Abstract:
A socket comprising an electrically conductive element, the element situated within a well such that a first end of the element extends above a first surface of the socket, the element capable of flexing to exert a first force on a pin inserted into the well upon application of a second force by a descending surface to the first end of the element.

Description:
BACKGROUND 
     1. Field 
     The present invention relates to pin sockets and, more particularly, to zero force insertion and extraction pin sockets. 
     2. Background Information 
     Current integrated circuit (IC) package configurations include a large number of pins by which electrical signals are transmitted to and from the circuits in the package. Pins are typically constructed of thin strips of copper, gold, or other electrical conductors which protrude from the IC package and which are typically connected to other, external circuits using solder joints. As ICs increase in complexity, the number of pins comprised by IC packages also increases. A collection of package pins is sometimes called a pin grid array (PGA). 
     IC packages are often coupled to circuits external to the IC using sockets. Sockets are mechanical couplers that are typically soldered directly in external circuits and which provide an electrical connection to the external circuit for IC packages which are inserted into the sockets. Sockets offer advantages over direct solder connections between ICs and the external circuits. For example, an IC package which is mounted in a socket can be installed and removed numerous times from the external circuit without soldering and unsoldering the package pins. 
     As the number of pins comprised by IC packages increases, it typically becomes more difficult to insert and remove the package pins from an associated socket because of the resistance encountered by the pins as they descent into the socket. Each pin may make electrical contact with a conductor in an associated socket pin receiver, the conductor in electrical contact with the external circuit. Electrical coupling between package pin and socket pin receiver conductor is typically accomplished through contact between the conductor in the socket receiver and the inserted pin. While the insertion and extraction resistance associated with contact to a single package pin is not substantial, for packages with large PGAs (sometimes on the order of hundreds of pins) the accumulated resistance may become an impediment to easy insertion and removal of the package pins into and out of the socket. The accumulated force may be so substantial that insertion of the package pins into the socket may result in damage to the package pins. 
     FIG. 1 shows an embodiment of a prior art socket  100  to alleviate resistance to insertion and removal of a pin  160  into a well  170  in a socket body  110 . Sockets for this purpose are typically called zero insertion force (ZIF) sockets. Before the pin  160  descends into the well  170 , a normal force Fx is applied to the head of an electrically conductive element  150 . The normal force Fx is typically applied using a member  120  coupled to a mechanical cam/lever assembly (not shown). The normal force Fx causes the element  150  to flex in a manner which provides the descending pin  160  an unobstructed path down into the well  170 . This unobstructed path reduces the amount of downward force Fz to be applied to insert the pin  160  to nearly zero. Once the pin  160  is inserted in the well  170 , the lever is operated to return the member  120  to a position that returns element  150  to a position in which it makes electrical contact with the pin  160 . In this position the element  150  exerts a normal force against the pin  160  to retain the pin  160  in the well  170  and create an electrical connection. The element  150  may descend through a bottom  130  of the socket body  110  and terminate in an end  140  which is capable of being soldered to an external circuit. 
     Several disadvantages are associated with the prior art socket embodiment shown in FIG.  1 . The socket may be complex and relatively costly to manufacture because of the additional parts and connections employed by the cam/lever action to flex the element  150 . It is typically difficult, for example, to manufacture such sockets as single-piece units. More parts require more material and commensurate more weight and expense. Because a lever action is used, clamping a pin may employ as many as three distinct motions—actuation of the lever to flex the element  150 , insertion of the pin  160  and reverse actuation of the lever to unflex the element  150 . Furthermore, variation of the normal force applied by the element  150  against the pin  160  cannot easily be accomplished without redesigning the shape and position of the element  150  and/or the dimensions of the well  170 . 
     SUMMARY 
     A socket includes an electrically conductive element situated within a well. The element is situated such that a first end of the element extends above a first surface of the socket. The element is capable of flexing to exert a force on a pin inserted into the well upon application of a force to the first end of the element by a descending surface. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The subject matter regarded as the invention is particularly pointed out and distinctly claimed in the concluding portion of the specification. The invention, however, may be further understood by reference to the following detailed description read with reference to the accompanying drawings. 
     FIG. 1 is a cutaway illustration of a prior art embodiment of a ZIF socket. 
     FIG. 2 is a cutaway illustration of an embodiment of a socket in accordance with the present invention showing an electrically conductive element in an unflexed position. 
     FIG. 3 is a cutaway illustration of an embodiment of a socket in accordance with the present invention showing an electrically conductive element in a flexed position. 
     FIG. 4 is a flowchart illustrating one embodiment of a method to secure a pin within a socket in accordance with the present invention. 
     FIG. 5 shows an embodiment of an actuator plate with a depression in accordance with the present invention. 
    
    
     DETAILED DESCRIPTION 
     The present invention comprises an embodiment of a socket and/or components thereof, including methods and apparatus&#39; that may be employed to implement such embodiments. The embodiments described herein enable a socket with several advantages over existing implementations. For example, some embodiments may be implemented using fewer parts than prior art implementations employing cams and/or levers. The embodiments described herein are merely illustrative, and one skilled in the art will appreciate that numerous modifications can be made which nonetheless fall within the scope of the present invention. 
     FIG. 2 is a cutaway illustration of an embodiment  200  of a socket in accordance with the present invention showing an electrically conductive element  260  in an unflexed position. The element  260  is situated inside a well  280  within a socket body  270  and is in contact with the socket body  270  at a lower end  250 . The lower end  250  may protrude beyond the socket body  270  is order to provide a solder point for coupling the element  260  to an external circuit. An upper end  240  of the element  260  may slide along a wall of the well  280 . A circuit package  210  is shown descending toward the socket body  270  with a force Fz. A pin  230  protruding from the package  210  descends into the well  280  without making contact with the unflexed element  260 . Because there is limited or no contact between the pin  230  and the element  260 , the force Fz is low. Of course, the figure merely illustrates the invention in one embodiment. 
     FIG. 3 is a cutaway illustration of an embodiment  300  of a socket in accordance with the present invention showing an electrically conductive element in a flexed position. The bottom surface of the package  310  has made contact with the top end  340  of the element  360  and continues to descend toward the socket body  370 . In this embodiment, the top end  340  of the element  360  slides down the wall of the well  380 , causing the element  360  to flex in a direction approximately normal to the direction of descent with a force Fx. This flexation of the element  360  results in the element  360  increasing the force of contact with the descending pin  330 . The resistance generated by contact with the top end  340  of the element  360  results in an increase in the force Fz. Electrons may be conducted from the circuit inside the package  310  to an external circuit coupled to the lower end  350  of the element  360 . The force Fx results in securing the pin  330  within the well  380 . 
     In another embodiment, the surface making contact with the top end  340  of the element  360  may not be the bottom surface of the package  310 , but may instead be the surface of a plate separate from the package  310 . Those skilled in the art will appreciate that flexation of the pin  330  may result from contact with any descending surface (for example the lower surface of a z-axis lever actuation plate). Those skilled in the art will also appreciate that fixing the contact surface while raising the socket body  370  would comprise an equivalent motion to descending the contact surface. 
     Other embodiments may provide a degree of wipe contact (low-normal force sliding contact) between the pin  330  and the element  360  during descent of the pin  330 . Wipe contact may be limited to maintain a low insertion force while at the same time providing for some abrasion of the pin  330  surface to clean the pin  330  surface to provide better electrical properties. 
     Different types of materials may be employed for the pin  230  and the element  260 . In one embodiment, the pin  230  and element  260  comprise copper or copper beryllium coated with nickel and then gold to provide sufficient electrical conductivity along with mechanical strength. The nickel and gold reduce oxidation of the copper core. The force Fz employed to flex the element  360  is a function of the curvature of the element  360  and the thickness of the element  360 , among other factors. These factors may also affect the impedance generated in the pin-element junction. Different applications may employ different permutations of these factors to adjust the force Fz to improved values for the particular application. In one embodiment involving a package comprising 418 pins, a maximum force for inserting all pins of the package into a socket is approximately 15 pounds. In this embodiment, each pin  330  is approximately 18 mil ({fraction (1/1000)} inch) across, with a round or flat cross section, and the element  360  is approximately 9-10 mil across, with a flat cross section. 
     The unflexed shape of the element  360  is illustrated as an equilateral triangle in the embodiment of FIG. 2, although the invention is not limited in this regard. Upon flexation, the element  360  takes on a more curved shape, but in some embodiments may maintain an abrupt angle at the point of contact with the pin  330  to provide improved contact with the surface of the pin  330 . 
     The top end  340  of the element  360  will, in one embodiment, slide approximately 20-30 mil units along the face of the well  380  to produce a sufficient flexation in the element  360 . In this embodiment, the well  380  has an approximate depth of 110 mil and the initial point of contact between the element  360  and the pin  330  occurs at approximately 40 mil below the top surface of the socket body  370 . The flexation of the pin  330  and the normal force Fx may be varied by adjusting the height of the top end  340  of the element  360  above the top surface of the socket body  370 , which permits design flexibility in both the amount of normal force Fx applied and also the thickness of the pin  330 . Typically, the greater the height of the top end  340  of the element  360  above the surface of the socket body  370 , the greater the potential normal force Fx which may result because of the greater potential flexation of the element  360 . Variable flexation of the element  330  may also provide for the use of pins  330  of different thickness&#39; without adjustment to the width of the well  380 . 
     The socket body  370  may be comprised of any material capable of sustaining the normal forced generated by insertion of the pin  330  into the well  380 . In one embodiment, the socket body  370  may be constructed from liquid crystal polymer (LCP). In another embodiment, the socket body  370  may be comprised of the compound FR4, well known in the art for constructing printed circuit boards (PCB). Using FR4 may be desirable when the external circuit to which the socket is coupled in a PCB, providing the same expansion coefficients between socket and the PCB to which it is mounted. 
     FIG. 4 is a flowchart illustrating one embodiment  400  of a method to secure a pin within a socket in accordance with the present invention. At  410  a pin with is part of a pin package is descended into a well with minimal or no contact with an element situated within the well. The pin package or other surface contacts the end of the element at  420 , and at  430  the element flexes in a direction normal to the direction of pin descent. The normal flexation of the element results in contact of the element with the descending pin at  440 . Electrons may then flow from a circuit within the package through the pin to an external circuit coupled to the element. 
     The pin, package, and element may comprise but are not limited to any of the possible embodiments described with respect to FIG.  1 . For example, in one embodiment the pin and element comprise a copper core coated with nickel and then gold. To prevent lateral motion of the end of the element across the surface of the package, the descending surface may include depressions which the end of the element enters and which help reduce lateral motion. An embodiment  500  of an actuator plate  502  with a depression  504  is shown in FIG.  5 . The plate  502  is adapted such that depression  504  is aligned to make contact with top end  340  of element  360  as the surface descends. 
     Sockets implemented in accordance with the present invention offer several advantages. Sockets implemented in accordance with the present invention may be constructed without cam/lever assemblies for actuation, which may be less complex and less costly to manufacture because of there may be fewer parts and connections required. Less parts require less material and commensurate less weight and expense. Because no lever action is used, clamping a pin requires only a single motion—descent of the pin  330  into the well  380 . Furthermore, variation of the normal force applied by the element  360  against the pin  330  can be accomplished by variation of the thickness of the element  360 , among other factors. 
     In summary, embodiments of an advantageous method and apparatus to actuate clamping of a pin in a socket have been disclosed. In one embodiment, contact between a descending surface and an element situated in a socket well causes the element to flex in a direction normal to the direction of descent. The flexed element makes contact with a pin coupled to a pin package as the pin descends into the well. Electrical contact is created between the circuit in the package through the pin to the element. 
     While certain features of the invention have been illustrated as described herein, many modifications, substitutions, changes and equivalents will now occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such embodiments and changes as fall within the true spirit of the invention.