Abstract:
A socket assembly comprising a base having a plurality of electrical contacts connectable to a circuit board, and a cover having a plurality of apertures. The cover is movable between a rearward (open) position, and a frontward (closed) position. In the open position, the apertures receive male contacts from an electronic component, for example a pin grid array package, such that the male contacts encounter no frictional resistance to their insertion into the apertures. In the closed position, the male contacts are held in a position of electrical connection with the contacts in the base. As the cover moves from the open to the closed position, it pushes the male contacts and base contacts together in a manner such that the base contacts “wipe” against the male contacts, thus removing debris and contaminants from the electrical contact region. In the closed position, electrical connection between the male contact and the base contact exists over a continuous length of their respective surfaces, thus providing a large electrical contact region for good conduction of electrical impulses.

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to the field of electrical connectors, and, more particularly, to a Zero Insertion Force (ZIF) socket assembly. 
     BACKGROUND OF THE INVENTION 
     Integrated circuits (ICs) are becoming smaller, more complex, and more prevalent. It is common for a modern electronic appliance, such as a computer, a video cassette recorder, or even a refrigerator, to have several IC components attached to a circuit board. Each IC is generally delivered as an enclosed package with a pin grid array (PGA) interface. The PGA interface is a set of electrically conductive pins arranged in a pattern, where each pin is an electrical connection to the functional portion of the IC. In order to install the IC in an electronic appliance, the pins must be electrically connected to appliance&#39;s main circuit board. It is thus desirable for there to be a simple mechanism that permits the IC to be quickly and easily attached to the circuit board, while minimizing the risk of damage. 
     One device that permits a simple, fast connection between an IC and a circuit board is a Zero Insertion Force (ZIF) socket assembly. A ZIF socket assembly is a device having set of contacts in electrical connection with the circuit board, where the contacts are disposed in a set of sockets. The device is arranged such that the pins of the IC can be inserted into the sockets without touching the contacts so that the pins do not encounter frictional resistance as they are inserted. Subsequent to the insertion of the pins, the device brings the pins and contacts into electrical connection, such that electrical impulses can flow freely between the pins and the circuit board by way of the contacts. 
     A number of ZIF socket devices have been proposed. A typical ZIF socket assembly has a contact which either touches the pin at a bend (see, e.g., Griffin, U.S. Pat. No. 4,375,309) or which crosses the pin so as to touch the pin only at a single point (see, e.g., Bright, et al., U.S. Pat. No. 4,988,310). These devices are not well-adapted for small scale PGAs (e.g., a PGA having pins arranged in a grid on centers spaced 0.050 inches apart) because the electrical contact region formed is small, and its effective size may be reduced even further by debris and contaminants which interfere with electrical conduction. While this type of connection may be acceptable for large-scale PGAs, when the PGA is miniaturized to the scale of about 0.050 inch centers, the small electrical contact region that results when the pin and contact touch only at a point may cause the quality of the electrical connection to be poor. By allowing the contact and the pin to touch each other over a continuous length of their surfaces, as well as wiping the contact and pin against each other to remove some debris and contaminants, the quality of the electrical connection for small-scale PGAs is improved. 
     SUMMARY OF THE INVENTION 
     A ZIF socket assembly in accordance with the invention allows for a small (e.g. 0.050 inch centers) PGA package to be brought into low-resistance electrical connection with a circuit board without the pins of the PGA encountering frictional resistance as contact is made. The ZIF socket assembly comprises a top plate and a base plate, each made of an electrically insulating material. The base plate has a plurality of contacts arranged in a pattern, each contact being disposed in an opening in the base plate. Each electrical contact has an adjoining tail which extends downward from the base plate and is electrically connectable to a circuit board. Each contact also has a portion that extends upward from the base plate which makes electrical contact with the pins of a PGA package that is to be received by the ZIF socket assembly. 
     The top plate, which has a plurality of apertures arranged in the same pattern as the contacts, is slidably attached over the base plate, such that it can move between a first position and a second position. Each socket has a narrow upper portion and a wide lower portion. Each contact is received in the wide lower portion of a corresponding aperture. When the top plate is in the first position, a PGA package with pins arranged in the same pattern as the contacts and apertures can be inserted into the top plate through the narrow upper portions of the apertures. As the pins are inserted, the narrow portions of the sockets guide the pins past the contacts so that the pins do not touch the contacts, thereby allowing the pins to be inserted with substantially no frictional resistance. 
     After the pins have been inserted into the sockets, the top plate is slid over the base plate from the first position to the second position, thereby causing the pins and contacts to be pushed together. The ZIF socket assembly preferably includes either a handle-driven cam mechanism which provides the force necessary to slide the top plate from the first position to the second position, or a set of slits into which a flat-tipped screwdriver may be received to provide the necessary force. Each contact includes two straight portions joined at a bend. As each pin moves closer to a contact, it pushes against the bend and deflects the contact so as to bring one of the straight portions of the contact into vertical alignment with the surface of the pin, such that the straight portion and the pin are in physical connection over a continuous length of their respective surfaces. As the contact is being deflected and brought into physical contact with the pin, the contact wipes against the pin, thereby removing contaminants and debris from the electrical contact region. The continuous length over which contact is made, as well as the wiping action, combine to form a good, low-resistance electrical connection between pins and contacts. 
     Other features of the invention are described below. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing summary, as well as the following detailed description of preferred embodiments, is better understood when read in conjunction with the appended drawings. For the purpose of illustrating the invention, there is shown in the drawings exemplary constructions of the invention; however, the invention is not limited to the specific methods and instrumentalities disclosed. In the drawings: 
     FIG. 1 is an exploded view of a ZIF socket assembly according to the present invention, including an exemplary camming means for transforming the ZIF socket assembly between two positions, the ZIF socket assembly being shown without contacts; 
     FIG. 2 is a perspective view of an alternative embodiment of a ZIF socket assembly in its first (open) position, using a different method for socket actuation; 
     FIG. 3 is a perspective view of a ZIF socket assembly in its second (closed) position; 
     FIG. 4 is a perspective view of a ZIF socket assembly, showing the side of the base plate from which the leads extend; 
     FIG. 5 is a sectional view of the ZIF socket assembly shown in FIG. 2 in its first (open) position, taken along line  5 — 5 , with an exemplary pin grid array package inserted into the ZIF socket assembly; 
     FIG. 6 is a sectional view of the ZIF socket assembly shown in FIG. 3 in its second (closed) position, taken along line  6 — 6 , with an exemplary pin grid array package inserted into the ZIF socket assembly; 
     FIG. 7 is a cutaway view of the ZIF socket assembly shown in FIG. 2, with sections taken along lines  5 — 5  and  7 — 7 ; 
     FIG. 8 is a perspective view of an embodiment of a ZIF socket assembly according to the invention, including a handle-driven camming device for transforming the ZIF socket assembly between two positions; 
     FIG. 9 is a top plan view of the embodiment of the ZIF socket assembly shown in FIG. 7, in its open position; 
     FIG. 9A is a sectional view of the ZIF socket assembly shown in FIG. 9, taken along line  9 A— 9 A; 
     FIG. 10 is a top plan view of the embodiment of the ZIF socket assembly shown in FIG. 7, in its closed position; 
     FIG. 11 is a sectional view of the ZIF socket assembly shown in FIG. 10, taken along line  11 — 11 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     An exemplary Zero-Insertion Force (ZIF) socket assembly  10  according to aspects of the invention comprises a top plate (or “cover”)  31  having a plurality of lead-in openings  36 , a base plate  32  having a plurality of openings  55 , and a plurality of electrical contacts  40  disposed in openings  55 . Top plate  31  and base plate  32  may be made of an electrically insulating material, preferably LCP plastic. Electrical contacts are made of an electrically conductive material, preferably a copper alloy with suitable plating. Openings  36  are arranged in any desired pattern in top plate  31 , and openings  55  are arranged in an identical pattern in base plate  32 . The pattern in which openings  36  and  55  are arranged corresponds to the arrangement of male contacts  61  of an electrical component, such as pin grid array package  60 , that is to be inserted into openings  36 . In a preferred arrangement, openings  36  and  55  are arranged in a rectangular grid pattern on 0.040- to 0.060-inch centers (i.e., the center of each opening  36  is between 0.040 and 0.060 inches away from the center a horizontally or vertically adjacent opening  36 ), with openings  36  having a 0.020-inch square opening. More preferably, openings  36  and  55  are arranged in a rectangular grid pattern having 0.050 inch centers. 
     Top plate  31  is slidably connected to base plate  32 . Top plate  31  has a pair of sides  51  and  52 , which lie parallel to each other and are disposed on opposing sides of top plate  31 . One or more guide members  34  depend from each of sides  51  and  52 . Each guide member  34  includes a protrusion  35 , which extends perpendicularly from the guide member  34  toward the center of top plate  31 . Base plate  32  has sides  58  and  59 , which lie parallel to each other and are disposed on opposing sides of base plate  32 . One or more tracks  33  are formed in each of sides  58  and  59 . Preferably, the number of tracks  33  on side  58  of base plate  32  is equal to the number of guide members  34  on side  51  of top plate  31 , and the number of tracks  33  on side  59  of base plate  32  is equal to the number of guide members  34  on side  52  of top plate  31 . In this configuration, each track has a guide member  34  to be received within it. Tracks  33  slidably receive guide members  34 . The length L 1  of each guide member  34  is shorter than the length L 2  of each track  33  by a distance D. Therefore, as each guide member  34  slides in its respective track  33 , it is able to move through a distance D, thereby permitting top plate  31  to move relative to base plate  32  along axis M through distance D. By moving frontward or rearward a distance D along axis M, top plate  31  is able to assume two distinct positions relative to base plate  32 : a frontward position (shown in FIGS.  3  and  6 ), and a rearward position (shown in FIGS.  2  and  5 ). When top plate  31  is in its rearward position relative to base plate  32 , ZIF socket assembly  10  is said to be in its “open” position. When top plate  31  is in its frontward position relative to base plate  32 , ZIF socket assembly  10  is said to be in its “closed” position. 
     Base plate  32  has a plurality of contact openings  55 . As noted above, contact openings  55  are arranged in the same pattern as lead-in openings  36  such that, when top plate  31  is in slidable disposition over base plate  32 , it is possible to slide top plate  31  over base plate  32  into such a position that each lead-in opening  36  lies directly over a corresponding contact openings  55 . 
     Disposed in each contact opening  55  is a contact  40  having a tail  38  to electrically connect the electronic component to a circuit board on which ZIF socket assembly  10  mounts. Each contact  40  comprises a straight lower portion  43 , a transitional U-shaped portion  41 , and a bent upper portion  42 . Bent upper portion  42  comprises a lower segment  42   a , a bend  42   b , and a distal segment  42   c . Bent upper portion  42  extends upwardly from U-shaped portion  41  at an oblique angle toward the rear of ZIF socket assembly  10 , until it reaches bend  42   b , from where it extends upwardly but at an angle toward the front of ZIF socket assembly  10 . U-shaped portion  41  and bent upper portion  42  of contact  40  are received in opening  36 . 
     Each opening  36  is a square or rectangular cavity formed in top plate  31  and defined by a set of four walls. The frontward wall  48  of each opening  36  is three-tiered, having a rearward section  48   a  toward the top of opening  36 , a median section  48   b , and a frontward section  48   c  toward the bottom of opening  36 . The other three walls  47  defining opening  36  are straight (untiered). Owing to the three-tiered arrangement of frontward wall  48 , each opening  36  has a narrow portion  45 , a middle-width portion  46 , and a wide portion  44 . Wide portion  44  of opening  36  receives U-shaped portion  41  of contact  40 . Middle-width portion  46  of opening  36  receives bent upper portion  42  of contact  40 . Tiered wall  48  has a horizontal section  49  between rearward portion  48   a  and median portion  48   b . When ZIF socket assembly  10  is in its open position (as depicted in FIG.  5 ), horizontal section  49  covers bent upper portion  42  of contact  40 , thus preventing stubbing of bent upper portion  42  by pin  61  while pin  61  is being inserted into opening  36 . 
     Pin grid array (PGA) package  60  comprises a plurality of pins  61 . ZIF socket assembly  10  allows pins  61  to make removable and solderless electrical contact with a circuit board. In order to prepare ZIF socket assembly  10  to receive pin grid array package  60 , ZIF socket assembly  10  is placed in the open position that is, top plate  31  is moved to its rearward position along axis M. As can be seen in FIGS. 5 and 7, in the open position of ZIF socket assembly  10 , narrow portion  45  of opening  36  is unobstructed because contact  40  is covered by horizontal portion  49  of tiered wall  48 , thus permitting narrow portion  45  of opening  36  to receive pin  61  without pin  61  touching contact  40 . Because pins  61  do not touch contacts  40  as they are inserted into opening  36 , no frictional resistance is encountered during the insertion process. 
     Because pins  61  do not touch contacts  40  during the insertion process, subsequent to inserting pins  61  into openings  36  it is necessary to move ZIF socket assembly  10  to the closed position in order to obtain electrical contact between pins  61  and contacts  40 . ZIF socket assembly  10  is moved to the closed position by applying a force to top plate  31  in the frontward direction along axis M. As top plate  31  moves frontward along axis M, it transports pins  61  along with it. Pins  61 , in turn, push against contacts  40  in the frontward direction, thereby causing contacts  40  to deflect toward the front of ZIF socket assembly  10 . As contacts  40  deflect, bent upper portion moves such that lower segment  42   a  is in a generally vertical orientation, parallel to the surface of pin  61 . In this position, pin  61  and lower segment  42   a  of bent upper portion  42  are in physical contact over a continuous portion of each of their lengths, thereby creating a large area of electrical contact which results in a low-resistance (e.g., &lt;20 mΩ) electrical connection between pin  61  and contact  40 . It should be noted that this continuous physical connection between contact and pin is in contrast to other ZIP socket assemblies where the contact and pin touch only at a point—the “point” being either at a bend or “elbow” along the contact, or a place at which a straight portion of the contact crosses the pin at approximately right angles. Additionally, as pin  61  is pushed against bent upper portion  42  and deflects toward the front of top plate  31 , bend  42   b  and lower segment  42   a  of bent upper portion  42  “wipe” against pin  61  before lower segment  42   a  finally comes to rest against pin  61 , thereby removing debris and contaminants from the electrical contact region of both contact  40  and pin  61 . Preferably, contact  40  and pin  61  “wipe” against each over a distance of at least 0.010 inches. This “wiping” effect, as well as the long, continuous region of electrical contact, contribute to the low resistance of the electrical connection that is formed between contact  40  and pin  61 . The desired force-deflection characteristic and wiping action is achieved by the shape of contact  40 , in particular U-shaped portion  41 . 
     While ZIF socket assembly  10  is in the closed position, the bending of contacts  40  biases contacts  40  toward pins  61  (i.e., toward the rear of top plate  31 ), thereby causing lower segments  42   a  of bent upper portions  42  to push against pins  61  with a force. This force, in turn, causes a frictional resistance against the removal of pins  61  from openings  36 . In order to remove pin grid array package  60  from ZIF socket assembly  10 , ZIF socket assembly  10  must be returned to the open position. By moving top plate  31  along axis M in the rearward direction, ZIF socket  10  is returned to the open position that it was in when pins  61  were inserted into openings  36  (shown in FIGS.  2  and  5 ). In this position, the contacts return to the position they were in when pins  61  were inserted with ZIF socket assembly  10  in the open position. In this open position, there is once again no contact between pins  61  and contacts  40 , so there is no longer a frictional resistance against the removal of pins  61  from openings  36 . In this open position, pin grid array package  60  can be removed easily from ZIF socket assembly  10 . 
     Contacts  40  are resilient. Therefore, when ZIF socket assembly  10  is in the closed position with pins  61  disposed in openings  36 , the bending of contacts  40 , as discussed above, causes contacts  40  to push against pins  61  in the rearward direction, thus biasing ZIF socket assembly  10  toward the open position. In one embodiment of the invention, each track  33  could have an anchor  37  along its upper surface, which holds top plate  32  in its closed position against the bias of contacts  40 . A notch (not shown) along the upper surface of protrusion  35  receives anchor  37  when guide member  34  is positioned as far forward as it will travel in track  33  (i.e., when top plate  31  is in its most forward position), thereby retaining ZIF socket assembly  10  in the open position by holding top plate  31  in the forward position relative to base plate  32 . Guide member  34  is sufficiently resilient that, when a force is applied to top plate  31  along axis M in the rearward direction, guide member  34  yields under the force, thereby permitting guide member  34  to slide past anchor  37  as top plate  31  moves rearward toward the open position. 
     Two exemplary preferred mechanisms are provided for applying the force along axis M that moves ZIF socket assembly  10  between the open and closed positions. 
     In a first preferred embodiment, force is applied to top plate  31  by means of a cam attached to a handle that can be worked manually (as depicted in FIGS.  1  and  8 - 11 ). Cam  22  is disposed in a cam-receiving channel  25 . Cam-receiving channel  25  is formed along a rear side  39  of base plate  32 . Channel  25  comprises a pair of curved recesses  27  disposed on opposing sides of base plate  32 , and a larger intermediate portion  28 . Channel  25  receives cam  22 . Cam  22  comprises a lobe portion  24 , and a pair of cylindrical portions  23   a  and  23   b  disposed on opposites sides of lobe portion  24 . As the sectional views of FIGS. 9A and 11 show, lobe portion  24  has an elliptical or oval profile which protrudes relative to the circular profile of cylindrical portions  23   a  and  23   b . The inner surfaces of curved recesses  27  are complementary in shape and size to the outer surface of cylindrical portions  23   a  and  23   b , so as to permit cam  22  to rotate within channel  25 . Intermediate portion  28  of cam-receiving channel  25  is of sufficient shape and size to provide space for lobe portion  24  to rotate within it as cam  22  rotates within channel  25 ; the rectangular prismatic shape depicted in the drawings is an exemplary shape for intermediate portion  28 . 
     Handle  21  provides means to transmit a torque to cam  22 , thereby causing cam  22  to rotate within channel  25 . Handle  21  has an arm portion  21 a that serves as a lever. A receptacle  29  is formed in handle  21 . A distal end of cylindrical portion  23   a  of cam  22  extends outwardly from cam  22  slightly beyond side  58  of base plate  32 . The distal end of cylindrical portion  23   a  received through receptacle  29  to join cam  22  with handle  21 . Receptacle  29  receives the distal end of cylindrical portion  23   a  snugly, such that cam  22  rotates when handle  21  rotates, with no slippage between cam  22  and handle  21 . Slippage may be further preventing by bonding the inner surface of receptacle  29  to the outer surface of the distal end of cylindrical portion  23   a . Bonding may be accomplished chemically, thermally, or as otherwise permitted by the materials of which cam  22  and handle  21  are made. Handle  21  provides means to rotate cam  22  from a first position (shown in FIGS. 9 and 9A) to a second position (shown in FIGS.  10  and  11 ). The first position corresponds to the open position of ZIF socket assembly  10 , and the second position corresponds to the closed position of ZIF socket assembly  10 . A structure (not shown) could retain handle  21  in the closed position, thereby maintaining the component pins  61  against contacts  40 . 
     A force-transmitting wall  75  is formed in top plate  31  adjacent to cam  22 . The lobe portion  24  of cam  22  abuts force-transmitting wall  75 . When ZIF socket assembly  10  is in its open position with top plate  31  in its rearward position relative to base plate  32 , cam  22  and handle  21  are in their first position. In order to move ZIF socket assembly  10  from the open position to the closed position, handle  21  is rotated from its first position to its second position. This rotation applies a torque to cam  22 , causing it to rotate. As it rotates, the orientation of lobe portion  24  changes from that shown in FIG. 9A to that shown in FIG.  11 . As lobe portion  24  changes orientation, its protrusion pushes against force-transmitting wall  75  in the frontward direction along axis M, thereby causing top plate  31  to slide forward along axis M relative to base plate  32 . When top plate  31  has moved as far forward as it will go (as permitted by the length of track  33 ), ZIF socket assembly  10  is in its closed position. 
     As discussed above, when ZIF socket assembly  10  is in the closed position with pins  61  inserted, it is biased toward the open position by resilient contacts  40 . ZIF socket assembly  10 , however, is retained in the closed position by anchors  37 , which, as discussed above, resist the movement of top plate  31  along axis M. In order to return ZIF socket assembly  10  to its open position, a force is applied to top plate  31  along axis M in the rearward direction. As discussed above, the resilience of guide members  34  allows top plate  31  to be dislodged from the grip of anchors  37  when top plate  31  is placed under such a rearward force. After the grip of anchors  37  has been released, the bias toward the open position caused by the resilience of contacts  40  takes over and pushes top plate  31  to its rearward position. During the movement of ZIF socket assembly  10  toward the open position, handle  21  may be manually operated to rotate cam  22  to the orientation shown in FIG. 9A, so it does not abut against force-transmitting wall  75  and prevent top plate  31  from moving rearward. 
     In another preferred embodiment, there is neither a handle nor a cam. Instead, top plate  31  has a pair of slits  76 . A first slit  76  is disposed toward the front of top plate  31 , and a second slit  76  is disposed toward the rear of top plate  31 . Slits  76  are cut all the way through from the top to the bottom of top plate  31 . Additionally a pair of slits  77  are disposed on base plate  32 , toward the front and rear, respectively. Base plate slits  77  are in vertical alignment with top plate slits  76  when top plate  31  is disposed over base plate  32  in the frontward (closed) position. When a flat-tip screwdriver  78  is inserted through one of top-plate slits  76  and one of base-plate slits  77 , tip  78   a  rests against an edge of base-plate slit  77 . In this way, the edge of base-plate slit  77  acts as a fulcrum, and the shank  78   b  of screwdriver  78  acts as a lever, which can be used to manually apply force to top plate  31  along axis M. When pin grid array package  60  has been inserted into openings  36  of top plate  31 , the force from screwdriver  78  can be used to move top plate  31  to the frontward position against the bias provided by contacts  40 , as discussed above. This movement of top plate  31  transforms ZIF socket assembly  10  from the open position to the closed position. ZIF socket assembly is retained in the closed position by the combination of anchors  37  (which, as discussed above, resist the movement of top plate  31  relative to base plate  32  along axis M) and one or more pins  79 . Pins  79  are complementary in size and shape to top-plate slits  76  and base-plate slits  77 , so as to fit within slits  76  and  77 . When pins  79  are inserted through top-plate slits  76  and base-plate slits  77 , they help to hold ZIF socket assembly in the closed position against the bias to the open position caused by the resilience of contacts  40 . When it is desired to return ZIF socket assembly  10  from the closed position to the open position, pins  79  are removed from slits  76  and  77 , and screwdriver  78  can also be used as a lever to apply a force to top plate  31  in the rearward direction along axis M, thus dislodging top plate  31  from the grip of anchors  37  and allowing ZIF socket assembly  10  to return to the open position from the closed position. 
     It is noted that the foregoing examples have been provided merely for the purpose of explanation and are in no way to be construed as limiting of the present invention. While the invention has been described with reference to preferred embodiments, it is understood that the words which have been used herein are words of description and illustration, rather than words of limitation. Further, although the invention has been described herein with reference to particular means, materials and embodiments, the invention is not intended to be limited to the particulars disclosed herein; rather, the invention extends to all functionally equivalent structures, methods and uses, such as are within the scope of the appended claims. Those skilled in the art having the benefit of the teachings of this specification, may effect numerous modifications thereto and changes may be made without departing from the scope and spirit of the invention in its aspects.