these exemplary embodiments are provided so that this disclosure will be thorough and complete and will fully convey the scope of this invention to those skilled in the art. In the description, details of well-known features and techniques may be omitted to avoid unnecessarily obscuring the presented embodiments. 
         [0026]    Referring now to  FIGS. 1-5 , one embodiment of the present invention is shown. As set forth herein, a function of this invention is to determine the presence of particles which adhere to either the pick-up head or nest surfaces which would result in either damage to screening masks or result in defective screening. 
         [0027]    Now referring to  FIG. 1 , a nest assembly  102  generally including a fixture  103  having a plurality of locating pins  104 . While two such pins are shown, it may be understood that any number of pins can be used to achieve accurate alignment of the system. The nest assembly  102 , as shown in  FIG. 1 , may be used as an operation point in the processing of green sheets. A pick-up head assembly  106  may be used to move green sheets between processing stations. The pick-up head assembly  106  may use vacuum or Bernouilli principles to lift, support, and transfer a green sheet during processing. The pick-up head assembly  106  may include a yoke  108  and a detection plate  110 . The yoke  108  may include inward facing flanges  112  which may support corresponding outward facing flanges  114  on the detection plate  110 . The detection plate  110  may be approximately 8 in square, 9/32 in thick, and weight about 5 lbs. The detection plate  110  may move freely, or float, within the confines of the yoke  108 . The yoke  108  may also include alignment holes  116  suitably fitted with a sleeve  118  to reduce friction and provide accurate alignment of the pick-up head assembly  106 , vis-a-vis the plurality of locating pins  104 . 
         [0028]    A series of pneumatic ports  120  may extend from an outer surface  122  to an inner surface  124  of the yoke  108 . The pneumatic ports  120  in combination with a film chamber  126  may be used to raise the detection plate  110  within the yoke  108 . While only two pneumatic ports are illustrated by the cross-sectional view in the figures, it may be understood that any number of pneumatic ports can be used to achieve sufficient vacuum lifting capacity required. In one embodiment, four pneumatic ports may be used to achieve sufficient vacuum lifting capacity (shown in  FIG. 5 ). The pneumatic ports  120  may be fitted to the film chamber  126  located adjacent to the inner surface  124  of the yoke  108 . The film chamber  126  may be, for example, Mylar. The pneumatic ports  120  may be connected to a hose  128  which may provide either compressed air, vacuum, or both to the film chamber  126  via the pneumatic ports  120 . 
         [0029]    A series of sensors  130  may be fitted in the yoke  108 . The sensors  130  may be used to determine the relative position of the detection plate  110  to the yoke  108 . It is apparent that any number of sensors can be used so long as the position of the detection plate  110  relative to the yoke  108  can be ascertained. As shown in  FIG. 1 , a bottom surface  132  of the detection plate  110  may protrude by a distance (X) from the lower surface  134  of the yoke  108  when the inward facing flanges  112  and outward facing flanges  114  are in an abutting relationship. Furthermore, a distance (Y) may exist between the detection plate  110  and the sensors  130  when the inward facing flanges  112  and outward facing flanges  114  are in an abutting relationship. 
         [0030]    The pick-up head assembly  106  may raise and lower above the nest assembly  102  to pick and place a green sheet or detect debris on the surface of the green sheet. When no debris is present on the green sheet the detection plate  110  may lay flat on the surface of the green sheet. When debris may be present either above or below the green sheet the detection plate  110  may not sit flat on the surface of the green sheet. 
         [0031]    Now referring to  FIG. 2 , the pick-up assembly  106  may be lowered on top of the nest assembly  102  illustrating the sensor set position when no debris is present. The locating pins  104  of the nest assembly  102  may engage with the alignment holes  116  (shown in  FIG. 1 ) in the yoke  108  to assure proper alignment of the yoke  108  relative to the nest assembly  102 . In particular, a green sheet  136  supported by a film material  138  may be positioned on the nest assembly  102 . The green sheet  136  may contain a template of thru-holes (for example vias) and the film material  138  may prevent the screened on paste from permeating through the vias and coming in contact with the nest assembly  102 . In one embodiment, the film material  138  may be “Melinex” or another commercially available film. With the green sheet  136  and film material  138  positioned on the nest assembly  106 , and the nest assembly  106  positioned below the pick-up head assembly  106 , the pick-up head assembly  106  may be lowered and the detection plate  110  may rest substantially uniform on the green sheet  136 . The sensors  130  may therefore be disposed a uniform distance (Y) above the plate. Stated differently, there should be no variation in dimension (Y) between the upper surface of the detection plate  110  and any of the sensors  130  shown in  FIG. 2 . 
         [0032]    Now referring to  FIG. 3 , the yoke  108  may be lowered on top of the nest assembly  102  illustrating the presence and detection of a piece of debris  140  on the green sheet  136 . If debris is present, as shown in the figure, the detection plate  110  will be displaced upward in the vicinity of the piece of debris  140 . The sensor set dimensions (Y) may not be maintained such that a variation in output will exist between two different sensors  130 . This output may be used to indicate the presence of the piece of debris  140  on the surface of the green sheet  136 . Therefore, the green sheet  136  should be rejected and cleaned prior to subsequent processing. 
         [0033]    The sensors  130  may include, for example, air gauges, linear variable differential transformer (LVDT), mechanical or other proximity sensors. It is also apparent that contact or non-contact type sensors may be used. Sensor output would typically be processed via typical signal processing techniques associated with a pick-up head reference point, and sensor outputs as a function of the sensor set dimension (Y). 
         [0034]    Alternatively, in one embodiment the sensors  130  may be positioned in the detection plate  110 . In this embodiment, the sensors  130  may detect the distance between the detection plate and the upper surface on the green sheet  136 . 
         [0035]      FIG. 3  illustrates a situation where debris may be carried by the green sheet  136 . It may be understood, however, that the embodiment is equally applicable to detect and eliminate the presence of debris which exists on the nest assembly  102  or between the green sheet  136  and the film material  138 . 
         [0036]    Now referring to  FIG. 4 , a sheet and nest cleaning device  142  (hereinafter referring to as cleaning device  142 ) is shown positioned adjacent to the pick-up head assembly  106  and in-line with the travel of the nest assembly  102 . The cleaning device  142  may be positioned above the nest assembly  102 . During a cleaning sequence, the cleaning device  142  may direct compressed air  144  in a plurality of directions at the nest assembly  102 . In addition to the compressed air  144  used to loosen debris, a vacuum  145  may be located in the center of the cleaning device  142  which may be used to remove the debris. In one embodiment, the cleaning device  142  may itself travel vertically to facilitate up close cleaning of the nest assembly  102  or a green sheet located on the nest assembly  102 . The cleaning method is described in greater detail below (see  FIGS. 6A-6G ). In one embodiment, the cleaning device  142  may include a sweeper, as shown in  FIG. 4A , with soft plastic bristles. The sweeper may be used to brush debris from the surface of the green sheet  136  or the nest assembly  102 . 
         [0037]    Now referring to  FIG. 5 , a cross-sectional view of  FIG. 4 , section A-A, in which the pneumatic ports  120 , the film chamber  126 , and the sensors  130  are shown. Four pneumatic ports  120  are shown, but as described above, any sufficient number of pneumatic ports in any sufficient configuration may be used. Similarly, four sensors  130  are shown, but any sufficient number of sensors able to detect some variation in the detection plate  110  may be used. The film chamber  126  may have a octagonal shape, although any sufficient shape may be used. 
         [0038]    Referring now to  FIGS. 6A-6G , exemplary process steps of cleaning and contamination detection of a loadhead assembly system in accordance with one embodiment of the present invention are shown. The loadhead assembly system may include three process stations, an input station, a load station, and a screen station. The three process stations may be in-line with one another with the load station being situated between the input station and the screen station. These three process stations may be referred to collectively as a process stream. The input station is where new green sheets may be introduced into the process stream. Specifically, an input tray shuttle moves from the input station to the load station where a pick-up head assembly picks up a green sheet and a film material. A detection plate located within the pick-up head assembly may be retracted during picking of the green sheet. The input tray shuttle may then move from the load station back to the input station. Next, a nest assembly moves from the screen station to the load station during which the surface of the nest assembly may be cleaned by a cleaning device. The pick-up head assembly places the green sheet and film material onto the nest assembly. The nest assembly, with the green sheet and film material, may move from the load station to the screen station and back to the load station during which a top surface of the green sheet may be cleaned. Next, the detection plate may be lowered within the pick-up head assembly and the pick-up head assembly may be lowered on top of the green sheet to initiate debris detection. Cleaning prior to debris detection may help eliminate debris from being compressed into the surface of the green sheet by the weight of the detection plate. 
         [0039]    Now referring to  FIG. 6A , an input tray shuttle  146 , loaded with a stack  148  of green sheets and film materials, may travel from an input station to a load station. Before picking a green sheet  136  and a film material  138  the detection plate  110  may be retracted into the yoke  108  by applying a suitable amount of vacuum to the hose  128 , as shown in the figure. Preferably, a vacuum of at least about 20 inHg to about 25 inHg may be required to lift a detection plate weighing about 5 lbs. The vacuum applied to the hose  128  may be delivered to the pneumatic ports  120  and film chamber  126  causing the detection plate  110  to retract against the film chamber  126 . Vacuum pressure may be maintained using, for example, a solenoid valve (not shown) or alternatively by applying continuous vacuum to the hose  128 . At this time, a piece of debris  150  may be present on the surface of the nest assembly  102 . 
         [0040]    Now referring to  FIG. 6B , the green sheet  136  and film material  138  may be picked up and raised by the pick-up head assembly  106 . As described above, the pick-up head assembly  106  may use vacuum or Bernouilli principles to lift the green sheet  136  and film material  138  during processing. Once the green sheet  136  and film material  138  have been lifted, the input tray shuttle  146  may return to the input station. 
         [0041]    Now referring to  FIG. 6C , the nest assembly  102  may be shuttled from the screen station to the load station all while passing beneath the cleaning device  142 . As the nest assembly  102  passes beneath the cleaning device  142 , the compressed air  144  and vacuum  145  may remove, for example, the piece of debris  150  (shown in  FIG. 6A ) from the surface of the nest assembly  102 . 
         [0042]    Now referring to  FIG. 6D , the pick-up assembly  106  may lower and deposit the green sheet  136  and the film material  138  on the nest assembly  102 . In some cases, a piece of debris  152  may exist within an active area on the surface of the green sheet  136 , as shown in the figure. The active area of the green sheet  136  may be the area in which the detection plate  110  rests during its detection sequence. The piece of debris  152  may be introduced into the process stream at any time and by any mode, and the existence of the piece of debris  152  is relevant, not how or when it may have been introduced. The piece of debris  152  may preferably be removed from the active area of the green sheet prior to initiating the detection sequence or else the piece of debris  152  may be compressed into the surface of the green sheet  136 . Generally, debris compressed into the surface of a green sheet may result in a defective green sheet. It may be understood that debris located outside the active area of the green sheet  136  may be less problematic for subsequent fabrication processes and future green sheet operation. 
         [0043]    Now referring to to  FIG. 6E , the nest assembly  102 , with the green sheet  136  and the film material  138 , may then be shuttled to the screen station and back to the load station all while passing beneath the cleaning device  142 . As the green sheet  136  passes beneath the cleaning device  142 , the compressed air  144  may free the debris  152  (shown in  FIG. 6D ) and the vacuum  145  may remove the debris  152  (shown in  FIG. 6D ) from the surface of the green sheet  136 . 
         [0044]    Now referring to  FIG. 6F , the detection sequence may be initiated. First, the vacuum pressure used to raised the detection plate  110  may be released and allow the detection plate  110  to move freely, or float, within the confines of the yoke  108 . In one embodiment, the hose  128  may be supplied with compressed air to break any residual vacuum between the film chamber  126  and the detection plate  110 . The pick-up assembly  106  may then be lowered on top of the nest assembly  102 . As described above, the locating pins  104  of the nest assembly  102  may engage with the alignment holes  116  (shown in  FIG. 1 ) in the yoke  108  to assure proper alignment of the yoke  108  relative to the nest assembly  102 . The detection plate  110  may rest on the green sheet  136 . The sensors  130  may therefore be disposed at some distance (Z) above the plate. In the case where the cleaning device  142  was successful in removing the piece of debris  152  the detection plate  110  may rest substantially uniform on the green sheet  136 , and there may be no variation in dimension (Z) between the upper surface of the detection plate  110  and any of the sensors  130 , as shown in the figure. 
         [0045]    Now referring to  FIG. 6G , the case where cleaning sequence was unsuccessful and the piece of debris  152  may remain on the surface of the green sheet  136 , is shown. In such cases, the detection plate  110  may not sit uniform causing some variation in dimension (Z) between various sensors  130 . In one embodiment, upon some indication that the piece of debris  152  may remain on the surface of the green sheet  136  another cleaning sequence may be initiated. Alternatively, the green sheet  136  with the piece of debris  152  may be rejected from processing for off-line cleaning. 
         [0046]    The descriptions of the various embodiments of the present invention have been presented for purposes of illustration, but are not intended to be exhaustive or limited to the embodiments disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments. The terminology used herein was chosen to best explain the principles of the embodiment, the practical application or technical improvement over technologies found in the marketplace, or to enable others of ordinary skill in the art to understand the embodiments disclosed herein.