Improved measuring system for electronic devices

Abstract

It is herein described a measuring system (100) including a probe head (100) which comprises a plurality of contact probes (1) and an interface board (9). The interface board (9) comprises an interface body (I) and a related test pad (9A, 9B, 9C) at each contact probe (1) of the plurality of contact probes, said contact probe (1) comprising a first end portion (2) that ends with a contact tip (2A) configured to abut onto a contact pad of a device under test and a second end portion (3) which ends with a contact head (3A) configured to abut onto the related test pad (9A, 9B, 9C) of the interface board (9), as well as a probe body (4) extended between the first end portion (2) and the second end portion (3) according to a longitudinal development axis (HH). Furthermore, each related test pad (9A, 9B, 9C) comprises at least one integrated resistive portion (11A, 11B, 11C).

Description

[0001] Title: Improved measuring system for electronic devices

[0002] DESCRIPTION

[0003] Field of application

[0004] The present invention relates to a measuring system adapted to perform the test of electronic devices integrated on a semiconductor wafer. The following description is made with reference to this application field with the only purpose of simplifying the exposition thereof.

[0005] Prior art

[0006] As it is well known, a probe head is basically a device adapted to electrically connect a plurality of contact pads of a microstructure, in particular an electronic device under test, or DUT, integrated on wafers, with corresponding channels of a testing apparatus that performs the functionality testing thereof, in particular electric, or generically the test.

[0007] The test, which is performed on integrated devices, is particularly useful for detecting and isolating defective devices as early as in the production phase. Normally, probe heads are therefore used for the electric test of electronic devices that are integrated on wafers before cutting and assembling them inside a chip containment package.

[0008] A probe head usually comprises a high number of rod-shaped contact elements or contact probes formed by special alloys with good electric and mechanical properties and provided with at least one contact portion with one of the contact pads of the device under test.

[0009] More particularly, a vertical probe head comprises a plurality of contact probes housed in guide holes made in at least one, preferably at least one pair of plate guides, parallel to each other and arranged at a certain distance, in order to leave a free area or air gap for the movement and possible deformation of the contact probes. The pair of guides in particular comprises an upper guide, arranged closer to the testing apparatus connected to the probe head, and a lower guide, arranged closer to a wafer comprising the devices under test, both guides being provided with respective guide holes within which the contact probes axially slide.

[0010] In particular, as visible in exemplifying Figure 1, each contact probe 1 comprises at least one first end portion 2 which ends with a contact end adapted to abut onto a pad or contact pad 8A of a device under test 8 integrated on a semiconductor wafer 8’, said contact end being indicated as contact tip 2A.

[0011] The first end portion 2 comprises a support part 2B adapted to be housed in a respective guide hole of a guide of a probe head comprising at least one contact probe 1 , in particular a guide hole 6A of a lower guide 6, namely a guide arranged close to the device under test 8 during the testing phases. The first end portion 2 also comprises, contiguous to the support part 2B, a protruding part 2C projecting from the lower guide 6 toward the device under test 8 and ends with the contact tip 2A to make the connection with the contact pads 8A of the device under test 8 by means of a pressing contact thereon.

[0012] Furthermore, 1 the contact probe 1 comprises a second end portion 3 which ends with a contact end adapted to abut onto a test pad T of an interface board 9 with a testing apparatus, said contact end being indicated as contact head 3A. The interface board 9 may be a board made according to the integrated circuit or PCB board techniques in contact with the testing apparatus or a space transformer interposed between the probe head and the PCB board. As well known, a space transformer comprises a first plurality of contact pads made on a first face thereof facing toward the probe head 10 (indicated as probe side pads) and a second plurality of contact pads made on a second face thereof, opposite the first face and facing toward the PCB board and thus the testing apparatus (indicated as test side pads), connected to each other by means of suitable electric connections inside the space transformer, the test side pads may be made with a distance of their centers (pitches) that is greater than the pitch of the probe side pads, namely the test pads T, which thus may be made with distances compatible with the distances between the contact pads 8A of the device under test and therefore allow the connection with the contact probes 1 closer to each other.

[0013] The interface board 9 along with the probe head 10, with its plurality of contact probes 1, form a so-called “measuring system” 100, commonly called in the field “probe card”.

[0014] Even the second end portion 3 of each contact probe 1 comprises a support part 3B adapted to be housed in a guide hole of a further guide of the probe head that comprises the contact probe 1, in particular a guide hole 7A of an upper guide 7, namely a guide positioned close to the interface board 9 with the testing apparatus.

[0015] The second end portion 3 further comprises, contiguous to the support part 3B, a protruding part 3C, projecting from the upper guide 7 in the direction of the interface board 9 and ends with the contact head 3A adapted to make the connection with the test pads T of said interface board 9, by means of a pressing contact thereon.

[0016] The second end portion 3 may also comprise an enlarged portion 5, i.e. a portion with increased diameter than the diameter of the rest of the contact probe 1 , in particular greater than the diameter of the upper guide holes 7A, said enlarged portion 5 being formed in the protruding part 3C, arranged between the support part 3B and the contact head 3A.

[0017] Finally, the contact probe 1 comprises a probe body 4, substantially rod-shaped and extended between the first end portion 2 and the second end portion 3, according to a longitudinal development axis HH of the contact probe 1, substantially in the z direction of the local reference of Figure 1. In particular, the contact probes 1 are arranged inside the probe head 10 with longitudinal development axes HH arranged parallel to each other and orthogonal to the lower guide 6 and to the upper guide 7.

[0018] In the following description, the term longitudinal will thus be used to indicate elements arranged according to a direction or a plane parallel to the longitudinal development axis HH, thus orthogonal to a development plane n of the device under test (and thus of the wafer in which it is integrated) and of the interface board with the testing apparatus.

[0019] As it is well known, the proper connection between the contact probes of the probe head and the contact pads of the device under test is ensured by the pressure of the probe head on the device itself, the contact probes, movable within the guide holes of the upper and lower guides, undergoing, during said pressing contact, a bending inside the air gap between the guides and a sliding inside the respective guide holes.

[0020] In Electrical Wafer Sort (EWS) testing applications, in particular of memories, a point-to-multipoint type resource sharing configuration, namely with a unique testing apparatus connected to a plurality of devices under test, is required.

[0021] In an implementation of this type in the prior art, as visible in exemplifying Figure 2, the use of a plurality of “protection” resistors 9’ is provided, generally of 300-330 , to be set up for each device under test 8, in particular in the interface board 9 close to the test pads T.

[0022] In this way, in the event of a failure of one of said devices under test, the respective protection resistor “isolates” the failure while still allowing the proper operation of the other devices connected to the same testing apparatus.

[0023] This solution, although effective and widely used, is particularly complex from the point of view of practical implementation.

[0024] Indeed, a test in which the potential of a single testing apparatus is fully used may also include 2000-2500 devices tested simultaneously, each of which can require up to twenty resistors.

[0025] It is therefore easy to calculate that the number of resistors to be installed may arrive to almost 50,000, said resistors having to find a place on a single device.

[0026] It is easy to understand how this request, as mentioned, is particularly burdensome and is also subject to multiple possibilities of error.

[0027] The technical problem of the present invention is thus to provide a configuration of a measuring system able to overcome the drawbacks still affecting the current prior art solutions, in particular in the parallel test of a plurality of devices.

[0028] An object of the invention is also to provide a solution that is highly effective.

[0029] A further object of the invention is to provide a solution that can be adapted according to specific testing needs.

[0030] Finally, an object of the invention is to provide a solution that is easy to maintain.

[0031] Summary of the invention

[0032] The solution idea underlying the present invention is to integrate the protection resistance function against failures of the devices under test in a contact probe.

[0033] Based on this solution idea, the technical problem is solved by a measuring system comprising a probe head and an interface board.

[0034] The interface board may be a PCB board or a space transformer.

[0035] The probe head comprises a plurality of contact probes.

[0036] The interface board comprises an interface body and a related test pad at each contact probe of the plurality of contact probes.

[0037] Each contact probe of the plurality of contact probes comprises a first end portion that ends with a contact tip configured to but onto a contact pad of a device under test and a second end portion that ends with a contact head configured to abut onto a related test pad of the interface board.

[0038] Each contact probe also comprises a probe body extended between the first end portion and the second end portion according to a longitudinal development axis.

[0039] Suitably, each related test pad comprises at least one integrated resistive portion.

[0040] Advantageously, the present solution allows eliminating the need to have multiple electrical protection resistors arranged singularly inside the testing apparatus and to have an integrated and specific solution that allows improving the overall electrical performance.

[0041] The integrated resistive portion may be made integral or be removably coupled to the related test pad, depending on the contingent needs and preferences in the production and maintenance phases.

[0042] According to a first embodiment of the invention, the at least one resistive portion is made at a contact area of a contact probe of the plurality of contact probes with the related test pad.

[0043] Advantageously, said solution allows concentrating the desired resistive features in the interest point, namely the point in which there is the connection of the contact probe with the related test pad.

[0044] Preferably, the at least one resistive portion has a longitudinal development dimension along the longitudinal development axis comprised between 10 pm and 200 pm and a transversal dimension, orthogonal to the longitudinal development axis, comprised between 20 pm and 100 pm. Advantageously, said dimensional ranges of the resistive portion, which allow obtaining the desired resistive values, fall within the optimal specifications required to integrate in the production of the current measuring systems and of the related probe heads with contact probes.

[0045] In some variants, the longitudinal dimension of the resistive portion, for instance, may be such as to correspond to the entire longitudinal dimension of the related test pad. In this case, the resistive portion thus emerges at both transversal faces of the test pad.

[0046] According to another embodiment, the at least one resistive portion is made at a part of perimeter of the related test pad.

[0047] Advantageously, the present embodiment distributes the needed resistivity of the related test pad onto an interface surface.

[0048] In a preferred embodiment, the at least one resistive portion is made at the entire perimeter of the related test pad.

[0049] Advantageously, the present embodiment distributes the needed resistivity of the related test pad between the surface on which the contact between the contact probe and the related test pad occurs and the current transmission surface from the test pad to the interface body of the interface board.

[0050] In another preferred embodiment, the at least one resistive portion is made at a part of perimeter of the related test pad corresponding to an outer surface of the test pad comprising a contact point of a contact probe of the plurality of contact probes with the related test pad. Advantageously, the present embodiment allows both concentrating the needed resistivity of the related test pad where the actual contact with the contact probe occurs, and distributing it on the entire affected surface. Moreover, said embodiment also makes it easier to disassemble the resistive portion, if possible.

[0051] According to another embodiment of the invention, the at least one test pad comprises a first pad portion comprising an outer surface of the test pad having a contact point of a contact probe of the plurality of contact probes with the related test pad and a second pad portion comprising a contact surface of the test pad with the interface body of the interface board, and the at least one resistive portion is interposed between the first pad portion and the second pad portion.

[0052] Advantageously, the present embodiment allows embedding the resistive portion into the related test pad, thus protecting it and allowing it to be formed according to the most suitable geometries for the desired resistive features, separating the portion of the pad on which the contact occurs from the portion adapted to exchange current with the interface body of the interface board according to said needs.

[0053] According to a preferred embodiment, the resistive portion has a resistance value comprised between 20 > and 400 □, preferably comprised between 25 > and 350 □, more preferably comprised between 300 > and 330 □.

[0054] Advantageously, the present embodiment allows eliminating the need to have multiple electrical protection resistors set up inside the testing apparatus and optimizing the resistance, now advantageously included in the related test pad, in relation to each device under test, thus improving the overall electrical performance of the measuring system thus made.

[0055] Preferably, the at least one resistive portion may be made of at least one plastic material.

[0056] Advantageously, the materials of said class are very efficient but at the same time easy to find and therefore low cost.

[0057] More preferably, the at least one resistive portion comprises partially electrically conductive composite materials or carbon materials or high resistivity metal materials.

[0058] Advantageously, these specific materials ensure optimal resistivity features, but also mechanical resistance ones, the latter feature being always required given the stresses to which the probes are subjected on the related test pads during the implementation of the various connections during the test operations.

[0059] The features and advantages of the measuring system according to the invention will be apparent from the description, made hereinafter, of embodiments thereof, given by way of indicative and nonlimiting example, with reference to the appended drawings.

[0060] Brief description of the drawings

[0061] In these drawings:

[0062] Figure 1 schematically shows a frontal view of a measuring system made according to the prior art;

[0063] Figure 2 schematically shows a memory EWS testing application with a point-to-multipoint type resource sharing configuration according to the prior art;

[0064] Figures 3A, 3B show variants of a first embodiment of a measuring system according to the present invention, whereas Figure 3C shows a top view thereof;

[0065] Figures 4A, 4B, 4C show variants of a second embodiment of a measuring system according to the present invention;

[0066] Figure 5 shows a third embodiment of a measuring system according to the present invention.

[0067] Detailed Description

[0068] With reference to these figures, there is shown a measuring system 100 made according to the present invention, specifically a section SI, S2, S3 including a probe head 10 having a plurality of contact probes 1 and at least one test pad 9A, 9B, 9C which replaces the test pad T according to the prior art.

[0069] It should be noted that the figures represent schematic views and are not drawn to scale, but instead they are drawn so as to enhance the important features of the invention. Furthermore, in the figures, the different pieces are shown schematically, since their shape may vary according to the desired application. Moreover, particular expedients illustrated in a figure in relation to an embodiment may also be used in one or more of the embodiments illustrated in the other figures.

[0070] Furthermore, structurally and functionally equal elements in the several figures, and in particular analogous to the prior art solutions as above described, are indicated hereinafter with the same alphanumeric references. In the following description, relative terms such as “above”, “below”, “upwards”, “downwards” will be used with reference to the illustrations of the probes and of the probe heads given in the figures with the only purpose of simplifying the exposition thereof.

[0071] Finally, indications of particular geometries (circular, rectangular) or of the arrangement of the elements (parallel, orthogonal, contiguous), as well as the term “substantially” are always to be intended in relation to physical elements and not to geometrically abstract ones, and therefore must always take into account the tolerances introduced by the passage from a pure mathematical / geometric world to the real world.

[0072] The test pad 9A, 9B, 9C according to the present invention is made to be implemented into a measuring system 100 which, in an EWS testing application, in particular of memories, unlike the prior art, does not need to be punctually connected to a related so-called protection resistor.

[0073] The test pad 9A, 9B, 9C, according to the invention, comprises a resistive portion 11A, 11B, 11C. Clearly nothing prevents from providing different resistive portions within a single test pad 9A, 9B, 9C.

[0074] In Figure 3A, an embodiment is specifically depicted, in which a test pad T according to the prior art and a test pad 9A according to the present invention and comprising the at least one resistive portion 11A, in this embodiment made at a contact area A of a contact probe 1 with the related test pad 9A, are represented close to each other.

[0075] Advantageously, said embodiment allows concentrating the desired resistive features in the interest point, namely the point in which there is a physical connection of the contact probe with the related test pad.

[0076] In a variant shown in Figure 3B, the longitudinal dimension of the resistive portion 11A coincides with that of the test pad 9A itself, in this way increasing the volume of material designed to carry out the resistive function, selected according to the specific test condition.

[0077] In general, the at least one resistive portion 11A according to this embodiment of the invention has a longitudinal dimension L comprised between 10 pm and 200 pm and a transversal dimension D comprised between 20 pm and 100 pm. In particular, herein and hereinafter, the term “longitudinal” will indicate directions, axes, planes along a longitudinal development axis HH of the contact probes 1 and the term “transversal” will indicate directions, axes, planes orthogonal to said longitudinal development axis HH.

[0078] Advantageously, said dimensional ranges fall within the optimal specifications required to integrate into the production of the current measuring systems and the related probe heads with contact probes, since, in particular, they are compatible with the transversal dimensions of the contact areas A of the contact heads 3A of the contact probes 1 on the test pads and with the longitudinal dimensions or thicknesses of said test pads.

[0079] Figure 3C shows a top view of the contact area A of Figures 3 A and 3B, a view that is common to the embodiment variants above indicated. In the present embodiment, it can be appreciated that the resistive portion is centred and coaxial in the contact area A of the test pad, but nothing prevents, of course, from positioning the resistive portion differently on the related test pad, in addition to providing different dimensions D, W in the transversal direction and in a depth direction, respectively. The dimension W in the depth direction may be comprised between 20 pm and 100 pm.

[0080] Instead, Figure 4A shows an embodiment in which a test pad T according to the prior art and a test pad 9B comprising a resistive portion 11B made at a part of perimeter of the related test pad 9B are close to each other.

[0081] In this way, an improved distribution of the desired resistivity on the entire test pad 9B is obtained.

[0082] Specifically, Figure 4A illustrates an embodiment in which the at least one resistive portion 1 IB is made at a part of perimeter of the test pad 9B corresponding to an outer surface of said test pad 9B that comprises the contact point between contact probe 1 and test pad 9B.

[0083] In other words, in this case a resistive portion 1 IB that covers the entire outer surface on which the contact probe 1 abuts onto the test pad 9B is provided.

[0084] The present embodiment allows both concentrating the resistivity of the test pad 9B where the actual contact with the probe occurs, and distributing it on the entire surface of the pad affected by said contact. Moreover, said embodiment simplifies a possible disassembly, if possible and needed, of the resistive portion 1 IB from the test pad 9B. In a variant shown in Figure 4B, the resistive portion 11B is instead made on a portion of perimeter of the test pad 9B corresponding to the separation surface between the test pad 9B and an interface body I of the interface board 9, in this way obtaining a shift of the resistive function on the surface where the test pad 9B exchanges a current flow with the interface board 9.

[0085] Still alternatively, in a variant shown in Figure 4C, the resistive portion 1 IB is made at the entire perimeter of the test pad 9B, completely surrounding it.

[0086] In this way, the present embodiment distributes the resistivity of the test pad 9B made by means of the resistive portion 11B between the surface where the contact occurs between contact probe 1 and said test pad 9B and the current transmission surface from the test pad 9B to the interface body I of the interface board 9.

[0087] In a further variant not represented, it is possible to provide for a test pad entirely made of resistive material, by selecting the structure, geometry and material in order to have a desired overall resistivity in addition to an appropriate electrical connection with the contact probe.

[0088] According to a further embodiment, shown in Figure 5, where a test pad T according to the prior art and a test pad 9C are shown close to each other, said test pad 9C includes a first pad portion 9C1 comprising an outer surface of the test pad 9C, where there is the contact point with the related contact probe 1, and a second pad portion 9C2 comprising the contact surface between test pad 9C and interface body I of the interface board 9. The test pad 9C further comprises a resistive portion 11C interposed between the first pad portion 9C1 and the second pad portion 9C2.

[0089] In the embodiment represented by way of example in Figure 5, the interface portion 11C is in the shape of an inverted wedge, inside the test pad 9C, so as to achieve a separation that does not provide for alternative paths for the current passing in said test pad 9C which bypass the resistive portion 11C.

[0090] Of course, nothing prevents from providing for different conformations of the resistive portion 11C that still allow subdividing the test pad 9C into two separated portions and that still force the current to pass through the resistive portion 11C without there being any alternative paths that could deviate from this crossing and therefore from obtaining a test pad with an integrated resistance.

[0091] Advantageously, the present embodiment allows embedding the resistive portion 11C into the test pad 9C, so as to protect it and make it according to the most suitable geometries to obtain the desired resistive features, by separating, based thereon, the pad portion 9C1 whereon the contact occurs from the pad portion 9C2 adapted to exchange current with the interface board 9.

[0092] In the above described embodiments, preferably the at least one resistive portion 11A, 1 IB, 11C has a resistance value greater than 20 □. In particular, in a preferred embodiment, the resistive portion 11A, 1 IB, 11C has a resistance value comprised between 20 > and 400 □, preferably between 250 > and 350 □, more preferably between 300 > and 330 □, so as to achieve the desired failure protection function of a corresponding device under test, as described in connection to the prior art.

[0093] Moreover, the resistive portion 11A, 1 IB, 11C is generally made integral inside the respective test pad 9A, 9B, 9C.

[0094] However, the resistive portion 11A, 11B, 11C may also be removably integrated to the test pad 9A, 9B, 9C, so that only said resistive portion 11A, 11B, 11C may be replaced for maintenance reasons. For instance, the resistive portion 11A, 11B, 11C is associated, in particular glued, with the related test pad 9A, 9B, 9C by an adhesive film.

[0095] Furthermore, nothing prevents from also adopting a plurality of different and separate resistive portions 11A, 11B, 11C, all made in the test pad 9A, 9B, 9C.

[0096] The resistive portion 11A, 11B, 11C may be made of different materials, depending on the contingent needs, both at a structural level and at a desired resistance level.

[0097] For the requirements of a memory EWS testing application, it is still preferred for the resistive portion to be made of plastic materials.

[0098] Preferably, from tests carried out by the Applicant, materials comprising partially electrically conductive composite materials or carbon materials or high resistivity metallic materials have been selected.

[0099] Indeed, these materials allow for a good balance precisely between the structural features, which are always required, and the resistive features sought, in particular for the memory EWS test.

[0100] Of course, a big difference is also made by the selected size of the resistive portion 11A, 1 IB, 11C, which also defines which material is most suitable in each case.

[0101] It is emphasized that the contact probe according to the present invention allows overcoming the drawbacks of the known solutions, primarily by eliminating the need for individual protection resistors to be assembled individually in the probe card, in particular in its interface board with the testing apparatus.

[0102] Moreover, advantageously, it is possible to get the resistive portion of the test pads, which acts as a protection resistor, closer to the device under test, thus improving the overall electrical performance.

[0103] Furthermore, advantageously according to the present invention, it is possible to vary the overall features of a measuring system thus made, by simply using test pads with different resistive features.

[0104] Still advantageously, it is possible to provide for different resistive portions that act as separation of the test pad crossed by the current flow, resistive portions removable or not and with different conformations, so as to be suitable for the various specific solutions for contingent needs.

[0105] It is also possible to maintain the measuring system more easily in case of problems with some test pads, with a usual replacement operation thereof.

[0106] Moreover, it is possible to provide for measuring systems in which different types of test pads according to the invention alternated to each other are adopted, or even, as also seen in the embodiments represented above, to provide test pads according to the invention close to test pads according to the prior art, depending on the different test needs to be carried out.

[0107] Obviously a person skilled in the art, in order to satisfy contingent and specific requirements, may make to the contact pads and to the measuring systems above described numerous modifications and variations, all included in the scope of protection of the invention as defined by the following claims.

[0108] In particular, it is possible to consider any shape of the contact probe as a whole and / or of the related test pad.

[0109] Finally, it is possible to provide the test pads of the present invention with further features, such as particular geometric configurations or, as said, different materials.

Claims

CLAIMS1. A measuring system (100) including a probe head (10) which comprises a plurality of contact probes (1) and an interface board (9), said interface board (9) comprising an interface body (I) and a related test pad (9A, 9B, 9C) at each contact probe (1) of said plurality of contact probes, said contact probe (1) comprising a first end portion (2) that ends with a contact tip (2A) configured to abut onto a contact pad of a device under test and a second end portion (3) which ends with a contact head (3A) configured to abut onto said related test pad (9A, 9B, 9C) of said interface board (9), as well as a probe body (4) extended between said first end portion (2) and said second end portion (3) according to a longitudinal development axis (HH), characterized in that each related test pad (9A, 9B, 9C) comprises at least one integrated resistive portion (11A, 1 IB, 11C).

2. The measuring system (100) according to claim 1, wherein said at least one resistive portion (11A) is made at a contact area (A) of a contact probe (1) of said plurality of contact probes with said related test pad (9A).

3. The measuring system (100) according to claim 2, wherein said at least one resistive portion (11A) has a longitudinal development dimension (L) along said longitudinal development axis (HH) comprised between 10 pm and 200 pm and a transversal dimension (D), orthogonal to said longitudinal development axis (HH), comprised between 20 pm and 100 pm.

4. The measuring system (100) according to claim 1, whereinsaid at least one resistive portion (1 IB) is made at a part of perimeter of said related test pad (9B).

5. The measuring system (100) according to claim 4, wherein said at least one resistive portion (1 IB) is made at an entire perimeter of said related test pad (9B).

6. The measuring system (100) according to claim 4, wherein said at least one resistive portion (1 IB) is made at a part of perimeter (P) of said related test pad (9B) corresponding to an outer surface of said test pad (9B) comprising a contact point of said contact probe (1) of said plurality of contact probes with said related test pad (9B) .

7. The measuring system (100) according to claim 1, wherein said at least one test pad (9C) comprises a first pad portion (9C1) comprising an outer surface of said test pad (9C) comprising a contact point of said contact probe (1) of said plurality of contact probes with said related test pad (9C) and a second pad portion (9C2) comprising a contact surface of said test pad (9C) with said interface body (I) of said interface probe (9), and said at least one resistive portion (11C) is interposed between said first pad portion (9C1) and said second pad portion (9C2).

8. The measuring system (100) according to any one of claims 1 to 7, wherein said at least one resistive portion (11A, 11B, 11C) has a resistance value comprised between 20 > and 400 □, preferably comprised between 25 > and 350 □, more preferably comprised between 300 > and 330 □.

9. The measuring system (100) according to any one of claims 1 to 8, wherein said at least one resistive portion (11A, 1 IB, 11C) is madeof at least one plastic material.

10. The measuring system (100) according to claim 9, wherein said at least one resistive portion (11A, 11B, 11C) comprises partially electrically conductive composite materials or carbon materials or high resistivity metallic materials.

11. The measuring system (100) according to any one of claims 1 to 10, wherein said at least one resistive portion (11A, 11B, 11C) is removably coupled with said at least one test pad (9A, 9B, 9C).

12. The measuring system (100) according to any one of claims 1 to 10, wherein said at least one resistive portion (11A, 11B, 11C) is integrally made inside said at least one test pad (9A, 9B, 9C).

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