DESCRIPTION

Field of application

The present invention refers to a probe card for an apparatus for testing electronic devices.

In particular, the invention regards, but not exclusively, a probe card for high temperature application and the description hereinafter is provided with reference to this field of application with the sole aim of simplifying the description thereof.

Prior art

As well known, a probe card is essentially a device adapted to electrically connect a plurality of contact pads of a microstructure, in particular an electronic device integrated on wafer, with corresponding channels of a test apparatus that performs the functionality verification, in particular electrical, or generally tests it.

The test performed on integrated devices in particular serves to detect and isolate faulty devices already at the manufacturing stage. Usually, the probe cards are thus used for electrically testing devices integrated on wafer before cutting or singling out the same and before the assembly thereof within a package for containing chips.

A probe card comprises a probe head in turn essentially including a plurality of mobile contacting elements or contact probes provided with at least one contact portion or tip for a corresponding plurality of contact pads of a device to be tested. The terms end or tip are hereinafter used to indicate an end portion, not necessarily sharply pointed.

Thus, it is known that the effectiveness and reliability of a measurement test depends, among other factors, also on the obtainment of a good electric connection between the device and the test apparatus, thus, on an ideal electrical probe /pad contact.

The widely used types of probe heads used in the technical field considered herein for testing integrated circuits include the so-called probe heads having cantilevered probes, also referred to as cantilever probe heads, which have probes protruding like a fishing rod over a device to be tested.

In particular, a cantilever probe head of the known type usually supports a plurality of flexible, generally wire-like probes, with preset electrical and mechanical properties. The probes, projecting cantilevered from the cantilever probe head, are substantially shaped to form a hook, due to the presence of a terminal portion substantially elbow curved having a generally obtuse internal angle.

The good connection between the probes of a cantilever probe head and the contact pads of a device to be tested is guaranteed by the pressure of the probe head on the device itself, the probes being subjected thereby to a vertical flexion (with respect to the plane defined by the device to be tested) in the opposite direction with respect to the movement of the device towards the probe head.

The hooked shape of the probe is such that, during the contact with the contact pads of the device to be tested and the displacement of the probes upwards beyond a pre-established contact point, usually referred to as "overtravel", the points of contact of the probe slide on the contact pads over a length commonly referred to as "scrub".

Also known in the field are the probe heads having vertical probes and referred to by the term "vertical probe heads". A vertical probe head essentially comprises a plurality of contact probes held by at least one pair of plates or guides substantially plate-like and parallel to each other. Such guides are provided with special holes and they are arranged at a given distance with respect to each other so as to leave a free zone or air gap for the movement and possibly deformation of the contact probes. In particular the pair of guides comprises an upper guide [upper die] and a lower guide [lower die], both provided with guide holes within which the contact probes axially slide, usually made of special alloy wires with good electrical and mechanical properties.

The good connection between the contact probes and the contact pads of the device being tested is also in this case guaranteed by the pressure of the probe head on the device itself, the contact probes, movable within the guide holes made in the upper and lower guides, being subjected to a flexion during such pressure contact within the air area between the two guides, and to a sliding within such hole guides.

Furthermore, the flexion of the contact probes in the air gap may be assisted through a suitable configuration of the probes or of the guide thereof, in particular using pre-deformed contact probes or suitably shifting the plates that comprise them.

Figure 1A schematically illustrates a probe head 1 comprising at least one plate or upper guide 2 and a plate or lower guide 3, having respective upper guide holes 2A and lower guide holes 3A within which there slides at least one contact probe 4.

The contact probe 4 has at least one end or contact tip 4A. In particular the contact tip 4A abuts on a contact pad 5A of a device 5 to be tested, performing the mechanical and electrical contact between said device and a test apparatus (not represented) regarding which the probe head forms an end element.

Generally, there are used probe heads with probes not fixedly constrained, but kept interfaced with a card, in turn connected to the test apparatus: this is the case of non-locked contact probes.

In this case, as illustrated in figure 1A, the contact probe 4 has a further contact tip 4B, in practice indicated as contact head, towards a plurality of contact pads 6A of the card 6. The good electrical contact between probes and the card is analogously guaranteed upon contact with the device to be tested by pressing the probes on the contact pads of the card.

In addition, the card 6 is held in position by means of a stiffener 8. The assembly of the probe head, the card and the stiffener forms a probe card, indicated in its entirety with 10 in Figure IB.

Thus, in the vertical probe technology it is also important to guarantee the good connection of the contact probes with the apparatus of test, in particular at the contact heads thereof and thus of the card.

Another critical parameter in the production of a probe head is the distance (the so-called pitch) between the centres of the contact pads on the device to be tested. The pitch of the integrated electronic devices, has become smaller and smaller as the relative manufacturing technology has been progressing, leading to a high packing of the contact probes 4 in the probe head 1, with the ensuing problems regarding positioning to avoid the mutual contact thereof. Such distance restrictions are slightly less strict instead as regards the contact pads on the card 6, given that such pads are suitable to be spaced further apart and arranged more freely, in particular in a more orderly manner, compared to those of the device to be tested.

There are known various technologies for obtaining the probe card 10 of the test apparatus.

In particular, a first solution exploits the techniques of the printed circuits for obtaining the card 10, which is also commonly referred to as PCB. This technology allows obtaining cards with active areas even of large dimensions, but with major restrictions with respect to a minimum value that can be attained for the pitch in conditions of high density of the contact pads on the device to be tested.

Also known is the ceramic based technology or MLC (Multilayer

Ceramic). This technology allows attaining extremely small pitches and much higher densities compared to the PCB technology, but it entails limitations regarding the maximum number of signals that can be used for the test and on the maximum dimension of the active area that can be accommodated on the card.

Lastly, there can be used the so-called hybrid technology in which the probe head is interfaced with an intermediate plate, commonly indicated as interposer, in turn connected to a mechanical support, commonly indicated as a plug and connected by means of welding bridges to the card. This technology offers considerable flexibility in terms of surface, pitch and signal density, but it is limited as regards the maximum number of signals that can be treated, also revealing poorer electromagnetic performance. Last but not least, the difficult automation capacity thereof also represents a disadvantage of the hybrid technology.

The mutual positioning of the elements forming the head is also a key parameter. In particular, various test methods require that the probe head be capable of withstanding high temperatures. However, in such case the thermal expansions of such elements that form the probe card may hinder the correct operation thereof. Actually, the elements that form the probe cards of the known type are usually fastened by means of screws. Thus, during testing under high temperatures, due to the various coefficients of thermal expansion of the materials such elements are made of and the fastening obtained by the screws, the elements tend to arc, causing the malfunctioning of the probe card as a whole, even leading to lack of contact with the contact pads of the device to be tested.

The technical problem on which the present invention is based is to provide a probe card adapted to support a probe head provided with a plurality of contact probes for the connection with an apparatus for testing electronic devices, in particular integrated on wafers, having the functional and structural features capable of allowing overcoming the limitations and the drawbacks that still affect the probe cards obtained through the known technologies, in particular allowing to manage the test at high temperature.

Summary of the invention

The solution idea on which the present invention is based is that of associating - in a floating manner - the probe head with a stiffener, so as to compensate the dimensional variations related to the thermal expansions that the elements that form the probe card are subjected to during the testing step and eliminate the possibility of deformation, in particular the curving, of the elements of the probe card coupled mechanically but made with materials having various coefficients of thermal expansion, in particular a supporting plate and an interface plate of the card itself.

According to such solution idea, the technical problem is overcome by a probe card for an apparatus for testing electronic devices and comprising at least one probe head which houses a plurality of contact probes, each contact probe having at least one contact tip suitable to abut against contact pads of a device to be tested, as well as a supporting plate of the probe head associated with a stiffener via an interface plate characterised in that it comprises a plurality of connecting elements with clearance between the supporting plate and the interface plate housed in a floating manner in a plurality of respective seats made in the supporting plate and a plurality of connecting elements without clearance between the interface plate and the stiffener.

More in particular, the invention comprises the following additional and optional features, considered separately or combined if required.

According to an aspect of the invention, each connecting element with clearance of the plurality of connecting elements with clearance may comprise a body and a head portion connected to each other, the head portion having at least one transverse dimension greater than a transverse dimension of the body so as to form a shoulder in a conformation with a substantially T-section and a corresponding seat of the plurality of respective seats may have a configuration corresponding and mating with that of the connecting element with clearance in a conformation with a substantially T-section and respective larger dimensions to allow the floating housing of the connecting element with clearance.

According to such aspect of the invention, each seat of the plurality of respective seats may comprise a body and a head portion connected to each other, the head portion having at least one transverse dimension greater than a transverse dimension of the body so as to form a shoulder adapted to abut against the shoulder of a corresponding connecting element with clearance of the plurality of connecting elements with clearance.

In addition, according to an aspect of the invention, at least one connecting element with clearance of the plurality of connecting elements with clearance and at least one corresponding seat of the plurality of respective seats may have substantially tubular bodies and head portions.

In particular, according to this aspect of the invention, such at least one connecting element with clearance and at least one corresponding seat may have respective bodies with diameter comprised between 3mm and 5mm and respective head portions with a diameter comprised between 5mm and 10mm.

According to another aspect of the invention, each seat of the plurality of respective seats may comprise a body and a head portion having larger dimensions of at least 10% compared to corresponding dimensions of a body and a head portion of a corresponding connecting element with clearance of the plurality of connecting elements with clearance housed floating in it.

According to such aspect of the invention, between the bodies of each connecting element with clearance and the respective seat there may be defined a first clearance, between the head portions of the connecting element with clearance and the respective seat there may be defined a second clearance and between the shoulders of the connecting element with clearance and the respective seat there may be defined a third clearance.

In particular, such first, second and third clearance may have values comprised between 50μηι and 350μηι, preferably ΙΟΟμιη.

According to another aspect of the invention, the first clearance may substantially have a zero value in the transverse direction and there may be defined a further clearance between the head portions of the connecting element with clearance and a respective seat at a face of the supporting plate facing a support of the probe card as a whole, such further clearance having a greater value than the third clearance.

According to this aspect of the invention, a space of predetermined thickness may be defined between the interface plate and a further face of the supporting plate. Furthermore, according to an aspect of the invention, the connecting elements with clearance of the plurality of connecting elements with clearance may be arranged according to radially disposed alignment directions and they may have - with the corresponding seats of the plurality of respective seats - a positive clearance only according to the alignment directions, a substantially zero clearance being established in the radial direction.

According to this aspect of the invention, the plurality of connecting elements with clearance may comprise at least three connecting elements with clearance arranged with alignment directions forming an angle of 60° between them.

Still according to this aspect of the invention, the connecting elements with clearance may have a substantially circular section of predetermined diameter and the corresponding seats may have an elongated section with smaller dimensions corresponding to the predetermined diameter and larger dimension corresponding to the sum of the predetermined diameter and twice the clearance.

In addition, according to another aspect of the invention, the interface plate may comprise contact portions with the supporting plate by means of at least one connecting elements with clearance of the plurality of connecting elements with clearance.

According to such aspect of the invention, the interface plate may comprise further contact portions with the stiffener by means of at least one connecting element without clearance of the plurality of connecting elements without clearance.

Furthermore, the probe card may comprise connecting elements without clearance between the probe head and the stiffener.

According to another aspect of the invention, the interface plate may comprise first discrete contact portions with the supporting plate by means of the connecting elements with clearance.

According to this aspect of the invention, the interface plate may comprise second contact portions with the stiffener and with the first contact portions by means of respective connecting elements without clearance of the plurality of connecting elements without clearance.

Furthermore, the interface plate may comprise a further contact portion between the probe head and the stiffener by means of respective further connecting elements without clearance of the plurality of further connecting elements without clearance.

According to an aspect of the invention, the connecting elements with clearance may be made with a material having a low coefficient of thermal expansion compared to a material that realizes the supporting plate.

Lastly, the connecting elements with clearance may be made of steel.

The characteristics and advantages of the probe card according to the invention shall be apparent from the description, provided for hereinafter, of an embodiment thereof provided by way of non-limiting example with reference to the attached drawings.

Brief description of the drawings

In such drawings:

Figure 1A schematically shows a contact probe for a vertical probe head obtained according to the prior art;

- Figure IB schematically shows a probe card adapted to support a vertical probe head obtained according to the prior art;

Figure 2 schematically shows a probe card according to an embodiment of the invention; Figures 2A-2C schematically show enlargements of a connecting element of the probe card of Figure 2 in various operating conditions;

Figure 3 schematically shows a probe card according to an alternative embodiment of the invention; and

Figures 3A-3B schematically show enlargements of a connecting element of the probe card of Figure 3 in various operating conditions; and

Figure 4 schematically shows an arrangement for the connecting elements of Figures 3A-3B.

Detailed description

With reference to such figures, and in particular Fto igure 2, a probe card comprising at least one probe head provided with a plurality of contact probes for testing electronic devices, in particular integrated on wafer, is indicated with 20 as a whole.

It should be observed that the figures represent schematic views of the system according to the invention and they were not drawn in scale, but in a way to highlight the major features of the invention.

In addition, the various aspects of the invention represented by way of example in the figures can obviously be combined with each other and be interchanged from one embodiment to the other.

In particular, as illustrated in figure 2, the probe card 20 comprises a probe head 21 which houses a plurality of contact probes 22, as well as a supporting element, in particular a supporting plate 23, commonly referred to as PCB, associated through an interface element, in particular an interface plate 25, to a stiffener 24 and adapted to be connected with a test apparatus (not shown). In particular, in the example illustrated in the figure, the probe head 21 is of the vertical type and comprises at least one plate or upper guide and one plate or lower guide, having respective holes within which there slide contact probes 22 solely by way of example. There can also be used a probe head of the cantilever type, the invention not being limited to a particular type of probe head.

In any case, the contact probes 22 comprise contact ends or tips adapted to abut against corresponding contacting pads of a device to be tested so as to obtain the desired contact, in particular electrical, between it and the probe card 20, and thus the test apparatus connected thereto.

Generally, the devices to be tested are circuits integrated on a wafer made of a semi-conductor material which - during the test stage - is arranged on a support 26, commonly referred to as card tray and part of a system usually referred to as prober, on which also the probe card 20 abuts.

Advantageously, according to the invention, the probe card 20 also comprises at least one connecting element 27 between the supporting plate 23 and the interface plate 25, such connecting element 27 being housed with clearance in a suitable seat 28 obtained in the supporting plate 23. Further connecting elements 27' without clearance are provided between the interface plate 25 and the stiffener 24 and between the probe head 21 and the stiffener 24.

In particular, the probe card 20 is provided with a plurality of connecting elements 27 with clearance in connection with contact portions 25A of the interface plate 25, the same having further contact portions 25B with the stiffener 24, suitably provided with lateral arms 24A which connect it to such further contact portions 25B of the interface plate 25 indeed.

More in particular, the connecting element 27 with clearance comprises a body 27B and a head portion 27C connected to the body 27B and having at least one transverse dimension larger than the transverse dimension of the body 27B so that the connecting element 27 with clearance is provided with suitable shoulders 27A adapted to go in abutment with corresponding shoulders 28A of the seat 28, as illustrated further in detail but still schematically in the enlargement of Figure 2A in inoperative conditions, i.e. in absence of mechanical stresses and/or thermal dilatation thereof. Suitably, as illustrated in such figure, the seat 28 shall have a configuration corresponding and mating with that of the connecting element 27 with clearance and respective larger dimensions to allow the housing floating therein of the connecting element 27 with clearance. Furthermore, at least one portion of the body of the connecting element 27 with clearance may penetrate into the interface plate 25 and be made integral therewith, in particular at the corresponding contact portion 25A, to obtain the desired integration between the connecting element 27 with clearance and the interface plate 25 indeed. It should be observed that in a transverse section, like the one shown in Figures 2A- 2C, the connecting elements 27 with clearance and the respective seats 28 have a capsized T-shape.

In case of substantially tubular elements, it can be provided for that the body 27B has a diameter D l comprised between 3mm and 5mm and the head portion 27C has a diameter D2 comprised between 5mm and 10mm, such values being deemed in inoperative conditions of the probe card 20, i.e. in absence of mechanical stresses and/or thermal expansions thereof.

Advantageously, the seat 28 has elements, in particular the body

28B and the head portion 28C, corresponding to elements of the connecting element 27 with clearance, in particular the body 27B and the head portion 27C, respectively, with dimensions enlarged by at least 10%, thus allowing the supporting plate 23 to expand following the increase of the operating temperature of the probe card 20, simultaneously avoiding any movement of the probe head 21, which would affect the good result of the test carried therewith.

In particular, the seat 28 comprises tubular elements with diameters and thicknesses of the bodies 28B and head portion 28C enlarged with respect to the corresponding diameters and thicknesses of the bodies 27B and head portions 27C of the connecting element 27 with clearance.

Thus, the connecting element 27 with clearance housed in the seat 28 has a first clearance Gl at the body 27B thereof with respect to the body 28B of the seat 28, a second clearance G2 at the head portion 27C thereof with respect to the head portion 28C of the seat 28 and a third clearance G3 at the shoulder 27A thereof with respect to the shoulder 28A of the seat 28. Suitable values of these clearances Gl , G2 and G3 are between 50μηι and 350μπι, preferably ΙΟΟμπι; furthermore the values of such clearances Gl, G2 and G3 may be identical or different with respect to each other according to needs. Obviously, the values of the clearances Gl, G2 and G3 shall depend on the applications of the probe card 20.

During the operation, when the interface plate 25 is placed on the support 26, the shoulder 27A of the connecting element 27 with clearance is at pressure contact on the shoulder 28A of the seat 28, as schematically illustrated in the enlargement of Figure 2B. In this case, the third clearance G3 becomes null and a space 29 of thickness Tk having dimensions identical to the third clearance G3 is established between the supporting plate 23 and the interface plate 25, as indicated also in Figure 2. The thickness Tk of the space 29 is determined by the suitable dimensioning of the connecting elements 27 with clearance, and in particular the head portion 27C thereof, having a thickness LI smaller than the thickness L2 of the head portion 28C of the respective seats 28. More particularly, the thickness LI is 10% smaller than the thickness L2. Also in this case, the values of the thicknesses LI and L2 shall depend on the applications of the probe card 20.

Concretely, the supporting plate 23 is connected to the interface plate 25 in a floating manner due to the presence of the connecting elements 27 with clearance housing floating elements in the respective seats 28.

Thus, in operating conditions which imply temperatures that cause a thermal expansion of the materials that the elements of the probe card 20 are made of, the supporting plate 23 may expand, for example according to the direction indicated by the arrow F in Figure 2. Advantageously, according to the invention, the use of the connecting elements 27 with clearance which allow connecting - with clearance -the supporting plate 23 with the interface plate 25, allows the supporting plate 23 to deform according to such thermal expansion without affecting the positioning of the probe head 21 within the probe card 20 and thus the correct operation of the card itself. In addition, even a possible thermal expansion of the interface plate 25 does not affect the positioning of the supporting plate 23 which is not fixedly constrained to the interface plate 25, in particular preventing the curving of such supporting plate 23 and thus a displacement of the probe head 21 , overcoming the drawbacks of the cards obtained according to the prior art. It should also be observed that any curving of the supporting plate 23, due to the presence of a gradient temperature therein, due to the different temperatures of the wafer and the test apparatus surrounding it, are compensated by the floating coupling obtained due to the connecting elements 27 with clearance, thus reducing the risks of breaking the supporting plate 23 itself.

In particular, the presence of the space 29 allows eliminating the risk of breaking the supporting plate 23 due to the curving thereof for a gradient temperature therein.

The mechanism related to the clearance between every connecting element 27 with clearance and the respective seat 28 is schematically illustrated in the enlargement of Figure 2C, where it is clear that the connecting element 27 with clearance remains correctly housed in the seat 28 thereof even in the presence of thermal expansion of the supporting plate 23 where such seat 28 is obtained, such thermal expansion being indicated by an arrow F also in Figure 2C.

Suitably, the connecting elements 27 with clearance are made using a material having a low coefficient of thermal expansion with respect to the material the supporting plate 23 is made of. More particularly, in a preferred embodiment, the supporting plate 23 is made using a material suitable for manufacturing printed circuits, such as FR4 (acronym for "Flame Retardant") while the connecting elements 27 with clearance are made of steel, the variations of the dimensions thereof, in particular the diameters D l and D2, thus being negligible with respect to the expansion of the supporting plate 23. Furthermore, the contact portions 25A of the interface plate 25 and the stiffener 24 may be made of the same material, in particular steel, so as to reduce movement in case of high temperature applications and, anyway, when there is a temperature capable of determining a thermal expansion of the supporting plate 23 as a whole .

The assembly made up of the supporting plate 23 and the probe head 21 is particularly housed in a suitable hole of the prober system, having dimensions at least equivalent to the length HD indicated in Figure 2, such length HD depending on the tester apparatus associated to the probe card 20.

According to an alternative embodiment of the invention, schematically illustrated in Figure 3, the probe card 20 is provided with a plurality of connecting elements 27 with clearance housed floating in respective seats 28 realised in the supporting plate 23.

As shown further in detail in Figure 3A, each connecting element 27 with clearance comprises a body 27B and a head portion 27C, the respective seat 28 being dimensioned so as to respectively have a body 28B with dimensions substantially corresponding to the body 27B of the connecting element 27 with clearance housed therein and a head portion 27C having larger dimensions, allowing, like in the previous embodiment, a floating housing of the connecting elements 27 with clearance in the respective seats 28. With respect to the previous embodiment, the first clearance Gl at the bodies 27B and 28B is substantially null in the transverse direction while the second clearance G2 at the head portions 27C and 28C and the third clearance G3 at the shoulders 27A and 28A remain present. Furthermore, the head portion 27C of the connecting elements 27 with clearance is obtained so as to establish a further clearance G4 with respect to a face of the supporting plate 23.

Such further clearance G4 is determined by the suitable combined dimensioning of the connecting elements 27 with clearance and the respective seats 28. In particular, the sum between the thickness of the head portion 27C of the connecting elements 27 with clearance and the third clearance G3 is greater than the thickness of the head portion 28C of the respective seats 28. The further clearance G4 is thus greater than the third clearance G3. Thus, having positioned the probe card 20 on the support 26, the head portions 27C of the connecting elements 27 with clearance, that project from the supporting plate 23, end up in direct contact and pressing contact against the support 26, as illustrated in Figure 3B.

Furthermore, there is a space 29 of thickness Tk between the supporting plate 23 and a contact portion 25A of the interface plate 25 at the respective contact element 27 with clearance, as also indicated in Figure 3. The thickness Tk of the space 29 is determined by the suitable dimensioning of the connecting elements 27 with clearance, and in particular the head portion 27C thereof, which has a thickness LI greater than the thickness L2 of the head portion 28C of the respective seats 28. More in particular, the thickness LI is 10% greater than the thickness L2. Also in this case, the values of the thicknesses LI and L2 shall depend on the applications of the probe card 20.

It should be observed that the configuration of the connecting elements 27 with clearance and the respective seats 28 shown in figures 3A and 3B, as well as the presence of the thickness 29 between the supporting plate 23 and the interface plate 25 in inoperative conditions may also be used for the probe card 20 illustrated in Figure 2.

According to the embodiment illustrated in Figure 3, the interface plate 25' particularly comprises a plurality of first contact portions 25Ά with corresponding connecting elements 27 with clearance. With respect to the previous embodiment, the first contact portions 25Ά may in this case be discrete portions, instead of portions of a layer the actual interface plate is made of.

Furthermore, the interface plate 25' comprises a further contact portion 25T3 between the probe head 21, in particular a portion 21A thereof, commonly referred to as spacer, incorporated in the supporting plate 23, and the stiffener 24, as well as a plurality of second contact portions 25'C between the contact portions 25A with the connecting elements 27 with clearance and the stiffener 24, even such second contact portions 25'C possibly being discrete portions.

A plurality of further connecting elements 27' without clearance are provided between the probe head 21 and the interface plate 25', as well as between the interface plate 25' and the stiffener 24. In particular, the further connecting elements 27' without clearance connect the contact portion 25T3 and the probe head 21 , the further contact portions 25'C and the contact portions 25Ά, as well as the further contact portions 25'C and the stiffener 24. The further connecting elements 27' without clearance may be obtained by means of simple screws.

Thus, the entire mechanism of the probe card 20 is substantially raised due to the further connecting elements 27' without clearance.

The correct positioning of the probe card 20 illustrated in Figure

3 may be guaranteed due to a suitable positioning of the connecting elements 27 and the respective seats 28.

According to an aspect of the invention, as schematically illustrated in Figure 4, the supporting plate 23 comprises at least three connecting elements 27 with clearance arranged in a plane π defined by the supporting plate 23 so that the aligning directions Xl-Xl , X2-X2, X3- X3 of the connecting elements 27 with clearance form an angle a of 120° therebetween. Generally, such angle a is equivalent to 360° /number of elements.

Thus, it should be observed that the corresponding seats 28 have a clearance G5, positive and radial, only along such aligning direction Xl-Xl, X2-X2, X3-X3, while they have a substantially null clearance in the transverse direction, so as to allow an expansion of the supporting plate 23 but simultaneously guaranteeing the correct positioning.

More in particular, according to an embodiment, the connecting elements 27 with clearance have a substantially circular section with diameter D and the respective seats 28 have an elongated section with smaller dimensioning Al corresponding to such diameter D and a larger dimensioning A2 equivalent to D+2G4, as indicated in such figure. Thus, this allows the movement of the connecting elements 27 with clearance within the seats thereof 28 only along the aligning directions Xl-Xl , X2- X2, X3-X3, only up to the narrowing of the respective seat 28 to a dimension equivalent to the diameter of the connecting element 27.

This configuration allows an accurate assembly of the supporting plate 23 on the interface plate 25 and guarantees the maintenance of the aligning even during the operation at high temperatures, in particular in presence of thermal expansions of the supporting plate 23.

Obviously, there can be provided for a plurality of connecting elements 27 with clearance, in particular more than three, distributed according to the radial development of the aligning directions thereof, the corresponding seats having clearance along such directions alone.

Actually, it should be observed that, contrary to the known cards which comprise probe heads placed on the support through supporting plates, which thus cannot be released from the probe heads or interface cards that guarantee the stiffening thereof, the probe card 20 according to the invention comprises an interface plate 25 completely released from the supporting plate 23 due to the use of connecting elements 27 with clearance housed floating in the seats 28 of the support. The suitable arrangement of such connecting elements 27 with clearance, for example as illustrated in Figure 4, guarantees the aligning of the probe head 21 even in the presence of vibrations due to the mechanical movement of the prober system, preventing any movements that are not expansions of the card.

It should be observed that the probe card 20 is at contact with pushing elements 30 of the test apparatus (not illustrated) adapted to push the supporting plate 23, which presses the connecting elements 27, which in turn end up at contact with the support 26. In particular, the pushing elements are obtained through the so-called pogo towers, provided with a plurality of needles or pogoes pin that directly lie on the supporting plate 23, indicated with 30A in figure.

The presence of the pushing elements 30, particularly allows drastically reducing and even eliminating the movement of the probe head 21 in the direction Z, normal to the plane π indicated in figure 4.

During the operation, when the supporting plate 23 is placed on the support 26, the shoulder 27A of the connecting element 27 with clearance is at pressure contact on the shoulder 28A of the seat 28, as schematically illustrated in the enlargement of Figure 3B. In this case, the third clearance G3 is nullified and the space 29 widens up to a thickness having dimensions equivalent to the sum between the initial thickness Tk and the third clearance G3.

It should be observed that during operation, even in case of elimination of the third clearance G3, there is however present a space between the supporting plate 23 and the support 26 given that the further clearance G4 is greater than the third clearance G3, the supporting plate 23 being kept in position even due to the pushing elements 30. Actually, the space, guaranteed by the further clearance G4, allows the probe card 20 to continue operating correctly even in the presence of dimensional changes of the constituting elements thereof, for example related to a thermal expansion.

In conclusion, advantageously according to the invention, there is obtained a probe card capable of correctly operating ,even in the presence of operating temperatures that imply the thermal expansion of the elements it is made of, thus overcoming the drawbacks of the cards currently available in the market.

The use of connecting elements housed with clearance in suitable seats, the supporting plate may expand following the increase of the operating temperature of the probe card without inducing the movement of the probe heads, so as to guarantee the correct operation of the probe card in operating conditions with high temperatures which affect the good operation of the known cards.

Advantageously, according to the invention, the positioning of the supporting plate is not affected by the possible thermal expansion of the interface plate, which is not fixedly constrained to the supporting plate.

In particular, the configuration of the probe card prevents the curving of the supporting plate, due to the presence of a temperature gradient therein, due to the different temperatures of the wafer and the test apparatus that surround it, which is compensated by the floating coupling obtained due to the connecting elements, thus reducing the risks of breaking the supporting plate, also due to the presence of a space between the supporting plate and the connecting portions of the interface plate.

Obviously, the probe card described above may be subjected, by a man skilled in the art with the aim of meeting contingent and specific needs, to numerous modifications and variants, all falling within the scope of protection of the invention as defined by the claims that follow.