Abstract:
In one implementation, a method is provided for constructing an interface module which includes constructing a board having a signal via through the board, and having at least one ground via extending through the board. The method further includes back drilling the signal via to create a center conductor hole above a remaining portion of the signal via and back drilling a shield opening in the board and at least part way into the at least one ground via such that a height of the center conductor hole is reduced. The method further includes plating the shield opening and the center conductor hole, and back drilling to remove a portion of the plating to electrically isolate the plated shield opening and the plated center conductor hole.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is an application under 35 USC 111(a) and claims priority under 35 USC 119 from Provisional Application Ser. No. 61/013,631, filed Dec. 13, 2007 under 35 USC 111(b). The disclosure of that provisional application is incorporated herein by reference. 
    
    
     BACKGROUND 
     Sophisticated electronic assemblies often employ dense arrays of electrical conductors to deliver signals from one area to another. Routing large groups of conductors in an efficient and organized manner often proves problematic for a variety of reasons. The overall assembly cost, form factor (size), conductor pitch, and complexity all typically must be taken into account to determine a suitable routing method. 
     For high performance semiconductor testers, sometimes referred to as automated test equipment or ATE, tester signals up to several gigahertz are funneled and delivered from relatively large circuit boards known as channel cards, to the leads of a very compact device under test or DUT. Often, several thousand signal paths provide the signal delivery scheme between the DUT and the tester electronics. In order to preserve fidelity for such high-frequency signals, the signal paths are constructed to provide as close to a matched fifty-ohm impedance as possible. Providing a closely matched impedance with a large number of signal paths is difficult. 
     Further, in the past, there is typically a connector between the cable and the interface module, which limits density, and does not allow for low cost contact. 
     What is needed is a tester interface module capable of delivering high frequency, high fidelity signals at low cost. Moreover, what is needed is a tester interface module and method capable of providing higher signal density with higher frequency and high fidelity at low cost. 
     SUMMARY 
     In one implementation, a method is provided for constructing an interface module which includes constructing a board having a signal via through the board, and having at least one ground via extending through the board. The method further includes back drilling the signal via to create a center conductor hole above a remaining portion of the signal via and back drilling a shield opening in the board and at least part way into the at least one ground via such that a height of the center conductor hole is reduced. The method further includes plating the shield opening and the center conductor hole, and back drilling to remove a portion of the plating to electrically isolate the plated shield opening and the plated center conductor hole. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The features and advantages of the present invention will be better understood with regard to the following description, appended claims, and accompanying drawings. 
         FIG. 1A  shows a coax side of an interface module. 
         FIG. 1B  shows the interface side of the interface module. 
         FIG. 1C  shows an enlarged top view of a portion of the interface module of  FIG. 1A . 
         FIG. 1D  shows a cut away side view of a coaxial cable receptacle of the interface module along the  1 D- 1 D line of  FIG. 1C . 
         FIGS. 2A-2G  show a cut away side view of a method for fabricating the interface module of  FIGS. 1A and 1B . 
         FIG. 3  shows a block diagram possible embodiment, which may include the interface module of  FIGS. 1A and 1B . 
         FIG. 4  a block diagram of one embodiment of a tester, which may include the interface module of  FIGS. 1A and 1B . 
     
    
    
     DESCRIPTION 
       FIG. 1A  shows a coax side  110  of an interface module  100 . A coaxial cable (not shown in  FIG. 1A ) mounts within a coaxial receptacle  195  in the coax side  110  of the interface module  100 . A plated center conductor via  120   c  and a plated shield conductor  120   s  are recessed within the coax side  110  of the interface module  100 . The plated center conductor via  120   c  and the plated shield conductor  120   s  are separated by a non-plated portion  130 . A shield pad  140  is shown partially surrounding the receptacle  195  opening. 
     Although not shown in  FIG. 1A , the shield pad  140  and the plated shield conductor  120   s  are in electrical contact with ground vias (not shown in  FIG. 1A ), which extend through the interface module  100 . The extent of the shield pad  140  will be dependent on the number and placement of the ground vias (not shown in  FIG. 1A ). The ground vias (not shown in  FIG. 1A ) extend through the interface module  100  and are in electrical contact with the ground plane  180 , shown in  FIG. 1B , on an interface side  160  of the interface module  100 . 
       FIG. 1B  shows the interface side  160  of the interface module  100 . The interface side  160  has the ground plane  180  and center conductor via pads  150 . 
       FIG. 1C  shows an enlarged top view of a portion of the interface module  100  of  FIG. 1A . Surface pads  141  and  142  are formed to contact the ground vias  170   a  and  170   c , and  170   b  and  170   d , respectively. As discussed above, the number and arrangement of ground vias and pads may vary. For example,  FIG. 1C  shows coaxial cable receptacles with 3 ground vias  170   e - g , and one shield pad  146 , and with 4 ground vias  170   a - d  and a pair of shield pads  141  and  142 . Other configurations are possible. 
       FIG. 1D  shows a cut away side view of a coaxial cable receptacle  195  of the interface module  100  shown in  FIG. 1A . The coaxial cable receptacle  195  has center conductor opening  115 , which is sized to accommodate a coaxial center conductor (not shown in  FIG. 1D ) has electrically conductive plating  120   c . The plating  120   c  extends over the Signal via  150   s . An opening  125 , which may be sized to accommodate a coaxial insulator (not shown in  FIG. 1D ), electrically separates the center conductor and a shield plating  120   s , which plates a shield opening  135 . As shown, the plating  120   s  in the shield opening  135  contacts the ground vias  170   a  and  170   b . In the embodiment of  FIG. 1D , the opening extends into the ground vias  170   a  and  170   b.    
       FIGS. 2A-2G  show a cut away side view of a method for fabricating the interface module  100  of  FIGS. 1A and 1B .  FIG. 2A  shows a side view of a partially fabricated interface module  100  ( FIGS. 1A &amp; 1B ). A typical printed circuit board process is used to form ground vias  270   a  and  270   b  and signal via  250  through the printed circuit board  205 . For example, the ground vias  270   a  and  270   b  and signal via  250  may be drilled, plated, and filled. The ground vias  270   a  and  270   b  and signal via  250  may be drilled through surface conductors  201  and  202 , as shown. 
     In  FIG. 2B , the signal via  250   e  is back drilled to create a center conductor opening  215 . Shown in  FIG. 2C , a shield opening  225  is drilled wider than the center conductor opening  215 . This is done after drilling the center conductor opening  215 , as shown in  FIG. 2C . The back drilling should at least partially expose, or even cut into a portion of the ground vias  270   e  and  270   f  as shown. 
     A plating  220  is deposited in the openings  225  and  215  as illustrated in  FIG. 2D . Thereafter, as shown in  FIG. 2E , a portion of the plating is removed by back drilling into the printed circuit board  205   d  to separate the shield plating  220   s  from the center conductor plating  220   c.    
       FIG. 2F  shows the surface conductor  202  ( FIG. 2A ) after etching to define a center conductor pad  202   c  and shield pads  202   a  and  202   b.    
     Turning to  FIG. 2G , a coaxial cable  290  is inserted into the interface module  200 . The shield  280  and center conductor  255  are electrically bonded to the shield plating  220   s  and the center conductor plating  220   c , respectively. For example, the shield  280  and center conductor  255  may be bonded with solder  287  and  257 , respectively, conductive epoxy, or other material capable of securing and making electrical contact. The interface side of the interface module  200  may optionally contact an interposer  203 . 
       FIG. 3  shows a block diagram possible embodiment  300 , which may include the interface module  100 . In this embodiment, a cable assembly  309  having many coaxial cables (not shown) connected at one side to a lower cable density electronics board  308  is coupled to a higher signal density interface board  304  with the interface module  305 . An interface side of the interface board  304  contacts an interposer  303 , preferably a compliant interposer  303 , which contacts the interface board  304 . The interface board  304  may contact one or more devices under test (not shown). Thus, signals from many (not shown) electronics boards  308  may be routed to a single interface board  304 . 
       FIG. 4  a block diagram of one embodiment of a tester  400 , which may include the interface module  100  (shown in  FIG. 1 ). The tester  400  includes a tester mainframe  402  that is in communication with a test head  408 . The test head  408  is connected to an interface board  406 . Signals from the test head  408  may be routed to the interface board  406  through the tester interface module (not shown in  FIG. 4 ), as illustrated in  FIG. 3 , for example. In the embodiment shown in  FIG. 4 , the interface board  406  is a device interface board or DIB. In operation, the device interface board  406  is electrically connected to a device under test (DUT)  404  for testing the DUT  404 . For example, the tester  400  may be an automated test equipment (ATE) system for testing integrated circuits, and the DUT  404  may be a semiconductor device including an integrated circuit. Thus, signals from the test head  408  may be routed to the interface board  406  through the interface module (not shown in  FIG. 4 ). 
     The tester mainframe  402  includes circuitry for generating test signals and evaluating test signals. The tester mainframe  402  sends test signals to the DUT  404  and receives test signals from the DUT  404  through the test head  408  and the interface board  406 . The DUT  404  may be a packaged silicon die including an integrated circuit to be tested. In another embodiment, the interface board  406  is a probe interface board, and the DUT  404  may be a semiconductor wafer including an integrated circuit to be tested. 
     Although the term “coaxial cable” is used herein for example purposes, the term is merely illustrative and intended to include axial cables in general including concentric cables such as coaxial cable, triaxial cable, or other multiaxial cable, as well as twinaxial cable, and non-concentric cable, and impedance controlled cable in general, or any assortment thereof. 
     The printed circuit board or printed wire board may be fabricated with printed circuit board sequential lamination technology known in the art. Further, although referred to as a printed circuit board or printed wire board, it may be any insulating board that allows via formation and back drilling. 
     The interface module may be a tester interface module for example. Nevertheless, the teachings herein apply to any interface module, which may also be referred to as an interface means, connection means, connector, adaptor, translator, etc. 
     Having described this invention in connection with a number of embodiments, modification will now certainly suggest itself to those skilled in the art. As such, the invention is not to be limited to the disclosed embodiments, except as required by the appended claims.