Patent ID: 12203776

DETAILED DESCRIPTION

Some types of packages are configured to measure various physical properties of an environment, such as temperature, humidity, light, sound, pressure, etc. In many instances, the package includes a sensor that is exposed directly to the environment to be tested. Thus, for example, a package that is configured to measure the temperature of a swimming pool may be positioned in an area of the pool where the sensor will be directly exposed to the pool water. Such packages are referred to herein as sensor packages.

Sensor packages contain sensors, but they also contain other circuitry, such as an analog front-end (AFE) circuit, to process the properties of the environment sensed by the sensor. This circuitry cannot be exposed to the environment, as doing so could damage the circuitry and render it inoperable. Accordingly, sensor packages are fabricated so that the sensor is exposed to the environment, but the remaining circuitry of the package is covered by the mold compound of the package. A sensor package may include a cavity in its mold compound, and the sensor is positioned inside this cavity.

Contemporary designs for sensor packages are unsatisfactory for multiple reasons, most of which are due to inefficiencies in the manufacturing process, and specifically due to inefficiencies in creating the sensor cavities mentioned above. For example, sensor cavities are created using complex and expensive molding equipment that is limited in its ability to create small sensor cavities. Each sensor cavity formed by this equipment should be of a minimum threshold size. This inability to create small sensor cavities limits each sensor package to a single cavity, and, thus, to a single sensor. While this challenge could theoretically be mitigated by increasing package size, such increases are highly undesirable, and most or all industries and customers demand decreasing package size instead of increasing package size. Furthermore, not only are sensor packages limited to a single sensor cavity and a single sensor, but sensor packages should be of a minimum threshold size so that even one sensor cavity can be accommodated. Thus, these sensor packages with only one sensor cannot be further decreased in size.

Further still, the complex and expensive molding equipment that is used to create the unsatisfactorily large sensor cavities is package-specific, meaning that the equipment generally cannot be re-used for multiple types of sensor packages. Instead, different equipment should be used to create sensor cavities in different types of sensor packages. Different equipment should be used even in the instance that multiple sensor cavity shapes are desired for the same type of sensor package. This repeated investment in different types of equipment introduces significant increases in design costs, manufacturing costs, development time, and manufacturing time.

This disclosure describes various examples of a sensor package and examples of techniques for manufacturing such a sensor package that overcome the challenges described above. Specifically, in contrast to other techniques for forming sensor cavities in sensor packages, some of the examples described below entail the use of components and techniques that result in miniature sensor cavities, which facilitates the reduction of sensor packages sizes and/or the incorporation of multiple sensor cavities and sensors in a single sensor package. In some examples, rings (e.g., plated metal rings) are positioned on a semiconductor die, circumscribing a semiconductor die sensor, prior to placing the semiconductor die in a mold chase to apply a mold compound. The ring prevents mold compound from flowing onto the sensor, thus creating a sensor cavity in the mold compound. Such rings may be composed of metal or non-metal materials, and they may be grown on the semiconductor die using a plating process or may be manufactured separately from the semiconductor die and coupled to the semiconductor die using an adhesive. Other examples described below entail the use of a solid member (e.g., studs) that is used to cover a semiconductor die sensor prior to placing the sensor in a mold chase. The solid member prevents mold compound from covering the sensor. The solid member is subsequently removed, thereby producing a sensor cavity in the mold compound. The solid member may be composed of metal or non-metal materials (e.g., compressible materials), and they may be grown on the semiconductor die using a plating process or may be manufactured separately from the semiconductor die and coupled to the semiconductor die using an adhesive. In some examples, the solid member may have a high coefficient of thermal expansion (CTE) so that, after the mold compound has been applied to the semiconductor die, a freezing temperature is applied to the solid member to cause the solid member to decrease in size and to facilitate removal of the solid member from the mold compound. These and other examples are now described with reference to the drawings.

FIG.1is a schematic diagram of a semiconductor wafer100, in accordance with various examples. For example, the semiconductor wafer100may be a silicon wafer. The semiconductor wafer100comprises multiple semiconductor dies102. The manufacturing techniques described below may be performed on individual semiconductor dies102(post-singulation), or the techniques may be more efficiently performed on a mass scale, e.g., simultaneously on multiple semiconductor dies102of the semiconductor wafer100(pre-singulation). For convenience and clarity, the remaining drawings show one semiconductor die102, with the understanding that the processes described herein as being performed on the semiconductor die102may also be performed (e.g., sequentially performed, simultaneously performed) on the remaining semiconductor dies102of the wafer100. In addition, although the portions of a wafer separated by scribe streets sometimes are not referred to as semiconductor dies until the wafer has been sawn (e.g., post-singulation), this disclosure nevertheless uses the term “semiconductor die(s)” to refer to dies both pre- and post-singulation. Thus, the intact wafer100is said to include multiple semiconductor dies102and, after the wafer100is sawn, the resulting separate portions of the wafer100are also referred to as semiconductor dies102.

FIGS.2A-12Btogether depict an example process flow implementing an example sensor packaging technique described herein. More specifically,FIG.2Ais a perspective view of a semiconductor die102. As explained above, the semiconductor die102may be singulated from the wafer100, or the semiconductor die102may be part of an intact wafer100. For purposes of this description, it is assumed that the semiconductor die102is part of an intact wafer100. The semiconductor die102includes a sensor200on an active surface204. For example, the sensor200may be configured to sense any of a variety of physical properties, such as humidity, light, sound, pressure, bulk acoustic waves, stress, temperature, current, voltage, power, motion, acceleration, magnetic fields, and other physical properties. The active surface204of the semiconductor die102also may include other circuitry, such as an analog front end (AFE) circuit coupled to the sensor200that is configured to receive and process signals from the sensor200in an appropriate manner. For the sake of simplicity, such circuitry is not expressly shown inFIG.2A. The semiconductor die102may further include multiple bond pads202that couple to circuitry on the active surface204.FIG.2Bis a top-down view of the structure ofFIG.2A.

FIG.3Ais a perspective view of the semiconductor die102having a plating seed layer300deposited thereupon. For example, the plating seed layer300may be a titanium plating seed layer. For example, the plating seed layer300may be a titanium tungsten plating seed layer. The plating seed layer300may be positioned on the active surface204of the semiconductor die102using any appropriate technique. For example, the plating seed layer300may be positioned on the active surface204using a sputtering technique. The plating seed layer300may have any suitable physical dimensions.FIG.3Bis a top-down view of the structure ofFIG.3A.

FIG.4Ais a perspective view of the semiconductor die102, the plating seed layer300, and a photoresist layer400on the plating seed layer300. As will be described with reference toFIGS.5A-8B, a photolithography and plating process is performed on the photoresist layer400to form a ring that circumscribes the sensor200. As briefly explained above, such a ring may be used to prevent mold compound from covering the sensor200during a mold compound application process (e.g., in a mold chase). In examples, the photoresist layer400is thicker than the plating seed layer300, although the scope of this disclosure is not limited as such. In examples, the thickness of the photoresist layer400determines a height of the ring described above. For instance, using a thicker photoresist layer400will produce a taller ring, and using a thinner photoresist layer400will produce a shorter ring. Target ring heights are application-specific and, as a result, any suitable thickness of the photoresist layer400that produces a target ring height may be used. For instance, taller rings may be more suitable for preventing mold compound from flowing onto the sensor200if the gap between the top and bottom members of a mold chase in which the mold compound is applied is greater, and shorter rings may be more suitable for applications in which the gap between the top and bottom mold chase members is smaller. In examples, the thickness of the photoresist layer400should be chosen so that the resulting ring is sufficiently short so that it fits within the mold chase that is to be used, but sufficiently tall so that it prevents mold compound from flowing onto the sensor200during application of the mold compound. Although the thickness of the photoresist layer400(and thus, the height of the ring) is application-specific, in examples, the thickness of the photoresist layer400ranges from 10 microns to 200 microns.FIG.4Bdepicts a top-down view of the structure ofFIG.4A.

FIG.5Ais a perspective view of the structure ofFIG.4Aafter a photolithography process has been performed, e.g., after a suitably-patterned mask has been positioned above the photoresist layer400, the area indicated by cavity500has been exposed, and the exposed area has been developed to remove the exposed area. As shown, the exposed and developed area may form a cavity500having a circular shape in a horizontal plane, with a platform502positioned in a center of the circle. In examples, the cavity500may have a different shape, such as an ovoid shape or a rectangular shape in the horizontal plane. In examples, the physical shape and the physical dimensions of the cavity500determine the physical shape and dimensions of the ring that is to be plated in the cavity500. For example, a diameter of the cavity500(e.g., inner diameter or outer diameter) may be selected as desired to produce a ring with a target diameter (e.g., inner diameter or outer diameter). Similarly, the thickness of the cavity500(e.g., the shortest distance between the inner and outer perimeters of the cavity500) may determine a thickness of the ring that is produced. In examples, the thickness of the cavity500(and, thus, the ring) ranges from 50 microns to 200 microns, with a smaller thickness providing the advantage of smaller form factors suitable for smaller applications (e.g., smartphones, digital watches, health monitors, etc.), and a greater thickness providing the advantage of robustness suitable for industrial applications (e.g., automotive, aviation, space, harsh conditions). In examples, the inner diameter of the cavity500(and, thus, the ring) ranges from 25 microns to 2 mm (e.g., in some examples, less than 100 microns), with a smaller inner diameter facilitating smaller package size, the inclusion of multiple sensors per package, reduced costs, and more precise control of direction and range of incident signals, and a greater inner diameter providing adequate protection for the sensor200, a broader view of the incident signal, and better detection of weak signals. In examples where the cavity500is rectangular, the cavity500(and thus, the ring) may have a length ranging from 25 microns to 2 mm and a width ranging from 25 microns to 2 mm. In examples, the position of the cavity500also determines a position of the ring. For instance, as shown inFIG.5A, the cavity500is positioned such that the platform502fully covers the sensor200.FIG.5Bis a top-down view of the structure ofFIG.5A.

FIG.6Adepicts a plating (e.g., electroplating) process performed to fabricate a ring in the cavity500. In particular, the plating seed layer300is used to plate a ring600filling the cavity500. Because the ring600is plated inside the cavity500, the ring600assumes the physical dimensions of the cavity500, such as the diameter, thickness, and height of the cavity500as described above. Accordingly, the description provided above regarding the dimensions of the cavity500(whether circular/ovoid or rectangular) also applies to the ring600(whether circular/ovoid or rectangular). In examples, the ring600is plated so that a top surface of the ring600is flush with, or approximately flush with (e.g., within 1 millimeter of), a top surface of the photoresist layer400. In examples, the ring600is composed of a metal such as copper, nickel, or aluminum. In examples, a top surface of the ring600may be plated with another layer or layers, such as nickel, nickel palladium, nickel gold, etc., in which case the top surface of this additional plating layer may be flush or approximately flush with the top surface of the photoresist layer400. The drawings do not depict such optional plating layers on top of the ring600. In examples, the greatest distance between the inner surface of the ring600and the sensor200is 5 microns or fewer.FIG.6Bis a top-down view of the structure ofFIG.6A.

InFIG.7A, the photoresist layer400is removed (e.g., stripped).FIG.7Bis a top-down view of the structure ofFIG.7A. The portion of the plating seed layer300that is not under the ring600is subsequently removed (e.g., chemically etched), leaving the structure shown inFIG.8A. AsFIG.8Ashows, the ring600is mechanically coupled to the semiconductor die102via the plating seed layer300, which is between the ring600and the semiconductor die102. As used herein, the term mechanically coupled means that a first component couples to a second component either directly or by way of a third component. A sensor cavity800is formed within the ring600, and the sensor200is positioned inside the sensor cavity800as shown. As described below, when a mold compound is applied, the ring600prevents the mold compound from covering the sensor200.FIG.8Bis a top-down view of the structure ofFIG.8A.

Assuming that the semiconductor die102is part of an intact wafer100, the wafer100is then diced so that the semiconductor die102is separated from the wafer100. The semiconductor die102is then coupled to a lead frame of a lead frame strip. For example, asFIG.9Ashows, the semiconductor die102is mounted on a die pad900of a lead frame. Bond pads202are coupled to conductive terminals902(e.g., leads) via bond wires904.FIG.9Ashows a few illustrative bond wires904, but in actual implementation, fewer or more bond wires904may be used.FIG.9Bis a top-down view of the structure ofFIG.9A.

The structure ofFIGS.9A and9Bis subsequently covered using a mold compound.FIG.10depicts a mold chase having a top member1000and a bottom member1002. The structure ofFIGS.9A and9Bis positioned inside the mold chase between the top member1000and bottom member1002. In examples, the height of the ring600may be selected so that, when the structure ofFIG.9Ais positioned inside the mold chase, the top surface of the ring600does not reach the bottom surface of the top member1000. This gap may be filled by a film1004, e.g., a film that is coupled to a bottom surface of the top member1000. The film1004serves multiple purposes. One purpose of the film1004is to prevent mold compound1006from flowing into the sensor cavity800within the ring600and covering the sensor200. Another purpose of the film1004is to mitigate a force transferred from the top member1000of the mold chase to the semiconductor die102via the ring600. Without the film1004, the ring600would make direct contact with the bottom surface of the top member1000, in which case a deleterious force may be transferred from the top member1000to the semiconductor die102via the ring600. Alternatively, without the film1004, the ring600would not make direct contact with the bottom surface of the top member1000, in which case mold compound1006would flow onto the sensor200and cover the sensor200. To achieve these purposes, the film1004may have certain properties. For example, the film1004may be composed of materials such as single layer or multi-layer polymer materials (e.g., polyester, polyvinyl resin, etc.). In examples, the film1004may have a compressibility ranging from 20% to 50% of the original thickness of the film1004in the uncompressed state. For instance, in some such examples, a film1004that is 100 microns in thickness could be compressed by 20 microns to 50 microns, resulting in a film1004that has a thickness of 50 microns to 80 microns. In examples, the film1004has a compressibility that ranges from 50% to 80% of the uncompressed thickness of the film1004. Adequate compressibility facilitates the mitigation of force being transferred to the semiconductor die102from the top member1000of the mold chase, but excessive compressibility may compromise the ability of the film1004to block mold compound flow. In examples, the film1004is sufficiently thick so that, when the mold chase is closed, the film1004and the ring600together block the undesirable flow of mold compound1006onto the sensor200.FIG.10shows the film1004covering most or all of the bottom surface of the top member1000, but in examples, the film1004is smaller so as to cover that portion of the bottom surface of the top member1000that aligns with the ring600. In yet other examples, the film1004is shaped to match a shape of the ring600. By reducing the size of the film1004, the mold compound1006may flow more freely and the creation of irregularities may be avoided. Conversely, reducing the size of the film1004may cause alignment problems when the mold chase is closed, e.g., the film1004may not make proper contact with the top surface of the ring600.

After application of the mold compound1006, the resulting structure is decoupled from the remainder of the lead frame strip, thereby producing the structure shown inFIG.11A. In particular,FIG.11Ais a perspective view of a completed sensor package1100. The sensor200is in the sensor cavity800which is formed by the ring600in the mold compound1006. The sensor200and the inner surface of the sensor cavity800are thus exposed to an exterior environment of the sensor package1100. In examples, a top surface of the ring600is flush or approximately flush (e.g., within 1 millimeter of) the top surface of the mold compound1006. Conductive terminals902are exposed to an exterior surface of the mold compound1006, as shown. In operation, the sensor200senses a physical property in the exterior environment of the sensor package1100. The sensor200sends analog signals to the AFE circuit on the semiconductor die102, which processes the analog signals from the sensor200and provides the processed signals to other circuitry either on the semiconductor die102or on a different semiconductor die for further processing and/or use.FIG.11Bis a top-down view of the structure ofFIG.11A.

FIG.12Ais a cross-sectional profile view of the sensor package1100. The height of the ring600may be reduced relative to the height shown inFIG.12Aby multiple techniques. As shown inFIG.12B, in some examples, a smaller mold chase may be used so that the overall thickness of the sensor package1100is decreased. By decreasing the thickness of the sensor package1100, the ring600may not be as tall as is the case inFIG.12A. As shown inFIG.12C, in some examples, a platform1200without electrical functionality (e.g., a “dummy” die) may be positioned between the semiconductor die102and the die pad900to elevate the semiconductor die102. The size of the mold chase is kept the same as that used for the sensor package1100ofFIG.12A. By elevating the semiconductor die102, the ring600may not be as tall as shown inFIG.12A.

FIG.13is a perspective view of the sensor package1100mounted on a printed circuit board (PCB)1300. Other circuits, semiconductor packages, etc. also may be mounted on the PCB1300, and the sensor package1100may communicate with such components. For example, the AFE circuit in the sensor package1100may communicate signals encoding sensed measurements of physical properties to other circuits on the PCB1300.

As explained above, sensor cavities formed using conventional techniques cannot be decreased in size to the degree suitable to fit multiple sensor cavities (and sensors) on a single sensor package, or to the degree suitable to decrease the size of a sensor package having a single sensor cavity (and sensor). However, the photolithography and plating techniques described above with respect toFIGS.2A-11Bare highly precise and enable the fabrication of sensor cavities that are substantially smaller than conventional sensor cavities. Accordingly, in examples, the sensor cavity800has a diameter range equivalent to the inner diameter range of the ring600and the cavity500, as described above. In contrast, conventionally-formed sensor cavities have substantially larger diameters ranging from 1 mm to 5 mm. Similarly, sensor cavities800having a rectangular shape may have a length range of 0.02 mm to 3 mm and a width range of 0.02 mm to 3 mm, and in contrast, conventionally-formed sensor cavities with rectangular shapes may have a length range of 1 mm to 5 mm and a width range of 1 mm to 5 mm.

Although the above-described photolithography and plating techniques are sufficiently precise to form sensor cavities800of relatively small size, other high-precision techniques also may be used to form small sensor cavities. In some examples, the photolithography and plating processes described above may be omitted, and rings fabricated separately (e.g., pre-fabricated rings) from the semiconductor die may be used instead.FIG.14depicts seven example pre-fabricated rings1400-1405, with each ring1400-1405having maximal physical dimensions matching the example dimensions given above for the ring600(whether circular/ovoid or rectangular) and/or cavity500(whether circular/ovoid or rectangular). The example rings1400-1405may be composed of metal (e.g., copper, nickel, aluminum, steel, metal alloys) or non-metal (e.g., ceramic, plastic, fiber) materials. In examples, the rings1400-1405may be punched or cut from a foil or a metal sheet. For instance, a sheet of metal (e.g., 30 gauge) may be punched or etched to form cavities, and the sheet may then be mounted to a saw tape on a flex frame. The flex frame may then be stretched and the sheet metal may be cut (e.g., using a diamond blade) into individual rings, which may then be mounted on top of the semiconductor die102.

The example ring1400has a rectangular shape with right-angle inner and outer corners1407,1408and an approximately uniform thickness. The example ring1401is similar to the rectangular ring1400with right-angle inner and outer corners1409,1410, but the ring1401includes a stairstep pattern on an outer surface of the ring1401. The stairstep pattern enables greater adhesive strength between the ring1401and the mold compound abutting the ring1401. The example ring1402has a rectangular shape with rounded outer corners1411and right-angle inner corners1412. The example ring1403has a circular shape with a vertical inner surface and a slanted outer surface. Like the stairstep pattern, the slanted outer surface enables greater adhesive strength between the ring1403and the mold compound abutting the ring1403. The example ring1404is similar to the ring1403except that it has a vertical outer surface instead of a slanted outer surface. The example ring1405has a circular shape similar to that of the ring1404, except that the ring1405has a stairstepped outer surface, as shown. The rings1400-1405are merely examples. The scope of this disclosure is not limited to the example rings1400-1405. Regardless of the shape of the ring used, the ring may be coupled to the semiconductor die102at any suitable time prior to application of the mold compound1006. For example, the ring may be positioned on the semiconductor die102prior to singulation of the semiconductor die102from the wafer100(e.g., using a gang-array technique to increase efficiency), after singulation (e.g., with the semiconductor die102positioned inside the mold chase), or at any other suitable time prior to application of the mold compound1006. In examples, the ring is coupled to the semiconductor die102using an adhesive, solder, epoxy, etc.

FIG.15is a flow diagram of a method1500that summarizes the techniques and process flows described above with respect toFIGS.2A-14. The method1500begins with providing a semiconductor die having a sensor (1502). The method1500includes positioning a ring encircling the sensor (1504). As explained in detail above, the ring may be positioned encircling the sensor using a photolithography and plating technique. As also explained above, the ring may be pre-fabricated and coupled to the semiconductor die and encircling the sensor using an adhesive. In either case, the precision of the technique used is superior to that used in conventional techniques to form sensor cavities, and thus the sizes of the resulting sensor cavities are significantly smaller than conventional sensor cavities. As a result, the various challenges described above are mitigated. The method1500comprises positioning the semiconductor die and the ring in a mold chase, with a film between the ring and a top member of the mold chase (1506). As explained, this film (e.g., film1004inFIG.10) mitigates forces transferred to the semiconductor die from the top member of the mold chase and via the ring. Further, this film prevents mold compound from flowing between the top of the ring and the top member of the mold chase and into the sensor cavity, thus protecting the sensor from being covered by the mold compound. The method1500includes covering the semiconductor die with a mold compound, with the ring (and, in examples, the film) precluding the mold compound from covering the sensor (1508).

The above description primarily relates to the formation of sensor cavities using rings (e.g., ring600), which results in the various benefits and advantages described above. However, other techniques for the formation of sensor cavities may be used in lieu of a ring. For example, a solid member (e.g., a stud) may be used to prevent mold compound from covering a sensor during the packaging process, thereby forming a sensor cavity in the mold compound of the sensor package. Various examples of techniques for the formation of sensor cavities using such solid members are now described in relation toFIGS.16A-35.

FIG.16Ais a perspective view of a semiconductor die1602having an active surface1608, which, in turn, has a sensor1606. The active surface1608also includes multiple bond pads1604.FIG.16Bis a top-down view of the structure ofFIG.16A.FIG.17Ais a perspective view of the semiconductor die1602having a seed layer1700deposited thereupon. In examples, the seed layer1700includes a metal such as titanium, titanium tungsten, etc.FIG.17Bis a top-down view of the structure ofFIG.17A.FIG.18Ais a perspective view of the semiconductor die1602with the seed layer1700and a photoresist layer1800on the seed layer1700. The description provided above for the plating seed layer300applies to the seed layer1700, and the description provided above for the photoresist layer400applies to the photoresist layer1800.FIG.18Bis a top-down view of the structure ofFIG.18A.FIG.19Ais a perspective view of the structure ofFIG.18A, except with a sensor cavity1900formed in the photoresist layer1800such that the seed layer1700is exposed through the sensor cavity1900. In examples, an appropriately-patterned mask is used to expose the area of the photoresist layer1800corresponding to the sensor cavity1900, and this area of the photoresist layer1800is subsequently exposed to form the sensor cavity1900. In examples, the sensor cavity1900is formed above the sensor1606. In examples, the sensor cavity1900and the semiconductor die1602have a combined thickness (or depth) approximately equivalent to that of the mold chase used to apply a mold compound to the structure ofFIG.19A. In examples, the sensor cavity1900and the semiconductor die1602have a combined thickness approximately equivalent to that of a target sensor package thickness. In examples, in a horizontal plane the sensor cavity1900is circular, and in other examples, the sensor cavity1900has an ovoid or rectangular shape. Other shapes are contemplated and included in the scope of this disclosure.

FIG.20Ais a perspective view of the structure ofFIG.19A, with a solid member2000having been plated (e.g., electroplated) in the sensor cavity1900using the seed layer1700. In examples, the solid member2000is composed of a metal such as copper, nickel, aluminum, etc. Because the solid member2000is plated within the sensor cavity1900, the solid member2000takes the form of the sensor cavity1900, having the same shape and size as the sensor cavity1900. In examples, the sensor cavity1900, and thus the solid member2000, has a diameter sufficiently large to cover all of the sensor1606. In examples, no dimension of the sensor cavity1900in the horizontal plane (e.g., diameter, length, or width) exceeds 0.90 mm, which is made possible due to the precise photolithography and plating processes described herein that are used to form the sensor cavity1900. In examples, the greatest distance between the sensor1606and the outer surface of the solid member2000is no more than 5 microns.FIG.20Bis a top-down view of the structure ofFIG.20A.

FIG.21Ais a perspective view of the structure ofFIG.20Awith the photoresist layer1800removed (e.g., stripped).FIG.21Bis a top-down view of the structure ofFIG.21A.FIG.22Ais a perspective view of the structure ofFIG.21A, except with the seed layer1700removed (e.g., chemically etched). However, the seed layer1700is not removed from under the solid member2000, as shown.FIG.22Bis a top-down view of the structure ofFIG.22A.

FIG.23Ais a perspective view of the structure ofFIG.22A, except with the semiconductor die1602mounted to a die pad2300of a lead frame in a lead frame strip, and the bond pads1604coupled to conductive terminals2302(e.g., leads) via bond wires2304, as shown.FIG.23Bis a top-down view of the structure ofFIG.23A.FIG.24is a cross-sectional profile view of a mold chase having a top member2404and a bottom member2402. The structure ofFIG.23Ais positioned inside the mold chase between the top member2404and the bottom member2402. A film2406, having physical properties and a composition similar to the film1004described above, is positioned between the top member2404and the solid member2000. For example, the film2406may be coupled to the bottom surface of the top member2404. The film2406may mitigate a force transferred from the top member2404to the semiconductor die1602via the solid member2000. In examples, the film2406may prevent a mold compound (e.g., mold compound2400) from covering a top surface of the solid member2000.FIG.25Ais a perspective view of the structure ofFIG.23Aafter the mold compound2400has been applied. As shown, the solid member2000is exposed and not covered by the mold compound2400. The structure ofFIG.25Ais considered to be a sensor package2500, with the solid member2000exposed to an exterior surface of the mold compound2400, as shown.FIG.25Bis a top-down view of the structure ofFIG.25A. The solid member2000may then be removed, for example by chemical etching, asFIG.26Adepicts. Removal of the solid member2000produces a sensor cavity1900in the mold compound2400through which the sensor1606is accessible and exposed to an exterior environment of the sensor package2500. In this way, the solid member2000has prevented mold compound (e.g., mold compound2400) from covering the sensor1606.FIG.26Bis a top-down view of the structure ofFIG.26A.

In some examples, the depth of the sensor cavity1900may be reduced using a variety of techniques. For instance, the size of the mold chase may be reduced, or a platform lacking electrical functionality may be used to raise the position of the semiconductor die (e.g., semiconductor die1602) in such a way that reduces the depth of the sensor cavity1900.FIG.27Ais a cross-sectional profile view of the sensor package2500. The depth of the sensor cavity1900may be reduced as shown inFIG.27B, in which the mold compound2400is applied using a smaller mold chase, thus reducing the overall thickness of the sensor package2500. In this way, the depth of the sensor cavity1900is reduced. InFIG.27C, a platform2600is provided to boost the height of the semiconductor die1602, thus reducing the depth of the sensor cavity1900. Other techniques also may be used to reduce the depth of the sensor cavity1900as desired.

FIG.28is a perspective view of the sensor package2500mounted on a PCB2700. Other circuitry also may be mounted on the PCB2700, and the sensor package2500may couple to other such circuitry as desired. In operation, the sensor1606senses a physical property and provides a signal to a circuit (e.g., an AFE circuit) in the sensor package2500that is configured to process the signal from the sensor1606. The circuit then outputs a signal to other circuitry either in the sensor package2500or on the PCB2700for further processing.

Because the sensor cavity1900is produced using highly precise photolithography and plating techniques, the sensor cavity1900may be substantially smaller in size than other, conventionally-produced sensor cavities. For example, no dimension of the sensor cavity1900in the horizontal plane (e.g., diameter, length, or width) exceeds 0.90 mm. Because the sensor cavity1900may be smaller in size than conventional sensor cavities, the sensor package2500may also be substantially smaller in size than conventional sensor packages. For the same reason, a sensor package2500may accommodate multiple sensor cavities (and sensors), while a conventional sensor package may only be able to accommodate a single sensor cavity (and sensor). Accordingly, the various advantages and benefits described above are realized by the sensor package2500and by other packages formed using the techniques described herein.

As explained above with respect toFIG.24, in some examples, a film2406is used to mitigate the transfer of force from the top member2404of the mold chase to the semiconductor die1602. In other examples, this transfer of force may be mitigated in other ways. For example, this transfer of force may be mitigated by introducing a gap between the top surface of the solid member2000and the bottom surface of the top member2404. However, mold compound may flow through this gap, thereby forming the structure shown inFIG.29A, in which a mold compound2800covers not only the semiconductor die1602but also the solid member2000.FIG.29Bis a see-through version ofFIG.29A, in which the solid member2000—which is fully covered by the mold compound2800—is visible. In such examples, the solid member2000may be removed by first grinding the mold compound2800until the solid member2000is exposed, asFIG.29Cshows. After the solid member2000is exposed, it may be removed, for example using a chemical etching technique (e.g., using diluted nitric acid).FIG.29Dshows the solid member2000having been removed. In this way, a sensor cavity1900is formed in the mold compound2800such that the sensor1606is exposed to an exterior environment of the sensor package2500.

The foregoing examples describe sensor packages having one sensor cavity. However, as explained, the techniques described herein facilitate the formation of sensor cavities that are significantly smaller than conventional sensor cavities. Accordingly, multiple sensor cavities may be formed in a single sensor package.FIG.30Ais a perspective view of a sensor package3000having sensor cavities2902,2904formed in a mold compound2900. A sensor2906is inside the sensor cavity2902, and a sensor2908is inside the sensor cavity2904.FIG.30Bshows a see-through view of the sensor package3000, with the sensors2906,2908positioned on an active surface2912of a semiconductor die2914. The sensors2906,2908and other circuitry on the active surface2912couple to the conductive terminals2910via bond pads2916and bond wires2918, as shown. Although two sensor cavities and sensors are shown inFIG.30B, any number of sensor cavities (and sensors) may be included in the sensor package3000.FIG.30Cshows the sensor package3000mounted on a PCB2920, which may also have other circuitry mounted thereupon, such as processing circuitry that receives signals from the sensors2906,2908, an AFE circuit that processes signals from the sensors2906,2908, etc. and processes the signals as desired.FIG.30Dis a schematic block diagram of the structure ofFIG.30C. Specifically,FIG.30Dshows the PCB2920on which the sensor package3000and processing circuitry2922are mounted. The sensor package3000couples to the processing circuitry2922. As explained above, the sensor package3000includes sensors2906,2908and an AFE circuit2924. The AFE circuit2924is configured to receive and process signals from the sensors2906,2908, and to output processed signals to the processing circuitry2922. The processing circuitry2922is configured to receive signals from the AFE circuit2924and to further process the signals as desired. In examples, the AFE circuit2924services multiple sensors, such as the sensors2906,2908. In contrast, conventional sensor packages include a single sensor and a single AFE circuit. By using one AFE circuit2924to process signals received from multiple sensors (e.g., sensors2906,2908), the space, time, and expense associated with using multiple AFE circuits is mitigated.

The above examples assume that the solid member2000is formed using a photolithography and plating process, which, as explained, is sufficiently precise so as to form relatively small solid members2000. However, other techniques also may be used to form the solid member2000. For example, the solid member2000may be formed separately from the semiconductor die and may subsequently be coupled to the semiconductor die using, e.g., adhesive.FIG.31depicts four example solid members that may be used in various examples. Each of the solid members depicted inFIG.31is representative of the solid member2000. For instance, a solid member3100is rectangular and has right-angle corners, as shown. A solid member3102is rectangular and has rounded corners, as shown. A solid member3104is circular and has an outer surface that is slanted in such a way that facilitates removal after a mold compound has been applied. A solid member3106is also circular and has a vertical outer surface. The scope of this disclosure is not limited to the particular examples shown inFIG.31. Various materials may be used to form the solid member2000, such as the example solid members shown inFIG.31. In examples, the solid member2000is metal (e.g., copper, nickel, aluminum, steel, metal alloy) and in other examples the solid member2000is non-metal (e.g., ceramic, plastic, fiber). In examples, the solid member2000may be coupled to the semiconductor die using an adhesive, solder, epoxy, etc. In examples, thermoplastic low-strength adhesives (e.g., in the range of 300 to 1000 g/sq. cm. peel strength) may be used to facilitate subsequent removal after the mold compound has been applied. In examples, the solid member2000is coupled to a semiconductor die (e.g., covering a sensor) at any suitable time prior to a mold compound being applied. For example, the solid member2000may be coupled to the semiconductor die before the semiconductor die is singulated from its wafer. In other examples, the solid member2000may be coupled to the semiconductor die post-singulation but prior to application of a mold compound. In examples, after the solid member2000has been coupled to a semiconductor die, the resulting structure may be placed inside a mold chase for application of a mold compound. In examples, a film (e.g., the film2606ofFIG.24) may be used to mitigate the transfer of force from a top member of the mold chase to the semiconductor die. In other examples, the film may be omitted and the resulting portion of mold compound on top of the solid member2000may be subjected to a grinding process so that the solid member2000may be exposed and removed, as described above.

In some examples, the solid member2000may include multiple portions. For example, the solid member2000may include a core portion composed of a metal or non-metal material and an outer portion, such as a metal, coupled to an outer surface of the core portion.FIG.32shows four such example solid members, each of which is representative of the solid member2000. For instance, an example solid member3200includes a rectangular core member3202having a metal plating3204coupled to an outer surface of the core member3202. The solid member3200has right-angle corners, as shown. An example solid member3206includes a rectangular core member3208having a metal plating3210coupled to an outer surface of the core member3208. The solid member3206has rounded corners, as shown. An example solid member3212includes a circular core member3214having a metal plating3216coupled to an outer surface of the core member3214. In examples, the metal plating3216has a slanted outer surface, as shown, which facilitates removal after a mold compound has been applied. An example solid member3218includes a circular core member3220having a metal plating3222coupled to an outer surface of the core member3220. In examples, the metal plating3222has a vertical outer surface, as shown. In examples, the core members are composed of a metal such as copper, nickel, aluminum, steel, or a metal alloy, or a non-metal such as ceramic, plastic, or fiber. In examples, any suitable plating metal may be used for the metal platings (e.g., metal platings3204,3210,3216,3222), such as titanium or titanium tungsten. Various other shapes, sizes, and materials are contemplated and included in the scope of this disclosure. The solid member2000(e.g., any of the solid members depicted inFIG.32) may be coupled to a semiconductor die using any suitable adhesive, epoxy, solder, etc. In examples, a thermoplastic low-strength adhesive (e.g., ethyl cyanoacrylate, diluted epoxies, etc.) may be used to facilitate subsequent removal after a mold compound has been applied.

After the solid member2000has been coupled to a semiconductor die, a mold compound may be applied as described above (e.g., as depicted inFIGS.23A-24). In examples, a film (e.g., film2606ofFIG.24) may be used during application of the mold compound, and in other examples, such a film may be omitted. If such a film is used, the solid member2000will not be covered by the mold compound. In such cases, the metal plating of the solid member2000(e.g., metal platings3204,3210,3216,3222inFIG.32) may be removed using a chemical etch, using heat (e.g., 260 degrees Celsius) to melt the metal plating, etc. After the metal plating has been removed, the core member (e.g., core members3202,3208,3214,3220inFIG.32) may be removed using gravity or by mechanically picking the core member out of the sensor cavity. The core member may be easily removed because, in at least some examples, it is coupled to the semiconductor die using a low-strength adhesive, as described above.FIG.33Ais a perspective view of a solid member2000abutting a mold compound3300in a sensor package3302, andFIG.33Bis a top-down view of the structure ofFIG.33A. The solid member2000incudes a core member3304and a metal plating3306, as described above. After application of an appropriate chemical etch, heat, etc. to remove the metal plating3306, the core member3304remains, asFIG.33Cshows. The core member3304is subsequently removed, leaving the completed sensor package3302asFIG.33Ddepicts.

Still other types of solid members2000are contemplated and included in the scope of this disclosure. In some examples, a solid member2000may be composed of a compressible material, such as polyimide, silicon gel foam, a spring, rubber, ceramic, plastic, fiber, etc. In examples, the compressible solid member2000has a compressibility that ranges from 20% to 50% of the uncompressed thickness of the solid member2000(e.g., if the solid member2000has an uncompressed thickness of 100 microns, it could be compressed by 20 microns to 50 microns, for a compressed thickness ranging from 50 microns to 80 microns). In examples, the solid member2000has a compressibility that ranges from 50% to 80% of the uncompressed thickness of the solid member2000. The lower end of this compressibility range is determined to maintain an approximately uniform thickness and smooth surface, while the upper end of this compressibility range is determined to provide a tight seal during molding and to compensate for non-coplanarities and non-uniform surfaces in the structures adjacent to the solid member2000. The compressible solid member2000will be compressed (e.g., reduce in thickness) as the mold chase is closed. However, a film, such as film1004or2606described above, may be omitted because the compressible solid member2000will maintain contact with the bottom surface of the top member of the mold chase as the mold chase is closed and after the mold chase is closed. In examples, the relationship between the thickness and the compressibility of the solid member2000is such that when the mold chase is closed, the solid member2000forms a seal with the bottom surface of the top member of the mold chase. For example, a thicker solid member2000may be used if the solid member2000has a greater compressibility, or a thinner solid member2000may be used if the solid member2000has a lower compressibility. In examples, the compressible solid member2000has a slanted outer surface that facilitates removal from the mold compound after the mold compound has been applied. Such a compressible solid member2000may be coupled to a semiconductor die, and specifically to a sensor of the semiconductor die, to protect the sensor from being covered by mold compound. In examples, the compressible solid member2000is coupled to the sensor of the semiconductor die using an adhesive, solder, epoxy, or any other suitable material.FIG.34Adepicts a perspective view of an example compressible solid member3400having a circular cross-section and a slanted outer surface3402;FIG.34Bdepicts a perspective view of an example compressible solid member3404having a circular cross-section and a non-slanted, vertical outer surface3406;FIG.34Cdepicts a perspective view of an example compressible solid member3408having a rectangular cross-section and a slanted outer surface3410;FIG.34Ddepicts a perspective view of an example compressible solid member3412having a rectangular cross-section and a non-slanted, vertical outer surface3414; andFIG.34Edepicts a profile view of a compressible solid member3416, which may be a spring. The various structures ofFIGS.34A-34Eare examples of compressible solid members2000. The spring compressible solid member3416ofFIG.34Emay be used if it is fully compressed so that no mold compound is able to flow through the solid member3416and onto the sensor on which the solid member3416is mounted. After the mold compound has been applied, the compressible solid member2000may be chemically removed (e.g., using a suitable etchant) or mechanically removed (e.g., using a pick). The adhesive used to couple the compressible solid member2000to the sensor of the semiconductor die may be removed (e.g., dissolved) using a suitable solvent, such as hydrochloric acid, sulfuric acid, isopropyl alcohol, toluene, xylene, etc. In the event that solder was used to couple the compressible solid member2000to the sensor of the semiconductor die, the solder may be reflowed and removed. In the event that an epoxy was used to couple the compressible solid member2000to the sensor of the semiconductor die, the epoxy may be removed using a suitable solvent, such as hydrochloric acid, sulfuric acid, isopropyl alcohol, toluene, xylene, etc.

In some examples, a solid member2000includes both a non-compressible component (e.g., metal) and a compressible component.FIG.35depicts a perspective view of an example solid member3500having a non-compressible component3502and a compressible component3504positioned on the non-compressible component3502. The non-compressible component3502may have any of the physical properties of the structures depicted in, e.g.,FIG.31, and the description of the structures ofFIG.31apply to the non-compressible component3502. The compressible component3504may have any of the physical properties of the structures depicted in, e.g.,FIGS.34A-34D, and the description of the structures ofFIGS.34A-34Dapply to the compressible component3504. The thicknesses of the non-compressible component3502and the compressible component3504may vary, so long as the total thickness of the solid member3500is such that the mold chase used to apply mold compound closes fully and such that the top surface of the compressible component3504makes contact with the bottom surface of the top member of the mold chase so that mold compound cannot enter a space therebetween. For a given thickness of the solid member3500, a relatively thicker non-compressible component3502results in a relatively thinner compressible component3504, and a relatively thinner non-compressible component3502results in a relatively thicker compressible component3504. A solid member3500having a thinner compressible component3504and a thicker non-compressible component3502may be advantageous when a deeper cavity is being used, and a solid member3500having a thicker compressible component3504and a thinner non-compressible component3502may be advantageous when a shallower cavity is being used. In examples, the compressible component3504constitutes at least 75% of the thickness of the solid member3500, and in other examples, the non-compressible component3502constitutes at least 75% of the thickness of the solid member3500. A thicker compressible component3504relative to the non-compressible component3502may be beneficial to better tolerate process variations, while a thicker non-compressible component3502relative to the compressible component3504may beneficial to produce consistency in cavity shapes and sizes. The non-compressible component3502may be coupled to a sensor of a semiconductor die using a thermoplastic low-strength adhesive (e.g., in the range of 300 to 1000 g/sq. cm. peel strength). As explained above, one benefit to using such an adhesive is that the solid member3500may be easily removed (e.g., using a pick) after a mold compound is applied. In examples, the compressible component3504couples to the non-compressible component3502using ethyl cyanoacrylate, diluted epoxies, etc., although other materials also may be used. The example solid member3500may be useful at least because the compressible component3504obviates the use of a film (e.g., film1004or2606, described above) for the reasons described above with respect to the compressible solid members shown inFIGS.34A-34E, and because the non-compressible component3502facilitates the use of a thermoplastic low-strength adhesive (e.g., in the range of 300 to 1000 g/sq. cm. peel strength) for easy subsequent removal after a mold compound is applied. In examples, after application of the mold compound, a suitable chemical(s) (e.g., using a suitable etchant) may be used to remove both the compressible component3504and the non-compressible component3502. One or both of the compressible and non-compressible component may be removed mechanically (e.g., using a pick). An adhesive or other material used to couple the non-compressible component3502to the sensor of the semiconductor die may be removed (e.g., dissolved) using, e.g., a solvent or other suitable material. As shown inFIG.35, the outer surface of the solid member3500may be slanted. Alternatively, as solid member3506shows, the outer surface may be non-slanted (vertical). The solid members3500and3506have circular cross-sections. However, in examples, solid members3508,3510may have rectangular cross-sections, with the solid member3508including a slanted outer surface and the solid member3510including a non-slanted (vertical) outer surface. The solid members3500,3506,3508, and3510are examples of a solid member2000.

In examples, the solid member2000may have physical properties similar to those provided above for the example structures ofFIG.31, except that the solid member2000may be composed of material with a high coefficient of thermal expansion (CTE), such as plasticized polyvinyl chloride (PVC), polytetrafluorotheylene (PTFE), polyvinylidene fluoride (PVDF), aluminum, etc. In examples, the high-CTE solid member2000has a CTE ranging from 40 PPM to 200 PPM. In examples, the high-CTE solid member2000is cut or punched from a foil, although any and all techniques for forming such solid members2000are contemplated. In examples, the outer surfaces of the high-CTE solid members2000are slanted for easy removal after mold compound has been applied, and in other examples, the outer surfaces of the high-CTE solid members2000are non-slanted (vertical). In examples, the high-CTE solid member2000is coupled to a sensor of a semiconductor die using a suitable adhesive, solder, epoxy, thermoplastic low-strength adhesive (e.g., in the range of 300 to 1000 g/sq. cm. peel strength, etc.). In examples, after the high-CTE solid member2000is coupled to the sensor, a mold compound is applied at high temperature (e.g., 150-200 degrees Celsius). A film, such as film1004or2606, may be positioned between the top surface of the high-CTE solid member2000and a bottom surface of a top member of the mold chase used to apply the mold compound, for example as shown inFIGS.10and24. After the mold compound has been applied, the high-CTE solid member2000is frozen (e.g., at 0 degrees Celsius or lower, depending on the composition of the high-CTE solid member2000), thus reducing the size of the high-CTE solid member2000. The high-CTE solid member2000may then be easily removed using either gravity or a mechanical pick tool. An insufficiently high CTE for the solid member2000will result in the high-CTE solid member2000being stuck in the mold compound or being difficult to remove from the mold compound. Conversely, an excessively high CTE for the solid member2000may result in excessive expansion during the aforementioned high-temperature mold compound application, resulting in a cavity in the mold compound after removal of the high-CTE solid member2000that may be unacceptably large. The adhesive or other material used to couple the high-CTE solid member2000to the sensor may be removed (e.g., dissolved) using a suitable solvent or any other suitable agent.

FIG.36is a flow diagram of a method3600that summarizes the techniques and process flows described above with respect toFIGS.16A-35. The method3600begins with providing a semiconductor die having a sensor (3602). The method3600includes covering the sensor with a solid member, with the solid member mechanically coupled to the sensor (3604). The method3600includes positioning the semiconductor die and the solid member in a mold chase (3606). The method3600includes covering the semiconductor die with a mold compound, with the solid member precluding the mold compound from covering the sensor (3608). The method3600includes decoupling the solid member from the sensor, thereby forming a cavity in the mold compound (3610). The sensor is in the cavity (3610). At least some of the various examples of the solid members (e.g., solid members2000) described above may be re-used in a second application after removal from a first application.

Unless otherwise stated, “about,” “approximately,” or “substantially” preceding a value means+/−10 percent of the stated value. The above discussion is illustrative of the principles and various embodiments of the present disclosure. Numerous variations and modifications will become apparent to those skilled in the art once the above disclosure is fully appreciated. The following claims should be interpreted to embrace all such variations and modifications.