Abstract:
A probe needle for a vertical needle type probe card is obtained that allows testing of electrical characteristics to be carried at high accuracy and that has high durability to reduce exchange work and cost. The configuration of a probe needle is formed to have a first bending portion bent towards a first lateral direction and a second bending portion bent towards a second lateral direction opposite to the first lateral direction at substantially 180° thereto. The stress exerted on the probe needle can be absorbed by the two bending portions at the left and right side. The deviation in the axis direction of the leading end of the probe needle can be reduced. Also, folding and bending of the probe needle can be prevented.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a probe needle for a probe card and a fabrication method thereof. More particularly, the present invention relates to a probe needle for a vertical needle type probe card and a fabrication method thereof. 
     2. Description of the Background Art 
     Among the processes of fabricating an IC, an LSI and the like, a wafer test process is known to test whether each chip on a wafer is an acceptable product or not. In this wafer testing, a probe card is generally attached to a device called a prober. The test is carried out by placing the probe needle of the probe card on a predetermined pad (electrode) on the wafer chip (referred to as overdrive operation) with at least a predetermined pressure (referred to as stylus pressure) to form contact. More specifically, a probe card is developed to test the electrical characteristics of a semiconductor device in the fabrication process of a semiconductor device. This probe card includes the conventional vertical needle type probe card. Particularly, a cobra probe card developed by IBM has attracted a wide range of attention, and is now beginning to be used for practical usage. 
     FIG. 8 is a schematic diagram showing a conventional cobra probe card. Referring to FIG. 8, the upper end of a cobra type probe needle  101  is attached in a vertical manner to an upper guide plate  102  in this conventional probe card. Also, a lower guide plate  103  for positioning an electrode  109  that will form contact with probe needle  101  is located beneath upper guide plate  102 . A through hole  104  is provided in lower guide plate  103  to guide probe needle  101 . The upper end of probe needle  101  is connected to a terminal (not shown) arranged around upper guide plate  102  via a wiring (not shown). The leading end of probe needle  101  forms contact with electrode  106  provided at the surface of a semiconductor device that is the subject of testing. This probe card is used to test the electrical characteristics of a semiconductor device. 
     FIG. 9 is a schematic diagram for describing an operation of the probe needle of the cobra probe card shown in FIG.  8 . Referring to FIG. 9, an external force  105  is exerted to bring probe needle  101  in contact with electrode  109 . External force  105  is exerted onto this probe card in the direction indicated by the arrow in FIG.  9 . When leading end  107  of probe needle  101  is in contact with electrode  109 , a portion  108  fixed to upper guide plate  102 , a portion  106  guided by lower guide plate  103 , a bent portion  111  absorbing the stress, and leading end portion  107  of probe needle  101  in contact with electrode  109  are arranged as shown in FIG.  9 . 
     The above-described probe needle  101  of the conventional cobra type probe card has two problems set forth in the following. 
     The first problem is that a great deflection is generated at bending portion  111  when leading end  107  of probe needle  101  is brought into contact with electrode  109  since bending portion  111  is formed so as to absorb the stress at that one portion. When leading end  107  of probe needle  101  is brought into contact with electrode  109 , probe needle  101  will contact the side surface of through hole  104  in lower guide plate  103 . As a result, the side surface of through hole  104  is scraped to generate scraps. The scraps will block through hole  104  to degrade the passage of probe needle  101 . Furthermore, probe needle  101  will be caught at the side surface of through hole  104  due to the friction between probe needle  101  and through hole  104 . There is a possibility that probe needle  101  will be stuck in through hole  104  so as not to protrude therefrom. Therefore, the height level of each leading end  107  of each the plurality of probe needles  101  will differ to result in step-graded levels. This means that there is variation in the penetration pressure of probe needle  101  to project into an aluminum oxide film (not shown) formed on electrode  109 . The contact pressure between electrode  109  and leading end  107  of probe needle  101  will become improper, so that testing of the electrical characteristics cannot be carried out at high accuracy. 
     The second problem is that the stress is concentrated at one bending portion  111  of probe needle  101  when leading end  107  of probe needle  101  forms contact with electrode  109  since probe needle  101  is formed so that the stress is absorbed at only one bending portion  111 . Repetitive usage with the stress always concentrated at one location will cause metal fatigue due to the repetitive loading. Probe needle  101  was sometimes broken into two pieces or permanently bent. Thus, the lifetime of probe needle  101  becomes shorter. This was not cost effective since extra cost is required for the exchange. 
     SUMMARY OF THE INVENTION 
     One object of the present invention is to provide a probe needle for a vertical needle type probe card that allows testing of electrical characteristics at higher accuracy. 
     Another object of the present invention is to provide a probe needle for a vertical needle type probe card that has high durability and that can reduce the exchange work and cost. 
     According to an aspect of the present invention, a probe needle for a vertical needle type probe card includes a bending portion. The bending portion includes a first bending portion that is bent towards a first lateral direction, and a second bending portion that is bent towards a second lateral direction that is opposite to the first lateral direction at approximately 180 degrees. By this structure, deflection is generated equally in the left and right directions in the probe needle of the present invention in contrast to a conventional cobra probe needle that has only one bending portion. The possibility of the leading end of the probe needle being within an axis identical to the initial one becomes higher. Furthermore, in contrast to the conventional cobra type probe needle having only one bending portion at which the stress exerted on the probe needle is absorbed, the probe needle of the present invention can have the exerted stress absorbed by at least two bending portions. Therefore, the resiliency of the entire probe needle increases. The probe needle of the present invention allows the contact pressure between the probe needle and the electrode to be substantially constant since deviation of the leading end portion is smaller than that of the conventional prove needle. Thus, a test result of higher accuracy can be obtained. Also, increase in the resiliency allows a greater stress to be absorbed. As a result, the possibility of being broken or permanently bent is reduced. The durability of the probe needle of the present invention is increased to result in a lower running cost. 
     According to the above-described structure, the radius of curvature of the first bending portion can be set greater than the radius of curvature of the second bending portion. This allows the rigidity to be increased than that of a probe needle having a bending portion of the same radius of curvature. The possibility of the probe needle being broken or bent becomes lower. Also, deviation of the leading end portion becomes smaller than that of a probe needle with first and second bending portion of the same radius of curvature. 
     Preferably, at least the first and second bending portions are formed of a sheet strip. This means that the portion absorbing the stress is sheet-like, and is bent in only one direction at the generation of a bending stress. By setting this bending direction so as to avoid an adjacent probe needle, the possibility of a bent probe needle contacting another adjacent probe needle is eliminated. Thus, accurate testing can be carried out. 
     Also, the first and second bending portions can have a bending shape of either substantially a S shape or a W shape. By providing a bending portion having a simple configuration of a S shape or a W shape, the probe needle of the present invention can be provided more inexpensively than that of a complicated needle shape. Furthermore, the time required for fabrication can be relatively shorter. 
     Further preferably, the first and second bending portions are formed of metal having shape memory property. This allows the probe needle of the present invention to be always restored to a constant shape with no residual strain. Therefore, the probe needle can be inserted or pulled out while maintaining a straight shape. The bending configuration is restored to the former shape by applying a heat treatment at the state installed at the guide plate. Therefore, the probe needle of the present invention can save the exchange work and cost, so that the running cost can be reduced. 
     According to another aspect of the present invention, a method of fabricating a probe needle for a vertical needle type probe card includes the steps of smelting and casting at least two types of metals, the step of sintering and molding the cast metal so as to include a first bending portion bent towards a first lateral direction and a second bending portion bent towards a second lateral direction opposite to the first lateral direction at approximately 180 degrees, and the step of applying a heat treatment on the cast metal so as to have shape memory property. By the fabrication method of the present invention, a probe needle can be provided that exhibits no buckling or deformation, and particularly improved in the spring characteristics. By applying a shape memory property, the probe needle can be inserted or drawn out in a straight shape. The former spring characteristics can be exhibited by restoring the bending configuration by applying a heat treatment in the state installed to the guide plate. According to the fabrication method of the present invention, the durability of the probe needle can be improved by increasing the resiliency. The exchange work and cost can be saved to reduce the running cost. 
     The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic diagram showing a vertical needle type probe card according to a first embodiment of the present invention. 
     FIG. 2 is a schematic diagram of the vertical needle type probe card of the first embodiment in a usage state. 
     FIG. 3 is a graph showing the relationship between the stress and displacement at the time of usage of the probe needle of the vertical needle type probe card of the first embodiment. 
     FIG. 4 shows a fabrication method of a probe needle of the vertical needle type probe card according to the first embodiment. 
     FIGS. 5,  6 , and  7  show the configuration of a probe needle of a vertical needle type probe card according to second, third and fourth embodiments, respectively, of the present invention. 
     FIG. 8 is a schematic diagram showing a probe card having a conventional cobra probe needle installed. 
     FIG. 9 is a schematic diagram of a probe card installed with a conventional cobra probe needle in a usage state. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Embodiments of the present invention will be described hereinafter with reference to FIGS. 1-7. 
     First Embodiment 
     Referring to FIGS. 1 and 2, a probe card according to a first embodiment of the present invention has a vertical needle type probe needle  1  attached to an upper guide plate  2  with an upper end in the vertical direction. Probe needle  1  has a S shape including a first bending portion  1   a  and a second bending portion  1   b . First bending portion  1   a  is formed so as to bend in a first lateral direction. Second bending portion  1   b  is formed to bend towards a second lateral direction opposite to the first lateral direction at substantially 180 degrees from the first lateral direction. A lower guide plate  3  for determining the position of probe needle  1  with respect to an electrode  9  that forms contact with probe needle  1  is located beneath upper guide plate. A through hole  4  for guiding probe needle  1  is formed in lower guide plate  3 . Probe needle  1  is connected to a terminal (not shown) arranged around upper guide plate  2  via a wiring (not shown). 
     Referring to FIG. 2, external stress  5  exerted towards this probe card is indicated by the arrow in FIG.  2 . When leading end  7  of probe needle  1  forms contact with electrode  9 , a portion  8  of probe needle  1  fastened to upper guide plate  2 , a portion  6  of probe needle  1  guided through lower guide plate  3 , first bending portion  1   a  and second bending portion  1   b  absorbing the stress, and leading end  7  of probe needle  1  in contact with electrode  9  are arranged as shown in FIG.  2 . By this S shape of first and second bending portions  1   a  and  1   b , deflection occurs substantially equally in left and right directions, in contrast to the concentrated deflection in conventional cobra probe needle  101  shown in FIG.  8 . Leading end  7  of probe needle  1  can be effectively prevented from being inclined. As a result, various disadvantages caused by the inclination of leading end  7  can be eliminated. 
     Since probe needle  1  of the first embodiment has two bending portions  1   a  and  1   b  that form a S shape, the stress on probe needle  1  can be absorbed substantially equally in left and right directions at two locations. In the case where the stress on leading end  7  of probe needle  1  is increased identically for both probe needle  1  of the present invention and probe needle  1  of the conventional cobra type, the amount of deflection is greater for probe needle  1  of the present invention than the conventional cobra type probe needle. Therefore, probe needle  1  is deflected within the same axis, so that a vertical state can be maintained with respect to the guide plate. As a result, the deviation of leading end  7  in the horizontal direction becomes smaller. Also, the stress per one location on probe needle  1  becomes smaller since the amount of deflection is greater. 
     Probe needle  1  is formed of a thread body or a sheet strip. Therefore, the portion of probe needle  1  absorbing the stress can be provided in a thread-like or sheet-like form. When the portion absorbing the stress takes a thread-like configuration, the bending process is facilitated to shorten the time required for fabrication. When the portion absorbing the stress takes a sheet-like configuration, deflection occurs only in one direction in response to the bending stress. By setting this deflection in a direction where there is no adjacent probe needle, the possibility of a deflected probe needle  1  forming contact with another adjacent probe needle can be eliminated. 
     The fabrication method of probe needle  1  of the first embodiment includes a step  200  for blending at least two types of metals to form probe needle  1 , a step  201  for smelting and casting the mixed metals, a step  202  for hot-working the cast metal, a step  203  for cold drawing or cold rolling the hot-worked metal, a step  204  for spring-forming the cold drawn or rolled metal, a step  205  for sintering the spring-formed metal into a S form, a step  206  for applying a heat treatment to the S shape metal so as to include shape memory property, a step  207  for pickling the metal subjected to the shape memory process, and a step  208  for testing and shipping the pickled metal. The fabrication process is characterized in including step  205  to form a S shape and step  206  to apply a shape memory process. These steps allow probe needle  1  to be manipulated while maintaining a straight state when probe needle  1  is inserted into upper guide plate  2  and lower guide plate  3 , or when pulling out probe needle  1  from upper guide plate  2  and lower guide plate  3 . Probe needle  1  can be restored to the S shape by applying a heat treatment after installation. 
     Second Embodiment 
     The state of installation and usage of a probe needle  21  according to a second embodiment of the present invention is similar to that of probe needle  1  according to the first embodiment shown in FIGS. 1 and 2. Referring to FIG. 5, probe needle  21  of the second embodiment has the radius of curvature of a second bending portion  21   b  that is located at the lower side set smaller than the radius of curvature of a first bending portion  21   a  located at the upper side. The rigidity of probe needle  21  can be increased than the case where second bending portion  21   b  is identical to first bending portion  21   a  in size. As a result, deviation of a leading end  27  generated by the contact pressure when probe needle  21  forms contact with electrode  9  becomes smaller than that of the S-shape probe needle  1  of the first embodiment having first and second bending portions  1   a  and  1   b  of the same size. 
     Third Embodiment 
     The state of installation and usage of a probe needle  31  according to a third embodiment of the present invention is similar to that of probe needle  1  of the first embodiment shown in FIGS. 1 and 2. Referring to FIG. 6, probe needle  31  of the third embodiment has the radius of curvature of a first bending portion  31   a  located at the upper side set smaller than the radius of curvature of a second bending portion  31   b  at the lower side. Accordingly, the rigidity of probe needle  31  can be increased than the case where first and second bending portion  31   a  and  31   b  are of the same size. In contrast to probe needle  21  of the second embodiment, probe needle  31  of the third embodiment has the bending portion of the greater radius of curvature (second bending portion  31   b ) located at the lower side. Therefore, the distance from the bending portion of the greater radius of curvature (second bending portion  31   b ) to leading end  37  is reduced. In general, the bending portion of a greater radius of curvature is more easily bent than a bending portion of a smaller radius of curvature. This means that the inclination of leading end  37  becomes smaller when the bending portion of a greater radius of curvature is closer to leading end  37  of the probe needle than when located remote from leading end  37  of the probe needle. In probe needle  31  according to the third embodiment, bending portion  31   b  of the greater radius of curvature is located at the side closer to leading end  37 . Therefore, deviation of leading end portion  37  caused by the contact pressure when probe needle  31  comes into contact with electrode  9  becomes smaller than that of probe needle  21  according to the second embodiment. 
     Fourth Embodiment 
     The state of installation and usage of a probe needle  41  according to a fourth embodiment of the present invention is similar to that of probe needle  1  of the first embodiment shown in FIGS. 1 and 2. Referring to FIG. 7, a vertical type probe needle  41  according to the fourth embodiment of the present invention is formed in a W-shape configuration including a first bending portion  41   a , a second bending portion  41   b , and a third bending portion  41   c . Probe needle  41  can have the stress exerted on leading end  47  absorbed by the three locations of first bending portion  41   a , second bending portion  41   b , and third bending portion  41   c . Therefore, the rigidity of probe needle  41  becomes higher than that of probe needles  1 ,  21 , and  31  of the first, second and third embodiments, respectively. As a result, deviation of leading end  47  caused by the contact pressure when probe needle  41  is brought into contact with electrode  9  becomes further smaller than that of probe needles  1 ,  21 , and  31 . 
     Although the present invention has been described and illustrated in detail, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, the spirit and scope of the present invention being limited only by the terms of the appended claims.