Method and apparatus for retaining a spring probe

METHOD AND APPARATUS FOR RETAINING A SPRING PROBE

The present invention relates to a spring probe block assembly of the type used in automatic test equipment (ATE), and more particularly to a spring probe block assembly for use in high bandwidth applications.

A spring probe block is used to provide a temporary spring contact surface between an integrated circuit or other electronic equipment and the test head of an automatic test equipment to perform necessary tests on the integrated circuit or other electronic equipment. A spring probe block assembly of the type used in automated test equipment is widely used and generally uses a similar structure. The spring probe block housing is typically machined from metal bar stock in an expensive process sequence that ensures the correct location and diameter of the bores that receive the press-fit coaxial probe and ground receptacle. In addition, solid metal structures generally serve to ground all circuit elements, and until recently were considered desirable for signal preservation performance. Also, some spring probe block housings are made of molded polymers instead of machined metals.

In both metal and polymer probe block housings, the coaxial probe connector has one end connected to a coaxial cable and the other end to a spring probe. Typically, one spring probe is provided for each signal line, and one or more spring probes are provided for each signal line to serve as a reference point (ground). In the case of a polymeric spring probe housing, the coaxial shield tube and the grounding spring probe associated with each signal line may be electrically insulated from its surroundings by the dielectric material of the polymeric housing. Isolation of each of these channels (consisting of the signal lines and their associated ground return loops) is essential to achieve high bandwidth. The ability to operate at higher bandwidths is important as the next generation of automated test equipment must be used to test integrated circuits faster as well as faster.

Many existing spring probe block assemblies have one or more drawbacks in their construction and are therefore not suitable for high bandwidth use. In particular, many prior art spring probe block assemblies (particularly those manufactured using a metal housing) provide a common ground for all ground probes. As discussed above, conventional grounding is not suitable for high bandwidth applications. Conversely, for high bandwidth applications, it is desirable to have a signal probe, and the associated ground probe is electrically isolated from other coaxial signals and ground probes.

Many prior art structures (using both metal and polymer housings) are not suitable for high bandwidth applications because of the presence of an excessively large ground return loop. 1A shows a prior art spring probe block assembly 10 using a polymer housing 12 . Ground probe 14 and signal probe 16 are inserted through hole 18 in the front of polymer housing 12 , and ground probe 14 is received in box contact 20 . The box contacts 20 are connected to a coaxial cable 23 and soldered to a coaxial connector 22 that receives a signal probe 16 .

As shown in Figure 1B, an excessive length of the ground loop (shown by dashed line 30) limits the bandwidth because it increases the inductance. The ground loop 30 travels from the tip of the signal probe 16 through the ground probe 14 into the box contact 20 and through the weld along the beam 32 of the box contact 20 and then coaxially. It runs along the conductive shield 36 of the connector 22 . The length of the ground loop is exacerbated by the thickness of the polymer housing 12 through which the signal and ground probes 14, 16 must pass.

It is known that at high speed the inductance of a given return current path is greater than its resistance. In practice, the fast return current follows the path of least inductance rather than the path of least resistance. It is also known that the minimum inductance return path lies just below the signal conductor. This means that minimizing the total ground loop area between the outgoing and return current paths minimizes the inductance as much as possible. Accordingly, in FIG. 1B , the ideal ground loop is shown by dashed line 38 . (See Howard Johnson and Martin Graham, "High-Speed Digital Construction: A Guide to Magic.")

In addition to the above drawbacks, the construction of many commercially available spring probe block assemblies requires additional parts or additional manufacturing steps to hold the grounded spring probe in the assembly. In some cases, a tubular receptacle is used to receive and hold a grounding spring probe. For example, as shown in FIG. 2 , after the bore 42 is machined into the housing 40 , the tubular metal receptacle 44 is press-fitted into the bore 42 in the metal spring probe block housing 40 , thereafter A grounding spring bore 46 is inserted by press fit into a receptacle 44 held in place. Since the grounding spring probe 46 itself has little flexibility, the receptacle 44 adds flexibility to the system to prevent damage to the grounding spring probe 46 . The use of the probe receptacle 44 requires additional assembly steps that are undesirable and additional parts to be stocked. In the case where a tubular receptacle is not used, the grounding spring probe is made of a so-called "banana band". The banana band allows the grounding spring probe to be inserted into the large bore and held within the bore by a friction fit. However, manufacturing spring probes from banana bands is difficult and expensive, and requires other types of spring probes used for signal and ground lines. Obviously, increased inventory, as well as added manufacturing difficulties and costs, is undesirable. In all of the situations described above, it is very difficult to replace a damaged ground spring probe without damaging the rest of the assembly.

Clearly, what is needed for a spring probe block assembly is to provide an electrically stable and cost effective approach to lowering the inductance path between the coaxial connector and its ground probe. Preferably, such a spring probe block assembly does not require a ground probe receptacle (and the associated cost, assembly labor and longer impedance paths). Also, the spring probe block assembly eliminates the need to use a grounding spring probe with a banana band when the grounding probe receptacle is not being used. Preferably, the spring probe block assembly facilitates replacement of the spring probe and coaxial connector within the block assembly without significant rework or destruction of the entire spring probe block assembly. In addition, the spring probe block assembly preferably resists high cable pulling forces that unintentionally disengage the coaxial connector during movement of the automated test rig.

1A is a cross-sectional view of a prior art spring probe block assembly;

1B is an enlarged perspective view of the probe connector and ground probe assembly of the spring probe block assembly of FIG. 1A;

2 is a perspective view of another prior art spring probe block assembly;

3A is a perspective view of one embodiment of the inventive spring probe block assembly described herein;

Fig. 3B is a front view of the front side of the spring probe block assembly of Fig. 3A;

Fig. 3c is a partial enlarged view of the front side of the spring probe block assembly of Fig. 3a;

Fig. 4A is a cross-sectional view taken along line 4-4 in Fig. 3B;

4B and 4C are exploded assembly views of the ground plate, the probe connector, and the ground probe shown in FIG. 4A, respectively.

5A-5C are cross-sectional views of another spring probe retaining structure.

6A is a cross-sectional view of a spring probe block assembly with an optical vacuum seal;

6B is a perspective view of a molded insert for providing an optical vacuum seal;

7A is a front elevational view of another embodiment of a spring probe block assembly described herein;

Fig. 7B is an enlarged view of the conductive retainer element of Fig. 7A;

8A and 8B are perspective views of another embodiment of a conductive retainer element of a spring probe block assembly described herein.

Fig. 8c is an enlarged view of the conductive retainer element of Figs. 8a and 8b;

9A and 9B are perspective views showing a retainer used in the embodiment of Figs. 7A, 8A and 8B.

The present invention relates to a spring probe block assembly for use in high bandwidth applications. The spring probe block assembly described herein electrically isolates the signal probe and its associated ground probe from other coaxial signals and ground probes, and provides a low inductance return path for the signal. The spring probe block assembly also eliminates the need for a spring probe using a ground receptacle or banana band.

In a preferred embodiment, the spring probe block assembly includes an insulating housing having a cavity in the front of the housing. A conductive retainer is positioned within the cavity adjacent the front side of the housing. The conductive retainer has a passageway for receiving a probe connector and a ground probe. A conductive retainer electrically connects the ground probe to the conductive shell of the signal probe connector to provide a low inductance ground return path for the associated signal. Preferably, the housing of the spring probe block assembly is formed of a dielectric insulating material having either non-static or static absorbing properties.

In one embodiment, the grounding probe is held in the conductive retainer by a normal force generated when the grounding probe is inserted into the retainer. Normal forces occur when the ground probe is deflected by the inclined sidewalls within the housing. When the grounding probe is deflected by the inclined sidewall, the grounding probe is held in the assembly by friction. In another embodiment, inserting the grounding probe into the retainer causes a clamping force generated on the probe connector body to maintain the probe connector, retainer, and grounding probe in a fixed relationship.

Another aspect of the present invention is a grounding element electrically connecting a grounding probe and a cable shield of a signal probe connector, wherein the grounding probe is elastically deformed by the grounding element to maintain a spring force between the grounding element and the grounding probe. For example, elastic deformation of the grounding element may occur by providing a bore having a non-linear axis and into which the grounding probe is inserted. When the grounding probe is inserted into a bore with a non-linear axis, elastic deformation of the grounding probe causes a spring force to be generated, holding the grounding probe in place.

Another aspect of the present invention is a method of retaining a spring probe within a housing. The method includes forming a bore having a non-linear axis in a housing, and thereafter inserting a linear spring probe into the bore. By inserting the linear spring probe into the non-linear bore, the spring probe is elastically deformed to maintain a spring force between the housing and the spring probe, thus holding the spring probe in place.

The present invention provides a cost effective approach for creating an electrically stable low inductance path between a coaxial connector and its ground probe when using a spring probe block assembly. The spring probe block assembly described herein allows for easy replacement of parts of the spring probe block assembly without significant rework or partial breakage. In addition, the structure prevents unintentional disengagement of the coaxial connector when subjected to high cable pulling force during use.

3A provides a perspective view of one preferred embodiment of the spring probe block assembly described herein. As shown in Figure 3a, the spring probe block assembly 50 includes a housing 52 formed by injection molding from a suitable insulating polymer material, such as glass fiber reinforced polyphtalamide (PPA). For some intended uses of the probe block assembly, it may be desirable to use a polymeric material with non-electrostatic properties, such as carbon fiber reinforced polyphthalamide. Housing 52 includes a cavity 54 shaped to receive a ground plate 56 in a sliding fit or press fit on its front face 53 . The ground plate 56 is configured to receive and retain both the ground spring probe 58 and the probe connector 60 . 3B and 3C , the probe connector 60 includes a signal spring probe 61 surrounded by a dielectric insulation 62 , followed by a conductive shield 64 . Thus, the signal probe 61 is insulated from ground. The conductive shield 64 of the probe connector 60 is in intimate contact with the ground plate 56 . A grounding spring probe 58 is slidably received within an opening 66 of the grounding plate 56 and contacts the grounding plate 56 in a manner described below. As shown, the dielectric material housing 52 surrounds and insulates the grounding element (grounding plate 56 and grounding spring probe 58), and isolates its associated signal lines from all other ground and signal lines that make a pair. Insulate. All grounds within the assembly are also insulated from the automatic test equipment chassis ground as well as other probe block assemblies that may be adjacent.

4A shows an enlarged cross-sectional view of a spring probe block assembly 50 having a single coaxial probe connector 60 and associated signal and ground probes 61 and 58 respectively. For greater clarity, FIGS. 4B and 4C show exploded views of the ground plate 56, the grounding spring probe 58, and the probe connector 60, respectively. As shown in FIG. 4A, cavity 54 extends into housing 52 and follows the general shape of the assembled set of grounding elements, cavity 54 comprising assembled probe connector 60, grounding plate 56, and sized in such a way as to inhibit axial and lateral movement of the spring probes 58 , 61 . In particular, the ground plates 56 each have openings 68 sized to receive the conductive shield 64 of the probe connector 60 and hold the shield by press fit, the probe connector 60 and the ground plate The interface between the openings 58 at 56 preferably causes elastic deformation of the ground plate 56 . Allowing elastic deformation of the ground plate 56 is desirable because the probe connector 60 has little flexibility, and doubling the number of flexible members from one to two effectively makes the ground plate 56 flexible. This results in less stringent member tolerances, improving the manufacturability of the probe block assembly 50 .

As discussed above, in high bandwidth applications it is desirable to provide a low inductance ground return path within the probe assembly. Accordingly, it is desirable to position the ground plate 56 as far forward as possible within the housing 52 to shorten the ground return path and keep it close to the signal path. Accordingly, in the preferred embodiment, the ground plate 56 is seated in the housing 52 such that the front surface 69 of the ground plate 56 is flush with the front surface 53 of the housing 52 .

On the other hand, the front surface 69 of the ground plate 56 may protrude slightly forward of the front surface 53 of the housing 52 . The seating depth of the ground plate 56 may be controlled by the position of the shoulder 71 within the cavity 54 .

The ground plate 56 is preferably symmetrical so that it can be inserted into the cavity 54 of the housing 52 without requiring a specific orientation. Further, the grounding plate 56 is preferably the grounding spring probe body 74 in the region of the spring probe plunger when the grounding spring probe body 74 is deformed by contacting the inclined sidewall 72 of the housing 52. It has sufficient thickness to prevent severe bending. In a preferred configuration, the ground plate 56 has an open channel 80 that bisects the ground spring probe through hole 66 to enhance the flow of plating processing fluid through the hole 66 during the manufacturing process. The grounding spring probe through hole 66 is preferably angular displacement of the grounding spring probe tip 59 when the grounding spring probe body is displaced by bending against the inclined sidewall 72 of the housing 52 and inserted into the assembly. positioned to compensate. In addition, the grounding spring probe tip 59 is preferably 3 about the axis of the signal probe connector 60 to minimize internal contact resistance within the grounding spring probe 58 and to prevent increased wear during extended cycles of the assembly. It is placed at an angle of less than a degree.

As noted above, the ground plate 56 has at least one through hole 66 sized to allow a sliding fit passage of the ground spring probe 58 . A grounding spring probe 58 is seated against an end wall 70 of a cavity 54 in the housing 52 . Preferably, the cavity 54 in the housing 52 includes a beveled sidewall 72 that progressively interferes with the grounding spring probe body 74 during insertion thereof, such that the grounding spring probe body 74 and the inclined sidewall Interference between 72 elastically deforms the grounding spring probe body 74 as shown in FIG. 4A. Interference between the grounding spring probe body 74 and the inclined sidewall 72 maintains a normal force at two points 76 between the grounding spring probe body 74 and the grounding plate 56 . The optional third contact point 76 may be obtained by increasing the inclination of the sidewall 72 to press the ground spring probe body 74 against the signal probe connector body shield 64 .

The grounding spring probe body 74 may be bent and held within the grounding plate 56 rather than by the sloped sidewalls 72 as described above. In particular, the grounding plate 56 may be provided in a shape to maintain a normal force to the grounding spring probe 58 without the use of the inclined sidewalls 72 within the housing 52 . 5A, the ground plate 56 may have a first bore 80 extending from the front surface 200 and a second bore 82 extending from the rear surface 201, the first and second bores 82 extending from the rear surface 201. The two bores 80 , 82 are slightly offset from each other. When the grounding spring probe body 74 is inserted into the first bore 80 from the front face 200, the grounding spring probe body applies a normal force against the grounding plate 56 so that it is held in place by a friction fit. As a result, the grounding spring probe body 74 is deflected. 5B, the ground plate 56 may alternately have a first bore 80' extending from the front surface 200 and a second bore 82' extending from the rear surface 201, The second bore 82 is positioned at an angle to the first bore 80 . As described above, when the grounding spring probe body 74 is inserted into the second bore 82' after being inserted into the first bore 80' from the front face 200, the grounding spring probe body 74 deflects. and the ground spring probe body 74 is held by friction fit by the normal force. As shown in FIG. 5C , the ground plate 56 may optionally be formed from a front portion 86 and a rear portion 88 , and a first bore 80 is formed from the front portion 200 from the front portion 86 . ) and a second bore 82 extends through the rear portion 80 from the rear surface 201 . When assembled within the housing 52, the respective front and rear portions 86, 88 of the ground plate are aligned with the first and second bores 80", 82" slightly offset from each other. Again, when the grounding spring probe body 74 is inserted into the second bore 82 after being inserted into the first bore 80 from the front face 200, the grounding spring probe body 74 is deflected and the normal force generated so that the grounding spring probe body 74 is held by friction fit.

It will be appreciated that the configuration shown in Figures 5a-5c can also be used with a probe assembly having a metal housing, without the use of a ground plate or retainer as described above. In particular, the spring probe holding method shown in FIGS. 5A-5C can be used with a metal housing for securing the grounding probe to the housing without using a receptacle for the grounding probe or requiring a pre-formed "banana band". Those skilled in the art will recognize that not using receptacles or pre-formed banana bands simplifies manufacturing and reduces the cost of the probe assembly, which is therefore highly desirable.

Additional configurations may be provided for the spring probe block assembly. For example, the housing 52 may have an access hole 90 in communication with the grounding probe body seat 70 to allow access of a tool (not shown) to the rear of the grounding spring probe body 74 . Access to such a tool will facilitate removal of the grounding spring probe when the spring plunger breaks in use. When used in applications requiring vacuum sealing of the device, the optional access aperture 90 may be sealed. A vacuum seal may be provided by having a removable plug that fills the access hole 90 .

If vacuum sealing of the device is desired, an optional sealing feature may be provided within bore 104 of cavity 54 as shown in FIGS. 6A and 6B . The sealing properties are preferably provided by a single molded insert 100 of flexible polymer comprising a collar 102 configured to fit within a bore 104 of a cavity at the back of the housing 52 . As shown in FIG. 6A , when the probe connector 60 is inserted into the housing 52 , the probe connector 60 presses the collar 102 of the flexible insert 100 against the wall of the bore 104 . This will provide a secure seal. In addition to the single molded insert 100 shown in FIGS. 6A and 6B, a separate collar or O-ring may be provided within each bore 104 of the cavity 52 to provide a seal. However, the use of individual O-rings significantly increases the assembly time of the device, as well as being prone to displacement during insertion of the probe connector 60 .

In the spring probe block assembly 50 described herein, the distance from the front surface 53 of the housing 52 to the grounding spring probe contact point 76 of the housing 52 is minimized and approached zero. That is, the ground spring probe body 74 contacts the ground plate 56 and forms a very low inductance path as close as possible to the front face 53 of the housing. As discussed above, a low inductance ground path is highly desirable and in fact required in many high bandwidth applications. Prior art spring probe block assemblies use longer electrical paths and, therefore, have higher self-inductance, making them unsuitable for high-speed test performance.

The spring probe block assembly described above also has the advantage of being easy to assemble, rework and replace. The polymer housing described herein uses flexible members to hold the spring probe body in place and to maintain electrical contact with each other, making it easy to assemble the spring probe block assembly or replace worn or broken parts. Thus, the spring probe block assembly described herein makes it possible to remove parts that are damaged and need to be replaced during the assembly process, as well as replace relatively inexpensive parts instead of replacing the entire assembly.

In applications where the spring probe block assembly must be sealed against vacuum, the present invention effectively seals by placing a sealing ring within each housing cavity around each probe connector 60 as described above. Seal compression is maintained by the spatial relationship between the parts. Because the housing 52 allows the vacuum seal to be positioned behind the location of the ground probe 58 , a seal around the ground probe 58 is not required.

<u>another embodiment</u>

Another embodiment of a spring probe block assembly 150 is shown in FIG. 7A. The spring probe block assembly 150 includes an insulating housing 152 , a signal probe contact 161 , a ground probe contact 158 , and a probe connector retainer 156 . In the first embodiment, the housing 152 is surrounded by a dielectric material and isolates all other ground and signal lines that pair the signal lines associated with the grounding element, and all grounds in the assembly are surrounded by adjacent probe blocks and automated test rig chassis equipment. insulate from As discussed above, the central cavity in both ends of housing 152 conforms to the general shape of the assembled set of grounding elements, and the cavity is axially axial with the assembled probe connector and grounding clamp when the spring probe is installed therein. and laterally pressed.

7A and 7B, the probe retainer 156 is a pair of stamped electrical ground clamps coupled together to form a clamped device to receive the signal probe connector 160 and the ground probe 158. (180). Ground clamp 180 has a centrally located and axially aligned loop 182 and a pair of spring arms 184 extending from each of the two ends. The ground clamp subassembly is preferably symmetrical, so that it can be inserted into the cavity of the housing 152 without any specific orientation, thus improving ease of assembly. The loop 182 of the ground clamp 180 is sized to receive a single spring probe connector 160 that is slidably engaged with a low insertion force (3.18 kg or less). A grounding spring probe 158 is inserted between the spring arms 184 and the arms 184 are displaced outward to generate a normal force against the single spring probe connector body 60 to hold the assembled element in place. . Preferably, one of the loops 182 of the ground clamp 180 is located behind the pressure ring 183 of the single probe connector 160, thus improving the pulling resistance of the device.

7A and 7B, the spring arm 184 of the grounding clamp 180 has a grounding probe 158 inserted therebetween so that the clamping force holds the grounding probe 158 in the axial groove of the housing 152. Angled outwardly in a scissors-like manner to press against 190 , to achieve proper alignment of ground probe 158 within housing 152 . The angle θ formed by the spring arm 184 is preferably greater than 22 degrees. Also, the sidewalls of the cavity within the housing preferably hold the spring arm 184 of the ground clamp 180 in a preload condition such that the preload on the spring arm 184 increases the open area between the spring arms 184 . , thus facilitating the insertion of the ground probe 158 . Such preload also increases the overall angle between the spring arm retraction chambers 192 and thus reduces the required insertion force.

8A and 8B, the spring arm 184' of the grounding clamp 180' generally engages the grounding probe 158 when the grounding probe 158 is inserted into the grounding clamp 180'. They are bent backwards towards each other so as to surround them. When the ground probe 158 is inserted into the ground probe receptacle of the ground clamp 180 , the clamping force seals the ground clamp 180 about the body of the signal probe connector 160 . If desired, each ground clamp 180' may be formed of an optional connecting web that allows simple folding of the ground clamp 180' to obtain the final orientation of the element. The optional connecting webs holding the ground clamps together are fragile and can be flexible if desired.

To increase cable pulling force, retainer 200 is preferably provided to be secured in a snap fit arrangement to rear surface 184 of housing 152 as shown in FIGS. 9A and 9B . Retainer 200 preferably includes latching arms 202 that engage mutually latching structures 204 of housing 152 . To facilitate assembly, retainer 200 will preferably be formed of two parts having mating tongues 204 and grooves 206 that interlock the two retainer parts 200 together. In addition, the housing 152 preferably has an offset cavity at the rear end of the housing for a pattern of cavities that allows for a probe connector, thus allowing the use of independent retainer portions. This reduces the manufacturing cost and increases the ease of assembly of the device. Preferably, the housing 152 has a passageway 208 that opens into the latching arm 202 of the retainer 200 so that the retainer 200 can be disengaged from the exterior of the housing 152 to be reworked onto the device. include

For the embodiments of the spring probe block assemblies 50 and 150 described herein, those skilled in the art will recognize that additions and modifications may be made without departing from the spirit and scope of the present invention. For example, the housings 52 and 152 of the assembly preferably have mounting holes 210 to allow the spring probe block assemblies 50 and 150 to be mounted within an automated test rig head. While it is contemplated that retainer elements (ground plate 56 and ground clamps 180, 180') may have shapes other than those shown herein, or may be used, for example, in a metal probe assembly housing, the spirit of the present invention and It is an embodiment which does not deviate from a category.