Electrical test probes, methods of making, and methods of using

Disclosed herein is an electronic test probe including a compression spring disposed in the housing in engagement with a plunger, the compression spring including a first section of coils including a first centerline and a second section of coils including a second centerline spaced apart from and parallel to the first centerline.

BACKGROUND

1. Technical Field

The disclosure relates generally to electronic test probes and, more particularly, to electronic test probes for testing integrated circuits (ICs).

2. Related Art

During testing, integrated circuit (IC) packages are removably mounted in sockets which in turn are mounted on a circuit substrate, commonly referred to as a device-under-test board, or DUT board. The sockets house individual electrical test probes for electrically connecting each terminal of a device to be tested to an individual circuit path on the DUT board. The DUT board is in turn electrically connected to computerized test equipment.

It is desirable to have a high integrity signal path from the test equipment to the device being tested and for the overall resistance of the signal path to be low and consistent. This is also true for each segment of the overall signal path—including the test probe housed in the test socket.

The electrical test probes can comprise electrically conductive metal components that are surface finished with an electrically noble metal such as gold or palladium cobalt. To assure the low and consistent resistance of the test probe, the metal components are precisely located in close proximity to each other, and the normal force between the components is kept high enough to keep the components in direct contact with each other and to break through any surface barriers that might be in place between the components.

It is desirable to have low and consistent resistance in electrical test probes. One way of achieving this is to ensure that electrical current flows from the sliding plunger to the barrel of the test probe with a minimum of contact resistance.

A need exists in the art for reliable, low contact resistance test probes and methods of making the same.

SUMMARY

Disclosed herein is an electronic test probe. The electronic test probe comprises a substantially cylindrical housing with a first end and a second end, and an opening disposed in the first end. A plunger is disposed in the housing, the plunger comprising a first end and a second end opposite the first end, the first end comprising a contact tip extending from the opening in the first end. A compression spring is disposed in the housing in engagement with the second end of the plunger, the compression spring comprising a first section of coils comprising a first centerline and a second section of coils comprising a second centerline spaced apart from and parallel to the first centerline.

Also disclosed herein is an electronic test probe comprising a substantially cylindrical housing with a first end and a second end, and an opening disposed in each of the first and second ends. A first plunger and a second plunger are disposed in the housing, each of the first and second plungers comprising a first end extending from one of the openings disposed in the housing and a second end comprising a bias-cut surface. A compression spring is disposed between the first and second plungers, the compression spring comprising a first end and a second end, the first and second ends of the compression spring each disposed in engagement with the bias-cut surface of one of the first and second plungers, the compression spring comprising a first section of coils comprising a first centerline and a second section of coils comprising a second centerline spaced apart from and parallel to the first centerline.

The above described and other features are exemplified by the following figures and detailed description. In the description, it should be noted that the terms “first,” “second,” and the like herein do not denote any order or importance, but rather are used to distinguish one element from another, and the terms “a” and “an” herein do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced items. The modifier “about” used in connection with a quantity is inclusive of the stated value and has the meaning dictated by the context (e.g., includes the degree of error associated with measurement of the particular quantity). Unless specified otherwise, the term “diameter” refers to the average diameter of the coils of a spring section, as measured along the major axis of the spring section. Finally, unless defined otherwise, technical and scientific terms used herein have the same meaning as is commonly understood by one of skill in the art to which this invention belongs.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Disclosed herein are electrical test probes comprising consistent and relatively low contact resistance (e.g., less than or equal to about 50 milliohms, more particularly about 25 milliohms to about 50 milliohms, more particularly still about 10 milliohms to about 35 milliohms), and methods of making and using the same. The test probes comprise a biasing member (e.g., compression spring members, cantilever beam biasing members, bellows contact biasing members, and/or the like, and combinations comprising at least one of the foregoing) that comprises at least two (2) sections, each of which comprises a centerline. The biasing members comprise spaced apart and parallel centerlines which, when used with certain plungers in the test probe, can force the exterior surface of the plungers against the interior of the barrel, ensuring that the majority of current flows through the barrel rather than through the spring, and providing relatively low contact resistance in comparison to other test probes without biasing members.

One exemplary embodiment of an electronic test probe100is shown inFIGS. 1A-1D, when taken together. As shown, test probe100can comprise a housing112, two opposing plungers120, and a biasing member130. Although illustrated herein with two plungers, it should be understood that the compression spring and plunger arrangements disclosed herein are applicable to test probes with a single plunger. Housing112can comprise a substantially longitudinal cylindrical shape with opposing ends112a,b, and an opening114disposed in each end112a,b. Although illustrated herein as substantially cylindrical, it should be understood that the housing112can comprise other geometries, depending on the application. Housing112will be referred to hereinafter as a barrel, as it is sometimes referred to in the art.

Each plunger120can comprise a substantially cylindrical body122, which can comprise an outer diameter sized and dimensioned to be received slidingly in the barrel112. Each plunger120can comprise a coaxially disposed reduced diameter end124defining a coaxially disposed probe tip128, and a bias-cut surface126disposed opposite the probe tip128.

Biasing member130is illustrated herein as a compression spring, but it should be understood that other types of biasing members can be utilized (e.g., cantilever beam biasing members, bellows contact biasing members, and/or the like, and combinations comprising at least one of the foregoing). For convenience, biasing member130will be referred to hereinafter as a compression spring or spring. Spring130can comprise a substantially longitudinal cylindrical shape comprising opposing ends, each end terminating in a terminating coil, which is closed square. Spring130can define a first coil section132and a second coil section134adjacent to the first coil section132. The first coil section132can define a first centerline132cand the second coil section134can define a second centerline134c, such that the centerlines132cand134care spaced apart and parallel to one another. The first and second coil sections132,134also define first and second diameters d1, d2, which can be the same or different.

Assembling the test probe can comprise disposing the spring and plungers in the barrel such the probe tip of each plunger extends from one of the openings in the barrel, and each end of the spring is disposed against one of the bias-cut surfaces of the plunger.

FIG. 2shows another embodiment of an exemplary electronic test probe200, which can comprise the same barrel212, plungers220and spring230as in the previous embodiment, and which can further comprise a ball bearing240disposed between each end230a,bof the spring230and the bias-cut surfaces226of the plungers220. The same materials and methods used in the previous embodiment can be used to form the present test probe200.

Assembling the test probe can comprise disposing the spring and plungers in the barrel such the probe tip of each plunger extends from one of the openings in the barrel, disposing the spring in the barrel, and disposing a ball bearing between each end of the spring and one of the bias-cut surfaces of the plunger.

FIG. 3shows another embodiment of an exemplary electronic test probe300, which can comprise the same barrel312and spring330as in the previous embodiment. Each plunger320can comprise a substantially cylindrical body322having an outer diameter sized and dimensioned to be slidingly received in the barrel312. Each plunger320can comprise a coaxially disposed reduced diameter end324disposed at one end of the body322, which defines a coaxially disposed probe tip328. An outwardly extending conical head326can be disposed opposite the probe tip328.

Assembling the test probe can comprise disposing the spring and plungers in the barrel such the probe tip of each plunger extends from one of the openings in the barrel, and disposing the spring in the barrel such that each end of the spring is disposed against one of the conical ends of the plunger, such that the conical end is disposed coaxially in the end coils of the spring.

FIG. 4shows another embodiment of an exemplary electronic test probe400, which can comprise the same barrel412and spring430as in the previous embodiment. Each plunger420can comprise a substantially cylindrical body422having an outer diameter sized and dimensioned to be slidingly received in the barrel412. Each plunger420can comprise coaxially disposed reduced diameter ends424,426disposed at each end of the body422. One of the reduced diameter ends can define a coaxially disposed probe tip428, and the other reduced diameter end can define an outwardly extending post426.

Assembling the test probe can comprise disposing the spring and plungers in the barrel such the probe tip of each plunger extends from one of the openings in the barrel, and disposing the spring in the barrel such that each end of the spring is disposed against one of the conical ends of the plunger, such that the post is disposed coaxially in the end coils of the spring.

FIG. 5shows another embodiment of an exemplary electronic test probe500, comprising the same barrel512and spring530as in the previous embodiment. Each plunger520can comprise a substantially cylindrical body522having an outer diameter sized and dimensioned to be slidingly received in the barrel512. Each plunger520can comprise a coaxially disposed reduced diameter end524disposed at one end of the body524, which can define a coaxially disposed probe tip528. A coaxially disposed bore526is defined in the body opposite the probe tip528.

Assembling the test probe comprises disposing the spring and plungers in the barrel such the probe tip of each plunger extends from one of the openings in the barrel, and disposing the spring in the barrel such that each end of the spring is disposed coaxially in one of the bores of the plungers.

In operation, when a force is exerted on any of the foregoing test probes, the design of the springs can cause the end of the spring and the exterior of the plunger body to be forced against the interior of the barrel. As a result, the side load is increased, thereby increasing the physical and/or electrical contact between the exterior of the plunger and the interior of the barrel. This results in an increase in the amount of electrical current that flows through the barrel, rather than through the spring, thereby minimizing the contact resistance of the test probe.

FIG. 6shows another embodiment of an exemplary electronic test probe600, comprising the same barrel612as in previous embodiments, and comprising a plunger620with an outwardly extending conical head as shown inFIG. 3C. The spring630can comprise a substantially longitudinal cylindrical shape comprising opposing ends630a,band defining three (3) coil sections, namely, a first coil section632, a second coil section634, and a third coil section636. Each of the coil sections632,634,636defines a centerline and a diameter, namely, the first coil section632defines a first centerline632cand a first diameter d3; the second coil section632defines a second centerline632cand a second diameter d4; and the third coil section632defines a third centerline632cand a third diameter d5. The first coil section632can be disposed between the second and third coil sections634,636. In the present embodiment, the centerlines632c,634cand636care all spaced apart and parallel to one another, and the diameters d4and d5of the second and third coil sections634,636can be less than the diameter d3of the first coil section632.

Assembling the test probe can comprise disposing the spring and plungers in the barrel such the probe tip of each plunger extends from one of the openings in the barrel, and disposing the spring in the barrel such that each end of the spring is disposed against one of the conical ends of the plunger, such that the conical end is disposed coaxially in the end coils of the spring.

In operation, a longitudinal force exerted on the test probe causes a side alignment of the plunger, and the reduced diameter of the end coils against the conical end of the plunger causes a rotational moment. As a result, physical and electrical contact between the exterior of the plunger and the interior of the barrel is maintained, increasing the amount of electrical current that flows through the barrel, rather than through the spring, thereby minimizing the contact resistance of the test probe.

FIG. 7shows another embodiment of an exemplary electronic test probe700, comprising the same barrel712as in previous embodiments, and a plunger720with an outwardly extending post head726as shown inFIG. 4A. The spring730can comprise a substantially longitudinal cylindrical shape comprising opposing ends730a,b, and defining three (3) coil sections, namely a first coil section732, a second coil section734, and a third coil section736. The first coil section732can be disposed between the second and third coil sections734,736. Each of the coil sections732,734,736defines a centerline and a diameter, namely, the first coil section732defines a first centerline732cand a first diameter d6; the second coil section734defines a second centerline734cand a second diameter d7; and the third coil section736defines a third centerline736cand a third diameter d8. In the present exemplary embodiment, the centerlines732c,734cand736care all spaced apart and parallel to one another, and the diameters d7and d8of the second and third coil sections734,736can be greater than the diameter of the first coil section d6.

Assembling the test probe can comprise disposing the spring and plungers in the barrel such the probe tip of each plunger extends from one of the openings in the barrel, and disposing the spring in the barrel such that each end of the spring is disposed against one of the conical ends of the plunger, such that the post is disposed coaxially in the end coils of the spring.

In operation, when a force is exerted on the test probe, the reduced diameter coils can causes a twisting moment of the plunger, thereby causing the exterior of the plunger to slide against the interior of the barrel.

FIG. 8shows another embodiment of an exemplary electronic test probe800, comprising the same barrel812as in previous embodiments, and a plunger820comprising an outwardly extending post head826as shown inFIGS. 4A and 7C. In the present embodiment, the spring830comprises a substantially longitudinal cylindrical shape comprising opposing ends830a,b, and defines four (4) coil sections, namely a first coil section832, a second coil section834, a third coil section836, and a fourth coil section838. The first coil section832is disposed adjacent to the second coil section834, the third coil section836is disposed adjacent to the first coil section832, and the fourth coil section838is disposed adjacent to the second coil section834. Each of the coil sections defines a centerline and a diameter, namely, first coil section832defines a first centerline832cand a first diameter d9; second coil section834defines a second centerline834cand a second diameter d10; third coil section836defines a third centerline836cand a third diameter d11; and fourth coil section838defines a fourth centerline838cand a fourth diameter d12. In the present exemplary embodiment, the centerlines832c,834c,836cand838care all spaced apart and parallel to one another. Also in the present exemplary embodiment, the diameters d9and d10of the first and second coil sections832,834are substantially the same, the diameters d11and d12of the third and fourth coil sections836,838are substantially the same, and are less than the diameters d9and d10of the first and second coil sections832,834.

Assembling the test probe can comprise disposing the spring and plungers in the barrel such the probe tip of each plunger extends from one of the openings in the barrel, and disposing the spring in the barrel such that each end of the spring is disposed against one of the conical ends of the plunger, such that the post is disposed coaxially in the end coils of the spring.

In operation, when the plunger posts are inserted into the reduced diameter end coils of the spring, it causes them to naturally align in an eccentric manner. When the spring and plunger are disposed in a cylindrical barrel with straight sidewalls, they become aligned in a concentric manner, causing the external surface of the plungers to be forced against the inside surface of the barrel.

Suitable materials for any of the foregoing barrels can comprise any electrically and thermally conductive material capable of withstanding the conditions in which the test probes will be utilized. Possible materials for the barrels can comprise brass, nickel, steel, stainless steel, and/or the like. Optionally, the surface of the barrels can comprise a coating of an electrically conductive material such as, but not limited to, gold, silver, platinum, palladium, and combinations and alloys thereof. The barrels can be formed using a variety of techniques such as tube drawing, deep drawing, automatic lathing, and/or the like. Optionally, other parts of the test probes can comprise a coating of the foregoing electrically conductive materials.

Suitable materials for any of the foregoing plungers can comprise any material having sufficient strength to withstanding the forces on the test probes, and capable of withstanding the conditions in which the test probes will be utilized. Possible materials for the plungers include, but are not limited to, steel, beryllium-copper, and/or the like, and combinations comprising at least one of the foregoing). The plungers can be formed using a variety of techniques such as automatic lathing, and the like. Optionally, the surface of the plungers can comprise a coating of an electrically conductive material such as, but not limited to, gold, silver, platinum, palladium, and combinations and alloys thereof.

Suitable materials for any of the foregoing compression springs can comprise any material that is capable of exerting a biasing force, and that is capable of withstanding the conditions in which the test probes will be utilized. Examples of suitable materials for the spring include relatively high tensile strength materials such as, but not limited to, stainless steel wire, music wire, and/or the like, and combinations comprising at least one of the foregoing. The springs can be formed using a variety of techniques (e.g., a coil winding machine, and the like).

Formation of the test probes can comprise forming the housing, biasing members, and plungers using any of the techniques described above. The spring can be formed by forming a plurality of coils having substantially the same diameter followed by defining the first and second coil sections (and corresponding spaced apart and parallel centerlines) by bending a region between the ends of the spring using a predetermined amount of force (e.g., with a coil winding machine).

Any combination of springs, plungers and contact tips can be used, provided that the combination results in a consistent normal force of the plunger against the interior sidewall of the barrel. For example, although the springs are illustrated herein as comprising closed end terminating coils, it should be understood that other types of terminating coil arrangements can be used (e.g., the ends of the spring can comprise full, half, and quarter turns of the terminating coil(s), and/or the like, with square ends, round ends, etc., which are open, closed, tapered, tucked in, turned in, and/or the like). Similarly, other arrangements of coil sections can be utilized other than those illustrated herein can be used, as well as other plunger geometries.

The test probes: 1) can provide contact resistance that is lower than test probes without a biasing member (e.g., less than or equal to about 50 milliohms, more particularly about 25 milliohms to about 50 milliohms, more particularly still about 10 milliohms to about 35 milliohms); 2) can provide more consistent contact resistance than other test probes without a biasing member; 3) can provide reduced material and manufacturing costs due to the elimination of internal components used in other test probes that comprise biasing members (e.g., a ball bearing, and the like); 4) can provide reduced material and manufacturing costs due to the elimination of components that are difficult to fabricate (e.g., a bias-cut plunger, and the like); and 5) can provide increased durability in comparison to test probes with external springs.