CONTACT PROBE FOR PROBE HEADS OF ELECTRONIC DEVICES AND CORRESPONDING PROBE HEAD

Abstract

A contact probe is disclosed having a first end portion with a contact tip adapted to abut onto a contact pad of a device under test, a second end portion with a contact head adapted to abut onto a contact pad of a board of a test equipment, a probe body extended between the first and the second end portions according to a longitudinal development axis, and an elastic stopper provided in an elastic portion of the probe body arranged contiguous to the second end portion. The elastic stopper is deformable between a first working condition, in which it has a transversal diameter greater than a transversal diameter of the probe body, and a second working condition in which it has a transversal diameter corresponding to the transversal diameter of the probe body.

Claims

1.-20. (canceled)

21. A contact probe having: a first end portion which ends with a contact tip adapted to abut onto a contact pad of a device under test; a second end portion which ends with a contact head adapted to abut onto a contact pad of a board of a test equipment; a probe body extended between the first end portion and the second end portion according to a longitudinal development axis and having a transversal diameter; and an elastic stopper provided in an elastic portion of the probe body arranged contiguous to the second end portion and having a transversal diameter, wherein the elastic stopper is elastically deformable between a first working condition, in which the transversal diameter of the elastic stopper is greater than the transversal diameter of the probe body, and a second working condition in which the transversal diameter of the elastic stopper is equal to the transversal diameter of the probe body, wherein the transversal diameter means a maximum transversal dimension of a section, even not circular, taken according to a plane orthogonal to the longitudinal development axis.

22. The contact probe of claim 21, wherein the elastic stopper includes an opening which is provided in the elastic portion of the probe body and defines therein two opposite arms which are able to move close and away according to a transversal direction orthogonal to the longitudinal development axis.

23. The contact probe of claim 22, wherein the opening is drop-shaped with decreasing dimensions along the elastic portion of the probe body towards the second end portion.

24. The contact probe of claim 22, wherein the opening extends along the elastic portion of the probe body over a length equal to a length of the elastic portion.

25. The contact probe of claim 22, wherein the opening has a non-symmetrical shape adapted to define an arm protruding with respect to a side wall of the contact probe.

26. The contact probe of claim 25, wherein the opening extends in correspondence of an arm which has a free end.

27. The contact probe of claim 26, wherein the free end of the arm faces a rounded portion of the probe body.

28. The contact probe of claim 22, wherein the opening has an oval shape adapted to define a first arm and a second arm which are equal, symmetrical and contiguous, protruding from opposite walls of the contact probe.

29. The contact probe of claim 22, wherein the opening has an oval shape interrupted at an arm and adapted to define a first portion therein having a first free end and a second portion having a second free end, the elastic stopper being C-shaped.

30. The contact probe of claim 21, wherein the probe body has a predeformed shape with a curvilinear configuration comprising a bow in rest conditions, when the contact probe is not in contact pressing onto a contact pad of a device under test, according to an arc having a value ranging between 1 and 5.

31. The contact probe of claim 21, further comprising a further opening, which extends along the probe body, being so formed by a first longitudinal arm and a second longitudinal arm, parallel to each other and extended along the longitudinal development axis, separated by the further opening.

32. The contact probe of claim 21, further comprising a portion with reduced section which forms a flexing neck positioned in the probe body in correspondence of the first end portion.

33. The contact probe according to claim 21, wherein the contact tip has a reduced transversal diameter of a diameter of a remaining part of the first end portion and a length according to the longitudinal development axis of between 300 m and 600 m.

34. The contact probe according to claim 21, wherein the contact head has a reduced transversal diameter of a diameter of a remaining part of the second end portion and a length according to the longitudinal development axis of between 100 m and 400 m.

35. The contact probe according to claim 21, wherein the contact tip has a reduced transversal diameter of a diameter of a remaining part of the first end portion and a length according to the longitudinal development axis between 300 m and 600 m and the contact head has a reduced transversal diameter of a diameter of a remaining part of the second end portion and a length according to the longitudinal development axis of between 100 m and 400 m.

36. The contact probe of claim 21, wherein the second end portion comprises an enlarged portion, having a transversal diameter greater than a diameter of a remaining part of the second end portion.

37. A probe head for verifying the functionality of a device under test comprising: a plurality of contact probes; a single upper guide provided with upper guide holes; and a single lower guide provided with lower guide holes, the upper guide holes and lower guide holes being adapted to house the plurality of contact probes; wherein each of the plurality of contact probes has: a first end portion which ends with a contact tip adapted to abut onto a contact pad of a device under test; a second end portion which ends with a contact head adapted to abut onto a contact pad of a board of a test equipment; a probe body extended between the first end portion and the second end portion according to a longitudinal development axis and having a transversal diameter; and an elastic stopper provided in an elastic portion of the probe body arranged contiguous to the second end portion and having a transversal diameter, wherein the elastic stopper is elastically deformable between a first working condition, in which the transversal diameter of the elastic stopper is greater than the transversal diameter of the probe body, and a second working condition in which the transversal diameter of the elastic stopper is equal to the transversal diameter of the probe body, wherein the term transversal diameter means maximum transversal dimension of a section, even not circular, taken according to a plane orthogonal to the longitudinal development axis; and wherein the elastic stopper is positioned between the single upper guide and the single lower guide, near the single upper guide.

38. The probe head of claim 37, further comprising an upper frame, associated with the single upper guide and provided with respective upper openings adapted to house the contact probes and a lower frame, associated to the single lower guide and provided with respective lower openings adapted to house the contact probes.

39. The probe head of claim 38, wherein the upper openings of the upper frame house the second end portions of the contact probes with clearance and wherein the lower openings of the lower frame house the first end portions of the contact probes with clearance, the contact tips projecting starting therefrom towards the device under test.

40. The probe head of claim 38, wherein the single lower guide has a thickness along said longitudinal development axis greater than a thickness of the single upper guide and wherein the upper frame has a thickness comparable to the thickness of the single lower guide and the lower frame has a thickness comparable to the thickness of the single upper guide, wherein comparable has the meaning that the difference between the thicknesses is 20%.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0048] In such drawings:

[0049] FIG. 1 schematically shows a frontal view of a probe head made according to the prior art;

[0050] FIG. 2 schematically shows a frontal view of a contact probe made according to the present invention;

[0051] FIGS. 3A-3B, 4A-4B, 5A-5B show respective frontal views of alternative embodiments of a detail of the contact probes made according to the present invention;

[0052] FIGS. 6A-6B schematically show respective frontal views of alternative embodiments of the contact probe according to the present invention;

[0053] FIGS. 7A-7C schematically show respective frontal views of alternative embodiments of a probe head according to the present invention.

MODES FOR CARRYING OUT THE INVENTION

[0054] With reference to said figures, and in particular to FIG. 2, it is described a contact probe made according to the present invention, overall indicated with 20.

[0055] It is worth noting that the figures are schematic views and are not drawn to scale, but instead they are drawn so as to emphasize the important features of the invention. Moreover, in the figures, different elements are depicted in a schematic manner, and their shape may vary depending on the desired application. Furthermore, particular features illustrated in a figure in relation to an embodiment can also be used in one or more of the embodiments illustrated in the other figures.

[0056] Furthermore, structurally and functionally equal elements in the different embodiments, which are illustrated in the various figures and described, are indicated with the same alphanumeric references.

[0057] Finally, in the following description, comparative terms such as over, under, upwards, downwards will be used referring to the illustrations of the probes and probe heads given in the figures only to simplify the exposition thereof.

[0058] The contact probe 20 comprises at least one first end portion 20A which ends with a contact end adapted to abut onto a pad or contact pad of a device under test and indicated as contact tip 20F, a second end portion 20B which ends with a contact end adapted to abut onto a contact pad of a board of a test equipment and indicated as contact head 20E and a probe body 20C which is rod-shaped and extended between the end portions 20A and 20B, along a longitudinal development axis HH of the probe, substantially along the direction z of the local reference of the figure.

[0059] The contact tip 20F has a length LA according to the direction z comprised between 300 m and 600 m, preferably equal to 450 m and the contact head 20E has a length LB according to the direction z comprised between 100 m and 400 m, preferably equal to 250 m.

[0060] The probe body 20C preferably has a transversal diameter DC with a value which is substantially constant and equal to the diameter of the first end portion 20A and to the diameter of the second end portion 20B, said diameters being preferably equal to each other.

[0061] Suitably, according to the present invention, the probe body 20C has a predeformed shape, in the example illustrated in FIG. 2 a bow shape, that is a bow shape with the curvature change point for example at a midpoint of the probe body 20C with respect to the extension thereof along the longitudinal development axis HH. The bow shape of the contact probe 20, in particular of the probe body 20C thereof, is in particular also present in non-working conditions of the probe, that is before the same bends and deforms during the test.

[0062] The bow predeformation of the contact probes 20 guarantees that the same bend in a same desired direction, also when housed in a single upper guide which is not able to facilitate said bending direction as the double shifted guides of the known solutions. It can be verified in a simple way that it is enough to predeform the probe body 20C according to an arc having a value ranging between 1 and 5, preferably between 2 and 3 in order to obtain the desired effect of forcing of the bending direction of the probes.

[0063] The contact probe 20 has an overall length L comprised between 2 mm and 8 mm. Such values are so when the contact probe 20 is in rest or non-working conditions, that is when it does not abut onto a contact pad of a device under test.

[0064] Preferably, for high-frequency applications, the contact probe 20 has an overall longitudinal extension L, which varies between 3 mm and 5 mm, preferably between 3.8 mm and 4.6 mm.

[0065] Such dimensional ranges for the overall extension of the contact probe 20 guarantee that the same can be used for high-frequency applications and remains elastic during the test, that it bends or compresses during the pressing contact of the contact tip thereof onto a contact pad of a device under test without plastically deforming, that is not in a definite way, so that it could be then reused.

[0066] The overall longitudinal extension L of the contact probe 20 can be furthermore reduced for particular applications which were more recently developed, down to values lower than 3 mm, preferably also lower than 2.5 mm.

[0067] Suitably according to the present invention, the contact probe 20 furthermore comprises an elastic stopper 21, made at an elastic portion of the probe body 20C arranged contiguous to the second end portion 20B and having a length LG comprised between 100 m and 400 m, preferably equal to 250 m.

[0068] In the embodiment example of FIG. 2, said elastic stopper 21 is made by an opening Ap which extends along the elastic portion 20G, preferably along all the longitudinal extension of the elastic portion 20G.

[0069] The presence of the opening Ap particularly defines two opposite portions in the elastic portion 20G which are able to move close and away according to a transversal direction, that is orthogonal to the longitudinal development axis HH, corresponding to the direction x of the local reference of the figure.

[0070] Preferably, the elastic stopper 21 has a symmetrical shape, so as to be able to provide a contrast action to a movement of the contact probe 20 with respect to a guide hole in which it is housed regardless of the bending direction of the predeformed shape thereof or without a pair of guides which performs an offset thereof, as it occurs in the known solutions, so as to guarantee a correct operation of a contact head which comprises said probes during testing and cleaning operations, also when the probe head is released from the test equipment.

[0071] It is underlined that the elasticity of the elastic stopper 21 furthermore advantageously allows the passage of the contact probe 20 into a respective guide hole during the assembly operations, as well as the extraction thereof by an operator during possible maintenance operations which require for example the removal and substitution of the same contact probe 20, anyway guaranteeing a correct holding even when the probe head which houses it is not in contact pressing onto a device under test or with a board of a test equipment, said elastic stopper 21 being able to efficiently contrast the movement of the contact probe 20 due to the effect of the force of gravity when the probe head is separated by the device under test or disassociated from the test equipment, as well as in presence of other transversal forces, such as during cleaning operations which are normally carried out by air jets.

[0072] More in particular, as schematically shown in the enlargement of FIG. 3A, said elastic stopper 21 is provided in the elastic portion 20G of the contact probe 20, by a drop-shaped opening Ap, that is with increasing dimensions along the elastic portion 20G towards the probe body 20C and a maximum opening value indicated as opening diameter Dap having a value comprised between 10 m and 30 m and a length Lap which is substantially equal to the length LG of the elastic portion in which the elastic stopper 21 is provided. The elastic stopper 21 thus substantially has the shape of a needle eye, the presence of the drop-shaped opening Ap defining two opposite portions in the elastic portion 20G, that is a first arm 21a and a second arm 21b, which are able to move close or away one another according to the transversal direction x.

[0073] More in particular, the drop-shaped opening Ap is sized so as to enlarge the elastic portion 20G up to dimensions greater than a guide hole made in a guide of a probe head which houses the contact probe 20, in particular an upper guide hole of an upper guide 31 above the elastic stopper 21. In other words, the elastic stopper 21 has a transversal diameter DG greater than a diameter DGF of an upper guide hole 31A made in the upper guide 31 and adapted to house the contact probe 20.

[0074] Thereby, the elastic stopper 21 is able to prevent or at least hinder the movement of the contact probe 20, once inserted in the probe head, upwards that is according to the direction z, considering the local reference of the figure, as will be better explained in the following, when the contact probe 20 is subjected to forces according to the direction z which are comparable to the force of gravity, that is in the normal working conditions of the probe head which houses the contact probe 20, also when not in test conditions and thus non resting onto a device under test, but also to transversal forces, that is in the direction x, that is in cleaning conditions made by air jets, as usual in the field.

[0075] In a preferred embodiment, as illustrated in FIG. 3A, the contact tip 20F has a transversal diameter DF reduced with respect to a transversal diameter DA of a remaining part of the first end portion 20A, transversal diameter meaning a maximum transversal dimension of a section, even not circular, taken according to a plane orthogonal to the longitudinal development axis HH, that is to the the direction z. In particular, the contact tip 20F has a transversal diameter DF comprised between 20-60%, preferably equal to 50% of the diameter DA of the first end portion 20A.

[0076] Similarly, the contact head 20E has a transversal diameter DE reduced with respect to a transversal diameter DB1 of a remaining part of the second end portion 20B. In particular, the contact head 20E has a transversal diameter DE comprised between 20-60%, preferably equal to 50% of the transversal diameter DB1 of the second end portion 20B.

[0077] By suitably dimensioning the lengths LA, LB of the contact tip 20F and of the contact head 20E, respectively, it is possible to increase the service life of the contact probes 20 which are so made and thus of the probe head which comprises then, said reduced portions which are substantially cylindrical in shape can wear out because of the effect of the touches on the contact pads without changing the shape of the transversal section thereof and thus the parameters which define the mechanical and electronic contact of the probes and the respective pad. This feature is particularly advantageous for the contact tips 20F which, in addition to the wear connected to the contact with the pads of the device under test, are also subjected to cleaning operations on abrasive cloths which further increase the wear thereof.

[0078] Furthermore, the presence of the contact tip 20F with reduced dimensions makes the contact probe 20 suitable for testing a device under test with contact pads with reduced area.

[0079] Suitably, the second end portion 20B is also provided with an enlarged portion 20D having a transversal diameter DB2 greater than the transversal diameter DB1 of the second end portion 20B outside said enlarged portion 20D (DB2>DB1). More in particular, the transversal diameter DB2 of the enlarged portion 20D is chosen so as to be greater than the diameter DGF of the upper guide hole 31A in which the contact probe 20 is housed (DB2>DFG), said enlarged portion 20D preventing a movement of the contact probe 20, downwards, in a direction opposite with respect to the direction z of the local reference of the figure.

[0080] Advantageously according to the present invention, the elastic stopper 21 is able to squash itself, moving the first arm 21a and the second arm 21b close to each other until the transversal diameter DG thereof reaches dimensions DG corresponding to those of the diameter DFG of the upper guide hole 31A in which the contact probe 20 is housed (DGDFG), so as to allow the passage also of the elastic portion 20G through said upper guide hole, as schematically shown in FIG. 3B. In these conditions, the opening Ap can reduce to null and the first arm 21a can rest onto the second arm 21b. It is thus possible, applying suitable tensile forces to the contact probe 20 which are able to overcome the elasticity of the arms 21a and 21b of the elastic stopper 21, to extract the contact probe 20 from the probe head in which it was assembled, allowing for example the substitution thereof. Such tensile forces are in particular upwards, that is according to the direction z of the local reference of the figures.

[0081] In other words, the elastic stopper 21 is elastically deformable between a first condition in which it has a transversal diameter DG greater than the transversal diameter DC of the probe body 20C and it is able to carry out a contrast action to a movement of the contact probe 20 with respect to a guide hole of an upper guide in which the probe is housed and a second working condition in which it has a transversal diameter DG which substantially corresponds to the transversal diameter DC of the probe body 20C and it is able to pass in the guide hole, substantially corresponding meaning that the difference between said diameters is 20%. The first working condition is thus a normal working condition, that is the test of a device under test carried out by the probe head which comprises the contact probes 20, said probes being in a pressing contact onto the pads of the device under test or the normal cleaning operations of said probe head, the transversal dimensions of the elastic stopper 21 contrasting possible upwards movements of the contact probe 20, while the second working condition corresponds for example to maintenance or assembly operations, when the contact probes 20 are made to pass through the guide holes.

[0082] According to an alternative embodiment not represented in the figure, the contact probe 20 can also comprise an elastic stopper 21 made by an opening with a shape which is non-symmetrical with respect to the longitudinal development axis HH thereof, only one of the arms defined by said asymmetrical opening protruding with respect to a side wall of the contact probe 20 so as to come into contrast with the upper guide above said elastic stopper 21.

[0083] According to another embodiment variation which is schematically illustrated in FIG. 4A, the elastic stopper 21 comprises an opening Ap with a non-symmetrical shape and which extends also at the first arm 21a, said first arm 21a thus having a free end 21c which faces a rounded portion 22 of the probe body 20C under said elastic stopper 21. According to said variation, only the first arm 21a protrudes with respect to a side wall of the contact probe 20 and is adapted to come into contrast with the upper guide 31 which houses said probe, said first arm 21a with free end 21c being the deformable portion of the elastic stopper 21.

[0084] Suitably, when the contact probe 20 is housed in the upper guide hole 31A, the opening Ap is inserted for a length Ld in said upper guide hole 31A, the first arm 21a being spaced apart from the second arm 21b and protruding with respect to the side wall of the contact probe 20 after said length Ld. The length Ld is preferably equal to 20-30% of the overall length Lap of the opening Ap.

[0085] More in particular, in rest conditions after assembly, the point of maximum side extension of the first arm 21a is anyway not in contact with the upper guide 31, so as to guarantee a correct transmission of the force on the contact head 20E of the contact probe 20 during the pressing contact of the contact tip 20F onto a pad of a device under test.

[0086] Also in this case, the elastic stopper 21 can be squashed, moving the first arm 21a and the second arm 21b close to each other until the transversal diameter DG reaches dimensions DG corresponding to those of the diameter DFG of the upper guide hole 31A in which the contact probe 20 is housed (DGDFG), so as to allow the passage thereof into the upper guide hole 31A, as schematically shown in FIG. 4B.

[0087] It is underlined that in any case the free end 21c of the first arm 21a does not rest onto the rounded portion 22 of the probe body 20C, so as to avoid any plastic deformation of said first arm 21a.

[0088] According to a further alternative embodiment illustrated in Figure the opening Ap has a substantially oval shape, still adapted to provide a first arm 21a and a second arm 21b which are substantially equal, symmetrical and contiguous and are able to be moved close in order to let the elastic stopper 21 pass through an upper guide hole which houses the contact probe 20. Such alternative embodiment has the advantage to be totally symmetrical and to reduce possible stress points in the elastic portion 20G where the opening Ap is made.

[0089] Furthermore, the opening Ap with a substantially oval shape can be interrupted for example at the first arm, providing a first portion 21a1 of first arm having a first free end 21c1 and a second portion 21a2 of first arm having a second free end 21c2, the elastic stopper 21 being in such case substantially C-shaped, as schematically shown in FIG. 5B.

[0090] According to this alternative embodiment, when the contact probe 20 is in contact pressing onto a contact pad of a device under test, the elastic stopper 21 can more easily deform in the direction z, in particular closing the C at the free ends 21c1 and 21c2 of the portions 21a1 and 21a2 of the first arm.

[0091] To improve the elasticity of the contact probes 20, it is provided a further opening 23, which extends along the probe body 20C, being so formed by at least one first longitudinal arm 24a and a second longitudinal arm 24b, which are substantially parallel to each other and extended along the direction z, and are separated by said opening 23, as schematically illustrated in FIG. 6A.

[0092] It is obviously possible to consider contact probes having a probe body 20C crossed by a plurality of opening 23 and thus provided with more than two longitudinal arms substantially extended along the direction z.

[0093] The contact probe 20 can further comprise a portion with reduced section which provides a flexing neck 25 positioned in the probe body 20C at the first end portion 20A, as schematically shown in FIG. 6B. Said flexing neck 25 is able to further improve the elasticity of the contact probe 20, at a section of the same subjected to high stresses, more in particular a section which is contiguous to a junction point of the longitudinal arms.

[0094] More in particular, said flexing neck 25 has a section reduced of 30-60% with respect to a section of the probe body 20C, more preferably equal to 50% of the section of the probe body 20C.

[0095] In the embodiment illustrated in FIG. 6B, the flexing neck 25 is preferably arranged at the centre of the contact probe 20, in a concentric way with respect the first end portion 20A, along the direction z and is obtained by a removal of material in a symmetric way between at least two opposite sides of the contact probe 20, so as not to negatively affect the bending mechanism of the contact probe 20 and the scrub of the contact tip 20F thereof.

[0096] Although the embodiment illustrated in FIG. 6B shows a contact probe 20 provided both with the further opening 23 and with the flexing neck 25 it is also possible to provide the same so as to comprise only the flexing neck 25.

[0097] The present invention also refers to a probe head of the type with vertical probes, only comprising a pair of guides provided with housing holes of a plurality of contact probes made as above illustrated.

[0098] More in particular, referring to FIG. 7A, it is described a probe head 30 comprising a plurality of probes made according to the embodiment illustrated in FIG. 2, that is contact probes which are predeformed to a bow and provided with an elastic stopper 21.

[0099] The probe head 30 comprises a first plate-shaped guide or upper guide 31, commonly indicated as upper die, provided with suitable upper guide holes 31A for housing the contact probes 20, as well as a second plate-shaped guide or lower guide 32, commonly indicated as lower die, also provided with suitable lower guide holes 32A for housing the contact probes 20. As seen in connection to the prior art, the upper guide 31 and the lower guide 32 are spaced apart from each other so as to define an air gap between them where the contact probes 20 are free to bend during the pressing contact of the contact tip portions 20F thereof onto a contact pad 35A of a device under test 35 integrated on a semiconductor wafer 36, the corresponding contact heads 20E abutting onto contact pads 37A of an interface board 37 with the test equipment of which the probe head 30 is an end element. As seen in connection with the prior art, said board 37 can be a so-called space transformer.

[0100] Suitably, the probe head 30 also comprises an upper frame 33, associated with the upper guide 31 and provided with respective upper openings 33A adapted to house the contact probes 20 and a lower frame 34, associated with the lower guide 32 and also provided with lower openings 34A for housing the contact probes 20. Preferably, the upper frame 33 and the lower frame 34 are ceramic or metallic elements.

[0101] More in particular, the upper frame 33 is fixedly connected to the upper guide 31 thanks to the use of connecting elements such as screws, pins or elastic films and analogously the lower frame 34 is fixedly connected to the lower guide 32 still by connecting elements such as screws, pins or elastic films. The upper frame 33 and the lower frame 34 are thereby integral with the upper guide 21 and the lower guide 32, respectively, and act as structural reinforcement elements thereof, as well as alignment instrument of the contact probes 20 during assembly of the probe head 30. It is thereby possible to use guides, preferably ceramic, with reduced thicknesses which simplify the sliding of the contact probes 20 inside the holes thereof.

[0102] As shown in FIG. 7A, the contact probe 20 is housed or integrated in the probe head 30 such that the second end portion 20B thereof is inserted in an upper guide hole 31A of the upper guide 31 with the enlarged portion 20D abutting with the undercut wall thereof onto an upper face of said upper guide 31, that is the face of the upper guide 31 facing the upper frame 33, thereby acting as holding element of the contact probe 20 to prevent the movement thereof downwards, in a opposite direction z of the local reference of FIG. 7A.

[0103] In particular, the upper guide hole 31A of the upper guide 31 is dimensioned so as to house the second end portion 20B under the enlarged portion 20D with clearance but to prevent the passage of said enlarged portion 20D, while the upper opening 33A of the upper frame 33 has dimensions adapted to house both the enlarged portion 20D and the contact head 20E of the contact probe 20.

[0104] Furthermore, advantageously according to the invention, the contact probe 20 is housed in the probe head 30 such that the elastic stopper 21 thereof is positioned under the upper guide hole 31A of the upper guide 31, so as to prevent or at least hinder a movement of the contact probe 20 upwards, that is according to the direction z of the local reference of FIG. 7A. Thereby, the elastic stopper 21 is positioned near the upper guide 31, near meaning that the elastic stopper 21 extends starting from a lower face of the upper guide downwards, that is in a direction opposite the direction z of the local reference of FIG. 7A.

[0105] The contact probe 20 further has the first end portion 20A housed in the lower guide hole 32A of the lower guide 32, dimensioned so as to house said first end portion 20A with clearance, while the contact tip 20F protrudes under the lower guide 32 towards the device under test 35 so as to abut onto a contact pad 35A thereof.

[0106] The upper guide 31 and the lower guide 32 as well as the upper frame 33 and the lower frame 34 are parallel to each other and extend along a reference plane n, which is the same along which also the semiconductor wafer 36 and the device under test 35 as well as the board 37 of the test equipment develop.

[0107] Furthermore, the lower guide 32 is suitably dimensioned so as to assist the movement of the contact probes 20 in overdrive during the testing operations when said probes abut onto the device under test 35.

[0108] More in particular, the lower guide 32 has a thickness H2 along the direction z greater than the thickness H1 of the upper guide 31, preferably equal to 1.8-2 times the thickness H1 of the upper guide 31. In a preferred embodiment, the upper guide 31 has a thickness H1 which varies from 0.100 mm to 0.150 mm, preferably equal to 0.125 mm while the lower guide 32 has a thickness H2 which varies from 0.150 mm to 0.300 mm, preferably equal to 0.254 mm.

[0109] Suitably according to the embodiment illustrated in FIG. 7A, the upper frame 33 has a thickness H3 comparable, preferably equal, to the thickness H2 of the lower guide 32 and the lower frame 34 has a thickness H4 comparable, preferably equal to the thickness H1 of the upper guide 31, comparable meaning that the difference between the two thicknesses is 20%.

[0110] Thereby, the assembly of the upper guide 31 and the upper frame 33 has a thickness comparable, preferably equal to the assembly of the lower guide 32 and of the lower frame 34, so as to guarantee a dynamic and elastic symmetry of the contact probe 20 and of the probe head 30 as a whole.

[0111] It is also possible to provide the probe head 30 housing therein a plurality of contact probes 20 made according to the embodiment of FIG. 6A, as schematically illustrated in FIG. 7B.

[0112] In such case, the contact probes 20 also comprise respective longitudinal openings 23 provided in the probe body 20C at the air gap between the upper guide 31 and the lower guide 32, said longitudinal openings 23 defining in the probe body 20C respective longitudinal arms 24a, 24b which improve the elasticity of the probes as a whole, in particular preventing the breakage of the same probes or of the contact pads of the device under test also in the case of short probes adapted to radiofrequency applications.

[0113] Furthermore, as schematically illustrated in FIG. 7C, the contact probes 20 can also be provided with respective flexing necks 25, which are suitably positioned at the end of the probe body 20C at the lower frame 34, possibly housed in the lower openings 34A of said lower frame 34, further improving the bending of the contact probes 20, so as to lower the risks of breakage of the same probes or of the pads of the device under test.

[0114] To conclude, the contact probe provided with at least one elastic stopper is adapted to be used in a probe head comprising only one upper guide and only one lower guide, said elastic stopper guaranteeing a correct holding of the probe inside said head, while removing the need to increase the diameter of the guide holes which house the probe, since said stopper can be passed through guide holes having diameters which are substantially corresponding to those of the probes by virtue of the elasticity thereof.

[0115] In particular, advantageously according to the present invention, the elasticity of the elastic stopper allows the passage of the contact probe into a respective guide hole during the assembly operations, as well as the extraction thereof by an operator during possible maintenance operations which require for example the removal or substitution of the same probe, still guaranteeing a correct holding also when the probe head which houses it is not in contact pressing onto a device under test or with a board of a test equipment thanks to the contrast made by said elastic stopper, which is able to prevent the movement of the probe because of the effect of gravity when the probe head is separated by the device under test or disassociated from the test equipment, as well as in presence of other transversal forces, such as during cleaning operations which are normally carried out by air jets.

[0116] Suitably, said elastic stopper is made so as to protrude with respect to at least one of the side walls of the probes, preferably with respect to both the side walls, so as to come into contrast with a guide above it to prevent displacements of the probes during the normal testing, maintenance or cleaning operations of the probe head which comprises them.

[0117] The contact probes can be furthermore predeformed so as to ease the uniform bending of the same when they are housed in a corresponding probe head, in particular during the contact pressing onto a device under test during the testing operations carried out by the probe head, so as to reduce to the minimum the risk of contact between adjacent probes, also without a pair of shifted guides such as in the known solutions.

[0118] Preferably, the probes comprise end contact portions having reduced transversal diameters and suitable lengths which are able to allow a wear thereof due to the effect of the testing or cleaning operations, increasing the service life of the probe head as a whole, in addition to allowing the testing of pads with reduced dimensions.

[0119] Suitably, the elastic stopper can be provided in a very simple way by an opening formed in the probe body and adapted to define at least one pair of portions of said body which are able to move close or away with respect to each other. The elastic stopper can also have an open shape at one of the arms thereof, which simplifies the deformation thereof when the contact probe is longitudinally subjected to the force of gravity or other transversal forces.

[0120] It is furthermore possible to provide the probes with openings made in the probe body thereof to form a plurality of longitudinal arms and/or of flexing necks so as to improve the elasticity of the probes as a whole.

[0121] It is thereby possible to provide the probes with particularly reduced overall lengths and thus adapted to applications in the more recent technologies, for example for very high-frequency applications using only a pair of guides, anyway guaranteeing the correct holding of the probes inside them.

[0122] The contact probe according to the present invention thereby allows to also overcome the drawbacks of the known solutions comprising double guides to provide an offset of the probes, which, in particular in presence of a great number of contact probes, can convey onto the device under test a transversal force which is able to cause undesired displacements thereof.

[0123] Obviously, a person skilled in the art, in order to meet contingent and specific requirements, may make to the contact probe and to the probe head above described numerous modifications and variations, all included in the scope of protection of the invention as defined by the following claims.

[0124] In particular, it is possible to consider any shape for the opening which provides the elastic stopper, in addition to the use of possible flexible materials for filling the same, as well as any number of longitudinal openings to form any number of arms in the probe body.

[0125] Finally, it is possible to provide the contact probe of the present invention with further expedients, such as other geometrical configurations of the contact tip and head portions or the presence of coating films.