Abstract:
A loading apparatus for loading a printed circuit board (PCB) stack including one or more PCB layers and transferring the PCB stack to an inspection probe includes a movable support unit, a guide unit and a cover. The guide unit is provided on the support unit and defines a depression portion in which the PCB stack is mounted. The cover is configured to cover the depression portion of the guide unit when closed, where the cover has multiple protrusions extending from a lower surface, which press the PCB stack into the depression portion when the cover is closed.

Description:
BACKGROUND 
       [0001]    Various embodiments relate to an apparatus for loading a printed circuit board (PCB) and, more particularly, to a PCB loading apparatus which holds and transfers a PCB for measuring a thickness thereof. 
         [0002]    To facilitate mass production of electronic devices having PCBs, it is desirable to be able to measure a priori the thicknesses of layers of the PCBs to be incorporated in the devices. 
         [0003]      FIG. 1A  shows a conventional PCB inspection system for measuring thicknesses of PCB layers a PCB stack P. The conventional PCB inspection system shown in  FIG. 1A  includes a PCB loading apparatus  100 , a control unit  140  for controlling operations of the loading apparatus  100 , an image camera  170  for acquiring positions of the PCB layers to be inspected, and an inspection probe  190  for measuring the thicknesses of the PCB layers. 
         [0004]    The PCB loading apparatus  100  includes a vacuum chuck  102 , which defines vacuum holes  105  in an upper surface thereof, and a PCB holder  110 , which is provided on an upper surface of the vacuum chuck  102  and defines fixing holes  115  penetrating therethrough. The vacuum chuck  102  is configured to generate a vacuum suction force. The number of fixing holes  115  penetrating through the PCB holder  110  is the same as the number of vacuum holes  105 . The PCB holder  110  is placed on the vacuum chuck  102  so that the fixing holes  115  communicate with respective vacuum holes  105 . 
         [0005]      FIG. 1B  shows the inspection probe  190  and the stack of PCB layers P of  FIG. 1A  in more detail. 
         [0006]    The inspection probe  190  includes a pair of probe tips  192  to be used for measuring the thicknesses of the PCB layers. The PCB stack P includes an inspection area T having pairs of inspection ports T1, T2 and T3, the number of which is the same as the number of the PCB layers. The inspection ports T1, T2 and T3 are provided with corresponding contact points CP1, CP2 and CP3, respectively, to be contacted by the probe tips  192  for measuring the PCB thicknesses. The contact points CP1, CP2 and CP3 are electrically connected to the PCB layers, respectively. 
         [0007]    A process for measuring the thicknesses of the PCB layers using the conventional PCB inspection system will now be described with reference to  FIGS. 1A and 1B . When the PCB stack P is loaded onto the PCB holder  110 , a vacuum suction force generated from the vacuum chuck  102  is applied to the PCB stack P through the vacuum holes  105  and the fixing holes  115  to hold the PCB stack P on the PCB holder  110 . After the loading of the PCB stack P has been completed, alignment of the PCB stack P is carried out based on both a position of the vacuum chuck  102  previously stored in the control unit  140  and a position of the PCB stack P with respect to the vacuum chuck  102  measured by the image camera  170 . Based on the result of the alignment, the vacuum chuck  102  transfers the PCB stack P to the inspection probe  190 . The inspection probe  190  successively brings the pair of probe tips  192  into contact with the contact points CP1, CP2 and CP3 of the inspection ports T1, T2 and T3 of the PCB stack P, thereby measuring the thicknesses of the PCB layers. 
         [0008]    However, the conventional PCB inspection system using the PCB loading apparatus  100  has a number of drawbacks. When the PCB stacks P are loaded onto the PCB holder  110 , their positions with respect to the vacuum chuck  102  may differ, e.g., depending on the operator who loads the PCB stacks P. Therefore, whenever a PCB stack P is loaded, alignment must be performed, resulting in increased inspection time. 
         [0009]    Furthermore, the PCB stack P is held on the PCB holder  110  only by the vacuum suction force of the vacuum chuck  102 . Thus, after the vacuum chuck  102  transfers the PCB stack P to the inspection probe  190 , its position with respect to the vacuum chuck  102  may change from that used for the alignment. In this case, the probe tips  192  may not exactly come into contact with the contact points CP1, CP2 and CP3 of the inspection ports T1, T2 and T3, thereby compromising the reliability of the inspection process. 
         [0010]    Accordingly, there exists a need for an apparatus capable of carrying out a PCB measurement operation in less time with enhanced reliability. 
       SUMMARY 
       [0011]    In accordance with a representative embodiment, a loading apparatus is provided for loading a printed circuit board (PCB) stack including one or more PCB layers and transferring the PCB stack to an inspection probe. The loading apparatus includes a movable support unit, a guide unit and a cover. The guide unit is provided on the support unit and defines a depression portion in which the PCB stack is mounted. The cover is configured to cover the depression portion of the guide unit when closed, where the cover has multiple protrusions extending from a lower surface, which press the PCB stack into the depression portion when the cover is closed. 
         [0012]    In accordance with another representative embodiment, a PCB inspection system is provided, including an inspection probe for measuring thicknesses of one or more PBC layers of a PCB stack, and a loading apparatus configured to load the PCB stack and to transfer the PCB stack to the inspection probe. The loading apparatus includes a movable support unit, a guide unit and a cover. The guide unit is positioned on the support unit and defines a depression portion for mounting the PCB stack therein. The cover is configured to cover the depression portion of the guide unit when closed, the cover having multiple protrusions extending from a lower surface, where the protrusions press the PCB stack into the depression portion when the cover is closed. 
         [0013]    In accordance with another representative embodiment, a method is provided for measuring a thickness of a PCB stack comprising one or more PCB layers using an inspection probe and a loading apparatus having a movable support unit and a guide unit provided on the support unit. The method includes loading the PCB stack into a depression portion of the guide unit, closing a cover over the depression portion, causing multiple protrusions extending from a lower surface of the cover to press the PCB stack into the depression portion of the guide unit, securing the PCB stack in an initial position, moving the loading apparatus to the inspection probe, and determining a thickness of the PC B stack using the inspection probe. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    Illustrative embodiments are best understood from the following detailed description when read with the accompanying drawing figures. It is emphasized that the various features are not necessarily drawn to scale. In fact, the dimensions may be arbitrarily increased or decreased for clarity of discussion. Wherever applicable and practical, like reference numerals refer to like elements. 
           [0015]      FIG. 1A  is a block diagram and cross-sectional view showing a conventional PCT thickness inspection system; 
           [0016]      FIG. 1B  is a cross-sectional view of a probe and a PCB stack of  FIG. 1A  in more detail; 
           [0017]      FIG. 2  is a block diagram and cross-sectional view of a loading apparatus, in accordance with a representative embodiment; 
           [0018]      FIG. 3  is a cross-sectional view of a guide unit and a cover of the loading apparatus of  FIG. 2 , in accordance with a representative embodiment; 
           [0019]      FIG. 4  is a plan view of a loading apparatus, in accordance with a representative embodiment; 
           [0020]      FIG. 5  is a block diagram and cross-sectional view of a PCB thickness inspection system using the loading apparatus, in accordance with a representative embodiment; and 
           [0021]      FIG. 6  is a graph for comparing performance of a PCB thickness inspection system using the loading apparatus in accordance with a representative embodiment and a conventional PCB thickness inspection system. 
       
    
    
     DETAILED DESCRIPTION 
       [0022]    Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings so that they can be readily implemented by those skilled in the art. However, the described embodiments are only exemplary and not to be construed to limit the scope of the invention thereto. 
         [0023]      FIG. 2  is a block diagram and cross-sectional view of a loading apparatus  300 , in accordance with a representative embodiment. The loading apparatus  300  includes a support unit  310  which can be moved by a motor, and a guide unit  320  which is fixed on the support unit  310 . The support unit  310  defines a depression portion  325  into which a PC B stack P is loaded. The PCB stack includes one or more stacked PCB layers. The loading apparatus  300  further includes a cover  330 , which is operable to cover and uncover the depression portion  325  of the guide unit  320 , and a control unit  340 , which stores an initial position of the loading apparatus  300  before loading the PCB stack P and controls movement of the loading apparatus  300 . 
         [0024]    The cover  330  is rotatably connected at one edge to the guide unit  320 , so that the cover  330  can open or close the depression portion  325 . Multiple protrusions  335  extend from a lower surface  332  of the cover  330 , the lower surface facing the depression portion  325  when the cover  330  is closed over the depression portion  325 . The protrusions  335  are configured to press the PCB stack P into the depression portion  325  towards the support unit  310  when the cover  330  is closed, thus preventing the PCB stack P from moving within the depression portion  325 . By virtue of the structure in which the protrusions  335  press against the PCB stack P, the PCB stack P is prevented from changing position, even when the loading apparatus  300  is moving. 
         [0025]    In the depicted embodiment, the depression portion  325  has a rectangular shape, where the sides of the rectangle are longer by about 1 mm to about 10 mm than predetermined lengths of the sides of the PCB stack P. The PCB stack P is loaded into the depression portion  325  such that the PCB stack P is brought into contact with a predetermined corner of the depression portion  325 . In this way, the initial position of the PCB stacks loaded into the depression portion  325  is same each time. Therefore, a separate alignment process is not required every time a PCB stack P is loaded into the depression portion  325 . 
         [0026]    Due to the shape and the lengths of the sides of the depression portion  325 , the loading apparatus  300  does not require an additional alignment process other than an initial alignment process for positioning the loading apparatus  300 . Therefore, time required for performing the inspection is reduced. 
         [0027]      FIG. 3  is a cross-sectional view of the guide unit  320  and the cover  330  of the loading apparatus  300  of  FIG. 2 , in accordance with a representative embodiment. 
         [0028]    When the cover  330  is in the closed position (indicated by solid lines), the protrusions  335  extending from the lower surface  332  of the cover  330  come into contact with an upper surface of the PCB stack P (positioned within the depression portion  325 ). A depth d of the depression portion  325  is less than the sum of a length w1 of the protrusions  335  extending from the lower surface  332  when the cover  330  is in the opened position and a predetermined thickness w2 of the PCB stack P. However, since the protrusions  335  are formed of an elastic material, such as rubber or elastic polymer, for example, they are compressible. Therefore, the sum of a length W1′ of the protrusions  335  protruding from the lower surface  332  when the cover  330  is in the closed position and the predetermined thickness w2 of the PCB stack P becomes substantially the same as the depth d of the depression portion  325 . Therefore, the initial position of the PCB stack P can be reliably maintained by the protrusions  335  which press the PCB stack P towards the support unit  310 , even while the loading apparatus  300  is moving. As a result, the probability of a failure of contact between a probe tip of the inspection probe and contact points of an inspection area T of the PCB stack P is reduced. Moreover, since the protrusions  335  are made of an elastic material, the PCB stack P is prevented from being damaged when the PCB stack P is pressed by the protrusions  335 . 
         [0029]      FIG. 4  is a plan view of the loading apparatus, in accordance with a representative embodiment. 
         [0030]    In the depicted embodiment, the cover  330  defines an opening  336  which exposes the inspection area T of the PCB stack P to the outside. The cover  330  also includes a perimeter part  334  that surrounds the opening  336 . The protrusions  335  (not shown in  FIG. 4 ) are located on the lower surface  332  of the perimeter part  334  of the cover  330 . 
         [0031]    The cover  330  may be made of a lightweight material, such as aluminum or gold-plated copper, for example, so that the operator who loads the PCB stack P can easily open and close the cover  330 . Furthermore, in order to reduce potentially negative effects of external electromagnetic waves passing through the opening  336  after the PCB stack P is loaded into the loading apparatus  300 , the protrusions  335  and/or the perimeter part  334  may be formed of materials that have the ability to absorb electromagnetic waves. 
         [0032]      FIG. 5  is a block diagram and cross-sectional view of a PCB thickness inspection system using the loading apparatus, in accordance with a representative embodiment. 
         [0033]    The PCB inspection system  500  includes the loading apparatus  300  of  FIG. 2 , and an inspection probe  400  having probe tips  402  to be successively contacted with contact points of the inspection area T (not shown in  FIG. 5 ) of the PCB stack P in order to measure thicknesses of the PCB layers. 
         [0034]    A process of measuring the thicknesses of the PCB layers is described below. First, the user opens the cover  330  of the loading apparatus  300  and loads the PCB stack P into the depression portion  325 . Before the cover  330  is closed, the PCB stack P is positioned such that one corner thereof is brought into contact with a predetermined corner of the depression portion  325 . The cover  330  is then closed, causing the protrusions  335  to press onto the PCB stack P, holding it in place within the depression portion  325  by pressing the PCB stack P into a bottom surface of the depression portion  325  (toward the guide unit  320 ). The control unit  340  transmits an inspection execution signal to the loading apparatus  300 , which moves towards the inspection probe  400  securely holding the PCB stack P. 
         [0035]    The probe tips  402  of the inspection probe successively contact the contact points of each PC B layer of the inspection area T of the PCB stack P, and measure input and output signals, enabling calculation of corresponding S21 values of signals passing through the respective PCB layers based on the measured input and output signals. Impedance of each PCB layer may be calculated based on the S21 values. Subsequently, the thickness of each PCB layer may be calculated based on the corresponding impedance. In this way, the thicknesses of the PCB layers and of the PCB stack P can be accurately determined, where the thickness of the PCB stack may be determined by adding the thicknesses of the PCB layers. 
         [0036]    As stated above, since the initial position of each PCB stack loaded into the depression portion  325  can be maintained, an additional alignment need not be performed every time the PCB stack P is loaded, thus reducing the time it takes to conduct the inspection. Furthermore, the initial position of the PCB stack P is reliably maintained by the protrusions  335  which press the PCB stack P into the depression portion  325  towards the support unit  310 , even while the loading apparatus  300  is moving. As a result, the probability of a failure of contact between probe tips  402  of the inspection probe  400  and contact points of an inspection area T of the PCB stack P is reduced, thus enhancing the reliability of the inspection. 
         [0037]      FIG. 6  is a graph showing performance of the PCB thickness inspection system using the loading apparatus  300 , in accordance with a representative embodiment, and performance of a conventional PCB thickness inspection system. 
         [0038]    The horizontal axis refers to the number of PCB thickness measurements, the left vertical axis refers to the time it takes to conduct each measurement, and the right vertical axis refers to an error rate of the PCB thickness measurement. 
         [0039]    Line  200  indicates an error rate of the PCB thickness measurement performed by the conventional inspection system, and line  600  indicates an error rate of the PCB thickness measurement performed by the PCB inspection system  500  using the loading apparatus  300 , in accordance with a representative embodiment. Further, line  210  indicates the time it takes to conduct the measurement using the conventional inspection system, and line  610  indicates the time it takes to conduct the measurement using the PCB inspection system  500 . 
         [0040]    Less time is needed to conduct the measurement when using the PCB inspection system  500  using the loading apparatus  300 , in accordance with a representative embodiment, e.g., since an additional alignment does not have to be conducted after the initial alignment process. Further, since the PCB stack P is effectively clamped in place by the protrusions  335  of the loading apparatus  300 , even when the loading apparatus  300  is moved to the inspection probe  400 , the position of the PCB stack P can be prevented from being changed. Therefore, the probability of failure of contact between the contact points of the inspection area of the PCB stack P and the probe tips  402  is reduced, enhancing the reliability of the measurement. 
         [0041]    While illustrative embodiments have been shown and described, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the scope of the present teachings, as indicated by the following claims. These and other variations would become clear to one of ordinary skill in the art after inspection of the specification, drawings and claims herein. The invention therefore is not to be restricted except within the spirit and scope of the appended claims.