Abstract:
An embodiment of the present invention provides a circuit board and a socket having mechanical connector for easily connecting and disconnecting a semiconductor integrated circuit device to and from the circuit board. Another embodiment further includes a sub-circuit board for electrically connecting the socket to the circuit board. The socket includes a socket body and a number of socket leads. The socket leads are shaped to compress elastically when inserted in a hole and thereby make contact between the socket leads and inner walls of the holes of the circuit board. The sub-circuit board has connection leads, which make contacts with the through holes of the circuit board in the same manner as the socket leads of the present invention.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention generally relates to a socket, a circuit board, and a sub-circuit board for a semiconductor integrated circuit device, and more particularly to structures and methods for connection and disconnection of the socket, the sub-circuit board, and the circuit board.  
           [0003]    2. Description of the Related Arts  
           [0004]    Semiconductor integrated circuit (IC) devices are tested by various methods in order to verify their reliability. These tests include an electrical characteristics test and a burn-in test. The electrical characteristics test determines whether the characteristics of a semiconductor IC fall within the specifications of the IC, and the burn-in test applies temperature, voltage, and/or operating signals that are beyond the normal operating levels, to a semiconductor IC to detect latent defects which might appear at an early stage of regular use of the IC.  
           [0005]    Generally, in testing, a semiconductor IC is placed in a socket that is fixed on a test circuit board that transfers electrical signals between the semiconductor IC and a tester. FIG. 1 through FIG. 3 are cross-sectional views showing three conventional methods for connecting a semiconductor IC  20  to a socket  70  and a test circuit board  80 .  
           [0006]    [0006]FIG. 1 shows a method for electrically connecting socket  70  and test circuit board  80 . This method is mainly employed in Burn-In Test. For connection between socket  70  and test circuit board  80 , connection leads  75  of socket  70  are inserted into through-holes  82  of test circuit board  80 , and fixed by a soldering.  
           [0007]    The connection method of FIG. 1 has a number of drawbacks. In particular, due to the use of solder  66 , the connection method of FIG. 1 may cause lead poisoning of worker. In addition, when either socket  70  or test circuit board  80  is defective, separating socket  70  from test circuit board  80  for replacement of the defective component is difficult. In particular, the separation process includes heating test circuit board  80  to melt solder  66 , and the heating may damage the wiring patterns (not shown) of test circuit board  80 . Further, extended use of socket  70  and test circuit board  80  degrades the integrity of the bond created by solder  66 , and the connection between socket  70  and test circuit board  80  becomes weak. This weakened connection can cause invalid test results.  
           [0008]    The connection method of FIG. 2 between socket  70  and a test circuit board  100  is mainly employed in test handlers for electrical characteristics test. In this method, a receptacle  87  serves as an intermediate connection medium between socket  70  and test circuit board  100 . Receptacle  87  is inserted into through hole  102  in test circuit board  100  and fixed by soldering. Then, connection leads  75  of socket  70  are inserted into respective receptacles  87 . Separation of socket  70  from test circuit board is relatively easy because connection leads  75  make only temporary contacts with receptacles  87 . However, the method in FIG. 2 has a number of disadvantages. First, to insert connection leads  75  into receptacles  85 , external forces must be applied. Second, when connection leads  75  are fine- pitched, the method in FIG. 2 has a higher probability of short circuits and/or current leakage between neighboring through holes  102  than the method in FIG. 1 because the diameter of the through holes  102  is greater than that of through holes  82 . In particular, each hole  102  must be wide enough to contain a receptacle  87 , and thereby the distance between neighboring through holes  102  is relatively small. Third, adding and installing receptacles  87  increase the cost of IC tests.  
           [0009]    To avoid the short circuits between neighboring through holes  102  in FIG. 2, a sub-circuit board  90  can be interposed between a socket  50  and test circuit board  100 , as shown in FIG. 3. Sub-circuit board  90  has socket  50  thereon, and wiring patterns in sub- circuit board  90  electrically connect the connection leads (not shown) of socket  50  to respective through holes  92  of sub-circuit board  90 . Connection pins  95  and receptacles  87  are respectively fixed to through holes  92  and through holes  102  by soldering. Then, connection pins  92  of sub-circuit board  90  are inserted into respective receptacles  87 . However, even though sub-circuit board  90  can reduce or eliminate the short circuit problem, the connection method still has high test cost due to the additional components such as receptacles  87 .  
         SUMMARY OF THE INVENTION  
         [0010]    An embodiment of the present invention provides a socket and a circuit board, with or without a sub-circuit board for semiconductor integrated circuit device. The structure of each component in this invention provides convenient connection and disconnection of the socket or the sub-circuit board to and from the circuit board and low test cost by eliminating the use of solder and receptacles in the circuit board.  
           [0011]    In accordance with an aspect of the present invention, the socket has distinctively shaped socket leads that are easily inserted into the through holes of circuit board. In addition, shape-induced elasticity of the socket leads provides a solid contact between the socket leads and the inner wall of the through holes.  
           [0012]    The circuit board includes through holes where the socket leads are inserted, and the inner wall of the through holes are plated with conductive abrasion-resistant materials. Respective through holes are connected to a tester by wirings of the circuit board.  
           [0013]    The sub-circuit board provides a connection between a socket, especially for fine-pitch semiconductor IC packages, and a circuit board. The sub-circuit board comprises through holes, wiring patterns which electrically connect the socket to the through holes, and connection leads. An end of each connection lead is fixed to the through holes, and the other end of the connection lead has a distinctive shape in the same manner as in the socket leads according to the present invention.  
           [0014]    Moreover, the elasticity given to the socket leads and the connection leads of sub-circuit board extends the life of the socket and the sub-circuit board, since the socket leads and the connection pins recover their shape as soon as they are pulled out from the through holes of the circuit board. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]    These and various other features and advantages of the present invention will be readily understood with reference to the following detailed description taken in conjunction with the accompanying drawings, wherein like reference numerals designate like structural elements, and, in which:  
         [0016]    [0016]FIG. 1 is a cross-sectional view showing a conventional connection method between a socket and a circuit board for testing a semiconductor integrated circuit device;  
         [0017]    [0017]FIG. 2 is a cross-sectional view showing another conventional connection method between the socket and the circuit board for testing the semiconductor integrated circuit device;  
         [0018]    [0018]FIG. 3 is a cross-sectional view showing still another conventional connection method between the socket and the circuit board for testing the semiconductor integrated circuit device;  
         [0019]    [0019]FIG. 4 is a perspective view showing an embodiment of a socket for testing a semiconductor integrated circuit device according to the present invention;  
         [0020]    [0020]FIG. 5 is a cross-sectional view showing a connection method between the socket of FIG. 4 and a circuit board;  
         [0021]    [0021]FIG. 6 is an enlarged view showing an outer connection portion of the socket lead of FIG. 4;  
         [0022]    [0022]FIG. 7A is a schematic cross-sectional view showing the outer connection portion of the socket lead of FIG. 4 before insertion to the circuit board;  
         [0023]    [0023]FIG. 7B is a schematic cross-sectional view showing the outer connection portion of the socket lead of FIG. 4 after insertion to the circuit board;  
         [0024]    [0024]FIG. 8 is a cross-sectional view showing another embodiment of the outer connection portion of a socket lead according to the present invention; and  
         [0025]    [0025]FIG. 9 is a cross-sectional view showing a connection method between a socket and a circuit board using a sub-circuit board according to the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0026]    Embodiments of the present invention will be described below with reference to the accompanying drawings.  
         [0027]    [0027]FIG. 4 is a perspective view showing an embodiment of a socket for testing a semiconductor integrated circuit device according to the present invention, and FIG. 5 is a cross-sectional view showing a connection between the socket of FIG. 4 and a circuit board. FIG. 6 is an enlarged view showing an outer connection portion of the socket lead of FIG. 4. This embodiment shows socket  10  and circuit board  30  for a burn-in test of a semiconductor integrated circuit device  20  in an SOP (Small Outline Package).  
         [0028]    As shown in FIGS. 4 and 5, socket  10  comprises a socket body  11  and socket leads  15 . Socket body  11  includes an upper body  12  and a lower body  13 , and socket leads  15 , which are integrated with lower body  13 , includes an inner connection portion  15   a , an elastic portion  15   b  and an outer connection portion  15   c . In testing, semiconductor integrated circuit device  20  is placed on lower body  13  so that outer leads  22  of semiconductor integrated circuit device  20  contact respective inner connection portions  15   a  of socket lead  15 . Upper body  12 , which sits on lower body  13 , has a cavity for semiconductor integrated circuit device  20  and is aligned with lower body  13  by guide bars  19 . Upper body  12  holds semiconductor integrated circuit device  20  and secures the contact between outer leads  22  of semiconductor integrated circuit device  20  and respective inner connection portions  15   a  of socket lead  15 . In particular, upper body  12  vertically moves up and down along guide bars  19  and applies pressure to elastic portions  15   b  of socket leads  15  so that inner connection portions  15   a  securely contact outer leads  22 .  
         [0029]    With reference to FIG. 5, socket lead  15  will be described hereinafter in detail. As mentioned above, each socket lead  15  comprises inner connection portion  15   a , elastic portion  15   b , and outer connection portion  15   c . Inner connection portion  15   a  makes a contact with outer leads  22  of semiconductor integrated circuit device  20 , and outer connection portion  15   c  makes a contact with circuit board  30 . Elastic portions  15   b  are bent so that inner connection portion  15   a  contacts outer lead  22  when upper body  12  sits on lower body  13 . That is, inner connection portions  15   a  contact outer leads  22  of semiconductor integrated circuit device  20  when upper body  12  of socket  10  moves down, and disconnect from outer leads  22  when upper body  12  moves up to release semiconductor integrated circuit device  20  from socket  10 .  
         [0030]    As shown in FIG. 6, outer connection portion  15   c  of this embodiment has a shape of elliptical hook for easy insertion and removal of outer connection portion  15   c  of socket lead  15  into and from a through hole  33  of circuit board  30 . In addition, this shape provides elasticity to outer connection portion  15   c  of socket lead  15 . The width d 1 , between the leftmost point and the rightmost point of outer connection portion  15   c , is greater than the diameter (d 2  in FIG. 7) of through hole  33 . When socket lead  15  is inserted into through hole  33 , outer connection portion  15   c  is squeezed in the direction of arrow “B” and pushes inner wall  32  of through hole  33  in the direction of arrow “A” to make a contact with through hole  33 . Through hole  33  connected to a tester (not shown) by wiring for transferring electrical signals between the tester and circuit board  30 . When socket lead  15  is removed from through hole  33 , outer connection portion  15   c  recovers its initial shape.  
         [0031]    [0031]FIG. 7A and FIG. 7B are schematic cross-sectional views respectively showing socket lead  15  before and after being inserted into circuit board  30 , respectively. With reference to FIG. 7 a  and FIG. 7 b , the outer connection portion  15   c  of socket lead  15  will be described in detail hereinafter.  
         [0032]    With reference to FIG. 7A, the appropriate width d 1  of the central portion of the outer connection portion  15   c  is determined by inner diameter d 2  of through hole  33  of circuit board  30 . Generally, width d 1  is greater than inner diameter d 2  to such degree that outer connection portion  15   c  maintains its elasticity without a plastic deformation of the elliptical hook shape of outer connection portion  15   c  after an extended use of socket  10 . Preferably, 0.1 mm difference between width d 1  and diameter d 2  can give the elasticity without plastic deformation to outer connection portion  15   c  of socket lead  15 . In one embodiment of the present invention, socket lead  15  is made of a conductive material such as copper on a copper alloy, and outer connection portion  15   c  is a loop of wire having a diameter of 0.27 mm. The loop has a width d 1  of about 0.86 mm and a height of about 1.94 mm. Through hole  33  is circular with a diameter of about 0.75 mm and inner wall  32  is made of materials such as copper and gold that are conductive, abrasion-resistant, and oxidation-resistant.  
         [0033]    In this embodiment, when outer connection portion  15   c  of socket lead  15  is in through hole  33  as shown in FIG. 7 b , the elastic force from the compressed elliptical hook shape of outer connection portion  15   c  maintains the contact between inner wall  32  of through hole  33  and outer connection portion  15   c . Herein, the location and size of the contact points between outer connection portion  15   c  and through hole  33  may be variously controlled by changing the shape and the degree of the bent portion of outer connection portion  15   c.    
         [0034]    Another advantage of the elliptical hook shape is a minimized friction between inner wall  32  of through hole  33  and outer connection portion  15   c  of socket lead  15  during insertion of socket lead  15  into through hole  33 . Since the lower half of outer connection portion  15   c  has a “V” shape, it is possible to minimize the friction which is caused when inserting outer connection portion  15   c  into through hole  33  of circuit board  30 . The “V” shape also helps align socket lead  15  with the associated through hole  33 . In particular, if socket lead  15  is slightly misaligned, the point end of outer connection portion  15   c  will guide socket lead  15  into proper alignment during insertion. The upper half of outer connection portion  15   c  has an inverted “V” shape, which minimizes the friction when removing outer connection portion  15   c  from through hole  33  of circuit board  30 .  
         [0035]    The length of outer connection portion  15   c  can be such that outer connection portion  15   c  does not protrude below the lower surface of circuit board  30 , when outer connection portion  15   c  is inserted in through hole  33  of circuit board  30 . In the case of the conventional socket, in which outer connection portion of socket lead should be connected to a circuit board by soldering, the outer connection portion protrudes from through hole below the lower surface of the circuit board. However, in the present invention, since outer connection portion  15   c  does not have to protrude from through hole  33  outside the lower surface of circuit board  30 , and the total height of circuit board  30  can be smaller than that of the circuit board for the conventional socket. Further, since the lower surface of circuit board  30  of the present invention is flat and even, the operation of an apparatus that loads and unloads the socket may be improved. Inner wall  32  of through hole  33  of circuit board  30  is made of conductive materials that are resistant to abrasion and oxidation, because inner wall  32  must withstand repeated insertion and removal of socket lead  15  into and from through  33 . Preferably, a gold layer can be plated on the inner wall  32  of through hole  33 , so that inner wall  32  can sustain its conductivity after an extended use of circuit board  30 .  
         [0036]    [0036]FIG. 8 is a cross-sectional view showing another embodiment of an outer connection portion  16   c  of a socket lead  16  according to the present invention. In FIG. 8, outer connection portion  16   c  of socket lead  16  has an  2 S 2  shape. When socket  10  is loaded on circuit board  30 , the end of outer connection portion  16   c  of socket lead  16  is inserted into through hole  33 . The dimension of “S” is selected to provide an elastic contact between inner wall  32  and outer connection portion  16   c . For example, the width between the rightmost point and the leftmost point of the “S” shape is greater than the inner diameter of through hole  33 . When being inserted into through hole  33 , outer connection portion  16   c  becomes somewhat squeezed and flat and pushes inner wall  32  of through hole  33  at points E and F, because “S” shaped outer connection portion  16   c  tries to expand against wall  32 .  
         [0037]    Next, an embodiment of a sub-circuit board according to the present invention will be described hereinafter.  
         [0038]    [0038]FIG. 9 is a cross-sectional view showing another connection method between a socket  50  and a circuit board  30  using a sub-circuit board  60  according to the present invention. Sub-circuit board  60  according to the present invention electrically connects socket  50 , especially for fine-pitch packages of semiconductor integrated circuit device, to circuit board  30 .  
         [0039]    In FIG. 9, sub-circuit board  60  includes a wiring pattern  68 , through hole  63  and connection pins  65 . Wiring pattern  68  electrically connects the outer connection portion (not shown) of socket  50  to respective through holes  63 . Solder  66  fixes connection pins  65  to respective through holes  63 . The outer connection portion of connection pin  66  are shaped for insertion into through hole  33  of circuit board  30  in the same manner as outer connection portion  15   c  in FIG. 5.  
         [0040]    The present invention can be applied in various ways. First, the shape of the outer connection portion is not limited to an elliptical hook shape or an  2 S 2  shape. That is, the outer connection portion of the socket can be formed in any shape that gives elasticity to the outer connection portion of socket lead and contacts the inner wall of the associated through hole. Second, the socket and the circuit board according to the present invention are not limited to those which are used for burn-in test or electrical characteristics test of semiconductor integrated circuit devices. That is, the present invention may be applied to a socket and a circuit board wherever the socket is connected to the circuit board. Third, the shape of the inner connection portion of socket lead is not limited to the shape described above. The inner connection portion can have various shapes according to the type of the outline of semiconductor integrated circuit device, including but not limited to shapes for CSPs (Chip Scale Packages) and FPBGA (Fine Pitch Ball Grid Array) packages. In the cases of CSPs and FPBGA packages, since the solder balls of the packages are equivalent of the outer leads of conventional plastic packages, the inner connection portions of sockets contact the solder balls.  
         [0041]    An experiment was carried out to evaluate the performance of the socket according to the embodiment in FIG. 5. The change of the width and the contact resistance of outer connection portions of socket leads were measured after repeated insertion and removal of the socket leads into and from the circuit board under a burn-in test condition. Initial widths of outer connection portion of four sockets were 0.86±0.03 mm, and the diameters of the through holes of circuit board were smaller than the width of the outer connection portion by about 0.1 mm. After the sockets were inserted and removed twenty times, the widths of the outer connection portions decreased by only about 0.017˜0.029 mm. Accordingly, this result proves that the outer connection portion of the socket can maintain its initial dimension up to twenty times of insertion and removal of the socket.  
         [0042]    Table 1 shows the change of contact resistance after repeated insertion and removal of six socket leads into and from the through holes of the circuit board.  
                                               TABLE 1                                       times   5   10   15   20   25   30           average   18.86   18.64   18.79   18.63   19.07   19.29               mΩ   mΩ   mΩ   mΩ   mΩ   mΩ                      
 
         [0043]    As shown in Table 1, the contact resistance change after thirty insertions and removals of the socket leads was only 0.43 mΩ. In other words, the quality of electrical connection between the socket and the circuit board was not seriously affected by repeated insertion and removal of the sockets into and from the through holes of the circuit board.  
         [0044]    In summary, the present invention can eliminate the soldering process for fixing socket leads to test circuit boards and reduce the total cost for testing semiconductor integrated circuit devices due to the non-use of receptacles, compared with conventional connection methods described earlier. Moreover, the present invention makes the replacement of a socket on a circuit board easy.  
         [0045]    Although embodiments of the present invention have been described in detail hereinabove, it should be clearly understood that many variations and/or modifications of the basic inventive concepts herein taught will still fall within the spirit and scope of the present invention as defined in the appended claims.