Microelectronic device having protected connections and manufacturing process thereof

A microelectronic device includes a chip housing a functional part and carrying first electrical contact regions in electrical connection with the functional part through first protected connections extending over or in the chip. A substrate has a first contact area and a second contact area, which is remote from the first contact area. The first contact area carries second electrical contact regions, and the second contact area carries external connection regions. The second contact regions and the external connection regions are in mutual electrical connection through second protected connections extending over or in the substrate. A protection-ring structure surrounds the first and second electrical contact regions and delimits a first chamber closed with respect to the outside. The first electrical contact regions and the second electrical contact regions are in mutual electrical contact.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to Italian Patent Application No. 102017000103511, filed on Sep. 15, 2017, which application is hereby incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a microelectronic device having protected connections and to the manufacturing process thereof.

BACKGROUND

As is known, one of the techniques most widely used for electrically connecting microelectronic devices to other electronic devices or apparatuses is wired connection. To this end, the device to be connected has pads bonded to one end of one or more metal wires, also referred to as “bonding wires.” Frequently, in particular when the microelectronic device operates in difficult environmental situations or in any case mechanical or chemical protection of the ends of the wires is required, the latter are protected, after bonding, by applying covering and protection masses, for example masses of thermosetting resin, such as epoxy resin, or the so-called moulding compound, or gels, such as an insulating gel, for example, potting gel, which protects the bonded ends from humidity.

However, for certain applications, it is difficult to find suitable protection materials. For instance, some materials are difficult to position in a precise way and may spread out and cover even functional parts of the device, thus jeopardizing operation thereof, for example in case of regions that must be free to move for proper operation (such as for sensing physical quantities or for actuation of a microelement), or regions that allow inlet/outlet of a fluid. In other cases, the materials are not chemically compatible with the external environment and may get damaged and no longer ensure protection. For instance, in case of pressure sensors inserted in the chamber for brake fluid, the latter may penetrate into the interface between the potting gel and the contact area, causing delamination and detachment of the gel. In other cases yet, these materials are not compatible and may get damaged or have insufficient performance in case of particular environmental or operating conditions (e.g., when operating at high pressures, they may deteriorate and no longer ensure protection).

SUMMARY

Embodiments of the present invention provide a solution that overcomes the drawbacks of the prior art.

According to the present invention, there are provided a microelectronic device and the manufacturing process.

For example, a microelectronic device comprises a chip housing a functional part and carrying first electrical contact regions in electrical connection with the functional part through first protected connections extending over or in the chip. A substrate has a first contact area and a second contact area, which is remote from the first contact area. The first contact area carries second electrical contact regions, and the second contact area carries external connection regions. The second contact regions and the external connection regions are in mutual electrical connection through second protected connections extending over or in the substrate. A protection-ring structure surrounds the first and second electrical contact regions and delimits a first chamber closed with respect to the outside. The first electrical contact regions and the second electrical contact regions are in mutual electrical contact.

In a particular embodiment, the microelectronic device is made up of two parts: a chip, which integrates the functional part of the device and has contact terminals or pads for electrical connection, and a substrate, which carries protected connections. The protected connections have a first end bonded to the pads of the chip and a second end, which is to be connected to the outside world. The area of the pads of the chip is surrounded by a first protection ring, and the area of the first ends of the substrate is surrounded by a second protection ring, having a shape and size that are congruent to those of the chip. The chip and the substrate are connected together; namely, the pads of the chip are bonded to the first ends of the substrate, and the first and second protection rings are bonded together. The first and second rings form in practice a composite ring that surrounds and protects, in the finished device, the pads of the chip and the first ends of the substrate. The second ends of the protected connections are arranged in an area remote from the first ends and may be connected to external pads. The substrate may be formed with a shape and size suitable for the application envisaged. Typically, it has a size that enables bonding of the second ends to an apparatus or further device arranged at a distance from the chip that allows the use of traditional protection materials, without any risk of damaging or jeopardizing operation of the chip or the protection ability of the protection material.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

FIGS. 1 to 3show an embodiment of a device1with protected connections. The device1comprises two parts: a chip2and a substrate3. The chip2and the substrate3are coupled and fixed together, in particular bonded, prior to installation in the use position, and are illustrated, respectively, inFIGS. 1 and 2, prior to mutual fixing.FIG. 3shows the device1after mutual bonding of the chip2and the substrate3.

The chip2may be of semiconductor material, such as silicon, or ceramic, glass, a polymer, such as Kapton, coupled to a strain gauge and incorporating a functional part4. The functional part4generally performs a typical function of the device1; for example, it is an element for transducing physical quantities into electrical quantities (pressure sensor, microphone, inertial sensor, gas sensor, etc.), a microactuator (micromirror, optical selector, micromotor, etc.), an electronic circuit (electronic component or more complex circuit capable of carrying out signal processing and/or performing calculations, etc.) or the like.

The functional part4is connected to the outside of the chip2and exchanges electrical signals through contact regions, for example, first pads7, arranged in a chip contact area9, on a surface2A of the chip2(FIG. 3). As illustrated schematically inFIGS. 1 and 3, the first pads7are electrically connected to the functional part4through first connection lines, here formed by buried connections10extending in the chip2. The first pads7are surrounded by a first protection ring11. The first protection ring11may be made of the same material as the first pads7or of a different material. For instance, the first pads7may be made of copper or aluminum, plated with silver or gold. The first protection ring11may be made of copper or aluminum plated with silver, gold, or nickel. Alternatively, the first protection ring11may be made of non-coated copper, or a polymer resistant to high temperature (higher than 275° C.) such as nylon, LCP (Liquid-Crystal Polymer), Kapton, Vespel.

Structures13other than the first pads7may also be arranged within the area delimited by the first protection ring16. For instance, this area may accommodate structures13that it is desired to be accessible after manufacture of the chip2and to be protected during use, such as trimming resistors, temperature sensors, and the like.

The substrate3has a first contact area and a second contact area, designated by18and19, housing respective contact regions. For instance, second pads15may be provided on the first contact area18, arranged on a first surface3A (FIG. 3) of the substrate3that, after bonding, faces the chip2. The second pads15are in the same number as the first pads7of the chip2, have the same layout and may have a similar size, so that they are aligned and may be bonded to the first pads7of the chip2. The second pads15may be made of copper or aluminium, plated with silver or gold.

The second pads15are surrounded by a second protection ring16, typically congruent with the first protection ring11(i.e., having the same shape, size, and position) so that it may be bonded to the latter. The second protection ring16may be of the same material as the first protection ring11, for example copper or aluminum plated with silver, gold, or nickel, non-coated copper, or a polymer resistant to high temperature, such as nylon or LCP.

The first and second protection rings11,16extend along a connected closed line, for example the perimeter of a rectangle with rounded corners, a circle, or an oval. Other shapes are, however, possible.

Further, on the second contact area19, the substrate3has external connections17, here on a second surface3B, opposite to the first surface3A. Alternatively, the external connections17may be arranged on the first surface3A of the substrate, like the second pads15. The external connections17are arranged remote from the chip2. For example, if the substrate3has a strip-like elongated shape, the second pads15may be arranged at a first end, and the external connections17may be arranged at a second end, opposite to the first end, of the strip. The external connections17may be formed by third pads and have larger sizes and/or a layout such as to simplify bonding to an external apparatus or other electronic device. Optionally, the external connections17may be surrounded by an outer protection ring20, represented by a dashed line inFIG. 2.

Second connection lines, which here form buried connections14, extend within the substrate3and connect the second pads15to the external connections17. Typically, each second buried connection14has a first end connected to a respective second pad15and a second end connected to a respective external connection17. However, more complex connection schemes may be envisaged, if so desired.

The substrate3is made of composite material, typically insulating material housing the second buried connections14. For instance, it may be made of flexible material such as Kapton, or of rigid material, such as a BT (Bismaleimide Triazine) laminate, or FR-4, or other material of printed-circuit boards. Alternatively, the substrate3may be multi-layered ceramic, e.g., LTCC (Low-Temperature Co-fired Ceramic). The second buried connections14may be arranged on a number of levels, if so desired, and exploit the known multi-layered PCB (Printed-Circuit Board) technologies, using internal layers of copper or other suitable material or multi-layered conductive/insulating inks.

As has been mentioned, the chip2and the substrate3are bonded or soldered together through the protection rings11,16, so as to form a composite ring25, which mechanically and chemically protects the contact area9. Further, the pads7,15are bonded together to provide electrical continuity between the first buried connections10and the second buried connections14. In practice, at the end of bonding, the composite ring25delimits and seals a first chamber26accommodating the pads7,15, bonded together (FIG. 3).

Bonding may be performed in a single step, by simultaneously soldering the pads7,15to each other and the protection rings11,16to each other, or in two separate steps, by soldering first the pads7,15and then the protection rings11,16.

For instance, if the pads7,15and the protection rings11,16are of the same material (copper or aluminum, either naked or plated) they may be brazed at low temperature, by applying a solder paste, for example a tin-based paste (which melts at 220° C.), on one of the two parts (chip2or substrate3) and pressing the two parts together at a low temperature (less than 300-400° C.). It is also possible to use a high lead bonding (Pb—Sn—Ag), which melts at 320° C. For instance, the solder paste may be applied by screen printing on the first pads7and on the first protection ring11, and soldering may be carried out at 290° C.

Alternatively, the pads7,15and the protection rings11,16may be bonded via a high-power ultrasound process, in a way known in the electronics sector.

During and after bonding, it is desirable to prevent oxygen from remaining trapped within the first chamber26, inside the composite ring25, because it could cause, in the long run, oxidation of the pads7,15and could thus lead to malfunctioning and failure.

To this end, bonding may be carried out at low pressure (as low as 10 mbar) using a gas-flushing technique, in particular with nitrogen, or at atmospheric pressure in a 100%-nitrogen environment, or again at atmospheric pressure in controlled environment, for example in forming gas (mixture of hydrogen and nitrogen, with at the most 10% hydrogen, for example 5% H2and 95% N2).

According to a different solution, the substrate3has a degassing hole21extending throughout the thickness of the substrate3and opening out onto the first surface3A of the substrate within the second protection ring16(FIG. 2). In this case, during bonding, any possible fumes deriving from the bonding process are free to exit from the first chamber26through the degassing hole21. At the end of the bonding process, the degassing hole21may be sealed, for example via a protective resin, such as an epoxy resin, at the same time removing the air present in the chamber. To this end, sealing may be carried out at low pressure (as low as 10 mbar), for example, in a nitrogen environment, or by filling the first chamber26with controlled atmosphere (100% nitrogen) or using forming gas (e.g., 5% H2and 95% N2).

In case of a two-steps soldering (either with pads7,15and protection rings11,16of the same material or when they are made of a different material), the pads7,15are soldered first, for example, as mentioned above, via a tin-based paste applied by screen printing, at low pressure (as low as 10 mbar) or at atmospheric pressure in controlled atmosphere.

Next, the protection rings11,16are bonded separately. If they are made of aluminum or copper, they may be bonded using tin-based paste or via a high-power ultrasound process, according to the techniques described above. If the protection rings11,16are of polymeric material, they may be bonded via high-power ultrasound.

The substrate may have different shapes. For example,FIG. 4shows a strip-shaped embodiment, with widened ends and second pads arranged aligned in a single row. In the example of embodiment ofFIG. 4, further, the external connections17are surrounded by the third protection ring20.

FIGS. 5 and 6show a chip102and a substrate103according to a different embodiment.

Here, the chip102has a generally circular shape and has four first projections105, arranged offset by 90° from each other, and projecting radially outwards from the periphery of the circular shape. Each first projection105here carries one or more first contact regions107, and the first contact region or regions107arranged on a same first projection105is/are surrounded by a respective first protection ring111. The chip102may, for example, be a pressure sensor, of ceramic material.

The chip102houses a functional part104electrically connected to the first pads107through first buried connections no extending in the chip102and represented only schematically, analogously to what described for the device1ofFIGS. 1-3.

The substrate103is here shaped as a quadrangular plate, for example rectangular or square, having a much greater area than the chip102, and comprises a frame portion internally delimiting an approximately cross-shaped through opening106. Four second projections108extend from the frame portion towards the inside of the through opening106, at 90° from each other. Each second projection108carries one or more second pads115, in the same number as the first pads107of the chip102. In practice, here, the first contact area is divided into four parts, each arranged on a respective second projection108. Also here, the second pads115have the same layout and may have the same size as the first pads107, so that they are aligned and may be bonded to the first pads107of the chip102.

The second contact region or regions115arranged on a same second projection105is/are surrounded by a respective second protection ring116, typically congruent with a respective first protection ring111(i.e., having the same shape, size, and position) so that they may be bonded together.

The substrate103further has a second contact area119, arranged near a corner of the substrate103, where external connections117may be arranged, for example pads. As illustrated schematically and as described for the external connections17of the substrate3ofFIG. 2, the external connections117of the substrate103are connected to the second contact regions115through second buried connections114, arranged in the substrate103.

The materials of the first and second contact regions107,115and of the first and second protection rings111,116may be the same as above mentioned.

Also in this case, the chip102and the substrate103are bonded together through the protection rings111,116so as to form composite rings that mechanically and chemically protect the areas of the pads107,115. Further, the pads107,115are bonded together.

In addition, the substrate103may have a degassing hole (not illustrated), as described with reference to the device1ofFIGS. 1-3.

FIGS. 7-9show an embodiment where a separate protection structure is provided for further components that do not require connection to the outside world during use of the device. In particular,FIG. 7shows a chip202with a circular shape, which houses a functional part204and is provided with a projection208, here having a rectangular shape. The projection208carries a chip contact area209, surrounded by a first protection ring211, and a protected area230, surrounded by a third protection ring231. First pads207are arranged within the first protection ring211, and structures to be protected213are arranged within the third protection ring232. The structures to be protected213are, for example, trimming elements that it is desired to be accessible after manufacture of the chip202, but that do not require connection to the outside world during use of the device and need to be protected during use.

Also here, the functional part204is electrically coupled to the first pads207through first buried connections210.

FIG. 8shows a part of a substrate203, for example strip-like shaped as inFIG. 2 or 4, which carries at an end thereof second pads215surrounded by a second protection ring216(first contact area218). A fourth protection ring232is arranged near the second protection ring216. The second pads215are congruent to the respective first pads207, the second protection ring216is congruent with the first protection ring211, and the fourth protection ring232is congruent with the third protection ring231. They are also arranged so as to be bondable together, as illustrated in the enlarged detail ofFIG. 9. In this case, the third and fourth protection rings231,232are bonded simultaneously and using the same technique for bonding the protection rings211,216. In this way, then, in addition to the electrical connection between the pads207,215and their mechanical and chemical protection within the first chamber226, a second composite ring231,232is obtained, which defines a second chamber227and mechanically and chemically protects also the structures to be protected213.

Also here, the substrate203may have through degassing holes (not shown), both inside the first chamber226and inside the second chamber227; further, second buried connections214extend within the substrate203towards external connections (not shown), which are similar to the external connections17ofFIG. 2.

FIGS. 10-11show another embodiment as a ceramic sensor. In particular,FIG. 10shows a chip302having a generally circular shape provided with a first projection308A and a second projection308B. The projections308A,308B have a generally rectangular shape and are arranged in diametrically opposite positions of the chip302.

The chip302, for example a multi-layered ceramic having a surface302A, houses electrical components defining a functional part304. The electrical components may be formed within the body of the chip302and/or on the surface302A. The functional part304is connected, via first buried connections310, to first pads307formed on the surface302A and arranged on the first projection308A. The pads307are surrounded by a first protection ring311. The second projection308B carries, on the surface302A of the chip302, structures to be protected313, surrounded by a third protection ring331. The structures to be protected313may be electrically connected to the functional part304or directly to the first pads307through buried connections305.

FIG. 11shows a support303to be fixed to the chip302ofFIG. 10. The support303is here formed by a frame340, having a quadrangular shape, and four arms341extending inwardly from the corners of the frame340. In detail, the arms341extend approximately along the two diagonals of the frame340and connect up, two by two, in proximity of the center of the support303. In the example illustrated, the arms341do not extend exactly as far as the center, but form two pairs of adjacent arms341that join together in a first and in a second coupling areas, close to the center and designated by342A,342B; the coupling areas342A,342B correspond approximately to the position of the projections308A,308B of the chip, to which they are intended to be coupled.

On the first coupling area342A, the support303has a second protection ring316, congruent with the first protection ring311, so that it may be bonded thereto. Second pads315are arranged in the second protection ring316, in the same number and with the same layout as the first pads307of the chip302. The second pads315are connected to second buried connections314, which extend along and internally to one of the arms341, up to a corner of the frame340where external connections317are provided. Here, the external connections317, formed on the same surface as the support303that carries the second protection ring316and the second pads315, are surrounded by an outer protection ring320.

Furthermore, in the embodiment ofFIG. 11, the arm341housing the second buried connections314also houses an electronic circuit350, for example an ASIC, for processing the signals supplied by the functional part304of the sensor, or alternatively the electronic circuit350may be embedded in the arm341.

On the second coupling area342B, the support303has a fourth protection ring332, congruent with the third protection ring331, so that it may be bonded thereto and thus close hermetically (together with the third protection ring331) the structures to be protected313.

In a manner not shown, the coupling areas342A,342B may have degassing holes like the degassing hole21ofFIG. 2.

For instance, the chip302may have a diameter of approximately 2-3 cm, and the substrate303may have a side of 10 cm.

FIGS. 12-14refer to an embodiment of a device401forming a pressure sensor for braking systems of motor vehicles. The device401comprises a chip402, here of semiconductor material and with a parallelepipedal shape, having a buried cavity450that may be seen inFIG. 13and delimits at the bottom a portion of the chip402forming a membrane451. The membrane451may house pressure-transducer elements, for example, piezoresistors (just one whereof is illustrated schematically inFIG. 12and is designated by452) or other elements capable of transducing stresses exerted on the membrane451into electrical signals, as, for example, described in US patent application US2005/208696.

The chip402has a surface402A carrying first pads407receiving the electrical signals generated by the pressure-transducer elements452through first buried connections410. The first pads407are surrounded by a first protection ring411.

The chip402is coupled to a substrate403illustrated inFIG. 14. Here, the substrate403is of a flexible type, for example formed by a printed-circuit board of Kapton, strip-shaped, with a first surface403A, a first end403B, and a second end403C. The substrate403may be configured like the substrate3ofFIG. 3and, at a first end, carries second pads (similar to the pads15and not visible) surrounded by a second protection ring (similar to the protection ring16), which, inFIG. 14, is bonded to the first protection ring411of the chip402and forms a composite ring425, like the composite ring25illustrated in the enlarged detail ofFIG. 3. The first pads407ofFIG. 12are then bonded to corresponding second pads (not visible, similar to the pads15ofFIG. 2), according to what is described above.

The second end403C of the substrate403carries external connections (not visible), which are similar to the external connections17ofFIG. 2and are surrounded by an outer protection ring that is similar to the outer protection ring20ofFIG. 2and is bonded to a further protection ring fixed to a casing460so as to form an outer composite ring461.

The casing460is here formed by a C-shaped container or support having a bottom surface462fixed to the chip402, for example glued. For instance, the chip402may be fixed with a glue layer or an adhesive-tape layer465. The casing460is of rigid material resistant to the fluids in which it is immersed; for example, it may be a multi-layered ceramic or metal with some parts of glass and pins of Kovar (glass-to-metal sealing technology). The casing460may have a generally tubular shape in side view (parallel to an axis Y of a Cartesian reference system XYZ) so as to define a side wall463(close to the second end403C of the substrate403) having a disk-like shape having peripherally a thread466. Further, the casing460houses external electrical connections467, which connect pads (not visible, formed on the bottom surface462and protected by the outer composite ring461) to external contacts468, which project from the side wall463. The external electrical connections467are typically embedded in the casing460.

In practice, the contacts468are connected, through the external electrical connections467, the pads (not visible) on the bottom surface462of the package460, the pads (not visible) on the second end403C of the substrate403, buried connections (not visible) extending in the substrate403, second pads (not visible) on the first end403B of the substrate403, the first pads407(FIG. 12) of the chip402, and the first buried connections410, to the pressure-transducer elements452ofFIG. 12.

In use, the casing460, with the chip402and the substrate403, is inserted in a chamber470to be filled with a brake fluid and screwed, via the thread466, to a corresponding internal thread471on brake calipers472.

FIGS. 15 and 16show a device501similar to the device1ofFIGS. 2 and 3, wherein the chip502is, for example, of silicon or ceramic and carries first connection lines510on its surface502A. The first connection lines510are formed in a first metal layer also extending over the area of the protection ring525and are covered by a dielectric layer505, for example, of silicon oxide, which is removed only in part within the first chamber526. Here, the dielectric layer505has one or more openings that expose the ends of the first connection lines510and form one or more reliefs505A. Contact portions507of metal material (one for each first connection line510) extend in part over the exposed ends of the first connection lines510and in part over the reliefs505A formed by the dielectric layer505and face the second pads515. They thus form first pads, similar to the first pads7ofFIG. 3. The contact portions507may be of the same material and have the same step as the first protection ring511; for example, they may be made of copper or aluminum, plated with silver or gold.

For the rest, except for the layout in a single row of the pads507,515, the device501ofFIGS. 15 and 16is the same as the device1ofFIGS. 1-3. Thus, the other parts of the device501are designated by the reference numbers ofFIGS. 1-3, increased by 500.

The advantages of the present device are evident from the above.

In particular, the presence of a substrate that in practice transfers the pads in a position remote from the chip makes it possible to provide the electrical connections with the outside world in a less critical position, where no materials are present that might damage the contacts or where the contact materials do not disturb operation of the device. The connections between the contacts of the chip and the corresponding contacts of the substrate are protected by rings that provide mechanical, chemical, and physical protection.

The rounded shape of the protection rings prevents the presence of areas where concentration of stresses may arise and could cause failure or cracking of the protection rings.

Finally, it is clear that modifications and variations may be made to the device described and illustrated herein, without thereby departing from the scope of the present invention, as defined in the attached claims. For instance, the various embodiments described may be combined so as to provide further solutions.

The chip2may even be a complex, non-monolithic, chip, for example formed by a multiple structure of a number of chips arranged on top of each other and bonded together.

In the embodiments ofFIGS. 6 and 11, the frame portion of the substrate303may extend along a closed line or an open line formed by stretches connected by the arms341.

The components to be protected13,213may be arranged within the first chamber26or within the second chamber227or within both; for example, some components may be provided within the first chamber26and others within the second chamber227, when the latter is present.

The shape of the substrate may be any according to the needs and the desired application; for example, in addition to the illustrated strip and quadrangular shapes, the substrate may also have a circular shape, or a polygonal shape, either regular or irregular.