Patent Description:
As known, the electric propulsion vehicles comprise control electronics of an electric motor. In particular, the control electronics associated with vehicles of this type comprises power modules and signal processing modules; furthermore, there are special connection structures, which require connecting pins of larger dimensions with respect to the electronic circuits used in other fields.

For example, <FIG> shows a power module <NUM>, wherein the electrical components (including any micro-electro-mechanical components) are connected to a printed circuit board through a solderless pressfit technique, according to a known solution.

In the embodiment shown in <FIG>, two dice, indicated with <NUM>, are attached to a dissipating plate <NUM>. The dice <NUM> may integrate electrical and/or electromechanical structures and have power and/or control each other or integrated in a same die.

Here, the dissipating plate <NUM> is formed by a DBC (Direct Bonded Copper) multilayer formed by a first and a second metal layer 2A, 2B and by an intermediate insulating layer 2C, for example of ceramic. At least one of the metal layers (here the first metal layer 2A) is shaped, so as to define reciprocally insulated conductive regions. Each die <NUM> is attached to a respective conductive region of the first metal layer 2A.

As also shown in <FIG>, pin holders <NUM> are attached to respective conductive regions of the first metal layer 2A of the dissipating plate <NUM>. Each pin holder <NUM> (<FIG>) is formed by a tubular body <NUM>, here of cylindrical shape, having an axial cavity <NUM> and provided with a pair of flanges <NUM> on its bases.

With reference again to <FIG>, <FIG>, the pin holders <NUM> are attached to the dissipating plate <NUM> through respective soldering regions <NUM>.

In particular, each soldering region <NUM> is arranged between one of the flanges <NUM> of the respective pin holder <NUM> and the dissipating plate <NUM>. Soldering regions <NUM> are also arranged between the dice <NUM> and the respective conductive regions of the first metal layer 2A.

Wires <NUM> are selectively soldered between pads (not visible) of the dice <NUM> and selective conductive regions of the first metal layer 2A to electrically connect the dice <NUM> to each other and to the outside, according to a desired electric diagram.

In particular, the connection to the outside is obtained through pins <NUM> fastened to the pin holders <NUM>.

The pins <NUM> have an elongated shape and may be shaped as shown in <FIG>. In particular, here, the pins <NUM> are rod-shaped elements, of a length comprised between <NUM> and <NUM> and a square section (for example with a side of <NUM>). Furthermore, they may be provided with enlarged stop zones for blocking with respect to a connection support <NUM>, described in detail hereinbelow.

The pins <NUM> have a first end 10A and a second end 10B.

The first end 10A of the pins <NUM> is preferably pointed and is force fitted into the axial cavity <NUM> of the respective pin holder <NUM> to obtain a press-fit.

The second end 10B of the pins <NUM> is here transversely holed (as a keyhole, see in particular <FIG>). The second end 10B of the pins <NUM> is thus elastically flexible in transversal direction with respect to its length, thus allowing the pins <NUM> to be fixed to the connection support <NUM>, as described hereinbelow.

The dissipating plate <NUM> is fixed to a housing <NUM>, for example of plastic. The housing <NUM> is formed by a side wall 13A and by a bottom wall 13B. The side wall 13A surrounds a chamber <NUM> and, on its edge opposite to the bottom wall 13B, has an inner peripheral notch <NUM> where the dissipating plate <NUM> is attached. In particular, the dissipating plate <NUM> is arranged so that the dice <NUM> and the pin holders <NUM> face the inside of the chamber <NUM> of the housing <NUM>; in practice the dissipating plate <NUM> closes the chamber <NUM> on one side.

A potting compound <NUM> may be provided inside the chamber for insulating and protecting the dice <NUM> and the electrical connections.

The bottom wall 13B of the housing <NUM> has a plurality of holes <NUM>, through which the pins <NUM> extend.

The connection support <NUM> is fixed to the housing <NUM> externally, to the bottom wall 13B thereof. The connection support <NUM> is made, for example, by a printed circuit board PCB and has, in turn, a plurality of through openings <NUM> aligned with the holes <NUM>.

The through openings <NUM> have conductive walls, for example have a surface metal coating (not shown), and are sized in such a way that the second end 10B of the pins <NUM> may be forced fitted and remain blocked into the through openings <NUM>, due to its elasticity, with a press-fit coupling.

In this manner, a good mechanical retention of the pins and a good electrical connection between the connection support <NUM> and the dice <NUM> are obtained without the need for soldering at the level of the connection support <NUM>, as often required for automotive applications.

The power module <NUM> described above is assembled by securing the dice <NUM> and the pin holders <NUM> to the dissipating plate <NUM>; then inserting the pins <NUM> into the pin holders <NUM>; fixing the dissipating plate <NUM> to the housing <NUM>, after introducing the potting compound <NUM>, and press-fitting the second ends 10B of the pins <NUM> into the connection support <NUM>.

In particular, fixing of the pin holders <NUM> is performed by soldering. To this end, a solder cream or paste is spread on the dissipating plate <NUM>; the pin holders <NUM> are suitably placed by a manipulating machine; then a warm reflow process, followed by a wet washing step, is performed.

The solder cream used to temporarily hold the pin holders <NUM> in place is generally formed by an emulsion of a flux and soldering alloy beads which has an adhesive effect. During the reflow step, most of the flux is removed and the soldering alloy beads melt, soldering the pin holders <NUM> to the dissipating plate <NUM>.

Therefore, in this step, before the soldering alloy beads are completely melted, the pin holders <NUM> are weakly held in place. Thus, it may occur that they move with respect to the desired position and, at the end of the process, are attached in the wrong position, displaced with respect to
the desired one by a space of almost one millimeter. As a result, the respective pins <NUM> are also misplaced, creating problems to the final manufacturer for their fitting into the through openings <NUM>.

Furthermore, the soldering process is expensive, since it requires two separate operations requiring a considerable amount of time and power to perform. Furthermore, in case further structures are provided to hold the pin holders <NUM> in place (in general metal fixtures), there is an increase in the quantity of metal. It means that, in case of furnace reflow, more heating energy is necessary, which leads to longer working time, more energy required, higher material costs and thus additional costs.

The reflow process may also lead to the generation of thermomechanical stresses detrimental to the electronic components.

<CIT> discloses a pin holder and connection mounted plate in accordance with the pre-characterizing part of claim <NUM> and for use in a power semiconductor module. The pin holder extends longitudinally and has flanges at its end. One of the flanges is soldered to a circuit carrier; the flanges have outer radii that may be chosen independently on one another.

<CIT> discloses ultrasonic welding methods for semiconductor modules.

The aim of the present invention is to provide a solution to the problems highlighted hereinabove.

According to the present invention, a mounted plate for connection of electronic components, a power module and an assembling method are provided, as defined in the attached claims.

For a better understanding of the present invention, an embodiment thereof is now described, purely by way of non-limiting example, with reference to the attached drawings, wherein:.

<FIG> show a pin holder <NUM> usable in a power module <NUM> shown in <FIG> and similar to the power module of <FIG>.

With reference to <FIG>, the pin holder <NUM> is formed by a tubular body <NUM>, in particular cylindrical, having an axial cavity <NUM>, a first flange <NUM> at a first base and a second flange <NUM> at a second base.

In particular, the first flange <NUM> has a greater diameter with respect to the second flange <NUM>.

For example, for a pin holder <NUM> having a height comprised between <NUM> and <NUM>, in particular of <NUM>-<NUM>, the first flange <NUM> may have an outer diameter comprised between <NUM> and <NUM>, in particular of <NUM>-<NUM>; and the second flange <NUM> may have an outer diameter comprised between <NUM> and <NUM>, in particular of <NUM>-<NUM>.

The pin holder <NUM> is also, for example, of copper or bronze.

The pin holder <NUM> of <FIG> is fixed through High Power Ultrasonic Welding, HPUS, to a bearing plate <NUM>, as shown in <FIG>.

<FIG> shows a mounted plate <NUM> formed by a bearing plate <NUM> to which the pin holders <NUM> are fixed.

The bearing plate <NUM> also bears dice <NUM>, integrating electrical and/or electro-mechanical structures; in particular, the dice <NUM> may have power and/or control functions, integrated separately from each other or in a same die. The dice <NUM> and the pin holders <NUM> are attached, here each in a respective conductive region of the first metal layer 2A, through an ultrasonic technique, without using reflow processes, as described hereinbelow.

The bearing plate <NUM> is formed by a DBC (Direct Bonded Copper) multilayer formed by a first and a second metal layer 25A, 25B and by an intermediate insulating layer 25C, for example of ceramic. At least one of the metal layers (here the first metal layer 25A), is shaped, so as to define conductive regions insulated from each other.

Wires <NUM> are selectively bonded between pads (not visible) of the dice <NUM> and respective regions of the first metal layer 25A.

In the mounted plate <NUM> of <FIG>, pins <NUM> have already been attached to the pin holders <NUM>. The pins <NUM> may be exactly like the pins <NUM> of <FIG>; in particular they have an elongated shape having a first end 31A intended to be press-fitted into the axial cavity <NUM> of a respective pin holder <NUM> and a second end 31B that is deformable, intended to be press-fitted into a connection support <NUM> (see <FIG>).

The mounted plate <NUM> may be attached to the power module <NUM> of <FIG>, comprising (similarly to the power module of <FIG>) a housing <NUM> formed by a side wall 33A and by a bottom wall 33B. The side wall 33A surrounds a chamber <NUM> and, on its edge opposite to the bottom wall 33B, has an internal peripheral notch <NUM> to which the dissipating plate <NUM> is attached. The dissipating plate <NUM> is arranged so that the dice <NUM> and the pin holders <NUM> face the inside of the chamber <NUM> of the housing <NUM> and, in practice, closes the chamber <NUM> on one side.

The bottom wall 33B of the housing <NUM> has a plurality of holes <NUM> in which the pins <NUM> extend. The pins <NUM> are also press-fitted, at a second end thereof, into through openings <NUM> of the connection support <NUM>, formed for example as a printed circuit board PCB, similarly to what previously described with reference to <FIG>.

As indicated above, the pin holders <NUM> and the dice <NUM> are attached to the bearing plate <NUM> through Ultra Power Ultrasound Welding, HPUS.

In particular, the pin holders <NUM> may be picked up and placed on the bearing plate <NUM> through a transducer <NUM> shown in <FIG>.

Specifically, the transducer <NUM> of <FIG> has a gripping portion <NUM> that is hollow and has a gripping cavity <NUM> that is cylindrical and has a diameter comprised between the diameter of the first flange <NUM> and the diameter of the second flange <NUM> of the pin holders <NUM>.

In an only schematically shown manner, the gripping portion <NUM> is coupled to vacuum generation means <NUM>, capable of creating a depression inside the gripping cavity <NUM>, and to welding ultrasonic energy generation means <NUM>.

Then, during the assembling step, the vacuum generation means <NUM> is activated and the transducer <NUM> picks up a pin holder <NUM>, sucking it so that the second flange <NUM> thereof (smaller) and the tubular body <NUM> are sucked inside the gripping cavity <NUM> and only the first flange <NUM> abuts against the base of the gripping element <NUM> of the transducer <NUM> (<FIG>). Then the transducer <NUM> places the pin holder <NUM> in a desired manner on the bearing plate <NUM> and welds it through the HPUS technique, following deactivation of the vacuum generation means <NUM> and activation of the welding ultrasonic energy generation means <NUM> (for example at a frequency comprised between <NUM> and <NUM>).

In practice, the transducer <NUM> presses the pin holder <NUM> against the bearing plate <NUM>, applying ultrasonic energy (at high frequency).

For example, the transducer <NUM> may operate at room temperature, with a power lower than 1kW, applying a force comprised between <NUM> and <NUM> N for <NUM>-<NUM> seconds.

The dice <NUM> may be welded with the same technique. In particular, in this case, the depression created in the gripping cavity <NUM> allows a die <NUM> to be held against the base of the transducer <NUM> and to be suitably placed on the bearing plate <NUM>, before welding.

If the components have wire connections of the type shown in <FIG>, the wires <NUM> are bonded to the bearing plate <NUM> and to the dice <NUM> through known techniques, for connecting the dice <NUM> to each other and/or to the pin holders <NUM>.

Then, the pins <NUM> may each be press-fitted into a respective pin holder <NUM> and the steps described above may be performed to complete assembling of the power module <NUM>.

In this manner, a very stable, resistant and accurate welding of the pin holders <NUM> (and of the dice <NUM>) is obtained, with lower costs with respect to the known solution.

In fact, due to the increased size of the first base <NUM> of the pin holders <NUM>, they may be picked up, held and accurately placed on the bearing plate <NUM>. In this manner, a bonding accuracy of ±<NUM> may be achieved, with a considerable improvement with respect to the current techniques.

As a result the pins <NUM> may also be placed in an accurate manner both in the pin holders <NUM> and in the connection support <NUM>.

Furthermore, the large surface of the first base <NUM> provides a wide attachment area, making it very stable even over time.

The high-pressure ultrasound welding process further allows the reflow step and the successive washing step previously used to be eliminated, reducing assembling costs thanks to both the elimination of per se expensive steps and the reduction of the number of steps.

Since the welding occurs at room temperature, thermal treatments may be eliminated, and thus any thermomechanical stress on the system may be reduced, increasing the production yield.

Finally, it is clear that modifications and variations may be made to the connection mounted plate, to the power module and to the assembling process described and illustrated herein without thereby departing from the protective scope of the present invention, as defined in the attached claims.

Claim 1:
A connection mounted plate of electronic, micro-mechanical and/or micro-electro-mechanical components, comprising a bearing plate (<NUM>) having at least one first and one second conductive region (25A) that are reciprocally insulated, the first conductive region bearing a semiconductor die (<NUM>) and the second conductive region bearing a pin holder(<NUM>) comprising a holed body (<NUM>) having a first end, a second end and an axial cavity (<NUM>) fittingly accommodating a connecting pin (<NUM>), wherein a first flange (<NUM>) projects transversely from the holed body (<NUM>) at the first end, a second flange (<NUM>) projects transversely from the holed body (<NUM>) at the second end, the first flange (<NUM>) has a larger area than the second flange (<NUM>) and is configured to be ultrasonically welded to a conductive bearing plate (<NUM>),
characterized in that the first flange of the pin holder (<NUM>) and the semiconductor die (<NUM>) are welded to the bearing plate (<NUM>) without interposed material.