Abstract:
A compression device has a frame sized to accept an integrated circuit package and a pressor. The frame includes a surface defining an opening with an axis and at least one ramp extending from the surface. The ramp or ramps have upper and lower flat portions, substantially parallel with a plane perpendicular to the axis, and a sloped portion at an angle relative to the plane, the sloped portion connecting the upper and lower flat portions. The pressor is configured to engage the ramp and rotate in response to applied force. When the pressor is engaged with the sloped portion(s) of the ramp(s), this rotation causes movement of the pressor along the axis. However, when engagement between the ramps and the pressor is in the flat portions of the ramp, continued movement of the pressor along the axis is limited in spite of any continued rotation.

Description:
TECHNICAL FIELD  
       [0001]     This invention relates to making connections between integrated circuit (IC) array packages and circuit boards, and more particularly to making temporary connections between IC array packages and circuit boards.  
       BACKGROUND  
       [0002]     Ball grid array (BGA) and land grid array (LGA) packages are becoming increasingly popular because of their low profiles and high densities. With a BGA package, for example, the rounded solder balls of the BGA are generally soldered directly to corresponding surface mount pads of a printed circuit board rather than to plated thru-holes which receive pins from, for example, a pin grid array (PGA) IC package.  
         [0003]     Sockets allow particular IC packages to be interchanged without permanent connection to a circuit board. More recently, sockets for use with BGA and LGA packages have been developed to allow these packages to be non-permanently connected (e.g., for testing) to a circuit board. However, problems can exist in attaching a BGA package to sockets using conventional compression devices that are subject to misuse. In some instances, users under-compress IC packages so that adequate contact is not made between the package and the socket. In other instances, users damage IC packages by over-compressing them in an attempt to compensate for the first problem.  
       SUMMARY  
       [0004]     This invention features a compression device for a socket terminal assembly. The socket terminal assembly provides a reliable, non-permanent and low-loss electrical interconnection between electrical contacting areas of an array package and connection regions of a substrate (e.g., printed circuit board) while duplicating the mating condition normally present between the electrical contacting areas and connection regions. The compression device allows users to adequately compress the array package to make electrical connections required for purposes such as testing, without damaging the array package through over-compression. The term “integrated circuit array package” is intended to mean those packages, including PGA, BGA and LGA packages. The term “substrate” is intended to mean any base member having electrical contact areas including printed circuit boards, IC chip substrates or the packages supporting such chip substrates.  
         [0005]     In one aspect of the invention, a compression device has a frame sized to accept an IC package including a surface defining an opening with an axis and at least one ramp extending from the surface. The ramp or ramps have upper and lower flat portions, substantially parallel with a plane perpendicular to the axis, and a sloped portion at an angle relative to the plane, the sloped portion connecting the upper and lower flat portions. The compression device also includes a pressor configured to engage the ramp and rotate in response to applied force wherein movement of the pressor along the axis is caused by such rotation when engagement between the ramps and the pressor is in the sloped portion of the ramps and continued movement of the pressor along the axis is limited when engagement between the ramps and the combined unit is in the flat portions of the ramp. Among other advantages, when the pressor is engaged with the sloped portion(s) of the ramp(s), this rotation causes movement of the pressor along the axis. However, when engagement between the ramps and the pressor is in the flat portions of the ramp, continued movement of the pressor along the axis is limited despite any continued rotation of the pressor.  
         [0006]     In another aspect of the invention, a compression device has a frame sized to accept an IC package including a surface defining an opening with an axis and two ramps extending from the surface. The ramps each comprise upper and lower flat portions, that are substantially parallel with a plane perpendicular to the axis, and a sloped portion at an angle relative to the plane, the sloped portion connecting the upper and lower flat portions. The compression device also includes an actuator engaging the upper surfaces of the ramps and a pressor engaging lower surfaces of the ramps. The pressor is attached to the actuator so that rotation of the actuator rotates the pressor inducing movement of the pressor along the axis.  
         [0007]     In another aspect, a compression device has a guide box having an interior cavity defined by walls, the interior cavity sized to accept an integrated circuit package. The compression device also has a lid attached to the guide box by a hinge pin and springs that bias the lid towards remaining in an open position relative to the guide box. The lid has a surface defining an opening with an axis; and two ramps extending from the surface with the ramps disposed symmetrically on opposing sides of the surface defining the opening. The ramps each comprise upper and lower flat portions, that are substantially parallel with the plane, and a sloped portion at an angle relative to a plane perpendicular to the axis, the sloped portion connecting the upper and lower flat portions. The compression device also has an actuator engaging upper surfaces of the ramps and a pressor engaging lower surfaces of the ramps. The pressor is attached to the actuator so that rotation of the actuator rotates the pressor inducing movement of the pressor along the axis. The actuator and the pressor form a combined unit defining gaps, the combined unit having bearing surfaces engaging the ramps with the gaps bracketing the ramps and rotation of the combined unit moving the bearing surfaces from engagement with the upper flat portion to engagement with the lower flat portion moves the pressor a predetermined distance along the axis.  
         [0008]     Embodiments of these aspects of the invention may include one or more of the following features. The compression device preferably has two ramps that are disposed symmetrically on opposing sides of the surface defining the opening. The compression device can also include an actuator attached to the pressor so that rotation of the actuator results in rotation of the pressor. The attached actuator and pressor form a combined unit having bearing surfaces defining gaps and engaging the ramps with the gaps bracketing the ramps. Rotation of the combined unit moving the bearing surfaces from engagement with the upper flat portion to engagement with the lower flat portion moves the pressor a predetermined distance along the axis. In some embodiments, the ramps also have end walls, extending vertically from upper and lower surfaces of the ramps, that limit rotational movement of the combined unit.  
         [0009]     The frame of the compression device can include a guide box and a lid. The guide box has an interior cavity defined by walls and sized to accept an integrated circuit package. The lid is attached to the guide box by a hinge pin and springs that bias the lid towards remaining in an open position. In some embodiments with these features, the compression device preferably also includes a latch mounted on the lid to engage the guide box when the lid is in a closed position. This engagement between the latch and guide box maintains the lid in its closed position against opening force exerted by the springs. The compression device preferably further includes a safety release capable of locking the latch to prevent inadvertent release of engagement between the latch and the guide box. More preferably, the safety release is mechanically connected with the actuator so that rotation and counter-rotation of the actuator, respectively locks and unlocks the latch. In some embodiments, the lock is integrally molded with the actuator.  
         [0010]     The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims. 
     
    
     DESCRIPTION OF DRAWINGS  
       [0011]      FIG. 1  is an exploded, somewhat diagrammatic view of an intercoupling component assembly, an integrated circuit package, and a support plate positioned over a printed circuit board.  
         [0012]      FIG. 2  is an exploded perspective view of an upper socket converter assembly that comprises the upper portion of the intercoupling component assembly shown in  FIG. 1 .  
         [0013]      FIGS. 3A-3C  are, respectively, top, cross-section, and side views of the lid shown in  FIGS. 1 and 2 .  
         [0014]      FIGS. 4A and 4B  are perspective views of, respectively, the compressing lever and pressor shown in  FIGS. 1 and 2 .  
         [0015]      FIG. 4C  is a side view of the engaged compressing lever and pressor from the side opposite the handle of the compressing lever. For clarity of illustration, these components are shown without the lid that they would be engaging. 
     
    
       [0016]     Like reference symbols in the various drawings indicate like elements.  
       DETAILED DESCRIPTION  
       [0017]     Referring to  FIG. 1 , a socket converter assembly  4  for interconnecting a BGA IC package  8  to surface mount pads  10  of a printed circuit board  12  is shown. Socket converter assembly  4  includes an upper socket converter assembly  16  for securing IC package  8  in socket converter assembly  4 . Upper socket converter assembly  16  is operable to compress IC package  8  a specified distance into engagement with lower socket converter assembly  20 , which serves as an intercoupling component between IC package  8  and printed circuit board  12 . Compression of IC package  8  brings rounded solder balls (not shown) attached to contacts on the undersurface of IC package  8  into contact with converter socket terminals  32  of lower socket converter assembly  20 . Converter socket terminals  32  are press-fit within holes in the insulative member  28  and provide an electrical connection between these solder balls and surface mount pads  10  of the printed circuit board  12 . In this embodiment, upper socket converter assembly  16  provides both (a) visual indications of when the desired amount of compression is achieved and (b) physical limits to prevent users from over-compressing IC package  8 . This helps users to adequately compress IC package  8  to make the electrical connections required for purposes such as testing, without damaging IC package  8  through over-compression.  
         [0018]     Lower socket converter assembly  20  is surface mounted to IC package  8  using solder ball attachments and supports IC package  8  and upper socket converter assembly  16 . Screws  24 , threaded through an electrically insulative member  28 , attach upper socket converter assembly  16  to lower socket converter assembly  20 . In this embodiment, electrically insulative member  28  supports converter socket terminals  32  and a guide box  36  which aligns solder balls on IC package  8  over converter socket terminals  32 . Socket converter assembly  4  is of the general type described in U.S. Pat. No. 5,877,554 issued to Murphy, the details of which being hereby incorporated by reference.  
         [0019]     Referring to  FIG. 2 , guide box  36  supports a lid assembly including a lid  40 , a compressing lever  44 , and a pressor  48 . Compressing lever  44  and pressor  48  are attached to one another so as to engage ramps  52  formed on an inner surface  54  of lid  40 . As will be described in greater detail below, ramps  52  are configured to limit the compression that pressor  48  exerts on IC package  8  when it is placed within an interior space  56  defined by walls  60 ,  64 ,  68  and corner posts  72  of guide box  36 . In this embodiment, three hinges  76  are mounted on back wall  68  of guide box  36 . A pin  78  is inserted through back receiving holes  80  in lid  40 , hinges  76 , and rear springs  84  to attach lid  40  to guide box  36 . Rear springs  84  bias lid  40  towards an open position. In other embodiments, other connectors including, but not limited to, snap fittings attach lid  40  to guide box  36 .  
         [0020]     Referring to  FIGS. 3A-3C , lid  40  includes a circular opening  88  with an axis  92 . Opening  88  extends through lid  40  with two ramps  52  protruding from inner surface  54  of opening  88 . As shown in  FIG. 3B , each ramp  52  has thickness t between ramp upper surfaces  96  and ramp lower surfaces  100 . Ramps  52  have a flat portion  104  on each end and sloped portions  108  extending between flat portions  104 . Flat portions  104  are substantially parallel with a plane  112  perpendicular to the axis  92  while sloped portions  108  are at an angle relative to plane  112 . Ramp flat portions  104  and associated ramp end walls  116  physically limit the movement of compressing lever  44  and pressor  48 .  
         [0021]     Referring to  FIGS. 3A and 3C , lid  40  also has tabs  120  that define a front recess  124  and a back recess  128 . Front receiving holes  132  and back receiving holes  80  extend through tabs  120  to provide attachment points on lid  40 . Lid  40  is attached to guide box  36  by resting lid  40  on guide box  36  so that hinges  76  extend into back recess  128  and then inserting hinge pin  78  through back receiving holes  80 , rear springs  84 , and hinges  76 . Similarly, latch  136  is attached to lid  40  by placing latch  136  in front recess  124  so that bore  140  is aligned with front receiving holes  132  and then inserting pin  78  through the holes  132  and bore  140 .  
         [0022]     Referring to  FIG. 4A , compressing lever  44  includes an integrally molded handle  144  extending radially outward from a body  148 . Body  148  has a cylindrical lower portion  152  sized to fit within opening  88  past ramps  52 . Lower portion  152  defines a keyhole  156 . Arched bearing surfaces  160  extend radially from lower portion  152  and are configured to fit within inner surface  54  of opening  88  and engage ramps  52 .  
         [0023]     Referring to  FIG. 4B , pressor  48  has arched bearing surfaces  160  radially extending from an upper portion  164 . Upper portion  164  and bearing surfaces  160  are sized so as to, respectively, fit within and engage ramps  52 . Key  168 , configured to fit within keyhole  156 , extends axially upward from upper portion  164 . When assembled, compressing lever  44  and pressor  48  are attached to each other with key  168  inserted into keyhole  156 . Thus, rotation of compressing lever  44  in response to force applied to handle  144  also causes the rotation of pressor  48  due to the engagement between key  168  and keyhole  156 . As shown in  FIG. 4C , engagement between key  168  and keyhole  156  also aligns bearing surfaces  160  on pressor  48  with those on compressing lever  44 . Bearing surfaces  160  have a height h chosen so that aligned bearing surfaces  160  define a gap  172  with a width w that is slightly larger than thickness t of ramps  52 . Compressing lever  44  and pressor  48  are inserted through opposing sides of opening  88  prior to attachment so that gap  172  is formed engaging ramps  52 .  
         [0024]     To operate the socket assembly, a user inserts IC package  8  and support plate  176  into upper socket converter assembly  16  of a socket converter assembly  4  attached to printed circuit board  12 . Support plate  176  distributes loads applied by action of pressor  48  substantially uniformly across the upper surface of IC package  8  and compensates for variations of IC package thickness between individual IC packages  8 . The user then rotates lid  40  from the open position shown in  FIG. 1  to a substantially horizontal closed position. In this position, latch  136  extends along front wall  60  with lip  180  engaging a lower edge  184  of front wall  60 . The user applies a gentle pressure to overcome the resistance of rear springs  84  which bias lid  40  towards remaining in its initial open position. The user also applies a gentle pressure to latch tab  188  to rotate latch  136  about the fulcrum provided by pin  78  so as to hold lip  180  clear of front wall  60  while closing lid  40 . After lid  40  reaches its closed position, user rotates lip  180  into engagement with the lower edge  184  of front wall  60 . Until released by pressure applied to latch tab  188 , this engagement maintains lid  40  in its closed position against the force exerted by rear springs  84 .  
         [0025]     While lid  40  is being closed, compressing lever  44  is maintained in the released position shown in  FIG. 1 . In this position, bearing surfaces  160  engage ramps  52  at a point where upper surfaces  96  of ramps  52  are level with the top of lid  40 . The engagement between ramps  52  and bearing surfaces  160  positions pressor  48  slightly above but not contacting support plate  176 . The user then uses handle  144  to rotate compressing lever  44  and, consequently, pressor  48  in the clock-wise direction. While this rotation is moving bearing surfaces  160  along sloped portions of ramps  52 , the engagement between ramps  52  and bearing surfaces  160  moves pressor  48  towards and into engagement with support plate  176  and, thus, support plate compresses IC package into engagement with converter socket terminals  32 . After this rotation moves bearing surfaces past sloped portions  108  to the lower flat portion  104  of ramps  52 , further clockwise rotation does not provide additional compression to IC package  8  as the engagement between bearing surfaces  160  and ramps  52  maintains pressor  48  at a fixed vertical position. Moreover, contact between bearing surfaces and ramp end walls  116  limits further clockwise rotation.  
         [0026]     Increasing numbers of pins on IC packages  8  require increasing amounts of force to achieve a desired degree of compression. Choosing ramp specifications to achieve this desired degree of compression allows users to smoothly exert the necessary force to engage IC packages  8  with converter socket terminals  32  while preventing over-compression and associated damage to IC packages being tested. For example, in an exemplary embodiment, clockwise rotation of handle  144  about 93 degrees lowers pressor  48  about 0.030 inch. The position of handle  144  provides users with a visual indication that the desired amount of compression has been achieved and ramp end walls  116  stop further clockwise rotation of the compressing lever  44  and pressor  48 . In addition, compressing lever body  148  includes a lock  192 . As the desired degree of compression is achieved, the user applies sufficient force to overcome the additional resistance arising as front spring  194  contacts ramp end wall  116 . This allows lock  192  to engage a back side of latch tab  188  thus preventing release of latch  136  by pressure accidentally applied to the front side of latch tab  188 . It is desirable to such accidental releases because the resulting sudden change in the degree of applied compression has the potential to damage IC package  8 .  
         [0027]     After testing, the user reverses the above process to release compression from IC package  8  so that it can be removed from socket converter assembly.  
         [0028]     A number of embodiments of the invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. For example, in this embodiment, a screw  196  is inserted through a first central bore  140 , defined in and extending through body  148 , and into a second central bore  200 , defined in pressor that extends through key  168  and upper portion  164  to attach pressor  48  to compressing lever  44 . First central bore  140  and second central bore  200  are aligned when key  168  is inserted in keyhole  156 . However, those skilled in the art will recognize that various fasteners can be used to attach pressor  48  to compressing lever  44  while remaining within the scope and spirit of the present invention. Similarly, a LGA IC package can be used in place of the BGA IC package discussed above. Accordingly, other embodiments are within the scope of the following claims.