Browser probe

A browser probe has a probe body including a signal line, a nose of electrical insulating material integral with and projecting from the probe body, a pin supported by the probe body and electrically conductively connected to the signal line, a spring exerting a biasing force on the pin, an electrically conductive probe tip supported by the nose at a distal end of the nose remote from the probe body, and a plurality of discrete resistors interposed between the pin and the probe tip within the nose. The resistors are supported independently of another so as to be slidable within the nose. The probe tip is electrically conductively connected to the signal line via the resistors and the pin under the biasing force exerted by the spring.

BACKGROUND

Representative embodiments relate to the testing of an electronic product, component, circuit or the like. In particular, representative embodiments are of test probes that may create temporary electrical connections to a device under test (DUT).

Electronic products typically include a circuit board or substrate bearing circuitry of the product. During the prototyping or throughout the course of the manufacturing of an electronic product electrical characteristics of the product are tested to ensure proper design of the product or to monitor the manufacturing processes. For example, in characterizing and troubleshooting electronic circuits there is a need to connect nodes of a circuit to measuring instrumentation such as an oscilloscope. This can be accomplished by establishing temporary electrical connections to the nodes. Different methods exist to accomplish this such as fixtured access which entails providing a controlled impedance line exiting the device under test (DUT)), temporarily solder-connecting a probe to the nodes, and contacting the nodes with a browser probe.

A browser probe is a device by which temporary connections to circuit nodes can be established quickly, and which can be moved easily to other nodes. This is where the name “browser” comes from—the ability to browse around circuit nodes of a DUT.

SUMMARY

A representative embodiment of a test probe has a probe body including a signal line, a nose of electrical insulating material integral with and projecting from the probe body, a pin supported by the probe body and electrically conductively connected to the signal line, a spring exerting a biasing force on the pin, an electrically conductive probe tip supported by the nose at a distal end of the nose remote from the probe body, and a plurality of discrete resistors interposed between the pin and the probe tip within the nose. The resistors are supported independently of another so as to be slidable within the nose. The resistors are also electrically conductively connected to one another, to the pin and to the probe tip, and the probe tip is electrically conductively connected to the signal line via the resistors and the pin under the biasing force exerted by the spring.

A representative embodiment of a test probe also has a probe body including a signal line, and an electrically conductive shield extending around the signal line, a nose of electrical insulating material projecting from the probe body and detachably mounted to the shield such that the nose can be detached from the probe body and attached back onto the probe body, a pin supported by the probe body and electrically conductively connected to the signal line, a spring exerting a biasing force on the pin, an electrically conductive probe tip supported by the nose at a distal end of the nose remote from the probe body, and at least one discrete resistor disposed within the nose as interposed between and electrically conductively connected to the pin and the probe tip. Each resistor is supported so as to be slidable within the nose. Also, the probe tip is electrically conductively connected to the signal line via the resistor(s) and the pin under the biasing force exerted by the spring.

A representative embodiment of a test probe also has a probe body including a pair of laterally spaced apart signal lines, and an electrically conductive shield extending around the signal lines, and a pair of probe tip assemblies each including a nose of electrical insulating material connected to the shield of and projecting from the probe body, a pin supported by the probe body and electrically conductively connected to a respective one of the signal lines, a spring exerting a biasing force on the pin, an electrically conductive probe tip supported by the nose at a distal end of the nose remote from the probe body, and a plurality of discrete resistors disposed within the nose as interposed between the pin and the probe tip. The discrete resistors of each of the probe tip assemblies are electrically conductively connected to one another, to the pin and to the probe tip of the assembly. The probe tip is electrically conductively connected to the respective one of the signal lines via the resistors and the pin under the biasing force exerted by the spring.

DETAILED DESCRIPTION

In the following detailed description, for purposes of explanation and not limitation, representative embodiments disclosing specific details are set forth in order to provide a thorough understanding of the present teachings. Descriptions of known systems, devices, materials, methods of operation and methods of manufacture may be omitted so as to avoid obscuring the description of the representative embodiments. Nonetheless, systems, devices, materials and methods that are within the purview of one of ordinary skill in the art may be used in accordance with the representative embodiments.

As used in the specification and appended claims, the terms ‘a’, ‘an’ and ‘the’ include both singular and plural referents, unless the context clearly dictates otherwise. Thus, for example, ‘a device’ includes one device and plural devices.

As used in the specification and appended claims, and in addition to their ordinary meanings, the terms ‘substantial’ or ‘substantially’ mean to within acceptable limits or degree. For example, ‘substantially cancelled’ means that one skilled in the art would consider the cancellation to be acceptable.

As used in the specification and the appended claims and in addition to its ordinary meaning, the term ‘approximately’ means to within an acceptable limit or amount to one having ordinary skill in the art. For example, ‘approximately the same’ means that one of ordinary skill in the art would consider the items being compared to be the same.

As used herein, the statement that two or more parts or components are “coupled” shall mean that the parts are joined or operate together either directly or indirectly, i.e., through one or more intermediate parts or components, so long as a link occurs. As used herein. “directly coupled” means that two elements are directly in contact with each other. As used herein, “fixedly coupled” or “fixed” means that two components are coupled so as to move as one while maintaining a constant orientation relative to each other.

Directional phrases used herein, such as, for example and without limitation, top, bottom, left, right, upper, lower, front, back, and derivatives thereof, relate to the orientation of the elements shown in the drawings and are not limiting upon the claims unless expressly recited therein. These directional phrases are intended to encompass different orientations of an element in addition to the orientation depicted in the drawings. For example, if an element were inverted with respect to the view in the drawings, an element described as “above” another element, for example, would now be “below” that element. Similarly, if an element were rotated by 90° with respect to the view in the drawings, an element described “above” or “below” another element would now be “adjacent” to the other element; where “adjacent” means either abutting the other element, or having one or more layers, materials, structures, etc., between the elements.

Representative embodiments of test probes will now be described in detail with reference to the attached figures.

Referring first toFIGS. 1-3, a test probe includes a probe body100and a probe tip assembly200integral with the probe body100. The probe body100includes a signal line10, and the probe tip assembly200includes an electrically conductive probe tip20(e.g., a gold-plated member) for contacting a test point (e.g., circuit node) of a device under test (DUT) and transmitting a signal from the test point to the signal line10.

The representative embodiment shown inFIGS. 1-8is a browser probe in which the probe body100includes two signal lines10, and a shield11, which is electrically conducting, and which has two probe tip assemblies200integral with the probe body100. The probe body100of this representative embodiment may also include an insulating housing12extending around the shield11, and a span-adjusting mechanism13operable to adjust a span of the electrically conductive probe tips20(as will be described in more detail later on with reference toFIGS. 1 and 8).

In addition, in this representative embodiment, the probe body100comprises coaxial cables each having a core constituting a respective one of the signal lines10, an electrically conductive ground shield11aextending around the core, and insulating dielectric14interposed between the core and the electrically conductive ground shield11a. The electrically conductive ground shields11aof the coaxial cables make up at least part of the shield11of the probe body100.

Referring toFIGS. 1, 2 and 4-6, each probe tip assembly200also includes an electrically conductive pin22, a spring24exerting a biasing force on the electrically conductive pin22, a nose26of electrical insulating material (e.g., plastic) connected to the shield11of and projecting from the probe body100, and at least one resistor28interposed between the electrically conductive pin22and the electrically conductive probe tip20. The nose26has a distal end, remote from the probe body100, and at which the nose26supports the electrically conductive probe tip20.

In the representative embodiment, a plurality of discrete resistors28are disposed within the nose26as interposed between the electrically conductive pin22and the electrically conductive probe tip20. The electrically conductive pin22and spring24may constitute a pogo pin which further includes a support23having an open-ended hollow section in which the spring24is disposed. The support23guides the electrically conductive pin22so as to be slidable in an axial direction of the probe tip assembly200. The resistors28are supported independently of one another and each of the resistors28is slidable within the nose26in the axial direction of the probe tip assembly200. Furthermore, the resistors28are electrically conductively connected to one another, to the electrically conductive pin22and to the electrically conductive probe tip20. Also, the electrically conductive probe tip20is electrically conductively connected to the signal line10via the resistors28and the electrically conductive pin22under the biasing force exerted by the spring24. In this respect, the support23of the pogo pin in the representative embodiment is of electrically conductive material and engages the electrically conductive pin22to establish the electrical connection between the electrically conductive probe tip20and the signal line10. Furthermore, the resistors28of each probe tip assembly200are disposed directly adjacent to each other, i.e., are in contact with each other, in an end-to-end arrangement.

FIG. 7shows an example of a resistor28of probe tip assembly200. In this example, the resistor28is an SMD resistor or what is commonly referred to as a surface mount resistor. The SMD resistor has a ceramic (e.g., Alumina) substrate28a, thin conductive films (a plating comprising Au, Ag, or Sn, for example) serving as conductors28bon opposite ends of the ceramic substrate28b, and a resistive element28cspanning the conductors28balong a major surface of the substrate28a. An electrically insulating cover or28dbearing identifying information, such as the resistance value, may be provided over the resistive element28cto encapsulate the resistive element. Thus, in an example of the representative embodiment in which the discrete resistors28are SMD resistors, a conductor28bof each SMD resistor is disposed against a conductor28bof each SMD resistor adjacent thereto such that the resistors28are electrically connected in series, and the electrically conductive pin22contacts a conductor28bof the resistor28closest to the probe body100. The biasing force of the spring24maintains the contact between the resistors28. Accordingly, the resistors28provide a resistance, between the electrically conductive probe tip20and a signal line10, which is the sum of the resistance values of the resistors28. And, although the spring24is schematically illustrated as a coil spring, other types of springs such as elastomeric elements may be used instead.

FIG. 3shows an SMD resistor disposed within nose26of a probe tip assembly200. In this example, the nose26has a generally conical shape and a passageway26aextending axially therethrough. A section of the passageway26abetween the electrically conductive probe tip20and electrically conductive pin22, and in which the resistors28are confined, may have a generally rectangular cross section complementary to the outer circumferential shape of SMD resistors. Thus, the SMD resistors are guided by the nose26within the passageway28afor movement in the axial direction of the nose26which, in this example, coincides with the axial direction of the probe tip assembly200. On the other hand, as shown inFIG. 5, a section of passageway28aat the distal end of the nose26may have a circular cross section complementary to the outer circumferential shape of part of the pin of the electrically conductive probe tip20which projects from the nose26. Thus, the electrically conductive probe tip20is also guided by the nose26within the passageway28afor movement in the axial direction of the probe tip assembly200.

The cross-sectional of the passageway26aextending through the nose26and the outer circumferential shapes of the resistors28and the electrically conductive probe tip20shown in the figures and described above are exemplary only, though. That is, in this representative embodiment, the passageway26amay have any cross-sectional shape(s) depending on the shapes of the resistors28and electrically conductive probe tip20.

A resistor very near the tip of a browser probe can effect low non-resonant loading. This minimizes the un-damped capacitance due to the conductive (metal) probe tip. However, the capacitance across a resistor provided adjacent the tip of a browser can make it difficult to achieve a high fidelity probe response because high frequency current will tend to flow through the capacitance of the resistor instead of through the resistance and cause significant peaking. There are two basic ways to limit this effect: a resistor having a relatively low resistance value can be employed to thereby cause more high frequency current to flow through the resistance, or a relatively long resistor can be employed to minimize the end-to-end capacitance of the resistor. Using a resistor having a lower resistance value will cause the mid-band input impedance of the probe to be lower thereby increasing the mid-band loading. Employing a relatively long resistor does reduce the end-to-end capacitance of the resistance but compromises the durability of the browser at its tip because stable resistive materials are typically brittle. In other words, the longer the resistor the more susceptible the resistor is to breaking.

A representative embodiment using multiple resistors in series, as described above, can limit the effect of end-to-end capacitance by effectively lengthening the resistor without compromising the strength and durability of the browser at its tips. The values of the resistors and the number can be optimized to minimize end-to-end capacitance that causes peaking while maximizing the bandwidth.

Furthermore, the browser probe may exhibit a low inductance to achieve high bandwidth. For a single-ended probe this is the inductance of the loop created by the connection: signal probe tip to ground of the probe, then from the ground of the probe to the DUT ground via a ground probe tip. For a differential probe (having two signal probe tips) this is the inductance of the loop created by the connection: + signal probe tip to probe ground on + side, + side ground to − side ground, and then − side ground to − side signal probe tip.

In addition, if the browser flexes, as may occur at the nose26, the resistors28may slide along one another at their ends without breaking. The nose26may be fabricated from a high quality polymer to ensure that it does not break when flexed. Also, the resistance is not severed due to the biasing force of the spring24that maintains the contacting state of the resistors28.

Referring now toFIG. 6, the nose26may also have an internal shoulder26bthat delimits the passageway26aat the distal end of the nose26. The electrically conductive probe tip20may have a first end portion20a, a second end portion20band an external shoulder20cbetween the first and second end portions20a,20b.

The first end portion20amay come to at least one point for contact with a test point of a DUT, e.g., may have a crown at its end as best shown inFIG. 6or may come to a single point. In any case, a tip of the browser probe may thus be characterized as “narrow” and “pointy” as opposed to “brunt” or “bulky”. A width of the electrically conductive probe tip20at its external shoulder20cis greater than the minimum width of the passageway26aat the internal shoulder26bof the nose26. In a non-testing position of the probe tip assembly200shown inFIGS. 1, 2 and 6in which the electrically conductive probe tip20is not engaged, the biasing force of the spring24urges the external shoulder20cof the electrically conductive probe tip20against the internal shoulder26bof the nose26such that the electrically conductive probe tip20is retained within the nose26.

Along with the nose26, the electrically conductive probe tip20forms a “needle-like” tip that extends well past the probe body100of the browser so that the tip can access hard to reach test points, allows for good visibility of the connection between the test point and the electrically conductive probe tip20, contributes to the ability of the probe to achieve a high bandwidth through its small geometry, and allows for the simultaneous use of multiple browsers to probe adjacent sets of test points.

Also, with an arrangement as described above, the electrically conductive probe tip20is provided with Z-axis compliance, namely, compliance in the axial direction of the probe tip assembly200. When attempting to place the probe tips of a browser probe against the test points on a DUT, any side-to-side movement of the browser probe will cause one or the other probe tip to lift off the DUT. By providing Z-axis compliance, namely, some compliance in the direction along which the probe is pressed towards the DUT, the probe tips may remain in contact with the DUT despite some side-to-side movement of the browser probe. Furthermore, the electrically conductive probe tip20will only retract into the nose26until it is flush with the end of the nose. At this point, the nose26takes any further load and protects the resistors28and pogo pin from additional compressive loads.

In addition, as mentioned above, in the representative embodiment ofFIGS. 1-8, the probe body100includes shield11extending around the signal lines10. The nose26of electrically insulating material is secured directly to the shield11. To this end, the nose26may be of plastic and may be threaded to the shield11such that the nose26can be removed from the shield and screwed back onto the shield11.

For example, the shield11may have an internally threaded end section11bintegral with the electrically conductive ground shield11aof the coaxial cable. The nose26has external threads which mate with the internal threads of the internally threaded end section11bof the shield11such that the nose26can be screwed onto and unscrewed from the shield11.

Accordingly, this facilitates the assembling or replacement of part of the probe. In particular, the electrically conductive probe tip20, plastic nose26, resistors28, and pogo pin can be a replaceable assembly that is screwable to the coax for easy assembly or replacement. In addition, a select part or parts, such as one or more resistors28, may be readily replaced or swapped out.

One example of the span-adjusting mechanism13by which a distance between the electrically conductive probe tips20of the probe tip assemblies200can be adjusted will now be described in detail with reference toFIGS. 1, 2 and 8. Because the distance between the probe tips can be adjusted the probe can accommodate for different spacings of probe test points on a DUT.

In this example, the shield11may also include a covering11cwrapped by the insulating housing12. The covering11cand hence, the insulating housing12, supports the internally threaded end sections11bof the shield that are integral extensions of the electrically conductive ground shields11aof the coaxial cables. In particular, the internally threaded end sections11bare independently supported such that at least one of the internally threaded end sections11bis swingable about an axis of rotation R. In the example shown inFIGS. 1, 2 and 8, both of the integral extensions of the ground shields11, namely, the internally threaded end sections11bof the shield, are supported in the probe so as to be swingable about respective axes of rotation parallel to each other. In this respect, the probe tip assemblies200may have additional components which allow the internally threaded end sections11bto move or bend relative to the core of the coaxial cable that may be rigid or semi-rigid. For example, with reference toFIG. 2, probe tip assembly200may include an electrically conductive swivel joint25that connects the core of the coaxial cable to the support23of the pogo pin.FIG. 2also shows various bushings (not numbered) by which the support23is supported by and within the shield11. The swivel joint25not only electrically conductively connects the support23of the pogo pin to the core but allows for limited bending of the internally threaded end section11bof the shield11relative to the core.

Moreover, pins11dmay be provided to support each internally threaded end section11bof the shield for rotation about axis R. The pins11dmay be integral with top and bottom plates of the covering11cof the shield11and extend into corresponding openings in the internally threaded end section11bof the shield. Alternatively, the pins11dmay be integral with the internally threaded end sections11bof the shield, the pins11dmay be discrete elements, or other forms of rotatable support may be used instead of the pins.

In any case, in this example of the representative embodiment, the noses26of the internally threaded end sections11bof the shield11are supported in the test probe so as to be swingable relative to the other about a respective axis of rotation. Also, the span-adjusting mechanism13has a cam element15that engages the internally threaded end sections11band is reciprocatable to swing the noses26about the axes of rotation and thereby adjust the span between the electrically conductive probe tips20of the probe tip assemblies. InFIGS. 1 and 8, reference numeral16designates a thumb slide that is integral with the cam element15and protrudes from the insulating housing12, and by which a technician can operate the span-adjusting mechanism13. Also,FIG. 8shows the internally threaded end sections11bbiased against the cam element15, which biasing may be self-induced due to resilience in the electrically conductive ground shields11aor which may be provided by springs.

FIG. 9shows another example of a span-adjusting mechanism13′. In this example a thumbwheel17protrudes from the insulating housing12and a threaded rod18is integral with the thumbwheel17at its center. The threaded rod18is also threadingly engaged with the internally threaded end sections11bof the shield11. Rotation of the thumbwheel17thus rotates the threaded rod18, and spreads the electrically conductive probe tips20apart or brings the electrically conductive probe tips20closer to one another. That is, in this example, the span-adjusting mechanism13′ may move the electrically conductive probe tips20linearly relative to each other. Alternatively, though, the threaded engagement between the threaded rod18and the internally threaded end sections11band the span-adjusting mechanism13′, in general, may be configured to cause the noses26to swing about axes of rotation, respectively, similar to the span-adjusting movement provided by the spin-adjusting mechanism13ofFIG. 8.

FIG. 10shows another representative embodiment of a test probe. In this representative embodiment, the test probe is a browser probe having a probe body100′ and probe tip assemblies200′. The probe body100′ of this embodiment includes an insulating substrate50, and signal lines10′ in the form of micro-strips of electrically conductive material extending on the substrate50. For example, the substrate50may have trenches therein, and the signal lines10′ may electrically conductive material filling the trenches. The probe tip assemblies200′ may be similar to the probe tip assemblies200as each including (refer toFIGS. 1 and 2) a nose26of electrically insulating material, an electrically conductive pin22and spring biasing the pin, an electrically conductive probe tip20supported by the nose26at a distal end thereof, and discrete resistors28interposed between the electrically conductive pin22and the electrically conductive probe tip20.

The stacking of discrete resistors of this representative embodiment allows for the total resistance to be distributed over a distance as desired in order to optimize the response. All the resistance in too short of a distance will typically exhibit excess end-to-end capacitance and frequency peaking. All the resistance spread over too long of a distance will exhibit excess series inductance and limit the BW. In an example of this representative embodiment that was bread boarded, eight 56.2 ohm 0201 resistors were used to create a 450 ohm distributed resistance which achieved a mid-band input impedance of 500 ohms on each side. As shown in the graphs ofFIGS. 11 and 12, the browser probe exhibited a very flat response (non resonant and centered about its 20 db or 10:1 attenuation) and a bandwidth of greater than 20 GHz.

Finally, embodiments of the inventive concept and examples thereof have been described above in detail. The inventive concept may, however, be embodied in many different forms and should not be construed as being limited to the embodiments described above. Rather, these embodiments were described so that this disclosure is thorough and complete, and fully conveys the inventive concept to those skilled in the art. Thus, the true spirit and scope of the inventive concept is not limited by the embodiment and examples described above but by the following claims.