Wirebonding fixture and casting mold

The present disclosure involves a method and apparatus for attaching two electrical dies by wire bonding and then encasing the assembly in a protective casting that works by arranging two dies into a fixture conducive to wire bonding. Doped epoxy may be immediately dispensed over the assembly to form a near-net-shape protective cover, or Drive Can.

TECHNICAL FIELD

The present disclosure relates generally to intravascular ultrasound (IVUS) imaging, and in particular, to a wirebonding fixture and casting mold for an IVUS ultrasound transducer, such as a piezoelectric micromachined ultrasound transducer (PMUT), used for IVUS imaging.

BACKGROUND

Intravascular ultrasound (IVUS) imaging is widely used in interventional cardiology as a diagnostic tool for assessing a vessel, such as an artery, within the human body to determine the need for treatment, to guide intervention, and/or to assess its effectiveness. An IVUS imaging system uses ultrasound echoes to form a cross-sectional image of the vessel of interest. Typically, IVUS imaging uses a transducer on an IVUS catheter that both emits ultrasound signals (waves) and receives the reflected ultrasound signals. The emitted ultrasound signals (often referred to as ultrasound pulses) pass easily through most tissues and blood, but they are partially reflected by discontinuities arising from tissue structures (such as the various layers of the vessel wall), red blood cells, and other features of interest. The IVUS imaging system, which is connected to the IVUS catheter by way of a patient interface module, processes the received ultrasound signals (often referred to as ultrasound echoes) to produce a cross-sectional image of the vessel where the IVUS catheter is located.

IVUS catheters typically employ one or more transducers to transmit ultrasound signals and receive reflected ultrasound signals. However, conventional catheters may create a separate wire-die sub assembly that is then placed into a stainless steel shell (also referred to as a can) and then epoxied with a specially doped epoxy. This shell or can is shaped to prevent acoustic echo off of the metal can. Preventing separation of the transducer from the can is important. However, this is not always achieved by conventional techniques.

Therefore, while conventional methods of producing and assembling transducers are generally adequate for their intended purposes, they have not been entirely satisfactory in every aspect.

SUMMARY

The present disclosure provides a method and apparatus for attaching two electrical dies by wire bonding and then encasing the assembly in a protective casting that works by arranging two dies into a fixture conducive to wire bonding. Doped epoxy may be immediately dispensed over the assembly to form a near-net-shape protective cover, or Drive Can.

DETAILED DESCRIPTION

For the purposes of promoting an understanding of the principles of the present disclosure, reference will now be made to the embodiments illustrated in the drawings, and specific language will be used to describe the same. It is nevertheless understood that no limitation to the scope of the disclosure is intended. Any alterations and further modifications to the described devices, systems, and methods, and any further application of the principles of the present disclosure are fully contemplated and included within the present disclosure as would normally occur to one skilled in the art to which the disclosure relates. For example, the present disclosure provides an ultrasound imaging system described in terms of cardiovascular imaging, however, it is understood that such description is not intended to be limited to this application. In some embodiments, the ultrasound imaging system includes an intravascular imaging system. The imaging system is equally well suited to any application requiring imaging within a small cavity. In particular, it is fully contemplated that the features, components, and/or steps described with respect to one embodiment may be combined with the features, components, and/or steps described with respect to other embodiments of the present disclosure. For the sake of brevity, however, the numerous iterations of these combinations will not be described separately.

There are primarily two types of catheters in common use today: solid-state and rotational. An exemplary solid-state catheter uses an array of transducers (typically 64) distributed around a circumference of the catheter and connected to an electronic multiplexer circuit. The multiplexer circuit selects transducers from the array for transmitting ultrasound signals and receiving reflected ultrasound signals. By stepping through a sequence of transmit-receive transducer pairs, the solid-state catheter can synthesize the effect of a mechanically scanned transducer element, but without moving parts. Since there is no rotating mechanical element, the transducer array can be placed in direct contact with blood and vessel tissue with minimal risk of vessel trauma, and the solid-state scanner can be wired directly to the imaging system with a simple electrical cable and a standard detachable electrical connector.

An exemplary rotational catheter includes a single transducer located at a tip of a flexible driveshaft that spins inside a sheath inserted into the vessel of interest. The transducer is typically oriented such that the ultrasound signals propagate generally perpendicular to an axis of the catheter. In the typical rotational catheter, a fluid-filled (e.g., saline-filled) sheath protects the vessel tissue from the spinning transducer and driveshaft while permitting ultrasound signals to freely propagate from the transducer into the tissue and back. As the driveshaft rotates (for example, at 30 revolutions per second), the transducer is periodically excited with a high voltage pulse to emit a short burst of ultrasound. The ultrasound signals are emitted from the transducer, through the fluid-filled sheath and sheath wall, in a direction generally perpendicular to an axis of rotation of the driveshaft. The same transducer then listens for returning ultrasound signals reflected from various tissue structures, and the imaging system assembles a two dimensional image of the vessel cross-section from a sequence of several hundred of these ultrasound pulse/echo acquisition sequences occurring during a single revolution of the transducer.

FIG. 1is a schematic illustration of an ultrasound imaging system100according to various aspects of the present disclosure. In some embodiments, the ultrasound imaging system100includes an intravascular ultrasound imaging system (IVUS). The IVUS imaging system100includes an IVUS catheter102coupled by a patient interface module (PIM)104to an IVUS control system106. The control system106is coupled to a monitor108that displays an IVUS image (such as an image generated by the IVUS system100).

In some embodiments, the IVUS catheter102is a rotational IVUS catheter, which may be similar to a Revolution® Rotational IVUS Imaging Catheter available from Volcano Corporation and/or rotational IVUS catheters disclosed in U.S. Pat. No. 5,243,988 and U.S. Pat. No. 5,546,948, both of which are incorporated herein by reference in their entirety. The catheter102includes an elongated, flexible catheter sheath110(having a proximal end portion114and a distal end portion116) shaped and configured for insertion into a lumen of a blood vessel (not shown). A longitudinal axis LA of the catheter102extends between the proximal end portion114and the distal end portion116. The catheter102is flexible such that it can adapt to the curvature of the blood vessel during use. In that regard, the curved configuration illustrated inFIG. 1is for exemplary purposes and in no way limits the manner in which the catheter102may curve in other embodiments. Generally, the catheter102may be configured to take on any desired straight or arcuate profile when in use.

A rotating imaging core112extends within the sheath110. The imaging core112has a proximal end portion118disposed within the proximal end portion114of the sheath110and a distal end portion120disposed within the distal end portion116of the sheath110. The distal end portion116of the sheath110and the distal end portion120of the imaging core112are inserted into the vessel of interest during operation of the IVUS imaging system100. The usable length of the catheter102(for example, the portion that can be inserted into a patient, specifically the vessel of interest) can be any suitable length and can be varied depending upon the application. The proximal end portion114of the sheath110and the proximal end portion118of the imaging core112are connected to the interface module104. The proximal end portions114,118are fitted with a catheter hub124that is removably connected to the interface module104. The catheter hub124facilitates and supports a rotational interface that provides electrical and mechanical coupling between the catheter102and the interface module104.

The distal end portion120of the imaging core112includes a transducer assembly122. The transducer assembly122is configured to be rotated (either by use of a motor or other rotary devices or methods) to obtain images of the vessel. The transducer assembly122can be of any suitable type for visualizing a vessel and, in particular, a stenosis in a vessel. In the depicted embodiment, the transducer assembly122includes a piezoelectric micromachined ultrasonic transducer (“PMUT”) transducer and associated circuitry, such as an application-specific integrated circuit (ASIC). An exemplary PMUT used in IVUS catheters may include a polymer piezoelectric membrane, such as that disclosed in U.S. Pat. No. 6,641,540, hereby incorporated by reference in its entirety. The PMUT transducer can provide greater than 75% bandwidth for optimum resolution in a radial direction, and a spherically-focused aperture for optimum azimuthal and elevation resolution.

The transducer assembly122may also include a housing having the PMUT transducer and associated circuitry disposed therein, where the housing has an opening that ultrasound signals generated by the PMUT transducer travel through. Alternatively, the transducer assembly122includes a capacitive micromachined ultrasonic transducer (“CMUT”). In yet another alternative embodiment, the transducer assembly122includes an ultrasound transducer array (for example, arrays having 16, 32, 64, or 128 elements are utilized in some embodiments).

The rotation of the imaging core112within the sheath110is controlled by the interface module104, which provides user interface controls that can be manipulated by a user. The interface module104can receive, analyze, and/or display information received through the imaging core112. It will be appreciated that any suitable functionality, controls, information processing and analysis, and display can be incorporated into the interface module104. In an example, the interface module104receives data corresponding to ultrasound signals (echoes) detected by the imaging core112and forwards the received echo data to the control system106. In an example, the interface module104performs preliminary processing of the echo data prior to transmitting the echo data to the control system106. The interface module104may perform amplification, filtering, and/or aggregating of the echo data. The interface module104can also supply high- and low-voltage DC power to support operation of the catheter102including the circuitry within the transducer assembly122.

In some embodiments, wires associated with the IVUS imaging system100extend from the control system106to the interface module104such that signals from the control system106can be communicated to the interface module104and/or vice versa. In some embodiments, the control system106communicates wirelessly with the interface module104. Similarly, it is understood that, in some embodiments, wires associated with the IVUS imaging system100extend from the control system106to the monitor108such that signals from the control system106can be communicated to the monitor108and/or vice versa. In some embodiments, the control system106communicates wirelessly with the monitor108.

An ultrasound transducer can be included in the IVUS imaging system100, for example in the transducer assembly122. The ultrasonic transducer has a small size and achieves a high resolution, so that it is well suited for intravascular imaging. In some embodiments, the ultrasonic transducer has a size on the order of tens or hundreds of microns, can operate in a frequency range between about 1 mega-Hertz (MHz) to about 135 MHz, and can provide sub 50 micron resolution while providing depth penetration of at least 10 millimeters (mm) Furthermore, the ultrasonic transducer is also shaped in a manner to allow a developer to define a target focus area based on a deflection depth of a transducer aperture, thereby generating an image that is useful for defining vessel morphology, beyond the surface characteristics. The various aspects of the ultrasound transducer and its fabrication are discussed in greater detail below.

In certain embodiments, the ultrasound transducer is a piezoelectric micromachined ultrasound transducer (PMUT). In other embodiments, the transducer may include an alternative type of transducer. Additional features can be added in the ultrasound transducer, and some of the features described below can be replaced or eliminated for additional embodiments of the ultrasound transducer. For additional details of fabricating such ultrasonic transducer, refer to U.S. Provisional Application 61/745,212, titled “Methods and Apparatus for Focusing Miniature Ultrasound Transducers” to Dylan Van Hoven, filed on Dec. 21, 2012, Provisional U.S. Patent Application 61/745,091 to Dylan Van Hoven, filed on December 21, entitled “Preparation and Application of a Piezoelectric Film for an Ultrasound Transducer”, and Provisional U.S. Patent Application No. 61/646,080 titled “DEVICE AND SYSTEM FOR IMAGING AND BLOOD FLOW VELOCITY MEASUREMENT” filed on May 11, 2012, Provisional U.S. Patent Application No. 61/646,074 titled “ULTRASOUND CATHETER FOR IMAGING AND BLOOD FLOW MEASUREMENT” filed on May 11, 2012, and Provisional U.S. Patent Application No. 61/646,062 titled “Circuit Architectures and Electrical Interfaces for Rotational Intravascular Ultrasound (IVUS) Devices” filed on May 11, 2012, the contents of each of which are hereby incorporated by reference in their entirety.

Traditionally, the ultrasound transducer is located on a wire-die sub assembly, which means that the electrical and mechanical systems are separate sub-assemblies. This leads to problems such as interconnection reliability, higher costs, more complicated fabrication steps, and inflexible configurability.

According to the various aspects of the present disclosure, provided is a method for attaching two electrical dies by wire bonding and then encasing the assembly in a protective casting that works by arranging two dies into a fixture conducive to wire bonding, but also such that doped epoxy may be immediately dispensed over the assembly to form a near-net-shape protective cover, also known as the Drive Can. By doing so, the present disclosure offers numerous advantages over the prior art. Some of these advantages include:Mechanical and electrical protection of the ASIC and MEMS interconnection during transport and assembly.Eliminate stainless steel can component cost.Integrated assembly reduces steps and variation during assembly.Allows for both flat and angled transducer arrangements.Can be performed at room temperature.

The method steps of the present disclosure are now discussed in more detail in view ofFIGS. 2-9, which contain illustrations of the can and wire bonding mixture and casting mold (thereafter referred to as either a bonding apparatus or a bonding fixture). The bonding apparatus may be used to perform wire bonding and molding of a transducer assembly.

FIG. 2is a diagrammatic perspective illustration of the bonding apparatus100. In the illustrated embodiment, the bonding apparatus100includes a bonding plate110, molding plates120-121, and a bottom plate130. The bonding plate110or the molding plates120-121may be positioned over and against the bottom plate130at different stages of fabricating a transducer assembly according to various aspects of the present disclosure.

Referring now toFIG. 3, the bonding plate110is positioned over and against the bottom plate130in a cross-sectional view in a wire bonding stage of fabrication. The molding plates120-121are not needed in this stage of fabrication and are thus not shown inFIG. 3. The bonding plate110includes a plurality of recesses or openings140(also shown in the perspective view ofFIG. 2). In the illustrated embodiment, each recess140has a sloped profile, that is, a wider opening at the top and a narrower opening at the bottom.

The bottom plate130contains a cavity150. The cavity150is shaped as a bottom portion of a transducer assembly. In other words, the cavity150partially defines the geometry and shape of the transducer assembly to be formed later. The cavity150of the bottom plate130also includes a pocket160and a pocket161. The pocket160is configured to accommodate a Piezoelectric Micromachined Ultrasound Transducer (PMUT) die170, and the pocket161is configured to accommodate an Application Specific Integrated Circuit (ASIC) die171. The PMUT is described in detail in U.S. Provisional Application 61/745,212, titled “Methods and Apparatus for Focusing Miniature Ultrasound Transducers” to Dylan Van Hoven, filed on Dec. 21, 2012, Provisional U.S. Patent Application 61/745,091 to Dylan Van Hoven, filed on December 21, entitled “Preparation and Application of a Piezoelectric Film for an Ultrasound Transducer”, and Provisional U.S. Patent Application No. 61/646,080 titled “DEVICE AND SYSTEM FOR IMAGING AND BLOOD FLOW VELOCITY MEASUREMENT” filed on May 11, 2012, Provisional U.S. Patent Application No. 61/646,074 titled “ULTRASOUND CATHETER FOR IMAGING AND BLOOD FLOW MEASUREMENT” filed on May 11, 2012, and Provisional U.S. Patent Application No. 61/646,062 titled “Circuit Architectures and Electrical Interfaces for Rotational Intravascular Ultrasound (IVUS) Devices” filed on May 11, 2012, the contents of each of which are hereby incorporated by reference in their entirety. The ASIC die171may include a plurality of conductive terminals and electrical circuitry configured to control the operation of the PMUT.

When the bonding plate110is pressed against and secured to the bottom plate130(for example by a fastening mechanism), the PMUT die170and the ASIC die171would be trapped in a fixed position in their respective pockets160and161. The recess140of the bonding plate110exposes a portion of the PMUT die170and a portion of the ASIC die171(or portions of the pockets160-161when they are empty). As such, a conductive element180may be attached to both the PMUT die170and the ASIC die171. In this manner, the PMUT die170and the ASIC die171may be electrically coupled together by the conductive element180. In the illustrated embodiment, the conductive element180is a bond wire. A commercially available wire bonder can be used to electrically attach the dies. Thus, the fabrication stage shown inFIG. 3may be referred to as a wire bonding mode. It is understood that other conductive elements may be used to implement the conductive element180in alternative embodiments.

A thin protective coating190is applied over the bond wire (i.e., the conductive element180as illustrated herein) to protect the bond wire from later processes, so that the bond wire does not become dislodged. The bonding plate110may then be removed. For reasons of simplicity,FIG. 3illustrates only a single recess140and a conductive element180being bonded to a respective PMUT die170and a respective ASIC die171. However, it is understood that a plurality of conductive elements may be bonded to a plurality of respective PMUT and ASIC dies simultaneously in this stage of fabrication, since the bonding plate110includes a plurality of recesses140(e.g., as shown inFIG. 2).

FIG. 4illustrates a cross-sectional view of the molding plates120-121being positioned over and against the bottom plate130after the removal of the bonding plate110. This occurs in a molding stage of the transducer assembly fabrication. As is shown inFIG. 4, the molding plate120is positioned over and against the molding plate121, and the molding plate121is positioned over and against the bottom plate130. The molding plates120-121may be secured to the bottom plate130by a fastening mechanism. The molding plate121includes a cavity200. The cavity200is shaped as a top portion of the transducer assembly. The cavity200is aligned with the cavity150of the bottom plate130. Thus, the cavities150and200collectively define the geometry and shape of the transducer assembly to be formed later. As shown inFIG. 4, portions150A and200A of the cavities150and200also collectively define a curved tip of the transducer assembly. In other words, the tip of the transducer assembly to be formed will have a curved or rounded tip.

The molding plate120includes an opening210, and the molding plate121includes an opening211. The openings210-211are vertically aligned with each other, although the opening211is narrower than the opening210in the illustrated embodiment. The opening211is also coupled to the cavity200. In other words, the opening211and the cavity200are in fluid communication with one another. The molding plate121also includes a vent gap220that is coupled to the cavity200and in fluid communication with the cavity200.

Epoxy (or another suitable fluid) may be injected to the cavities150and200through the openings210-211. In other words, the epoxy material may flow through the openings210,211, and into the cavities150and200, until the cavities150and200are filled. The vent gap220may aid the flow of the epoxy material, for example through a suction force in some embodiments. The injection path is illustrated via the arrows shown inFIG. 4.

The molding plate121also includes an opening240that exposes a portion of the pocket that holds the ASIC die171, as well as an opening241that exposes a portion of the pocket that holds the PMUT die170. These openings240-241are filled by shut-off pins250-251during the epoxy injection. The shut-off pins250-251respectively make physical contact with the top surfaces of the ASIC die171and the PMUT die170such that the surfaces of the ASIC die171and the PMUT die170are not exposed to the epoxy during the epoxy injection. A perspective view of the shut-off pins250-251is illustrated inFIG. 5.

The epoxy filling the cavities150and200is then allowed to cure at a high temperature. In some embodiments, the epoxy is cured in an oven at a temperature that is around 0 degrees Celsius for about 2 to 8 hours. The cured epoxy, along with the PMUT die170and the ASIC die171collectively form a transducer assembly300(shown inFIG. 5), which is also referred to as a cast can. The PMUT die170and the ASIC die171are partially encapsulated or surrounded enclosed by the cured epoxy, which forms a packaging of the transducer assembly. The conductive element (e.g., the bond wire)180(shown inFIG. 3) is also encapsulated by the cured epoxy. The packaging material (i.e., the cured epoxy) has a substantially uniform material composition throughout. The packaging material also supports the PMUT die170and the ASIC die171in a fixed position relative to each other. The packaging material also defines an outer surface of the ultrasound transducer assembly.

The bottom plate130also includes openings270and271that are coupled to the cavity150. Ejector pins280-281(also shown inFIG. 5) are inserted into the openings270-271, respectively. After the curing of the epoxy, the molding plates120-121are carefully removed. The ejector pins280-281may then be used to remove the transducer assembly300, as shown inFIG. 5.

FIGS. 6-8illustrate various cross-sectional and perspective views of the transducer assembly300, the outer shell or surface of which is defined by the packaging material formed by the cured epoxy. As discussed above, the transducer assembly300includes a rounded or curved tip300A. The curved tip300A is located proximate to the PMUT die170. In some embodiments, the curved tip300A has a spherical shape. The transducer assembly300also includes recesses310-311. The recess310exposes a portion of the ASIC die171, and the recess311exposes a portion of the PMUT die170. As discussed above, the recesses310-311are formed by the shut-off pins250-251occupying the openings240-241and coming into physical contact with (and thereby protecting) the ASIC die171and the PMUT die170during the epoxy injection and curing process.

The ASIC die171includes conductive terminals320(shown inFIG. 8, and also referred to as conductive pads) that are exposed by the recess310. Referring now toFIG. 9, wires350may be welded to the ASIC die171, for example through the conductive terminals320. A paralyne coater370may then be coated around the transducer assembly300. The coating may be done in a conformal manner. A drive cable380is then glued to the base of the transducer assembly300. In some embodiments, the wires350may also be attached to the ASIC die171if a shut-off area over the conductive terminals320is not required. In certain alternative embodiments in which the wires350are already attached to the ASIC die171, the drive cable380may also be over-molded by the epoxy in the injection molding process.

Among other things, at least the following elements of the present disclosure are believed to be novel:1. Casting a doped epoxy can over a wire-bonded assembly.2. Casting a doped epoxy can over an angled wire-bonded assembly.3. Using shut-off pins to protect the transducer surface and cable attachment pads.4. Using high lubricity plating on the tool to insure easy ejection.5. Using ejector pins to separate the case part from the tool.6. Using a distal vent to draw epoxy into the tool. (A vacuum may be applied.)7. Conformal coating the cast epoxy can.8. Attaching the cast can to a Drive Cable.

FIG. 10is a flowchart of a method500of fabricating an ultrasound transducer assembly. The method500includes a step510of loading a Piezoelectric Micromachined Ultrasound Transducer (PMUT) die and an Application Specific Integrated Circuit (ASIC) die in a first pocket and a second pocket of a first cavity of a bottom plate. The method500includes a step520of positioning a bonding plate over and against the bottom plate in a manner such that the PMUT die and the ASIC die are held in a fixed position. The bonding plate includes a recess that exposes portions of the PMUT die and the ASIC die. The method500includes a step530of placing a conductive element in the recess. The conductive element electrically interconnects the PMUT die and the ASIC die. The method500includes a step540of removing the bonding plate. The method500includes a step550of positioning a molding plate over and against the bottom plate in a manner such that a second cavity of the molding plate is aligned with the first cavity of the bottom plate. The first and second cavities collectively define a shape of the ultrasound transducer assembly. The method500includes a step560of injecting a packaging material into the first and second cavities through a first opening of the molding plate that is in fluid communication with the first and second cavities. The packaging material encapsulates the conductive element and at least partially encapsulating the PMUT die and the ASIC die therein. The method500includes a step570of curing the packaging material, thereby forming the ultrasound transducer assembly, wherein the cured packaging material defines an outer surface of the ultrasound transducer assembly.

In some embodiments, the packaging material comprises epoxy. In some embodiments, the molding plate includes a second opening that exposes a portion of the PMUT die when the molding plate is positioned against the bottom plate. The method500may further include a step of placing a shut-off pin in the second opening during the injecting so as to prevent the packaging material from coming into contact with a surface of the PMUT die. In some embodiments, the molding plate includes a third opening that exposes a portion of the ASIC die when the molding plate is positioned against the bottom plate. The method500may further include a step of placing a further shut-off pin in the third opening during the injecting so as to prevent the packaging material from coming into contact with a surface of the ASIC die. In some embodiments, the step530of placing the conductive element comprises wire-bonding the PMUT die and the ASIC die. In some embodiments, the method500further includes a step of applying a protective coating around the conductive element in the recess before the removing of the bonding plate. In some embodiments, the method500further includes the following steps: removing the transducer assembly; applying a paralyne coating around the transducer assembly; and attaching the transducer assembly to a drive cable.

One aspect of the present disclosure involves a bonding apparatus for bonding a plurality of electrical dies. The bonding apparatus includes: a bottom plate that includes a first cavity, wherein the first cavity includes a first pocket configured to accommodate a Piezoelectric Micromachined Ultrasound Transducer (PMUT) die and a second pocket configured to accommodate an Application Specific Integrated Circuit (ASIC) die; a bonding plate configured to be positioned over and against the bottom plate, the bonding plate including a recess, wherein when the bonding plate is positioned against the bottom plate: the PMUT die and the ASIC die would be trapped in a fixed position; and the recess exposes a portion of the first pocket and a portion of the second pocket; a molding plate configured to be positioned over and against the bottom plate, wherein the molding plate includes: a second cavity that is aligned with the first cavity when the molding plate is positioned against the bottom plate, such that the first and second cavities collectively define a shape of a transducer assembly; a first opening that is coupled to the second cavity, wherein the first opening exposes a portion of the first pocket when the molding plate is positioned against the bottom plate; a second opening that is coupled to the second cavity, wherein the second opening exposes a portion of the second pocket when the molding plate is positioned against the bottom plate; and a third opening that is in fluid communication with the first and second cavities such that a fluid can flow into the first and second cavities through the third opening.

In some embodiments, the bonding apparatus further includes a first shut-off pin configured to be positioned inside the first opening of the molding plate such that, when the molding plate is positioned against the bottom plate, the first shut-off pin makes physical contact with an upper surface of the PMUT die.

In some embodiments, the bonding apparatus further includes a second shut-off pin configured to be positioned inside the second opening of the molding plate such that, when the molding plate is positioned against the bottom plate, the second shut-off pin makes physical contact with an upper surface of the ASIC die.

In some embodiment, the molding plate further includes a vent gap that is in fluid communication with the second cavity.

In some embodiments, the molding plate is a first molding plate, and further comprising a second molding plate that is configured to be positioned over and against the first molding plate, wherein the second molding plate includes a fourth opening that is in fluid communication with the third opening.

In some embodiments, the transducer assembly has a curved tip.

In some embodiments, the curved tip is located proximate to the PMUT die and has a spherical shape.

In some embodiments, the recess of the bonding plate is configured to allow for an electrical connection between the PMUT die and the ASIC die.

In some embodiments, the electrical connection comprises a bond wire.

Another aspect of the present disclosure involves an ultrasound transducer assembly. The ultrasound transducer assembly includes: a Piezoelectric Micromachined Ultrasound Transducer (PMUT) die that includes a PMUT device; an Application Specific Integrated Circuit (ASIC) die that is physically separated from the PMUT die, the ASIC die including a plurality of conductive terminals; a conductive element that electrically couples the PMUT die and the ASIC die together; a packaging material that encapsulates the conductive element and partially encapsulates the PMUT die and the ASIC die therein, wherein the packaging material has a substantially uniform material composition throughout and includes a first opening that exposes a surface of the PMUT device, and wherein the packaging material supports the PMUT die and the ASIC die in a fixed position relative to each other and defines an outer surface of the ultrasound transducer assembly.

In some embodiments, the packaging material is epoxy.

In some embodiments, the conductive element comprises a bond wire.

In some embodiments, the ultrasound transducer assembly of claim further includes a protective layer coated around the bond wire.

In some embodiments, the ultrasound transducer assembly further includes a layer conformally coated around the packaging material.

In some embodiments, the layer contains paralyne.

In some embodiments, the ultrasound transducer assembly further includes wires attached to a drive cable, wherein the wires are electrically coupled to the ASIC die.

In some embodiments, the packaging material includes a second opening that at least partially exposes the conductive terminals.

In some embodiments, the packaging material has a rounded tip near the PMUT die.

Another aspect of the present disclosure involves a method of fabricating an ultrasound transducer assembly. The method includes: loading a Piezoelectric Micromachined Ultrasound Transducer (PMUT) die and an Application Specific Integrated Circuit (ASIC) die in a first pocket and a second pocket of a first cavity of a bottom plate; positioning a bonding plate over and against the bottom plate in a manner such that the PMUT die and the ASIC die are held in a fixed position, wherein the bonding plate includes a recess that exposes portions of the PMUT die and the ASIC die; placing a conductive element in the recess, the conductive element electrically interconnecting the PMUT die and the ASIC die; thereafter removing the bonding plate; positioning a molding plate over and against the bottom plate in a manner such that a second cavity of the molding plate is aligned with the first cavity of the bottom plate, wherein the first and second cavities collectively define a shape of the ultrasound transducer assembly; injecting a packaging material into the first and second cavities through a first opening of the molding plate that is in fluid communication with the first and second cavities, the packaging material encapsulating the conductive element and at least partially encapsulating the PMUT die and the ASIC die therein; and curing the packaging material, thereby forming the ultrasound transducer assembly, wherein the cured packaging material defines an outer surface of the ultrasound transducer assembly.

In some embodiments, the packaging material comprises epoxy.

In some embodiments, the molding plate includes a second opening that exposes a portion of the PMUT die when the molding plate is positioned against the bottom plate, and further comprising: placing a shut-off pin in the second opening during the injecting so as to prevent the packaging material from coming into contact with a surface of the PMUT die.

In some embodiments, the molding plate includes a third opening that exposes a portion of the ASIC die when the molding plate is positioned against the bottom plate, and further comprising: placing a further shut-off pin in the third opening during the injecting so as to prevent the packaging material from coming into contact with a surface of the ASIC die.

In some embodiments, the step of placing the conductive element comprises wire-bonding the PMUT die and the ASIC die.

In some embodiments, the method further includes a step of applying a protective coating around the conductive element in the recess before the removing of the bonding plate.

In some embodiments, the method further includes the following steps: removing the transducer assembly; applying a paralyne coating around the transducer assembly; and attaching the transducer assembly to a drive cable.