Probe head for high voltage tests

Abstract

It is herein disclosed a probe head (100) for testing a device under test (DUT) of the type having at least one first pad (DUTa) and one second pad (DUTb) that is different from the first pad (DUTa), the probe head (100) having a plurality of contact probes (10) with a body (10p) extended between a first end portion (10a) and a second end portion (10b) adapted to contact respective pads, wherein said contact probes (10) are divided into first contact probes (10'), which are grouped into at least one group (10g) and are configured to contact, as a group, a corresponding first pad (DUTa) of the device under test (DUT), and into at least one second contact probe (10") configured to contact a corresponding second pad (DUTb) of the device under test (DUT) that is different from the first pad (DUTa), and at least one guide (40) equipped with guide holes (40h) for housing at least one portion of the contact probes (10), wherein the guide (40) comprises a first face (FA) facing, during the test, toward the device under test (DUT) and a second face (FB) opposite the first face (FA). The probe head also comprises a protective element (50) which, during the test, is arranged between the first face (FA) of the guide (40) and the device under test (DUT), said protective element (50) comprising a body (50') equipped with holes (50h) in which the first contact probes (10') are housed, wherein said body (50') is configured as a protection barrier against emissions of molten metal coming from the device under test (DUT) toward the first face (FA) of the guide (40), thus preventing said emissions from reaching the guide (40).

Description

[0001] Title: Probe head for high voltage tests

[0002] DESCRIPTION

[0003] Field of application

[0004] The present invention relates to a probe head adapted to perform the testing of electronic devices integrated on a semiconductor wafer, for instance to perform high voltage tests. The following description is made with reference to this field of application with the only purpose of simplifying the exposition thereof.

[0005] Prior art

[0006] As it is well known, a probe head is essentially a device adapted to electrically connect a plurality of contact pads of a microstructure, particularly an electronic device integrated on a semiconductor wafer, with corresponding channels of a testing apparatus which performs the functionality testing thereof.

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

[0008] A probe head essentially comprises a plurality of contact probes housed in a pair of supports or guides which are substantially plate-shaped and parallel to each other. These plate-shaped supports are equipped with guide holes and are located at a certain distance from each other, so as to leave a free area or air gap for the movement and possible deformation of the contact probes, which are normally formed by wires of special alloys with good electrical and mechanical properties.

[0009] The contact probes generally extend between a first end portion, intended to contact the pads of the device under test, and a second end portion, intended to contact a space transformer or a printed circuit board (PCB) associated with the probe head.

[0010] The correct operation of a probe head is basically linked to two parameters: the vertical movement (or overtravel or overdrive) of the contact probes and the horizontal movement (or scrub) of the contact tips of these probes on the pads during the contact with the device under test. All these features are carefully evaluated and calibrated in the manufacturing step of a probe head, and the good electrical connection between contact probes and device under test should always be ensured.

[0011] Furthermore, the need of performing high voltage tests, for instance (but not only) in the automotive field, is increasingly common nowadays. Specifically, in recent years, the demand for power electronic components has increased dramatically due to the production of electric cars, with the need of performing tests at very high voltages, greater than 2000 V (even up to 10000 V), and at high currents, even greater than 3000 A. In these cases, the applied voltages are so high that damaging phenomena may occur, such as for instance the onset of electric arcs or the emission of molten metal material from the pads of the device under test toward the probe head. In the latter case, a localized accumulation of high energy occurs in a restricted area of the device under test, which triggers the aforementioned metal emission phenomenon (similar to an explosion, also referred to as “metal splash” or “metal evaporation”), which causes dirtying the exposed parts of the probe head. This phenomenon is not due to the contact between the device under test and the probes of the probe head, instead it is due to a failure of the device under test itself. These phenomena, in the long run, dirty the guide holes of the lower guide and, due to this phenomena, the contact probes get stuck inside said guide holes, which is an undesired effect. Moreover, the molten metal spread from the device may cause a short circuit between the gate and the source, which is obviously to be avoided.

[0012] Since the probe head is not responsible for the trigger of the above mentioned phenomenon of molten metal emission from the device under test, it is desirable to protect said probe head during the test.

[0013] The technical problem of the present invention is to devise a probe head having structural and functional features as to allow overcoming the limitations and drawbacks still affecting the known solutions, in particular a probe head that is properly protected during high voltage tests.

[0014] Summary of the invention

[0015] The solution idea underlying the present invention is to provide the probe head with a protective element (herein also indicated as “shield”) arranged at the guide, in particular arranged between the lower guide and the device under test, so as to block with its own body the molten metal emissions from the device during the test, thus preventing said emissions from reaching the guide. Particularly, the protective element comprises holes in which the contact probes intended to contact the power pads of the device under test are housed, wherein said holes do not act as a guide, but as a housing of the terminal part of the probes. Said protective element may move together with the contact probes or may be a fixed element of the probe head. The solution of the present invention thus does not provide for an attempt of avoiding the phenomenon of molten metal emission from the device under test, instead it provides for avoiding short circuits between the pads of the device under test and protecting the guide holes, by creating a protection barrier for the probe head.

[0016] Based on this solution idea, the above technical problem is solved by a probe head for testing a device under test of the type comprising at least one first pad and one second pad that is different from the first pad, said probe head comprising a plurality of contact probes including a body extended between a first end portion and a second end portion adapted to contact respective pads, wherein said contact probes are divided into first contact probes, which are grouped into at least one group and are arranged and configured to contact, as a group (in particular all together in said group, i.e. simultaneously), a same corresponding first pad of the device under test, and into at least one second contact probe configured to contact a corresponding second pad of the device under test that is different from the first pad, and at least one guide comprising guide holes for housing at least a portion of the contact probes, wherein said guide comprises a first face facing, during the test, the device under test and a second face opposite the first face, characterized in that it comprises a protective element which, during the test, is arranged between the first face of the guide and the device under test, the protective element comprising a body equipped with holes in which the first contact probes are housed, wherein said body is configured as a protection barrier against emissions of molten metal coming from the device under test toward the first face of the guide, thus preventing said emissions from reaching the guide.

[0017] In this way, the protective element, which is arranged and configured to be a shield protecting the guide of the probe head, protects said probe head from the emissions of molten metal coming from the pads of the device under test, in particular from the first pad, which is a power pad (for instance, it may be the source of a power device), whereas the second pad may be for instance the gate.

[0018] More particularly, the invention comprises the following additional and optional features, taken individually or in case in combination. Said additional and optional features are defined for instance in dependent claims 2 to 14.

[0019] According to an aspect of the present invention, the probe head may comprise a plurality of groups of first contact probes, each of said groups being intended to contact a respective first pad of a plurality of first pads on a semiconductor wafer, wherein, for each of said groups, the respective first contact probes (i.e. the probes of a group) are configured to contact all together said respective first pad, and wherein said groups of first contact probes are alternated with second contact probes, each of the second contact probes being arranged to contact a respective second pad of a plurality of second pads on the semiconductor wafer.

[0020] According to an aspect of the present invention, the protective element may be divided into a plurality of portions separated from each other, each of said portions housing a corresponding group of first contact probes.

[0021] According to an aspect of the present invention, the body of the protective element may be plate-shaped and may lie in a plane that is substantially parallel to a plane in which the guide lies.

[0022] According to an aspect of the present invention, the protective element may be removably connected to the probe head.

[0023] According to an aspect of the present invention, the first pad may be a source pad of the device under test and the second pad may be a gate pad or drain pad of the device under test.

[0024] According to an aspect of the present invention, the group of first contact probes may comprise a number of first contact probes from 50 to 350, so as to allow the passage of a high voltage signal via said first contact probes. According to an aspect of the present invention, the protective element may house in its holes just the first contact probes.

[0025] According to an aspect of the present invention, the protective element may be of a ceramic material.

[0026] According to an aspect of the present invention, the protective element may comprise protruding portions projecting from the body thereof toward the device under test.

[0027] According to an aspect of the present invention, the probe head may also comprise a conductive portion (metallization) that is formed on the guide and that includes at least one group of the guide holes, said conductive portion being configured to contact and short circuit the first contact probes (in particular the first contact probes of the group of first contact probes) housed in said group of guide holes, said probes being configured to carry a same determined type of signal, in particular a high voltage signal.

[0028] According to an aspect of the present invention, the protective element may be integral with the contact probes and may move together with said contact probes.

[0029] Alternatively, according to an aspect of the present invention, the contact probes may be adapted to move with respect to the protective element, which is a fixed component of the probe head. In this case, the holes of the protective element may have a diameter greater than the diameter of the guide holes of the guide. According to an aspect of the present invention, the probe head may be shaped (structured) so as to define a cabin in fluid communication with a supply line adapted to supply pressurized gas into said cabin.

[0030] According to an aspect of the present invention, the protective element may form at least a part of said cabin.

[0031] According to an aspect of the present invention, the holes of the protective element may be sized so as to allow the passage of the pressurized gas supplied toward the cabin.

[0032] The features and advantages of the probe head according to the invention will be apparent from the following description of an exemplary embodiment thereof given by way of non-limiting example with reference to the attached drawings.

[0033] Brief description of the drawings

[0034] In these drawings:

[0035] - figure 1 schematically shows a probe head according to the present invention;

[0036] - figure 2 shows a probe head according to an embodiment of the present invention;

[0037] - figure 3A shows a detail of a probe head without protective element and figure 3B shows a detail of a probe head with a protective element according to embodiments of the present invention; - figure 4 shows a probe head according to an alternative embodiment of the present invention; and

[0038] - figure 5A shows a detail of the probe head of figure 4 with accumulation of metal on the protective element, and figure 5B shows the replacement of said protective element.

[0039] Detailed description

[0040] With reference to these figures, reference number 100 globally and schematically indicates a probe head according to the present invention for testing a device under test (herein indicated with the acronym DUT - acronym for “Device Under Test”), for instance a probe head adapted to perform the test of electronic devices integrated on a semiconductor wafer.

[0041] 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 represented schematically, and their shape can vary depending on the desired application. Moreover, it should be noted that, in the figures, identical reference numbers refer to elements which are identical in shape or function. Finally, particular expedients described in relation to an embodiment illustrated in a figure can also be used for the other embodiments illustrated in the other figures.

[0042] It is noted that, unless expressly stated, described process steps can also be reversed if necessary. Moreover, it is noted that, in the context of the present invention, the term “probe head” is used to indicate a test system without being limited by the presence or not of particular components. In general, said term thus indicates a set of components associable with further components (for instance a space transformer and / or a PCB and / or a test apparatus) for testing devices integrated on a semiconductor wafer, and thus in general it indicates a test system for testing electronic devices. Moreover, the association of the probe head 100 with an interface board such as a space transformer and / or a PCB is indicated in the field as “probe card”.

[0043] The probe head 100 is thus adapted to connect with an apparatus (not illustrated in the figures) to perform the test of devices under test DUT integrated on a semiconductor wafer (indicated with reference number 23), for instance to perform tests at high voltage.

[0044] As illustrated in figure 1, the probe head 100 comprises a plurality of contact elements or contact probes 10 which are slidingly housed therein and intended to connect the device under test DUT integrated on the semiconductor wafer 23 with the test apparatus.

[0045] In order to house the contact probes 10, the probe head 100 comprises at least one guide 40 comprising guide holes 40h within which said contact elements 10 can slide. The guide holes 40h are thus suitably configured to house at least a portion of the contact probes 10 and to guide said contact probes 10 in their overtravel movement and scrub movement during the test. The guide 40 comprises a first face FA facing, during the test, the device under test DUT (said first face FA being thus a lower face according to the reference of the figures) and a second face FB opposite the first face FA (said face FB thus being an upper face according to the reference of the figures) .

[0046] In the embodiment illustrated in the figures, the guide 40 is a lower guide (i.e. it is the closest guide to the device under test) and the probe head 100 also comprises an upper guide 60, which comprises corresponding guide holes 60h and is separated from the lower guide by an air zone or gap G, even if the present invention is not limited to this specific configuration and the upper guide 60 may not be present or there may also be one or more intermediate guides (not illustrated in the figures), depending on the needs and / or circumstances.

[0047] Furthermore, the probe head 100 may comprise a housing F (only a part of this housing is depicted in figure 1 in a schematic way) adapted to contain at least part of the contact probes 10, wherein the lower guide 40 and the upper guide 60 are separated by said housing F, which also acts as a protection element.

[0048] Each contact probe 10 comprises a body lOp which extends along a longitudinal axis H-H between a first end portion 10a and a second end portion 10b, which are adapted to contact respective contact pads. By way of example, the first end portion 10a (also called contact tip) is adapted to contact pads of the device under test DUT integrated on the semiconductor wafer 23, whereas the second end portion 10b (also called contact head) is adapted to contact pads 20p of a space transformer or of a printed circuit board (PCB), said component being generically identified with reference number 20 and being generically called in the present description as “interface board 20”. Clearly, though the end portions 10a and 10b in the figures end with a pointed shape, they are not limited thereto and may be of any shape suitable to the needs and / or circumstances.

[0049] In the example of figure 1 , for the sake of simplicity, only one device under test DUT and six contact probes 10 for testing said device are illustrated, even though it should be understood that the figures are provided only by way of non-limiting example of the present invention and any number, even high, may be provided.

[0050] In many er applications, for instance in the automotive field, the device under test DUT comprises a first type of pads (hereinafter called “first pads” and indicated with reference “DUTa”), which are characterised by very high voltages and are generally large in size (for instance with sides or diameter of a few millimeters), and a second type of pads (hereinafter called “second pads” and indicated with reference “DUTb”), which are used for lower voltages and are thus different from the first pads DUTa. Generally, in light of the very high voltages of the first pads DUTa, many contact probes are used to contact said pads, in order to distribute the current among several probes during the test.

[0051] In particular, according to an embodiment of the present invention, the contact probes 10 are divided into first contact probes, herein identified with reference number 10’, and into second contact probes, herein identified with reference number 10”. More particularly, the first contact probes 10’ are grouped in at least one group (identified with reference number 10g) and are configured to contact, as a group, a corresponding first pad DUTa of the device under test DUT. In this way, the first contact probes 10’, which are grouped in the group 10g, are all adapted to simultaneously contact a same pad of the device under test DUT, in particular a power pad (i.e. they are arranged to contact, together in said group 10g, a same first pad DUTa). As above indicated, the device under test DUT also comprises at least one second pad DUTb, which is contacted by at least one second contact probe 10”, which is generally arranged alternately with the first contact probes 10’, said second pad DUTb being different from the first pad DUTa.

[0052] By way of example, as above mentioned, the first pad DUTa may be a source pad of the device under test DUT, whereas the second pad DUTb may be a gate pad (or a drain pad) .

[0053] Furthermore, as above discussed, since the voltage on the first pad DUTa is very high, the group 10g of first contact probes 10’ comprises a high number of said probes, for instance a number which may vary from 50 to 350, however without being limited by a particular number; in this way, there are multiple contact probes in contact with the first power pad DUTa, so as to easily allow the high voltage signal passage.

[0054] As above indicated, in high voltage tests, unwanted phenomena may occur, such as the emission of molten metal from the pads of the device under test DUT toward the probe head 100 (comparable to a real explosion, also indicated in the field as “metal splash” or “metal evaporation”). It is known that said phenomenon does not depend on the features of the probe head 100, and thus it is not linked to a contact problem of the pads of the device under test DUT (in particular of the first pads DUTa) with the contact probes 10, instead it is linked to a failure of the device itself.

[0055] For the above reasons, the present invention does not provide for an attempt to inhibit the occurrence of the phenomenon of molten metal emission from the device under test DUT, instead it provides for protecting the probe head by containing the above phenomenon, for instance avoiding short circuits between the pads of the device under test DUT (in particular between source and gate) and suitably protecting the guide holes.

[0056] Advantageously according to the present invention, in order to effectively protect the probe head 100, it also comprises a protective element 50 (also called “shield”) associated with the guide 40.

[0057] In the context of the present invention, the term “associated” indicates that the protective element 50 is arranged close to the guide 40 and forms a set of elements along with it, for instance substantially parallel to each other and suitably spaced apart.

[0058] Particularly, the protective element 50 is arranged between the first face FA of the guide 40 and the device under test DUT. It comprises a body 50’ including holes 50h where the first contact probes 10’ are housed, said body 50’ being configured as a protection barrier against the molten metal emissions coming from the device under test DUT toward the first face FA of the guide 40, thus preventing said emissions from reaching the guide 40.

[0059] In an embodiment of the present invention, as depicted in figure 2, the contact probes 10 are arranged in the guide 40 in such a way that there is a plurality of groups 10g of first contact probes 10’, each of said groups 10g being intended to contact a specific first pad DUTa (in this case, there can be multiple devices under test and thus multiple first pads DUTa on the semiconductor wafer 23). In this way, for each of the above groups 10g, the first contact probes 10’ are adapted to contact a respective first pad DUTa all together. These groups 10g of first contact probes 10’ are alternated with second contact probes 10”, which are arranged to contact respective second pads DUTb (as seen above, there may be multiple devices under test and thus multiple second pads DUTb on the semiconductor wafer 23).

[0060] The various pads may be pads of a same device under test DUT or they may be the respective pads of different devices on the semiconductor wafer 23, without any limitation for the scope of the present invention.

[0061] In this embodiment of figure 2, the protective element 50 may be divided into a plurality of portions 50p separated from each other, each of said portions 50p housing a corresponding group 10g of first contact probes 10’ in its holes 50h, and thus each portion 50p is at a corresponding first power pad DUTa. This division allows a greater ease of assembly, especially in the case of numerous contact probes. Figures 3A and 3B show the advantages of the present invention, where, in the absence of the protective element 50 (figure 3A), portions of molten metal (indicated with reference P) from the device under test DUT would hit the guide 40, thus blocking the probes in the guide holes 40h and causing a short circuit between the first pad DUTa and the second pad DUTb (for instance a short circuit between source and gate of the device) . Suitably, thanks to the protective element 50 of the present invention (figure 3B), the molten metal emissions are blocked by said protective element 50, which is arranged and shaped (configured) to intercept the metal portions P before they reach the guide 40, thus easily solving this problem which occurs at high voltages.

[0062] In an embodiment, the protective element 50 is removably connected to the probe head 100. The fact that the protective element is removable is advantageous since in this way it is possible to replace it after a certain accumulation of metal.

[0063] Furthermore, in an embodiment, the body 50’ of the protective element 50 is plate-shaped and lies in a plane a that is substantially parallel to a plane p where the guide 40 lies, even if obviously other configurations fall within the scope of the present invention.

[0064] The protective element 50 may be made of a ceramic material (as the guide 40), even if the present invention is not limited by the materials used.

[0065] In an embodiment of the present invention, the protective element 50 houses in its holes 50h only the first contact probes 10’ in its holes, i.e. the probes intended to contact the first pad DUTa (which is the power pad of the device). In this way, the first contact probes 10’ are suitably separated from the second contact probes 10”, thus avoiding short circuits between source and gate.

[0066] Furthermore, to ensure a suitable separation between the first contact probes 10’ and the second contact probes 10”, and thus to ensure that the emitted molten metal portions do not cause a short circuit between different pads of the device under test DUT, the protective element 50 comprises protruding portions (indicated with reference number 50s) projecting below from its body 50’ toward the device under test DUT. The protruding portions 50s thus act as a further protective barrier, further separating the first contact probes 10’ from the second contact probes 10”, since said protruding portions 50s (which extend from the lower face of the protective element 50 toward the device under test DUT) are between said first contact probes 10’ and said second contact probes 10”, thus suitably isolating them.

[0067] As above indicated, preferably, the protective element 50 only comprises the first contact probes 10’ which are grouped in the group 10g, even if this is not necessary since the above mentioned protruding portions 50s in any case ensure the desired separation among the different types of contact probes, also blocking the most lateral emissions of molten metal coming from the device under test DUT.

[0068] Therefore, in a preferred embodiment, the protective element 50 only comprises the first contact probes 10’, while the second contact probes 10” (e.g., the gate probes) are external to said protective element 50, i.e., they are not included in it.

[0069] Moreover, if on the one hand the separation between the first contact probes 10’ and the second contact probes 10” is ensured (which are insulated from each other by means of the protective element 50), said first contact probes 10’ may instead be short-circuited by the molten metal portions deposited on the protective element 50, which in some circumstances may be desirable since it causes the distribution of the current among the various power probes. In order to enhanced this phenomenon and further increase the performance of the probe head 100 as a whole, the first contact probes 10’ may be short-circuited by a metallization on the guide 40, in this way short-circuiting probes of a same domain, in particular a high voltage domain. Said metallizations allow reducing the probe burning phenomenon; for instance, let us consider the case in which a certain power pad of a device under test is contacted by a probe which is short-circuited with other probes that carry power signals sharing the same power supply. In this case, when the current from this supply meets the metallization that short circuits all of the probes of this domain, it is divided among all of the short-circuited probes, thus allowing the reduction of the equivalent resistance and inductance compared to the case in which this current remains confined in a single probe up to the PCB. Moreover, in case of devices with different ground / power domains on the device then joined on the PCB, the metallization allows reducing the loop inductance between a power and its ground.

[0070] The presence of metallizations on the guide, which short-circuit groups of probes and create a common conductive plane, allows reducing noise and increasing the performance of the probe head.

[0071] To this end, still with reference to figure 1, in an embodiment of the present invention, the probe head 100 also comprises a metallization (also called “conductive portion” and indicated with reference number 30) which is formed on the guide 40 and includes at least one group 40hg of the guide holes 40h, in particular the guide holes 40h corresponding to the holes 50h in which the group 10g is housed. In this way, the conductive portion 30 is configured to contact and short circuit the first contact probes 10’ of the group 10g, which are housed in said group 40hg of guide holes and are configured to carry of a same determined type of signal, in particular a very high voltage signal.

[0072] In the embodiment shown in figure 1, the guide 40 is a lower guide, even though the conductive portion 30 may be formed on other possible guides of the probe head 100. Moreover, in the embodiment illustrated in figure 1, the conductive portion 30 is a surface portion formed on the first face FA of the guide 40, even though other embodiments may also be implemented.

[0073] Obviously, as above indicated, the present invention is not limited by the number and arrangement of the conductive portions, which may be selected based on the needs and / or circumstances, as described for instance in international patent application no. PCT / EP2017 / 082180 in the name of the Applicant.

[0074] In the embodiments of figures 2, 3A and 3B, the protective element 50 is a movable component of the probe head 100. In particular, in this embodiments, the protective element 50 is integral with the contact probes 10 and moves along with the said contact probes. In this case, the diameter of the holes 50h of the protective element 50 may for instance substantially coincide with the diameter of the contact probes 10, which are thus constrained thereto.

[0075] In particular, as illustrated in the example of the figures, the protective element 50 is integral with the group 10g of first contact probes 10’ (e.g., the probes that contact the source pad) to protect the lower guide 40, said protective element 50 moving with all of the probes of the above source groupe 10g in the overdrive movement.

[0076] Alternatively, in an embodiment illustrated in figure 4, the contact probes are adapted to move with respect to the protective element 50, which instead is a fixed component of the probe head 100 and does not move during the overdrive movement of said probes. In this case, the holes 50h of the protective element 50 have a diameter greater than the diameter of the guide holes 40h of the guide 40.

[0077] In the context of the present invention, the term “diameter” indicates a dimension measured in a direction that is substantially orthogonal to the longitudinal axis H-H of the contact probes 10 (and thus in a substantially transversal direction) .

[0078] In other words, in this embodiment, the protective element 50 is connected and integral to the guide 40 (unlike what has been seen in figures 2 and 3A-3B), and may be easily removed and replaced (for instance by means of connection elements such as screws between said guide and said protective elment) when the metal accumulation starts compromising the holes 50h (which, as seen above, are wider than the contact probes) for the passage of the contact probes, in particular of the first contact probes 10’.

[0079] In general, it is the guide 40 that has the function of guiding the contact probes 10, whereas the protective element 50 may not configured to perform this task, but it is still important that in this embodiment there is not an excessive accumulation of metal in the holes in order to prevent the probes from getting stuck.

[0080] Moreover, in the example of figure 4, each group 10g is further divided into subgroups of first probes 10’ (for instance subgroups of four probes), but said probes are anyway always in contact with the same first pad DUTa (for instance, the division into subgroups may help the distribution of the signal on the PCB 20), even if obviously this is in no way limiting for the scope of the present invention.

[0081] Figures 5A-5B show the case in which metal portions P are deposited on the protective element 50 and the case in which the latter is removed when the metal accumulation starts compromising the opening of the holes 50h, respectively; this embodiment thus has the advantage of allowing an easier removal of the protective element 50, even if the embodiment of figure 2, not having the problem of the probes getting stuck in the holes 50h, requires fewer replacements. Therefore, preferably, the protective element is integral and moves with the probes, so that its holes may get dirty without causing problems to the operation of the probe head.

[0082] Finally, in an embodiment of the present invention (in particular in the case of a static shield 50 as in figure 4), the probe head 100 is structured to define at least one cabin 70 that is in fluid communication with a supply line 701 (being part of means external to the probe head 100) adapted to supply pressurized gas (indicated with reference A) into said cabin 70, which is open toward the device under test DUT, so as to supply air in that area. By way of example, the air passages toward the cabin 70 are formed through a suitable shape / configuration of the walls of the housing F and of the guide 40, as well as through the use of specific ceramics and / or other materials, and said cabin 70 has one or more suitable openings (in particular upper openings), so as to allows conveying the pressurized gas A thereinto (and then toward the semiconductor wafer 23). In this embodiment, the contact probes are partially housed in the cabin 70. Thanks to the cabin 70, it is possible to create an overpressure in the test area, thus avoiding the formation of electric arcs, according to the Paschen law.

[0083] In other words, the probe head 100 comprises the cabin 70 in its lower portion, said cabin 70 interfacing with the device under test DUT.

[0084] In an embodiment of the present invention, the protective element 50 contributes forming the cabin 70, i.e. it itself is a portion of said cabin 70 (in particular, it represents the upper portion or wall, with apposite openings for the passage of the pressurized gas - corresponding to the above upper openings -, and thus it is its terminal portion).

[0085] Furthermore, still referring to the embodiment of figure 4, the holes 50h of the protective element 50 are sized to allow the passage of the pressurized gas A introduced into the cabin 70 through the supply line 701, which ensures a greater cleaning of said holes 50h and at the same time the inhibition of the phenomenon of electric arc generation.

[0086] In conclusion, the present invention thus allows brilliantly overcoming the technical problem, by providing the above probe head and solving all of the prior art drawbacks in a simple manner.

[0087] Advantageously according to the present invention, the molten metal emissions coming from the device under test during the test of the latter at high voltage are blocked by the protective element, which is for example a shied arranged and shaped to intercept the emitted metal before it reaches the guide, said metal impacting on its lower face.

[0088] In the absence of the above protective element, the metal would deposit onto the contact probes and onto the ceramic guide, causing short circuits and potentially blocked guide holes, whereas the presence of the shield protects the guide; in some examples, due to the metal deposited on the shield, the source probes may be shorted together without causing problems for the test, while electrical separation between them and the gate is maintained.

[0089] Obviously, in order to meet contingent and specific requirements, a person skilled in the art can bring to the above-described probe head several modifications and variants, all falling within the scope of protection of the invention as defined by the following claims.

Claims

CLAIMS1. A probe head (100) for testing a device under test (DUT), said device under test being of the type comprising at least one first pad (DUTa) and at least one second pad (DUTb) that is different from the first pad (DUTa), said probe head (100) comprising:- a plurality of contact probes (10) comprising a body (lOp) extended between a first end portion (10a) and a second end portion (10b), said end portions being adapted to contact respective pads, wherein said contact probes (10) are divided into first contact probes (10’), which are grouped into at least one group (10g) and are configured to contact, as a group, a corresponding first pad (DUTa) of the device under test (DUT), and into at least one second contact probe (10”) configured to contact a corresponding second pad (DUTb) of the device under test (DUT), said second pad being different from the first pad (DUTa); and- at least one guide (40) equipped with guide holes (40h) for housing at least a portion of the contact probes (10), wherein said guide (40) includes a first face (FA) facing, during the test, the device under test (DUT), and a second face (FB) opposite the first face (FA), characterized in that it also comprises a protective element (50) which, during the test, is arranged between the first face (FA) of the guide (40) and the device under test (DUT), said protective element (50) comprising a body (50’) which is equipped with holes (50h) in which the first contact probes (10’) are housed, wherein said body (50’) is configured as aprotection barrier against emissions of molten metal from the device test (DUT) toward the first face (FA) of the guide (40), thus preventing said emissions from reaching the guide (40).

2. The probe head (100) according to claim 1, comprising a plurality of groups (10g) of first contact probes (10’), each of said groups (10g) being adapted to contact a respective first pad (DUT a) of a plurality of first pads on a semiconductor wafer (23), wherein, for each of said groups (10g), the respective first contact probes (10’) are configured to contact all together said respective first pad (DUTa), and wherein said groups (10g) of first contact probes (10”) are alternated with second contact probes (10”), each of said second contact probes (10”) being arranged to contact a respective second pad (DUTb) of a plurality of second pads on the semiconductor wafer (23).

3. The probe head (100) according to claim 2, wherein the protective element (50) is divided into a plurality of portions (50p) separated from each other, each of said portions (50p) housing a corresponding group (10g) of first contact probes (10’).

4. The probe head (100) according to any one of the preceding claims, wherein the body (50’) of the protective element (50) is plate-shaped and lies in a plane (a) substantially parallel to a plane (P) in which the guide (40) lies.

5. The probe head (100) according to any one of the preceding claims, wherein the protective element (50) is removably connected to said probehead (100).

6. The probe head (100) according to any one of the preceding claims, wherein the first pad (DUTa) is a source pad of the device under test (DUT), and wherein the second pad (DUTb) is a gate or drain pad of the device under test (DUT), and wherein the group (10g) of first contact probes (10’) comprises a number of first contact probes (10’) from 50 to 350, so as to allow the passage of a high voltage signal via said first contact probes (10’).

7. The probe head (100) according to any one of the preceding claims, wherein the protective element (50) houses only the first contact probes (10’) in its holes (50h).

8. The probe head (100) according to any one of the preceding claims, wherein the protective element (50) is made of a ceramic material.

9. The probe head (100) according to any one of the previous claims, wherein the protective element (50) includes protruding portions (50s) projecting from the body (50 j thereof toward the device under test (DUT).

10. The probe head (100) according to any one of the preceding claims, comprising a conductive portion (30) which is formed on the guide (40) and includes at least one group (40hg) of the guide holes (40h), said conductive portion (30) being configured to contact and short-circuit the first contact probes (10’) of the group (10g) of first contact probes, which are housed in said group (40hg) of guide holes and are adapted to carry a same specific type of signal, in particular a high voltage signal.

11. The probe head (100) according to any one of the preceding claims, wherein the protective element (50) is integral with the contact probes (10) and moves together with said contact probes (10).

12. The probe head (100) according to any one of the claims from 1 to 10, wherein the contact probes (10) are adapted to move with respect to the protective element (50), which is a fixed component of said probe head (100), and wherein the holes (50h) of said protective element (50) have a diameter that is greater than a diameter of the guide holes (40h) of the guide (40).

13. The probe head (100) according to any of the previous claims, characterized in that it is structured so as to define a cabin (70) in fluid communication with a supply line (701) adapted to supply a pressurized gas (A) inside said cabin (70), wherein the protective element (50) forms at least a part of said cabin (70).

14. The probe head (100) according to claims 12 and 13, wherein the holes (50h) of the protective element (50) are sized to allow the passage of the supplied pressurized gas (A) toward the cabin (70).

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