Abstract:
A device under test (DUT) board for testing is electrically connected to a solder ball of a package. A contactor of the board is directly attached to the solder ball. Thus, there is little influence by bouncing of a power source and ground, even when an LSI under test is operated at high speed and low voltage, and malfunctions are rare.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a device under test (DUT) board and a testing method using the DUT board, in particular, a DUT board and a testing method using the DUT board applied to a high-speed LSI. 
     2. Discussion of Background 
     Along with a high speed, a large capacity and expansive functions of LSI, the trend of packaging is in a transition to a ball grid array (BGA). A device for testing is also developing into one applicable to an increased number of pins and various testing modes in conformity with a function of LSI and with a package. 
     FIG. 18 illustrates a structure of a conventional testing device. In FIG. 18, numerical reference  1000  designates a device for testing (hereinafter referred to as a tester) constructed by a tester body  1004  and a test head  1006 . The tester body  1004  includes a timing generator  1001  for generating a necessary timing signal as a condition for testing, a waveform formatter  1002  determining a waveform of rise and fall timing, and a unit for measuring a power source and a DC  1003  having a power source for driving a device, a DC measuring unit of the device and so on. 
     Further, the test head  1006  transfers a signal between an LSI under test  1005  based on a control signal obtained form the tester body  1004  through a cable  1018 . 
     When the LSI under test  1005  is tested, a test signal is generated from a tester driver  1008  of a pin electronics  1007  accommodated in the test head  1006 . The test signal is applied to the LSI under test  1005  through a POGO pin  1009 , a wire  1011  of a DUT board  1010 , a socket  1012 , an electrode  1013  of the socket, a package  1014  and a wire  1015  of the package  1014 . 
     Further, a reaction signal from the LSI under test  1005  is transmitted to a tester comparator  1016  of the pin electronics  1007  through a similar path to that described above. Based on a comparation with an expected value  1017  conducted in the tester comparator  1016 , it is judged whether or not the LSI under test  1005  operates as designed in the tester body  1004 , wherein the tester body  1004  receives a result of the comparation from the test head  1006 . 
     FIG. 19 a  is a cross-sectional view of a part of a conventional socket when a package is installed in the conventional socket. The socket  1012  has a contactor  2014  for electrically connecting with the package  1014  and the DUT board  1010 . FIG. 19 b  is an enlarged cross-sectional view of a portion  2000  in FIG. 19 a , in which a solder ball  2011  is interposed in the contactor  2014 . 
     However, in the conventional socket, the conventional DUT board, and the testing method using these, an influence of a power source and a ground bounce becomes conspicuous by an inductance L when an operation of the LSI under test  1005  is operated at a higher speed and in a lower voltage, whereby the LSI under test  1005  is efficiently operated. 
     Specifically, the inductance L of an electrode of the socket is 20 nH per a line. Therefore, provided that the LSI under test  1005  is operated at 1000 Mz, a gate count is 1M gates, an operating ratio of the gate is 40%, a switching time is 300 ps, and the number of electrodes of a power source is 200, a bounce on the ground side has characteristics that a consumption current of 1 MG×0.4 ×10 uA=4A and a back voltage of 20 nH/200 pin×4A/300 ps=1.3V. 
     Similarly, the power source of the device suffers from a similar problem. Provided that the power source is 2.5V, the voltage becomes 1.2V with a drop of the voltage of 1.3V, whereby the operation becomes deficient. Therefore, it is necessary to reduce the inductance per a pin. If the bounce is planned to restrict within 5% of the voltage of the power source, it is 2.5V×0.05=0.125V. 
     In case of the above example, because 1.3V occurs at 20 nH, 0.125V leads 1.92 nH. In other words, in case of the contactor of the ordinarily used socket, a length of 1 mm corresponds to about 1 nH, the length of the electrode should be about 2 mm. Accordingly, there is a problem that a function test for verifying a logic becomes defective in use of the conventional socket and the conventional DUT board. 
     SUMMARY OF THE INVENTION 
     According to a first aspect of the present invention, there is provided a DUT board electrically connected with electrodes of a package for testing comprising contactors, on which the electrodes of the package are mounted to be directly attached to the contactors. 
     According to a second aspect of the present invention, there is provided the DUT board according to the first aspect of the invention, wherein the contactors are a strip-like metallic plate having spring elasticity, in which a longitudinal notch is formed at a center. 
     According to a third aspect of the present invention, there is provided the DUT board according to the first aspect of the invention, wherein the contactor is a metallic plate having spring elasticity in which a notch in a U-like shape is provided and a part of the metallic plate is obliquely bent while maintaining a part of the metallic plate plan along the notch. 
     According to a fourth aspect of the present invention, there is provided the DUT board according to the third aspect of the invention, wherein the contactor is obliquely bent so as to be partly curved along a notch. 
     According to a fifth aspect of the present invention, there is provided the DUT board, wherein the contactor is bent while maintaining a part of the contactor plane. 
     According to a sixth aspect of the present invention, there is provided the DUT board according to the third aspect of the invention, wherein the contactor is obliquely bent, and in the bent portion, parallel lines or grid-lines are formed on a surface of the contactor along a notch. 
     According to a seventh aspect of the present invention, there is provided the DUT board, wherein the contactor is obliquely bent, and in the bent portion, a dot-like protrusion is provided on a surface thereof along a notch. 
     According to an eighth aspect of the present invention, there is provided the DUT board according to the first aspect of the invention, wherein the contactor is bent in a V-like shape. 
     According to a ninth aspect of the present invention, there is provided the DUT board according to the first aspect of the invention, a pattern is formed on a principle surface of the contactor. 
     According to a tenth aspect of the present invention, there is provided the DUT board according to the second aspect of the invention, further comprising a slide for opening and closing the contactor. 
     According to an eleventh aspect of the present invention, there is provided the DUT board according to the third through the eighth aspects of the invention, further comprising a guiding mechanism for constantly maintaining a position of the electrodes of the package, and a pushing mechanism for pressing the electrodes of the package and the contactors. 
     According to a twelfth aspect of the present invention, there is provided the DUT board according to the ninth aspects of the invention, further comprising a guiding mechanism for constantly maintaining a position of the electrodes of the package, a pushing mechanism for pressing the electrodes of the package and the contactors, and a conductive rubber provided between the electrodes of the package and the contactors. 
     According to a thirteenth aspect of the present invention, there is provided the DUT board according to the tenth through the twelfth aspects of the invention, further comprising a structure of separating and securing. 
     According to a fourteenth aspect of the present invention, there is provided a testing method using the DUT board according to the tenth and twelfth aspects of the invention, wherein the electrodes of the package and the contactors are freely connected and disconnected, and an inductance is reduced. 
     According to a fifteenth aspect of the present invention, there is provided a testing method using the DUT board according to the thirteenth aspect of the invention, wherein the DUT board is freely connected and disconnected, and an inductance is reduced. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A more complete appreciation of the invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detail description when considered in connection with the accompanying drawings, wherein: 
     FIG. 1 is a cross-sectional view of a part of a DUT board equipped with a package according to Embodiment 1 of the present invention; 
     FIG. 2 is a perspective view of a contactor, on which an electrode of the package is mounted according to Embodiment 1 of the present invention; 
     FIG. 3 is a perspective view of a part of a slide according to Embodiment 1 of the present invention; 
     FIG. 4 is a perspective view of an entire slide according to Embodiment 1 of the present invention; 
     FIG. 5 schematically illustrates an entire DUT board according to Embodiment 2 of the present invention; 
     FIGS. 6 a  and  6   b  illustrate a structure of a connecting portion between a contact substrate and a mother board according to Embodiment 2 the present invention. 
     FIG. 7 schematically illustrates a structure of the contact substrate using another fixing method according to Embodiment 2 of the present invention; 
     FIG. 8 schematically illustrates a structure of the mother board using another fixing method according to Embodiment 2 of the present invention; 
     FIG. 9 is a perspective view of a contactor according to Embodiment 3 of the present invention; 
     FIG. 10 is a cross-sectional view of a part of a DUT board, on which a package is mounted, according to Embodiment 3 of the present invention; 
     FIG. 11 is a side view of a contactor according to Embodiment 3 of the present invention; 
     FIG. 12 is a side view of another contactor according to Embodiment 3 of the present invention; 
     FIGS. 13 a - 13   d  are perspective views of other contactors according to Embodiment 3 of the present invention. 
     FIG. 14 is a side view of another contactor according to Embodiment 3 of the present invention; 
     FIG. 15 a  schematically illustrates a state in which an electrode of a package is not in contact with a contactor according to Embodiment 4 of the present invention; 
     FIG. 15 b  schematically illustrates a state in which the electrode of the package is in contact with the contactors according to Embodiment 4 of the present invention; 
     FIG. 15 c  is a cross-sectional view taken along a line  15   c — 15   c  of FIG. 15 b  and viewed in a direction of an arrow; 
     FIG. 16 is a cross-sectional view of a part of a DUT board, on which a package is mounted, according to Embodiment 5  of the present invention;    
     FIG. 17 is a cross-sectional view of a part of another contactor according to Embodiment 5 of the present invention; 
     FIG. 18 illustrates a structure of a conventional testing device; 
     FIG. 19 a  is a cross-sectional view of a part of a conventional socket with an enlarged view of an electrode of a package and a contactor; and 
     FIG. 19 b  is an enlarged cross-sectional view of a portion at which an electrode of a package is in contact with a contactor of the conventional socket. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A detailed explanation will be given of preferred embodiments of the present invention in reference to FIGS. 1 through 17 as follows, wherein the same numerical references are used for the same or similar portions and description of these portions is omitted. 
     Embodiment 1 
     Hereinbelow, Embodiment 1 of the present invention will be described. 
     FIG. 1 is a cross-sectional view of a part of a DUT board, on which a package is mounted, according to Embodiment 1 of the present invention. In FIG. 1, a contactor  11  is provided at a position corresponding to a solder ball  14  of the package  13 . Further, the contactor protrudes about 2 mm from an upper surface of the DUT board  10 . The contactor  11  is embedded in a through hole  15  of the DUT board  10  and electrically connected to an inner wiring pattern  17  of the DUT board  10  by solder  16 . 
     Further, FIG. 2 illustrates a state that the electrode of the package is mounted on the contactor. In FIG. 2, the contactor  11  has a notch  21  in a longitudinal direction at approximately the center of a strip-like metallic plate  20  having spring elasticity, for example, phosphor bronze, so that the solder ball  14  is interposed in the notch  21 . Only a lower portion of the opening and closing notch  21  is embedded in the through hole  15  of the DUT board  10 . 
     FIG. 3 illustrates a part of a slide. A hole  31  is provided on a hard and insulative slide substrate  32 , such as ceramic. The contactor  11  is inserted in the hole  31  and slid so that the contactor  11  is opened and closed. 
     The contactor  11  is ordinarily opened. When the substrate  32  is slid, the contactor  11  closes by its own elasticity. After the solder ball  14  of the package  13  is inserted in the contactor  11 , the slide motion is canceled, and the solder ball  14  of the package  13  is interposed in the contactor  11  by returning spring elasticity. 
     FIG. 4 is an entire view of the slide. In FIG. 4, the slide has a sliding mechanism  41  utilizing a principle of lever, wherein the slide substrate  32  is slid by pushing up the lever  42  to open the contactor. A distance between a fulcrum  43  of the lever  42  and a center of a shaft of the sliding mechanism  41  is practically about 1 mm, by which the contactor  11  can be completely opened and closed. After mounting the package  13 , the lever  42  is pushed down to interpose the solder ball  14  of the package  13  the contactor  11  by the spring elasticity. 
     According to Embodiment 1, by directly attaching the contactor to the board, it is possible to reduce an inductance L and to reduce noise that occurs between a power source and a ground and reflection noise of a signal line, whereby an operation test of a high-speed function is realized with an excellent anti-noise property and stability. 
     Embodiment 2 
     When a contactor is directly embedded in a DUT board, an entire DUT board should be repaired or exchanged to deal with deterioration of properties of the contactor, and breakage of the contactor. Because time and cost are required, the following DUT board may be used to deal therewith. 
     FIG. 5 illustrates an entire DUT board according to Embodiment 2. In FIG. 5, the DUT board  30  includes a test head  106 . Further, the DUT board  30  is divided into two portions of a substrate  51  for receiving a signal (hereinbelow, referred to as a mother board) and a substrate  52  in contact with an LSI subjected to a test. In the contact substrate  52 , the contactor  11  is embedded and a slide substrate  32  is provided. 
     Further, FIG. 6 a  is a structural side view illustrating a connecting portion between the contact substrate and the mother board. In FIG. 6 a , a step-like structure  61  is provided in the mother board  51  to be connected to the test head  106 . A protruding electrode  62  is provided on the mother board  51 . The contact substrate  52  also has a similar step-like structure, on which a protruding electrode  63  is provided. FIG. 6 b  is a detailed plan view of connection of the mother board  51 . An electrical connection is attained by placing the protruding electrode  62  in tight contact with the protruding electrode. The contact substrate  52  and the mother board  51  are secured by a screw  53 . 
     Further, FIG. 7 is a structural view of the contact substrate according to other method of fixing. In FIG. 7, a thread  72  is provided in a lower portion of the contact substrate  71 . A protruded electrode is provided on a bottom surface of the contact substrate  71 . A contactor  11  is provided on an upper surface of the contact substrate  71 . 
     FIG. 8 illustrates a structure of a mother board according to the other fixing method. In FIG. 8, a thread  82  is provided to screw the lower thread  72  of the contact substrate  71  at a substantially central portion of the mother board  81 . A protruded electrode  62  is provided around the thread  82  at a position where the protruded electrode  62  is electrically and tightly in contact with the protruded electrode provided on a bottom surface of the contact substrate  71 . A step-like structure is provided so that an upper surface of the mother board  81  is substantially in conformity with the upper surface of the contact substrate  71  when the contact substrate  71  is screwed. 
     For example, nickel with gilt finish is used in the protruded electrode of the contact substrate  71  and the protruded electrode  62  of the mother board  81  for improving electrical stability and a resistance to rotting. 
     According to Embodiment 2, by using the separable DUT board, a time and a cost for repairing and exchanging are reduced, whereby a cost for testing is reduced. 
     Embodiment 3 
     FIG. 9 is a perspective view of a contactor according to Embodiment 3 of the present invention. In FIG. 9, the contactor  500  is a metallic plate having spring elasticity, in which a notch in a U-like shape is provided; and the notch is obliquely bent while maintaining a part of the notch plane along the notch. Thus, an electrode  501  as a contact portion with a solder ball is constructed. 
     FIG. 10 is a cross-sectional view of a part of a DUT board, on which a package is mounted, according to Embodiment 3 of the present invention. In FIG. 10, the contactor  500  is installed on the DUT board at a position corresponding to the solder ball  503  of the package  502 . A guiding mechanism  505  is installed for positioning the package  502  so that the solder ball  503  is sufficiently in contact with the electrode  501  of the contactor  500 . 
     Further, the package  502  moves only in a vertical direction of the DUT board  504  along the guiding mechanism. In order to obtain an appropriate contact pressure between the solder ball  503  and the electrode  501 , a pushing mechanism  515  is provided to push the package  502  toward the DUT board  504 . 
     FIG. 11 is a side view of another contactor. In FIG. 11, the contactor has a feature like the contactor illustrated in FIG.  9  and has an electrode  506  curved along a solder ball. FIG. 12 is a side view of another contactor. In FIG. 12, the contactor has a feature same as the contactor illustrated in FIG.  9  and has an electrode  507  bent so as to receive force from a solder ball in a vertical direction. 
     FIGS. 13 a - 13   d  are perspective views of other contactors. In FIGS. 13 a - 13   d , the contactors have a feature that is the same as the contactor illustrated in FIG.  9  and have electrodes  508  through  511  on which the surface for contacting a solder ball has parallel or grid-like lines. 
     FIG. 14 is a side view of another contactor. In FIG. 14, the contactor has a feature same as the contactor illustrated in FIG.  9  and has an electrode  512 , on which surface in contact with a solder ball, a dot-like protrusion  513  is provided. 
     The DUT board according to Embodiment 3 has a structure enabling to separate and secure the DUT board as in Embodiment 2. 
     According to Embodiment 3, in comparison with Embodiment 2, it is possible to mount a further short electrode on the DUT board to reduce an inductance L. Further, a contact area between the electrode and the solder ball is increased, whereby a secure contact is obtainable even though a contact point is deviated a little. 
     Embodiment 4 
     FIG. 15 a  illustrates a state that an electrode of a package is not in contact with contactors according to Embodiment 4. In FIGS. 15 b  and  15   c , the contactor  514  in a V-like shape, made of a metal such as tungsten, are mounted on a DUT board  504  at a position corresponding to a solder ball  503  of a package  502 . The DUT board  504  has a similar structure and a similar effect to those in Embodiment 3 other than two contactors  514  are required for one solder ball  503 . 
     The DUT board has a structure enabling to separate and secure as in Embodiment 2. 
     Embodiment 5 
     FIG. 16 is a cross-sectional view of a part of a DUT board, on which a package is mounted, according to Embodiment 5 of the present invention. In FIG. 16, a patterned contactor  518  is mounted on the DUT board  504 . When a solder ball  503  is pushed toward the DUT board  504 , the solder ball  503  is electrically connected to the contactor  518  through a metallic plate  516  and a conductive rubber  519 . However, the conductive rubber  519  is mutually electrically insulated from other electrodes so that only a contactor  518  corresponding to a specific solder ball  503  is electrically connected to the conductive rubber. Further, an insulative guiding mechanism  517  is provided to fix the metallic plate  516  in an appropriate position. 
     FIG. 17 is a cross-sectional view of a part of another contactor according to Embodiment 5 of the present invention. In FIG. 17, the contactor  520  has recesses and protrusions. The protrusions are in contact with corresponding solder balls in the package via the conductive rubber to be electrically connected. 
     Further, in use of a metallic plate (not shown) having a cross-sectional structure with recesses and protrusions as in the contactor illustrated in FIG. 17, which metallic plate has a similar role to that in the metallic plate  516 , contact force between the solder balls and the contactors through the conductive rubber is improved, whereby an electrical connection is assured. 
     As in the DUT board according to Embodiment 2, the DUT board according to Embodiment 5 has a structure enabling to separate and secure. 
     According to Embodiment 5, since the patterned electrode is used in the DUT board, the inductance L is further reduced. Further, since the conductive rubber is used, a minute pressure force between the electrode and the solder ball is realized. Further, since the metallic plate is in contact with the solder ball, an oxide of the solder ball, dust, and so on are not deposited on a surface of the conductive rubber, and even though these are deposited, it is possible to easily remove these by, for example, cleaning by alcohol. 
     The first advantage of the DUT board according to the present invention is that an anti-noise property is excellent and an operation is stable. 
     The second advantage of the DUT board according to the present invention is that the package is freely and easily mounted or dismounted. 
     The third advantage of the DUT board according to the present invention is that minute pressure force between the electrode and the contactor is obtainable and an electrical connection is secured. 
     The fourth advantage of the DUT board according to the present invention is that a time and a cost for repairing or exchanging are reduced and a cost for testing is reduced. 
     According to the fifth advantage of the testing method of the DUT board according to the present invention is that an anti-noise property is excellent and an operation test of a high-speed function becomes stable. 
     Obviously, numerous modifications and variations of the present invention are possible in right of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described herein.