Contact probe with improved current carrying capacity for high frequency applications

Abstract

The contact probe 20 comprises a probe body 20C having at least one pair of arms 22a, 22b extending between a first end 20A and a second end 20B and separated by a slot 21 made in the probe body 20C according to the longitudinal direction of extension of the contact probe 20. The probe preferably comprises at least one conductive insert 25 disposed in a bending plane α of the contact probe 20 and extending into the contact probe 20 along the longitudinal direction of extension. The conductive insert 25 is made of a first material having a lower specific electrical resistivity than a second material from which the contact probe 20 is made. The conductive insert 25 is a power transmission element, and the arms 22a, 22b are structural support elements for the contact probe 20 during deformation of the probe body 20C.

Description

[Technical field]

[0001] The present invention relates to a contact probe for high frequency applications having improved current carrying capacity. [Background technology]

[0002] The present invention relates particularly, but not exclusively, to contact probes configured to be housed in a vertical probe head for testing electronic devices integrated on a wafer, and the following disclosure makes reference to the technical field of this application solely for purposes of simplifying the discussion thereof.

[0003] As is well known, a probe head is a device configured to electrically connect a number of pads or contact pads of a microstructure, such as an integrated circuit, with corresponding channels of a test device.

[0004] Tests performed on integrated devices are particularly useful for detecting and isolating defective devices as early as the manufacturing stage. Probe heads are therefore usually used for the electrical testing of multiple devices integrated on a wafer before their cutting and assembly in a chip-containing package. It is known to denote an integrated circuit subject to such test operations as a DUT (English acronym: "Device Under Test").

[0005] The probe head may essentially be substantially plate-shaped and comprise a number of movable contact elements or contact probes held by at least a pair of supports or dies parallel to one another, said plate-shaped supports being provided with suitable holes and arranged at a specific distance from one another so as to leave a free space or air gap for the movement and possible deformation of the contact probes during the test operation. The pair of plate-shaped supports in particular comprises an upper plate-shaped support or upper die and a lower plate-shaped support or lower die, both provided with respective guide holes in which the contact probes slide axially, usually made of a wire of a special alloy having good electrical and mechanical properties.

[0006] A good connection between the contact probes and the contact pads of the device under test is ensured by the pressure of the probe head against the device itself, the contact probes being movable in guide holes made in the upper and lower plate-like supports, undergoing bending in the air gap between the two plate-like supports and sliding in the guide holes during said pressure contact. This type of probe head is usually called a probe head with a vertical probe or a "vertical probe head".

[0007] In some cases, a number of contact probes are rigidly fixed to the head itself at an upper plate-like support: such a probe head is called a "blocked probe head".

[0008] More frequently, however, contact heads with probes are used that are not rigidly fixed but are interfaced to so-called boards, possibly by means of microcontact boards: such probe heads are called "unblocked probe heads". A microcontact board is usually called a "space transformer", since, besides contacting the probes, it also makes it possible to spatially redistribute the contact pads realized thereon with respect to the contact pads of the device under test, in particular to relax the center-to-center distance constraints of the pads made on the space transformer with respect to those made on the device under test, which are instead determined by the architecture and technology of the device itself.

[0009] The correct operation of a vertical probe head is essentially linked to two parameters: the vertical movement, or overtravel, of the contact probes, and the horizontal movement, or scrubbing, of the contact tips of said contact probes on the contact pads of the device under test. Indeed, it is known to be important to ensure the scrubbing of the contact tips, making it possible to scrape the contact pads on the surface, removing impurities, for example in the form of a thin layer or film of oxide, thus improving the contact made by said contact probes, and thus by the probe head as a whole.

[0010] All these features must be evaluated and calibrated during the manufacturing process of the probe head, since proper electrical connection between the probe and the device under test, and in particular between the contact tips of the probe and the contact pads of the device under test, must always be ensured.

[0011] Equally important is ensuring that the pressure contact of the contact tips of the probes against the contact pads of the device is not so high as to result in damage to the probes or pads themselves.

[0012] This problem is especially felt in the case of so-called short probes, i.e. probes with a rod-shaped body, which have a limited length and in particular an overall dimension lower than 5000-7000 μm. Probes of this kind are used, for example, for high-frequency applications, where the reduced length of the probe limits the self-inductance phenomenon associated with the transmission of high-frequency signals. In particular, the term "high-frequency applications" denotes probes capable of transmitting signals having a frequency higher than 1000 MHz.

[0013] However, in this case, the reduced length of the contact probes dramatically increases the stiffness of the probes themselves, which implies an increase in the force exerted by each contact tip on, for example, the contact pads of the device under test, which could result in the breakage of said pads with irreparable damage to the device under test, a situation that should clearly be avoided. Even more dangerous, the increase in stiffness of the contact probes due to the reduction in their overall length increases the risk of breakage of the probes themselves.

[0014] It is known to reduce the stiffness of a short probe by making its respective body parts into a number of arms parallel to one another and extending longitudinally along said body parts, as shown diagrammatically in Figures 1A and 1B. A probe head comprising a contact probe with respective body parts formed by a number of arms is for example disclosed in the published international application (PCT) WO 2016 / 146476 dated 22 September 2016 in the name of the same applicant.

[0015] In particular, with reference to said figure, there is shown a contact probe 10 having a body 10C extending between first and second ends, in particular so-called contact tips 10A configured to abut contact pads of a device under test (not shown), and further contact pads for connection with a test apparatus, in particular so-called contact heads 10B configured to abut contact pads of a space transformer connected to said test apparatus (also not shown).

[0016] For example, in the case of a so-called short probe used in high frequency applications, the contact probe 10 has a length L of less than 5000 to 7000 μm.

[0017] In the embodiment shown in FIG. 1A, a probe body 10C includes a cut or slot 11 extending longitudinally along said body 10C and defines at least a pair of arms 12a and 12b.

[0018] Obviously, it is possible to make the probe body 10C also with multiple arms, thanks to the realization of a corresponding multiple longitudinal slots. For example, in the embodiment shown in Figure 1B, the body 10C of the contact probe 10 comprises two longitudinal slots 11a and 11b forming three arms 12a, 12b, and 12c.

[0019] The contact tip 10A and contact head 10B generally have a tapered shape and terminate in respective contact areas 13A and 13B.

[0020] The term "contact area" here and below denotes the end area of ​​the contact probe intended to contact a device under test or a testing apparatus, said contact area or end area not necessarily being pointed as shown in the figures. Usually, the contact area has a limited surface area, in particular having an extension smaller than the lateral section of the corresponding end, and may be arranged centrally with respect to the longitudinal axis of symmetry of the contact probe 10 or decentered with respect to it.

[0021] Preferably, the contact head 10B also comprises an enlarged portion 14 having a diameter D2 larger than the diameter D1 of the body 10C of the contact probe 10; in this way, respective undercut portions 14s of the enlarged portions 14 are defined relative to the probe body 10C, which are configured to abut against a guide housing the contact probe 10 and provide retention thereof in its longitudinal direction.

[0022] As already mentioned, electrical contact between the contact probe 10 and the space transformer on the one hand and the device under test (not shown) on the other hand is obtained by pressure abutment of the contact areas 13a, 13b of the probe against the respective contact pads.

[0023] Advantageously, the presence of multiple arms 12a-12c formed in the probe body 10C allows to reduce the stiffness of the probe 10 as a whole and, consequently, the pressure applied to the respective contact pads, while maintaining sufficient elasticity of the probe body to ensure its bending during pressing contact of the contact areas 13a, 13b onto the contact pads.

[0024] While improving the operation of the contact probe 10 from a mechanical standpoint, the presence of multiple arms formed within its body 10C entails a reduction in the current capacity of the probe and increases its electrical resistance, which precludes its use for transmitting high frequency and high current signals, the term "high current" referring to signals having a current value greater than 800 mA. Summary of the Invention [Problem to be solved by the invention]

[0025] The technical problem of the present invention is therefore to conceive a contact probe having functional and structural characteristics that ensure a correct operation of the probe at such current values, sufficient elasticity of the contact probe and a reduced risk of its breakage, as well as a suitable force exerted by the associated contact area while abutting against the corresponding contact pad, thus allowing its use in high frequency applications for transmitting high frequency signals, whilst eliminating the limitations and drawbacks that still affect contact probes made according to the prior art. [Means for solving the problem]

[0026] The solution idea underlying the present invention is to provide a contact probe comprising at least one conductive insert arranged according to its longitudinal extension direction, which increases the probe's ability to pass electric current and makes it suitable for the transmission of high current signals, thus minimizing its electrical resistance, said probe also having a body made with multiple arms so as to make it possible to make short probes suitable for high frequency applications.

[0027] In particular, contact probes made according to embodiments include such conductive inserts positioned within the bending plane, and preferably as far as possible along the neutral axis of the probe, i.e., at the location of least stress, to maximize current carrying capacity and minimize electrical resistance while at the same time not affecting the mechanical performance of the probe over its operating temperature range.

[0028] Based on the above-mentioned solution idea, the technical problem is solved by a contact probe comprising a probe body with at least a pair of arms extending between a first end and a second end and separated by a slot made in the probe body depending on the deployment direction of the contact probe, which comprises at least one conductive insert extending inside the contact probe along a longitudinal deployment direction arranged in a bending plane of the contact probe, the conductive insert being made of a first material having a specific electrical resistivity lower than the specific electrical resistivity of a second material of which the contact probe is made, the conductive insert being an element that carries the electric current and the arms being structural support elements of the contact probe during deformation of the probe body.

[0029] In particular, the invention comprises the following further and optional features taken individually or, where appropriate, in combination:

[0030] According to an aspect of the present invention, the first material may have a specific electrical resistivity of less than 30 μΩ·cm.

[0031] In particular, the first material may be a conductive or semiconductive material with low electrical resistivity selected from gold (Au), copper (Cu), silver (Ag), aluminum (Al), platinum (Pt) and alloys thereof, preferably silver, and the second material may be a structurally stable conductive material selected from nickel, tungsten, cobalt, palladium or alloys thereof, such as nickel-manganese, nickel-cobalt, nickel-palladium or nickel-tungsten, palladium-cobalt alloys, palladium-based ternary and quaternary alloys, preferably palladium-cobalt.

[0032] It should be noted that, according to another aspect of the invention, the conductive insert may have a lateral dimension, perpendicular to the longitudinal direction of deployment, which is lower than the corresponding lateral dimension of the arm, preferably lower than 20 μm.

[0033] In particular, the lateral dimension of the conductive insert may be equal to 20% to 60% of the smallest value of the corresponding lateral dimension of the arm.

[0034] Furthermore, in accordance with another aspect of the present invention, the conductive insert may be located substantially in the plane of bending and at a location of minimum stress along the neutral axis of the contact probe.

[0035] Preferably, a conductive insert may be disposed within the slot.

[0036] Additionally, the conductive insert may include a plurality of parallel foils disposed within the slot.

[0037] Alternatively, in accordance with another aspect of the invention, a conductive insert may be made on the inside of one of the arms.

[0038] The contact probe may also include at least one arm made from a first low electrical resistivity material to form a conductive insert.

[0039] In accordance with a further aspect of the invention, the conductive insert may have a length equal to the length of the slot.

[0040] Additionally, the probe body may include an alternating arrangement of arms and conductive inserts.

[0041] According to another aspect of the invention, the conductive insert may comprise a conductive central insert disposed within the slot and further conductive portions made of a first material and preferably fully embedded within a second material forming the contact probe, fabricated within the first and second ends of the contact probe.

[0042] Preferably, the conductive insert extends along the entire contact probe and may be exposed to the second material at first and second contact areas created at the first and second ends of the contact probe, respectively.

[0043] Additionally, the conductive inserts may include at least one conductive insert extending longitudinally in each of the arms.

[0044] Additionally, the conductive insert extending through each of the arms may be made to be fully incorporated within the second material forming the arm or to emerge at the sidewalls of the slot.

[0045] In this case, the conductive insert may further comprise a conductive central insert disposed in the slot.

[0046] According to another aspect of the invention, the conductive insert may have a length along the longitudinal deployment direction that is less than a length of the contact probe.

[0047] Alternatively, the conductive insert may have a length along the longitudinal extension direction such that it emerges from the second material forming the contact probe.

[0048] The technical problem of the present invention is also solved by a probe head for testing the function of an integrated device under test, comprising a plurality of contact probes with at least one end configured to abut against a contact pad of the integrated device under test, which is made as described above and comprises a contact probe having an arm and a probe body with at least one conductive insert.

[0049] According to another aspect of the invention, the probe head may include a first plurality of contact probes having an arm and a probe body with at least one conductive insert, and a second plurality of contact probes having an arm and a probe body lacking at least one conductive insert.

[0050] Additionally, the probe head may include only a plurality of contact probes having arms and a probe body with at least one conductive insert.

[0051] The characteristics and advantages of the contact probe according to the invention will become apparent from the following description of embodiments thereof, given by way of non-limiting example, with reference to the accompanying drawings, in which: FIG. [Brief description of the drawings]

[0052] [Figure 1A] 1A-1D show schematic diagrams of different embodiments of a contact probe made according to the prior art; [Figure 1B] 1A-1D show schematic diagrams of different embodiments of a contact probe made according to the prior art; [Figure 2A] 2A-2C show schematic front views in longitudinal section and respective views in lateral section of an embodiment of a contact probe according to an embodiment of the present invention; [Figure 2B]2A-2C show schematic front views in longitudinal section and respective views in lateral section of an embodiment of a contact probe according to an embodiment of the present invention; [Figure 2C] 2A-2C show schematic front views in longitudinal section and respective views in lateral section of an embodiment of a contact probe according to an embodiment of the present invention; [Figure 2D] 2A-2C show schematic front views in longitudinal section and respective views in lateral section of an embodiment of a contact probe according to an embodiment of the present invention; [Figure 3A] 1A and 1B show schematic front views of alternative embodiments of a contact probe, respectively in longitudinal section and in transverse section; [Figure 3B] 1A and 1B show schematic front views of alternative embodiments of a contact probe, respectively in longitudinal section and in transverse section; [Figure 3C] 1A and 1B show schematic front views of alternative embodiments of a contact probe, respectively in longitudinal section and in transverse section; [Figure 3D] 1A and 1B show schematic front views of alternative embodiments of a contact probe, respectively in longitudinal section and in transverse section; [Figure 4A] 1A and 1B show schematic front views of alternative embodiments of a contact probe, respectively in longitudinal section and in transverse section; [Figure 4B] 1A and 1B show schematic front views of alternative embodiments of a contact probe, respectively in longitudinal section and in transverse section; [Figure 4C] 1A and 1B show schematic front views of alternative embodiments of a contact probe, respectively in longitudinal section and in transverse section; [Figure 4D]1A and 1B show schematic front views of alternative embodiments of a contact probe, respectively in longitudinal section and in transverse section; [Figure 5A] 1A and 1B show schematic front views of alternative embodiments of a contact probe, respectively in longitudinal section and in transverse section; [Figure 5B] 1A and 1B show schematic front views of alternative embodiments of a contact probe, respectively in longitudinal section and in transverse section; [Figure 5C] 1A and 1B show schematic front views of alternative embodiments of a contact probe, respectively in longitudinal section and in transverse section; [Figure 5D] 1A and 1B show schematic front views of alternative embodiments of a contact probe, respectively in longitudinal section and in transverse section; [Figure 6A] 1A and 1B show schematic front views of alternative embodiments of a contact probe, respectively in longitudinal section and in transverse section; [Figure 6B] 1A and 1B show schematic front views of alternative embodiments of a contact probe, respectively in longitudinal section and in transverse section; [Figure 6C] 1A and 1B show schematic front views of alternative embodiments of a contact probe, respectively in longitudinal section and in transverse section; [Figure 6D] 1A and 1B show schematic front views of alternative embodiments of a contact probe, respectively in longitudinal section and in transverse section; [Figure 7A] 1A and 1B show schematic front views of alternative embodiments of a contact probe, respectively in longitudinal section and in transverse section; [Figure 7B] 1A and 1B show schematic front views of alternative embodiments of a contact probe, respectively in longitudinal section and in transverse section; [Figure 7C] 1A and 1B show schematic front views of alternative embodiments of a contact probe, respectively in longitudinal section and in transverse section; [Figure 7D] 1A and 1B show schematic front views of alternative embodiments of a contact probe, respectively in longitudinal section and in transverse section; [Figure 8A] 1A and 1B show schematic front views of alternative embodiments of a contact probe, respectively in longitudinal section and in transverse section; [Figure 8B] 1A and 1B show schematic front views of alternative embodiments of a contact probe, respectively in longitudinal section and in transverse section; [Figure 8C] 1A and 1B show schematic front views of alternative embodiments of a contact probe, respectively in longitudinal section and in transverse section; [Figure 8D] 1A and 1B show schematic front views of alternative embodiments of a contact probe, respectively in longitudinal section and in transverse section; [Figure 9A] 1A and 1B show schematic front views of alternative embodiments of a contact probe, respectively in longitudinal section and in transverse section; [Figure 9B] 1A and 1B show schematic front views of alternative embodiments of a contact probe, respectively in longitudinal section and in transverse section; [Figure 9C] 1A and 1B show schematic front views of alternative embodiments of a contact probe, respectively in longitudinal section and in transverse section; [Figure 9D] 1A and 1B show schematic front views of alternative embodiments of a contact probe, respectively in longitudinal section and in transverse section; [Figure 10A] 1A and 1B show schematic front views of alternative embodiments of a contact probe, respectively in longitudinal section and in transverse section; [Figure 10B] 1A and 1B show schematic front views of alternative embodiments of a contact probe, respectively in longitudinal section and in transverse section; [Figure 10C] 1A and 1B show schematic front views of alternative embodiments of a contact probe, respectively in longitudinal section and in transverse section; [Figure 10D] 1A and 1B show schematic front views of alternative embodiments of a contact probe, respectively in longitudinal section and in transverse section; [Figure 11] 1 illustrates generally an embodiment of a probe head including a contact probe made in accordance with an embodiment of the present invention; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0053] With reference to the above figures, and in particular to FIG. 2A, a contact probe, generally designated by the reference numeral 20, made in accordance with an embodiment of the present invention is herein described.

[0054] It should be noted that the figures represent schematic views and are not drawn to scale, but instead are drawn to highlight important features of the invention. Moreover, in the figures, different parts are drawn schematic, since their shapes may differ depending on the desired field of application.

[0055] As can be seen with respect to known solutions, the contact probe 20 comprises a probe body 20C extending between first and second ends, in particular a contact tip 20A configured to abut a contact pad of a device under test (not shown), and a contact head 20B configured to abut a further contact pad of a space transformer connected to a test apparatus (not shown).

[0056] Preferably, the contact probe 20 may be a so-called short probe having a total length LS of less than 6000 μm, so as to be suitable for high frequency applications.

[0057] In an example embodiment, the probe body 20C may have a length LC comprised between 500 μm and 4000 μm, the contact tip 20A may have a length LA comprised between 150 μm and 1000 μm, and the contact tip 20B may have a length LB comprised between 50 μm and 500 μm, and the overall length LS of the contact probe 20 may be comprised between 700 μm and 5500 μm.

[0058] In the embodiment shown in Fig. 2A, the probe body 20C comprises a slot 21 extending in its longitudinal development direction (i.e. along the axis z of the local reference system of the figure) along the probe body 20C and defining at least a pair of arms 22a and 22b. In particular, the slot 21 extends in the longitudinal direction by a length L1 that is less than or equal to the length LC of the probe body 20C, for example comprised between 500 μm and 4000 μm, and may be centrally located with respect to the probe body 20C, as shown in the figure. Furthermore, the slot 21 has a transverse dimension D1 perpendicular to the longitudinal development direction of the contact probe 20 (i.e. along the x-axis of the local reference system of the figure) having a value comprised between 5 μm and 50 μm, so as to produce the arms 22a and 22b with respective transverse dimensions D2a and D2b having values ​​comprised between 5 μm and 40 μm.

[0059] In the embodiment shown in FIG. 2A, the arms 22a and 22b have lateral dimensions D2a and D2b of equal value, but it is clearly possible to make the arms have lateral dimensions of different values, for example obtained by a slot 21 that is not centrally positioned with respect to the lateral extension of the probe body 20C.

[0060] It is obviously possible to make the probe body 20C with multiple arms by virtue of the realization of a corresponding number of longitudinal slots, sized and spaced apart as required, depending on the needs of the final contact probe 20 application.

[0061] The contact tip 20A and the contact head 20B preferably have a tapered shape and terminate in first and second contact areas 23A, 23B configured for pressing contact with the respective contact pads of the device under test and the space transformer, respectively, said contact areas not necessarily being pointed and / or centrally located with respect to the corresponding ends.

[0062] Preferably, the contact head 20B also comprises an enlarged portion 24 having a diameter Db larger than the diameter Dc of the probe body 20C, where herein and below the term diameter refers to the maximum lateral dimension even in the case of non-circular elements.

[0063] In this way, respective undercut portions 24s of the enlarged portions 24 are defined relative to the probe body 20C, which are configured to abut against guides housing the contact probes 20 to achieve their retention in the longitudinal direction (i.e. according to the axis z of the local reference system of the figure) and to prevent, for example, the probes from slipping out of the probe head housing them when they are not in pressing contact with the device under test or during cleaning operations.

[0064] In particular, the diameter Dc of the probe body 20C has a value comprised between 15 μm and 130 μm, and the diameter Db of the enlarged portion 24 has a value comprised between 25 μm and 200 μm.

[0065] Preferably, the contact probe 20 according to the embodiment also includes a conductive insert 25 that extends into the probe along its longitudinal deployment direction. In particular, the conductive insert 25 is made of a conductor or semiconductor material having a specific electrical resistance lower than that of the material of which the contact probe 20 is made; further, the conductive insert 25 is disposed within the bending surface α of the contact probe 20, that is, within the plane defined by the axes x and z shown in the figure corresponding to the plane of the drawing.

[0066] Preferably, the conductive insert 25 is disposed substantially within the bending surface along the so-called neutral axis of the contact probe 20, that is, at the minimum stress position of the probe itself within the bending surface α. In particular, as is well known, the neutral axis is the axis in the cross-section of a beam or shaft, such as the contact probe, along which there is no longitudinal stress or strain.

[0067] In this way, the conductive insert 25 can maximize the current capacity of the contact probe 20, minimize its electrical resistance, and, on the other hand, not affect the mechanical performance of the probe as a whole. It is confirmed that the contact probe 20 maintains these characteristics within its entire temperature range, that is, between -55°C and +150°C or higher.

[0068] The conductive insert 25 has a reduced lateral dimension D (D < D2a and D < D2b), particularly smaller than the lateral dimensions D2a and D2b of the arms 22a and 22b of the probe body 20C.

[0069] In this way, while the conductive insert 25 has the main function of increasing the current capacity of the contact probe 20, the arms 22a and 22b have a general supporting function, and these different functions are defined by the lateral dimensions of the components in addition to the materials of which they are made.

[0070] In the following, precisely to highlight the different functions of the above-mentioned components, the material from which the contact probe 20 is made is referred to as the "structurally stable material" and the material from which the conductive insert 25 is made is referred to as the "low electrical resistivity material".

[0071] The contact probe 20 with the conductive insert 25 is suitable for transmitting high current signals, i.e. signals having a current having a value greater than 800 mA.

[0072] The conductive insert 25 preferably has a lateral dimension D equal to 20% to 60% of the minimum of the lateral dimensions D2a, D2b of the arms 22a, 22b. In particular, the conductive insert 25 may be in the form of a metal foil arranged along the probe body 20C and having a length at least equal to the length LI of the slot 21, said metal foil being arranged within the slot 21 itself, preferably centrally with respect thereto.

[0073] In particular, the conductive insert 25 has a lateral dimension D of a particularly reduced value, preferably less than 20 μm.

[0074] In this way, the conductive insert 25 does not actually perform any structural support function within the contact probe 20; the support effect is provided by the side arms 22a and 22b, which have diameters D2a and D2b larger than the diameter D of the conductive insert 25 and are made of a material that is structurally stable relative to that of which the conductive insert 25 is made. Instead, the presence of the conductive insert 25 increases the overall capacity of the contact probe 20 to carry current because it is made of a material with low specific electrical resistivity, i.e., high electrical conductivity.

[0075] The low specific electrical resistivity material of which the conductive insert 25 is made may be a metal selected from gold (Au), copper (Cu), silver (Ag), aluminum (Al), platinum (Pt) and alloys thereof, preferably silver, or a suitably doped semiconducting material, while the structurally stable material forming the contact probe 20 may be selected from nickel, tungsten, cobalt, palladium or alloys thereof, such as nickel-manganese, nickel-cobalt, nickel-palladium or nickel-tungsten, palladium-cobalt alloys, palladium-based ternary and quaternary alloys, preferably palladium-cobalt. In particular, the material of which the conductive insert 25 is made has a specific electrical resistivity (ρ) of less than 30 μΩ·cm.

[0076] Essentially, the structurally stable material from which the contact probe 20 is made is chosen to ensure the integrity of the probe during its pressing contact against the device under test and its bending, while the low electrical resistivity material from which the conductive insert 25 is made is chosen to maximize the current carrying capacity and reduce the resistance of the contact probe 20 it contains.

[0077] Furthermore, the presence of side arms 22a and 22b serves to shield so-called wire currents due to currents flowing within conductive insert 25 when placed inside said side arms 22a and 22b, the shielding action being particularly advantageous in the case of radio frequency applications (RF).

[0078] In the embodiment of Figure 2A, the conductive insert 25 extends only within the slot 21, as shown by the sections of Figures 2B to 2D cut through the lateral planes π1 to π3 shown in Figure 2A, in particular the first plane π1 located at the slot 21 and the conductive insert 25, the second plane π2 located at the contact head 20B (in particular at the enlarged portion 24 of diameter Db), and the third plane π3 located at the probe body 20C of diameter Dc where the slot 21 is not present.

[0079] In this embodiment, it is emphasized that the conductive insert 25 is preferably located in the low load areas where the material from which it is made is subjected to the minimum tensile and compressive loads. In this way, it is possible to control the yield of the low specific electrical resistivity material from which the conductive insert 25 is made and to maintain the thermal relaxation performance of the structurally stable material from which the rest of the contact probe 20 is made. The conductive insert 25 may in particular be located in the bending plane α of the contact probe, at its neutral axis, i.e. at its minimum stress location.

[0080] Preferably, based on the values ​​of the diameter Dc of the probe body 20C and of the diameter D1 of the slot 21, the conductive insert 25 can be made in the form of a number of parallel foils made of a conductor or semiconducting material with low specific electrical resistance to minimize the specific electrical resistance and maximize the current carrying capacity without significantly increasing the force of the contact probe 20 during impact, since the influence of these thin foils on the mechanical performance of the contact probe 20 is limited. Moreover, it is emphasized that in this case too, the foils can be preferably kept in the minimum tensile and compressive load areas, i.e. in the slot 21.

[0081] The probe body 20C can also be made by interleaving the support arms and conductive inserts.

[0082] In general, the arrangement and number of the conductive inserts and support arms are determined always taking into account the pitch value between the pads of the device under test and in order to avoid any possible contact between the conductive inserts and / or support arms which may result in electrical problems, but also mechanical problems, contact between said components which may lead to greater forces during impact of the contact probe against the contact pads with the risk of subsequent damage.

[0083] Advantageously, according to this embodiment, the conductive insert 25 disposed within the slot 21 is separated by the support arms 22a and 22b through air, which acts as an electrical insulator and mechanical separator.

[0084] Alternatively, the contact probe 20 may comprise a conductive insert 25 arranged in a support arm, for example, support arm 22a, as shown in FIG. 3A, or a plurality of conductive inserts 25a and 25b arranged in support arms 22a and 22b, respectively, as shown in FIG. 4A; in this way, the insert or plurality of conductive inserts are still cut at planes π1-π3 shown in FIGS. 3A and 4A, and are completely embedded in the structurally stable material forming the contact probe 20, as shown in the sections of FIGS. 3B-3D and 4B-4D, arranged similarly to that of FIG. 2A.

[0085] According to the above embodiment alternative, it is emphasized that the structurally stable material from which the probe, and in particular the support arms 22a and 22b, are made reduces the risk of breakage of the insert 25 embedded therein, or of the inserts 25a, 25b, which are made of a mechanically weaker low specific electrical resistivity material.

[0086] Although not shown in either FIG. 3A or FIG. 4A, it is also possible to make conductive insert 25 or conductive inserts 25a and 25b having dimensions larger than those of slot 21.

[0087] According to an alternative embodiment shown in FIG. 5A, the contact probe 20 may also have arms made of a low specific electrical resistivity material forming a conductive central insert 25; in this case, the contact probe 20 has the conductive insert 25 and the support arm 22b separated by a slot 21, as shown in FIG. 5A and in the sections of FIGS. 5B-5D cut at the planes π1-π3 arranged as described above.

[0088] In this case, the conductive insert 25 has dimensions similar to those of the support arm 22b.

[0089] Although not shown in FIG. 5A, it is also possible to construct both arms 22a and 22b from a low specific electrical resistivity material; in this case, contact probe 20 includes a pair of conductive inserts separated by slot 21.

[0090] According to a further alternative embodiment shown in FIG. 6A, the conductive insert 25 may comprise a conductive central insert 25c arranged in the slot 21, as in the embodiment shown in FIG. 2A, and further conductive portions 26a-26d formed from a low specific electrical resistivity material and arranged in the probe body 20C near the contact head 20B and the contact tip 20A so as to be completely embedded in the structurally stable material forming the contact probe 20, as shown in the sections of FIGS. 6B-6D cut at the planes π1-π3 arranged as previously described in FIG. 6A.

[0091] These further conductive portions 26a-26d make it possible to further increase the overall current carrying capacity of the contact probe 20 with respect to the embodiment shown in Fig. 2A, even if the overall dimensions of the contact probe 20 do not make it possible to accommodate a conductive insert formed by a plurality of foils having a sufficiently large diameter D or suitable for carrying current values ​​of more than 800 mA. It is emphasized that these further conductive portions 26a-26d are completely embedded in the contact probe 20, in particular in a structurally stable material that is mechanically resistant with respect to the low specific electrical resistivity material of which it is formed and of which the conductive insert 25 is made, so that it makes it possible to increase the current carrying capacity of the contact probe 20 without significantly affecting its structural stability.

[0092] Alternatively, as shown in FIG. 7A, and in particular as shown in the sections of FIGS. 7B-7D cut at the plane π1-π3 shown in FIG. 7A and arranged as described above, the contact probe 20 comprises a conductive insert 25 made to extend in a central portion along the entire contact probe 20, for example from the slot 21 but also outside the slot 21, along the contact tip 20A to the first contact area 23A, and along the contact head 20B to the second contact area 23B.

[0093] In this way, the conductive insert 25 further increases the current carrying capacity of the contact probe 20, for example with respect to the embodiment shown in Fig. 2A, without introducing any weak areas in the structurally stable material of which the contact probe 20 is made, in particular thanks to the partial embedding at the contact tip 20A and at the contact head 20B. Moreover, such a conductive insert 25, which extends from the contact head 20B to the contact tip 20A of the contact probe 20 along its entire longitudinal development, preferably forms a preferential, unobstructed path for the current flowing through said probe.

[0094] According to a further alternative embodiment shown in Fig. 8A, the contact probe 20 comprises a conductive insert 25 extending in the longitudinal direction and formed by at least two conductive inserts 25a, 25b arranged in the two arms 22a and 22b, in particular in their centers, so as to be integrated by the structurally stable material of which the contact probe 20 is made. In the embodiment shown in this figure, the conductive inserts 25a, 25b extend along the entire extension of the contact probe 20, up to the edge of the contact head 20B of the contact tip 20A, as they appear against the structurally stable material of which the contact probe 20 is made, as shown in the section of Figs. 8B-8D cut in the plane π1-π3 shown in Fig. 8A and arranged as described above.

[0095] Obviously, it is possible to make the conductive inserts 25a and 25b extend in the arms 22a and 22b for a length less than the entire length of the contact probe 20, either only in the slot 21 or completely embedded in a structurally stable material, the length of the conductive inserts 25a and 25b being selected based on the current carrying capacity required for the contact probe 20 for its particular application.

[0096] Furthermore, it is possible to make conductive inserts 25a and 25b extending in arms 22a and 22b to emerge in slot 21, as shown in Figure 9A; in particular, conductive inserts 25a and 25b are made in side walls SLa and SLb of slot 21 itself, as shown in the sections of Figures 9B to 9D cut at planes π1 to π3 shown in Figure 9A and arranged as described above.

[0097] In this manner, the contact probe 20 appears to be compatible with different manufacturing methods used in the art of the present invention adapted to manufacturing processes having different constraints.

[0098] Furthermore, as shown in Fig. 10A, it is possible to make the contact probe 20 with a conductive insert 25 formed by a plurality of conductive inserts extending longitudinally within the contact probe 20; in particular, the conductive insert 25 comprises a pair of conductive inserts 25a and 25b arranged in the arms 22a and 22b, and a conductive central insert 25c arranged in the slot 21. In the illustrated embodiment, as shown in the sections of Figs. 10B-10D cut in the planes π1-π3 shown in Fig. 10A and arranged as described above, the conductive inserts 25a and 25b extend along the entire extension of the contact probe 20 up to the edges of the contact tip 20a and of the contact head 20B, and the conductive central insert 25c extends up to the contact areas 23a and 23b.

[0099] Such a conductive insert 25 makes it possible to maximize the overall current carrying capacity of the contact probe 20 and ensure the possibility of using such a contact probe 20 also for reduced pitch applications, without significantly affecting its mechanical behavior, which remains governed by structurally stable materials, and without increasing its overall lateral dimensions, in particular the diameter Dc of the probe body 20C, and the overall dimensions of the probe, relative to the previously described embodiments.

[0100] The invention also relates in particular to a probe head 30 comprising a plurality of contact probes 20 made as described above, each having at least one contact end, in particular end 20A, configured to abut a contact pad 40A of an integrated device under test 40. Such a probe head may be used in applications with high frequency and high current signals, each contact probe 20 having an overall length LS of less than 5000-7000 μm and comprising a conductive insert 25 configured for the current carrying capacity required for the specified application.

[0101] As shown diagrammatically in Fig. 11, the probe head 30 may comprise at least one plate-like support or guide, preferably a pair of guides 31, 32 with a number of guide holes 31A, 32A arranged to slidably accommodate a contact probe 20 according to the embodiment of Fig. 2A, by way of example only, having a second contact end, in particular a contact head 20B, arranged to abut against a contact pad 50A of a PCB 50 connected to a test device (not shown). Preferably, the guide hole is dimensioned to have a transverse diameter smaller than the diameter Db of the contact head 20B, so that the enlarged portion 24 can abut against the face F1 of the guide 31 and ensure a correct holding of the corresponding contact probe 20. The term "diameter" in any case denotes the maximum transverse dimension also in case of non-circular holes.

[0102] Alternatively, the contact probes 20 may be welded to a support of the probe head 30, particularly at their ends placed in the test apparatus, with each contact tip 20A in any case configured to abut against a pad 40A of the device under test 40.

[0103] A contact probe having at least one conductive insert interleaved based on the needs of a particular application, the contact probe having the conductive insert being arranged to transmit a high current signal. And it is emphasized that it is also possible to make the probe head with contact probes that do not have such inserts.

[0104] In summary, a contact probe made according to an embodiment of the present invention makes it possible to solve the problem of transmitting high current signals while ensuring a reduced mechanical resistance of the probe as a whole and limited forces on the pads, so as to reduce, if not eliminate, the risk of breaking the pads or even the probe, especially in the case of short probes (i.e. with a length of less than 5000-7000 μm). The presence of a conductive insert, preferably made of a low specific electrical resistance material, makes it possible to obtain a contact probe with a low electrical resistance value with respect to the probes currently used in the technical field. Moreover, since said conductive insert is arranged in the bending plane of the contact probe comprising it, it can improve the mechanical strength of the probe as a whole.

[0105] In particular, the above-mentioned contact probes, thanks to their reduced dimensions, smaller than 5000-7000 μm, have particularly high-performance operating characteristics suitable for their use in high-frequency applications, in particular at frequencies greater than 1000 MHz, and the presence of slots in the body of the contact probe makes it possible to reduce its stiffness and dramatically reduces the likelihood of breaking the probe, while ensuring a suitable reduction in the pressure exerted by the corresponding contact tip, avoiding possible breakage of the contact pads of the device under test and of the probe itself.

[0106] Furthermore, the use of a conductive insert having dimensions suitable for placement within the contact probe keeps its overall dimensions virtually unchanged and enables its use for fine pitch applications.

[0107] In particular, advantageously, according to the present invention, the combined use of the support arm and of the conductive insert makes it possible to make short or ultra-short probes that minimize electrical resistance and maximize current carrying capacity over a wide temperature range, in particular from -55°C to +150°C and above.

[0108] Tests carried out by the Applicant itself have shown that it is possible to obtain contact probes that apply a maximum force of 2.5-3 g against the pads of the device under test and the space transformer, respectively, avoiding damage to these pads or to any of the contact bumps, while guaranteeing a minimum force of 1.0-1.5 g to ensure good electrical contact between the probes and the contact pads / bumps, while facilitating correct management of the load even in products with a larger number of probes (more than 30,000).

[0109] Advantageously, the contact probe according to an embodiment of the present invention represents a geometrically scalable solution, where the combined use of support arms and conductive inserts ensures accurate fatigue resistance even in extreme conditions of a 1M contact with a maximum applied vertical displacement (100 μm OD [overdrive]) and reduced thermal relaxation (force variation of less than 10% after 100 h at maximum applied displacement in addition to controlling the plastic deformation of the contact probe as a whole).

[0110] Furthermore, the presence of the enlarged portion at the contact head end ensures correct retention of the contact probe inside the probe head, especially when the probe head is not abutting the device under test or also during cleaning operations.

[0111] Finally, the advantages connected with the fact that the contact probes can be made in a simple manner and at low cost should not be overlooked, since they can be made using conventional photolithographic methods, or using MEMS techniques (microelectromechanical systems) or even by laser techniques, starting from a multilayer material comprising a structurally stable material of which the contact probes are made and a low specific electrical resistivity material of which the conductive inserts are made, in particular a multilayer material having layers of structurally stable material and low specific electrical resistivity material grown parallel to the longitudinal development direction of the probe and its arms.

[0112] The considerations made are also valid for different embodiments not specified here but which are in any case the subject of the invention, such as, for example, a probe head with a single guide and a probe blocked in the corresponding contact head, etc. Furthermore, the measures adopted with respect to the embodiments may also be used for the other embodiments and can be freely combined with one another, even in numbers greater than two.

[0113] Obviously, in order to meet non-specific and specific requirements, those skilled in the art may make numerous modifications and variations to the contact probe described above, all of which fall within the scope of protection of the present invention as defined by the following claims.

[0114] For example, it is possible to make a contact probe without any enlargement or to provide it with a suitable stopper made protruding from the probe body to ensure correct positioning and retention of the probe inside the probe head, possibly in combination with an enlargement at the contact head end.

Claims

1. A contact probe (20) comprising a probe body (20C) extending between a first end (20A) and a second end (20B) and having at least a pair of arms (22a, 22b) separated by a slot (21) made in said probe body (20C) according to a longitudinal deployment direction of the contact probe (20), at least one of the arms (22a, 22b) has at least one conductive insert (25a, 25b) arranged in a bending plane (α) of the contact probe (20) and extending inside the contact probe (20) along the longitudinal direction of development, said conductive inserts (25a, 25b) are made of a first material having a specific electrical resistivity lower than the specific electrical resistivity of a second material of which said contact probe (20) is made, and have a transverse dimension (D) perpendicular to said longitudinal extension direction that is lower than the corresponding transverse dimension (D2a, D2b) of said arms (22a, 22b); A contact probe (20), wherein the conductive inserts (25a, 25b) are power transmission elements and the arms (22a, 22b) are structural support elements for the contact probe (20) during deformation of the probe body (20C).

2. The contact probe (20) of claim 1, wherein the first material has a specific electrical resistivity of less than 30 μΩ·cm.

3. 2. The contact probe (20) of claim 1, wherein the first material is a conductive or semiconductive material with low specific electrical resistivity selected from gold (Au), copper (Cu), silver (Ag), aluminum (Al), platinum (Pt), and alloys thereof, and the second material is a structurally stable conductive material selected from nickel, tungsten, cobalt, palladium, or alloys thereof, nickel-manganese, nickel-cobalt, nickel-palladium or nickel-tungsten, palladium-cobalt alloys, palladium-based ternary and quaternary alloys.

4. The contact probe (20) of claim 1, wherein the first material is silver and the second material is palladium-cobalt.

5. The contact probe (20) of claim 1 , wherein the conductive inserts (25a, 25b) have the lateral dimension (D) less than 20 μm.

6. 2. The contact probe (20) of claim 1, wherein the lateral dimension (D) of the conductive inserts (25a, 25b) is equal to 20% to 60% of the smallest value of the lateral dimensions (D2a, D2b) of the arms (22a, 22b).

7. The contact probe (20) of claim 1, wherein the conductive inserts (25a, 25b) have a length (L1) equal to a length of the arms (22a, 22b).

8. The contact probe (20) of claim 1 , wherein the probe body (20C) comprises an alternating arrangement of the arms (22a, 22b) and conductive inserts (25, 25a, 25b, 25c).

9. 2. The contact probe (20) of claim 1, wherein the conductive insert (25a, 25b) comprises further conductive portions (26a-26d) made of the first material and fully embedded within the second material of which the contact probe (20) is made.

10. The contact probe (20) of claim 9, wherein the further conductive portions (26a-26d) are realised in the first end (20A) and the second end (20B) of the contact probe (20).

11. 2. The contact probe (20) of claim 1, wherein the conductive insert (25a, 25b) extends along the entire contact probe (20) and appears to the second material in first and second contact areas (23A) and (23B) made at the first and second ends (20A) and (20B) of the contact probe (20), respectively.

12. The contact probe (20) of claim 1 , wherein the conductive inserts (25a, 25b) comprise respective conductive inserts (25a, 25b) extending longitudinally in the arms (22a, 22b).

13. 13. The contact probe (20) of claim 12, wherein each of the conductive inserts (25a, 25b) extending in each of the arms (22a, 22b) is made to be fully embedded within the second material forming the arm (22a, 22b).

14. 13. The contact probe (20) according to claim 12, wherein each of the conductive inserts (25a, 25b) extending in each of the arms (22a, 22b) is made to emerge at a side wall (SLa, SLb) of the slot (21).

15. The contact probe (20) of claim 1, wherein the conductive inserts (25a, 25b) have a length along the longitudinal direction of deployment that is less than a length (LS) of the contact probe (20).

16. The contact probe (20) of claim 1, wherein the conductive inserts (25a, 25b) have a length along the longitudinal direction of development such that they emerge from the second material forming the contact probe (20).

17. A probe head (30) for testing an integrated device (40) comprising a plurality of contact probes (20) having at least one end (20A) configured to abut against a contact pad (40A) of the integrated device (40), A probe head (30) made according to any one of claims 1 to 16 and comprising a plurality of contact probes (20) having a probe body (20C) with arms (22a, 22b) and at least one conductive insert (25a, 25b).

18. 20. The probe head (30) of claim 17, comprising: a first plurality of contact probes (20) having a probe body (20C) with arms (22a, 22b) and at least one conductive insert (25a, 25b); and a second plurality of contact probes (20) having a probe body (20C) with arms (22a, 22b) and lacking at least one conductive insert (25a, 25b).

19. 20. The probe head (30) of claim 17, comprising only the plurality of contact probes (20) having the probe body (20C) with the arms (22a, 22b) and the at least one conductive insert (25a, 25b).

Images