Patent Description:
As is known, environmental sensors are sensors that enable detection of magnitudes of the external environment, such as pressure or humidity. The fields of use of environmental sensors are extremely varied. Among other applications, there has recently been a widespread use of environmental sensors in so-called wearable devices, such as watches, bracelets, and smartbands, which also enable detection of body parameters.

An environmental sensor normally comprises a sensor die, for example of a MEMS (MicroElectroMechanical System) type, and a control circuit, integrated in a separate control chip, also referred to as ASIC (Application-Specific Integrated Circuit) chip. The sensor die and the control chip are enclosed within a packaging structure (normally referred to as package), which comprises a supporting structure, normally of ceramic, and a lid. Defined in the supporting structure is a cavity, in which the sensor die and the control chip are housed. The sensor die is normally stacked on the control chip. The lid is arranged so as to close partially the cavity and has a detection port that enables coupling of the sensor die with the external environment to enable measurement of the magnitude to be detected. In other cases, the cavity can be defined between the supporting structure and the lid, for example thanks to the shape of the lid itself. The cavity is, moreover, as a rule, filled with a protective material, for example a potting gel, which has the property of transmitting the magnitude to be detected, at the same time preventing direct exposure of the sensor and of the control chip to the external environment, which may be harmful for the electronic components and the electrical connections, such as the bonding wires. Also in the case of devices commonly used as wearable devices, in fact, environmental sensors may be exposed to aggressive agents, for example chlorine in the water of a swimming pool, seawater, mineral oils or substances present on the skin, such as sweat or some perfumes. If, for the sensor die and for the control device, an acceptable level of protection can frequently be obtained with just the gel, there, however, arises the problem of sealing also the device in which the environmental sensor is incorporated. Between the environmental sensor and the casing of the device a gap is, in fact, present, which must be sealed to prevent entry of aggressive agents. The task is rendered problematical by the packaging structures of known environmental sensors. Known solutions use gaskets and a shell, which encloses both the sensor and the gaskets, keeping them pre-loaded. Other solutions use complex metal lids, with a dome-shaped portion that covers the control chip (having an area that is much greater than that of the sensor die) and is radiused to a substantially cylindrical neck. The neck has the dual function of guaranteeing coupling of the sensor die with the external environment and of defining a sealing surface for receiving the gasket (O-ring or the like). The solution, however, presents limits both because the lid is complex and costly to produce and on account of the problems that arise during the soldering step. In fact, the potting material has a coefficient of thermal expansion that is much greater than that of the material forming the lid. During soldering, the potting material may exert on the dome-shaped portion forces that tend to detach the lid from the supporting structure. The result is a substantial risk of failure or weakening of the connection between the lid and the supporting structure.

<CIT> discloses a packaged environmental sensor comprising a supporting structure, a sensor die, incorporating an environmental sensor and arranged on a first side of the supporting structure and a control chip, coupled to the sensor die and arranged on a second side of the supporting structure opposite to the first side. A ring integrally and monolithically formed with the supporting structure extends from the first side thereof. The ring is open towards the outside in a direction opposite to the supporting structure and the sensor die is housed inside the ring.

<CIT> discloses a packaged environmental sensor that comprises a supporting structure, a sensor die, incorporating an environmental sensor and arranged on a first side of the supporting structure, and a control chip, coupled to the sensor die and arranged on a second side of the supporting structure opposite to the first side. Other examples of known a packaged environmental sensors are disclosed in <CIT>.

The aim of the present invention is to provide a packaged environmental sensor that will enable the limitations described to be overcome or at least mitigated.

According to the present invention, a packaged environmental sensor is provided, as defined in claim <NUM>.

For a better understanding of the invention, some embodiments thereof will now be described, purely by way of non-limiting example and with reference to the attached drawings, wherein:.

With reference to <FIG>, an electronic device is designated as a whole by the reference number <NUM> and may be an electronic device of any type, in particular, but not exclusively, a wearable device, such as a watch, a bracelet, or a smartband, a computer, such as a mainframe, a personal computer, a laptop, or a tablet, a smartphone, a digital musical player, a digital camera, or any other device adapted to process, store, transmit, or receive information. The electronic device <NUM> may be a general-purpose computer system or may be embedded in a device, an apparatus, or a further system.

The electronic device <NUM> comprises a processing unit <NUM>, data-storage media <NUM>, and a packaged environmental sensor <NUM>, and may moreover be provided with an input/output (I/O) device <NUM> (for example a keypad, a mouse, or a touchscreen), a wireless interface <NUM>, peripherals <NUM>,. N, and possibly further auxiliary devices, here not illustrated. The components of the electronic device <NUM> may be coupled in communication with one another directly and/or indirectly through a bus <NUM>. The electronic device <NUM> may moreover comprise a battery <NUM>. It should be noted that the scope of the present invention is not limited to embodiments that necessarily have one or all of the devices listed.

The processing unit <NUM> may comprise, for example, one or more microprocessors, microcontrollers, and the like, according to the design preferences.

The data-storage media <NUM> may comprise volatile memory devices and non-volatile memory devices of various kinds, for example SRAMs and/or DRAMs in the case of volatile memories, and solid-state memories, and magnetic and/or optical disks in the case of non-volatile memories.

With reference to <FIG>, the electronic device <NUM> comprises a casing <NUM> that houses a printed-circuit board (PCB) <NUM> and at least part of the components. In particular, the packaged environmental sensor <NUM> is mounted on the PCB <NUM> either directly or via a socket <NUM>. In addition, the packaged environmental sensor <NUM> communicates with the outside world through an opening <NUM> in the casing <NUM>. The gap between the margin of the opening <NUM> and the packaged environmental sensor <NUM> is sealed by a gasket <NUM>, for example an O-ring.

The packaged environmental sensor <NUM> may be any sensor adapted to detect a magnitude of the external environment. By way of non-limiting example, the packaged environmental sensor <NUM> may be a pressure sensor, a humidity sensor, a temperature sensor, or some other environmental sensor.

As shown in <FIG>, the packaged environmental sensor <NUM> comprises a supporting structure <NUM>, a sensor die <NUM>, a control chip (or ASIC chip) <NUM>, and a collar-shaped ring <NUM>.

The supporting structure <NUM> is, for example, of ceramic and has a first face 17a, to which the sensor die <NUM> is fixed by a die-attach region <NUM>, and a second face 17b opposite to the first face 17a.

Ring-attach regions 23a-c, for example, of a metal solder paste, are arranged on the first face 17a of the supporting structure <NUM> around the sensor die <NUM>. In one embodiment, the ring-attach regions 23a-c extend along respective closed continuous paths. In particular, the ring-attach regions 23a-c are in a geometrical relationship of similarity with one another, and one of the ring-attach regions 23a-c is conformable to a margin of the ring <NUM> bonded to the supporting structure <NUM>. Furthermore, the ring-attach regions 23a-c are nested within one another without mutual contact. For instance, the ring-attach regions 23a-c may be three circular or elliptical concentric rings and are separate from one another. It is understood, however, that the shape and number of the ring-attach regions 23a-c may be freely selected according to the design preferences, for example so as to correspond to the shape and dimensions of the lids available or in any case used. For instance, the ring-attach regions 23a-c may have a polygonal shape. In turn, the dimensions of the lids are selected according to the dimensions of the gaskets <NUM>.

The sensor die <NUM> contains an environmental sensor <NUM>. In particular, the sensor die <NUM> may contain a MEMS detection structure, for example a membrane structure that may function as pressure sensor or sensor for detecting some other environmental magnitude, such as temperature or humidity.

A cavity <NUM> is formed in the second face 17b of the supporting structure <NUM> and houses the control chip <NUM>. In one embodiment, a step <NUM> is formed around one or more sides of the control chip <NUM>. Consequently, in practice, the control chip <NUM> is housed in a recess on the bottom of the cavity <NUM>, and therefore on the opposite side of the supporting structure <NUM> with respect to the sensor die <NUM>. The control chip <NUM> may comprise control circuits for driving the MEMS structure and for conversion of the physical magnitudes transduced into useful signals.

The sensor die <NUM> and the control chip are coupled together by bonding wires <NUM> between contact pads <NUM> of the sensor die <NUM> and contact pads <NUM> on the first face 17a of the supporting structure <NUM>, connection lines <NUM> embedded in the supporting structure <NUM> between the contact pads <NUM> and contact pads <NUM> on the step <NUM> of the supporting structure <NUM> around the control chip <NUM>, and bonding wires <NUM> between the contact pads <NUM> and contact pads <NUM> of the control chip <NUM>. Further contact pads <NUM>, bonding wires <NUM>, contact pads <NUM>, and connection lines <NUM> connect the control chip to conductive solder pads <NUM>, with which the supporting structure <NUM> is bonded to a PCB <NUM>. In turn, the PCB <NUM> is mechanically and electrically coupled to the socket <NUM> (or directly to the PCB <NUM> in the absence of the socket <NUM>). Alternatively, the supporting structure <NUM> can be soldered directly to the PCB <NUM>.

A protective structure <NUM>, for example a glob-top structure, fills at least part of the cavity <NUM> and incorporates the control chip <NUM> and the bonding wires <NUM>.

The ring <NUM> is defined by an annular wall and is bonded to one of the ring-attach regions 23a-23c (in the example of <FIG>, to the intermediate fixing region 23b, with respect to which the margin of the ring <NUM> is conformable). In one embodiment, the ring <NUM> has a frustoconical shape, and its generatrix G forms (externally) an angle α greater than <NUM>° with a plane parallel to the first face 17a of the supporting structure <NUM>. Alternatively, the ring <NUM> may be cylindrical. The gasket <NUM> that seals the gap between the margin of the opening <NUM> of the casing <NUM> and the packaged environmental sensor <NUM> is arranged around the ring <NUM>.

The ring <NUM> is open on both of its bases. The small base 21a of the ring <NUM> is bonded to the first face 17a of the supporting structure <NUM> and has a profile conformable to one of the ring-attach regions 23a-c, in particular to the intermediate ring-attach region 23b. The large base 21b of the ring <NUM> is open towards the outside in a direction opposite to the supporting structure <NUM>. The height of the ring <NUM> is such that the sensor die <NUM> is completely contained within the ring <NUM>.

Moreover, the ring <NUM> is at least in part filled with a protective layer <NUM> that completely englobes the sensor die <NUM> and the bonding wires. The protective layer <NUM> is of a material that has the characteristics of coupling the sensor die <NUM> to the environmental magnitude to be measured and, at the same time, protects the sensor die <NUM>, the bonding wires <NUM>, and the pads <NUM> from aggressive external agents. For instance, the protective layer <NUM> may a silicone potting gel.

As mentioned, the dimensions of the ring <NUM> are in relation with the dimensions of the opening <NUM> to be sealed and of the gasket <NUM>.

In the embodiment of <FIG>, a packaged environmental sensor <NUM> is identical to the packaged environmental sensor <NUM> already described, except for the dimensions of the ring, which is here designated by the number <NUM>. In this case, the ring <NUM> has dimensions compatible with those of the outermost ring-attach region 23a and, through the latter, is bonded to the first face 17a of the supporting structure <NUM>.

<FIG>, where elements already described are designated by the same reference numbers, represents a packaged environmental sensor <NUM> according to a different embodiment of the invention. The packaged environmental sensor <NUM> comprises a supporting structure <NUM>, the sensor die <NUM>, and the control chip <NUM>. In this case, the control chip <NUM> is bonded to the supporting structure <NUM> using the flip-chip technique. The cavity <NUM>, which is obtained in the second face 217b of the supporting structure <NUM> and houses the control chip <NUM>, does not need steps around the control chip <NUM> itself. Moreover, connection lines <NUM> connect the contact pads <NUM> on the first face 217a of the supporting structure <NUM> to a first set of contact pads <NUM> of the control chip <NUM>, and a second set of contact pads <NUM> to solder pads <NUM> of the supporting structure <NUM>. Formed on the first face 217a of the supporting structure <NUM> are ring-attach regions 223a-c, also in this case three having a circular shape and being concentric with respect to one another. The ring <NUM> is bonded to the innermost ring-attach region 223c.

The packaged environmental sensor described affords several advantages. In the first place, the control chip, which is located on the opposite side of the supporting structure with respect to the sensor die, is enclosed in a space that, in use, may be conveniently sealed with the gasket between the collar and the margin of the opening in the casing of the electronic device, where the packaged environmental sensor is installed. Consequently, the packaged environmental sensor is never exposed to the physically and/or chemically aggressive external environment. Therefore, not only is the control circuit in intrinsically safer conditions as compared to known environmental sensors, but there is also greater freedom of choice of the protective material in which the control circuit is embedded. Furthermore, the control chip is isolated from the external light so as to remain immune therefrom even though its surface may be sensitive to light.

The shape and dimensions of the ring are regardless of the dimensions of the control chip, which has an area that is typically five to six times larger than that of the sensor die. The control chip can be conveniently housed in a cavity of the supporting structure of ceramic, and the dimensions of the ring may be conveniently chosen on the basis of the structural and dimensional characteristics of just the sensor die.

The shape of the ring may be extremely simple because no particular connectors are necessary, as instead happens in some known environmental sensors especially between areas that protect the control chip, which are extensive and have a rectangular shape, and the circular neck for coupling to the O-ring that functions as gasket.

The shape, dimensions, and number of the ring-attach regions may be selected with the highest flexibility according to the design preferences. It is thus possible to produce on a vast scale a large number of examples of the supporting structure itself, to the advantage of manufacturing costs. Given the presence of a plurality of ring-attach regions, the same type of supporting structure can be used with lids and gaskets of various size, without any need for costly interventions of customization.

During the soldering steps, the shape of the ring, whether cylindrical or frustoconical with the small base bonded to the supporting structure, enables accommodation of the higher degree of thermal expansion of the potting material as compared to that of the material forming the ring, without causing damage to the structure itself. As represented by the arrows in <FIG>, in particular, the forces generated by the different coefficients of thermal expansion in a direction parallel to the first face of the supporting structure are discharged on the side walls, which can withstand the load without any risk. In a direction perpendicular to the first face of the supporting structure, instead, the potting material can expand freely outwards without exerting forces that tend to detach the ring from the supporting structure.

Claim 1:
A packaged environmental sensor comprising:
a supporting structure (<NUM>; <NUM>; <NUM>);
a sensor die (<NUM>), incorporating an environmental sensor and arranged on a first side (17a; 217a) of the supporting structure (<NUM>; <NUM>; <NUM>);
a control chip (<NUM>), coupled to the sensor die (<NUM>) and arranged on a second side (17b; 217b) of the supporting structure opposite to the first side (17a; 217a); and
a ring (<NUM>; <NUM>; <NUM>) open towards the outside in a direction opposite to the supporting structure (<NUM>; <NUM>; <NUM>), the sensor die (<NUM>) being housed inside the ring (<NUM>; <NUM>; <NUM>);
characterized by a plurality of ring-attach regions (23a-c; 223a-c) on the first side of the supporting structure (<NUM>; <NUM>; <NUM>) around the sensor die (<NUM>);
wherein the ring (<NUM>; <NUM>; <NUM>) is bonded to the first side of the supporting structure (<NUM>; <NUM>; <NUM>) by one of the ring-attach regions (23a-c; 223a-c);
and wherein the ring-attach regions (23a-c; 223a-c) extend along respective closed continuous paths and are nested inside each other without mutual contact.