AND CORRESPONDING PROBE HEAD

DESCRIPTION

Technical Field

The present invention relates to a testing head of a testing equipment of electronic devices.

The invention relates in particular, but not exclusively, to a testing head with vertical probes for the testing of electronic devices, in particular integrated on wafer and the following description is made with reference to this field of application with the only aim of simplifying its presentation.

Background Art

As is well known, a testing head is essentially a device adapted to put into electrical connection a plurality of contact pads of a microstructure, in particular an electronic device integrated on wafers, with corresponding channels of a testing equipment that performs its functionality check, in particular the electrical one, or generically the testing.

The test performed on integrated devices is particularly useful to detect and isolate flawed devices already in the manufacturing stage. Usually, the probe cards are thus used for electrically testing wafer integrated devices before their cutting and assembling in a chip containment package.

A testing head in particular comprises a plurality of movable contact elements or contact probes held by at least a pair of plates or guides substantially in the shape of plates and parallel between each other. Such guides are equipped with apposite holes and located at a certain distance between them so as to leave a free zone or an air zone for the movement and possible deformation of the contact probes. The pair of guides comprises in particular an upper guide and a lower guide, , the adjective "upper" and "lower" being used in the field with reference to a testing head during its working and corresponding to the illustration of the figures, the testing head being positioned between the testing equipment (above) and a wafer comprising the devices to be tested (below).

Both guides are equipped with guide holes wherein the contact probes slide axially, normally formed by wires of special alloys having good electrical and mechanical properties.

The testing head is further completed by an envelope or case arranged between the upper and lower guides, normally made in ceramic and adapted to contain the probes.

The good connection between the contact probes and respective contact pads of the device to be tested is assured by the pressure of the testing head on the device itself, i.e. on the wafer that comprises it, the contact probes, movable within the guide holes made in the upper and lower guide, being subjected to a bending in occasion of such pressing contact, within the free zone between the two guides and a sliding within such guide holes.

Testing heads of this kind are commonly named vertical probe heads.

Vertical probe heads substantially have a free zone wherein a bending of the contact probes happens, and is thus indicated as bending zone; the bending of the contact probes can be further helped by a suitable configuration of the probes themselves and/ or a suitable positioning of the guides.

In some cases, the contact probes are bound to the testing head in correspondence to the upper guide in a fixed manner, for example by means of bonding: this is the case of blocked probe head.

More frequently, however, testing heads are used with probes that are not bound in a fixed manner, but held interfaced to a spatial transformation board, commonly indicated as "space transformer" being in a probe card which includes the testing head: this is the case of unblocked probe head.

A probe card comprising an unblocked vertical probe head is schematically shown in figure 1 , where for sake of illustration simplicity only one contact probe of the plurality of probes normally comprised in such testing head is illustrated.

In particular, the probe card 10 comprises the testing head 1 arranged between a space transformer 8 and a device to be tested 7 and in turn comprising at least one upper guide 3 and a lower guide 4, made by means of plate-shaped supports substantially plane and parallel between them and having respective upper guide holes 3A and lower guide holes 4A within which the respective contact probes 2 slide.

The testing head 1 also comprises a case 5, which functions as stiffener and that contains the contact probes 2, arranged between the upper and lower guides, 3 and 4. The case 5 in particular extends in correspondence of an air or bending zone 6 between such guides.

Each contact probe 2 has a substantially rod-like body 2C and at least one end or contact tip 2A. With the terms end and tip it is indicated here and beyond a non necessarily sharp end section. In particular, the contact tip 2A abuts onto a contact pad 7A of the device to be tested 7, making the mechanical and electrical contact between said device and a testing equipment (not represented) whose probe card 10 forms a terminal element.

In the example illustrated in figure 1 , the contact probe 2 has a further contact end, usually indicated as testing head 2B, towards a plurality of contact pads 8A of the space transformer 8. The good electric contact between probes and space transformer is assured in a similar manner to the contact with the device to be tested by means of the pressure of the terminal portions, in particular of the tip or the head, of the contact probes on the respective contact pads.

The upper guide 3 and the lower guide 4 are opportunely distanced from the air or bending zone 6 that allows the deformation of the contact probes 2, the upper guide holes 3A and lower guide holes 4A being sized so as to allow a sliding of a respective probe inside them. A further zone called floating zone is defined between the upper guide 3 and the space transformer 8; such floating zone 9 is set so as to grant a movement of the contact heads 2B in occasion of the pressing contact of the testing head 1 - and thus of the contact probes 2 - onto the device to be tested 7, in particular of the contact tips 2A onto the contact pad 7A, still assuring the contact of the contact heads 2B with the contact pads 8A of the space transformer 8. In the case of a testing head realized in the technology so-called "with shifted plates", the contact probes 2, also indicated as "buckling beams", are made as straight, with a transversal section constant for their whole length, preferably rectangular. It is known to realize this type of testing heads by superimposing the guides so as to put into correspondence the respective guide holes, insert the contact probes into such guide holes, distance the guides to form the bending zone and then offset or shift such guides, provoking a deformation of the body of the probes, in a substantially central position, as illustrated in Figure 1. In this case, they are called shifted plate testing heads.

It is worth remembering that the proper working of a testing head, and thus of the probe card that contains it, is fundamentally bound to two parameters: the vertical movement, or overtravel, of the contact probes and the horizontal movement, or scrub, of the respective contact ends, in particular the contact tips 2A, whose scrub allows to superficially "clean" the contact pads 7 A of the device to be tested 7, improving the contact made by the testing head 1 for its entire working life.

It is also important to ensure that the floating zone 9 of the contact probes 2B of the contact heads 2 is sized so as to ensure that these heads are properly contacted onto the contact pad 8A of the space transformer 8.

All these characteristics are to be evaluated and calibrated during the steps of manufacturing of a testing head, the good electrical connection between probes and device to be tested always having to be guaranteed.

The contact ends of the contact probes, in particular the contact tips with the pads of the devices to be tested, are subjected to accumulation of material, generally indicated as dirt, during their use, which decreases their performance and may compromise the proper contact of the probes with the device to be tested, when the scrub of these tips is not able to provide electrical contact with the pads anyway.

It is therefore known to perform cleaning operations, in particular of the contact tips, by means of abrasive cloths. Obviously, such cleaning operations involve the consumption of a portion of the terminal portion of the probes, in particular of the contact tip, and are therefore limited in number precisely by the length of that tip, which becomes shorter at each cleaning. In particular, any subsequent abrasion of the terminal portion, namely of the contact tip, should be limited to the tapered probe portion projecting from the lower guide, which indeed realizes the contact tip.

The number of cleaning operations of the testing head actually determines its working life and consequently the working life of the probe card that contains it.

It is known from the International Patent Application (PCT) published on October 16, 2014 with No. WO 2014/ 167410 on behalf of the present Applicant to use a spacer element, removably interposed between the containment element and one of the upper and lower guides, so as to adjust the length of the terminal portions of the contact probes, in particular, in correspondence of the contact tips.

Although advantageous in various respects, such testing head has a drawback due to the fact that the variation in the length of the terminal portions by means of the removal of the spacer or of a layer thereof inevitably also modifies the air or bending zones of the contact probes, thereby modifying the contact dynamics and introducing problems in terms of the force exerted by the probes on the contact pads and also of the scrub allowed on them, in addition to modifying the deformation suffered by the probes in such free zone, with the risk of permanent deformations or entrapments of such probes in the respective guide holes.

The technical problem at the basis of the present invention is that of providing a testing head for electronic devices integrated on wafers, having structural and functional characteristics so as to allow an adequate number of cleaning operation of the contact probes comprised into the corresponding testing head without functional loss, overcoming the limitations and the drawbacks that still afflict the testing heads realized according to the prior art, in particular by guaranteeing a force exerted by the probes and the essential scrub mechanisms for a proper contact between probes and contact pads throughout the entire working life of the testing head and of the probe card that comprises it, even in case of subsequent cleaning operations.

Disclosure of Invention

The solution idea of the present invention is that of realizing a testing head comprising at least one couple of upper and/ or a couple of lower guides as well as at least one spacer element or spacer set inside the testing head, easily removable and possibly peelable, the removal of which, although partial, does not modify the extension of the bending zone of the probes, and thus the force exerted by them, in particular by exploiting the free zone that separates such couple of guides.

On the base of this solution idea, the technical problem is solved by a testing head of a testing equipment of electronic devices comprising a plurality of contact probes inserted into guide holes made in at least one upper support and in one lower support, at least one of these supports comprising a couple of parallel guides being separated by a free zone, as well as at least one spacer element interposed between the guides of an upper and/ or a lower support, in correspondence of such free zone.

In particular, the testing head according to the present invention comprises a plurality of contact probes inserted into guide holes realized in at least one upper support and one lower support, a bending zone for the contact probes being defined between such upper and lower supports, the contact probes having each at least one terminal portion projecting from the lower support with a first length and ending with a contact tip adapted to abut onto a respective contact pad of a device to be tested, as well as a second terminal portion projecting from the upper support with a second length and ending with a contact tip adapted to abut onto a contact pad of a space transformer. Suitably, one of said upper and/ or lower supports may comprise at least one couple of upper and/ or lower guides being plate-shaped and parallel between them, separated by a free zone of prefixed length, at least one spacer element being interposed between such at least one couple of upper and/ or lower couple of guides, said spacer element being removable to adjust the first length of the first terminal portion of the contact probes by changing the length of the free zone approaching the guides of the at least one couple of upper and/ or lower guides.

More in particular, the invention comprises the following additional and optional characteristics, taken individually or in combination, if needed.

According to one aspect of the invention, the spacer element may have an height inferior or equal to the length of the free zone. Furthermore, the spacer element may have at least one portion projecting with respect to the testing head, and in particular with respect to the upper and/ or lower support.

According to another aspect of the invention, the spacer element may comprise a plurality of overlapping and singularly removable layers. Moreover, the layers may be joined between them, particularly by means of a layer of adhesive material.

Additionally, the spacer element may be associated with the upper and/ or lower support, in particular by means of a layer of adhesive material.

According to another aspect of the invention, the layers may have respective portions projecting from the testing head and in particular from the upper and/ or lower support.

More in particular, such projecting portions of such layers may have different lengths from layer to layer. Furthermore, such layers may have a numbering applied onto the respective portions projecting from their face, such numbering being written or engraved or embossed or made by means of any other technique on projecting portions or one or more distinctive marks, formed by notches or reliefs, of any form and made with any suitable technique, in the number corresponding to the desired numbering.

According to another aspect of the invention, the testing head may comprise an upper support including a first and a second upper guide and a lower support including a first and a second lower guide, plate- shaped and parallel, separated by respective free zones, as well as at least one couple of spacer elements, each disposed between such couples of upper and lower guides in correspondence with the respective free zones.

According to another aspect of the invention, the spacer element may have an elongated shape, substantially rectangular.

More specifically, the spacer element may have a shape chosen between a paddle formed by an elongated body and by a head and a tab.

Alternatively, the spacer element may comprise at least a couple of semi-frames, substantially extended along opposite and parallel sides of said at least one couple of upper and/ or lower guides of the upper and/ or lower supports.

More in particular, the semi-frames that form the spacer element may have such dimensions to project with respect to said at least one couple of upper and/ or lower guides of the upper and/ or lower supports or may comprise at least one elongated portion adapted to project with respect to said at least one couple of upper and/ or lower guides of the upper and/ or lower supports.

According to another aspect of the invention, the spacer element may be made of a plastic material, transparent or semi-transparent, or of a ceramic material, or of a metallic material or of an organic material or of silicon, preferably of Kapton®.

Furthermore, according to another aspect of the invention, the testing head can comprise a plurality of spacers disposed between the couple of upper and/ or lower guides of the upper and/ or lower supports in positions, number and shape such as not to interfere with a proper working of the contact probes and thus of the testing head.

The invention also relates to a probe card for a testing equipment of electronic devices comprising at least one testing head and at least one space transformer, the testing head being equipped with a plurality of contact probes adapted to abut onto a plurality of contact pads of the space transformer, realized as described above.

According to an aspect of the invention, the probe card may further comprise retaining means adapted to join at least the couple of upper and/ or lower guides of the upper supports, as well as the spacer element, provided with proper housing seats for said retaining means.

More in particular, such housing seats for the retaining means may be holes and/ or open housings having dimensions suitable to host the retaining means.

Such retaining means may further join the space transformer to the upper support.

Moreover, the housing seats may be positioned in correspondence of a perimeter portion of the upper and/ or lower supports and/ or in a central position of such upper and/ or lower supports, the central position being contiguous and concentric to the perimeter portion.

Finally, the present invention relates to a method for restoring a testing head comprising a plurality of contact probes inserted into guide holes realized in at least one upper support and one lower support, each of said contact probes having at least one first terminal portion projecting from said lower support with a first length and ending with a contact tip adapted to abut onto a respective contact pad of a device to be tested, as well as one second terminal portion projecting from the upper guide with a second length and ending with a contact head adapted to abut onto one contact pads of the space transformer, at least one of said upper and/ or lower supports comprising at least one couple of upper and/ or lower guides being plate-shaped and parallel to each other, separated by a free zone of a predetermined length, at least one removable spacer element being interposed between said at least one couple of upper and/ or lower guides, possibly equipped with a plurality of layers overlapping and individually removable, the method being characterized by comprising the steps of:

de-joining the at least one couple of upper and/ or lower guides;

removing the spacer element or one of the layers composing it;

approaching the upper and/ or lower guides of the couple; and

joining again the upper and/ or lower guides,

so as to adjust the first length of the first terminal portion of the contact probes by means of a change of the length of the free zone and subsequent movement of the contact probes towards the device to be tested and restoring a proper working of the testing head.

In particular, the step of removing can comprise a slipping of the spacer element or of one of the layers composing it off.

The characteristics and the advantages of the testing head according to the invention will result from the description, made below, of an example of its embodiment, given in an indicative and non limitative way with reference to the annexed drawings.

Brief Description of Drawings

In such drawings:

Figure 1 schematically shows a probe card of electronic devices, in particular integrated on wafers, realized according to the prior art;

- Figure 2 schematically shows a section view of a probe card comprising a testing head, realized according to an embodiment of the invention;

Figures 3A-3C, 4A-4C, 5A-5D schematically show respective section views of the probe card comprising alternative embodiments of a testing head realized according to the invention;

Figure 6 schematically shows a top view of the probe card according to the invention;

Figures 7A-7D schematically show in respective top views further alternative embodiments of a detail of the testing head realized according to the invention; and

Figures 8A-8D schematically show in respective top views further alternative embodiment of a detail of the testing head realized according to the invention.

Modes for Carrying Out the Invention

With reference to such figures, and in particular to Figure 2, reference 20 globally and schematically indicates a probe card realized according to the invention.

It should be noted that the figures represent schematic views and are not drawn in scale, but are instead drawn so as to emphasize the important features of the invention.

Furthermore it should be noted that arrangements shown with reference to a particular embodiment can obviously be used in combination with other embodiments. Moreover, the same numeral references are used in the various figures to indicate structurally and functionally corresponding elements.

The probe card 20 comprises a testing head 21 , in turn comprising a plurality of contact probes 22 housed in suitable guide holes of respective upper support 23 and lower support 24 being plate-shaped and parallel one another. The testing head 21 also comprises a containment element or case 25 extended between the upper support 23 and the lower support 24, in correspondence with a free zone or bending zone 26 wherein the contact probes 22 may further deform in occasion of the pressing contact of the probes onto the device to be tested 27.

The illustrated testing head 21 is indeed of the "with shifted plates" kind and the upper and lower supports 23, 24 are opportunely shifted, the contact probes 22 housed in the respective guiding holes of such guides being thus predeformed and being subjected, in occasion of the contact between the testing head 21 and the device to be tested 27, to a further bending and deformation.

In particular, the testing head 21 illustrated in Figure 2 is of the unblocked vertical probe type and each of the contact probes 22 has respective terminal portions 21A and 2 IB adapted to make a mechanical and electric contact with respective contact pads; in particular, a first terminal portion 21A ends with a contact tip 22A adapted to abut onto a contact pad 27A of the device to be tested 27, while a second terminal portion 2 IB ends with a contact head 22B adapted to abut onto a contact pad 28A of a space transformation layer or space transformer 28. In this way, the contact probes 22 make the mechanical and electric contact between the device to be tested 27 and a testing equipment (not represented), the probe card 20 being a terminal element thereof. With the term "terminal portion" it is meant, here and beyond, a part of the contact probes 22 that projects with respect to the guides and thus to the case 25, in particular in direction of the device to be tested 27 or of the space transformer 28, respectively. Moreover, as previously highlighted, with the term tip it is indicated a not necessarily sharp terminal portion.

The first terminal portion 21A of the contact probes 22 in correspondence of the contact tip 22A extends in a first zone 29A between the lower support 24 and the device to be tested 27; in particular, the first terminal portion 21A projects from the lower support 24 with a suitable first length LA, with reference to an ideal plan determined by the device to be tested 27, corresponding to the length of the first zone 29A when the testing head 21 is in pressing contact onto the device to be tested 27. Such first zone 29A allows a movement of the contact tips 22A of the contact probes 22 on the contact pad 27A of the device to be tested 27 during the working of the testing head 21 and of the probe card 20 that includes it and is thus indicated as scrub zone 29A.

Similarly, the second terminal portion 2 IB of the contact probes 22 in correspondence of the contact head 22B extends in a second zone 29B between the upper support 23 of the testing head 21 and the space transformer 28; in particular, the second terminal portion 2 IB projects from such upper support 23 with a suitable second length LB, with reference to an ideal plan determined by the space transformer 28, such second length LB corresponding to the length of the second zone 29B when the testing head 21 is in pressing contact into the space transformer 28, in a manner similar to the device to be tested 27. This second zone 29B allows a movement of the contact heads 22B of the contact probes 22 during the working of the testing head 21 and of the probe card 20 which comprises it and is thus indicated as a floating zone 29B.

It should be noted that the first terminal portion 21A reduces its length LA as the testing head 21 is used due to the passages on the abrasive cloth of its tips, as explained in connection with the prior art. Substantially, the first terminal portion 21A is consumed during each cleaning operation of the relative contact tip 22A. In the case of testing heads having vertical probes of the "buckling beam" type as shown in Figure 2, the contact probes 22 also exhibit friction problems within the respective guide holes, which can make difficult or even prevent the sliding of the probes within them.

Suitably, according to the present invention, the use of a plurality of guides, preferably two, parallel to each other to form at least one of the upper and/ or lower supports of the testing head, also allows to reduce these friction problems.

In the case illustrated in Figure 2, the testing head 21 therefore comprises at least one upper support 23 comprising a first upper guide 23A and a second upper guide 23B, being plate-shaped and parallel, separated by at least one free zone 40 having a height Ls and a lower support 24 comprising a single lower guide, always indicated with 24, having respective guide holes within which the contact probes 22 slide. Between the second upper guide 23B and the lower guide 24 the bending zone 26 is defined, wherein the contact probes 22 may further deform in occasion of the pressing contact of the testing head 21 onto the device to be tested 27.

As already indicated, during the testing operations carried out by the probe card 20, i.e. when the testing head 21 is in pressing contact onto the device to be tested 27 and onto the space transformer 28, the contact probes 22 bend in correspondence of the bending zone 26, that extends between the second upper guide 23B and the lower guide 24 and has an additional length L corresponding to the height of the case 25.

Advantageously, according to the invention, in the embodiment schematically illustrated in Figure 2, the testing head 21 further comprises at least one spacer element or spacer 30, arranged between couples of corresponding guides of the upper and/ or lower support. In particular, in the case illustrated in Figure 2, such spacer 30 is arranged between the first and the second upper guide 23A, 23B of the upper support 23, in correspondence with the free zone 40, and has a height H substantially corresponding to the length Ls of such free zone 40, in particular inferior or equal to such second length Ls (H< Ls). More in particular, the testing head 21 comprises at least one couple of spacers 30 arranged on opposite sides of the testing head 21 , as illustrated in Figure 2.

More in general, the testing head 21 comprises a plurality of spacers 30 arranged between the first and the second upper guide 23A, 23B of the upper support 23.

Such spacers 30 can be made for example of a plastic material, in case transparent or semi-transparent, of a ceramic material, of a metallic material, of an organic material or of silicon, preferably of Kapton®.

Moreover, the spacers 30 can be made in such way as to have portions 300 projecting with respect to the testing head 21 , so as to simplify the gripping and the removal of the spacers themselves, once the testing head 21 has been removed from the probe card 20 and thus decoupled from the space transformer 28, as will be explained below.

Suitably, the spacers 30 comprise one or more layers being overlapped or aligned with each other and singularly removable or peelable; the layers composing the spacers 30 can simply be laid one on another, or possibly joined among them by means of appropriate means, for example an adhesive material, such as glue, in particular with reduced seal force, so as to allow the separation of the layers one from another in an easy manner. The testing head 21 of Figure 2 comprises spacers 30 composed by three layers, indicated as 30a, 30b and 30c, meant as a non-limiting example, the spacers 30 being able to comprise any number of layers, possibly even just one. Preferably, the layers 30a-30c have equal thickness, the sum of the thicknesses of all the layers 30a-30c determining the height H of the spacer 30.

Obviously, it is possible to consider layers having different thickness one from another, the sum of the thicknesses of all the layers still determining the height H of the spacer 30. Optionally, films of adhesive materials, in particular with reduced seal force, are interposed between such layers.

Advantageously, according to the present invention, the testing head 21 provided with a spacer 30 as described above allows to adjust the length LA of the terminal portions 21A of the contact probes 22 by changing the length Ls of the free zone 40 between the couples of guides, for example the first and second upper guide 23A, 23B as illustrated in the figure, thus overcoming the problem of the consumption of the contact tips 22A during the working life of the testing head 21 , the use of at least one upper and/ or lower support formed by a couple of guides, besides improving the sliding of the contact probes 22.

It is in particular possible to proceed to the removal of one or more layers of the spacers 30 for a desired adjustment of the length LA of the first terminal portions 21A of the contact probes 22, by changing the length Ls of the free zone 40 between couples of guides, even in a fine manner. Suitably, it is possible to remove the testing head 21 from the probe card 20, slipping one or more layers composing such spacers 30 off and subsequently to reassemble the testing head 21 on the space transformer 28, thus reassembling the probe card 20: the removal of one or more layers of the spacers 30 reduces the height H of the spacers 30 themselves, approaching the guides comprised in the upper and/ or lower supports 23, 24 and thus pushing the contact probes 22 towards the device to be tested 27 when the space transformer 28 is repositioned on the testing head 21 , i.e. reinstating the first length LA of the first terminal portion 21A of such probes, length that was shortened because of the consumption of the contact probes 22 in correspondence of the respective contact tips 22A.

It should be noted that it is customary to realize the contact heads

22B of the contact probes 22 so as to have at least one portion with a diameter larger than the upper guide holes made in the first upper guide 23A so as to prevent the probes from sticking out even in the absence of a device to be tested 27 on which such probes abut onto, diameter meaning a maximum transverse dimension of a section of said portion orthogonal to a longitudinal development axis of the contact probe, as schematically illustrated in Figure 3A.

As described above, the testing head 21 comprises an upper support 23 formed by a couple of guides 23A, 23B and the spacer 30 arranged between the first upper guide 23A and the second upper guide 23B in correspondence with the free zone 40, in particular comprising three layers, 30a, 30b and 30c, and having a height H smaller than or equal to the length Ls of the free zone 40.

Suitably, the layers 30a-30c of the spacers 30 can be made in such way as to have projecting portions 300 from the testing head 21. In the alternative embodiment illustrated in Figure 3 A, such projecting portions 300 have different lengths from one layer to another of a same spacer 30, so as to ease the removal of the same number of layers for the different used spacers 30. Suitably, such projecting portions 300 have equal lengths for corresponding layers of the different spacers 30, for example the projecting portion of the layer which is closer to the upper guide 23 A than all the spacers 30 has a same length, such length being still greater than the length of the following layers, gradually closer to the second upper guide 23B. In particular, such projecting portions 300 have a gradually decreasing length from the layer closer to the first upper guide 23A to the layer closer to the second upper guide 23B.

It is also possible to contemplate a numbering for such layers 30a- 30c, for example with increasing numbering starting from the closest one to the first upper guide 23A, this numbering being applied onto the projecting portion 300 of the spacer 30, for example, in correspondence of its face Fc facing the space transformer 28. This way, by looking at the testing head 21 from the side of the space transformer 28, once the testing head 21 has been removed from the probe card 20, it is immediately possible to verify that all the spacers 30 comprise the desired number of layers simply by reading that numbering on all the projecting portions 300 of the layers of such spacers 30 closest to the first upper guide 23A and thus to the space transformer 28. Such numbering may be in the form of a number written or engraved or made by means of embossing or any other technique on these projecting portions 300. Alternatively, the numbering may include a plurality of distinctive signs, such as notches or reliefs, of any form and made by means of any suitable technique, in a number corresponding to the desired numbering; in this case, for example, a layer identified as the first layer, such as layer 30a of Figure 3B, comprises only one notch or relief, such as an engraved or embossed spot; similarly, the second layer 30b may have two engraved or embossed spots and the third layer 30c, three engraved or embossed spots.

It is of course possible to provide spacers 30 with projecting portions of increasing lengths from the layer closest to the first upper guide 23A to the one closest to the second upper guide 23B as schematically illustrated in Figure 3C.

It is also possible to apply the numbering onto the layers 30a-30c of the spacers 30 in correspondence of a face Fc' opposite with respect to the face Fc, particularly facing the second upper guide 23B.

The just made considerations may also be applied even in case it is the lower support 24 that is formed by a couple of guides, as well as in case both supports are, the testing head comprising one couple of upper guides 23A, 23B and one couple of lower guides 24A, 24B.

For example, according to an alternative embodiment schematically illustrated in Figure 4A, the testing head 21 comprises an upper support 23 comprising only one upper guide, always indicated with 23, and a lower support 24 comprising a first lower guide 24A and a second lower guide 24B, being plate-shaped and parallel, still separated by a free zone 40 having a height Ls.

The testing head 21 further comprises at least one spacer 30 arranged between the first lower guide 24A and the second lower guide 24B in correspondence of the free zone 40 and has an height H corresponding to the length Ls of said free zone 40. More in particular, the testing head 21 comprises at least one couple of spacers 30 arranged on opposite sides of the testing head 21.

More generally, the testing head 21 comprises a plurality of spacers 30 arranged between the first lower guide 24A and the second lower guide 24B of the lower support 24.

Also in this case, the spacers 30 may be realized so as to have portions 300 projecting with respect to the testing head 21 , in order to facilitate its gripping and removal and may include one or more superimposed layers, individually removable or peelable, in the illustrated example three layers 30a-30c.

In the alternative embodiment illustrated in Figure 4B, the layers 30a-30c of the spacers 30 can be realized so as to have portions 300 projecting from the testing head 21 of different lengths from one layer to another of a same spacer 30, particularly gradually decreasing from the first lower guide 24A, so as to facilitate the removal of the same number of layers for the different spacers 30 used, also allowing applying a numbering, in particular in correspondence of a face Fc facing the first lower guide 24A or onto an opposite face Fc' facing the second lower guide 24B. The numbering may be in the form of a number written or engraved or embossed or otherwise made on these projecting portions 300 or comprise a plurality of distinctive marks, such as notches or reliefs, of any shape and made by means of any suitable technique in number corresponding to the desired numbering.

Also in this case, it is possible to contemplate a dual configuration with layers having increasingly longer length portions starting from the first lower guide 24A, as illustrated in Figure 4C.

It should be emphasized that this alternative embodiment, thanks to the use of couples of guides to realize the lower support 24, further improves the sliding of the probes right in correspondence with the terminal portions comprising the contact tips, reducing the risk of entanglement of such probes when these portions shorten.

According to a further alternative embodiment illustrated in Figure 5A, the testing head 21 comprises an upper support 23 comprising a first upper guide 23A and a second upper guide 23B and a lower support 24 comprising a first lower guide 24A and a second lower guide 24B, plate-shaped and parallel, still separated by respective free zones 40u, 40d.

The testing head 21 further comprises at least one couple of spacers 30u and 30d, each arranged between the couples of correspondent guides. In particular, an upper spacer 30u is arranged between the first upper guide 23A and the second upper guide 23B of the upper support 23 in correspondence of an upper free zone 40u and has a height H, substantially corresponding, in particular smaller than or equal to the length Lsu of this upper free zone 40u; similarly, a lower spacer 30d is arranged between the first lower guide 24A and the second lower guide 24B at a lower free zone 40d and has a height HI, substantially corresponding, in particular smaller than or equal to the length Lsd of that lower free region 40d.

Also in that case, the spacers 30 may be realized so as to have projecting portions with respect to the testing head 21 , so as to facilitate their gripping and removal and so as to comprise one or more overlapping layers, individually removable or peelable, in particular three layers 30a-30c.

In the alternative embodiments illustrated in Figures 5B and 5C, the layers 30a-30c of the spacers can be realized so as to have projecting portions from the testing head 21 having different lengths from one layer to another of a same spacer 30. In the illustrated alternative embodiments, these projecting portions have gradually decreasing lengths, respectively increasing starting from the first upper guide 23A or from the first lower guide 24A towards the second upper guide 23B or the second lower guide 24B.

As for the above-described embodiments, it is also possible to contemplate to apply a numbering in correspondence of the projecting portions of the spacer so as to facilitate the removal of the same number of layers for the different used spacers 30, in particular in correspondence of one face Fc thereof facing the first upper guide 23A or lower guide 24A or of an opposite face Fc' facing the second upper guide 23B or lower guide 24B. The numbering may be in the form of a number written or engraved or embossed or otherwise made on these projecting portions 300 or can otherwise comprise a plurality of distinctive marks, such as notches or reliefs, of any shape and realized by means of any suitable technique in a number corresponding to the desired numbering.

It is of course possible to use spacers having different configuration between the first and the second upper guide 23A, 23B with respect to those between the first and second lower guides 24A, 24B, as schematically illustrated in Figure 5D, where, by way of example and not limitation, the layers 30a-30c of the spacers 30u between the first and the second upper guides 23A and 23B have projecting portions of different lengths, in particular gradually decreasing starting from the first upper guide 23A to the second upper guide 23B, while the layers of the spacers 30d between the first and second lower guides 24A, 24B have projecting portions of equal length from one layer to the other. Asymmetric or dual configurations are equally possible.

It should be noted that the presence of upper and lower spacers allows the maximum degree of freedom in adjusting the length LA of the terminal portion 21A comprising the contact tip 22 A, such adjustment being symmetrically or asymmetrically made on both sides of the testing head 21 , possibly even by changing the inclination between the guides of the supports.

It should also be noted that all the illustrated embodiments of the testing head according to the present invention allow for an adjustment of the length of the terminal portion of the contact probes comprising the contact tips and thus undergoing to the consumption, by changing the length of the free zones between couples of guides, without altering the length of the bending zone of the probes themselves and hence the dynamics of movement of the same, in particular in terms of applied force and of scrub.

Additionally, for the probe card 20 that comprises said testing head 21 , the floating zone 29B for the contact heads 22B of the contact probes 22 is suitably guaranteed as maintained constant so as to ensure a constant and proper contact with the space transformer 28, contact being made by those contact heads 22B indeed, which abut onto the contact pads 28A of the space transformer 28. In fact, while allowing the adjustment of the length LA of the terminal portion 21A comprising the contact tip 22A of the contact probes 22, the probe card 20 according to the present invention has a floating zone 29B having a length that is kept constant and unchanged during such adjustment.

The probe card 20 also comprises respective retaining means 32 adapted to join the different components of such probe card, in particular the couple of guides of the upper and/ or lower support, as well as the spacers 30, provided for this purpose with suitable housing seats for the retaining means 32. Such retaining means 32 can also be used to join the space transformer 28 and the case 25.

As illustrated in Figure 6, wherein the probe card 20 is shown from the side of the space transformer 28, with the same in transparency, the retaining means 32 are substantially arranged along a perimeter portion 40P of the upper guide 23 (in the first upper guide 23A, if any) with an essentially ring-shaped form. In the illustrated example, the probe card 20 comprises spacers substantially realized in a paddle- shape in correspondence of the vertexes of the upper support 23 of a substantially rectangular shape. Retaining means 32' are also provided, being positioned in a central portion 40C of the upper support 23, the central portion 40C being contiguous and concentric to the perimeter portion 40P. The retaining means 32, 32' can for example be realized by means of screws, particularly flat-headed screws, housed in respective threaded holes.

It is of course possible to provide different configurations for the spacers 30, which can be arranged in a different number, symmetrically or not, and at different positions than those shown in Figure 6.

It is also possible to use an additional adhesive film to associate the spacer 30 to the upper support 23 or to the lower support 24, in particular to a guide comprised therein, thereby avoiding the spacer being crossed by the retaining means 32, 32'.

In a particularly simplified embodiment, the spacers 30 are simply laid to a guide of the couple of guides of the upper and/ or lower support 23, 24, their holding in position being assured by the closing of the guides one onto the other during the normal working of the testing head 21. Also in case the spacers 30 are formed by a plurality of layers 30a- 30c, it is possible to simply superimpose them to each other on the a guide of said upper and/or lower supports 23, 24, the superimposed layers 30a-30c being then held in position due to the pressure exerted by the closing of the guides one onto another.

A spacer 30 can conveniently have the shape of a paddle, as schematically illustrated in Figure 7A.

In particular, in this case, the spacer 30 comprises an elongated body 33 and a head 34, for example circular, possibly bearing a hole 35 having such dimensions to allow it to be crossed by the retaining means 32, 32'. Such form of the spacers 30 turns out particularly advantageous, allowing an easy gripping of the spacers in correspondence of the elongated body 33 at time of their removal. Such elongated body 33 indeed projects with respect to the testing head 21 , particularly to the upper support 23 and/or the lower support 24. Furthermore, the major dimensions of the head 34 with respect to the elongated body 33 guarantee a good repartition of the pressure loading in occasion of the tightening of the corresponding retaining mean 32, 32'.

It is also possible to realize the spacers 30 as tabs 36, substantially rectangular, suitably provided with holes 35 to allow the passage of the retaining means 32, 32', as schematically illustrated in Figure 7B.

The paddle-like and tab-like embodiments define spacers 30 having an elongated shape, substantially rectangular, and in particular having a dimension much greater than the other. Such spacers 30 anyway have a superficial area smaller than the one of the supports 23, 24 and the couples of guides composing them, possibly, in particular much smaller with respect to a whole board or layer of the testing head 21.

The spacers 30 realized by means of paddles or tabs are constructively very simple and allow to contemplate their distribution in the desired positions with respect to the testing head 21 and to the space transformer 28, due to their contained transversal dimension, as well as a proper gripping of the same due to the elongated longitudinal dimension that projects with respect to the testing head 21.

Alternatively, the spacers 30 can be realized by means of couples of semi-frames 301 or 30r, substantially extended along opposite and parallel sides of the testing head 21 and in particular of the upper support 23 and/ or the lower support 24, possibly provided with holes 35 for the passage of the retaining means 32 in the positions contemplated for the probe card 20, as schematically illustrated in Figure 7C. Such semi-frames that realize the spacers 30 can be sized so as to project with respect to the testing head 21 and in particular to the upper support 23 and/ or the lower support 24, so as to make it easier to grip them and to allow applying a numbering.

More in particular, the semi-frames 301 and 30r that realize the spacer 30 comprise respective lateral portions 311, 31r that project with respect to the testing head 21 , and in particular to the upper support 23 and/or the lower support 24, as indicated in Figure 7C.

The spacers 30 realized in the form of semi-frames 301, 30r introduce a degree of freedom and allow to separately handle one side of the probe card 20 with respect to another, for example in terms of layers to be eliminated, so as to realize a tilting of a guide with respect to the other, when needed in case of a mismatch in the corresponding planarities. In addition, the use of semi-frames allows to the spacers 30 to adapt to testing heads 21 of different sizes, simply by approaching or displacing the semi-frames 301, 30r.

Finally, it is also possible to realize the spacers 30 in the form of couples of semi-frames 301 and 30r, being substantially extended along opposite and parallel sides from the testing head 21 and in particular of the upper support 23 and/ or of the lower support 24 and having such dimensions to extend within its central portion 40C. Such semi-frames can be provided with holes 35 for the passage of the retaining means 32 in the positions contemplated in the perimeter portion 40P of the upper support 23 and additional holes 35' for the passage of the additional retaining means 32' in the positions contemplated in the central portion 40C of the upper support 23, as schematically illustrated in Figure 7D.

As previously, the semi-frames that realize the spacers 30 can be sized so as to project with respect to the testing head 21 and in particular to the upper support 23 and/or the lower support 24, so as to ease the gripping and to allow applying a numbering. In particular, such semi-frames 301, 30r may comprise respective lateral portions 311, 31r that project with respect to the testing head 21 and in particular to the upper support 23 and/ or to the lower support 24, as indicated in Figure 7D.

It should be noted that the use of semi-frames 301, 30r that extend themselves also within the central portion 40C of the upper support 23 increases the number of retaining points of the semi-frames themselves, thanks to the coupling of the additional holes 35' and the additional retaining means 32'.

Furthermore, the semi-frames 301, 30r may comprise suitable recesses 37 so as to limit the material of such semi-frames to the surrounding areas of the holes 35 and the additional holes 35'. Thus, the spacers 30 made by means of such semi-frames are lightened while still guaranteeing an improved seal force.

It is also possible to realize the semi-frames that compose the spacers 30 with dimensions such as to be flush with the testing head 21 and in particular with the upper support 23 and/ or with the lower support 24, further providing them with at least one elongated portion adapted to project from the testing head 21 and from the corresponding tab-like support to facilitate the gripping of the spacer 30 and to allow applying a numbering. Any number of gripping tabs may be contemplated, depending on the overall size of the semi-frames as well as on the applications of the probe card 20, positioned so as not to interfere with the normal working of the probe card 20 that includes the spacers 30.

By using the spacers 30 equipped with holes 35, 35' for the housing of the retaining means 32, 32', of the type illustrated in Figures 7A-7D, it is possible to regulate the length LA of the first terminal portions 21A of the contact probes 22, unblocking such retaining means 32 and the additional retaining means 32', if any, in particular by means of removing the relative screws, followed by a step of removing the spacers 30 or of at least one of their layers 30a-30c, with a partial disassembling of the testing head 21.

The removal of the spacers 30 or of at least one of their layers 30a- 30c allows to perform an approach of at least one couple of guides that form the upper support and/ or the lower support with subsequent movement of the contact probes 22 toward the device to be tested 27, so as to compensate for a shortening of the corresponding first terminal portions 21A comprising the contact tips 22A and to restore in a simple and fast way the proper working of the testing head 21. In particular, it should be underlined that the removal of the spacers 30 or of at least one of their layers 30a-30c does not have an impact on the length LB of the floating zone 29B of the contact heads 22B, which remains constant and guarantees a proper housing of the contact heads 22B of the contact probes 22. More importantly, the elongation of the first terminal portions 21A comprising the contact tips 22A happens without modifying the bending zone 26 of the contact probes 22, and thus does not modify its impact force and the scrub on the device to be tested 27.

In essence, the testing head 21 according to the invention allows to implement a method of adjusting the length of the first terminal portions 21A comprising the contact tips 22A of the contact probes 22 comprised therein, so as to restore the proper working of such testing head 21.

Advantageously, according to the invention, the method comprises a step of unblocking the retaining means 32 and 32 ', if any, for example by means of loosening or removing of respective screws, followed by a step of removing the spacers 30 or at least one of their layers 30a-30c.

At this point, the method comprises a step of approaching the couple of guides that form the upper support 23 and/ or the lower support 24 with a reduction of the Ls length of the relative free zone 40 and a subsequent displacement of the contact probes 22 toward the device to be tested 27; in particular, this way the contact probes 22 project from the lower guide 24, restoring the length LA of the first terminal portions 21A comprising the contact tips 22A. This step of approaching the couple of the upper support guides 23 and/ or the lower support guides 24 is in particular carried out so that the length of the first terminal portions 21A comprising the contact tips 22A is brought back at a value corresponding to a proper working of the testing head 21.

It should be noted that, once having adjusted the length of the first terminal portions 21A comprising the contact tips 22A by removing the spacers 30 or one of the layers 30a-30c that compose them, provision should be made for restoring the retaining means 32 and the additional retaining means 32', if any, for example by means of screwing back the corresponding screws, to join again the elements of the testing head 21 and of the probe card 20.

It is of course possible to perform further removals a layer of the spacers 30 and to approach the couples of guides also at a later stage of the working life of the testing head 21 and of the probe card 20 that comprises it, in particular when the first terminal portions 21A comprising the contact tips 22A of the contact probes 22 have been further shortened because of the use and the cleaning operations and have a length smaller to a length corresponding to a proper working of the testing head 21 and of a probe card 20 that comprises it.

Moreover it is possible to perform such removals even more times, in the case of spacers 30 provided with a plurality of layers, performing this way subsequent regulations of the length of the first terminal portions 21A comprising the contact tips 22A of the contact probes 22.

The working life of the testing head 21 and of the probe card 20 that comprises it thus results opportunely extended with respect to the known solutions according to which the shortening of the first terminal portions 21A comprising the contact tips 22A of the contact probes 22 implicates the end of the use of the testing head 21 and of the probe card 20 that comprises it, unless realizing complicated replacements of the testing head itself.

Finally, it is possible to perform the removal of a layer of the spacer

30 and the nearing of a couple of guides between them also in an asymmetrical manner, so as to differently adjust the length of the first terminal portions 21A of the contact probes 22 in case of a misalignment of the respective contact tips 22A due to the tolerances of the process of manufacturing the probes themselves. It is also possible to contemplate an asymmetrical removal of such layers so as to adjust the distance between the upper and/ or lower guides in case of planarization and or tilting problems of the guides themselves, so as to guarantee an equal distance between the guides along their whole area. In an advantageous alternative embodiment of the invention, it is possible to realize the spacers 30 so as to include open housings 38 for the retaining means 32, as in the embodiments illustrated in Figures 8A-8D. Such open housings 38 allow in particular to slip the spacers 30 or one of the layers 30a-30c comprised therein off, without totally removing the retaining means 32, in particular the relative screws, a simple loosening of said means being sufficient and in particular allowing the removal of the spacers 30 themselves or of one of the layers that make them simply slipping off and with no disassembly, even partial, of the testing head 21.

In this case, the method according to the invention comprises a step of removal performed by slipping the spacers 30 or at least one of their layers 30a-30c off.

A further tightening of such retaining means 32 and additional retaining means 32', if any, ensures the desired coupling of the couple of guides that realize the upper and/ or lower supports as well as an approach between the guides themselves and thus the restoring of the dimensions of the first terminal portions 21A comprising the contact tips 22A and ensuring the proper working of the testing head 21 itself as well as the probe card 20 that comprises it.

More in particular, it is possible to realize the spacers 30 with shapes similar to those illustrated before, that thus present the same advantages. For example, the spacer can have an elongated and substantially rectangular shape, as a paddle, formed by an elongated body 33 and a head 34, or a tab 36, substantially rectangular, and being in case equipped with open housings 38, as schematically illustrated in Figures 8A and 8B respectively. The open housings 38 have dimensions suitable to host the retaining means 32 or additional retaining means 32'.

It should be noted that the open housings 38 define in the spacers

30 at least one material portion 39, 39' which may be partially surmounted by the retaining means 32, 32', similarly to a fork, the retaining means 32, 32' comprising for example flat head screws, so as to achieve the proper holding of the spacers 30 by means of the retaining means 32, 32' indeed.

Alternatively, the coupling between the spacer 30 and the testing head 21 , in particular one of the guides that compose the upper support 23 and/ or the lower support 24, can only be by lying or of the adhesive type, the retaining means 32, 32' not crossing the spacer 30 but only other elements of the testing head 21 , for example the couples of support guides 23, 24, the case 25, the space transformer 28, and so on.

It is immediately understood that it is anyway possible to eliminate such a spacer 30 or one of the layers 30a-30c that compose it by means of a simple loosening of the retaining means 32, 32' and by moving said spacer or a layer thereof in the direction of the longitudinal development thereof and away from the testing head 21 and in particular from the upper support 23 and/ or the lower support 24, as indicated by the arrow F in Figures 8A and 8B, such retaining means 32, 32' passing in correspondence of an opening of the open housings 38.

In particular, the elongated shape of the paddles or tabs allows to guarantee a slipping of the spacers 30 or of one of the layers 30a-30c that compose them off, in an easy manner, also without having to apply high value forces.

Alternatively, the spacers 30 can be made by means of couples of semi-frames, 301 and 30r, suitably provided with open housings 38 in correspondence of the retaining means 32 positioned for example at the perimeter portion 40P of the upper support 23 and of further open housings 38', if any, in correspondence of the other retaining means 32' positioned for example in correspondence of the central portion 40C of the upper support 23, as schematically illustrated in Figure 8C and Figure 8D, respectively. In a similar way, such open housings 38, 38' can be positioned in correspondence of the retaining means 32, 32' of the perimeter or central portion of the lower support 24.

Suitably, such semi-frames 30r and 301 that realize the spacers 30 can be sized so as to project with respect to the testing head 21 and in particular to the upper or lower supports 23, 24, so as to be easily grippable and to allow also applying a numbering, in particular on each of the layers that compose it, as previously explained. In this case, the semi-frames 301, 30r can comprise respective lateral portions 311, 31r that project with respect to the testing head 21 and in particular to the upper or lower supports 23, 24, as indicated in Figures 8C and 8D.

It is immediately understood that also in this case it is possible to eliminate a spacer 30 or one of the layers 30a-30c that make it by simply loosening the retaining means 32, 32' and moving the semi- frames 301 and 30r or one of their layers moving away from the testing head 21 , as shown by the arrows Fl and F2 in Figures 8C and 8D, in this case the retaining means 32 and 32' being also allowed to pass from the openings of the open housings 38, 38'.

Since the spacers 30 realized by means of semi-frames are structurally stronger than the paddles or the tabs, by virtue of their greater extension with respect to the area of the upper or lower support 23, 24, it is possible in this case to apply forces of higher value than those used for example in the case of the spacers 30 made by means of paddles or tabs.

As before, it is possible to realize the semi-frames that make up the spacers 30 with such dimensions that they result flushed with the testing head 21 , in particular with the upper support 23 or lower support 24, then providing them with at least one elongated portion adapted to project from the testing head 21 and in particular from the upper support 23 or lower support 24 in a tab-like manner to facilitate the gripping of the spacer 30 and to allow applying a numbering.

Using spacers 30 provided with open housings 38, 38' for the housing of the retaining means 32, 32' of the type illustrated in Figures 8A-8D, it is possible to adjust the length LA of the first terminal portions 21A of the contact probes 22 simply by loosening the retaining means 32 and the additional retaining means 32', if any, in particular by means of a partial de-screwing of the respective screws, followed by a slipping of the spacers 30 or at least of one of their layers 30a-30c, if any, while maintaining the structural integrity of the testing head 21.

In the case of spacers 30 realized by means of semi-frames, structurally more solid and able to withstand greater forces than the paddles or the tabs, it is possible to contemplate a slipping of the spacers 30, if any, possibly even without a prior marked loosening of the retaining means 32, 32'.

As already explained, the removal of the spacers 30 or of at least one of their layers 30a-30c allows to perform an approach of the guides that form the upper and/ or lower support of the testing head 21 with subsequent moving of the contact probes 22 toward the device to be tested 27, so as to compensate for a shortening of the relative first terminal portions 21A comprising the contact tips 22A of the contact probes 22 and to restore in a simple and fast way the proper working of the testing head 21 and of the probe card 20 which comprises it.

It will thus be needed to tighten the retaining means 32 and the additional retaining means 32', if any, in particular by screwing back the corresponding screws, to re-join anew the elements of the testing head 21 and of the probe card 20. In any case, it should be emphasized that the use of open housings 38 allows to avoid an even partial disassembly of the testing head 21 to remove the spacers 30 or one of their layers.

It is of course possible to perform further removals of a layer of the spacers 30, also at a later stage of the working life of the probe card 20, as well as to perform such removal several times, in the case of spacers 30 comprising a plurality of layers, with consequent successive adjustments of the length LA of the first terminal portions 21A of the contact probes 22 and finally to perform the removal of a layer of the spacer 30 also in an asymmetrical manner, as previously explained.

It should be noted that all the illustrated embodiments of the probe card according to the present invention allow for the adjustment of the length of the terminal portion of the contact probes comprising the contact tips and therefore subject to consumption without modifying the length of the bending zone of the probes and therefore their dynamics of movement, in particular in terms of scrub and especially of force exerted on pads. Furthermore, such adjustment does not change the length of the floating zone, thus ensuring an unchanged and proper housing of the contact heads of the probes and ensuring their contact with the space transformer.

In conclusion, the testing head with spacer according to the invention turns out having a longer working life, since it is possible to contemplate a large number of cleaning operations of the respective tip with a subsequent adjustment of the length of the terminal portions of the contact probes that project with respect to the lower support so that it is equal to or greater than the length corresponding to a proper working of the testing head. This way also the working life of the probe card comprising such a testing head is increased.

The presence of the spacers allows to restore in an easy and quick way the proper working of the probe card itself after a period of operation that has led to a shortening of the terminal portions of its contact probes, without affecting their movement dynamic and, above all, the force exerted by them, due the fact that the length of the bending zone of the probes is maintained constant.

Suitably, the spacers are realized so as to extend on limited areas, even although significantly limited as in the case of columnar, paddle or tab shaped embodiments, with respect to the area of the guides of the testing head; such spacers can be positioned at will, both in number and position. Furthermore, it has to be noted that spacers of reduced dimensions, in particular not extended as whole guides, have less flatness problems and are thus more easily manageable.

In addition, it is possible to perform further adjustments of the length of the terminal portions of the contact probes at different stages of the working life of the testing head that includes them, particularly whenever said terminal portions comprising the contact tips are shortened due to the use and have a shorter length than a length corresponding to a proper working of the testing head, also allowing to modify the length of the terminal portions in a different way for different contact probes in case of misalignment of the respective contact tips due to the tolerances of the manufacturing process of the probes themselves.

Obviously an expert in the field may make several modifications and variations to the testing head described above in order to meet contingent and specific requirements, all within the scope of protection of the invention as defined by the following claims.