Abstract:
A blade probe card includes a plurality of blades that each includes a first end connected to a printed circuit board and a second end. A probe member is attached to the second end of each blade and extends outward to make contact with a device under test. A ground member is attached to the second end of each blade. The blade probe card also includes a common ground member that is separate from the printed circuit board and coupled to the ground member of each blade. Each blade may also include a first conductive signal trace and two or more conductive ground traces formed on a surface of each blade. The first conductive signal trace electrically connects the probe member to a contact on the printed circuit board. The two or more conductive ground traces are adjacent to the conductive signal trace and reduce crosstalk between the blades.

Description:
RELATED APPLICATION DATA AND CLAIM OF PRIORITY 
     This application claims the benefit of, and priority to, U.S. Provisional Patent Application No. 60/777,187, entitled PLATING OF PROBE ELEMENTS ON A REUSABLE SUBSTRATE, filed Feb. 27, 2006, the contents of which are incorporated by reference for all purposes as if fully set forth herein. 
    
    
     FIELD OF THE INVENTION 
     This invention relates generally to blade probes and blade probe cards used in the testing of wafer-based semiconductor devices. 
     BACKGROUND 
     In the testing of wafer based semiconductor devices, probe cards are typically used to provide electrical interconnection between a testing system and the semiconductor wafer. An exemplary type of probe card often used in high speed applications is a blade probe card. In such probe cards, “blades” (which are typically coupled to, and supported by, a printed circuit board) carry signal and ground paths. 
       FIG. 1A  depicts a conventional blade  100 , and  FIG. 1B  depicts two blades  100  connected to printed circuit board  102 . Referring specifically to  FIG. 1A , blade  100  comprises a ceramic material, e.g., 96% alumina, with a microstripline on surface  100   a . More specifically, signal path  100   c  and ground path  100   b  are provided on surface  100   a . Ground path  100   b  is electrically connected to ground plane  102   a  at interface “I.” Signal path  100   c  is electrically connected, e.g., soldered, to probe needle  100   d . Probe needle  100   d  is configured to probe a contact pad of a semiconductor device during testing thereof. For example, probe needle  100   d  may comprise tungsten, beryllium copper, or paliney 7. 
     As depicted in  FIG. 1B , a plurality of blades  100  are placed on PCB in circular form. For purposes of explanation, only two blades  100  are depicted in  FIG. 1B , but the approach is applicable to probe cards having any number of blades. 
     The bandwidth of such a system may be explained based on a complete closed circuit, and as such, the bandwidth of one single blade is not relevant in a practical application. As a result, three different angles, e.g., 7.5 degrees, 90 degrees, and 180 degrees, between the blades are simulated for existing structure of  FIGS. 1A-1B . It is apparent that different angles will have different electric and magnetic field patterns that will result in different bandwidths. As expected, the 180 degree configuration has the lowest bandwidth and the case when the signal is closest to the ground (the 7.5 degree configuration) will have the widest bandwidth.  FIG. 3  depicts a table that summarizes the results for a conventional blade card in the 7.5 degree, 90 degree, and 180 degree configuration with a conventional blade supplying the ground. As depicted in  FIG. 3 , with 90 degrees between the blades, the bandwidth at −1 dB is 3.3 GHz. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the figures of the accompanying drawings like reference numerals refer to similar elements. 
         FIG. 1A  depicts a conventional blade connected to printed circuit board. 
         FIG. 1B  depicts two conventional blades connected to a printed circuit board. 
         FIGS. 2A-2C  depict blades (and a blade probe card) configured according to an embodiment of the invention. 
         FIG. 3  depicts a table that summarizes the results for a conventional blade card in the 7.5 degree, 90 degree, and 180 degree configuration with a conventional blade supplying the ground. 
         FIG. 4  depicts a table that includes data for two blades similar to those depicted in  FIGS. 2A-2C  separated by 90 degrees. 
         FIG. 5  is a graph that depicts the performance, with the frequency (in GHz) on the X-axis versus at various dB values on the Y-axis, of a conventional blade card and a blade card configured in accordance with an embodiment of the invention. 
         FIG. 6  depicts a portion of a blade probe card including a printed circuit board and a plurality of blades configured according to one embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION 
       FIGS. 2A-2C  depict blades (and a blade probe card) configured according to an embodiment of the invention.  FIG. 2A  depicts a portion of probe card  200  including PCB  202  and two blades  204  separated by 90 degrees. Blade  204  includes surface  204   a  and  204   b , and comprises, for example, a ceramic material, e.g., an alumina-based material. As described in more detail hereinafter, a coplanar wave guide, having the signal trace surrounded by impedance matched ground traces, is defined for blade  204 . 
     More specifically, blade  204  includes conductive traces  206   a ,  206   b , and  206   c  that are formed on surface  204   a . Conductive traces  206   a ,  206   b , and  206   c  are separated electrically by portions of ceramic, i.e., clear portions  208   a  and  208   b . All, or substantially all, of surface  204   b  may be covered with the same conductive material. Alternatively, different conductive materials may be used. 
     Conductive traces  206   a ,  206   b , and  206   c  may be formed, and separated from one another, by an additive process, e.g., plating the traces on the ceramic material, or a subtractive process, e.g., removing portions of a conductive layer covering the surface  204   a . Conductive traces  206   a  and  206   c  are ground traces, and conductive trace  206   b  is a signal trace which is electrically connected, e.g., soldered or brazed, to probe needle  210 . Conductive trace  206   a  is electrically connected to ground member  212 . 
       FIGS. 2B and 2C  depict details of blade  204 . For example,  FIG. 2B  depicts the connection between probe needle  210  and conductive trace  206   b .  FIG. 2B  also depicts the interface “I” portion of conductive trace  206   b  which is configured to be electrically connected to an appropriate area of PCB  202  (See  FIG. 2A ). Further,  FIG. 2C  depicts the connection between ground member  212  and the majority conductive material on surface  204   b , as well as non-conductive portions, i.e.,  208   c  and  208   d , of surface  204   b , e.g., portions  208   c  and  208   d  are not covered by a conductive material in contrast to the rest of surface  204   b . According to one embodiment of the invention, the ground member  212  is substantially parallel to probe needle  210 , as depicted in  FIGS. 2A-2C . 
     In contrast to the data provided for the conventional blades in the table depicted in  FIG. 3 ,  FIG. 4  depicts a table that includes data for two blades similar to those depicted in  FIGS. 2A-2C  separated by 90 degrees. Compared to a conventional bandwidth result of 3.3 GHz at −1 dB, a bandwidth of 20.9 GHz at −1 dB has been achieved using a blade probe card configured in accordance with an embodiment of the invention. 
       FIG. 5  is a graph that depicts the performance, with the frequency (in GHz) on the X-axis versus at various dB values on the Y-axis, of a conventional blade card and a blade card configured in accordance with an embodiment of the invention. The conventional blade card measurements are depicted in the graph marked “Conventional” which includes the data point previously recited at m 2  (3.3 GHz at −1 dB), and the blade measurements for a blade card configured in accordance with an embodiment of the invention are marked “Present Invention” and includes the data point previously recited at m 1  (20.9 GHz at −1 dB). 
     A similar result to that described above, e.g., a coplanar wave guide configuration with improved bandwidth, may be achieved by various different configurations of the conductive traces and the probe needles. For example,  FIG. 6  depicts a portion of probe card  300  including PCB  302  and a plurality of blades  304  configured according to one embodiment of the invention. Blade  304  includes surfaces  304   a  and  304   b . In this configuration, probe needles  310  and ground members  312  are provided on opposite sides of the blade, as opposed to in substantial vertical alignment (as in  FIG. 2A ). Conductive traces  306   a ,  306   b , and  306   c  are provided on surface  304   a , while substantially all of surface  304   b  is covered with conductive material  306   d . Conductive traces  306   a  and  306   c  are ground traces, and conductive trace  306   b  is a signal trace. Signal trace  306   b  is electrically coupled to probe needle  310 , and ground conductive material  306   d  is electrically connected to ground member  312 . Ground member  312  is electrically connected to ground ring  314 . As with the other embodiments of the invention depicted herein, not all of the conductive connections, e.g., the connection between ground traces  306   a  and  306   c  to the rest of the ground system) are depicted in the figures. As depicted in  FIG. 6 , end portions of ground members  312  are raised in relation to corresponding probe needles  310 , facilitating contact with ground ring  314 . 
     According to one embodiment of the invention, a blade may be modified to short a signal probe, e.g., probe needle  310 , and a raised ground probe, e.g., ground member  312 . The signal probe may then be used to apply ground from the PCB to the DUT&#39;s ground pad and short ground to the ground ring. This raised ground ring provides a much shorter path for the return current and enables a further increase in bandwidth. 
     According to the invention, improvements in the bandwidth may be provided (at least in part) because of the reduced ground path. That is, the ground path loop goes through the ground ring, or other appropriate ground structure, as opposed to conventional blade probe cards, where the ground loop runs from one blade to the next. More specifically, in conventional blade probe cards, the ground loop tends to pass through the PCB structure so the electrical fields and magnetic fields are radiated all over the board. According to the one embodiment of the invention, the ground loop length is reduced by using a ground member, e.g., ground member  212  depicted in  FIG. 2A , between the blade and a ground ring. Thus, the injected signal passes through the IC being tested, and from the ground probe and shorted to the ground member. This reduces the ground loop length and the amount of energy that is radiated, thus providing for higher bandwidth and less impedance variations. 
     The ground member may have a “U” shape such that it may rest on top of the blade for ease of installation. The ground member may be mechanically bonded to both the blade and the ground ring, and in certain exemplary embodiments of the present invention, the ground member may be integrated as part of the blade or the ground ring, e.g., unitary with the blade or the ground ring. 
     As provided herein, according to one embodiment of the invention, high frequency traces are changed to a coplanar wave guide configuration (as opposed to a microstripline configuration), where the coplanar waveguide configuration provides less dielectric loss compared to microstripline configuration, and reduced crosstalk between probes. 
     When optimizing a probe card using impedance matching, additional desirable results may include, without limitation, (a) reduced probe needle length, and (b) reduced probe height, where the reduced length and height tend to result in less dielectric and conductor losses. 
     In contrast to conventional blade cards having large bandwidth variation for different angles, e.g., 2-16 GHz, blade probe cards according to the present invention have less bandwidth variation, e.g., ˜1 GHz, and are substantially independent from assembly angle for two blades. 
     According to one embodiment of the invention, the achieved bandwidth also depends on the circular loop size (or other structure not necessarily a circular loop), which may be defined by the die size being tested. For example, rather than a circular wire loop, a full plane conductor (or any other shape) may be used if practical in a given configuration. 
     As depicted herein and described above, according to one embodiment of the invention, a coplanar waveguide configuration is utilized rather than a conventional microstripline configuration. The coplanar waveguide configuration may be used separate from or in combination with the depicted ground ring. According to another embodiment of the invention, a ground ring (or other appropriate structure) may be used with either a coplanar wave guide as described herein, or with a microstripline configuration. In the embodiments depicted in  FIGS. 2A and 6 , both of these features, e.g., a coplanar waveguide configuration and the ground ring, are provided. 
     Thus, according to one embodiment of the invention, a strip line configuration blade is configured with a ground member coupled to another ground structure, e.g., a ground ring, in order to minimize deviations from a desired characteristic impedance, e.g., 50 ohm, all the way to the probe tip. 
     According to certain exemplary embodiments of the present invention, a coplanar wave guide configuration blade is provided without the ground member and ground ring. This provides a reduction in crosstalk between adjacent blades. In such a configuration, a ground pad may be provided adjacent the signal pad on the PCB (as there is no ground ring/member). 
     While embodiments of the invention have been described primarily with reference to conductive traces deposited, e.g., plated, on ceramic blade probes, the invention is not limited to these examples. For example, the approach may be implemented using blades marketed by Rogers Corporation of Chandler, Ariz. For example, Rogers Corporation markets a RO4000 series hi-freq circuit material that may be machined or otherwise configured to define a coplanar waveguide. 
     Although the blade probe card is depicted and described herein with reference to specific embodiments, the invention is not intended to be limited to the details depicted. Rather, various modifications may be made in the details within the scope and range of equivalents of the claims and without departing from the invention.