WO2025242528A1

WO2025242528A1 - Probe card having a simplified structure

Info

Publication number: WO2025242528A1
Application number: PCT/EP2025/063361
Authority: WO
Inventors: Riccardo Vettori
Original assignee: Technoprobe SpA
Current assignee: Technoprobe SpA
Priority date: 2024-05-21
Filing date: 2025-05-15
Publication date: 2025-11-27
Anticipated expiration: 2026-11-21

Abstract

TEC163BWO - 23 - ABSTRACT A probe card for testing a device under test is described, said probe card having a plurality of contact elements, a containment structure configured to house the contact elements, an interface board adapted to interface the probe card with a test equipment, and at least 5 one connection system configured to connect the containment structure and the interface board to each other. The connection system is equipped with a connection element comprising a first portion through which it is fixedly connected to the interface board, and a second portion projecting from the interface board and housed in a recess formed in the 10 containment structure, and at least one elastic element which is inside the recess and connected, at a first end thereof, to the second portion of the connection element and, at a second end thereof, to the containment structure, said elastic element being in a compressed configuration under the action of the connection element and exerting a reaction elastic force 15 which maintains the containment structure and the interface board in mutual contact. (Fig. 1)

Description

Title: Probe card having a simplified structure

DESCRIPTION

Field of application

The present invention refers to a probe card adapted to carry out testing of electronic devices integrated on a semiconductor wafer, for example a large probe card for testing memory devices. The following description relates to this field of application with the only purpose of simplifying its exposition.

Prior art

As it is well known, a probe card is essentially a device adapted to put in electrical connection a plurality of contact pads of a microstructure, in particular an electronic device integrated on a semiconductor wafer, with corresponding channels of a test equipment which tests the functionality thereof, in particular its electrical functionality.

In particular, the test performed on integrated circuits is used to detect and isolate defective circuits already in the production step. Normally, probe cards are thus used to test integrated circuits before cutting and assembling them within a chip-containing package.

A probe card generally comprises a probe head equipped with a plurality of movable contact probes that are held by at least one pair of supports or guides substantially platelike and parallel to each other. Said platelike supports are provided with guide holes and are placed at a certain distance from each other so as to provide a free region or air gap for the movement and the possible deformation of the contact probes, which are usually made of wires of special alloys with good electrical and mechanical properties.

The contact probes generally extend between a first end portion, intended for contacting contact pads of the device under test, and a second end portion, intended for contacting a space transformer or a printed circuit board (PCB) that are associated with the probe head.

Thus, the use of a space transformer, which is generally in the form of an MLC (acronym of the term “Multi Layer Ceramic”), serves the purpose of redistributing the signals transported by the contact probes and thereby of allowing a redistribution of the contact pads on the PCB, although in this way the probe card comprises an additional component and there is no direct connection between the contact heads of the probe and the PCB.

This problem is particularly felt in the case of large probe cards, such as for example probe cards for testing memory devices such as DRAM.

Even more in particular, this problem is felt in the case of test equipment (such as, for example, the machines “Cellcia” produced by Tel for testing memories on 12 -inch wafers) that integrate some components that are traditionally integrated on probe cards, such as, for example, mechanical components for the planarization and stiffening of the PCB and interposer. In this case, the connection between the probe card and the test equipment takes place through tightening with a vacuum suction system, on a flat rigid structure (which planarizes the PCB) . Overdrive is carried out by means of a VAC suction system which raises the semiconductor wafer together with the chuck housing it and puts it in contact with the probes (an axis motorized along the z-axis is generally not used).

This modern test equipment thus requires very light probe cards (in some applications, the probe cards should not exceed 1.3 Kg).

In accordance with some known solutions, probe cards with contact microprobes made by means of MEMS technology are used, in particular probes of the micro-cantilever type, directly integrated on the PCB, in particular welded on the PCB. However, the current solutions with the above-mentioned micro-cantilever probes do not allow to cover the layouts of the contact pads of the devices under test to be expected in the future, so that there is the need to move on to solutions with vertical probes, namely, with probes having a longitudinal extension and passing through ceramic guides.

It is thus desirable to use a vertical-probe technology in the above-mentioned applications, wherein the contact heads of the vertical probes interface directly with the PCB.

The technical problem of the present invention is to provide a probe card having such structural and functional features to allow overcoming the limitations and the drawbacks that currently affect the known solutions, in particular a probe card that allows to use vertical contact probes and at the same time has a simplified structure that makes it light and easy to interface with the most modern test equipment.

Summary of the invention

The solution idea underlying the present invention is to provide a probe card wherein the probe head (namely, the assembly comprising guides and housing) is directly connected to the PCB through a connection system comprising an elastic element so as to prevent a too rigid tightening between said components, thereby allowing their thermal expansion during the test without mechanical stresses, which stresses can even cause an undesired deformation of the probe card.

Based on said solution idea, the above-mentioned technical problem is solved by a probe card for testing a device under test, said probe card comprising a plurality of contact elements adapted to contact contact pads of the device under test, a containment structure configured to house at least partially the contact elements, an interface board adapted to interface the probe card with a test equipment, and at least one connection system configured to connect the containment structure and the interface board to each other, wherein said at least one connection system comprises a connection element (or tightening element) comprising a first portion through which it is integrally (or fixedly) connected to the interface board, and a second portion projecting from said interface board and housed in a recess formed in the containment structure, and at least one elastic element that is arranged in said recess and connected, at a first end thereof, to the second portion of the connection element and, at a second end thereof, to the containment structure, said elastic element being in a compressed configuration under the action of the connection element (that is, it compressed by the connection element) and exerting a reaction elastic force which maintains the containment structure and the interface board in connection with each other (for example, in mutual contact).

More in particular, the invention comprises the following additional and optional features, taken individually or in combination if needed. Said additional and optional features are illustrated, for example, in the dependent claims.

According to an aspect of the present invention, the second portion of the connection element may comprise a body and a head portion having at least one transverse dimension (that is, a direction that is orthogonal to a longitudinal direction along which the connection element extends, wherein said longitudinal direction may be parallel to a longitudinal direction of the contact probes) that is greater than a corresponding transverse dimension of said body, thereby defining a first shoulder.

According to an aspect of the present invention, the elastic element may be connected to the second portion at the first shoulder.

According to an aspect of the present invention, the second portion of the connection element may have at least one transverse dimension (also in this case, a direction that is orthogonal to a longitudinal direction along which the connection element extends, wherein said longitudinal direction may be parallel to a longitudinal direction of the contact probes) that is greater than a corresponding transverse dimension of its first portion, thereby defining a second shoulder abutting onto the interface board.

According to an aspect of the present invention, the connection element may be fastened to the interface board by means of a threaded connection.

According to an aspect of the present invention, the first portion of the connection element may comprise a thread for forming said threaded connection, said first portion being housed in the interface board.

According to an aspect of the present invention, the connection system may comprise a bush (or a nut or more in general a tightening element, generally at least partially hollow and internally threaded, capable of receiving the connection element) into which the first portion of the connection element is screwed (in general, inserted), said bush or nut being housed in a seat formed in the interface board.

According to an aspect of the present invention, the recess formed in the containment structure may have at least one dimension that is greater than a corresponding dimension of the second portion of the connection element.

According to an aspect of the present invention, the at least one elastic element may be in the form of a curved plate.

According to an aspect of the present invention, the probe card may comprise a plurality of connection systems arranged at specific positions of said probe card.

According to an aspect of the present invention, the containment structure may include a housing comprising a body equipped with openings for housing the contact elements.

According to an aspect of the present invention, the containment structure may comprise at least one guide equipped with a plurality of guide holes in which portions of the contact elements are housed.

According to an aspect of the present invention, the probe card may comprise a first guide or lower guide and a second guide or upper guide, each equipped with a respective plurality of guide holes.

Whichever the configuration of the containment structure may be, what matters is that it comes in contact with the interface board (for example, but not necessarily, through the guide, or directly through the housing, or in any suitable way).

According to an aspect of the present invention, the housing may be arranged between the first guide and the second guide and may support said guides.

According to an aspect of the present invention, the interface board may be a printed circuit board.

According to an aspect of the present invention, the contact elements may be vertical contact probes comprising a first end adapted to contact the contact pads of the device under test and a second and opposite end adapted to contact the interface board.

The present invention also refers to a method for assembling a probe card comprising the steps of:

- providing a containment structure;

- providing an interface board; and

- connecting the containment structure and the interface board with each other.

The step of connecting comprises a step of inserting (for example, screwing) a first portion of a connection element into the interface board with consequent compression, by means of a second portion of said connection element, of an elastic element connected to said second portion of said connection element and to the containment structure, with generation of a reaction elastic force which maintains the containment structure and the interface board in connection with each other (for example, in mutual contact).

The features and advantages of the probe card and of the method according to the invention will become apparent from the following description of an embodiment thereof, given by way of nonlimiting example with reference to the accompanying drawings.

Brief description of the drawings

In the drawings:

- Figure 1 shows an exemplary probe card according to the present invention;

- Figure 2 shows a detail of the probe card according to embodiments of the present invention;

- Figures 3A and 3B show an example of steps for assembling the probe card of Figure 1 ; and

- Figures 4A-4C show top views and respective exemplary lateral views of an elastic element according to embodiments of the present invention.

Detailed description

With reference to those figures, reference number 1000 globally and schematically indicates a probe card according to the present invention for testing a device under test (herein indicated with the acronym DUT), in particular a probe card adapted to carry out testing of electronic devices integrated on a semiconductor wafer.

It should be noted that the figures represent schematic views and are not drawn to scale, but instead they are drawn so as to emphasize the important features of the invention. Furthermore, in the figures, the different elements are schematically depicted, and the shape thereof can change depending on the desired application. Furthermore, it should be noted that, in the figures, identical reference numerals refer to identical elements in terms of shape or function. Finally, arrangements described in relation to an embodiment illustrated in a figure can also be used for the other embodiments illustrated in the other figures.

It is also be noted that, unless it is expressly stated to the contrary, process steps can also be inverted if necessary.

It is further noted that, in the context of the present invention, the expression “probe card” is used to indicate a testing system without being limited to the presence or absence of specific components. In general, said expression thus indicates an assembly of components (for example, the components of a probe head and interface boards interfaced thereto, such as, for example, a PCB) associable with further components (for example, components of a test equipment) for testing devices integrated on the semiconductor wafer, and thus generally indicates a system for measuring electronic devices.

The probe card 1000 is thus adapted to connect to an equipment (not shown in the figures) to carry out the test of devices under test DUT integrated on a semiconductor wafer (indicated with reference number 23), for example, it may be a large probe card for testing memory devices, for example, DRAMs. The maximum dimensions of the probe card 1000 of the present invention as a whole can even be about 350 mm. For example, if the probe card 1000 has a mainly circular shape (and thus comprises circular guides), its maximum diameter can be about 350 mm. Clearly, the above-illustrated application is merely an example and the probe card 1000 of the present invention can be used to test many other electronic devices, and it can have any shape and size.

As illustrated in Figure 1, the probe card 1000 comprises a plurality of contact elements 10 adapted to contact contact pads (indicated with reference DUTp) of the device under test DUT.

The probe card 1000 also comprises a containment structure (reference 20) configured to house at least partially the contact elements 10.

It is noted that the assembly formed by the contact probes 10 and the containment structure 20 is usually indicated as “probe head” in the field.

In one embodiment, the containment structure 20 comprises a housing (indicated with reference 20’) comprising a body equipped with openings for housing the contact elements 10, and it also comprises at least one guide 20g 1 equipped with a plurality of guide holes 20g lh in which portions of the contact elements 10 are slidingly housed. More in particular, as it is illustrated in the figures, there may be a first guide or lower guide (still indicated with reference 20g 1) and a second guide or upper guide 20g2, each equipped with a respective plurality of guide holes 20glh and 20g2h, which are separated by an air gap. In this case, the housing 20’ is arranged between the lower, first guide 20g 1 and the upper, second guide 20g2 and supports said guides.

The probe card 100 also comprises an interface board (reference 30), such as, for example, a printed circuit board (PCB), adapted to interface the probe card with the test equipment.

Suitably, the contact elements 10 are vertical contact probes (still indicated with reference 10) extended along a longitudinal axis H-H, comprising a first end 10a adapted to contact the contact pads DUTp of the device under test DUT and a second and opposite end 10b adapted to contact contact pads (not indicated in the figures) of the interface board 30. In the embodiment illustrated in the figures, the above-mentioned contact probes 10 are free to deform in the overdrive step, in particular said deformation occurs in the air gap between the lower, first guide 20g 1 and the upper, second guide 20g2.

In one embodiment, in order to prevent the force response as a function of overdrive from saturating, the body of the above-mentioned vertical contact probes 10 has a non-rectilinear shape, in particular, it may have an S shape.

In order to produce a light and easy-to-handle probe card, the probe head, in particular the containment structure 20, is directly connected to the interface board 30.

To this end, according to the present invention, the probe card 1000 comprises a connection system (globally indicated with reference 40) configured to connect the containment structure 20 and the interface board 30 to each other.

Advantageously according to the present invention, the connection system 40 does not rigidly fasten the containment structure 20 and the interface board 30 to each other, but allows said components to expand following thermal expansions without creating mechanical stresses. It is noted that the containment structure 20 and the interface board 30 are made of materials having different coefficients of thermal expansion (CTE). For example, the housing may be made of materials having a low CTE (for example, between 3 and 7 ppm/ °C), whereas the interface board may be made of materials having CTEs between 12 and 17 ppm/ °C, without any limitation of the scope of the present invention.

This result is obtained thanks to the fact that the connection system 40 comprises two different portions, namely a tightening or connection element (indicated with reference 40a) and an elastic element (reference 40b) connected thereto, as will be detailed below.

In particular, as illustrated in the detail of Figure 2 (which shows a section of the elastic element 40b), the connection element 40a comprises a first portion 40a 1 through which it is fixedly and rigidly connected to the interface board 30, and a second portion 40a2 projecting from said interface board 30. The second portion 40a2 is housed in a recess or seat 20r formed in the containment structure 20. In other words, the connection element 40a is formed by a part (namely, the first portion 40a 1) which is housed in the interface board 30 and is rigidly fastened to said interface board 30 and thus ensures the integral connection of said connection element therewith, and a part (namely, the second portion 40a2) which is not housed in the interface board 30 and projects therefrom, in particular, projects from the bottom.

The elastic element 40b is arranged in the recess 20r formed in the containment element 20 and is connected, at a first end 40b 1 thereof, to the second portion 40a2 of the connection element 40a and, at a second end 40b2 thereof, to the containment structure 20, in particular to the housing 20’. The elastic element 40b therefore allows an indirect connection (through it) between the containment structure 20 and the interface board 30, said connection thus being a non-rigid connection.

More in particular, the elastic element 40b is in a compressed configuration under the action of the connection element 40a, which causes the compression thereof and thus causes the generation of a reaction elastic force F which maintains the containment structure 20 and the interface board 30 in connection with each other (for example, in mutual contact). Only by way of example, Figures 3A and 3B show the compression of the elastic element 40b in the step of assembling the probe card 1000. In the assembling step, the elastic element 40b is thus compressed against the inner wall of the housing 20’ by the connection element 40a while the latter is inserted with its first portion 40a 1 into the interface board 20, consequently exerting the above-mentioned reaction elastic force F.

The elastic element 40b is thus configured to force the containment structure 20 and the interface board 30 into mutual approach, pushing said components against each other. By way of example (for example, based on a specific shape of the connection element, as will be also illustrated below), the elastic element 40b may generate a force F like the one indicated in Figures 1 and 3B, which pushes the containment structure 20 toward the interface board 30, namely upward; in any case, other less preferred configurations can also be considered, what matters is that the above- mentioned components are moved toward each other.

Suitably, the above-described solution avoids making tightening devices exerting hundreds of Kg that hinder the free expansion of the two components connected with each other, namely the containment structure 20 and the interface board 30. In fact, on one hand, the first portion 40a 1 of the connection element 40a is, at least partially, fixedly housed in the interface board 30, on the other hand the second portion 40a2 is connected to the elastic element 40b which in turn is connected to the containment structure 20, in particular to the housing 20’, thereby ensuring the above-mentioned floating tightening.

It is also noted that, although for simplicity reasons the figures show a single connection system 40, the probe card 100 may comprise a plurality of connection systems 40 arranged at specific positions. The various connection systems 40 are uniformly arranged in the probe card 1000, thereby obtaining a uniform tightening force F.

As mentioned above, the connection system 40 allows the connection between the connection system 20 and the interface board 30, wherein the upper, second guide 20g2 comprises a suitable opening to allow the connection element 40a, which is connected to the housing 20’ by means of the elastic element 40b, to pass through, thereby putting said upper, second guide 20g2 of the containment structure 20 in contact with the PCB.

In one embodiment of the present invention, the second portion 40a2 of the connection element 40a comprises a body and a head portion having at least one transverse dimension that is greater than a corresponding transverse dimension of said body, thereby defining a first shoulder S. In this way, the elastic element 40b is connected (fastened) to the second portion 40a2 at said first shoulder S by means of its first portion 40b 1.

The recess 20r formed in the containment structure 20 has dimensions that are greater than the corresponding dimensions of the connection element 40a, in particular, it has at least one dimension that is greater than a corresponding dimension of the second portion 40a2 of the connection element 40a, thereby allowing the advantageous connection by means of the elastic element 40b as described above.

Referring again to Figure 2, in a particular embodiment, the second end 40b2 of the elastic element 40b is arranged in a cavity formed in the housing 20’, although the present invention is not limited to this configuration and, in general, what matters is that said second end 40b2 is connected to the containment structure 20.

As illustrated in the non-limiting example of the figures, the second portion 40a2 of the connection element 40a has at least one transverse dimension that is greater than a corresponding transverse dimension of its first portion 40al, thereby forming a second shoulder (indicated with reference S’) abutting onto the interface board 30.

In the illustrated example, the connection element 40a has thus a section varying along the longitudinal direction of the contact probes 10, in particular widening from the first portion 40a 1 to the second portion 40a2, which is the extension of the first portion 40a 1 into the recess of the containment structure 20 and which has a terminal head having a widened shape, as mentioned above.

In one embodiment, the connection element 40a is fastened to the interface board 30 by means of a threaded connection. More in particular, the first portion 40a 1 of the connection element 40a comprises a thread that allows it to be screwed into the interface board 30, thereby allowing said first portion 40a 1 to be housed in the interface board 30, as already mentioned above.

Even more in particular, the connection system 40 comprises a bush (indicated with reference 40bus, or a bolt/ nut or, more in general, a tightening element, generally at least partially hollow and internally threaded, capable of receiving the connection element to allow fastening said connection element) which is housed in a suitable seat 30s formed in the interface board 30 and is fixedly connected, for example glued, to said interface board 30. In this way, the first portion 40a 1 of the connection element 40a is screwed (in general, inserted) in said bush or nut 40bus, thereby forming said threaded connection between said connection element 40a and said interface board 30. The bush or the nut is not limited to particular shapes.

The connection element 40a is thus in the form of a compression screw, which fact is very advantageous since the height of the non-threaded neck abutting onto the interface board 30 (namely, the height of the second portion 40a2 of the connection element, as measured along the longitudinal axis of the contact probes 10) allows to control the compression of the elastic element 40b and thus the force generated by it.

In one embodiment of the present invention, the elastic element 40b is in the form of a plate, in particular of a curved plate (for example, pierced in the center to allow the connection element 40a to pass through), although the present invention is not limited to a specific configuration of said elastic element 40b. Figures 4A-4C show examples of shapes of the elastic element 40b (namely, it can have a circular, rectangular or cross profile, or it can be shaped in any suitable way), wherein, based on such conformation thereof, in the assembling step said elastic element is compressed generating the above-mentioned force F.

It is thus evident from the above that the present invention also refers to a related method for assembling the probe card, wherein during fastening of the connection element 40a to the interface board 30, there is the compression of the elastic element 40b, as previously described.

In conclusion, the present invention thus allows to brilliantly overcome the technical problem, providing the above probe card and solving all the drawbacks of the prior art.

Advantageously, according to the present invention, the probe head is not rigidly tightened/ fastened to the interface board, thereby avoiding that possible temperature variations during the test create mechanical stresses due to the different CTEs of the coupled elements, which would cause a deformation of the probe card.

The uniformly distributed elastic elements allow to create a force that pushes the interface board against the containment structure of the probe head (or viceversa), thereby obtaining a mechanical contact between the heads of the contact probes and the pads formed on said interface board.

The combination of a tightening bush or nut and of a compression screw (namely, the above-mentioned connection element) also allows to control the compression of the spring and thus the generated force.

Thanks to the structure adopted, the probe card of the present invention is light and has a very simple structure, even if it can be large in size. Obviously, a person skilled in the art, in order to meet particular needs and specifications, may carry out several changes and modifications to the above-described probe card and method, all included in the protection scope of the invention as defined by the following claims.

Claims

1. A probe card (1000) for testing a device under test (DUT), said probe card (1000) comprising:

- a plurality of contact elements (10) adapted to contact contact pads (DUTp) of the device under test (DUT);

- a containment structure (20) configured to house at least partially the contact elements (10);

- an interface board (30) adapted to interface the probe card (1000) with a test equipment; and

- at least one connection system (40) configured to connect the containment structure (20) and the interface board (30) to each other, wherein said at least one connection system (40) comprises:

• a connection element (40a) comprising a first portion (40a 1) through which it is fixedly connected to the interface board (30), and a second portion (40a2) projecting from said interface board (30) and housed in a recess (20r) formed in the containment structure (20); and

• at least one elastic element (40b) that is arranged in said recess (20r) and connected, at a first end (40b 1) thereof, to the second portion (40a2) of the connection element (40a) and, at a second end (40b2) thereof, to the containment structure (20), said elastic element (40b) being in a compressed configuration under the action of the connection element (40a) and exerting a reaction elastic force (F) which maintains the containment structure (20) and the interface board (30) in connection with each other.

2. The probe card (1000) according to claim 1, wherein the second portion (40a2) of the connection element (40a) comprises a body and a head portion having at least one transverse dimension that is greater than a corresponding transverse dimension of said body, thereby defining a first shoulder (S), and wherein the elastic element (40b) is connected to said second portion (40a2) at said first shoulder (S).

3. The probe card (1000) according to claim 1 or 2, wherein the second portion (40a2) of the connection element (40a) has at least one transverse dimension that is greater than a corresponding transverse dimension of its first portion (40al), thereby defining a second shoulder (S’) abutting onto the interface board (30).

4. The probe card (1000) according to any one of the preceding claims, wherein the connection element (40a) is fastened to the interface board (30) by means of a threaded connection.

5. The probe card (1000) according to claim 4, wherein the first portion (40a 1) of the connection element (40a) comprises a thread for forming said threaded connection, said first portion (40a 1) being housed in the interface board (30).

6. The probe card (1000) according to claim 5, wherein the connection system (40) comprises a bush or a nut (40bus) into which the first portion (40al) of the connection element (40a) is screwed, said bush or nut (40bus) being housed in a seat (30s) formed in the interface board (30).

7. The probe card (1000) according to any one of the preceding claims, wherein the recess (20r) formed in the containment structure (20) has at least one dimension that is greater than a corresponding dimension of the second portion (40a2) of the connection element (40a).

8. The probe card (1000) according to any one of the preceding claims, wherein the at least one elastic element (40b) is in the form of a curved plate.

9. The probe card (1000) according to any one of the preceding claims, comprising a plurality of connection systems (40) arranged at specific positions of said probe card (1000).

10. The probe card (1000) according to any one of the preceding claims, wherein the containment structure (20) includes a housing (20’) comprising a body equipped with openings for housing the contact elements (10).

11. The probe card (1000) according to any one of the preceding claims, wherein the containment structure (20) comprises at least one guide (20g 1) equipped with a plurality of guide holes (20g lh) in which portions of the contact elements are housed (10).

12. The probe card (1000) according to claims 10 and 1 1, comprising a first guide or lower guide (20g 1) and a second guide or upper guide (20g2), each equipped with a respective plurality of guide holes (20glh, 20g2h), wherein the housing (20’) is arranged between said first guide (20g 1) and said second guide (20g2) and supports said guides.

13. The probe card (1000) according to any one of the preceding claims, wherein the interface board (30) is a printed circuit board (PCB).

14. The probe card (1000) according to any one of the preceding claims, wherein the contact elements (10) are vertical contact probes comprising a first end (10a) adapted to contact the contact pads (DUTp) of the device under test (DUT) and a second and opposite end (10b) adapted to contact the interface board (30).

15. A method for assembling a probe card (1000) comprising the steps of: - providing a containment structure (20);

- providing an interface board (30); and

- connecting the containment structure (20) and the interface board (30) with each other, wherein said step of connecting comprises a step of inserting a first portion (40a 1) of a connection element (40a) into the interface board (30) with consequent compression, by means of a second portion (40a2) of said connection element (40b), of an elastic element (40b) connected to said second portion (40a2) of said connection element (40a) and to the containment structure (20), with generation of a reaction elastic force (F) which maintains the containment structure (20) and the interface board (30) in connection with each other.