Abstract:
An IC socket is provided with first and second contact pins and a socket body supporting said first and second contact pins. The first contact pin is used to establish a connection with a first terminal of a semiconductor package, while the second contact pin is used to establish a connection with a second terminal of said semiconductor package. The first and second terminals have different heights from a mount face of the semiconductor package.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an IC socket for establishing electrical connections with a semiconductor package, suitably used in LSI tests, such as function tests and burn-in tests. 
     2. Description of Related Art 
     The progress in integration degree and function of LSIs (Large Scale Integrated Circuit) due to the advance in the semiconductor technology is accompanied by the fact that an increasing number of external terminals are required for signal inputs and outputs of an LSI. Additionally, an increasing number of terminals are required for testing an LSI due to the recent tendency that functions integrated within the LSI have become more complex. It is desirable that the number of terminals used only for LSI tests should be as small as possible since such terminals are not used by users in the actual use. Although various efforts have been made to decrease the number of test terminals, including commonly using terminals for test and actual use and serially inputting and outputting test signals, the number of test terminals is currently on the increase. 
     The number of terminals mountable onto an LSI package is physically limited, and this makes it difficult to connect all the contact pads of an LSI chip with external terminals of an LSI package. This tendency is particularly remarkable for SIPs (System In Package). Therefore, test terminals are not given high priority in providing connections with external terminals of the LSI package, since test terminals are not necessary in the actual use of the LSI; however, the lack of test terminals is undesirable for improving the reliability of LSIs. 
     The inventor considers that one approach for providing a desired number of test terminals is to use an IC package including both of a ball grid array (BGA) and a land grid array (LGA); such IC package is referred to as BGA/LGA hybrid package, hereinafter. The ball grid array, composed of an array of solder balls, is used to establish physical and electrical connection with a printed circuit board, and the land grid array, composed of an array of lands, is only used in the LSI test. Such package structure allows providing a desired number of test terminals for an IC package with a reduced package size. 
     One issue is to establish electrical connections with both of the ball grid array and land grid array. In general, IC sockets are used for establishing electrical connections with BGA packages or LGA packages (BGA/LGA packages) in conducting functional tests and burn-in tests of LSIs. A variety of IC sockets have been developed to provide secure electrical connections between LSIs and terminals of IC sockets without damaging the LSIs. For instance, Japanese Laid Open Patent Application No. Jp-A2003-123923 (hereinafter, the &#39;923 application) and the corresponding U.S. Patent Application Publication No. 2005/070134 disclose an IC socket for testing a BGA package. The disclosed IC socket is composed of a socket body and a plurality of contacts to be connected with solder balls of a BGA package. The socket body has a plurality of mounting-holes into which the contacts are inserted. Each of the mounting holes has a through hole which is penetrated in the height direction of the body, and a support hole for supporting the contact. Each of the contacts has an upright piece extending through the through-hole and a support piece extending from the upright piece to be inserted into the through-hole from a top surface side of the socket body. A contact portion to be brought into contact with the solder ball is formed at a tip end portion of the upright piece and the support piece is extending from a proximal end portion of the upright piece. 
     Additionally, Japanese Laid Open Patent Applications No. Jp-A2002-246131 (hereinafter, the &#39;131 application) and Jp-A Heisei 11-86992 (hereinafter, the &#39;992 application) disclose IC sockets provided with plungers to be connected with solder balls, the plungers being biased against solder balls with coil springs. Specifically, the &#39;131 application discloses an IC socket in which contact pins are disposed through a socket body to provide electrical connections between solder balls of a BGA package and a printed circuit board. Each contact pin includes first and second plungers. The first plunger is electrically connected to one of the solder balls and the second plunger is electrically connected to a terminal provided on the printed circuit. Between the first plunger and the second plunger provided are a cylindrical body and an elastic member. The cylindrical body is struck against the first plunger on one end, and slidably accommodates the second plunger at the other end. An elastic member is disposed between the cylindrical body and the second plunger, and the first and second plungers are biased away from each other by the elastic member. 
     The &#39;992 application discloses a spring connector used in an IC socket which provides electrical connections between a solder ball of a BGA package and a printed circuit board. The spring connector is provided with a cylindrical body and a plunger. One end of the cylindrical body is closed with a bottom plate, and a protrusion formed of solder is provided on the bottom plate. The cylindrical body is made of conductive material. The other end of the cylindrical body is open, and the plunger is slidably inserted into the cylindrical body through the opening. A spring is provided in the cylindrical body, biasing the plunger toward the solder ball of the BGA packages. 
     Furthermore, Japanese Laid Open Patent Application Jp-A2001-196144 (hereinafter, referred to as the &#39;144 application) discloses an IC socket for an LGA package. The IC socket disclosed in the &#39;144 application is provided with a housing plate with a concave portion, and an array of terminals provided in the concave portion. The terminals are arranged at the positions corresponding to lands of the land grid array package. Each of the terminals has a bent spring plate and a pair of side plates. The spring plate is allowed to expand and shrink in the thickness direction of the housing plate. When the spring plate is expanded, the upper end of the spring plate protrudes from the surface of the concave portion of the housing plate. The side plates are provided to sandwich the spring plate and to extend in the thickness direction of the housing plate. The spring plate is provided with protrusions which are slidably contacted with the side plates. 
     Nevertheless, the IC socket structures disclosed in the above-mentioned applications are not adapted to the BGA/LGA hybrid package. The contact points of the respective external terminals of the IC socket structures disclosed in the above-mentioned applications are coplanar on the same plane; however, such structures are not preferable for the BGA/LGA hybrid package. In the BGA/LGA hybrid package, the contact points of the ball grid array are not coplanar with those of the land grid array. The use of any of the IC socket structures disclosed in the above-mentioned applications for establishing electrical connections with a BGA/LGA hybrid package results in poor electrical connections or excessive contact pressure. 
     SUMMARY 
     In one embodiment, an IC socket is provided with first and second contact pins and a socket body supporting said first and second contact pins. The first contact pin is used to establish a connection with a first terminal of a semiconductor package, while the second contact pin is used to establish a connection with a second terminal of said semiconductor package. The first and second terminals have different heights from a mount face of the semiconductor package. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other objects, advantages and features of the present invention will be more apparent from the following description of certain preferred embodiments taken in conjunction with the accompanying drawings, in which: 
         FIG. 1A  is a section view illustrating an exemplary structure of a BGA/LGA hybrid package; 
         FIG. 1B  is a plan view illustrating the exemplary structure of the BGA/LGA hybrid package; 
         FIG. 2  is a view showing an exemplary structure of an IC socket used for testing a conventional BGA/LGA package; 
         FIG. 3  illustrates the structure in which the IC socket shown in  FIG. 2  is in contact with the BGA/LGA hybrid package shown in  FIG. 1  to establish electrical connections; 
         FIG. 4  illustrates an exemplary structure of an IC socket according to a first embodiment of the present invention; 
         FIG. 5A  is an enlarged view of illustrating the structure of the IC socket according to the first embodiment; 
         FIG. 5B  is a section view illustrating the structure of the contact pins of the IC socket according to the first embodiment; 
         FIG. 6A  is an enlarged view of illustrating the structure of the IC socket according to a second embodiment; 
         FIG. 6B  is a section view illustrating the structure of the contact pins of the IC socket according to the second embodiment; 
         FIG. 7A  is an enlarged view of illustrating the structure of the IC socket according to a third embodiment; 
         FIG. 7B  is a section view illustrating the structure of the contact pins of the IC socket according to the third embodiment; and 
         FIG. 8  illustrates the states of the plunger members in the third embodiment, when the same forces are applied to the plunger members. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Before describing preferred embodiments of the present invention, a detailed description is given of an exemplary structure of the BGA/LGA hybrid package and the testing thereof with reference to  FIGS. 1 to 3 , in order to facilitate the understanding of the present invention. 
       FIG. 1  illustrates an exemplary structure of a BGA/LGA hybrid package, which is denoted by the numeral  10 . The BGA/LGA hybrid package  10  includes a substrate  11  and a pair of LST dies  12  provided on an upper face of the substrate  11 . Provided on the rear surface (the mount face) of the substrate  11  are solder balls  13  which function as external terminals to be attached to a printed circuit board  15 ; the portion of the BGA/LGA hybrid package  10  in which the solder balls  13  are arrayed is referred to as the BGA portion and denoted by the numeral X in  FIG. 1A . Additionally, lands  14 , which functions as test terminals, are arrayed on the rear surface of the substrate  11 ; the portion of the BGA/LGA hybrid package  10  in which the lands  14  are arrayed is referred to as the LGA portion and denoted by the numeral Y in  FIG. 1A . As shown in  FIG. 1B , the array of the lands  14  is surrounded by the array of the solder balls  13 . The array of the solder balls  13  is positioned in the BGA portion X in  FIG. 1A , and the array of the lands  14  is positioned in the LGA portion Y in  FIG. 1A . 
     The array of the solder balls  13  are used to establish physical and electrical connections with a printed circuit board  15  in the actual use, while the array of lands  14  is used only in the LSI test; the lands  14  in the LGA portion are not connected with the printed circuit board  15  in the actual use. 
     One issue is to establish electrical connections with the solder balls  13  and the lands  14  in testing the BGA/LGA hybrid package  10 . IC sockets used for testing conventional BGA/LGA packages are not suitable for testing BGA/LGA hybrid packages.  FIG. 2  illustrates a typical structure of an IC socket used for testing a conventional BGA/LGA package. An IC socket used for testing a BGA/LGA package is typically provided with a socket body  20  and a plurality of contact pins  30 . The contact pins  30  each include a barrel member  32  and a plunger member  34 . Provided within each barrel member  32  is an elastic member, typically a coil spring, for biasing the plunger member  34  towards a BGA/LGA package to be tested. 
     When a conventional BGA/LGA package is tested, the BGA/LGA package is placed on the contact pins  30  and desired pressure is applied onto the BGA/LGA package to establish connections between external terminals of the BGA/LGA package and the plunger members  34 . The biasing members within the barrel members  32  allow the plunger members  34  to probe the external terminals of the BGA/LGA package with appropriate contact pressure. 
     It should be noted that positions of the external terminals of a conventional BGA/LGA package are coplanar on the same plane. Therefore, an IC socket for testing a BGA/LGA package is typically structured so that the plunger members  34  protrude from the barrel members  32  with the same protruding length, that the barrel members  32  have the same length, and that the biasing members within the barrel members  32  have the same elastic characteristics. 
     The use of the TC socket shown in  FIG. 2  for the BGA/LGA hybrid package  10 , however, do not establish proper electrical connections with both of the solder balls  13  and the lands  14 , because the tips of the contact pins  30  are coplanar on the same plane. When the contact pins  30  prepared for the BGA portion are just in contact with the solder balls  13 , the contact pins  30  prepared for the LGA portion are not in contact with the lands  14  as shown in  FIG. 3 . Although may achieve electrical connections with both of the solder balls  13  and the lands  14 , the IC socket shown in  FIG. 2  applies different contact pressures on the solder balls  13  and the lands  14 . When the BGA/LGA hybrid package  10  is pressed towards the socket body  20  so that the contact pins  30  for the LGA portion are in contact with the lands  14  with proper contact pressure, excessive contact pressure may be applied to the solder balls  14 , which may result in undesirable crush of the solder balls  14 . When the BGA/LGA hybrid package  10  is pressed so that the contact pins  30  for the BGA portion are in contact with the lands  14  with proper contact pressure, on the other hand, the contact pressure applied to the lands  14  is excessively reduced. The difference in the applied pressure between the solder balls  13  and lands  14  results in different contact impedances, which may making it impossible to conduct appropriate LSI tests. 
     In the following, preferred embodiments of the present invention will be described in detail. Those skilled in the art will recognize that many alternative embodiments can be accomplished using the teachings of the description of the embodiments and that the invention is not limited to the embodiments illustrated for explanatory purposes. 
     First Embodiment 
     In a first embodiment, as shown in  FIG. 4 , an IC socket is provided with a socket body  300 , first contact pins  110  and second contact pins  210 . The first contact pins  110  are spring pins used to establish electrical connections with the solder balls  13 , and the second contact pins  210  are spring pins used to establish electrical connections with the lands  14 . 
     The first and second contact pins  110  and  210  are arrayed in accordance with the arrangement of the solder balls  13  and the lands  14  (See  FIG. 1B ). The first contact pins  110  are positioned opposed to the solder balls  13  and the second contact pins  210  are positioned opposed to the lands  14 . The distance between adjacent two of the second contact pins  210  may be smaller than that between adjacent two of the first contact pins  110 . The lands  14  are small-sized compared with the solder balls  13 , and this allows reducing the distance between adjacent two of the second contact pins  210 . 
     The first contact pins  110  each include a barrel member  112  fixed with the socket body  300 , and a plunger member  114  slidably inserted into the barrel member  112 . Correspondingly, the second contact pins  210  each include a barrel member  212  fixed with the socket body  300 , and a plunger member  214  slidably inserted into the barrel member  212 . 
     When the BGA/LGA hybrid package  10  is mounted on the IC socket according to the first embodiment, as shown in  FIG. 4 , the distance between the solder balls  13  and the socket body  300  is different from that between the lands  14  and the socket body  300 ; the difference between these distances is referred to as the terminal height difference E, hereinafter. In the first embodiment, the first contact pins  110  and second contact pins  210  are structured to absorb the terminal height difference E, and to thereby allow the first and second contact pins  110  and  210  to be contacted with the solder balls  13  and the lands  14 , respectively, with the same contact pressure. This allows successfully conducting LSI tests. 
       FIG. 5A  is an enlarged view partially illustrating the structure of the IC socket in the portion around the first and second contact pins  110  and  210 . As shown in  FIG. 5B , each barrel member  112  accommodates a biasing member  116  for biasing the plunger member  114  towards the BGA/LGA hybrid package  10 . Correspondingly, each barrel member  212  accommodates the biasing member  216  for biasing the plunger member  214  toward the BGA/LGA hybrid package  10 . In one embodiment, the biasing members  116  and  216  may be formed of coil springs or blade springs. In an alternative embodiment, the biasing members  116  and  216  may be formed of elastic material. 
     Referring back to  FIG. 5A , the barrel members  112  and  212  have the same length, while the plunger members  114  and  214  have different lengths. Specifically, the barrel members  112  of the first contact pins  110  have a length of A (hereinafter, referred to as the barrel length A), and the plunger members  114  of the first contact pins  110  protrude from the barrel members  112  with a protruding length of B (hereinafter, referred to as the protruding length B). On the other hand, the barrel members  212  of the second contact pins  210  have the same length as the barrel members  112  of the first contact pins  110  (that is, the barrel length A), while the plunger members  214  protrude from the barrel members  212  with a protruding length of C (hereinafter, referred to as the protruding length C). 
     In the unused state of the IC socket (that is, the state in which first and second contact pins  110  and  210  are not contacted with BGA/LGA hybrid package  10 ), the protruding length C of the plunger members  214  is different from the protruding length B of the plunger members  114 , so that the distance between the tips of the plunger members  114  and the surface of the socket body  300  is longer by the terminal height difference E than the distance between the tips of the plunger members  214  and the surface of the socket body  300  in the unused state. In this embodiment, the first and second contact pins  110  and  210  are structured so that the difference between the protruding length C of the plunger members  214  and the protruding length B of the plunger members  114  is identical to the terminal height difference E. In other words, the protruding length C of the plunger members  214  is longer than the protruding length B of the plunger members  114  by the terminal height difference E. 
     Additionally, the biasing members  116  and  216  are structured so that the plunger members  114  and  214  are withdrawn into the barrel members  112  and  212  with the same withdrawal length when the same forces are applied to the plunger members  114  and  214 . More specifically, the biasing members  116  and  216  may be formed of springs having the same spring modulus in one embodiment. Alternatively, the biasing members  116  and  216  may be formed of elastic materials with the same elastic coefficient, or the same elastic material. 
     The structure described above allows the plunger members  114  and  214  to be in contact with the solder balls  13  and the lands  14  of the BGA/LGA hybrid package  10  with substantially the same contact pressure. 
     Second Embodiment 
       FIG. 6A  is an enlarge view illustrating the structures of an IC socket according to a second embodiment, especially depicting the structures of first contact pins  120  used for establishing connections with the solder balls  13  and second contact pins  220  used for establishing connections with the lands  14 . In the second embodiment, the structure of the second contact pins  220  is modified from that in the first embodiment. 
     Specifically, the first contact pins  120  each include a barrel member  122  and a plunger member  124 , and the second contact pins  220  each include a barrel member  222  and a plunger member  224 . As shown in  FIG. 6B , each barrel member  122  accommodates a biasing member  126  for biasing the plunger member  124  towards the BGA/LGA hybrid package  10 , and each barrel member  222  accommodates a biasing member  226  for biasing the plunger member  224  towards the BGA/LGA hybrid package  10 . 
     Referring back to  FIG. 6A , the barrel members  122  and  222  have different lengths, while the plunger members  124  and  224  have the same length in this embodiment. Specifically, the barrel members  122  of the first contact pins  120  have a length of A (hereinafter, referred to as the barrel length A), and the plunger members  124  protrude from the barrel members  122  with a protruding length of B (hereinafter, referred to as the protruding length B). On the other hand, the barrel members  222  of the second contact pins  220  has a length of D (hereinafter, referred to as the barrel length D), while the plunger members  224  protrude from the barrel members  222  with a protruding length identical to that of the plunger members  124 . 
     It should be noted that the barrel length A of the barrel members  122  of the first contact pins  120  is different from the barrel length D of the barrel members  222  of the second contact pins  220 , so that the distance between the tips of the plunger members  214  and the surface of the socket body  300  is longer by the terminal height difference E between the solder balls  13  and the lands  14  than the distance between the tips of the plunger members  224  and the surface of the socket body  300  in the unused state. In this embodiment, the first and second contact pins  110  and  210  are structured so that the difference between the barrel length A of the barrel members  122  and the barrel length D of the barrel members  222  is identical to the terminal height difference E. In other words, the barrel length A of the barrel members  122  is longer by the terminal height difference E than the barrel length D of the barrel members  222 . 
     Additionally, the biasing members  126  and  226  are structured so that the plunger members  124  and  224  are withdrawn into the barrel members  122  and  222  with the same withdrawal length, when the same forces are applied to the plunger members  124  and  224 . More specifically, the biasing members  126  and  226  may be formed of springs having the same spring modulus in one embodiment. Alternatively, the biasing members  126  and  226  may be formed of the same elastic material. 
     The structure described above allows the plunger members  124  and  224  to be in contact with the solder balls  13  and the lands  14  of the BGA/LGA hybrid package  10  with substantially the same contact pressure. 
     Third Embodiment 
       FIG. 7A  is an enlarge view illustrating the structures of an IC socket according to a third embodiment, especially depicting the structures of first contact pins  130  used for establishing connections with the solder balls  13  and second contact pins  230  used for establishing connections with the lands  14 . In the third embodiment, the structures of the first and second contact pins  130  and  230  are modified from those in the first and second embodiments. 
     Specifically, the first contact pins  130  each include a barrel member  132  and a plunger member  134 , and the second contact pins  220  each include a barrel member  232  and a plunger member  234 . As shown in  FIG. 7B , each barrel member  132  accommodates a biasing member  136  for biasing the plunger member  124  towards the BGA/LGA hybrid package  10 , and each barrel member  232  accommodates a biasing member  236  for biasing the plunger member  224  towards the BGA/LGA hybrid package  10 . 
     Referring back to  FIG. 7A , the barrel members  132  and  232  have the same barrel length of A, while the plunger members  134  and  234  protrude from the barrel members  132  and  232  with the same protruding length of B in the unused state of the IC socket (that is, the state in which first and second contact pins  130  and  230  are not contacted with BGA/LGA hybrid package  10 ). 
     In this embodiment, the biasing members  136  and  236  are configured to have different elastic characteristics. The biasing members  136  and  236  are structured so that the plunger members  134  and  234  are respectively withdrawn into the barrel members  132  and  232  with different withdrawal lengths, when the same forces are applied to the respective plunger members  134  and  234 , respectively. Preferably, the biasing members  116  and  216  may be formed of springs having different spring moduli in one embodiment. The use of springs, such as coil springs and blade springs, is preferable in terms of easiness of adjustment of the biasing forces applied to the plunger members  134  and  234 . Alternatively, the biasing members  116  and  216  may be formed of elastic materials with different elastic coefficients. 
     More specifically, applying the same forces to the plunger members  134  and  234  causes different changes in the protruding lengths of the plunger members  134  and  234  from the barrel members  132  and  232 , as shown in  FIG. 8 . When forces of the same certain strength are commonly applied to the plunger members  134  and  234 , the plunger members  134  are withdrawn into the barrel member  132  with a withdrawn length of b 1  to reduce the effective protruding length of the plunger members  134  down to B 1 , while the plunger members  234  are withdrawn into the barrel member  232  with a withdrawn length of b 2  to reduce the effective protruding length of the plunger members  234  down to B 2 . 
     When the IC socket according to the third embodiment is attached with the BGA/LGA hybrid package  10  to establish electrical connections, the BGA/LGA hybrid package  10  is pressed with a predetermined pressure so that the difference between the effective protruding lengths B 1  and B 2  is identical to the terminal height differences E between the solder balls  13  and the lands  14 . In other words, the BGA/LGA hybrid package  10  is pressed so that the withdrawn length of the plunger members  134  into the barrel members  132  is larger than that of the withdrawn length of the plunger members  234  into the barrel members  232  by the terminal height difference E between the solder balls  13  and the lands  14 . This allows the plunger members  124  and  224  to be in contact with the solder balls  13  and the lands  14  of the BGA/LGA hybrid package  10  with substantially the same contact pressure. 
     As described above, the above-described IC socket structures according to the first to third embodiments allows establishing electrical connections with solder balls and lands of a BGA/LGA hybrid package with substantially the same contact pressure, avoiding crush of solder balls potentially caused by excessive pressure. This is effective for conducting a proper IC test. 
     It is apparent that the present invention is not limited to the above-described embodiments, but may be modified and changed without departing from the scope of the invention.