Abstract:
For testing a high density BGA package, a central pressure block is designed to press against the chip of the package during test in a test socket. High density socket probe causes high pressure against the package, especially the area under the chip. With the central pressure block of the present invention, the high density BGA package is prevented from deformation because the central pressure block pressing downward against the chip, which balances the pressure coming upward from the high density socket probes under the circuit board in the area under the chip.

Description:
BACKGROUND 
       [0001]    1. Technical Field 
         [0002]    The present invention relates to a test socket for testing a ball grid array (BGA) package, especially suitable for testing a high density BGA package. 
         [0003]    2. Description of Related Art 
         [0004]      FIG. 1  is a prior art test socket 
         [0005]      FIG. 1  is a prior art test socket  100  having a top cover  10  and a socket seat  13 . A hinge mechanism  12  is configured between the top cover  10  and the socket seat  13  so that the top cover  10  is able to close against the socket seat  13  during test. The top cover  10  has a frame  102 , and a window  101  surrounded by the frame  102 . 
         [0006]      FIGS. 2A˜2B  is the socket seat of  FIG. 1 . 
         [0007]      FIG. 2A  shows that the socket seat  13  has a central recess  133  and a seat wall  132  surrounding the recess  133 . A flatbed  135  is configured on the bottom of the recess  133  and surrounded by the seat wall  132 . An array of socket probe  14  is configured in the flatbed  135  of the socket seat  13 . 
         [0008]      FIG. 2B  is a section view according to line AA′ of  FIG. 2A . The recess  133  is surrounded by the seat wall  132 . The socket probe  14  is protruded above the top surface of the flatbed  135 . The socket probe  14  is elastic so as to provide a pressure upward against the ball grid of a BGA package under test. The elasticity of the socket probe  14  is provided by an underlain spring  141 . 
         [0009]      FIGS. 3A˜3C  is a prior art of a relatively lower density BGA package. 
         [0010]      FIG. 3A  is a top view of a relatively lower density BGA package  200 . The package has a chip  16  mounted on the center top of a circuit board  15 . A metal frame  17  braces the periphery of the circuit board  15  to strengthen the package  200  and prevent the package  200  from being deformed. 
         [0011]      FIG. 3B  is a section view according to line BB′ of  FIG. 3A .  FIG. 3B  shows that the chip  16  is mounted on the center top of the circuit board  15 . The metal frame  17  braces the periphery of the circuit board  15 . The relatively lower density ball grid array  18  is configured on the bottom of the circuit board  15 . 
         [0012]      FIG. 3C  is a bottom view of  FIG. 3A .  FIG. 3C  shows that the relatively lower density ball grid array  18  is configured on a bottom of the circuit board  15 . 
         [0013]      FIGS. 4A˜4B  is prior art of a relatively lower density BGA package under test 
         [0014]      FIG. 4A  shows the relatively lower density BGA package  200  under test. The top cover  10  of the test socket  100  closes down against the socket seat  13 . A peripheral pressure unit  21  pressing against the BGA package  200 . Please pay attention that the peripheral pressure unit  21  presses the metal frame  17  only. There is no pressure pressing against the chip  16  from top. 
         [0015]      FIG. 4B  shows the relatively lower density BGA package  200  keeps the same profile after test. Please pay attention that the lower density socket probes  14  applies lower pressure against the circuit board  15  under the chip  16 . However, package deformation shall occur when the number of probes  14  is relatively higher. Nowadays, higher and higher the ball grid array for a BGA package becomes as the semiconductor technology is improved swiftly. 
         [0016]      FIGS. 5A˜5C  is a prior art of a relatively higher density BGA package. 
         [0017]      FIG. 5A  is a top view of a relatively higher density BGA package  300 . The package  300  has a chip  162  mounted on the center top of a circuit board  15 . A metal frame  17  braces the periphery of the circuit board  15  to strengthen the package  300  and prevent the package  300  from being deformed. 
         [0018]      FIG. 5B  is a section view according to line CC′ of  FIG. 5A .  FIG. 5B  shows that the chip  162  is mounted on the center top of the circuit board  15 . The metal frame  17  braces the periphery of the circuit board  15 . A relatively higher density ball grid array  182  is configured on the bottom of the circuit board  15 . 
         [0019]      FIG. 5C  is a bottom view of  FIG. 5A .  FIG. 5C  shows that the relatively higher density ball grid array  182  is configured on a bottom of the circuit board  15 . 
         [0020]      FIGS. 6A˜6B  is a prior art of a relatively higher density BGA package under test 
         [0021]      FIG. 6A  shows the relatively higher density BGA package  300  under test. The top cover  10  of the test socket  100  closes down against the socket seat  13 . A peripheral pressure unit  21  pressing against the relatively higher density BGA package  300 . Please pay attention that the peripheral pressure unit  21  presses the metal frame  17  only. There is no pressure pressing against the chip  162  from top. 
         [0022]      FIG. 6B  shows the high density BGA package  300  is deformed under the chip  162  during test because huge pressure pressing against the circuit board  15  due to the high density probes  142  in the area under the chip  162 . Please pay attention to the socket probes  142  under the chip  16 . The higher number of probe  142  applies a higher pressure against the circuit board  15  in the area under the chip  16 . Package deformation occurs during test. The deformation may cause break to the chip  162 . Some 17 gram pressure a socket probe  142  contributes, if say, 20*20 probes under the circuit board  15  in the area under the chip  162 , there shall be 20*20*17=6800 gram pressure applying against the circuit board  15  under the chip  162 . The 6800 gram is a high pressure during test, which may cause a permanent damage to the BGA package  300  if test under the traditional test socket  100 . 
         [0023]    A solution to prevent the package deformation problem for testing a high density BGS package is eager to submit. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0024]      FIG. 1  is a prior art test socket 
           [0025]      FIGS. 2A˜2B  is the socket seat of  FIG. 1 . 
           [0026]      FIGS. 3A˜3C  is a prior art of a relatively lower density BGA package. 
           [0027]      FIGS. 4A˜4B  is prior art of a relatively lower density BGA package under test 
           [0028]      FIGS. 5A˜5C  is a prior art of a relatively higher density BGA package. 
           [0029]      FIGS. 6A˜6B  is a prior art of a relatively higher density BGA package under test 
           [0030]      FIGS. 7A˜7C  is a peripheral pressure unit of an embodiment according to the present invention. 
           [0031]      FIGS. 8A˜8C  is a central pressure block of the embodiment according to the present invention. 
           [0032]      FIGS. 9A˜9C  is a combination status for the central pressure block combining the peripheral pressure unit according to the present invention. 
           [0033]      FIGS. 10A˜10B  is a relatively higher density BGA package under test according to the present invention. 
           [0034]      FIG. 11  is a cooling unit configured on a top of the central pressure block under testing. 
           [0035]      FIGS. 12A˜12B  pictures of an actual test socket according to the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0036]    The peripheral pressure unit is modified and a central pressure block  210  is newly created to match with the modified pressure unit  250 . The improved test socket solves the deformation problem for a relatively higher density BGA package during test. 
         [0037]    A central pressure block is designed to press against the relatively higher density BGA package  300  under test so that the circuit board  15  under the chip  162  shall not be deformed by the pressure upward from the spring probes  142 . The central pressure block  210  has an upper block  214  and a lower block  213 . The lower block  213  is protruded downward from the upper block  214 . The lower block  213  is configured to press against the high density BGA package  300  from top during test. 
         [0038]      FIGS. 7A˜7C  is a peripheral pressure unit of an embodiment according to the present invention. 
         [0039]      FIG. 7A  shows a top view of the improved peripheral pressure unit. A peripheral pressure unit  250  has a central recess  256 . A rectangular wall  254  has four corners  254 C, the rectangular wall  254  surrounds the central recess  256 ; an upper flat  251  extends outward from a top of the wall  254 ; a lower flat  253  extends inward from a bottom of the wall  254 . A window  255  is enclosed by the lower flat  253 . 
         [0040]    The opening  255  is configured in the bottom center of the recess  256 . The dimension of the rectangular wall  254  is designed to fit in the recess  133  of the BGA test socket  100 . There are four L-shaped top flats  251 , each top flat  251  is configured to bracket one of the four corners of the rectangular wall  254 . At least a blind hole  252  is made on each top flat  251 . A spring  22  is suitable to fit in the blind hole  252  with upper portion protruded above the top surface of the top flat  251  so that the top cover  10  is able to press against the spring  22  when the socket  100  closes. The dimension of the rectangular wall  254  is designed to fit in the recess  133  of the socket  100 . The dimension of the opening  255  is designed to be larger than the dimension of the chip  162  so that the backside of the chip  162  is able to fully expose after the peripheral pressure unit  250  fits in the recess  133 . An opening  257  is formed between two neighboring top flat  251 . Please pay attention that the opening  257  extends downward to the top surface of the bottom flat  253  ( FIG. 7C ). 
         [0041]      FIG. 7B  is a section view according to line DD′ of  FIG. 7A .  FIG. 7B  shows the peripheral pressure unit  250  has a recess  256  and a window  255  configured in the bottom center of the recess  256 . The peripheral pressure unit  250  has a top flat  251 , a rectangular wall  254 , and a bottom flat  253 . The upper flat  251  extends outward from a top of the wall  254 ; the lower flat  253  extends inward from a bottom of the wall  254 . A window  255  is enclosed by the lower flat  253 . 
         [0042]      FIG. 7C  is a side view to  FIG. 7A .  FIG. 7C  shows that the rectangular wall  254  is partially cut away in between the upper flat  251  so that the opening  257  extends downward to the top surface of the bottom flat  253 . 
         [0043]      FIGS. 8A˜8C  is a central pressure block of the embodiment according to the present invention. 
         [0044]      FIG. 8A  is a top view of the central pressure block  210 . The central pressure block  210  has an upper block  214 . There are four side tabs  211 ; each tab  211  extends from one of the four sides of the upper block  214 . The side tab  211  is designed to fit in the opening  257  of the peripheral pressure unit  250 . There are two blind holes  212  made in the left side tab and right side tab  211 . Each of the blind holes is designed to house a spring  22 . The spring  22  is configured to protrude above the top surface of the central block  214  so that the top cover  10  is able to close down and presses against the central pressure block  210  during test. 
         [0045]      FIG. 8B  is a section view according to line EE′ of  FIG. 8A . The central pressure block  210  has an upper block  214  and a lower block  213 . The lower block  213  is protruded downward from a center bottom of the upper block  214 . 
         [0046]      FIG. 8C  is a bottom view of  FIG. 8A . The lower block  213  is protruded downward from the upper block  214 . The dimension of the lower block  213  is near or larger than that of the chip  162  under test so that the lower block  213  is able to press against the chip  162  during test. 
         [0047]      FIGS. 9A˜9C  is a combination status for the central pressure block combining the peripheral pressure unit according to the present invention. 
         [0048]      FIG. 9A  is a top view of a combination status of the peripheral pressure unit  250  combining the central pressure block  210 . The upper block  214  fits in the recess  256  of the peripheral pressure unit  250 . The side tabs  211  fit in the opening  257  of the peripheral pressure unit  250 . 
         [0049]      FIG. 9B  is a section view according to line FF′ of  FIG. 9A .  FIG. 9B  shows that the upper block  214  fits in the recess  256  of the peripheral pressure unit  250 . The lower block  213  fits in the window  255  of the peripheral pressure unit  250 . 
         [0050]      FIG. 9C  is a side view of  FIG. 9A .  FIG. 9C  shows that the side tab  211  fits in the opening  257  of the peripheral pressure unit  250 . 
         [0051]      FIGS. 10A˜10B  is a relatively higher density BGA package under test according to the present invention. 
         [0052]      FIG. 10A  shows a relatively higher density BGA package  300  is configured in the test socket  100  for test. The relatively higher density BGA package  300  is pressed by the peripheral pressure unit  250  against a periphery of the package  300 , and pressed by the central pressure block  210  against the center of the package  300  so that the circuit board  13  is not deformed by the pressure coming from the socket probe  142 . 
         [0053]      FIG. 10B  shows the relatively higher density BGA package  300  during the period of the test.  FIG. 10B  shows that the circuit board  15  is not deformed by the pressure coming from the higher density socket probes  142 . With the present invention, the relatively higher density BGA package  300  keeps the same profile during test. 
         [0054]      FIG. 11  is a cooling unit configured on a top of the central pressure block under testing. 
         [0055]      FIG. 11  shows that a cooling unit  29  is able to contact the top of the central pressure block  210  so that the heat generated from the chip  162  can be transferred to the cooling unit for heat dissipation. 
         [0056]      FIGS. 12A˜12B  pictures of an actual test socket according to the present invention. 
         [0057]      FIG. 12A  is a top view of the socket  100  loaded with the modified peripheral pressure unit  250  according to the present invention, however, without having a chip inside in the picture. An array of the socket probe  14  is shown in the center of the socket seat  13 . 
         [0058]      FIG. 12B  is a top view of the socket  100  loaded with the modified peripheral pressure unit  250  and the central pressure block  210  according to the present invention. 
         [0059]    Both the peripheral pressure unit  250  and the central pressure block  210  are made of metal so that the heat generated from the package  162  can be conducted for heat dissipation during test. 
         [0060]    While several embodiments have been described by way of example, it will be apparent to those skilled in the art that various modifications may be configured without departing from the spirit of the present invention. Such modifications are all within the scope of the present invention, as defined by the appended claims.