Side vented pressure sensor device

A semiconductor sensor device has a pressure sensing die and at least one other die mounted on a substrate, and electrical interconnections that interconnect the pressure sensing die and the at least one other die. An active region of the pressure sensing die is covered with a pressure sensitive gel material, and a cap having a cavity is mounted over the pressure sensing die such that the pressure sensing die is positioned within the cavity. The cap has a side vent hole that exposes the gel covered active region of the pressure sensing die to ambient atmospheric pressure outside the sensor device. Molding compound on an upper surface of the substrate encapsulates the at least one other die and at least a portion of the cap.

BACKGROUND OF THE INVENTION

The present invention relates generally to semiconductor sensor devices, and, more particularly, to a pressure sensor device having a side vent.

Semiconductor sensor devices, such as pressure sensors, are well known. Such devices use semiconductor pressure sensor dies to sense the ambient atmospheric pressure. These dies are susceptible to mechanical damage during packaging and environmental damage when in use, and thus they must be carefully packaged. Further, pressure sensor dies, such as piezo-resistive transducers (PRTs) and parameterized layout cells (P-cells), do not allow full encapsulation because that would impede their functionality.

FIG. 1(A)shows an cross-sectional side view of a conventional packaged semiconductor sensor device100having a metal lid104.FIG. 1(B)shows a perspective top view of the sensor device100partially assembled, andFIG. 1(C)shows a perspective top view of the lid104.

As shown inFIG. 1, a pressure sensor die (P-cell)106, an acceleration-sensing die (G-cell)108, and a micro-control unit die (MCU)110are mounted on a lead frame flag112, electrically connected to lead frame leads118with bond wires (not shown), and covered with a pressure sensitive gel material114, which enables the pressure of the ambient atmosphere to reach the pressure sensitive active region on the top side of the P-cell106, while protecting all of the dies106,108,110and the bond wires from mechanical damage during packaging and environmental damage (e.g., contamination and/or corrosion) when in use. The entire die/substrate assembly is encased in a mold compound102and covered with the lid104, which has a vent hole116that exposes the gel-covered P-cell106to ambient atmospheric pressure outside the sensor device100.

One problem with the sensor device100is the high manufacturing cost due to the use of a pre-molded lead frame, the metal lid104, and the large volume of the pressure sensitive gel material114. Accordingly, it would be advantageous to have a more economical way to package dies in semiconductor sensor devices.

DETAILED DESCRIPTION

Detailed illustrative embodiments of the present invention are disclosed herein. However, specific structural and functional details disclosed herein are merely representative for purposes of describing example embodiments of the present invention. Embodiments of the present invention may be embodied in many alternative forms and should not be construed as limited to only the embodiments set forth herein. Further, the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments of the present invention.

One embodiment of the present invention is a semiconductor sensor device comprising (i) a substrate, (ii) a pressure sensing die and at least one other die mounted on the substrate, (iii) electrical interconnections between the pressure sensing die and the at least one other die, (iv) pressure sensitive gel material covering an active region of the pressure sensing die, (iv) a cap having a cavity formed therein mounted over the pressure sensing die, and (v) molding compound on an upper surface of the substrate encapsulating the at least one other die and at least a portion of the cap. The pressure sensing die is positioned within the cavity, and the cap has a side vent hole formed thereon that exposes the gel covered active region of the pressure sensing die to ambient atmospheric pressure outside the sensor device.

Another embodiment of the present invention is a method of assembling a semiconductor sensor device. A pressure sensing die and at least one other die are mounted on a substrate. The pressure sensing die and the at least one other die are electrically interconnected. An active region of the pressure sensing die is covered with pressure sensitive gel material. A cap having a cavity formed therein, and a side vent stack formed thereon, is mounted over the pressure sensing die such that the pressure sensing die is positioned within the cavity. The at least one other die and at least a portion of the cap are encapsulated with a molding compound on an upper surface of the substrate. Singulation is performed through the substrate and the molding compound such that at least a portion of the side vent stack is severed from the cap, thereby forming a vent opening in the cap that exposes the gel-covered active region of the pressure sensing die to ambient atmospheric pressure outside the sensor device.

FIG. 2shows an cross-sectional side view of a packaged semiconductor sensor device200in accordance with an embodiment of the present invention. The exemplary configuration of the sensor device200forms a land grid array (LGA) type surface-mount package. Note that alternative embodiments are not limited to LGA packages, but can be implemented for other package types, such as (without limitation) ball grid array (BGA) type packages and other package types that can be assembled as a two-dimensional array of sensor devices on a single substrate.

The sensor device200includes a pressure sensor die202and a micro-control unit die (MCU)204mounted on (e.g., physically attached and electrically coupled to) a pre-formed substrate206, and an acceleration-sensing die208mounted on the MCU204. The pressure sensor die (aka P-cell)202is designed to sense ambient atmospheric pressure, while the acceleration-sensing die (aka G-cell)208is designed to sense gravity or acceleration in one, two, or all three axes, depending on the particular implementation. The MCU204controls, for example, the operations of and the processing of signals generated by the P-cell202and the G-cell208. Note that, in some embodiments, the MCU204may implement both the functionality of an MCU and that of one or more other sensors, such as an acceleration-sensing G-cell, in which latter case, the G-cell208may be omitted.

The substrate206comprises a core dielectric material210with traces212and solder resist214formed thereon. Further, vias216are formed through the substrate206. At the bottom of the substrate206, pad openings in the solder resist214expose LGA contacts218. The traces212and LGA contacts218may be formed using known photolithography techniques.

The P-cell202and the MCU204are die-bonded to the substrate206, and the G-cell208is die-bonded to the MCU204using, for example, conventional, electrically insulating die-attach adhesive220. Those skilled in the art will understand that suitable alternative die-bonding means, such as die-attach tape, may be used to attach some or all of these dies. The P-cell202, the MCU204, and the G-cell208are well-known components of semiconductor sensor devices and thus detailed descriptions thereof are not necessary for a complete understanding of the present invention.

The electrical interconnection between the P-cell202and the MCU204is provided via one or more shared trace(s)212of the substrate206by respective, associated bond wires222wire-bonded between (i) bond pads on the P-cell202and the MCU204and (ii) the trace(s)212using a suitable, known wire-bonding process and suitable, known wire-bonding equipment. Similarly, the electrical interconnection between the MCU204and the G-cell208is provided by wire-bonding between other bond pads on the MCU204and bond pads on the G-cell208. Furthermore, the electrical interconnection between the MCU204and the outside world is provided via one or more trace(s)212of the substrate206by bond wires222wire-bonded between still other pads on the MCU204and the trace(s)212. The bond wires222are formed from a conductive material such as aluminium, gold, or copper, and may be either coated or uncoated. Note that, in alternative designs, the G-cell208can be electrically connected to the MCU204using suitable flip-chip, solder-bump techniques instead of or in addition to wire-bonding.

A pressure sensitive gel material224, such as a silicon-based gel, is deposited over the P-cell202and its associated bond wires222. The pressure sensitive gel material224enables the pressure of the ambient atmosphere to reach the active region of the P-cell202, while protecting the P-cell202and its associated bond wires222from (i) mechanical damage during packaging and (ii) environmental damage (e.g., contamination and/or corrosion) when in use. Examples of suitable pressure sensitive gel material224are available from Dow Corning Corporation of Midland, Mich. The gel material may be dispensed with a nozzle of a conventional dispensing machine, as is known in the art.

A cap226having sidewalls238with a cavity240formed therein is mounted over the gel-covered P-cell202such that gel-covered P-cell202resides in the cavity240, thereby providing a protective cover for the P-cell202. The cap226is formed of a durable and stiff material, such as plastic, teflon, metal, or other suitable material, so that the P-cell202is protected. The cap226may be secured on the substrate206using a suitable adhesive. The cap226is sized and shaped depending on the size and shape of the P-cell202. Accordingly, depending on the implementation, the cap226may have any suitable shape, such as a box, cylindrical, or hemispherical shape.

The cap226has a vent stack228, which may have any suitable shape, such as a tubular-shape having a circular, oval, square, triangular, or other shaped cross-section, with an opening or vent hole230formed therein. The vent hole230allows the ambient atmospheric pressure immediately outside the sensor device200to reach (i) the pressure sensitive gel material224and therethrough (ii) the active region of the P-cell202. As will be described in further detail below, the vent hole230may be formed during a saw singulation process that is used to separate individual sensor devices in a two-dimensional array of the sensor devices from one another. The singulation process separates a distal end234of the vent stack228from the cap226, and the distal end234may be left inside the molding compound of an adjacent sensor device during manufacturing. Thus, distal end234shown inFIG. 2is actually associated with a sensor device (not shown) that was adjacent to the sensor device200before the two devices were separated using saw singulation, and not from the sensor device200itself.

The MCU204, the G-cell208, their associated bond wires222, and the cap226are encapsulated within a suitable mold compound232. The mold compound232may be a plastic, an epoxy, a silica-filled resin, a ceramic, a halide-free material, the like, or combinations thereof, as is known in the art.

The sensor device200can be manufactured with less cost than comparable prior-art sensor devices, like those based on the conventional design of the sensor device100ofFIG. 1, because the sensor device200can be manufactured with fewer steps. For example, conventional sensor devices such as the sensor device100require a separate step, such as drilling, to form the vent hole116in the lid104, and this hole-forming process may be performed before or after the lid104is attached to the sensor device100. As described below, the vent hole230of the sensor device200may be formed during the saw singulation process, which separates sensor devices in a two-dimensional array from one another. Thus, together, the vent hole230is formed and the sensor devices are separated in a single step.

As another example, conventional sensor devices such as the sensor device100may require additional steps to prevent the molding compound and other debris coming into contact with the P-cell and pressure sensitive gel material during manufacturing. These additional steps may include separate steps to (i) protect the P-cell during application of the molding compound or (ii) die-bond the P-cell to the lead frame after the molding compound has been applied. In contrast, the P-cell202of the sensor device200may be die-bonded to the substrate206in a single stage along with the die-bonding of the MCU204and the G-cell208. Then, during application of the molding compound, the cap226of the sensor device200completely encloses the P-cell202without any openings, thereby preventing the molding compound and debris from entering the cap226. It is not until the saw singulation process (i.e., after the molding compound is applied) that the vent hole230of the sensor device200is formed.

As yet another example, conventional sensor devices such as the sensor device100may require the molding compound to be applied over two or more steps. For instance, the sensor device100requires molding compound to be applied separately to the lead frame. As illustrated below, the sensor device200may be assembled by applying the molding compound in a single step.

The vent hole230of the sensor device200may also be less susceptible to clogging than the vent hole of comparable sensor devices, like those based on the conventional design of the sensor device100ofFIG. 1, because of the manner in which the vent hole230is formed and the location of the vent hole230. In some prior-art sensor devices, the vent hole is formed, for example, by drilling the vent hole, after the lid or cap is placed over the P-cell. Forming the vent hole after the lid or cap is in place may result in debris from the drilling process entering the lid or cap. Further, by forming the vent hole230on the side of the sensor device200, as opposed to on top of the device, the vent hole230may be less susceptible to being clogged during use by debris due to gravity or other forces, depending on the orientation of the sensor device. Note that, according to alternative embodiments, the vent stack228may extend from the sidewall238at an angle other than 90 degrees. For example, vent stack228may extend away from cap226at a downward angle toward the substrate206.

FIGS. 3(A)-3(G)show cross-sectional side views that illustrate steps of an exemplary method of manufacturing multiple instances of the sensor device200ofFIG. 2.

FIG. 3(A)illustrates the step of conventional pick-and-place machinery (not shown) having attached multiple instances of the P-cell202, the MCU204, and the G-cell208to the substrate206for a one- or two-dimensional array of sensor devices. The MCU dies are attached to respective locations on the substrate206using the die-attach adhesive220such as a suitable die-bonding epoxy. The die-attach adhesive220is dispensed on a top surface of the substrate206using a known dispensing device (not shown), and the pick-and-place machinery places the MCU dies on the die-attach adhesive to attach the MCU dies to corresponding locations on the substrate206. The die-attach adhesive may subsequently be cured in an oven or via light waves to harden the die-attach adhesive. The P-cells202and the G-cells208are attached in a similar manner using pick-and-place machinery and die-attach adhesive.

FIG. 3(B)illustrates the step of wire-bonding the bond wires222to electrically connect (i) the P-cells202to the corresponding trace(s)212on the substrate206, (ii) the MCU dies204to the corresponding trace(s)212on the substrate206, and (iii) the G-cells208to the corresponding MCU dies204.

Another way of electrically connecting a semiconductor die is through flip-chip bumps (not shown) attached to an underside of the semiconductor die. The flip-chip bumps may include solder bumps, gold balls, molded studs, or combinations thereof. The bumps may be formed or placed on the semiconductor die using known techniques such as evaporation, electroplating, printing, jetting, stud bumping, and direct placement. The semiconductor die is flipped, and the bumps are aligned with corresponding contact pads (not shown) of the structure (e.g., the substrate or another die) to which the die is mounted.

FIG. 3(C)illustrates the step of dispensing the gel material224onto and around the P-cells202. The gel material224may be dispensed with a nozzle of a conventional dispensing machine (not shown), as is known in the art.

FIG. 3(D)illustrates the step of placing a respective cap226over each gel-coated P-cell. As shown, the distal end234of each vent stack228is closed. Further, each vent stack228, with the exception of the vent stack228on the right-most cap226, extends partially above the substrate of an adjacent sensor device. The caps may be attached to the substrate206using a suitable cap-attach adhesive (not shown) or may simply be placed into position and secured later using the molding compound232as described below. In the event that cap-attach adhesive is used, the cap-attach adhesive may be dispensed on a top surface of the substrate206using a known dispensing device (not shown), and the side walls238of each cap226are placed on the lid-attach adhesive to attach the side walls to the substrate206. The lid-attach adhesive may be subsequently cured in an oven.

FIG. 3(E)illustrates the step of positioning a top mold302over, and a bottom mold304under, the sensor devices200for application of the molding compound232.

FIG. 3(F)illustrates the step of applying the molding compound232the sensor devices200. As shown, the molding compound232completely covers the caps226, the MCUs204, the G-cells208, and the bonding wires222that electrically connect (i) the MCUs204to the corresponding trace(s)212on the substrate206and (ii) the G-cells208to the corresponding MCUs204. One way of applying the molding compound is using a nozzle of a conventional dispensing machine, as is known in the art. Since the caps226completely cover their respective P-cells without any openings formed therein, the caps226prevent the molding compound and debris from reaching the P-cells during application of the molding compound.

The molding compound232is typically applied as a liquid polymer, which is then heated to form a solid by curing in a UV or ambient atmosphere, whereby an array of the semiconductor sensor devices200is formed on the substrate206. The molding compound232can also be a solid that is heated to form a liquid for application and then cooled to form a solid mold. In alternative embodiments, other encapsulating processes may be used. Subsequently, an oven is used to cure the molding compound232to complete the cross linking of the polymer.

FIG. 3(G)illustrates the step of the individual semiconductor sensor devices200being separated from each other by a singulation process. Singulation processes are well known and may include cutting the substrate206with a saw blade306or a laser (not shown). When the molding compound is applied to the devices, the presence of the molding compound makes it difficult, if not impossible, from looking at the top of the devices, to distinguish where one sensor device ends and another sensor device begins. Therefore, the substrate206may be cut from the bottom side of the substrate206, where the LGA grid patterns of the devices are visible.

As the singulation process separates the individual sensor devices, a cut is made through each vent stack228in each cap226such that each vent stack228is cut in two. As a result, the proximal end236of each vent stack228has a vent hole230formed therein, and the distal end234of each vent stack228, with the exception of the vent stack in the right-most sensor device, remains lodged in the molding compound of the corresponding adjacent sensor device. The vent stack of the right-most sensor device remains lodged in excess molding compound that is separated by the singulation process and discarded. Note that, in some embodiments, the singulation process may completely remove the vent stack228of a cap226, thereby forming a hole in the sidewall238of the cap226. Further, the device200may be designed such that, when the distal end234of the vent stack228is separated from the cap226, no portion of the distal end234remains in the adjacent device.

FIG. 4shows an cross-sectional side view of a packaged semiconductor sensor device400in accordance with another embodiment of the present invention. The sensor device400is similar to the sensor device200inFIG. 2with analogous elements having similar labels, with the exception that the molding compound432does not cover the top of the cap426. The sensor device400is assembled in a manner similar to that described above in relation to FIGS.3(A)-(G). However, the steps of placing the caps and positioning the top and bottom molds as shown inFIGS. 3(D) and 3(E)may be performed as shown inFIG. 5.

FIG. 5illustrates the step of positioning the top mold502, the bottom mold504, and the caps426for application of the molding compound432. As shown, the caps426are placed upside down on the bottom mold504. Then, the substrate406is turned upside down and lowered such that the gel-coated P-cells402are positioned within the caps426. Note that the caps426may be secured to the substrate406using adhesive as described above. The top mold502is positioned on top of the bottom side of the substrate406. When the top and bottom molds502and504are filled with the molding compound, the molding compound does not cover the tops of the caps426due to the contact between the tops of caps426and the bottom mold504. As a result, the tops of the caps426of the sensor devices400are exposed (i.e., not covered with molding compound) as shown inFIG. 4.

AlthoughFIGS. 2 and 4show the sensor devices200and400each having a P-cell and a G-cell, those skilled in the art will understand that, in alternative embodiments, the G-cell and its corresponding bond wires may be omitted.

Further, althoughFIGS. 2 and 4show the sensor devices200and400each having only the P-cell202/402positioned within the cap226/426), those skilled in the art will understand that, in alternative embodiments, the one or both of the G-cell208/408and the MCU204/404may also be positioned within the cap226/426. Accordingly, the cap226/426may be sized and shaped to house the G-cell208/408and/or the MCU204/404in addition to the P-cell202/402.

AlthoughFIGS. 2 and 4show embodiments in which the G-cell208/408is mounted on the MCU204/404with the electrical interconnection provided by wire-bonding, those skilled in the art will understand that the electrical interconnection between such dies can, alternatively or additionally, be provided by appropriate flip-chip assembly techniques. According to these techniques, two semiconductor dies are electrically interconnected through flip-chip bumps attached to one of the semiconductor dies. The flip-chip bumps may include solder bumps, gold balls, molded studs, or combinations thereof. The bumps may be formed or placed on a semiconductor die using known techniques such as evaporation, electroplating, printing, jetting, stud bumping, and direct placement. The semiconductor die is flipped, and the bumps are aligned with corresponding contact pads of the other die.

It will be understood that, as used herein, the term “electrical interconnection” refers to a connection that may be made using one or more of bond wires, flip-chip bumps, traces, and other conductors used to electrically interconnect one die to another die or a substrate.

Although sensor devices of the present invention were described as being assembled in an array of sensor devices, embodiments of the present invention are not so limited. According to alternative embodiments, sensor devices of the present invention may be assembled individually. In such embodiments, a vent hole such as the vent hole230may be formed therein using a sawing process. Note, however, that the sawing process would not be used to separate sensor devices from one another, and each individual sensor device would not contain a distal end (e.g.,234) from an adjacent device that was severed during the sawing process.

By now it should be appreciated that there has been provided an improved packaged semiconductor sensor device and a method of forming the improved packaged semiconductor sensor device. Circuit details are not disclosed because knowledge thereof is not required for a complete understanding of the invention.

Although the invention has been described using relative terms such as “front,” “back,” “top,” “bottom,” “over,” “above,” “under” and the like in the description and in the claims, such terms are used for descriptive purposes and not necessarily for describing permanent relative positions. It is understood that the terms so used are interchangeable under appropriate circumstances such that the embodiments of the present invention described herein are, for example, capable of operation in other orientations than those illustrated or otherwise described herein.

As used herein, the term “mounted on” covers situations in which a first element is mounted directly on a second element with no other intervening elements, as well as situations in which there are two or more intervening elements between the first element and the second element.

The embodiments covered by the claims in this application are limited to embodiments that are enabled by this specification and correspond to statutory subject matter. Non-enabled embodiments and embodiments that correspond to non-statutory subject matter are explicitly disclaimed even if they fall within the scope of the claims.