Probe card for an apparatus for testing electronic devices with improved thermal control
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- TECHNOPROBE
- Filing Date
- 2025-12-11
- Publication Date
- 2026-08-06
Smart Images
Figure EP2025086580_06082026_PF_FP_ABST
Abstract
Description
[0001] Title: "Probe card for an apparatus for testing electronic devices with improved thermal control"
[0002] DESCRIPTION
[0003] Technical Field
[0004] The present invention relates to a probe card of an apparatus for testing electronic devices.
[0005] The invention relates particularly, but not exclusively, to a probe card comprising a space transformer interposed between a plurality of contact probes and a board for connection with a testing apparatus and the following description is made with reference to this field of application with the only purpose of simplifying the exposition thereof.
[0006] Background Art
[0007] As it is well known, a probe card is essentially a device adapted to electrically connect a plurality of pads or contact pads of a microstructure, in particular an electronic device integrated on a wafer, with corresponding channels of a testing apparatus which performs the testing thereof.
[0008] The test performed on integrated devices is used in particular to detect and isolate defective devices as early as in the production phase. Usually, the probe cards are thus used for the electrical testing of the devices integrated on wafers or chips before cutting or singulating and assembling them inside a containment package.
[0009] A probe card comprises a probe head essentially including in turn a plurality of mobile contact elements or probes provided with at least one end portion or contact tip adapted to abut onto a corresponding plurality of contact pads of the device under test. The terms end or tip mean here and below an end portion of said probes, being not necessarily pointed.
[0010] The contact head is interfaced to an intermediate board called space transformer which has contact pads formed on opposite faces thereof with centres at a different distance between a face and the opposite one, suitably connected with each other by means of connections, in particular metal tracks, formed inside the space transformer itself, so as to allow a relaxation between the distancesbetween the centres of the probes from the probe head to a mam plate or board, also indicated as main PCB, since it is usually formed using the techniques for printing circuits or PCB (“Printed Circuit Board”), a technology that allows to form boards with active areas, i.e. provided with contact pads, being even large-sized, although with major limitations with respect to a minimum reachable value for the pitch between the centres of the contact pads.
[0011] In vertical probe heads, the contact probes have a first end portion, or contact tip, adapted to abut onto contact pads of a device under test and a second end portion or contact head adapted to abut onto contact pads formed on a first face of said space transformer, in particular a face arranged towards the probe head and thus the device under test, having in turn corresponding contact pads formed on a second face, in particular a face facing the main board and thus the testing apparatus.
[0012] Suitable contact structures or elements are arranged in an interface layer arranged between the space transformer and the main board. Said contact elements may encompass conductive balls and pillars, i.e. usually-metal structures made in a sphere or cylinder shape and arranged so as to mechanically and electrically connect the second face of the space transformer with a first face of the main board, in particular the face facing the probe head and thus the device under test.
[0013] The assembly of the probe head, of the main plate or board, of the intermediate board or space transformer and of the interconnection layer forms a probe card, globally and schematically indicated with 10 in Figure 1.
[0014] In particular, the probe card 10 thus comprises a probe head 1, in the example in the figure comprising a containment structure 2 of a plurality of vertical probes 3; the containment structure 2 can comprise at least one guide or a pair of upper and lower guides, having respective guide holes in which the contact probes 3 slide.
[0015] Each contact probe 3 has at least one first end portion or contact tip 3A which abuts onto a contact pad 5A of a device under test 5 integrated on a semiconductor wafer 6, realizing the mechanical andelectrical contact between the device under test and a testing apparatus (not represented) which said probe head 1 forms an end element of.
[0016] Moreover, each contact probe 3 has a second end portion or contact head 3B adapted in turn to realize the contact with a plurality of contact pads formed on an intermediate board or space transformer 4, connected to a main plate or board 7 by an interface layer 8, the main board 7 being connected in turn to the testing apparatus, indeed.
[0017] The main board 7 is also kept in place by means of a stiffener (not illustrated), which is configured to make the whole assembly more rigid and resistant and allows the flatness defects to be reduced, in particular in connection with the space transformer 4, which has generally very reduced thicknesses and which has thus considerable flatness problems.
[0018] The spatial transformation performed by the space transformer 4 concerns in particular the distances between the centres of the contact pads formed on the opposite faces thereof, in particular a first face FA facing the probe head 1 at the contact heads 3B of the contact probes 2 and connected by means of suitable metallizations to a second plurality of contact pads formed on a second opposite face FB thereof facing the main board 7, said second plurality of contact pads having a different spatial distribution, in particular with centres of the pads at a greater distance, namely greater pitches compared to the pitch of the first plurality of contact pads, which are instead distributed in a manner substantially corresponding to the contact pads 5A of the device under test 5 so that the space transformer 4 can perform the desired spatial transformation, by moving away the contact pads formed on the second face FB thereof with respect to the contact pads formed on the first face FA thereof. They are commonly referred to as probe side pad or fine pitch and as PCB side pad or large pitch to indicate the contact pads on the first face FA and on the second face FB, respectively.
[0019] In the vertical probe technology, it is important to ensure the good connection of the contact probes with the device under test, particularly at the contact tips thereof, and with the testing apparatus, particularly at the contact heads thereof and thus at the space transformer, whichplays a very important role especially in the testing operations of integrated circuits formed according to the most recent integration technologies which provide for contact pads on the devices under test which are extremely close and very small in size, constraints which are poorly compatible with the PCB technology through which the main board of the probe card is formed.
[0020] The mutual positioning of the elements composing the probe card turns out to be an extremely important parameter for a correct operation of the card itself and the different technologies used to make said elements introduce flatness problems which complicate the configuration of the card as a whole and especially in connection with the mutual positioning of the space transformer and main board. Even the presence of the stiffener, which makes the whole assembly more rigid and resistant, generally does not allow the flatness defects of the space transformer to be eliminated in a sufficient way and the correct and complete contact thereof with the main board to be ensured.
[0021] The whole thing is further complicated by the operating temperature of the card itself, in particular in case of testing operations at extreme temperatures. In that case, in fact, the thermal expansions of the elements composing the probe card can affect the correct behaviour thereof, in particular due to the different thermal expansion coefficients of the different materials which said elements are made of. It is in fact usual to bind together the elements composing a probe card by means of screws, which, in particular during temperature testing operations, apply to the different boards a constraint which tends to cause a warpage thereof, resulting in a malfunction of the probe card as a whole, to the limit even in the lack of contact of the contact probes of the probe head with the contact pads of the device under test.
[0022] This problem is particularly felt in the case of large-sized probe cards, such as for example the probe cards for the testing operations of storage devices such as DRAMs. For this type of probe cards, the lack of control of the thermal expansion of the components involves considerable problems in the testing phase.
[0023] Moreover, during the testing operations, the contact probes heatup due to the passage of the several signals, increasing the heat that is present inside the probe head, in particular in case of a probe head provided with a very high number of contact probes.
[0024] Similarly, the abutment of said contact probes onto the pads of the space transformer and the transport of the signals therein from the probe side pads to the PCB side pads produce an undesirable heat that accumulates in the probe card, in particular in the space transformer through which the thermal power generated by the probes, indicated as passive thermal power, passes.
[0025] However, most of said passive thermal power is conveyed and dispersed at the device under test, although a part remains confined in the space transformer. The passive thermal power that must be dissipated by the space transformer is limited to overall values of approximately 30W of equivalent electrical power and it is usually transported outside the space transformer toward the main board simply by the system of welds and metal tracks that are already present in the space transformer, in the interface layer and in the main board.
[0026] However, the most recent probe cards also comprise active components or dies, which can be positioned in mechanical and thermal contact with the space transformer. Said active components generate an active thermal power che is completely discharged in the space transformer. Unfortunately, said active thermal power has values that are equal to 30-35W of equivalent electrical power for each of the active components. Considering the use of even only a limited number of active components, for example four components arranged in contact with the space transformer, this results in an active thermal power that is higher than 100W of equivalent electrical power, that cannot be dissipated simply by the transport through the welds.
[0027] The technical problem underlying the present invention is to devise a probe card, having such structural and functional features as to allow the limitations and drawbacks still affecting the probe cards formed with known technologies to be overcome, promoting the removal of the heat being produced during the testing operations and limiting the increase in the operating temperature of the probe card and the probehead contained therein.
[0028] Disclosure of Invention
[0029] The solution idea underlying the present invention is to provide the probe card with an active thermal exchange mechanism, in particular using a cooling fluid (cooling) circulating in microfluidic channels arranged in a microfluidic cooling system in thermal contact with the space transformer to draw heat therefrom and transport it outside the probe card.
[0030] Based on said solution idea the technical problem is solved by a probe card adapted to be inserted in an apparatus for testing electronic devices, said probe card comprising at least one probe head housing a plurality of contact probes, each contact probe having at least one first end portion adapted to abut onto contact pads of a device under test and a second end portion adapted to abut onto corresponding contact pads formed on a first face of a space transformer facing the device under test, as well as a main board connected to the space transformer by means of an interface layer provided with a plurality of mechanical and electrical connection elements between the space transformer and the main board, characterized in that it further comprises a microfluidic cooling system including one or more microfluidic channels provided with respective microfluidic passages in which a cooling fluid circulates, said microfluidic channels being in thermal contact with the space transformer to collect and dissipate heat therefrom.
[0031] More particularly, the invention comprises the following additional and optional features, taken individually or in combination if necessary.
[0032] According to an aspect of the invention, the probe card can comprise at least one active device positioned in mechanical and thermal contact with the space transformer.
[0033] Furthermore, the heat of the space transformer can be generated by a passive thermal power due to a passage of current signals in the contact probes during testing operations of the device under test and by an active thermal power generated by the at least one active device.
[0034] According to another aspect of the invention, the microfluidic cooling system can be formed in an interface layer interposed betweenthe space transformer and the mam board and in mechanical and thermal contact with at least one second face of the space transformer facing the main board.
[0035] Furthermore, said microfluidic cooling system can comprise one or more microfluidic channels provided with respective microfluidic passages of the cooling fluid and formed in areas of the interface layer that are devoid of connection elements.
[0036] The microfluidic channels can also be associated with the second face of the space transformer by means of mechanical support, by means of material deposited at the interface with the space transformer, by welding or by sintering.
[0037] According to another aspect of the invention, the microfluidic cooling system can further comprise a distributor of the cooling fluid, provided with an inlet fluid passageway and an outlet fluid passageway connected at opposite ends of the microfluidic passages of the microfluidic channels, said inlet fluid passageway providing to the microfluidic passages an inlet cooling fluid flow and said outlet fluid passageway collecting an outlet cooling fluid flow from the microfluidic passages.
[0038] Still according to another aspect of the invention, the microfluidic cooling system can be formed as a frame comprising the microfluidic channels and the inlet and outlet fluid passageways.
[0039] Furthermore, according to another aspect of the invention, each of the microfluidic channels can have a dimension in an orthogonal direction to the space transformer that is equal to a dimension of the connection elements in said direction.
[0040] According to another aspect of the invention, the probe card can comprise at least one first metallization layer formed on the second face of the space transformer and comprising respective first portions formed at each of the microfluidic channels, said first portions of the first metallization layer having a thermal interface function to increase a thermal exchange between the microfluidic channels and the space transformer.
[0041] The probe card can further comprise a second metallization layerformed at a first face of the mam board facing the space transformer and comprising respective second portions formed at each of the microfluidic channels, said second portions of the second metallization layer and the first portions of the first metallization layer in combination with each other being adapted to transport electric signals along the microfluidic channels.
[0042] According to another aspect of the invention, at least one of the microfluidic passages can be open on the second face of the space transformer, the cooling fluid coming into contact with said second face.
[0043] Still according to another aspect of the invention, the microfluidic cooling system can be formed in contact with a second face of the main board, whose first face is in contact with the interface layer.
[0044] In particular, according to said aspect of the invention, the microfluidic cooling system can comprise one or more microfluidic channels provided with respective microfluidic passages and formed in the interface layer, one or more secondary inlet microfluidic passages and one or more secondary outlet microfluidic passages formed in the main board and in fluid contact with one of said microfluidic passages formed in the interface layer.
[0045] Said microfluidic cooling system can further comprise a fluid distributor provided with a manifold having at least one first inlet fluid passageway adapted to supply an inlet cooling fluid flow to the secondary inlet microfluidic passages via respective inlet connection conduits and a second outlet fluid passageway adapted to draw an outlet cooling fluid flow from the secondary outlet microfluidic passages via respective outlet connection conduits.
[0046] According to another aspect of the invention, at least one of said secondary inlet microfluidic passages and of said secondary outlet microfluidic passages can be formed by means of a via within the main board.
[0047] Finally, said via can comprise at least one metallization layer extended along inner side walls thereof.
[0048] The features and advantages of the probe card according to the invention will be apparent from the following description of exemplaryembodiments thereof given by way of non-limitmg examples with reference to the attached drawings.
[0049] Brief description of the drawings
[0050] In the drawings:
[0051] - Figure 1 shows a schematic sectional view of a probe card formed according to the prior art;
[0052] - Figure 2 shows a schematic sectional view of a probe card according to an embodiment of the invention;
[0053] - Figures 3A-3C show respective schematic axonometric and sectional views of portions of the probe card of Figure 2;
[0054] - Figures 4A-4D show respective schematic sectional views of portions of the probe card of Figure 2 according to alternative embodiments of the invention;
[0055] - Figure 5 shows a schematic sectional view of a probe card according to a further alternative embodiment of the invention;
[0056] - Figures 6A-6B show respective schematic axonometric and sectional views of portions of the probe card of Figure 5; and
[0057] - Figure 7 shows a schematic sectional view of a portion of the probe card of Figure 5 according to an alternative embodiment of the invention.
[0058] Detailed description
[0059] With reference to the figures, and particularly to Figure 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 wafers, formed according to the present invention, is globally indicated with 20.
[0060] It should be noted that the figures represent schematic views of the card according to the invention and are not drawn to scale, but instead they are drawn so as to emphasize the important features of the invention.
[0061] Moreover, the several aspects of the invention represented by way of example in the figures are obviously combinable with each other and interchangeable from one embodiment to another.
[0062] In the following description, relative terms such as “above”,below , upward , downward , upper , lower will be used referring to the illustrations of the different elements given in the figures only to simplify the exposition thereof.
[0063] Finally, indications of particular geometries (circular, rectangular) or of the arrangement of the elements (parallel, orthogonal, contiguous) as well as the term “substantially” are always to be intended in connection with physical and not geometrically abstract elements, and thus they must always take into consideration the tolerances introduced by the transition from a pure mathematical / geometric world to the real world.
[0064] In particular, as illustrated in Figure 2, the probe card 20 comprises a probe head 11 including a containment element 12 housing a plurality of contact probes 13, eight in the example, only for simplicity of illustration, a contact head 11 actually comprising a much higher number of contact probes 13. Considering the case of a probe head 11 of the unblocked probe vertical type, the containment element 12 comprises at least one upper board or guide and a lower board or guide, having respective guide holes through which the contact probes 13 slide and made integral by an appropriate housing.
[0065] Each of the contact probes 13 comprises at least one first end portion or contact tip 13A adapted to abut onto a corresponding contact pads 15A of a device under test 15, in particular integrated on a semiconductor wafer 16, so as to establish the desired contact, in particular an electrical contact, between the contact probes 13 of the probe head 11 and the contact pads 15A of the device under test 15.
[0066] Each contact probe 13 further comprises a second end portion or contact head 13B adapted to establish the contact with a main board 17 or main PCB for connection with a testing apparatus (not illustrated). A rod-shaped probe body is arranged between the contact head 13B and the contact tip 13A and substantially arranged along a longitudinal development direction of the contact probe 13, that is in particular orthogonal to a plane on which the semiconductor wafer 16 is arranged, where the device under test 15 is integrated, that is along the Z axis of the local reference of Figure 2.The probe card 20 further comprises an intermediate board arranged between the probe head 11 and the main board 17 and adapted to perform a spatial transformation, in particular in connection with the distribution of contact pads on the opposite faces thereof and for this reason indicated as space transformer 14.
[0067] The space transformer 14 has a first face FA facing the probe head 11 (in the operating conditions, i.e. when the space transformer 14 is inserted into a probe card 20 comprising the contact head 11 and inserted as an end element of a testing apparatus), a first plurality of contact pads being formed on said first face FA, onto which the contact heads 13B of the contact probes 13 abut. Said first face FA is also indicated as probe side face.
[0068] The space transformer 14 further has a second face FB facing the main board 17 in the operating conditions and connected thereto at an interface layer 18. Said second face FB is thus also indicated as tester side face.
[0069] The space transformer 14 is usually formed as an organic multilayer or MLO (acronym for “MultiLayer Organic”) associated with a rigid support, for example glued thereto, said MLO including a plurality of layers of organic material that form a plurality of non-conductive layers, one or more conductive layers being arranged on said non-conductive layers in a suitable configuration, adapted to make the internal conductive paths to connect the contact pads arranged on the faces thereof. The rigid support is preferably a ceramic support.
[0070] Alternatively, in place of an organic multilayer MLO, it is also possible to use a ceramic-based multilayer or MLC (acronym for “MultiLayer Ceramic”), that comprises a plurality of layers of rigid ceramic material with a high degree of flatness, interspersed with conductive layers that connect contact pads made on the opposite faces of the space transformer 14.
[0071] Furthermore, the space transformer 14 can be formed as a silicon multilayer in which suitable connection metal tracks are formed, also indicated as SI (acronym for “Silicon Interposer”) .
[0072] The probe card 20 can also comprise a stiffener (not illustrated)associated with the mam board 17 and adapted to improve the flatness thereof and to avoid the warpage thereof, in particular in case of an increase in temperature during the operation of the probe card 20, i.e. during the testing operations.
[0073] In accordance with the most recent embodiments, active devices or dies 19 are further arranged on the space transformer 14, in particular at the first face FA thereof facing the contact head 11 (probe side face) . These active devices 19 can be mounted on the space transformer 14 by welding or other bonding system.
[0074] As it is well known, said active devices 19 have a high power consumption, which can reach 30-35W for each single device. Considering to house on the space transformer 14 four active devices 19 (only two being visible in the Figures), arranged in particular outside an active area of the space transformer 14, i.e. the area where the contact pads are formed, onto which the contact heads 13B of the contact probes 13 abut, this results in an additional power of 120-140W that is fed into the space transformer 14 and that results in an active thermal power PT2 having a much higher value than a passive thermal power PT1 that passes through the space transformer 14 due to the signals, in particular the currents, that pass through the contact probes 13 during the normal testing operations of the device under test 15 based on the well-known Joule effect. As already explained in connection with the prior art, said passive thermal power PT1 is in fact only linked to a residue of the power linked to the current that passes through the contact probes 13, most of which is instead discharged just on the device under test 15.
[0075] Advantageously according to the present invention, the space transformer 14 is associated with a thermal dissipation system, in particular a microfluidic cooling system 30, that is adapted to draw thermal power, i.e. heat from the space transformer 14 and for transporting it outside the probe card 20 so as to be able to disperse it and consequently cool the space transformer 14 itself. In particular, the microfluidic cooling system 30 according to the present invention is able to collect and disperse the passive thermal power PT1 that passesthrough the space transformer 14 in a very effective manner, using a cooling fluid flowing in microfluidic passages arranged in suitable microfluidic channels, as explained in more detail below. Said microfluidic cooling system 30 is also able to collect and disperse the active thermal power PT2 that passes through the space transformer 14 when active devices 19 are present.
[0076] In a first embodiment, schematically illustrated in Figure 2, the microfluidic cooling system 30 is formed at the interface layer 18 between the space transformer 14 and the main board 17 of the probe card 20. Suitably, the microfluidic cooling system 30 is in thermal contact with the space transformer 14, so as to be able to collect and disperse heat, i.e. the thermal power contained in said space transformer 14, in particular using a cooling fluid flowing in microfluidic passages formed in suitable microfluidic channels. Here and below, two elements are indicated as in thermal contact when they are able to exchange heat, i.e. thermal power with each other.
[0077] More particularly, as schematically illustrated in Figure 3A, the microfluidic cooling system 30 comprises a distributor 31 provided with one or more microfluidic channels 34, in the example in the figure two by simple way of example, formed in the interface layer 18, provided each with a microfluidic passage 33 for a suitable fluidic material, in particular a cooling fluid adapted to collect and transport heat. The microfluidic channels 34 are formed at areas that are suitably free of connection elements 18A, such as for example spherical elements or connection balls included in the interface layer 18. The connection elements 18A are formed on the space transformer 14 at the second face FB thereof and have dimensions that are suitable for contacting the main board 17 above the space transformer 14 so as to create the mechanical and electrical connection between said elements of the probe card 20. It is also possible to consider an interface layer 18 comprising local welds, conductive elastomers or elastic microprobes (spring probes) as connection elements, always forming areas that are free of said connection elements 18A for the positioning of the microfluidic channels 34A, 34B of the microfluidic cooling system 30.The microfluidic channels 34A and 34B are substantially straight and arranged along a longitudinal development axis of the space transformer 14, in particular the Y axis of the local reference in the figures.
[0078] It is possible to envisage different geometries, in particular nonstraight ones, for example L-shaped or broken-line-shaped, for said microfluidic channels 34A, 34B so as to adapt to the topology of the connection elements 18A of the interface layer 18.
[0079] In the example of Figure 3A, the microfluidic cooling system 30 comprises two straight microfluidic channels 34A and 34B provided with respective microfluidic passages 33A and 33B connected to respective fluid passageways 32 of the microfluidic cooling system 30. More particularly, the microfluidic cooling system 30 comprises a fluid inlet conduit or inlet fluid passageway 32A that receives an inlet flow Fin of fluidic material, that is thus distributed in the microfluidic passages 33A and 33B of the microfluidic channels 34A and 34B and collected as an outlet flow Font by the fluid outlet conduit or outlet fluid passageway 32B. In particular, the inlet fluid passageway 32A and the outlet fluid passageway 32B are connected at opposite ends of each microfluidic passage 33A and 33B of the microfluidic channels 34A and 34B.
[0080] The microfluidic cooling system 30 is illustrated in Figure 3B, which shows a section along the BB axis of Figure 3A, in which the microfluidic channels 34A and 34B are indicated with the respective microfluidic passages 33A and 33B formed in the interface layer 18 in areas that are devoid of the connection elements 18A. A sectional view of said microfluidic cooling system 30 along the CC axis of Figure 3A is shown in Figure 3C.
[0081] In the embodiment of Figures 3A-3C, the microfluidic channels 34A and 34B have height development dimensions along the Z axis of the local references in the figures that are equal to those of the connection element 18A in the same direction. In other words, the connection elements 18A and the microfluidic channels 34A and 34B have equal dimension i.e. heights in the direction of the Z axis, which isthe orthogonal direction to the space transformer 14 and thus also to the device under test 15, said elements being coplanar under normal use conditions of the probe card 20. It is noted that the term “equal” indicates here and below that the dimensions concerned differ by a maximum of ±10% from each other, always taking into account the tolerances that are typical of a physical and not mathematically pure world.
[0082] Thereby, the microfluidic channels 34A and 34B also form mechanical support elements of the main board 17 and are in contact with the latter and with the space transformer 14. In particular, said microfluidic channels 34A and 34B can be suitably made of a material with a sufficient stiffness to ensure a proper mechanical support for the main board 17.
[0083] The interface layer 18 of Figure 3B comprises four connection elements 18A and two microfluidic channels 34A, 34B by simple way of illustration, since the number of connection elements 18A and microfluidic channels 34A, 34B may vary according to needs.
[0084] In an embodiment, microfluidic channels 34A and 34B and connection elements 18A have sections with an equal area, so as to maintain a homogeneous impact of the interface layer 18 equipped with the microfluidic cooling system 30 on the space transformer 14.
[0085] Suitably, the microfluidic cooling system 30 can be made in the form of a frame comprising the microfluidic channels 34A and 34B and the fluid passageways, in particular the inlet fluid passageways 32A and the outlet fluid passageways 32B. In other words, the microfluidic channels 34A and 34B and the inlet and outlet fluid passageways 32A and 32B can be built into the body or integral with each other, in the form of a frame. Said frame is then inserted, together with the connection elements 18A, on the second face FB of the space transformer 14. In particular, said frame can be simply placed on the space transformer 14 by positioning of the microfluidic channels 34A and 34B in the areas that are free of the connection elements 18A and following underfilling process to fix the frame. In that case, a suitable filling material is deposited at the interface between the microfluidicchannels 34A and 34B and the second face FB of the space transformer 14. The frame can further comprise the inlet and outlet fluid passageways 32A and 32B, built into the body or integral with the microfluidic channels 34A and 34B.
[0086] As an alternative, the microfluidic channels 34A and 34B can be welded or connected by means of a sintering material on the second face FB (tester side face) of the space transformer 14.
[0087] In an alternative embodiment, as shown in Figure 4A, it is possible to form on the space transformer 14, in particular on the second face FB (tester side face) thereof, a first metallization layer 35 having first portions 35A and 35B formed at the areas where the micro fluidic channels 34A and 34B are to be positioned.
[0088] Suitably, the first metallization layer 35 can serve as a thermal pad for the microfluidic channels 34A and 34B connected thereto, i.e. as an interface that is able to improve the thermal exchange between the elements connected thereto. In that case, it is possible to weld said microfluidic channels 34A and 34B (or the frame comprising them) directly on the first metallization layer 35, increasing the thermal exchange performed by the cooling fluid flowing through the microfluidic passages 33A and 33B formed in said microfluidic channels 34A and 34B.
[0089] In a further alternative embodiment, schematically illustrated in Figure 4B, the probe card 20 comprises a second metallization layer 36 provided with respective second portions 36A and 36B formed at the microfluidic channels 34A and 34B at the interface with the main board 17 and in contact with a first face FC thereof. The micro fluidic channels 34A and 34B can thereby be used to transport signals from the space transformer 14 to the main board 17 since they are provided with metalized portions that connect them to the space transformer 14 and to the main board 17, respectively.
[0090] It is immediately evident that said embodiment allows the areas that are free of the connection elements 18A on the space transformer 14 to be “recovered”, the microfluidic channels 34A and 34B positioned in said areas still performing the mechanical and electrical contactbetween the space transformer 14 and the interface layer 18 similarly to the connection elements 18A that have been “sacrificed” to give way to said microfluidic channels 34A and 34B. Thereby, the probe card 20 as a whole does not lose efficiency in carrying the electric signals, although having areas on the space transformer 14 that are devoid of connection elements 18A.
[0091] In that case, the microfluidic channels 34A and 34B can be made of a conductive material, in particular a metal one, so as to allow the desired passage of signals, such as single-domain or multi-domain ground, power or I / O signals. The microfluidic passages 33A and 33B inside said microfluidic channels 34A and 34B do not cause an interruption in signal transmission.
[0092] Furthermore, the whole microfluidic cooling system 30 can be made of a conductive material, in particular a metal one, in the form of a monolithic frame arranged on the space transformer 14 so that the microfluidic channels 34A and 34B thereof are positioned in areas that are free of connection elements 18A.
[0093] As an alternative, it is possible to make the distributor 31 of the microfluidic cooling system 30 of an insulating material, then metallizing only the microfluidic channels 34A and 34B that have to transport electric signals. In a preferred embodiment, the distributor 31 is made of silicon carbide.
[0094] In that case, it is also possible to connect the portions of the first and second metallization layers 35A and 36A of the first microfluidic channel 34A to a first type of signal, for example a ground one, while the portions of the first and second metallization layers 35B and 36B of the second microfluidic channel 34B can be connected to a second type of signal, for example a power one, both microfluidic channels 34A and 34B being connected in a same distributor 31 and provided with suitable metal tracks for the connection with the different signals to be transported. As mentioned, it is also possible to consider the transport of I / O signals or of two different power signals in the case of multidomain applications.
[0095] According to a further alternative embodiment illustrated in Figure4C, the microfluidic passages 33A and 33B formed in the microfluidic channels 34A and 34B can have a round-shaped section. In particular, different shapes may be taken into consideration for the sections of said microfluidic passages 33A and 33B such as for example square, rectangular, oval, rhomboid or parallelepiped, to name a few. Similarly, the shape of the section of the microfluidic channels 34A and 34B may also differ from that illustrated in the Figures and may be selected from square, rectangular, round, oval, rhomboid or parallelepiped, to name a few.
[0096] It is also possible to form the microfluidic channels 34A and 34B with an open section, for example U-shaped, as schematically shown in Figure 4D. In that case, the microfluidic passages 33A and 33B extend up to the second face FB of the space transformer 14 (tester side face). In that case, the cooling fluid comes into direct contact with the space transformer 14 at the second face FB thereof and it is thus selected so as not to cause damages to the material which the space transformer 14 is made of. As shown in Figure 4D, it is still possible to form the first metallization layer 35 with first portions 35A1, 35A2 and 35B1, 35B2 at one or both arms of the U-shaped section of the microfluidic channels 34A and 34B connected at the second face FB of the space transformer 14.
[0097] It is immediately evident that the direct contact of the cooling fluid flowing in the microfluidic passages 33A and 33B with the space transformer 14 increases the efficiency of the thermal exchange performed due to the microfluidic cooling system 30. Moreover, in that case it is possible to form microfluidic passages 33A and 33B with sections having a greater area than the above-illustrated embodiments, increasing the flow rate of the flowing cooling fluid and thus the thermal exchange with the space transformer 14.
[0098] The interface layer 18 of Figures 4A-4D comprises four connection elements 18A and two microfluidic channels 34A and 34B by simple way of illustration, since the number of connection elements 18A and microfluidic channels 34A, 34B may vary according to the requirements.In the alternative embodiment schematically illustrated in Figure 5, the probe card 20 comprises a microfluidic cooling system 40 arranged in contact with the main board 17 at a second face FD thereof and provided with channels that pass through it to perform the thermal exchange with the space transformer 14. In the embodiment illustrated in Figure 5 eight contact probes 13, two active devices 19 and two micro fluidic channels formed in the interface layer 18 are shown by simple way of illustration, since the number of said elements may vary based on the requirements and on the different applications of the probe card 20.
[0099] As illustrated in more detail in Figure 6A, the microfluidic cooling system 40 provides a cooling fluid supply through the main board 17 with a distributor 41 placed at the tester side, i.e. on the second face FD of the main board 17 facing the testing apparatus (not illustrated) provided with at least one manifold 42 connected by means of secondary microfluidic passages 45, 46 that pass through the main board 17 to corresponding micro fluidic channels 44 provided with micro fluidic passages 43 and formed at the interface layer 18.
[0100] More particularly, as schematically shown in Figure 6A, the manifold 42 provides an inlet cooling fluid flow Fin to a secondary inlet microfluidic passage 45A, formed in the main board 17 and connected to a microfluidic passage 43 of a microfluidic channel 44 formed in the interface layer 18, in an area that is free of connection elements 18A. Furthermore, the distributor 41 draws an outlet cooling fluid flow Font through a secondary outlet microfluidic passage 46A also connected to the microfluidic passage 43 of the microfluidic channel 44 formed in the interface layer 18.
[0101] Suitably, a plurality of secondary inlet micro fluidic passages 45 and a plurality of secondary outlet microfluidic passages 46 are put in connection with a single microfluidic passage 43 of a same microfluidic channel 44, as schematically shown in Figure 6B which shows a sectional view of the portion of the probe card 20 of Figure 6A along the YY axis. As it will be clarified below, the presence of these pluralities of secondary inlet microfluidic passages 45 and secondary outletmicrofluidic passages 46 in connection with the same microfluidic passage 43 is able to create a swirling pattern of the cooling fluid inside said microfluidic passage 43 and consequently increase the thermal exchange with the space transformer 14 with which the micro fluidic channel 44 in which the microfluidic passage 43 is formed is in mechanical and thermal contact.
[0102] More particularly, as illustrated by way of example in Figure 6B, the microfluidic passage 43 formed in the microfluidic channel 44 is in contact with a first secondary inlet microfluidic passage 45A, a second secondary inlet microfluidic passage 45B and a third secondary inlet microfluidic passage 45Cs, as well as with a first secondary outlet microfluidic passage 46A and a second secondary outlet microfluidic passage 46B, so as to generate inside the microfluidic passage 43 a first inner flow of cooling fluid FR1 between the first secondary inlet microfluidic passage 45A and the first secondary outlet microfluidic passage 46A, a second inner flow of cooling fluid FR2 between the second secondary inlet microfluidic passage 45B and the first secondary outlet microfluidic passage 46A, a third inner flow of cooling fluid FR3 between the second secondary inlet microfluidic passage 45B and the second secondary outlet microfluidic passage 46B and a fourth inner flow of cooling fluid FR4 between the third secondary inlet microfluidic passage 45C and the second secondary outlet microfluidic passage 46B. Said inner flows of cooling fluid FR1, FR2, FR3 and FR4 are able to generate a fluid vortex inside the microfluidic passage 43 of the micro fluidic channel 44.
[0103] In that case, the manifold 42 comprises a first inlet fluid passageway 42A that supplies the inlet cooling fluid flow Fin to the secondary inlet microfluidic passages 45A, 45B and 45C via respective inlet connection conduits 47A, 47B and 47C. Furthermore, the manifold 42 comprises a second outlet fluid passageway 42B that draws the outlet cooling fluid flow Fout from the secondary outlet microfluidic passages 46A and 46B via respective outlet connection conduits 48A and 48B.
[0104] It is possible to form the secondary microfluidic passages 45 and46 for injecting and drawing the cooling fluid inside the mam board 17 by means of so-called vias, preferably using vias that are already present in an active area of said main board 17. It is in fact well known that vias are nothing but empty passages that pass through a board or plate.
[0105] Suitably, the vias that are already formed in the main board 17 are also metallized along the inner side walls thereof. In their normal use, they are usually filled with an insulating material, such as a resin, in a specific step of the manufacturing process of the main board 17.
[0106] According to this alternative embodiment, schematically shown in Figure 7, in the main board 17 some vias 50 are left void of resin or other filling material so as to form the secondary inlet 45A, 45B, 45C and outlet 46A, 46B micro fluidic passages in the main board 17.
[0107] Suitably, said vias 50 comprise a metallization layer 51 extended along the respective inner side walls.
[0108] Thereby, the vias 50 equipped with the metallization layer 51 are able to form secondary microfluidic passages adapted to transport not only the cooling fluid but also electric signals, such as single-domain or multi-domain I / O, ground or power signals.
[0109] The secondary micro fluidic passages thus formed by said vias 50, when used for the transport of electric signals, are advantageously insulated from each other, due to the dielectric material which the main board 17 is made of, typically FR4 (Flame Resistant n.4), i.e. a composite material formed by soaking a fiberglass fabric with a flameretardant epoxy resin matrix, created to manufacture printed circuits (PCB).
[0110] In particular, by connecting an electric signal, such as for example a ground signal, to the metallization layer 51 of one or more of the vias 50 it is possible to form a ground plane of the main board 17.
[0111] It should be noted that the microfluidic cooling system 40 is extremely effective since it substantially comprises a multiplicity of supplies and returns formed by the secondary inlet microfluidic passages 45A, 45B, 45C and by the secondary outlet microfluidic passages 46A and 46B formed in the main board 17, due to which thecooling fluid is alternately injected and drawn, inside a single chamber, i.e. the microfluidic passage 43 formed in the microfluidic channel 44.
[0112] This allows to create a plurality of local vortices that alternate at the inlet and outlet of the cooling fluid, i.e. the inner cooling fluid flows FR1, FR2, FR3 and FR4 that are present in the micro fluidic passage 43. Thereby, the temperature of the cooling fluid passing through the microfluidic passage 43 of the microfluidic channel 44 remains substantially uniform therein.
[0113] On the contrary, according to the previous embodiment, the inlet cooling fluid flow Fin has a lower temperature with respect to the outlet cooling fluid flow Font, which creates a thermal gradient along the longitudinal development direction of the micro fluidic passages 43, corresponding to the Y axis in the figures.
[0114] In other words, the microfluidic cooling system 40 according to the alternative embodiment of Figures 5, 6A-6B and 7 allows a homogeneous cooling of the space transformer 14 to be obtained, the flow of cooling fluid flowing in the microfluidic passages 43 of the microfluidic channels 44 of said system having a thermal gradient that is practically zero in the longitudinal development direction of the microfluidic passages 43 and thus of the microfluidic channels 44 (Y axis).
[0115] Suitably, compared to the microfluidic cooling system 30 according to the embodiment of Figures 2, 3A-3C and 4A-4D, the microfluidic cooling system 40 according to the embodiment of Figures 5, 6A-6B and 7, has a greater fluid flow capacity, a greater efficiency and a greater uniformity in heat removal.
[0116] In conclusion, advantageously according to the invention, the probe card provided with a microfluidic cooling system is able to effectively disperse the heat passing through the space transformer thereof, for example during the testing operations of an integrated device, especially in case of power signals. Moreover, such a probe card finds a particular application in cases in which active devices which produce a non-negligible active thermal power which is discharged in the space transformer are placed on the space transformer.It is noted that the active thermal power generated by the active devices is located in particular on the face of the space transformer facing the probe head and thus toward the device under test, in extremely reduced spaces, where the dissipation thereof turns out to be extremely important for a correct operation of the space transformer and of the probe card as a whole, more so in applications in which said probe card has to operate at high temperatures (so-called “hot conditions”) .
[0117] Suitably, the microfluidic cooling system according to the present invention is able to dissipate the heat produced inside the space transformer during the testing operations, indicated as passive thermal power, but also that produced by any active device housed on the space transformer and thermally connected thereto, indicated as active thermal power.
[0118] Thereby, the probe card turns out to be suitable for applications in which the testing operations considerably heat the card as a whole, ensuring a correct operation thereof and avoiding any deformation of the elements composing it, deformation which could affect the good outcome of the testing operations, in addition to being suitable for use when a plurality of active devices are housed on the space transformer of said probe card.
[0119] The heat dispersion turns out to be further improved in the case in which the cooling fluid flowing in the microfluidic passages of the microfluidic channels of the microfluidic cooling system is put in direct contact with the space transformer itself.
[0120] Moreover, the microfluidic channels of the microfluidic cooling system associated with the probe card can also be used to transport electric signals, such as single-domain or multi-domain I / O, ground or power signals, compensating for the loss of connection elements in the areas in which said microfluidic channels are positioned and thus maintaining the overall efficiency of the probe card.
[0121] Said microfluidic channels can also be suitably made of a material with a sufficient stiffness to ensure also a mechanical support for the main board.Furthermore, it is possible to envisage different shapes for the section of the microfluidic passages formed in the microfluidic channels so as to adapt to the applications and materials being used.
[0122] Finally, using a microfluidic cooling system provided with a distributor and secondary microfluidic passages formed in the main board so as to emerge in a microfluidic passage of a single microfluidic channel, it is possible to increase the thermal exchange with the space transformer due to cooling fluid vortices generated by a plurality of fluid supplies and returns made by said secondary microfluidic passages, which also allow a homogeneous temperature of the cooling fluid to be maintained as it flows through the microfluidic passage. The so-obtained probe card has improved fluid flow capacity, efficiency and uniformity in heat removal.
[0123] Obviously, in order to meet contingent and specific requirements, a person skilled in the art will be allowed to bring several modifications and alternatives to the above-described probe card, all falling within the scope of protection of the invention as defined by the following claims.
Claims
CLAIMS1. A probe card (20) adapted to be inserted in an apparatus for testing electronic devices, said probe card (20) comprising at least one probe head (11) housing a plurality of contact probes (13), each contact probe (13) having at least one first end portion (13A) adapted to abut onto contact pads (15A) of a device under test (15) and a second end portion (13B) adapted to abut onto corresponding contact pads formed on a first face (FA) of a space transformer (14) facing said device under test (15), as well as a main board (17) connected to said space transformer (14) by means of an interface layer (18) provided with a plurality of mechanical and electrical connection elements (18A) connecting said space transformer (14) and said main board (17), characterized in that it further comprises a microfluidic cooling system (30, 40) including one or more microfluidic channels (34A, 34B, 44) provided with respective microfluidic passages (33A, 33B, 43) in which a cooling fluid circulates, said microfluidic channels (34A, 34B, 44) being in thermal contact with said space transformer (14) to collect and dissipate heat therefrom.
2. The probe card (20) according to claim 1, characterized in that it comprises at least one active device (19) positioned in mechanical and thermal contact with said space transformer (14).
3. The probe card (20) according to claim 2, characterized in that said heat of said space transformer (14) is generated by a passive thermal power (PT1) due to a passage of current signals in said contact probes (13) during testing operations of said device under test (15) and by an active thermal power (PT2) generated by said at least one active device (19).
4. The probe card (20) according to claim 1, characterized in that said microfluidic cooling system (30) is formed in an interface layer (18) interposed between said space transformer (14) and said main board (17) and in mechanical and thermal contact with at least one second face (FB) of said space transformer (14) facing said main board (17).
5. The probe card (20) according to claim 4, characterized in- 25 -that said microfluidic cooling system (30) comprises one or more microfluidic channels (34A, 34B) provided with respective microfluidic passages (33A, 33B) of said cooling fluid and formed in areas of said interface layer (18) that are devoid of connection elements (18A).
6. The probe card (20) according to claim 5, characterized in that said microfluidic channels (34A, 34B) are associated with said second face (FB) of said space transformer (14) by mechanical support, by means of material deposited at the interface with said space transformer (14), by welding or by sintering.
7. The probe card (20) according to claim 5, characterized in that said microfluidic cooling system (30) further comprises a distributor (31) of said cooling fluid, provided with an inlet fluid passageway (32A) and an outlet fluid passageway (32B) connected at opposite ends of said microfluidic passages (33A, 33B) of said microfluidic channels (34A, 34B), said inlet fluid passageway (32A) providing to said microfluidic passages (33A, 33B) an inlet cooling fluid flow (Fin) and said outlet fluid passageway (32B) collecting an outlet cooling fluid flow (Font) from said microfluidic passages (33A, 33B).
8. The probe card (20) according to claim 7, characterized in that said microfluidic cooling system (30) is formed as a frame comprising said microfluidic channels (34A, 34B) and said inlet and outlet fluid passageways (32A, 32B).
9. The probe card (20) according to claim 5, characterized in that each of said microfluidic channels (34A, 34B) has a dimension in an orthogonal direction (Z) to said space transformer (14) that is equal to a dimension of said connection elements (18A) in said direction (Z).
10. The probe card (20) according to claim 5, characterized in that it comprises at least one first metallization layer (35) formed on said second face (FB) of said space transformer (14) and comprising respective first portions (35A, 35B) formed at each of said micro fluidic channels (34A, 34B), said first portions (35A, 35B) of said first metallization layer (35) having a thermal interface function to increase a thermal exchange between said microfluidic channels (34A, 34B) and said space transformer (14).
11. The probe card (20) according to claim 10, characterized in that it further comprises a second metallization layer (36) formed at a first face (FC) of said main board (17) facing said space transformer (14) and comprising respective second portions (36A, 36B) formed at each of said microfluidic channels (34), said second portions (36A, 36B) of said second metallization layer (36) and said first portions (35A, 35B) of said first metallization layer (35) in combination with each other being adapted to transport electric signals along said microfluidic channels (34A, 34B).
12. The probe card (20) according to claim 5, characterized in that at least one of said microfluidic passages (33A, 33B) is open on said second face (FB) of said space transformer (14), said cooling fluid coming into contact with said second face (FB) .
13. The probe card (20) according to claim 1, characterized in that said microfluidic cooling system (40) is formed in contact with a second face (FD) of said main board (17), whose first face (FC) is in contact with said interface layer (18).
14. The probe card (20) according to claim 13, characterized in that said microfluidic cooling system (40) comprises one or more microfluidic channels (44) provided with respective microfluidic passages (43) and formed in said interface layer (18), one or more secondary inlet microfluidic passages (45A, 45B, 45C) and one or more secondary outlet microfluidic passages (46A, 46B) formed in said main board (17) and in fluid contact with one of said micro fluidic passages (43) formed in said interface layer (18).
15. The probe card (20) according to claim 14, characterized in that said microfluidic cooling system (40) further comprises a fluid distributor (41) provided with a manifold (42) having at least one first inlet fluid passageway (42A) adapted to supply an inlet cooling fluid flow (Fin) to said secondary inlet microfluidic passages (45A, 45B, 45C) via respective inlet connection conduits (47A, 47B, 47C) and a second outlet fluid passageway (42B) adapted to draw an outlet cooling fluid flow (Font) from said secondary outlet microfluidic passages (46A, 46B) via respective outlet connection conduits (48A, 48B).
16. The probe card (20) according to claim 14, characterized in that at least one of said secondary inlet microfluidic passages (45A, 45B, 45C) and of said secondary outlet microfluidic passages (46A, 46B) is formed by means of a via (50) within said main board (17).
17. The probe card (20) according to claim 16, characterized in that said via (50) comprises at least one metallization layer (51) extended along inner side walls thereof.