Abstract:
The invention is a method and apparatus for a probe tip contact for electrically coupling a substrate to a probe tip. The apparatus, in one embodiment, comprises a wrap-around contact that is precision formed utilizing a hydroform tool and brazed to a surface of a substrate. In another embodiment, the apparatus comprises a contact flange, a mounting flange extending from a first edge of the contact flange in an orientation substantially perpendicular to the contact flange, and a substantially circular indentation formed in the contact flange adapted for accommodating movement of said probe tip relative to said substrate.

Description:
FIELD OF THE INVENTION 
   The present invention generally relates to measurement probes. More specifically, the present invention relates to probe contacts for electrical wires and similar conductors. 
   BACKGROUND OF THE INVENTION 
   Voltage measurement probes couple an electrical signal from a device under test (DUT) to a test and measurement instrument, such as an oscilloscope and the like. Measurement probes include a probe head, a transmission line, such as a coaxial cable, and a connector housing having a signal connector, such as a BNC, SMA, BMA connector and the like, which connects to a mating signal connector on the measurement instrument. The probe head generally includes a metal tube or housing having a substrate disposed therein. A probing tip (or socket) is disposed in a holder that is inserted into one end of the probe head. The probe tip or socket extends from the holder and is electrically coupled to the substrate. The substrate has passive or active circuitry formed thereon that provides high impedance to the circuit generating the signal under test. The substrate circuitry is electrically coupled to the transmission line. The other end of the transmission line is electrically coupled to the signal connector. 
   The electrical connection between the substrate and the probe tip (or socket) is facilitated by a contact that extends over an end of the substrate. Conventional probe tip contacts are typically formed from electrically conductive materials such as gold foil, ribbon, or an electrically conductive elastomer. While conventional contacts have generally proven to be effective means of establishing electrical connections, such contacts are frequently prone to mechanical wear, misalignment, breakage and punch-through, typically resulting in degradation of the contact and outright failure or loss of the electrical connection. Thus, the reliability of conventional probe tip contacts over time is compromised. 
   Furthermore, conventional probe tips are typically permanently fixed to the contacts (e.g., by soldering) to maintain a reliable electrical connection. This makes removal of probe tips (e.g., for replacement) difficult and costly. 
   Thus, there is a need in the art for a probe tip contact that is capable of establishing a flexible, yet reliable long-term electrical coupling between a substrate and a probe tip. 
   SUMMARY OF THE INVENTION 
   The disadvantages of the prior art are overcome by the present invention of an apparatus for electrically coupling a substrate to a probe tip. The apparatus, in one embodiment, comprises a wrap-around contact that is precision formed utilizing a hydroform tool and brazed to a surface of a substrate. In another embodiment, the apparatus comprises a contact flange, a mounting flange extending from a first edge of the contact flange in an orientation substantially perpendicular to the contact flange, and a substantially circular indentation formed in the contact flange adapted for interfacing with said probe tip. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     So that the manner in which the above recited embodiments of the invention are attained and can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to the embodiments thereof, which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments. 
       FIG. 1  is an exploded view of a portion of an exemplary probe head in which embodiments of the present invention may be used; 
       FIGS. 2A and 2B  are isometric views of one embodiment of a probe tip contact of the probe head of  FIG. 1 ; and 
       FIG. 3  is an isometric view of a second embodiment of a probe tip contact according to the present invention. 
   

   To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. 
   DETAILED DESCRIPTION 
     FIG. 1  depicts an exploded view of an exemplary probe head assembly  100  for use in a modular probe (not shown) in which the present invention may be used. Measurement probes are well known in the art. One example of a measurement probe that may be advantageously adapted to benefit from the present invention is the Venom family of probes, which are commercially available from Tektronix Inc., of Beaverton, Oreg. However, one skilled in the art will appreciate that the teachings of the present invention may be implemented in other types of measurement probes and, as such, the exemplary probe head should not be considered limiting. 
   A probe head assembly  100  generally comprises a housing  102  (shown in phantom), a substrate  104 , a probe tip holder  106 , and one or more probe tips  108  formed of an electrically conductive material such as copper or aluminum. In one embodiment, the housing  102  is a tubular structure within which the substrate  104  is disposed, and the housing  102  is typically formed of a conductive material, such as nickel plated brass, and the like. The substrate  104  comprises a plurality of passive and active electrical components (not shown) mounted thereon to form a circuit for illustratively measuring and/or processing various electrical signals (e.g., voltage or current, among others). In one embodiment, the substrate  104  comprises a printed circuit board (PCB). Although not explicitly shown in  FIG. 1 , a first end  110  of the substrate  104  extends past a first end  112  of the housing  102  and into a hollow cavity  114  in the probe tip holder  106 . 
   The probe tip holder  106  comprises a socket  116  having one or more bores  117  (e.g., bores  117   1 , and  117   2 ) for respectively receiving and guiding the one or more probe tips  108 , and for securing the probe tips  108  in a fixed position relative to the socket  116 . In particular, the one or more probe tips  108  each comprises a shank  122  having a first end  120 , a second end  124 , and a head  118 . In one embodiment, the head  118  has a diameter greater than a diameter of the shank  122 , and is coupled to the first end  120  of the shank  122 . The second end  124  of the shank  122  extends a distance from the head  118 , and in one embodiment, the second end  124  may be tapered. 
   During fabrication, the second end  124  and shank  122  slidably extend through the socket bore  117  and extend a distance beyond an outer surface of the socket  116 . It is noted that the bores  117  of the socket  116  are sized to receive the diameter of the shank  122 . Furthermore, the head  118  of the probe tip  108  has a diameter greater than the diameter of the socket bores  117 . Accordingly, the head  118  of the probe tip  108  abuts an inner surface of the socket  116 , thereby preventing the probe tip  108  from disengaging from the socket  116  of the probe tip holder  106 . It is further noted that in one embodiment, the head  118  or shank  122  may be keyed to prevent the probe tip  108  from rotating and/or further securing the probe tip  108  within the socket  116 . It is noted that the probe tip  108  may be formed as a lathe-turned piece, or by any other conventional manner. As will be discussed in further detail below, the substrate  104  and contacts  126 , which are coupled to the substrate  104 , secure the head  118  of the probe tip  108  against an inner surface of the socket  116 . In one embodiment, an insulating material (e.g., a plastic) is disposed in the bore  117  to isolate the probe tip  108  from the socket  116 . Alternatively, substantially the entire socket  116  may be formed of an insulating material, such as a plastic or rubber material so that the socket  116  is not electrically conductive. 
   At least one contact  126  is coupled to the substrate  104  (e.g., by brazing, soldering or conductive adhesive) to facilitate the electrical connection between the substrate  104  and the one or more probe tips  108 . Referring to  FIG. 1  and to  FIGS. 2A and 2B  together, in one embodiment, the contact  126  comprises a unitary formed conductive flange that wraps around and extends over the first edge  110  of the substrate  104 . The contact  126  comprises a contact flange  128  and a mounting flange  134 . 
   The contact flange  128  includes a substantially circular indentation  137 . The indentation  137  is sized to receive a top portion of the head  118  of the probe tip  108 , and the head  118  and indentation  137  together form a ball-and-socket joint  160 . The ball-and-socket joint  160  accommodates movement of the probe tip  108  in 2 axes: forward motion (i.e., through the socket  116 ) and motion in a direction perpendicular to the probe tip&#39;s forward motion. Therefore, unlike prior art probe tips that are fixed in place, the probe tip  108  is allowed some degree of movement relative to the substrate  104  and contact  126 , while still maintaining an electrical connection with the substrate  104 . Moreover, because the probe tip  108  is not permanently fixed to the contact  126 , the probe tip  108  may be easily removed for replacement. In one embodiment, an optional bore  138  is disposed approximately through the center of the indentation  137 . The optional bore  138  is sized to receive a spur  119  formed on the head  118  of the probe tip  108 . Thus, the presence of a spur  119  of the head  118  of the probe tip  108  will not disrupt the electrical connection between the probe tip  108  and the substrate  104  (via the contact  126 ) when the probe tip  108  shifts relative to the contact  126 . Moreover, in one embodiment, while the probe tip  108  is allowed to move relative to the socket  116  (i.e., not keyed), the spur  119  allows the probe tip  108  to move without dislocating from the ball-and-socket joint  160 . 
   The mounting flange  134  extends from a first edge  140  of the contact flange  128  in a substantially perpendicular orientation relative to the contact flange  128 . Optionally, an opposing second flange  136  (see  FIG. 2B ) extends from a second opposing edge  142  of the contact flange  128 , substantially parallel to the first edge  140 , to facilitate alignment of the contact  126  with the substrate  104 . In one embodiment, the contact  126  comprises both a mounting flange  134  and an opposing second flange  136 , and both flanges  134 ,  136  are adapted to be fixed (e.g., by brazing), respectively, to first and second sides  162 ,  164  of the substrate  104 . Fixing both flanges  134 ,  136  to the substrate  104  facilitates alignment of the contact  126  with the substrate  104  (i.e., so that the contact flange  128  is substantially parallel with the edge  110  of the substrate  104 ), which in turn facilitates proper alignment of the probe tips  108  within the probe head assembly  100 . In one embodiment, the mounting flange  134  and opposing second flange  136  have different lengths (e.g., the mounting flange  134  has a length that is greater than the length of the second flange  136 ). It is noted that the contact flange  128  is spaced apart from the edge  110  of the substrate  104  a distance to provide sufficient clearance for the spur  19  to pass through the bore  138  of the contact flange  128  without interfering with the edge  110  of the substrate  104 . 
   The mounting flange  134  comprises a solder flange  130 . The solder flange  130  is coupled (e.g., integrally formed) at a distal end  144  opposite the first edge  142  of the contact flange  128 . In one embodiment, the distal end  144  is tapered, and the solder flange  130  is circular in shape. 
   In one embodiment, at least one aperture  150  is formed in the mounting flange  134  between the first edge  142  and the distal end  144 . In the embodiment shown in  FIGS. 2A and 2B , a single aperture  150  is illustratively shown. The aperture  150  forms a fillet between a bonding pad  148  of the substrate  104  and the mounting flange  134  to increase the strength of the solder/brazing contact joint  146 . 
   Furthermore, the solder flange  130  comprises at least one aperture (i.e., a second aperture)  152  formed therein. The second aperture  152  also forms a fillet between the bonding pad  148  of the substrate  104  and the mounting flange  134  to increase the strength of the solder/brazing contact joint  146 . 
     FIG. 3  depicts an isometric view of a second embodiment of a probe tip contact  300  according to the present invention. The contact  300  is substantially similar to the contact  126  described with reference to  FIGS. 2A and 2B  and comprises a unitary formed conductive flange that wraps around and extends over the first edge  110  of the substrate  104 . The contact  300  comprises a contact flange  302  coupled to a mounting flange  304  along a first edge  308  of the contact flange  302 . The contact flange  302  and the mounting flange  304  may be formed in any configuration described herein with reference to the contact flange  128  and mounting flange  134  of  FIGS. 2A and 2B . In one embodiment, the contact flange  302  includes a substantially circular indentation  318  having an aperture  320  formed therein. The contact flange  302  illustrated in  FIG. 3  further comprises at least two tabs  306   a  and  306   b  (hereinafter collectively referred to as “tabs  306 ”) that extend outward from second and third edges  310  and  312 , respectively, of the contact flange  302 . The second and third edges  310 ,  312  are substantially perpendicular to the first edge  308  and substantially parallel to each other, so that the tabs  306  are positioned on opposite edges of the contact flange  302 . In one embodiment, the tabs  306  bend slightly so that a free edge  314   a  or  314   b  is substantially perpendicular to the contact surface  316  of the contact flange  302 . 
   The tabs  306  reduce the tendency of the contact  300  to deform under loading by assuming some of the load that is normally transmitted to the contact  300 . That is, in the process of moving the contact  300  off the first end  110  of the substrate  104 , a stress condition is created where the full load of the probe tip  108  is transmitted into the contact surface  316 . This load could cause the contact  300  to deform, or to transmit shear load into the contact joint  146 . The tabs  306  assume a portion of the load that would normally be transmitted to the contact  300  under these conditions, thereby reducing the stresses on the contact  300  and the tendency of the contact  300  to deform under heavy loading. 
   The contact  126  is formed in a shape and material that is adapted not only to fit closely to and mate with the first end  110  of the substrate  104 , but to facilitate connection to the probe tip  108  as well. In one embodiment, the contact  126  is precision formed by hydroforming and then brazed to the substrate  104 . In an exemplary hydroforming process, the contact  126  is manufactured by inserting a chem-milled blank into a negative die and forming the blank into shape using a Neutonian fluid. The hydroforming process produces a contact piece  126  that is mechanically robust and substantially resistant to mechanical wear or breakage. The formed contact  126  is then attached to a bonding pad  148  on the substrate  104 , for example, by brazing to form a brazed contact/substrate joint  146 . Alternatively, the contact  126  may be manufactured by other production means, such as stamping, among others. 
   In one embodiment, the contact/substrate joint  146  is fixed and heated by loading both ceramic hybrid and formed, plated wrap-around contacts  126  into a stainless steel fixture on a water-cooled tower and raising the fixture up into an induction coil. Oxide-free brazing, and a precise controllable temperature ramp may be insured by employing a quartz envelope containing a reducing atmosphere and a timer on the induction power supply. Brazing of the contact  126  to the substrate  104  will produce a secure mechanical and electrical connection that substantially prevents wear of the contact/substrate joint  146  and subsequent misalignment of the contact  126  relative to the probe tips  108 . In one embodiment, brazing of the contact/substrate joint  146  is accomplished using a brazing alloy such as a silver/tin or silver/germanium brazing alloy, among others. 
   Thus, the contact  126  of the present invention provides a reliable electrical connection between a substrate  104  and a probe tip  108 . Each contact  126  is formed in shape to fit closely with an edge  110  of the substrate  104  and to facilitate an electrical connection with a respective probe tip  108 . The contact is shaped to form a ball-and-socket joint with the head of a probe tip, which insures reliable electrical coupling of the probe tip to the substrate without the need to permanently fix the probe tip to the substrate or contact. Hydroforming of the contact results in a contact piece that is mechanically robust and substantially resistant to mechanical wear or breakage. Brazing of the contact to the substrate results in a secure mechanical and electrical connection that substantially prevents wear of the contact/substrate joint and subsequent misalignment of the contact relative to the probe tip or substrate. Therefore, the contact remains substantially fixed in position, insuring a reliable mechanical and electrical performance. 
   While foregoing is directed to the preferred embodiment of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.