DECOUPLING METHOD FOR SEMICONDUCTOR DEVICE

A sensor package includes a packaging formed by a package bottom, first and second sidewalls extending upwardly from first and second opposite sides of the package bottom, and third and fourth sidewalls extending upwardly from third and fourth opposite sides of the package bottom, the sidewalls and package bottom defining a cavity. An integrated circuit is attached to the package bottom. A plate extends between two of the sidewalls within the cavity and is spaced apart from the package bottom. Sensors are attached to a top surface of the plate on opposite sides of an opening. Wire bondings electrically connect pads on a top face of the sensor to corresponding pads on a top face of the integrated circuit, for example by passing through the opening in the plate or passing past a side end of the plate. A lid extends across and between the sidewalls to close the cavity.

TECHNICAL FIELD

This disclosure is directed to the field of packaging for sensors and, in particular, to packages that decouple sensors within the packages from mechanical stresses placed on the packages themselves.

BACKGROUND

Certain sensors, such as microelectromechanical systems (MEMS) sensors, are typically packaged together with an application specific integrated circuit (ASIC). In such a sensing package, a challenge in the packaging is to provide for long-term stability and operation, and to reduce mechanical stresses placed on the sensors, for example, during manufacturing steps such as soldering or due to mismatches in the coefficient of thermal expansion (CTE) between the sensors and the package.

Ceramics are known to have mechanical properties that make them advantageous for use in packages carrying semiconductor-based sensors. For example, ceramics are rigid in nature and their properties exhibit stability over time. In addition, different ceramics with a variety of different CTEs are available, making the matching between CTEs of the packages and the sensors easier. Where a mismatch is present, due to expansion over temperature at different rates between the packages in question and the sensors, mechanical stresses are imposed on the sensors. These sensors may have mechanical components integrated therein and are therefore particularly sensitive to mechanical stresses, with such stresses potentially reducing the stability and lifetime of the sensors and possibly altering the performance of the sensors. Therefore, the use of ceramic packaging materials matched in CTE to the sensors is of interest.

A specific challenge faced during manufacture of sensing packages is that mechanical stress levels on the packages themselves after being soldered to a printed circuit board (PCB) may be high and such stresses may be coupled through to the sensors, causing drifting of the performance of the sensors as a result of the mechanical stresses applied thereto.

Another challenge is that sensors are often calibrated after a final test, compensating for drift caused by process variations (both front-end and back-end) but prior to being soldered to a PCB and, as stated, the soldering itself may induce stresses and result in drift. It is therefore desired for package designs to be created that that are able to decouple the sensors themselves from the stresses placed on their packages.

SUMMARY

Disclosed herein is a sensor package including a packaging and an integrated circuit. The packaging is formed by a package bottom, first and second sidewalls extending upwardly from first and second opposite sides of the package bottom, and third and fourth sidewalls extending upwardly from third and fourth opposite sides of the package bottom. The first, second, third, and fourth sidewalls and the package bottom define a cavity. The integrated circuit is attached to the package bottom. A plate extends between at least two of the sidewalls within the cavity and is spaced apart from the package bottom. At least one sensor is attached to a top surface of the plate. Wire bondings electrically connect pads on a top face of the at least one sensor to corresponding pads on a top face of the integrated circuit. A lid extends across and between the first, second, third, and fourth sidewalls to thereby close the cavity.

The plate may extend between the first and second sidewalls and may have an opening formed therein through which the wire bondings pass to electrically connect the pads on the top face of the at least one sensor to the corresponding pads on the top face of the integrated circuit.

The first sidewall may be formed by a first portion extending upwardly from the first side of the package bottom and a second portion extending upwardly from a distal end of the first portion, with the second portion being thinner than the first portion in a stair-stepped shape so as to define a first support shelf. The second sidewall may be formed by a first portion extending upwardly from the second side of the package bottom and a second portion extending upwardly from a distal end of the second portion, with the second portion of the second sidewall being thinner than the first portion of the second sidewall in a stair-stepped shape so as to define a second support shelf.

The plate may be carried by and extends between the first and second support shelves.

The plate extend between the first and second sidewalls and have an opening formed therein, with the at least one sensor being first and second sensors attached to the top surface of the plate on opposite sides of the opening. In this situation, the wire bondings may include first and second wire bondings. The first wire bondings may pass through the opening to electrically connect the pads on the top face of the first sensor to the corresponding pads on the top face of the integrated circuit. The second wire bondings may pass through the opening to electrically connect the pads on the top face of the second sensor to the corresponding pads on the top face of the integrated circuit.

The packaging and plate may be constructed from ceramic.

The lid may be constructed from metal.

The integrated circuit may be an application specific integrated circuit (ASIC).

Vias may be formed within the package bottom to electrically connect pads on a top surface of the package bottom to corresponding pads on a bottom surface of the package bottom, and additional wire bondings may electrically connect the pads on the top surface of the package bottom to corresponding pads on the top face of the integrated circuit.

The plate may extend between the third and fourth sidewalls, adjacent to the first sidewall. In this instance, the wire bondings may extend past a side end of the plate to electrically connect the pads on the top face of the at least one sensor to the corresponding pads on the top face of the integrated circuit.

The plate may be sized to extend outwardly from the first sidewall toward the second sidewall but not reach the second sidewalls.

The first sidewall may be formed by a first portion extending upwardly from the first side of the package bottom and a second portion extending upwardly from a distal end of the first portion, with the second portion being thinner than the first portion in a stair-stepped shape so as to define a first support shelf, and the plate may be carried by the first support shelf.

The second sidewall may have a substantially constant thickness.

The plate may extend between the third and fourth sidewalls, adjacent to the first sidewall, with the plate being sized to extend outwardly from the first sidewall toward the second sidewall but not reach the second sidewall. In this instance, the at least one sensor may be first and second sensors attached to the top surface of the plate. Together with this, the wire bondings may be first and second wire bondings. The first wire bondings may extend past a side end of the plate to electrically connect the pads on the top face of the first sensor to the corresponding pads on the top face of the integrated circuit. The second wire bondings may extend past the side end of the plate to electrically connect the pads on the top face of the second sensor to the corresponding pads on the top face of the integrated circuit.

Also disclosed herein is a method of making the devices described above. The method may include steps of: a) attaching an integrated circuit to a top surface of a package bottom of a package; b) attaching at least one sensor to a top surface of a plate on opposite sides of an opening formed in the plate; c) mounting the plate between sidewalls of the package in a spaced apart fashion from the top surface of the package bottom; d) electrically connecting pads on a top face of the at least one sensor to corresponding pads on a top face of the integrated circuit using wire bondings; and e) affixing a lid to extend across and between the sidewalls to thereby close a cavity within the package defined by the sidewalls and the package bottom.

Electrically connecting the pads on the top face of the at least one sensor to the corresponding pads on the top face of the integrated circuit may include passing the wire bondings through an opening in the plate.

The method may include, prior to a), providing the package as having a package bottom, first and second sidewalls extending upwardly from first and second opposite sides of the package bottom, and third and fourth sidewalls extending upwardly from third and fourth opposite sides of the package bottom. In c), the plate may be mounted to extend at least between the first and second sidewalls.

The package may be provided as having the first sidewall formed by a first portion extending upwardly from the first side of the package bottom and a second portion extending upwardly from a distal end of the first portion, with the second portion being thinner than the first portion in a stair-stepped shape so as to define a first support shelf, and as having the second sidewall formed by a first portion extending upwardly from the second side of the package bottom and a second portion extending upwardly from a distal end of the second portion, with the second portion of the second sidewall being thinner than the first portion of the second sidewall in a stair-stepped shape so as to define a second support shelf. Together with this in c), the plate may be mounted between the sidewalls of the package by affixing a bottom surface of the plate to the first and second support shelves.

The method may include prior to c), electrically connecting pads on the top surface of the package bottom to corresponding pads on the top face of the integrated circuit using third wire bondings.

Electrically connecting the pads on the top face of the at least one sensor to the corresponding pads on the top face of the integrated circuit may include passing the wire bondings past a side end of the plate.

The method may also include, prior to a), providing the package as having a package bottom, first and second sidewalls extending upwardly from first and second opposite sides of the package bottom, and third and fourth sidewalls extending upwardly from third and fourth opposite sides of the package bottom. In this instance, in c), the plate may be mounted to extend from the first sidewall.

The package may be provided as having the first sidewall formed by a first portion extending upwardly from the first side of the package bottom and a second portion extending upwardly from a distal end of the first portion, with the second portion being thinner than the first portion in a stair-stepped shape so as to define a first support shelf. In c), the plate may be mounted between the sidewalls of the package by affixing a bottom surface of the plate to the first support shelf.

DETAILED DESCRIPTION

The following disclosure enables a person skilled in the art to make and use the subject matter disclosed herein. The general principles described herein may be applied to embodiments and applications other than those detailed above without departing from the spirit and scope of this disclosure. This disclosure is not intended to be limited to the embodiments shown, but is to be accorded the widest scope consistent with the principles and features disclosed or suggested herein. In addition, in the below description, where any individual wire bonding connecting two pads is described, understand there may instead be multiple such wire bondings connected between a corresponding number of pads on the same surfaces/faces/devices in the same fashion.

Now described with initial reference toFIGS.1-4is a sensor package10. The sensor package10includes a package11that is shaped as a rectangular box with an open top defining a cavity19, with a lid12affixed over the open top of the package11to close the cavity19. The package11is constructed from ceramic and the lid12is constructed from either metal or ceramic.

The interior of the package11includes four sidewalls, with two of the sidewalls11a,11bopposite each other across the bottom11cof the package11being shown in the cross section ofFIG.2, and the two other sidewalls not being shown but have, in an embodiment, a shape and configuration like that of sidewalls11a,11b. The sidewall11ais formed as a thick portion18aextending upwardly from the package bottom11cand a thin portion18bextending upwardly from the thick portion18ain a stair-stepped shape to define a support shelf15a. Similarly, the sidewall11bis formed as a thick portion18cextending upwardly from the package bottom11cand a thin portion18dextending upwardly from the thin portion18cin a stair-stepped shape to define a support shelf15b. A plate16is supported within the cavity19by the support shelves15a,15bthat the bottom surface of the plate16is adhesively bonded to, with the plate extending between the support shelves15a,15b. The plate16is sized to fully close off a lower portion of the cavity19(the lower portion of the cavity being the portion of the cavity below the support shelves15a,15b) and has an opening25defined therein.

An application specific integrated circuit (ASIC)20is attached to the upper surface of the package bottom11c, with wire bonding20aconnecting pad20fon the top face of the ASIC 20 to pad20band via20cwithin the package bottom11cof the package that are in turn connected to dual-flat no lead (DFN) pad13on the bottom surface of the package bottom11c. A first sensor21is attached to the top surface of the plate16adjacent the support shelf15a, and a second sensor22is attached to the top surface of the plate16adjacent the support shelf15b. The first sensor21may be a microelectromechanical systems (MEMS) device such as an accelerometer, and the second sensor22may be another MEMS device such as a gyroscope.

Indeed, the sensors21,22are silicon based and may be any suitable sensors that either include mechanical components (e.g., MEMS components, optical components, etc.) or electrical components sensitive to the piezoelectric effect (e.g., at least one piezo-resistor and/or a Hall effect sensor).

A wire bonding21apasses through the opening25in the plate16to connect pad21bon the top face of the sensor21to corresponding pad20don the top face of the ASIC 20, and a wire bonding22apasses through the opening25in the plate16to connect pad22bon the top face of the sensor22to corresponding pad20eon the top face of the ASIC 20.

To ease a full understanding, a top plan view of the plate16with the sensors21,22attached to the top surface thereof opposite to each other across the opening25is shown inFIG.3, with the various wire bondings not being shown for ease of reading. Likewise, a top plan view of the package bottom11cshowing the placement of the ASIC 20 and the support shelves15a,15bis shown inFIG.4, with the various wire bondings not being shown for ease of reading.

As a result of soldering the sensor package10to a printed circuit board (PCB), mechanical stresses (e.g., normal and/or shear stresses, generally lateral but also out of plane) are applied to the sensor package10. The advantage of the design of the sensor package10is that while mechanical stresses placed on the package11are imparted to the package bottom11cthrough the mechanical connection to the PCB, those mechanical stresses are not ultimately passed through to the plate16, and are therefore not imparted to the sensors21,22on the top surface of the plate16. While the ASIC 20 will be subjected to the stresses imparted to the package11(which are transmitted to the ASIC 20 through its connection to the top surface of the package bottom11c), the ASIC contains solely electrical components and does not contain mechanical components, and as such its proper operation is not impacted.

This design of the sensor package10therefore results in a significant reduction in stresses passed to the sensors21,22, contributing to a longer service life and more predictable behavior. In addition, the performance of the sensors21,22themselves may be increased, as their performance will be similar to what it would be if the sensor package10was a standalone device and not attached to a PCB. This in turn may help reduce the amount of testing to be performed.

Additional designs and process flows for forming those designs (as well as the design ofFIG.2) will be described below, with it being understood that those designs have the same benefits and advantages as that of the sensor package10ofFIG.2described hereinabove.

Now described with reference toFIGS.5A-5Fis a process flow for forming the sensor package10ofFIG.2. The process flow begins with the provision or formation of the package11, as shown inFIG.5A. Thereafter, the ASIC 20 is attached to the top surface of the package bottom11cand the sensors21,22are attached to the top surface of the plate16on opposite sides of the opening25, as shown inFIG.5B.

Wire bonding20ais then used to connect pad20fon the top face of the ASIC 20 to corresponding pad20band via20con the top surface of the package bottom11c, as shown inFIG.5C, and then the assembled plate16is mounted within the package11such that it is affixed to and extends between the support shelves15a,15b, as shown inFIG.5D. This mounting of the plate16is accomplished by dispensing adhesive on the support shelves15a,15b, positioning the plate16into the appropriate place, and then performing a curing. Next, wire bondings21a,22aare passed through the opening25and used to connect pads21b,22bon the top faces of the sensors21,22to corresponding pads20d,20eon the top face of the ASIC 20, as shown inFIG.5E. As should be understood, the opening25is sized and shaped so as to provide access to the top face of the ASIC 20 and allow for the wirebonding tool to form the desired wire bond connections.

The lid12is then affixed over the tops of the sidewalls11a,11bto seal off the cavity19within the package11, as shown inFIG.5F. This completes the formation of the sensor package10.

An alternative to the design of the sensor package10is now described with reference toFIG.6. In this alternative, instead of the plate16extending completely across the cavity19between shelves15a,15b, the plate16may be shorter in length and affixed to just one shelf15a, as shown in the sensor package10′ ofFIG.6. Notice that in this instance, the sidewall11bis constant in thickness, and the shelf15b(ofFIG.2) is not present. Again, the other sidewalls are not shown but in an embodiment may be constructed similar to each sidewall11aor sidewall11b. Through this design, an opening need not be formed in the plate16since a portion of the chamber will be left open adjacent the plate16. Thus, here, the wire bondings21a,22bextend past the side end of the shelf15ato connect pads21b,22bon the top faces of the sensors21,22to corresponding pads20d,20eon the top face of the ASIC 20. As can be observed in the top plan view of the plate16inFIG.7, both sensors15a,15bare carried by the plate16adjacent the sidewall11a. In addition, as can be observed in the top plan view of the package bottom11cinFIG.8, the ASIC 20 is positioned adjacent to the sidewall11bto permit the wire bondings21a,22bto easily reach its pads.

Now described with reference toFIGS.9A-9Fis a process flow for forming the sensor package10′ ofFIG.6. The process flow begins with the provision or formation of the package11, as shown inFIG.9A. Thereafter, the ASIC 20 is attached to the top surface of the package bottom11cand the sensors21,22are attached to the top surface of the plate16adjacent to each other, as shown inFIG.9B.

Wire bonding20ais then used to connect pad20don the top face of the ASIC 20 to corresponding pad20bon the top surface of the package bottom11c, as shown inFIG.9C, and then the assembled plate16is mounted within the package11such that it rests on the support shelf15a, as shown inFIG.9D. This mounting of the plate16is accomplished by dispensing adhesive on the support shelf15apositioning the plate16into the appropriate place, and then performing a curing. Next, wire bondings21a,22aare passed past the side end of the plate16and used to connect pads21b,22bon the top faces of the sensors21,22to pads20d,20eon the top face of the ASIC 20, as shown inFIG.9E. The lid12is then affixed over the tops of the sidewalls11a,11bto seal off the cavity19within the package11, as shown inFIG.9F. This completes the formation of the sensor package10′.

Other embodiments of sensor packages and process flows for manufacturing those embodiments are now described. Beginning with the embodiment of the sensor package10″ ofFIG.10, the ASIC 20 may be embedded within the plate16, with the sensors21and22being attached to opposite faces of the ASIC 20 (wherein techniques known to those skilled in the art are used for encapsulating the ASIC 20 within the plate with coplanar upper and lower surfaces). In greater detail, as shown, the plate16is affixed to and extends across the tops of the sidewalls11a,11bto seal off the cavity19, with the ASIC 20 being embedded in a central location within the plate16. Sensor21is attached to the top face of the ASIC 20 and wire bonding21ais connected to and extends between pad21bon the top face of the sensor21and corresponding pad20don the top face of the ASIC 20. A wire bonding20jconnects pad20ion the top face of ASIC 20 to pad20kon the top surface of the plate16. Pad20kon the top surface of the plate16is connected to pad20mon the bottom surface of the plate16by via20l, and wire bonding20aconnects pad20mon the bottom surface of the plate16to pad20bon the top surface of the bottom11cof the package11. Sensor22is attached to the bottom face of the ASIC 20 and wire bonding22ais connected to and extends between pad22bon the top face of the sensor22and corresponding pad20non the bottom surface of the plate16. Via20gconnects pad20non the bottom surface of the plate16to pad20oon the top surface of the plate16, and a wire bonding20hconnects the pad20oon the top surface of the plate16to corresponding pad20eon the top face of the ASIC 20.

Now described with reference toFIGS.11A-11Fis a process flow for forming the sensor package10″ ofFIG.10. The process flow begins with the provision of formation of the plate16as having the ASIC 20 embedded therein, as shown inFIG.11A. Thereafter, the sensor22is attached to the bottom face of the ASIC 20, as shown inFIG.11B, and then a wire bonding22ais connected to and extends between pad22bon the top face of the sensor22and corresponding pad20fon the bottom face of the plate16, as shown inFIG.11C.

Next, the plate16is flipped, as shown inFIG.11D, and the sensor21is attached to the top face of the ASIC 20, as shown inFIG.11E. After that, a wire bonding21ais connected to and extends between pad21bon the top face of the sensor21and pad20don the top face of the ASIC 20, as shown inFIG.11F. Additionally, wire bonding20jconnects pad20ion the top face of the ASIC 20 to pad20kon the top surface of the plate16. The assembled plate16is mounted within the package11such that it rests on and extends between the support shelves15a,15b, as shown inFIG.11G. This mounting of the plate16is accomplished by dispensing adhesive on the support shelves15a,15b, positioning the plate16into the appropriate place, and then performing a curing. During this step, a wire bonding20ais connected to and extends between pad20mon the bottom face of the ASIC 20 and pad20bon the top surface of the package bottom11c. The lid12is then affixed over the tops of the sidewalls11a,11bto seal off the cavity19within the package11, as shown inFIG.11H, thereby completing formation of the sensor package10″.

Instead of the sensors21,22being attached to opposite faces of the ASIC 20 as in the sensor package10″ ofFIG.10, they may instead be attached to the same face of the ASIC 20 as shown in the sensor package10′″ ofFIG.12. In greater detail, as shown, the plate16is affixed to and extends across the tops of the sidewalls11a,11bto seal off the cavity19, with the ASIC 20 being embedded in a central location within the plate16. Sensors21,22are attached to the top face of the ASIC 20. Wire bonding21ais connected to and extends between the pad21bon top face of the sensor21and corresponding pad20don the top face of the ASIC 20, and sensor22is attached to the top face of the ASIC 20 opposite to the sensor21and wire bonding22ais connected to and extends between pad22bon the top face of the sensor22and corresponding pad20eon the top face of the ASIC 20. Wire bonding20jconnects pad20jon the top face of the ASIC 20 to pad20kon the top surface of the plate16. Wire bonding20aconnects pad20mon the bottom surface of the plate16to pad20bon the top surface of the bottom11cof the package11. Via20lconnects pad20kon the top surface of the plate16to pad20mon the bottom surface of the plate16. Via20cconnects pad20bon the top surface of the bottom11cof the package11to pad13on the bottom surface of the bottom11cof the package11.

Now described with reference toFIGS.13A-13Eis a process flow for forming the sensor package10′″ ofFIG.12. The process flow begins with the provision of formation of the plate16as having the ASIC 20 embedded therein, as shown inFIG.13A. Thereafter, the sensors21,22are attached to the top face of the ASIC 20, as shown inFIG.13B, and then wire bondings21a,22aare connected to and extending between pads21a,22aon the top faces of the sensors21,22and corresponding pads20d,20eon the top face of the ASIC 20, as shown inFIG.13C. Additionally, wire bonding20jis connected between pad20ion the top face of the ASIC 20 and pad20kon the top surface of the plate16.

Next, the assembled plate16is mounted within the package11such that it rests on and extends between the support shelves15a,15b, as shown inFIG.13D. This mounting of the plate16is accomplished by dispensing adhesive on the support shelves15a,15b, positioning the plate16into the appropriate place, and then performing a curing. During this step, a wire bonding20ais connected to and extends between pad20mon the bottom surface of the plate16and corresponding pad20bon the top surface of the package bottom11c. The lid12is then affixed over the tops of the sidewalls11a,11bto seal off the cavity19within the package11, as shown inFIG.13E, thereby completing formation of the sensor package10′″.

As has been explained, the sensor packages10,10′,10″,10′″ described herein reduce the mechanical stresses placed on the sensors21,22. In fact, this reduction has been found by the Inventors to be on the order of 40.34% to 49.4%, as shown in the graphs ofFIGS.14A and14Bthat show the deformation of the sensors21,22as a result from stresses imparted by being soldered to a PCB.

Finally, it is clear that modifications and variations may be made to what has been described and illustrated herein, without thereby departing from the scope of this disclosure, as defined in the annexed claims.