Abstract:
A device to access and/or verify connections between a chip package and a printed circuit board (“PCB”), specifically within packages lacking back-side measurement access, includes a housing for insertion between the chip package and PCB. A passageway in the housing connects an entrance and an exit from the housing. The entrance is disposed on an end of the housing facing away from the chip package. The exit is disposed on a side of the housing below the chip package such that the passageway is directed at a signal path between the chip package and the PCB. A conductor disposed in the passageway is movable between a retracted position in which a contact end of the conductor is disposed within the passageway of the housing and an extended position in which the contact end of the conductor is disposed outside of the housing and in contact with the signal path.

Description:
TECHNICAL FIELD 
   The present disclosure relates generally to testing signal paths and connections between a chip package and a printed circuit board, and more particularly to an apparatus that can be inserted between a chip package and a printed circuit board to test such connections. 
   BACKGROUND 
   A chip package is the housing in which a computer chip is placed and which is soldered to a printed circuit board (hereinafter “PCB”). The chip package is soldered to the PCB at multiple, evenly-spaced locations to create multiple signal paths between the chip and the PCB (referred to herein as signal paths between the chip package and the PCB). The ability to provide more and more input/output connections to a chip that is increasingly shrinking in size is an ever-present problem. Additionally, the multiple connections between the chip package and the PCB must be tested, and the ever-decreasing size of such items can complicate that task. 
   One conventional method for testing the connections providing the signal paths between the chip package and the PCB includes providing vias (or holes) through a bottom surface of the PCB that allow access to the connections between the PCB and the chip package. Then, probes from a test device can be inserted into the vias to contact the connections to thereby test the signal paths between the PCB and the chip package. However, this method requires access to the back of the PCB, which may not be available for a PCB installed in a device. Additionally, this method may not provide accurate test measurements because of the test location on the underside of the PCB. Typically, specifications are developed for data signals exiting the chip package. Such signals may have different performance or characteristics if measured at the via on the opposite side of the PCB instead of at the exit of the chip package. 
   Another conventional test method is to connect trace wires to the connections between the PCB and the chip package during the manufacturing process and to route the trace wires outside of the profile of the chip package. Then, a test probe can be connected to the trace wires to test the connections. However, this method requires additional manufacturing cost to provide the trace wires and adversely adds length, reflections, and/or other loss to the signal path in question. 
   Therefore, a need exists in the art for a device for testing the signal path connections between a chip package and a PCB. Additionally, a need exists in the art for a device for testing the exit connections of a chip package when mounted to a PCB. 
   SUMMARY 
   The invention provides a device for testing the connections between a chip package and a PCB. The device comprises an insulating housing that is sized to fit between the chip package and the PCB and between rows of solder connections connecting the chip package to the PCB. A stop member of the housing prevents insertion of the housing between the solder connections beyond a desired point. A spacer may be provided on the housing to adjust the insertion distance of the housing between rows of solder connections. The housing comprises a passageway having an entrance into the housing and an exit from the housing. The entrance into the housing is disposed on the end of the housing on which the stop member is disposed, and the exit from the housing is disposed on a side of the housing at a location away from the stop member. A conducting probe is disposed in the passageway of the housing and is movable between a retracted position in which a contact end of the conductor is disposed within the passageway of the housing and an extended position in which the contact end of the conductor is disposed outside of the housing (through the exit) to contact a solder connection between the chip package and the PCB. When contacting the solder connection, the conductor provides a signal path from the connection to a location outside of a profile of the chip package for transmission to a testing device, such as an oscilloscope. A spring connected to the housing and the conductor biases the conductor to the retracted position. 
   These and other aspects, objects, features, and embodiments of the invention will become apparent to a person having ordinary skill in the art upon consideration of the following detailed description of exemplary embodiments exemplifying the best mode for carrying out the invention as presently perceived. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is perspective view of a chip package disposed on a PCB. 
       FIG. 2  is a cross-sectional view of a device for testing connections between a chip package and a PCB according to an exemplary embodiment, wherein the device is disposed in a non-testing position. 
       FIG. 3  is a cross-sectional view of a device for testing connections between a chip package and a PCB according to an exemplary embodiment, wherein the device is disposed in a testing position. 
       FIG. 4  is a cross-sectional view of a system for testing connections between a chip package and a PCB according to an exemplary embodiment. 
   

   DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
   The invention is directed to a device for testing signal path connections between a chip package and a PCB. In particular, the invention can provide a device that fits between the chip package and the PCB and between solder connections connecting the chip package to the PCB, wherein the device includes a conductor that can be positioned to contact a solder connection on one end and to provide access for connection to a testing probe on its other end. 
   Turning now to the drawings, in which like numerals indicate like elements throughout the figures, exemplary embodiments of the invention are described in detail. 
     FIG. 1  is perspective view of a chip package  104  disposed on a PCB  102 . As illustrated in  FIG. 1 , the chip package  104  is soldered to the PCB  102  by multiple solder connections  106  (hereinafter referred to as “solder balls  106 ”). The solder balls  106  are arranged in a ball grid array via which the solder balls  106  are evenly spaced in the x and y directions. Accordingly, for a particular PCB  102  or chip package  104 , the distance between the solder balls  106  in the x and y directions can be a standard distance for an industry, a particular manufacturer, or a particular PCB  102  or chip package  104 . 
   An exemplary testing device will be described with reference to  FIGS. 2 and 3 .  FIG. 2  is a cross-sectional view of a device  200  for testing connections between a chip package  104  and a PCB  102  according to an exemplary embodiment, wherein the device  200  is disposed in a non-testing position.  FIG. 3  is a cross-sectional view of a device  200  for testing connections between a chip package  104  and a PCB  102  according to an exemplary embodiment, wherein the device  200  is disposed in a testing position. The cross section is taken through the device  200  at a point between the chip package  104  and the PCB  102 . Accordingly, only the solder balls  106  and the PCB  102  are illustrated in  FIGS. 2 and 3 , and the chip package  104  is not visible. 
   The device  200  includes a housing  202  that is sized to fit between the chip package  104  and the PCB  102  and between two rows of solder balls  106  connecting the chip package  104  to the PCB  102 . The housing  202  is made of a suitable non-conductive material, such as plastic. 
   The housing  202  comprises a stop member  202   a  that limits insertion of the housing  202  between the solder balls  106  when the stop member  202   a  contacts a first solder ball in a row of solder balls  106 . As illustrated in  FIGS. 2 and 3 , the housing  202  comprises two stop members  202   a , one on each side of the housing  202 . The stop member  202   a  comprises a portion of the housing  202  that is wider than a width of the housing  202  that is positioned between two rows of solder balls  106 . 
   The housing  202  further comprises a passageway  202   b  through the housing  202 . The passageway  202   b  comprises an entrance  202   c  into the housing  202  and an exit  202   d  from the housing  202 . The entrance  202   c  is positioned in the housing  202  such that the entrance  202   c  is directed away from the solder balls  106 . The exit  202   d  is positioned in the housing  202  such that a path of the passageway  202   b  is directed toward one of the solder balls  106  at the exit  202   d . Because the dimensions of a given ball grid array are known, the housing  202  can be sized and the passageway  202   b  can be appropriately situated such that the exit  202   d  of the passageway  202   b  is directed toward the position of one of the solder balls  106 . 
   A conductor  204  is disposed in the passageway  202   b  of the housing  202 . The conductor  204  comprises a contact end  204   b  for making contact with one of the solder balls  106 . The conductor  204  also comprises a probe end  204   a  for making contact with a tip end  302  of a probe of a testing device (not shown), such as an oscilloscope. The probe end  204   a  is disposed at the entrance  202   c  of the housing  202 , and the contact end  204   b  is disposed at the exit  202   d  of the housing  202 . The conductor  204  is made of a suitable conductive material, such as copper. 
   The conductor  204  is movable within the passageway  202   b  of the housing  202  between a first position and a second position. The first position is illustrated in  FIG. 2  in which the contact end  204   b  of the conductor  204  is entirely within the passageway  202   b  of the housing  202 . The second position is illustrated in  FIG. 3  in which the conductor  204  is pushed into the passageway  202   b  in the direction D such that the contact end  204   b  exits the housing  202  via the exit  202   d  and contacts one of the solder balls  106 . 
   The device  200  further comprises a biasing member  206  that biases the probe end  204   a  of the conductor  204  away from the housing  202 . As illustrated in  FIGS. 2 and 3 , the biasing member  206  comprises a leaf-type spring contacting the housing  202  on one side and contacting the conductor  204  on another side. The conductor  204  comprises a recess  204   c  which holds the biasing member  206 . In an exemplary embodiment, the biasing member  206  can comprise an extension of the housing  202  and can be formed from the same material as the housing  202 . In an alternative exemplary embodiment, the biasing member  206  can be a separate component that is coupled to the housing  206 . The biasing member  202  can be formed from a non-conductive material. 
   The conductor  204  further comprises a probe receptacle  204   d  for receiving a tip end  302  of a test probe of a testing device (not shown). As illustrated in  FIGS. 2 and 3 , the probe receptacle  204   d  comprises a cup-shaped portion into which the tip end  302  of the test probe can be inserted. The probe receptacle  204   d  helps maintain a position of the test probe in contact with the probe end  204   a  of the conductor  204 . 
   When the tip end  302  of the test probe is moved in the direction D illustrated in  FIG. 3 , the biasing member  206  is compressed, thereby allowing the conductor  204  to move in the direction D such that the contact end  204   b  of the conductor  204  exits the housing  202  in a direction toward one of the solder balls  106 . The conductor  204  can be moved against the force of the biasing member  206  until the contact end  204   b  of the conductor  204  contacts one of the solder balls  106 , thereby providing a signal conducting path from the contacted solder ball to the tip end  302  of the test probe. Accordingly, the connection of the chip package  104  to the PCB  102  can be tested at the contacted solder ball, thereby allowing testing of the connection at an exit point of the chip package  104  and at a location between the chip package  104  and the PCB  102 . 
   When the tip end  302  of the test probe is moved in a direction opposite to the direction D illustrated in  FIG. 3 , the force of the biasing member  206  moves the conductor  204  in a direction opposite to the direction D, such that the contact end  204   b  of the conductor  204  is retracted into the passageway  202   b  of the housing  202  to the position illustrated in  FIG. 2 . 
   The cutaway section C illustrated in  FIGS. 2 and 3  demonstrates that the device  200  can be sized as desired to reach the last solder ball in a row of solder balls  106  for a known ball grid array. Alternatively, the device  200  can be sized to reach at least the middle solder ball in a row of solder balls  106 . In this case, the device  200  can be inserted from opposite sides of the chip package  104  to reach all of the solder balls  106 . 
   Additionally, the device  200  can be sized to fit between two rows of solder balls  106  for a known ball grid array. As illustrated in  FIGS. 2 and 3 , the device  200  can be sized with little tolerance between the solder balls  106 . Such a configuration can allow the solder balls  106  to guide insertion of the device  200  and to position the device  200  such that the exit  202   d  of the passageway  202   b  is disposed properly with regard to the solder ball to be tested. Alternatively, the device  200  can comprise a width that has a larger tolerance between the solder balls  106 . In this case, the operator can align the edge of the housing  202  comprising the exit  202   d  of the passageway  202   b  along the line of solder balls  106  having the solder ball to be tested. 
   In alternative exemplary embodiments, other suitable types of biasing devices may be used. For example, a coil spring can be positioned around the conductor  204  between the housing  202  and the recess  204   c  or the probe receptacle  204   d  to bias the conductor  204  in a direction away from the housing  202 . 
   The exemplary conductor  204  illustrated in  FIGS. 2 and 3  comprises a square contact end  204   b . However, any suitable shape of the contact end  204   b  may be provided. For example, the contact end  204   b  may comprise a point that contacts the solder ball. Alternatively, the contact end  204   b  may comprise a convex or concave shape. A concave shape can be formed to correspond with a round shape of the solder balls  106  to provide a larger area of connection between the conductor  204  and the solder ball being tested. 
   In an alternative exemplary embodiment, the biasing member  206  may be omitted. In this case, an operator may push or pull the conductor  204  within the passageway  202   b  of the housing  202  to position the conductor  204  as desired. Additionally, the recess  204   c  may be omitted. 
   In another alternative exemplary embodiment, the probe receptacle  204   c  on the probe end  204   a  of the conductor  204  may be omitted. In this case, the tip end  302  of the test probe may make contact with any exposed portion of the conductor  204 . Alternatively, the conductor  204  may be connected directly to the test device (not shown), such as an oscilloscope, without the use of a test probe. 
   The exemplary embodiment illustrated in  FIGS. 2 and 3  shows the passageway  202   b  within the housing  202  having a slight angle such that the conductor  204  enters one end of the housing  202  and exits via a side of the housing  202 . However, any suitable path for the passageway  202   b  may be used. For example, the passageway  202   b  can comprise a straight path into an end of the device  200  and out a side of the device  200 . Alternatively, the passage way can comprise a bend having a sharper or shallower angle than the angle illustrated in  FIGS. 2 and 3 . 
   In certain exemplary embodiments, the conductor  204  can exit the housing  202  such that the contact end  204   b  of the conductor  204  contacts the solder ball at a right angle. However, other geometries are suitable to provide a signal path from the solder ball being tested to the conductor  204 . 
   Although described as a device  200  for testing solder connections between a chip package  104  and a PCB  102 , the invention is not limited to testing such connections. For example, the device  200  can be used to test plug type connections of a chip package  104  that is plugged into a PCB  102 . 
     FIG. 4  is a cross-sectional view of a system  400  for testing connections between a chip package  104  and a PCB  102  according to an exemplary embodiment. As illustrated in  FIG. 4 , the system  400  comprises a signal device  200   s  and a ground device  200   g . The signal device  200   s  and the ground device  200   g  comprise components similar to those discussed above for the device  200  with reference to  FIGS. 2 and 3 . The signal device  202   s  is provided to test a signal from one of the solder balls  106  by contacting the solder ball with the conductor  204   s , and the ground device  202   g  is provided to provide a ground path by contacting another one of the solder balls  106  with the conductor  204   g . The exemplary embodiment illustrated in  FIG. 4  is useful when the testing requires a ground return path or when a ground return path can enhance the test results for the solder ball being tested. 
     FIG. 4  also illustrates the use of a spacer  402  on the ground device  200   g  for locating the contact end  204   b  of the conductor  204  next to a desired one of the solder balls  106 . Since the dimensions of a given ball grid array are known, suitably sized spacers  402  can be provided to dispose the contact end  204   b  of the conductor  204   g  next to any of the solder balls  106 . In an exemplary embodiment, the spacer  402  can comprise a non-conductive element that clips onto the housing  202   g  of the device  200   g . Additionally, multiple spacers can be used in series on the housing  202   g  to dispose the conductor  204   g  next to the desired one of the solder balls  106 . The spacer  402  can be used with any of the exemplary devices described herein. 
   In an exemplary embodiment, the device  202   s  and the device  202   g  can be connected to create a combination device. For example, in an exemplary embodiment, the housings  202   s  and  202   g  can be an integral housing connected near the stop members. In an alternative exemplary embodiment, one or both of the housings  202   s ,  202   g  can be extended to connect together in a sliding relationship such that the signal conductor  204   s  can contact one of the solder balls  106  and the ground conductor  204   g  can contact another one of the solder balls  106 . In an exemplary embodiment, the housings  202   s ,  202   g  can comprise complementary groove and rail connectors to provide the sliding relationship. 
   Thus, the exemplary embodiments described herein can allow testing of connections between a chip package  104  and a PCB  102 . The exemplary devices described herein can be inserted between the chip package  104  and the PCB  102  and between rows of signal path connections between the chip package  104  and the PCB  102 . Then, the conductor  204  can be moved from its retracted position to its extended position to contact one of the connections, thereby providing a signal path from the contacted connection to a point outside the profile of the chip package  104 . A test probe contacting the probe end  204   a  of the conductor  204  can convey the signal to a testing device, such as an oscilloscope. When testing of the connection is completed, the biasing member  206  of the device  200  moves the conductor  204  from its extended position to its retracted position, and the device  200  can be removed from between the chip package  104  and the PCB  102 . A spacer can be added to the device  200  to position the device  200  for testing another connection between the chip package  104  and the PCB  102 . 
   Using the exemplary device  200  described herein can allow access to test connections between a chip package  104  and a PCB  102  even if vias are not provided on a back side of the PCB  102  and even if other test traces are not provided. 
   Although specific embodiments of the invention have been described above in detail, the description is merely for purposes of illustration. It should be appreciated, therefore, that many aspects of the invention were described above by way of example only and are not intended as required or essential elements of the invention unless explicitly stated otherwise. Various modifications of the disclosed aspects of the exemplary embodiments, in addition to those described above, can be made by a person of ordinary skill in the art, having the benefit of the present disclosure, without departing from the spirit and scope of the invention defined in the following claims, the scope of which is to be accorded the broadest interpretation so as to encompass such modifications and equivalent structures.