Patent Description:
Specifically, the invention relates to a particular probe-holder support structure and corresponding probes (on the whole defined with the term "probe head") capable of enabling a facilitated assembly and a better functionality during test.

Probe cards for electronic tests have long been known and used.

The "probe card" is an interface between test system and wafer, used during test of devices. Its purpose is to connect electrically circuits of the device (in the wafer) and resources of tester (see <FIG> prior art).

As schematized in <FIG>, still prior art, typically a "probe card" is in its turn formed by:.

The probe head <NUM> is made up by a structure that keeps probes in position and by the probes themselves.

In the case of vertical probes, typically it (i.e. the probe head) comprises two generally ceramic perforated plates which act as a guide and where probes are inserted. Such ceramic plates are in the form of an upper ceramic plate and a lower ceramic plate that are generally defined in technical jargon as "Guide Plates" and they are indicated in <FIG> with the numbering (1Top) and (1Bot) (i.e. upper and lower).

When coupled, they form the inner seat in which probes are housed with the probe ends protruding from such ceramic plates through holes so as to be in contact with the wafer on one side and on the opposite side with the electrical communication towards PCB (see <FIG>).

Such upper and lower ceramic plates have at their ends (<FIG> shows the left and right end in section) a vertical extension (EV) like a column that branches off vertically from the flat surface (SP).

In this way, as it is well inferable from <FIG>, the upper and lower plate are in direct contact to each other through such vertical extensions (EV) that represent a contact edge of the two said plates. With respect to them, the flat surface of the plate (SP) is raised thus forming the seat for probes.

In addition, the coupling between the upper plate (1Top) and the lower one (1Bot) is helped by two further supports (Sup1, Sup2) positioned like a bearing column at the two ends of the seat, thus delimiting the same seat on the right and on the left (still see <FIG>).

Further supports can be only one of annular shape in the case that the entire probe head is circular depending on shapes. In fact, <FIG> shows a section thereof.

Even if structurally complex, this structure enables the correct mechanical functioning of probes which buckle inside the probe head during the contact with wafer, thus enabling to manage dimensional and geometrical tolerances of parts and to keep the contact force under control.

Thus, during test, electrical signals are sent from the machine and they are transmitted through the pcb to the wafer by means of probes (see <FIG>).

Probes are inserted into the support forming part of the probe head and must have electrical and mechanical properties.

They must have electrical properties because their purpose is to contact pads in the wafer with the contacts of pcb of the probe card. They must have mechanical properties because they must ensure the electrical contact for numerous test cycles, bearing continuous buckles without damaging the wafer, thereby enabling to manage dimensional and geometrical tolerances of the parts and to keep the contact force under control.

Thus, they must have a geometry and optimized materials.

A particularly felt technical issue concerns the facility of assembly of probes in their support (i.e. the probe head <NUM> described in prior art) and solicitations to which the same probe is subject during its functioning.

At the current state of art, solutions do not enable an easy assembly of probes in their support and the probe, during its working cycle, is subject to high solicitations which reduce their lifespan.

Publications <CIT>, <CIT> and <CIT> are further known.

Therefore, the aim of the present invention is to provide a new solution which lessens at least the above-mentioned problems.

In particular, the aim of the present invention is to provide a new geometry of probe which reduces remarkably the probabilities of damaging the probe and facilitates its mounting at the same time.

These and other aims are achieved with the contact probe, according to claim <NUM>.

Such contact probe (<NUM>) for electronic tests comprises:.

According to the invention, said lower part (<NUM>) comprises an enlarged head (13D) having a lower surface (13D') which in use is intended to rest at least partially onto a horizontal surface (<NUM>, X), preferably or generally the lower plate.

Said enlarged head (13D) further comprises an upper surface which branches off radially from the central body, said enlarged head developing longitudinally for a certain length and ending with said lower surface (13D') which branches off radially from the end portion (13c) to which it is connected.

Such lower surface (13D') is thus configured so as tc form, in a rest condition of the unbuckled probe, an inclination (α) with respect to the horizontal surface (<NUM>, X) onto which it rests.

Therefore, in a rest condition, it rests onto a limited area of the entire lower surface (13D') for example that can also be assimilated to a point.

In condition of buckle of the probe, there is instead at least one buckled position in which said lower surface (13D') moves to rest entirely onto the horizontal surface thus zeroizing said angle (α).

Thus, the lower surface (13D') has a working which entails an oblique cut and thus the formation of such surface with a certain inclination with respect to a horizontal plane (see <FIG>).

Thanks to such probe configuration, when it is buckled in work condition, or measurement condition, a sort of roto-translation occurs such that it entirely rests through such lower surface (13D') onto the surface of the lower plate and then it discharges the buckling force onto the support surface in a normal way, i.e. orthogonally.

This enables much more stability of the probe and thus measurement precision.

As explained below, the bevel generating the lower surface (13D') has generally small angles, for example comprised between approximately <NUM> and <NUM> angular degrees.

On the basis of the description above, a probe head is described here as well, comprising:.

Advantageously, the lower plate (<NUM>) can be mounted slidingly along at least one vertical guide (<NUM>) with respect to the support (<NUM>) so that said lower plate (<NUM>) is movable between a position spaced from the support (<NUM>), in which said probe is in rest condition, and a position in which the lower plate is in contact against the support and with the probe which is, in said position of the lower plate, buckled in said work condition.

This solution greatly facilitates the mounting of the probe head assembly.

Here is also described a method for mounting a probe head according to the description above and comprising the insertion phases of the probes from the holes of the upper plate (<NUM>) so that each probe is positioned with the opposite end protruding from the corresponding hole of the lower plate (<NUM>), the lower plate being arranged with play with respect to the support (<NUM>) to which it is fixed and wherein, after the insertion of all the probes, the sliding phase of the lower plate along the guide thereof is provided so as to move it against the support (<NUM>) thus zeroizing the play and positioning the probes in buckled work position in which, in said buckled position, the lower surface (13D') of the probe is entirely lying onto the surface of the lower plate.

Further advantages can be inferred from dependent claims.

Additional features and advantages, according to the invention, will become apparent from the following description of embodiments thereof, given only by way of non-limiting example, with reference to the attached drawings, wherein:.

<FIG> shows a probe <NUM> with a particular geometry described below and positioned in the seat delimited above by the plate or upper stopper (<NUM>) and below by the plate or lower stopper (<NUM>) (they are generally ceramics).

Differently from the introduced prior art, the upper plate and the lower plate are of substantially flat shape so that they do not form such perimetrical edge like a column, as per the prior art, through which they are in contact. This is also highlighted in <FIG> showing top <NUM> and bottom <NUM>.

Specifically, as shown in <FIG>, in correspondence of their ends (since <FIG> is a section of a part of the probe head, it only shows the left end) top and bottom are not in direct contact with each other. In such type of solution, the support <NUM> is instead interposed (generally of annular shape as per <FIG>) and its presence is also evident in <FIG>.

Therefore, differently from prior art, top and bottom are without columns (EV) (see comparison between <FIG> prior art and <FIG>) and are two substantially flat elements for their entire extension surface.

In fact, <FIG> shows an end part, particularly the left one, where the portion of upper and lower stopper is highlighted, they are substantially flat and without the vertical extension (EV) of prior art such that they are not in direct contact with each other.

According to the present solution, as shown in <FIG> and <FIG>, now the support <NUM> is instead interposed between the two upper and lower plates such that said two plates, with a substantially flat shape are separated from each other and joined only through the support <NUM> which spaces them and delimits the seat for probes together with connection means described below.

The position of support <NUM>, although represented in <FIG> in correspondence of the edge of plates, could also be inside the edge or in a position generically near to the edge and be of variable widths depending on constructive needs.

Therefore, the upper stopper is fixed to the interposed support <NUM> with suitable screws or bolts in general <NUM> schematized in <FIG>.

The lower stopper <NUM> has a certain "play" with respect to the bearing structure <NUM> and it is well highlighted in <FIG> with the wording "Mounting play".

As clearly shown in <FIG> on the left ("mounting phase"), a centering pin <NUM> is provided which inserts into a suitable hole <NUM> of the lower stopper <NUM>. The assembly is such as not to prevent the lower stopper <NUM> from sliding vertically towards the upper stopper <NUM> and thus towards the support <NUM>.

In fact, the hole <NUM> forms for this purpose a countersink, i.e. an enlarged part, which houses the enlarged head of pin <NUM>.

The pin <NUM> has a threaded front part <NUM> which engages with a corresponding threaded hole of the support <NUM> while the opposite part to the threaded one, i.e. the rear part <NUM>, forms an enlarged head <NUM> which inserts into the countersink of hole <NUM>.

When the pin <NUM> is inserted into the lower stopper through the hole <NUM>, its front part <NUM> engages with the threading of support <NUM> thoroughly to the threaded hole. The length of pin <NUM> is such that, once screwing has been completed, the plate <NUM> is still spaced from the support <NUM>, position indicated in <FIG> on the left (mounting phase) with the enlarged head <NUM> which stops against the shoulder <NUM> of the hole countersink. Essentially, in this position, the shoulder <NUM>' formed by the enlarged head <NUM> of pin <NUM> goes bucks against the shoulder <NUM> of countersink of hole <NUM>. Essentially, in this position the shoulder <NUM>' formed by the enlarged head <NUM> of pin <NUM> bucks against the shoulder <NUM> of countersink of hole <NUM> keeping the plate raised at the play distance shown in <FIG>.

In this way, the pin <NUM> becomes a vertical sliding guide which enables to guide along it the plate <NUM> in an approaching/moving away motion to/from the support <NUM>.

The guide plate <NUM>, when the pin <NUM> has been screwed and the screw <NUM> has not been screwed, is then free to approach and move away from the support <NUM> to a maximum distance named "mounting play".

The thickness of pin head <NUM> is lower than the total depth of countersink of hole <NUM> into which the pin is inserted and the depth of countersink is such that, when the lower plate is brought to the shelter of support <NUM> thus zeroizing the play, the pin head <NUM> is still hidden inside the hole <NUM> (see <FIG> "final mounting").

Therefore, the pin <NUM> screws thoroughly to the support <NUM> and in this position the length of screw <NUM> is such as to keep the lower plate <NUM> at a certain distance (named "mounting play" or play) with respect to the support <NUM>. The pin <NUM> acts as a guide for vertical sliding and when the lower plate <NUM> approaches in contact with the support <NUM>, then the probe positioned inside between the upper and lower plate bends and said bent (or generically buckled) position is kept after the lock of plate <NUM> near support <NUM>. Said lock of plate <NUM> to the support <NUM> without play occurs thanks to the fixing screw <NUM> (preferably four fixing screws), which is also screwed into the support <NUM> through the plate <NUM> but with such a length that, when thoroughly screwed, it forces the plate to buck against the support <NUM> (exactly like the solution of the upper plate <NUM>).

As well shown in <FIG> on the right (final mounting), the lower stopper <NUM>, thanks to pin <NUM>, is in this way vertically sliding along the pin <NUM> which acts in this way as a vertical guide, such that the lower pin <NUM> can approach/move away from the upper stopper <NUM> according to an orthogonal direction to the plane of the two said stoppers, precisely because the pin acts as a guide.

Before fastening the screw <NUM> and locking the whole, the probe head must be mounted onto the probe card. Then the whole can be fixed with the screw or bolt <NUM> which brings the plate <NUM> against the support <NUM> and with probes in bent work condition.

It is obvious that the probe head must be mounted onto the probe card/interposer before tightening screw/s or bolt/s <NUM> given that otherwise the probe would not have any surface to contact on the side of the plate <NUM> thereby being free to jump out through the passage hole made in the plate <NUM> itself.

In fact, in <FIG> on the right (final mounting), the probe is shown in bent work position and no element in contact with the probe is shown above the plate <NUM> with the sake of simplifying the drawing only. It is obvious that without an element which is in electrical contact with the probe the probe itself would jump out of the hole.

In this embodiment, the probe buckles elastically, for example it bends, and pre-charges but with a stress reduction achieved thanks to the conformation of the probe itself described below.

Specifically, with reference to <FIG> and <FIG>, the probe <NUM> has an upper part <NUM> which connects to the central curved shank <NUM> (the part which bends or buckles in general). On the opposite side the lower part <NUM> is provided which connects to the central shank <NUM>.

The upper part <NUM> ends with a contact part <NUM>' equipped with a contact tip which in use contacts the probe card.

Therefore, such contact part <NUM>' has a certain inclination with respect to the plane of the probe card (see the inclination of axis (Z, S) in <FIG> and in <FIG>).

The angle between the direction of the contact part <NUM>' and the axis Z (axis orthogonal to the plane of the probe card) obviously changes from a rest condition of the probe (as per <FIG>) and a pre-charging condition in which the probe is bent or buckled in general (as per <FIG>).

The contact part <NUM>' connects to the part <NUM>'' with the following conformation described specifically in <FIG> (unbent probe condition).

A rear wall (<NUM>''p) parallel to axis Z and a front wall (<NUM>''a) with geometry suitable for being handled.

Specifically, such front part (<NUM>"a) forms a side opposite to the rear part (<NUM>"p) which progressively moves away from it according to a certain angle and then connects again to the central body <NUM> through a transversal part (<NUM>"d), thus forming a sort of tooth or step (<NUM>"d).

Therefore, considering a reference axis Z as per <FIG>, the wall (<NUM>''p) is parallel to axis Z while the front wall (<NUM>''a) forms an inclined side with respect to said wall (<NUM>''p).

The axis Z is an axis orthogonal to a horizontal reference plane X (see for example <FIG>).

Through such conformation, the probe can be handled in a precise and repeatable way by a manipulator.

The production process of probes provides for their mounting onto a suitable support which allows their electrochemical growth and all the subsequent processes after growth. At the moment of mounting the probe head, such probes must be taken by a manipulator and transferred inside the holes present on the ceramics of the ceramic plates (i.e. the upper and lower plate). Thus, such manipulator holds probes from the portion (<NUM>) described above, which must have a suitable geometry adapted to make the manipulator hold strong and repeatable, in accordance to the description.

<FIG> broadly shows a schematization concerning the manipulator hold. The geometric detail of the holding area can be obviously varied depending on needs.

Specifically, as described, the front wall (<NUM>"a) progressively moves away from the rear wall (<NUM>"p) in such a way as to connect then to the central shank <NUM> of the probe, receding with a part (<NUM>''d) which forms a protuberance or tooth.

Therefore, the upper stopper <NUM> has the hole <NUM> to enable the insertion of the probe to control its buckling way.

The hole <NUM> is generally frustoconical and then it provides a conical wall which enlarges diametrically starting from the surface <NUM>' towards the surface <NUM>" (see <FIG>).

This hole conformation facilitates centering and inserting the probe from above through the upper plate.

The inclination of the lateral wall of hole <NUM>, i.e. the conical wall, enables in use to the surface (<NUM>''p) to lie entirely onto said lateral wall of hole <NUM> as shown in <FIG> and as explained below, after buckling.

The lower part of probe provides instead an enlarged head (13D) with an inclined lower base, i.e. with a certain inclination (like an inclined plane).

Specifically, the enlarged head comprises an upper surface which connects to the body <NUM> and, from the opposite side, a lower surface. The two upper and lower surfaces are not parallel to each other.

In fact, in an unbuckled condition of the probe and thus in rest condition, the lower surface is inclined of a certain degree with respect to the horizontal reference plane (like an inclined plane).

More specifically, the enlarged head (13D) is formed by a body (<FIG> shows a geometry in axonometry thereof), whose lower basis is an inclined surface of a certain angle with respect to a horizontal plane (X) (see enlarged <FIG> angle (α) between axis X and axis S' or rather <FIG>).

Such lower inclined basis (13D') is on the opposite side to the connection with the part of central flexible or deformable body <NUM>. As shown in <FIG>, the contact part (13c) continues from it which protrudes from the hole of plate <NUM> to create the contact with wafer.

The hole <NUM> is frustoconical as well in such a way as to enable, also in this case, a certain excursion of the contact part (13c) after buckling (the same is for the hole of the upper plate).

In this way, in use, during the probe bending, the head (13D) is dragged to a movement due to the overall buckling of the probe thereby bringing the inclined plane (13D') constituting the lower base of the enlarged head, as mentioned, to contact entirely the surface <NUM>, thereby discharging normally force as per <FIG> and reducing the cutting load. Essentially, in a buckled configuration, the enlarged head <NUM> of the probe firmly rests onto the surface constituting its support base (13D').

In this buckled configuration, the opposite part of the probe, i.e. the part <NUM> inserted in the hole <NUM> will be with the surface (<NUM>"p) resting onto the hole's wall.

Therefore, the probe geometry is such that, after buckling, the enlarged head (13D) which rests onto the lower plate <NUM> lies with its base (<NUM>'D) entirely or almost entirely onto the surface of lower plate <NUM> discharging the force normally (i.e. in an orthogonal way to the surface of plate <NUM>) and, contextually, the opposite part <NUM> inserted in the hole <NUM> rests onto the wall of hole with the rear part (<NUM>''p).

Therefore, dimensionally, both the probe geometry, including its length, and the support geometry (upper and lower plate and corresponding reciprocal distance) are such that in buckled position the probe is in the configuration of <FIG>, i.e. with the inclined side (13D') in contact through its entire surface area which constitutes it with the plate surface.

Essentially, in an initial condition, as per <FIG>, the probe touches the lower plane <NUM> in a point (P) while, after buckling, the entire surface (13D') rests onto the plane <NUM> after inclination of the probe, thereby zeroizing the inclination angle of surface (13D') and discharging force onto the support plane with a reaction orthogonal to the support plane.

Therefore, this kind of probe structure correlated to geometry of plates inside which it is mounted, enables the probe to be correctly and above all firmly positioned, firmly resting onto the lower plate <NUM> and close to the hole <NUM> in contact with a wall thereof in correspondence of upper plate.

This gives great stability and ensures an optimal reliable functioning.

As shown in <FIG> and in <FIG>, the probe is structurally an elongated body having a longitudinal development line thereof (obviously of electrically conductive material).

Such longitudinal development line comprises the central part <NUM> (or central body) normally with a constant section.

Such central part <NUM> is generally curved and thus has a certain radius of curvature which obviously increases when the probe is bent in use.

This central part, as still shown in <FIG> and <FIG>, is comprised between two portions, i.e. the upper portion <NUM> (or first portion <NUM>) whose end is intended to contact the probe card in use and the lower portion <NUM> (or second portion <NUM>) whose end in intended to contact wafer in use.

<FIG>, <FIG> and <FIG> show as axis Z an axis orthogonal to a plane X and thus an axis orthogonal to the plane of probe card and of wafer after mounting, or in an equivalent way an axis orthogonal to the two plates <NUM> and <NUM> between which the probe is comprised when mounted in its probe head.

The so-called enlarged head (13D), as shown in <FIG> for example, represents an enlargement area of transversal section relative to central part <NUM>. Essentially, moving along the development line of the central part <NUM>, generally with transversal constant section, an area where such transversal section is greater is intercepted and this represents the enlarged head (13D) which has a predetermined longitudinal length.

As shown in <FIG>, the enlarged head branches off from the central part <NUM> enlarging in a symmetrical way from a side and from the other side of the central part (see also <FIG>).

The enlarged head forms a base (13D') which is beveled. Therefore, it is inclined of a certain angle with respect to a hypothetical horizontal support plane which is represented by surface <NUM> of <FIG> when the probe is positioned in orthogonal position with its axis Z of <FIG> with respect to such support surface <NUM>. Essentially, said base (13D') of the enlarged head forms a bevel with a certain angle with respect to an above-described plane orthogonal to the axis Z.

Such angle is preferably comprised in a range between <NUM> and <NUM> degrees.

As per <FIG>, a last part with reduced transversal section connects to such enlarged head which retraces the measure of transversal section relative to the central body <NUM> and with longitudinal development according to the defined axis Z.

Therefore, for mounting the entire probe head, the upper plate <NUM> is connected to the support <NUM> with the screw or anyway with connection means <NUM>.

The lower plate <NUM> connects with vertical play with respect to the support <NUM>, through the pin <NUM> already described above.

Therefore, in this case, the lower plate <NUM> is spaced from the support <NUM>.

All probes are inserted through the holes of the upper plate.

Each hole of the upper plate has obviously its corresponding one aligned with the lower plate as shown in <FIG>, even if <FIG> shows only one couple of holes and then a single probe, only for sake of simplicity.

The diametral width of the hole relative to the upper plate <NUM> is such that the whole probe can be inserted into the space between the two plates (<NUM>, <NUM>) exactly as shown in <FIG>.

Specifically, the probe part intended to rest onto the lower plate <NUM>, i.e. the enlarged part (13D) has such a maximum diametral width as to pass through the hole <NUM> of the upper plate <NUM> without being able to pass through the corresponding hole of plate <NUM> onto which it rests.

Once all probes have been arranged, the entire assembly upper-lower plate and probes which shape the probe head, is positioned in work position thereby positioning it as per the prior art between PCB and wafer with reference to <FIG>.

In this way, probes will be on one side (the one corresponding to the lower plate <NUM>) in contact with wafer and on the opposite side in electrical contact with PCB.

Once the probe head has been arranged, screws or connection means <NUM> in general relative to the lower plate are tightened to eliminate play and make the lower plate <NUM> buck against the support <NUM> as per <FIG> (final mounting) and to put all probes in buckling work condition.

In this condition, as per <FIG>, the base of enlarged head entirely rests onto the plate's plane thus discharging force in normal way.

Essentially, the inclination of support base (13D') of enlarged head (13D) is such that, when the probe has been pre-charged and buckles, such support base rotates from the position of <FIG> to the position of <FIG>, entirely resting onto the plane of plate <NUM> and discharging force according to a normal direction.

Obviously, as clearly visible from attached drawings, the lower plate <NUM> has a preferably conical hole and anyway having such a diameter as to stop the passage of enlarged head (13D) (see for example <FIG>).

As already described, the probe goes on downstream of the enlarged head (13D) with an end contact part passing through the hole (21b) of lower plate <NUM> and representing the other portion in electrical contact with wafer.

As a whole, this solution is stable and functional and makes mounting much simpler with respect to prior art.

Obviously, as per the prior art, the constructive material of probes is electrically conductive material.

Claim 1:
A contact probe (<NUM>) for electronic tests comprising:
- An, in use, upper part (<NUM>) having an end portion (<NUM>') whose end is intended to contact a first electronic component;
- A, in use, lower part (<NUM>) having an end portion (13c) whose end is intended to contact a second electronic component;
- A generally elongated and deformable central body (<NUM>), said central body being interposed between said upper part (<NUM>) and lower part (<NUM>);
- Said lower part (<NUM>) comprising an enlarged head (13D) having a lower surface (13D') which in use is intended to rest at least partially onto a horizontal surface (<NUM>, X), said lower surface (13D') being beveled so as to have an inclination forming an angle (α) with respect to the horizontal surface (<NUM>, X) onto which it rests, in use, in a rest condition of the unbuckled probe and, in a buckle condition of the probe, there is at least one buckled position in which said lower surface (13D') moves to rest entirely onto the horizontal surface thus zeroizing said angle (α);
- Characterized in that:
- Said enlarged head (13D) comprises an upper surface which branches off radially from the central body, said enlarged head developing longitudinally for a certain length and ending with said lower surface (13D') which branches off radially from the end portion (13c) to which it is connected.