WO2019129585A1

WO2019129585A1 - Probe head having vertical probes with respectively opposite scrub directions

Info

Publication number: WO2019129585A1
Application number: PCT/EP2018/085959
Authority: WO
Inventors: Roberto Crippa
Original assignee: Technoprobe S.P.A.
Priority date: 2017-12-28
Filing date: 2018-12-19
Publication date: 2019-07-04
Also published as: TW201930893A

Abstract

A probe head (20) having vertical probes for testing a device under test (29) integrated on a semiconductor wafer (29') comprises at least one upper guide (22) and at least one lower guide (23) separated from each other by an air gap (26), the lower guide (23) being provided with a plurality of lower guide holes (25) and the upper guide (22) being provided with a plurality of first upper guide holes (24s) for housing a plurality of first contact probes (21s), as well as with a plurality of second upper guide holes (24d) for housing a plurality of second contact probes (21d), those contact probes (21s, 21d) comprising a first end (27) adapted to contact pads of a device under test, and a second end (27A). Suitably, the first upper guide holes (24s) and the second upper guide holes (24d) are offset with respect to the lower guide holes (25), the offset of the first upper guide holes (24s) being opposite to the offset of the second upper guide holes (24d), wherein the first end(27) of the first contact probes (21s) has a scrub direction (DscrubSX) opposite to a scrub direction (DscrubDX) of the first end(27) of the second contact probes (21d).

Description

PROBE HEAD HAVING VERTICAL PROBES WITH RESPECTIVELY OPPOSITE SCRUB DIRECTIONS

DESCRIPTION

Field of application

The present invention refers to a probe head comprising a plurality of vertical probes with an improved load distribution on a semiconductor wafer. More in particular, the present invention refers to a probe head having vertical probes for testing a device under test integrated on a semiconductor wafer, the probe head comprising at least one upper guide and one lower guide separated from each other by an air gap and provided with guide holes for slidingly housing a plurality of contact probes having ends adapted to abut onto contact pads of the device under test, and the following description is made with reference to this application field with the only purpose of simplifying the exposition thereof.

Prior art

As it is well known, a probe head is an electronic device adapted to electrically connect a plurality of contact pads of a microstructure, such as an integrated device, with corresponding channels of a testing apparatus that performs the functionality testing thereof, in particular electric, or generically the test.

The test, which is performed on integrated devices, is particularly useful for detecting and isolating defective circuits as early as in the production phase. Normally, probe heads are therefore used for the electric test of devices that are integrated on wafers before cutting and assembling them inside a chip containment package.

A probe head essentially comprises a plurality of movable elements or contact probes retained by at least one pair of supports or guides that are substantially plate-shaped and parallel to each other. The guides are provided with suitable guide holes and are arranged at a certain distance from each other in order to create a free zone or air gap for the movement and the possible deformation of the contact probes, which are slidingly housed in those guide holes. The pair of guides comprises in particular an upper guide and a lower guide, both provided with guide holes within which the contact probes axially slide, such probes being usually made of wires of special alloys with good electric and mechanical properties.

The proper connection between the contact probes and the contact pads of the device under test is ensured by the pressure of the probe head on the device itself, the contact probes undergoing, during the pressing contact, a bending inside the air gap between the guides and a sliding inside the respective guide holes. Probe heads of this type are commonly called“probe heads having vertical probes” or“vertical probe heads”.

Substantially, the vertical probe heads have an air gap in which a bending of the contact probes occurs, the bending being usually helped by a suitable configuration of the probes themselves or of the guides thereof, as schematically illustrated in figure 1.

In particular, figure 1 schematically illustrates a probe head 1 comprising at least one plate-shaped support or upper guide 2, usually indicated as “upper die”, and a plate-shaped support or lower guide 3, usually indicated as “lower die”, having respectively guide holes 4 and 5 within which a plurality of contact probes 6 slides.

Each contact probe 6 ends at an end with a contact tip 7 intended to abut onto a contact pad 8 of a device under test integrated on a wafer 9, so as to perform the mechanical and electric contact between the device under test and a testing apparatus (not shown), which the probe head forms a terminal element of.

The term“contact tip” indicates herein an end area or region of the contact probe intended to contact a contact pad, this end area or region being not necessarily pointed.

In some cases, the contact probes are fixedly fastened to the probe head itself at the upper plate-shaped support: such probe heads are referred to as“blocked probe heads”.

However, more frequently, probes are not fixedly fastened, but held interfaced to a board, possibly through a micro-contact board provided with a plurality of contact pads: such probe heads are referred to as“unblocked probe heads”. The micro-contact board is usually called“space transformer” since, besides contacting the probes, it also allows spatially redistributing the contact pads made thereon with respect to the contact pads on the device under test, in particular relaxing the distance constraints between the centers or pitches of the pads themselves.

In this case, as illustrated in figure 1 , each contact probe 6 has a further end area or region ending with a so-called contact head 7 A towards a contact pad 8A of a plurality of contact pads of a space transformer 9A. The proper electric connection between probes 6 and space transformer 9A is ensured by the pressure abutment of the contact heads 7A of the contact probes 6 onto the contact pads 8A of the space transformer 9A analogously to the contact between the contact tips 7 with the contact pads 8 of the device under test integrated on the wafer 9.

As indicated in figure 1 , the upper guide 2 and the lower guide 3 are suitably spaced apart by an air gap 10 which allows the contact probes 6 to deform. Finally, the guide holes 4 and 5 are dimensioned so as to allow the contact probes 6 to slide therein.

The correct operation of a probe head having vertical probes is basically linked to two parameters: the vertical movement, or overtravel, of the contact probes and the horizontal movement, or scrub, of the contact tips of these contact probes. It is notoriously important to ensure the scrub of the contact tips so as to allow the superficial scratching of the contact pads, in particular the pads of the device under test, removing the impurities formed thereon for instance in the form of a thin layer or oxide film or other accumulated dirt, thus improving the contact performed by the probe head by means of its probes.

All these features should be evaluated and calibrated in the manufacturing step of a probe head, and the proper electric connection between probes and device under test should always be ensured.

According to a known methodology, the contact probes 6 are initially made straight, with a constant cross-section along their entire length, possibly rectangular, and generally thinned and possibly pointed at the ends to form the contact ends, in particular the contact tip 7 and the contact head 7A as illustrated in figure 1. Successively, the probe head is formed by superimposing the upper guide 2 and the lower guide 3 in order to match the respective guide holes, namely by aligning the respective centers according to a direction orthogonal to the guides, inserting the contact probes 6 into said guide holes, spacing the upper guide 2 from the lower guide 3 to form the air gap 10 and then shifting said guides, thus causing a deformation of the body of the contact probes 6, in a substantially central position, as illustrated in figure 1. In this case the probe heads are referred to as probe heads with shifted plates and the contact probes 6 are also indicated as“buckling beam”.

Furthermore, the relative movement (shift) of the upper guide 2 and of the lower guide 3 determines a deformation direction of the contact probe 6 and thus the movement direction of the respective contact tip 7 on the contact pad 8 of the device under test integrated on a wafer 9, which is indicated as scrub direction D scrub in figure 1.

It is also possible to use already pre-deformed probes, the movement between the guides in this case accentuating said pre-deformation.

It is also known that for a probe head with vertical probes and shifted plates, such as the one illustrated in figure 1 , when the contact tips 7 of the contact probes 6 contact the contact pads 8 of the device under test integrated on a wafer 9, the deformation of the probes 6 causes a bending that is substantially identical for all the contact probes 6, so that each contact tip 7 exerts a scrub in the direction D scrub on the contact pads 8.

However, this simultaneous scrub movement of all the contact tips 7 of the plurality of contact probes 6 comprised in the probe head 1 generates a shear force on the wafer 9 that comprises the devices under test, namely a force acting in the direction Dscrub which is equal to the sum of the forces generated by all probes (all acting in the same direction Dscrub) on all contact pads 8, said shear force on the wafer 9 thus reaching high values. In particular, the term shear force indicates herein a force substantially parallel to the wafer 9, which defines a plane substantially parallel to the one in which the upper guide 2 and the lower guide 3 lie, at a face thereof facing the probe head 1 , which face is the face on which the contact pads 8 are formed and onto which the contact tips 7 of the contact probes 6 abut.

Since the probe heads usually comprise thousands of probes, the shear force due to the scrub of the contact probes may be of several tens of kilos and therefore may cause a considerable side movement of the wafer 9 when the probe head presses thereon.

Furthermore, as illustrated in figure 2A, it is also known to use vertical probe heads for testing in parallel a plurality of devices under test or chips 1 1A arranged on the wafer 9, in particular on the face of the wafer 9 facing the probe head 1 , these chips 1 1A comprising the contact pads 8 onto which the contact tips 7 of the contact probes 6 abut. As illustrated in figure 2B, the number and density of the contact pads 8 of the chips 1 1A on the wafer 9 corresponds to the number and density of the contact pads 8A of the space transformer 9A, these contact pads 8A being formed on a face thereof facing the probe head 1 , indicated with FI in figure 1 ; in particular the contact pads 8A of the space transformer 9A are distributed inside a plurality of contact areas 1 IB substantially corresponding to the chips 1 1A of the wafer 9 and also having a density equal to that of the chips 1 1A. For simplicity of illustration, only two chips 1 1A of the wafer 9, as well as only two corresponding contact areas 1 1B of the space transformer 9A, are shown in figures 2A and 2B.

When testing chips 1 1A having a high density of contact pads 8, a probe head like the one illustrated in figure 1 results in a corresponding high density of the contact pads 8A of the space transformer 9A for each contact area 1 1B; in a known manner, from said contact areas 1 1B suitable conductive tracks 12 extend in order to route the signals carried by the contact probes 6, in particular towards other contact pads formed on an opposite face of the space transformer 9A, indicated with F2 in figure 1 , with greater distances and less density with respect to the contact pads 8A formed on the face F 1.

It is noticed that, analogously to the distribution of the chips 1 1A on the wafer 9, the contact areas 1 IB distributed on the space transformer 9A, in particular on the face FI thereof facing the probe head 1 , are also close to each other, which makes the signal routing towards the testing apparatus (not shown in figure 1) complicated, the space available for the necessary conductive tracks 12 being reduced and in particular only arranged at the outer sides of the contact areas 1 IB.

More particularly, when the parallel test involves more chips 1 1A of the wafer 9, the space transformer 9 A should comprise an equal number of contact areas 1 IB, which should be contiguous precisely like the chips 1 1A of the wafer 9, which leads to complicated designs of the conductive tracks 12, for which only the area surrounding the plurality of contact areas 1 IB is available, as illustrated in figure 2B.

The technical problem of the present invention is to provide a probe head having structural and functional features so as to allow overcoming the limitations and drawbacks which still affect the known solutions, in particular able to reduce the shear force exerted on the wafer by the contact probes thereof.

Summary of the invention

The solution idea at the basis of the present invention is to provide a probe head having vertical probes wherein guide holes of an upper guide and guide holes of a lower guide are suitably offset (shifted) with respect to an axis orthogonal to the guides, so that it is possible to identify two groups of contact probes in the probe head, the probes of the first group being arranged in the probe head in a specular way with respect to the probes of the other group, namely with a specular deformation due to the offset of the guide holes.

On the basis of this solution idea, the above technical problem is solved by a probe head having vertical probes for testing a device under test integrated on a semiconductor wafer, the probe head comprising at least one upper guide and at least one lower guide separated from each other by an air gap, the lower guide being provided with a plurality of lower guide holes and the upper guide being provided with a plurality of first upper guide holes for housing a plurality of first contact probes, as well as with a plurality of second upper guide holes for housing a plurality of second contact probes, those contact probes comprising a first end adapted to contact pads of a device under test, and a second end, such a probe head being characterized in that the first upper guide holes and the second upper guide holes are offset with respect to the lower guide holes, the offset of the first upper guide holes being opposite to the offset of the second upper guide holes, wherein the first end of those first contact probes has a scrub direction opposite to a scrub direction of the first end of those second contact probes. More particularly, the invention comprises the following additional characteristics, taken individually or in combination if required.

According to an aspect of the present invention, the first upper guide holes and the second upper guide holes can be arranged in at least one first area and in at least one second area of the upper guide, wherein the first ends of the first contact probes in the first area have the scrub direction opposite to the scrub direction of the first ends of the second contact probes in the second area, resulting in distinct areas of the probe head having opposite shear forces on the semiconductor wafer.

According to an aspect of the present invention, the probe head can comprise a first area including only the first upper guide holes, and a second area including only the second upper guide holes, resulting in only two distinct areas of the probe head having opposite shear forces on the semiconductor wafer, wherein a free zone of the upper guide separates the first upper guide holes in the first area from the second upper guide holes in the second area.

According to another aspect of the present invention, the free zone can have a length between 50 pm and 1500 pm, preferably between 500 pm and 800 pm.

According to another aspect of the present invention, the first area and the second area can correspond to respective different areas of the device under test or to respective different devices under test of the semiconductor wafer.

According to another aspect of the present invention, the probe head can comprise a plurality of first areas, including the first upper guide holes, and a plurality of second areas, including the second upper guide holes, each of those areas including guide holes arranged in rows, wherein the first areas are arranged alternated with the second areas, resulting in a plurality of rows of the probe head having opposite shear forces on the semiconductor wafer.

According to yet another aspect of the present invention, the first and second contact probes can comprise a rod-like body extending along a longitudinal axis between the first end and the second end, wherein the first contact probes are deformed and arranged in a specular way with respect to the second contact probes.

According to yet another aspect of the present invention, the upper guide can be divided into a first upper guide and a second upper guide, the first upper guide and the second upper guide being independent from each other.

Furthermore, the first and second upper guide can be separated by an additional free zone, this additional free zone having a length between 50 pm and 1500 pm, preferably between 500 pm and 800 pm.

According to yet another aspect of the present invention, at least the lower guide can be provided as one piece.

The present invention also relates to a probe card for a testing apparatus of electronic devices, comprising at least one probe head made as above indicated, and a space transformer adapted to perform a spatial transformation of the pitches of the contact pads on a face thereof facing the probe head and contact pads on a second and opposite face thereof.

According to another aspect of the present invention, the space transformer can comprise contact areas comprising those contact pads, these contact areas being separated by a further free zone.

According to another aspect of the present invention, the contact areas of the space transformer can correspond to different areas of the device under test integrated on the semiconductor wafer. Alternatively, the contact areas of the space transformer can correspond to different devices under test integrated on the semiconductor wafer.

Finally, the space transformer can comprise conductive tracks or paths crossing the further free zone.

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

In those drawings:

- figure 1 schematically shows a probe head according to the prior art;

- figure 2A schematically shows a plurality of chips of a semiconductor wafer tested by the probe head of figure 1 ;

- figure 2B schematically shows a plurality of contact areas of a space transformer interfaced to the probe head of figure 1 ;

- figure 3 schematically shows a probe head according to the present invention;

- figure 4 schematically shows a plurality of contact areas of a space transformer interfaced to the probe head of figure 3;

- figure 5 schematically shows a probe head according to an alternative embodiment of the present invention; and

- figure 6 schematically shows a guide of a probe head according to an alternative embodiment of the present invention.

Detailed description

With reference to those figures, and in particular to figure 3, a probe head for testing electronic devices integrated on a semiconductor wafer according to the present invention is globally and schematically indicated with the reference number 20.

It is worth noting 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. Moreover, in the figures, the different elements are depicted in a schematic manner, their shape varying depending on the application desired. It is also noted that in the figures the same reference numbers refer to elements that are identical in shape or function. Finally, particular features described in relation to an embodiment illustrated in a figure are also applicable to the other embodiments illustrated in the other figures. The probe head 20 comprises at least one plate-like support or upper guide 22 and one plate-like support or lower guide 23, which are spaced from each other by a suitable gap 26. The probe head 20 further comprises a plurality of contact probes which slide inside guide holes made in the upper guide 22 and in the lower guide 23.

In particular, according to an embodiment of the present invention, the probe head 20 comprises a plurality of first contact probes 21s, arranged in a first portion of the probe head 20, in particular in the left portion according to the local reference system of figure 3 and for this reason indicated hereinafter as left probes 21s, and a plurality of second contact probes 2 Id, arranged in a second distinct portion of the probe head 20, in particular in the right portion still according to the local reference system of figure 3 and for this reason indicated hereinafter as right probes 2 Id.

More in particular, the lower guide 23 comprises a plurality of lower guide holes 25, whereas the upper guide 22 comprises a plurality of first upper guide holes 24s, for slidingly housing the sole left probes 21s, and a plurality of second upper guide holes 24d, for slidingly housing the sole right probes 2 Id, as it will be described in detail in the following. In the following description, the first upper guide holes 24s will be indicated as upper left guide holes 24s, whereas the second upper guide holes 24d will be indicated as upper right guide holes 24d, the terms right and left being understood as previously according to the local reference system of figure 3 for the sole purpose of facilitating the understanding of the description.

Even more particularly, the left upper guide holes 24s are consecutive to each other and made in a first area A1 of the upper guide 22, and the right upper guide holes 24d are also consecutive to each other and made in a second area A2 of the upper guide 22, as it will be clarified hereinafter.

Suitably, the first area A1 of the upper guide 22, where the left upper guide holes 24s are made, substantially corresponds to the extension of a first device under test or chip comprised in a semiconductor wafer 29’ to be tested by means of the probe head 20. Analogously, the second area A2 of the upper guide 22, where the right upper guide holes 24d are made, substantially corresponds to the extension of a second device under test or chip comprised in the semiconductor wafer 29’. For the sake of simplicity, all the devices under test comprised in the semiconductor wafer 29’ will be hereinafter indicated with reference number 29.

Alternatively, the first area A1 of the upper guide 22, where the left upper guide holes 24s are made, and the second area A2 of the upper guide 22, where the right upper guide holes 24d are made, may correspond to a respective first and second area of a same device under test or chip 29 comprised in the semiconductor wafer 29’ to be tested by the probe head 20. The first and second areas could for instance correspond to areas dedicated to different types of signals or to areas having a different density of contact pads.

In other words, the first area A1 and the second area A2 correspond to respective different areas or regions of the device under test 29 or to respective different devices under test 29 of the semiconductor wafer 29’.

Furthermore, in this embodiment, the left upper guide holes 24s are separated from the right upper guide holes 24d by an area of the upper guide 22 where guide holes are not present, this area being thus indicated as free zone 30. As a result, the first area A1 and the second area A2 of the upper guide 22 are separated from each other by said free zone 30.

For simplicity of illustration, figure 3 only shows three left probes 21s and three right probes 2 Id, this figure being provided just by way of non-limiting example of the scope of the present invention, since the number of left probes 21s and of right probes 2 Id may vary according to needs and/or circumstances. In a preferred embodiment, the number of left probes 21s is substantially identical to the number of right probes 2 Id, the number of left probes 21s corresponding to the number of the left upper guide holes 24s and the number of right probes 2 Id corresponding to the number of right upper guide holes 24d, the number of left upper guide holes 24s being thus preferably equal to the number of right upper guide holes 24d.

Each left probe 21s and each right probe 2 Id comprises a rod-like body 21’ having a pre-fixed longitudinal H-H axis and axially sliding in the left and right upper guide holes 24s and 24d of the upper guide 22 and in the lower guide holes 25 of the lower guide 23, the rod-like body 21’ ending with a first end or contact tip 27, this longitudinal H-H axis extending in the direction indicated by the y axis (vertical axis) in the reference system of figure 3.

More particularly, the contact tip 27 is adapted to abut onto contact pads 28 of the device under test or chip 29 of the semiconductor wafer 29’. It is observed that the semiconductor wafer 29’ may comprise a plurality of devices under test 29, figure 3 showing by way of example two devices under test, each comprising three contact pads 28, wherein a device under test is tested by the left probes 21s, and the other device under test is tested by the right probes 2 Id.

Furthermore, in the example illustrated in figure 3, the probe head 20 is of the type having non-fastened probes and the left and right contact probes 21 s and 2 Id end with a second end or contact head 27A which is adapted to abut onto contact pads 28A of an interposer or space transformer 29A.

It is noticed that the left and right upper guide holes 24s and 24d of the upper guide 22 are moved (shifted) from each other along a longitudinal axis Z-Z of the upper guide 22 (substantially orthogonal to the H-H axis and parallel to the x axis - horizontal axis - of the reference system of figure 3) with respect to the lower guide holes 25 of the lower guide 23, the H-H axis being substantially orthogonal to the guides 22 and 23; the shift of the left and right upper guide holes 24s and 24d with respect to the lower guide holes 25 is thus adapted to deform the body 21’ of the left probes 21s and of the right probes 2 Id. In other words, the left upper guide holes 24s are offset (shifted) with respect to the lower guide holes 25, as well as the right upper guide holes 24d are offset (shifted) with respect to the lower guide holes 25, with respect to said H-H axis. Namely, the centers of the guide holes 24s and 25, as well as the centers of the guide holes 24d and 25, are not arranged on a same axis orthogonal to the upper guide 22 and to the lower guide 23.

In particular, the offset direction of the left and right upper guide holes 24s and 24d with respect to the lower guide holes 25 determines the deformation of the contact probes and thus the horizontal movement or scrub direction of the respective contact tips 27 on the contact pads 28 of the device under test 29, this scrub occurring in a direction parallel to the device under test 29 and to the wafer 29’ comprising it (namely according to the x axis of the reference system of figure 3). Between each contact probe and each guide hole a clearance is defined, whose width is determined by the dimensions of the guide holes with respect to a diameter of the probes, intended herein as the maximum transversal dimension, even in case of probes with non-circular section, this clearance allowing the horizontal movement of the probes.

In particular, the maximum transversal dimensions or diameters of the guide holes are comprised between 20 pm to 150 pm, preferably between 35 pm and 1 10 pm, whereas the clearance between probes is comprised between 5 pm to 30 pm, preferably between 8 pm and 15 pm.

As previously noticed, the scrub of the contact probes generates an undesired shear force on the device under test 29 and on the wafer 29’ comprising it, the direction of this force being determined by the deformation of the body 21’ of the contact probes of the probe head 20.

Advantageously according to the present invention, the offset of the left upper guide holes 24s with respect to the lower guide holes 25 is different from the offset of the right upper guide holes 24d with respect to the lower guide holes 25, in particular opposite thereto, so that the left probes 21s are deformed and arranged in a specular way with respect to the right probes 2 Id in the probe head 20.

In particular, the offset of the left upper guide holes 24s with respect to the lower guide holes 25 is in a direction parallel to the x axis of figure 3 and opposite with respect to the offset of the right upper guide holes 24d with respect to the lower guide holes 25. As a result, in the probe head 20, the deformation of the left contact probes 21s is specular with respect to the deformation of the right contact probes 2 Id, this deformation being due to the above-mentioned offset and determining the scrub direction of the respective contact tips 27.

Specifically, the left upper guide holes 24s are moved towards the left (left- shifted) with respect to the lower guide holes 25, according to the local reference of figure 3, whereas the right upper guide holes 24d are moved towards the right (right- shifted) with respect to the lower guide holes 25, still according to the local reference of figure 3. Namely, both the left upper guide holes 24s and the right upper guide holes 24d are moved outwards the probe head 20, but in an opposite direction. According to the embodiment of figure 3, the offset of the guide holes and the specular arrangement of the left probes 21s with respect to the right probes 2 Id results in that the free zone 30 is obtained in the upper guide 22. In the free zone 30 guide the holes are not present, this free zone 20 being substantially defined at the center of the upper guide 22. The free zone 30 extends along the longitudinal axis Z-Z of the upper guide 22 and it has a length along this axis Z-Z greater than that of each space between two contiguous lower guide holes 25 in the lower guide 23. In particular, the free zone 30 has a length comprised between 50 pm and 1500 pm, preferably between 500 pm and 800 pm.

As for the left probes 21s, the horizontal movement direction (scrub direction) of the contact tips 27 on the contact pads 28 of the device under test 29 is indicated as left scrub direction DscrubSX in figure 3, this scrub occurring in the same direction and orientation of the x axis of figure 3. In this case, in each left probe 21s, the contact head 27A precedes the contact tip 27 with respect to the left scrub direction DscrubSX.

As for the right probes 2 Id, the horizontal movement direction (scrub direction) of the contact tips 27 on the contact pads 28 of the device under test 29 is indicated as right scrub direction DscrubDX in figure 3, this right scrub direction DscrubDX being opposite to the left scrub direction DscrubSX and thus being in the same direction of the x axis but in an opposite orientation with respect to that of the x axis of figure 3. In each right probes 2 Id, the contact head 27A precedes the contact tip 27 with respect to the right scrub direction DscrubSX, i.e. the contact head 27A follows the contact tip 27 with respect to the x axis.

Therefore, the first end or contact tip 27 of the left probes 21s has a left scrub direction DscrubSX opposite to the right scrub direction DscrubDX of the first end 27 of the right probes 2 Id.

In other words, with respect to the reference system of figure 3, specifically with respect to the x axis, the left scrub direction DscrubSX is opposite the right scrub direction DscrubDX, in particular the left scrub direction DscrubSX is in the positive direction of the x axis whereas the right scrub direction DscrubDX is in the negative direction of the x axis.

This configuration of the contact probes of the probe head 20 has the great advantage that, since the left scrub direction DscrubSX of the left probes 21s is opposite the right scrub direction DscrubDX of the right probes 2 Id, the transversal or shear forces exerted by the left probes 21 s on the device under test 29 and thus on the semiconductor wafer 29’ are substantially compensated by the shear forces exerted by the right probes 2 Id. The resultant of the forces in the direction of the x axis of figure 3, namely the resultant of the shear forces that are parallel to a face FA of the semiconductor wafer 29’ facing the probe head 20, exerted by the contact probes of the probe head 20, is thus substantially null, resulting in a compensated load on the semiconductor wafer 29’.

As previously indicated, the contact head 27A is adapted to abut onto contact pads 28A of an interposer or space transformer 29A.

In particular, the space transformer 29A is adapted to perform a spatial transformation of the distances between the centers (transformation of the pitches) of the contact pads on opposite faces thereof. In particular, on a first face FB of the space transformer 29A facing the probe head 20, the contact pads 28A have a pitch equal to that of the contact pads 28 of the device under test 29, whereas the contact pads (not illustrated) on a second and opposite face FC of the space transformer 29A have a pitch equal to that of contact pads on a printed circuit board o PCB (also not illustrated) which generally the space transformer 29A connects to, in particular they have a pitch greater than the pitch of the contact pads 28 A, thus performing the desired spatial transformation and allowing an easier arrangement of the contact pads on the second and opposite face FC, as well as an easier connection with the PCB and thus with the testing apparatus.

As shown in greater detail in figure 4, the contact pads 28A of the space transformer 29A are arranged in certain areas 31 of the space transformer 29 A, herein and hereinafter called contact areas 31 of the space transformer 29A, these contact areas 31 being thus present on face FB of the space transformer 29A facing the probe head 20 and corresponding to respective devices under test or chips 29 arranged on the semiconductor wafer 29’, or corresponding to different areas or regions of a same device under test 29, as previously indicated.

It is noticed that, although figure 4 only shows two contact areas 31 , the present invention is not limited thereto, and the number of contact areas 31 , as well as the number of contact pads comprised therein, may vary according to needs and/or circumstances, figure 4 being provided just by way of non-limiting example of the present invention.

The space transformer 29A further comprises conductive tracks or paths

32 for routing the signals carried by the contact probes, in particular the left probes 21s and the right probes 2 Id, towards the contact pads arranged on the other face FC of the space transformer 29A, these conductive tracks or paths 32 originating from the contact pads 28A of the space transformer 29A. For simplicity of illustration, just some of all the conductive tracks or paths 32 are shown in figure 4. It is also possible to use conductive planes for connecting the pads arranged on the two opposite faces of the space transformer 29A.

As previously noticed, the specular or symmetrical arrangement of the contact probes inside the probe head 20 results in the free zone 30 in the upper guide 22. Suitably, the presence of this free zone 30 allows spacing the contact areas 31 comprising the contact pads 28A in contact with the contact heads 27A of the probes, thus defining a corresponding further free zone 33 between two different contact areas 31 of the space transformer 29A, wherein the contact pads 28A are not present in the further free zone 33.

In other words, in the example of figures 3 and 4, the presence of the free zone 30 due to the specular arrangement of the left probes 21s with respect to the right probes 2 Id leads to define the corresponding further free zone

33 between two different contact areas 31 of the space transformer 29A, wherein the contact heads of only the left probes 21s abut onto a first contact area, and wherein the contact heads of only the right probes 2 Id abut onto a second contact area. In general, there are left contact areas, onto which only the left probes 21s abut, and right contact areas, onto which only the right probes 2 Id abut.

It is clear that the possibility of spacing different contact areas 31 of the space transformer 29A allows greatly facilitating the rearrangement of the conductive tracks or paths 32 for routing the signals carried by the contact probes of the probe head 20. In fact, the presence of the further free zone 33 allows performing the routing of the signals by means of the conductive tracks or paths 32 which cross also this further free zone 33, differently from what occurs in the known solutions where the contact areas have at least one side in common and the routing of the signals is only performed at the sides which are not in common (outer routing).

In the embodiment of figures 3 and 4, the left upper guide holes 24s, as well as the right upper guide holes 24d, are grouped in specific areas of the upper guide 22, in particular the first area A1 and the second area A2, these areas A1 and A2 corresponding to a respective left or right contact area 31 , each contact area 31 corresponding to a particular area or region of the device under test 29 or corresponding to a respective device under test 29 of the semiconductor wafer 29’.

The contact areas 31 may thus exactly correspond to respective different devices under test or chips 29 of the semiconductor wafer 29’. Alternatively, different contact areas 31 may correspond to different portions or areas of a same device under test 29, for instance a first contact area of the space transformer 29A may correspond to a power area of the chip 29, and a second contact area of the space transformer 29A may correspond to a signal area of the chip 29. These different portions of a same device under test 29 may also be two functionally identical portions but with different density and pitch between the pads, as it happens in case of multi-pitch devices. It is also possible to provide a completely arbitrary division of the device into areas, simply with the purpose of improving the load distribution thereon and on the wafer.

From the above, it is clear that the present invention also relates to a probe card for a testing apparatus of electronic devices comprising the probe head 20, the space transformer 29A and possibly a printed circuit board or PCB (not illustrated in the figures) interfaced with the space transformer 29A for connecting to a testing device (not illustrated in the figures), the space transformer 29A comprising the contact areas 31 separated by the further free zone 33.

In a preferred embodiment of the present invention, the further free zone 33 has a length comprised between 50 pm and 1500 pm, preferably between 500 mih and 800 mih.

According to an alternative embodiment of the present invention, the assembling of the probe head 20 may be facilitated by adopting a configuration in which the probe head 20 comprises, instead of the upper guide 22, a first upper guide 22s and a second upper guide 22d, those first and second upper guides 22s and 22d being separated from each other and independent, as schematically illustrated in figure 5. In this embodiment, the upper guide 22 is thus divided into a first upper guide 22s and into a second upper guide 22d. In the rest of the description, analogously to what previously done, the first upper guide 22s will also be called left upper guide 22s, whereas the second upper guide 22d will also be called right upper guide 22d.

In particular, the left and right upper guides 22s and 22d are arranged along a same horizontal axis according to the local reference of figure 5, namely they are arranged along a longitudinal axis thereof parallel to the x axis of figure 5 and indicated in the figure as Z’-Z’ axis. The left and right upper guides 22s and 22d have each a length less than half the length of the lower guide 23 or may have a length equal to half the lower guide 23.

In particular, the left upper guide 22s comprises the left upper guide holes 24s, whereas the right upper guide 22d comprises the right upper guide holes 24d.

According to this embodiment, when the contact probes of the probe head 20 contact the contact pads 28 of the device under test 29, the left upper guide 22s is spaced and separated along the Z’-Z’ axis from the right upper guide 22d by an additional free zone 30’, this additional free zone 30’ having a length preferably comprised between 500 pm and 1500 pm and in turn allowing the presence of the further free zone 33 between contact areas of the space transformer interfaced to the probe head 20.

Suitably, by adopting the embodiment of figure 5, the assembling of the probe head 20 is much simpler.

According to another embodiment of the present invention, the left probes 21s and the right probes 2 Id are arranged into consecutive and alternating rows in the upper guide 22, such rows of left and right probes alternating to each other as shown in figure 6 (which illustrates a guide, for example the upper guide 22, of the probe head 20). In this case, there are not only two areas A1 and A2 having opposite scrubs, but a plurality of consecutive areas having opposite scrubs.

In particular, in the embodiment of figure 6, there is a plurality of first areas (only two first areas A1 and Al’ are shown for the sake of simplicity) including the left upper guide holes 24s, and a plurality of second areas (only two second areas A2 and A2’ are shown for the sake of simplicity) including the right upper guide holes 24d, each of these areas including guide holes arranged in single rows, wherein these areas are arranged alternating to each other, resulting in a plurality of rows of the probe head 20 having opposite shear forces on the semiconductor wafer 29’.

It is also observed that, in this embodiment, all the considerations made in relation to the embodiments of figures 3-5 are still valid, i.e. the offset of the left upper guide holes 24s with respect to the lower guide holes 25 is different from the offset of the right upper guide holes 24d with respect to the lower guide holes 25, in particular opposite thereto, so that the left probes 21s are deformed and arranged in a specular way with respect to the right probes 2 Id in the probe head 20: therefore, the left probes 21s in the rows of the first areas have a left scrub direction DscrubSX opposite to the right scrub direction DscrubDX of the right probes 2 Id in the rows of the second areas. The difference is that the right and left guide holes 24s and 24d are now arranged in different consecutive and adjacent rows of the upper guide 22 (or the lower guide 23), so that no free zone in the guide is formed between the different areas. Furthermore, in this embodiment, the contact probes are preferably already pre-deformed.

In conclusion, the present invention provides a probe head adapted to test an electronic device integrated on a semiconductor wafer, wherein a plurality of first contact probes or left probes is deformed and arranged in a substantially specular way with respect to a plurality of second contact probes or right probes. This configuration is obtained thanks to the presence of upper guide holes made in an upper guide and being suitably offset with respect to lower guide holes made in a lower guide. In other words, in the probe head having vertical probes of the present invention, the guide holes of the upper guide and the guide holes of the lower guide are suitably offset (shifted) with respect to an axis orthogonal to the guides, so that it is possible to identify two groups of contact probes in the probe head, the probes of the first group (left probes) being arranged in the probe head in a specular way with respect to the probes of the other group (right probes), namely with a specular deformation due to the offset of the guide holes.

Advantageously according to the present invention, the left contact probes have a scrub movement opposite the scrub movement of the right contact probes since they have a specular deformation. As a result, the whole transverse or shear load exerted by these contact probes on a device under test and on the semiconductor wafer is substantially compensated, namely the resultant of the forces that are exerted by the probe head and are parallel to a face of the device under test facing the probe head is thus substantially null. This allows a more precise test and prevents phenomena such as the side movement of the semiconductor wafer due to the non- compensated side forces (shear forces) of the contact probes.

Furthermore, the probe head according to the present invention allows increasing the distance between the contact areas where the contact pads of a space transformer are made. In particular, it is possible to maintain a high density of the contact tips in contact with the contact pads of the device under test, meanwhile spacing the contact areas of the space transformer, thus greatly facilitating the routing of the signals carried by the contact probes of the probe head. It is in fact noticed that according to the present invention it is possible to form conductive tracks or paths in the space transformer also in the free zones defined between different contact areas, these contact areas corresponding both to different chips and to different portions of a same chip.

Finally, the adopted configuration allows a very easy alignment of the probe head, as no different modules are used and the lower guide is preferably provided as one piece, the different scrubs being only by properly changing the shift between the guide holes of the upper and lower guides. For this reason, also an arrangement of the probes into alternating rows is possible.

Obviously, a person skilled in the art, in order to meet particular needs and specifications, can carry out several changes and modifications to the probe head and to the probe card described above, all included in the protection scope of the invention as defined by the following claims.

Claims

1. A probe head (20) having vertical probes for testing a device under test (29) integrated on a semiconductor wafer (29’), said probe head (20) comprising at least one upper guide (22) and at least one lower guide (23) separated from each other by an air gap (26), said lower guide (23) being provided with a plurality of lower guide holes (25) and said upper guide (22) being provided with a plurality of first upper guide holes (24s) for housing a plurality of first contact probes (21s), as well as with a plurality of second upper guide holes (24d) for housing a plurality of second contact probes (2 Id), said contact probes (21s, 2 Id) comprising a first end (27) adapted to contact pads of a device under test, and a second end (27A), said probe head (20) being characterized in that said first upper guide holes (24s) and said second upper guide holes (24d) are offset with respect to said lower guide holes (25), the offset of said first upper guide holes (24s) being opposite to the offset of said second upper guide holes (24d), wherein the first end (27) of said first contact probes (21s) has a scrub direction (DscrubSX) opposite to a scrub direction (DscrubDX) of the first end (27) of said second contact probes (2 Id).

2. The probe head (20) according to claim 1 , characterized in that said first upper guide holes (24s) and said second upper guide holes (24d) are arranged in at least one first area (Al) and in at least one second area (A2), respectively, of said upper guide (22), wherein the first ends (27) of said first contact probes (21s) in said first area (Al) have the scrub direction (DscrubSX) opposite to the scrub direction (DscrubDX) of the first ends (27) of said second contact probes (2 Id) in said second area (A2), resulting in distinct areas of the probe head (20) having opposite shear forces on the semiconductor wafer (29’).

3. The probe head (20) according to claim 2, comprising a first area (Al) including only the first upper guide holes (24s), and a second area (A2) including only the second upper guide holes (24d), resulting in only two distinct areas of said probe head (20) having opposite shear forces on the semiconductor wafer (29’), wherein a free zone (30) of said upper guide (22) separates the first upper guide holes (24s) in the first area (Al) from the second upper guide holes (24d) in the second area (A2).

4. The probe head (20) according to claim 3, characterized in that said free zone (30) has a length between 50 pm and 1500 pm, preferably between 500 pm and 800 pm.

5. The probe head (20) according to claim 3 or 4, characterized in that said first area (Al) and said second area (A2) correspond to respective different areas of said device under test (29) or to respective different devices under test (29) of said semiconductor wafer (29’).

6. The probe head (20) according to claim 2, comprising a plurality of first areas (Al , Al’), including the first upper guide holes (24s), and a plurality of second areas (A2, A2’), including the second upper guide holes (24d), each of said areas (Al , Al’, A2, A2’) including guide holes arranged in rows, wherein the first areas (Al , Al’) are arranged alternated with the second areas (A2, A2’), resulting in a plurality of rows of said probe head (20) having opposite shear forces on the semiconductor wafer (29’).

7. The probe head (20) according to claim 1 or 2, characterized in that said upper guide (22) is divided into a first upper guide (22s) and a second upper guide (22d), said first upper guide (22s) and said second upper guide (22d) being independent from each other.

8. The probe head (20) according to claim 7, characterized in that said first and second upper guide (22s, 22d) are separated by an additional free zone (30’), said additional free zone (30’) having a length between 50 pm and 1500 pm, preferably between 500 pm and 800 pm.

9. The probe head (20) according to any one of the preceding claims, characterized in that said first and second contact probes (21s, 2 Id) comprise a rod-like body (21’) extending along a longitudinal axis (H-H) between the first end (27) and the second end (27A), wherein said first contact probes (21s) are deformed and arranged in a specular way with respect to said second contact probes (2 Id).

10. The probe head according to any one of the preceding claims, wherein said lower guide (23) is provided as one piece.

1 1. A probe card for a testing apparatus of electronic devices, comprising at least one probe head (20) made according to any one of the preceding claims, and a space transformer (29A) adapted to perform a spatial transformation of the pitches of the contact pads (28A) on a face thereof (FB) facing said probe head (20) and contact pads on a second and opposite face thereof (FC).

12. The probe card according to claim 1 1 , wherein said space transformer

(29A) comprises contact areas (31) comprising said contact pads (28A), said contact areas (31) being separated by a further free zone (33).

13. The probe card according to claim 12, characterized in that said contact areas (31) of said space transformer (29A) correspond to different areas of said device under test (29) integrated on said semiconductor wafer (29’).

14. The probe card according to claim 12, characterized in that said contact areas (31) of said space transformer (29A) correspond to different devices under test (29) integrated on said semiconductor wafer (29’).

15. The probe card according to claim 12, wherein the space transformer (29A) comprises conductive tracks or paths (32) crossing said further free zone (33).