Abstract:
A socket for testing a BGA package capable of avoiding problems like deformation of external terminals of the BGA package or failing to detect a defective BGA package and a test method using the socket are provided. The socket for testing a BGA package connects solder balls (or solder bumps) as external terminals of the BGA package via a mesh, a pressure conductive rubber (PCR) as a middle connection unit, and a channel connection means of a socket board. A plane board having POGO pins or a printed circuit pattern can be used for the channel connection means.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a packaging for integrated circuits, and more particularly, to a socket for testing a ball grid array (hereinafter referred to as BGA) package and-a test method using the socket. 
     2. Description of the Related Art 
     After fabrication of semiconductor devices, an electrical die sorting (EDS) test determines which of the devices are good. The good devices are packaged and electrically tested further. In the testing, the packaged devices are placed in sockets corresponding to their package forms. Plastic packages having outer leads have been widely used in the industry. However, many packages such as ball grid array packages, fine-pitch ball grid array packages, and chip scale packages have solder balls or solder bumps as external terminals. 
     Sockets for the testing have various methods of construction and shapes according to the outer forms of packages. That is, in the case where the packages have a dual in-line package (DIP) form, a small out-line package (SOP) form, a quad flat package (QFP) form, or a BGA package form, the shape and construction of the sockets are each different. 
     As the size of electrical devices have become small these days, the packages using solder balls or solder bumps have replaced packages using leads. 
     Typical sockets for testing the BGA package having solder balls or solder bumps include POGO pins that contact the solder balls or the solder bumps. Such sockets are disclosed in U.S. Pat. No. 5,545,050, which is herein incorporated as reference in its entirety. 
     The POGO pins can cause several problems in testing the BGA package. 
     First, when the tips of the POGO pins being used for a channel connection means are connected to the solder balls or the solder bumps, the POGO pins may scratch and damage the solder balls or the solder bumps, producing visual defects such as burrs. 
     Second, since the POGO pins are constructed to have a pin type in number “1” shape, the POGO pins connect solder ball/bump pads to a socket board, even if the solder balls or the solder bumps are not attached to a package body of semiconductor devices due to mistakes in assembling. Accordingly, a defective BGA package in which the solder balls or the solder bumps are not attached cannot be detected. 
     SUMMARY OF THE INVENTION 
     To solve the above problems, it is a first object of the present invention to provide an apparatus for testing a BGA package capable of connecting solder balls as the external terminals of the BGA package to a tester by using a pressure conductive rubber (hereinafter referred to as a PCR) and a mesh and thereby preventing damage to the solder balls and accurately detecting a defective BGA package in which the solder balls are not attached. 
     It is a second object of the present invention to provide a method for electrically testing the BGA package. 
     To achieve the first object of the present invention, there is provided an apparatus for testing a BGA package. The apparatus includes: a socket board having a channel connection means; a middle connection unit composed of a PCR attached to the socket board; a mesh having holes in which solder balls are inserted and being attached to the middle connection unit; and a frame unit attached to the edges of the middle connection unit and the mesh, for fixing and aligning the middle connection unit and the mesh, including an alignment means. 
     According to an embodiment of the present invention, the socket board is a plane having a plurality of POGO pins as the channel connection means. 
     According to another embodiment of the present invention, the socket board is a plane having a printed circuit pattern as the channel connection means. 
     According to still another embodiment of the present invention, the BGA package is a strip-type package including a unit package or several packages attached to one strip. 
     It is preferable to further include a contactor, which applies pressure to the BGA package so that the external terminals of the BGA package contact the middle connection unit via the mesh. 
     Preferably, the PCR of the middle connection unit contains conductive particles including nickel (Ni) and gold (Au), and the conductive particles are vertically arranged in a silicon rubber, and the frame unit includes a supporting board of the middle connection unit, a height-adjusting means, and an alignment means for aligning the middle connection unit and the height-adjusting means. 
     To achieve the second object of the present invention, there is provided a method for electrically testing a BGA package, comprising the steps of: loading the BGA package on a pressure conductive rubber; aligning the solder balls of the BGA package in holes of the mesh of the socket; connecting the solder balls to conductive particles of a PCR via the mesh by applying pressure to the upper part of the BGA package; connecting the conductive particles of the PCR to a channel connection means of a socket board; and connecting the channel connection means to channels of a tester. 
     According to preferred embodiments of the present invention, a plane having the POGO pins or a plane having the printed circuit pattern can be used for the channel connection means. The BGA package may be constructed of a unit package or several packages. Preferably, the mesh forms several holes in which the solder balls of the BGA package are inserted. 
     According to the present invention, damage or variation occurring in the external terminals can be prevented by using the middle connection unit and the mesh as a means for connecting the socket board to the solder balls as the external terminals of the BGA package. Also, errors in an open/short test can be reduced by smoothly connecting the external terminals and the socket board to each other. Thus, a defective BGA package in which the solder balls are not attached can be accurately detected in a final electrical test. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The features and advantages of the present invention will become more apparent by describing in detail preferred embodiments of the invention with reference to the attached drawings in which: 
     FIG. 1 is a sectional view of a pressure conductive rubber (PCR) in contact With a BGA package, 
     FIG. 2 is a plan view of PCRs of a middle connection unit attached to a supporting board of the middle connection unit of a frame unit; 
     FIG. 3 is a sectional view taken along line III-III′ of FIG. 2; 
     FIG. 4 is a plan view of a mesh attached to the middle connection unit; 
     FIG. 5 is a sectional view taken along line V-V′ of FIG. 4; 
     FIG. 6 is a schematic sectional view of a BGA package loaded on a socket for electrically testing according to a first embodiment of the present invention; 
     FIG. 7 is a schematic sectional view of a BGA package connected to the socket for electrically testing by a contactor according to the first embodiment of the present invention; 
     FIG. 8 is a schematic sectional view of a BGA package connected to the socket for electrically testing by the contactor according to a second embodiment of the present invention; 
     FIG. 9 is a schematic sectional view illustrating a variation of solder balls of the BGA package in the case where a mesh is not used in the present invention; 
     FIG. 10 is a plan view of the surface of a socket board according to the second embodiment of the present invention; 
     FIG. 11 is an exploded plan view illustrating several BGA packages attached to one strip and moved during steps according to the third embodiment of the present invention; and 
     FIG. 12 is a sectional view illustrating a strip-type BGA package connected to the socket for electrically testing according to the third embodiment of the present invention. 
     Use of the same reference numerals in different figures indicate identical or similar items. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Embodiment 1: Socket for electrically testing a BGA package in the case where a plane board having POGO pins as a channel connection means of a socket board is used. 
     FIG. 1 is a sectional view of a pressure conductive rubber (PCR) in contact with a BGA package. 
     Referring to FIG. 1, in the structure of a pressure conductive rubber (PCR)  102  having conductivity caused by external-pressure, conductive particles  106  are arranged between an insulating rubber  104  with a predetermined pitch. Thus, the insulating rubber  104  has no conductivity in the state in which external pressure is not applied. However, the insulating rubber  104  is compressed when a predetermined external pressure is applied, and thus a stroke occurs and the conductive particles  106  which are vertically arranged come into contact each other such that they are electrically connected in the vertical direction. 
     Thus, when a BGA package in which solder balls  108  are used as an external connection means is pressed from above, the solder balls  108  of a BGA package body  100  apply external pressure pressing the PCR  102 , and thus electrical connection (ON) of the vertical direction can be realized. Also, a region without pressure is electrically insulated (OFF). 
     The PCR  102  having conductivity caused by external pressure as a means for connecting the solder balls to a socket board has effects as follows. That is, the solder balls are not damaged and thus have no visual defects. Also, in the case where the solder balls  108  are missing (i.e., not attached to the BGA package body  100  due to defects in assembling), the PCR  102  is not pressed and thus it is not contacted. Accordingly, a defective BGA package in which one or more of the solder balls are not attached may be accurately detected in a final electrical test. 
     Since the insulating rubber  104  is made of silicon rubber, the insulating rubber  104  has a thermal expansion coefficient similar to that of the semiconductor wafer. The smaller difference in thermal expansion coefficient of the insulating rubber  104  and the BGA package body  100  is less likely to cause miscontact between the conductive particles  106  in the insulating rubber  104  and the BGA package body  100  when temperature changes during electrical testing. Further, the PCR  102  is not materially degraded when used between −40° C. and +150° C. Also, since the chief ingredients of the conductive particles  106  are nickel (Ni) and gold (Au), the conductive particles  106  have excellent conductivity. Furthermore, in the case where the PCR  102  is used instead of conventional POGO pins, the life span of the PCR  102 , having 50,000 or more cycles, is increased. 
     FIG. 2 is a plan view of PCRs of a middle connection unit attached to a supporting board of the middle connection unit of a frame unit. 
     Referring to FIG. 2, the PCR  102  as a middle connection unit for connecting a socket board and a BGA package is conceptually explained in the FIG. 1, but in the plan view, the PCR  102  will be more concretely described. Explaining in detail, a PCR  102 A (FIG. 3) for fixing is first attached to a supporting board  120  of the middle connection unit. The supporting board  120  is composed of metal or plastics and punched in the middle portion and has a plane shape. Another PCR  102 B (FIG.  3 ), being acted by external pressure, is attached to the PCR  102 A and fixed. At this time, the conductive particles  106  in the PCRs  102 A and  102 B may be attached in an arranged state so as to be connected to each other. Also, alignment holes  124  for an alignment means are at four corners of the supporting board  120  of the middle connection unit. Accordingly, when the supporting board  120  of the middle connection unit is assembled in the socket board, a channel connection means on the socket board, for example, POGO pins or a printed circuit pattern, is fitted to the conductive particles  106  of the supporting board  120  such that they come into electrical contact. This is possible by inserting a screw  122  of FIG. 6 as an alignment means into each of the alignment holes  124  of the supporting board  120  of the middle connection unit and by fixing the screw. Accordingly, the screws  122  removably attach the supporting board  120  of the middle connection unit to the socket board. Thus, a worn out middle connection unit containing the PCR is easily replaced. 
     FIG. 3 is a sectional view taken along line III-III′ of FIG.  2 . 
     Referring to FIG. 3, the PCR  102 A for fixing is first attached to the supporting board  120  of the middle connection unit, and the PCR  102 B being acted by external pressure is attached to the PCR  102 A. At this time, the conductive particles  106  of the PCRs  102 A and  102 B are arranged to provide conductivity when external pressure is applied. 
     FIG. 4 is a plan view of a mesh attached to the middle connection unit. 
     Referring to FIG. 4, a mesh  121  is attached to the middle connection unit including PCR  102  of FIG.  2 . The mesh  121  determines the sitting location of solder balls as an external terminal of the BGA package and prevents variation of solder balls when the BGA package is electrically tested at a high temperature for a long time. The mesh  121  has four alignment holes  123 , in which screws  122  (FIG. 6) composed of an insulating material such as plastic are inserted for aligning in a main body  129 , and many holes  127  in which solder balls of the BGA package sit. The holes  127  are constructed at the same interval as that of the conductive particles  106  of the PCR  102  shown in FIG.  2 . The mesh  121  is an important means for electrically testing the BGA package together with the middle connection unit. 
     FIG. 5 is a sectional view taken along line V-V′ of FIG.  4 . 
     Referring to FIG. 5, solder balls of the BGA package sit in the holes  127  formed in the main body  129 , and the holes  127  can be connected to the conductive particles of the PCR. 
     FIG. 6 is a schematic sectional view of a case where the BGA package is loaded on a socket for electrical testing according to a first embodiment of the present invention. 
     Referring to FIG. 6, the socket for electrical testing according to the first embodiment of the present invention includes: a socket board  125  having POGO pins  118  as a channel connection unit; a middle connection unit having the PCR  102  on the socket board  125 ; a mesh  121  having holes in which solder balls  108  are inserted, on the middle connection unit; and a frame unit  132  having an alignment means  122  for fixing and aligning on the edges of the middle connection unit  102  and the mesh  121 . 
     Reference numeral  116  indicates a performance board of a tester and indicates a board having a channel connection terminal of the tester. Reference numeral  122  indicates an alignment means, and preferably, screws may be used as alignment means. Reference numeral  118  indicates POGO pins, and the POGO pins  118  are connected to the conductive particles  106  of the PCR  102  by elasticity of a spring in the inside the POGO pins  118 . 
     Reference numeral  107  indicates a height-adjusting means. The structure of the height-adjusting means is same as that of the supporting board  120  of the middle connection unit shown in FIG. 2, and the height-adjusting means  107  adjusts only the thickness and thereby makes the surface of the socket for electrically testing the BGA package level. If the height-adjusting means  107  is not used, variations such as lifting of the middle connection unit can occur in the course of repeating an electrical test, and thus, the conductive particles  106  of the PCR  102  can become disconnected from the POGO pins  118  of the socket board  125 . 
     Here, the shape of the frame unit  132  can be modified without limit. Since further modifications are possible by a person skilled in the art according to the structure of the facility used or requirements of an user, the shape of the socket for electrically testing the BGA package shown in the present invention is illustrative and not liming. 
     The preferable thickness, contact resistance, inductance, and capacitance of the PCR  102  of the socket for electrically testing a BGA package according to the present invention are 0.4 to 0.88 mm, 5 mΩ or less, 0.7 to 0.88 nH, and 1 pF or less, respectively. The PCR  102  provides better electrical connections than conventional POGO pins. Accordingly, when the socket for electrically testing a BGA package according to the present invention is applied to a final electrical test and a burn-in test, the occurrence of open failures due to the unstable contact between the solder balls and the socket of the BGA package or visual defects arising from damage or variation to the solder balls are remarkably reduced. 
     FIG. 7 is a schematic sectional view of a case where the BGA package is connected to the socket for electrically testing by a contactor according to the first embodiment of the present invention. 
     Referring to FIG. 7, a contactor includes a package pusher  110 , an inserter  112  and a socket guide  114 . The BGA package put into the inserter  112  by the package pusher  110  first sits on the holes in the mesh  121 , for sitting solder balls. Subsequently, when external pressure, that is, contact force is applied to the package pusher  110 , the solder balls  108  as an external connection unit, at the bottom side of the BGA package body  100  press the PCR  102 . Accordingly, the solder balls  108  of the BGA package and the POGO pins  118  of the socket board  125  are connected to each other respectively via the PCR  102 . The socket board  125  is again connected to channels of a tester via the performance board  116  and thereby an electrical test for a BGA package is performed. 
     Embodiment 2: Socket for electrically testing a BGA package in the case where a plane board having a printed circuit pattern as a channel connection means of a socket board is used. 
     In the second embodiment of the present invention, a channel connection means of the socket board is the same as that of the first embodiment of the present invention except for use of a printed circuit pattern instead of POGO pins of the first embodiment in the socket for electrically testing the BGA package. Accordingly, to avoid repetition, the above descriptions for the first embodiment are also relied on for the second embodiment, and explanations of the same or overlapping matters are omitted. 
     FIG. 8 is a schematic sectional view of a case where the BGA package is connected to the socket for electrically testing by the contactor according to the second embodiment of the present invention. 
     Referring to FIG. 8, the socket for electrically testing the BGA package according to the second embodiment of the present invention includes: a socket board  126  having a printed circuit pattern (see FIG. 10) as a channel connection means; a middle connection unit having the PCR  102  on the socket board  126 ; a mesh  121  having holes in which the solder balls  108  are inserted, on the middle connection unit; a frame unit  132  having an alignment means  122  for fixing and aligning on the edges of the middle connection unit and the mesh  121 ; and a contactor applying external pressure to the BGA package body  100 . The frame unit  132  includes a supporting board  120  of the middle connection unit, a height-adjusting means  107 , and an alignment means  122 , that is, screws. The contactor includes a package pusher  110 , an inserter  112 , and a socket guide  114 . Reference numeral  116  indicates a performance board of a tester and particularly indicates a board having a channel connection terminal of the tester. 
     FIG. 9 is a schematic sectional view illustrating variation of solder balls of the BGA package in the case where a mesh is not used in the present invention. 
     Referring to FIG. 9, the socket for electrically testing the BGA package according to the present invention can be used for a reliability test having a special purpose such as a burn-in test. The burn-in process is a test process applying an electrical signal to the BGA package at a high temperature of at least 125° C. for at least an hour. As shown, if the mesh  121  is not used, external pressure (contact) applied at a high temperature for a long time flattens solder balls  108 ′ attached to a BGA package body  100 ′. Accordingly, the mesh  121  added according to the present invention provides paths capable of being properly connected to conductive particles  106 ′ of a PCR  102 ′. The structure of a contactor  117  has a different shape from that of contactors shown in FIGS. 7 and 8. Accordingly, various modifications of the contactor  117  are possible in accordance with the features of devices used. 
     FIG. 10 is a plan view of the surface of a socket board according to the second embodiment of the present invention. 
     Referring to FIG. 10, the surface of a socket board  126  contacts with the conductive particles of the middle connection unit composed of the PCR such that they come into electrical contact. For this purpose, a printed circuit pattern  128  is formed as a channel connection unit, and a contact portion  130  is formed in the printed circuit pattern  128 . The contact portion  130  of the printed circuit pattern  128  preferably has the same interval as those of the conductive particles of the middle connection unit and of the holes for the solder balls in the mesh. The surface of the contact portion  130  of the printed circuit pattern  128  may be gold-plated to improve the conductivity of the contact portion contacting the conductive particles. 
     A method for electrically testing a BGA package according to the second embodiment of the present invention is the same as that for the first embodiment of the present invention, except that the conductive particles  106  of the middle connection unit  102  are connected to the contact portion  130  of the printed circuit pattern  128  instead of the POGO pins in the socket board. 
     Embodiment 3: Socket for electrically testing a strip-type BGA package. 
     In the first and second embodiments of the present invention, the socket for a BGA package including a unit package is mainly described, but in this third embodiment, a socket for electrically testing a strip-type BGA package will be described. 
     FIG. 11 is an exploded plan view illustrating several BGA packages attached to one strip and moved during steps according to the third embodiment of the present invention. 
     Referring to FIG. 11, BGA packages  146  before being separated by the piece are processed in a strip  144  composed of polyimide. The strip  144  performs an electrical test in the state that the strip  144  is moved into a strip carrier  142  and fixed. 
     FIG. 12 is a sectional view illustrating a strip-type BGA package connected to the socket for electrically testing according to the third embodiment of the present invention. 
     Referring to FIG. 12, the structure of the socket for electrically testing the strip-type BGA package is the same as those of the first and second embodiments mentioned above. It is only different in that the sizes of the middle connection unit  102  and the mesh  121  are extended so as to test several packages at one time. At this time, a channel connection means of a socket board  125  or  126  is POGO pins or a printed circuit pattern. 
     Thus, according to the present invention described above, first, damage or variation occurring in the external terminals can be prevented by using the middle connection unit and the mesh as a means for connecting the solder balls as the external terminals of the BGA package and the socket board. Second, errors in an open/short test can be reduced by smoothly connecting the external terminals and the socket board to each other. Third, a defective BGA package in which the solder balls are not attached can be accurately detected in a final electrical test. 
     Although the invention has been described with reference to particular embodiments, the description is only an example of the inventor&#39;s application and should not be taken as a limitation. Various adaptations and combinations of features of the embodiments disclosed are within the scope of the invention as defined by the following claims.