Patent Application
20110254111
Small acoustic devices, including acoustic transducers, are being employed in a number of applications, including gas flow detectors, and structural flaw detectors for buildings, bridges, pressure piping. In some applications, an acoustic transducer only transmits acoustic signals. In other applications, an acoustic transducer only receives acoustic signals. In still other applications, an acoustic transducer transmits acoustic signals and receives acoustic signals. Generally, acoustic transducers convert received electrical signals to acoustic signals when operating in a transmit mode, and/or convert received acoustic signals to electrical signals when operating in a receive mode. In particular, in many devices and applications, the acoustic signal that is transmitted and/or received is an ultrasonic signal.
Acoustic transducers are manufactured using a variety of different technologies, including piezoelectric ultrasonic transducers and microelectromechanical system (MEMS) transducers. In the past, acoustic transducers have been manufactured with processes where the acoustic transducer element is placed in a metal, ceramic, or plastic package and a lid is bonded to the package. In a typical configuration, an electrical signal produced by the acoustic transducer is provided through a lead or wire from the package to an external amplifier provided on an external circuit board to which the packaged acoustic transducer is attached or connected.
However, there is a continuing need for improved packages for acoustic devices to address specific requirements of various environments in which they are employed.
What is needed, therefore, is an acoustic device having a package that can provide beneficial characteristics for various environments where the packaged acoustic device is deployed.
In an example embodiment a device comprises: an electrically conductive lead frame having an aperture therethrough, the electrically conductive lead frame including a plurality of leads including at least one ground lead configured to be connected to an electrical ground; a semiconductor die including at least one acoustic transducer disposed above the aperture in the electrically conductive lead frame, the at least one acoustic transducer being configured to convert between acoustic energy and an electrical signal; an acoustic horn integrally connected to the lead frame, the horn extending from the lead frame and comprising a throat positioned adjacent to the acoustic transducer and a mouth opening at an opposite end of the acoustic horn from the throat; an electrically conductive and acoustically transmissive screen disposed over the mouth of the acoustic horn; and an electrically conductive lid configured together with the base portion of the housing to define a cavity, wherein the acoustic transducer is positioned within the cavity, and wherein the electrically conductive lid is directly connected to the ground lead.
In another example embodiment a device includes: a housing structure including having a base portion integrated with a plurality of electrically conductive leads including at least one ground lead, the housing structure including an aperture extending through a first side thereof; an electrically conductive lid configured together with the housing structure to define a cavity therein; and at least one acoustic transducer disposed within the cavity and disposed above the aperture in the housing structure, wherein the electrically conductive lid is directly connected to the ground lead.
In yet another example embodiment, a device comprises: a housing structure including having a base portion integrated with a plurality of electrically conductive leads including at least one ground lead, the housing structure including an aperture extending through a first side thereof; an electrically conductive lid configured together with the housing structure to define a cavity therein; and at least one acoustic transducer disposed within the cavity and disposed above the aperture in the housing structure, wherein the electrically conductive lid is directly connected to the ground lead.
The example embodiments are best understood from the following detailed description when read with the accompanying drawing figures. It is emphasized that the various features are not necessarily drawn to scale. In fact, the dimensions shown in the drawings may be arbitrarily increased or decreased for clarity of discussion. Wherever applicable and practical, like reference numerals refer to like elements.
In the following detailed description, for purposes of explanation and not limitation, example embodiments disclosing specific details are set forth in order to provide a thorough understanding of an embodiment according to the present teachings. However, it will be apparent to one having ordinary skill in the art having had the benefit of the present disclosure that other embodiments according to the present teachings that depart from the specific details disclosed herein remain within the scope of the appended claims. Moreover, descriptions of well-known apparati and methods may be omitted so as to not obscure the description of the example embodiments. Such methods and apparati are clearly within the scope of the present teachings.
Unless otherwise noted, when a first device is said to be connected to a second device, this encompasses cases where one or more intermediate devices may be employed to connect the two devices to each other. However, when a first device is said to be directly connected to a second device, this encompasses only cases where the two devices are connected to each other without any intermediate or intervening devices. Similarly, when a signal is said to be coupled to a device, this encompasses cases where one or more intermediate devices may be employed to couple the signal to the device. However, when a signal is said to be directly coupled to a device, this encompasses only cases where the signal is directly coupled to the device without any intermediate or intervening devices. As used herein, “approximately” means within 10%, and “substantially” means at least 75%. As used herein, when a first structure, material, or layer is said to cover a second structure, material, or layer, this includes cases where the first structure, material, or layer substantially or completely encases or surrounds the second structure, material or layer.
The inventors have recognized that there are a number of factors that can affect the performance of a packaged acoustic device in different applications.
One factor whose importance has been appreciated by the inventors have is the acoustic loss of the package. U.S. patent application Ser. No. 12/619,963, filed on 17 Nov. 2009 in the names of Timothy LeClair et al., discloses a packaged acoustic device which can provide a low acoustic loss. U.S. patent application Ser. No. 12/619,963 is incorporated herein by reference for all purposes as if fully set forth herein.
Another factor that can present itself in some applications is electrical signal loss in the leads or conductors between the packaged acoustic transducer device and an electrical device (e.g., an amplifier) to which the device is connected, particularly when the acoustic transducer device is operating in a receive mode and is transmitting its received signal to a receiver amplifier. U.S. patent application Ser. No. 12/710,636, filed on 23 Feb. 2010 in the names of Timothy LeClair et al., discloses a packaged acoustic device in which an electronic device (e/g., an amplifier) is included in the same package as the acoustic transducer. U.S. patent application Ser. No. 12/619,963 is incorporated herein by reference for all purposes as if fully set forth herein.
The inventors have also appreciated that in some applications, a packaged acoustic transducer can be exposed to externally-generated electromagnetic radiation that can interfere with the proper operation of the acoustic transducer. Such electromagnetic interference (EMI) can cause signal integrity issues for the packaged acoustic device. For example, consider a system where a first packaged acoustic transducer device transmits an acoustic signal at a resonant frequency which is detected by a first packaged acoustic transducer device to measure or control some operating characteristic of a system. In particular, under some circumstances EMI can disturb the resonant frequency of one or both the acoustic resonators, thereby causing the first (transmit) acoustic resonator to operate at a different resonant frequency than the second (receive) acoustic resonator, thereby degrading the overall performance.
With an appreciation of these factors, the inventors have provided an acoustic transducer in various embodiments can achieve desired performance in various operating environments, and particularly in the presence of EMI.
For illustration purposes only, in one embodiment semiconductor die 100 has dimensions of approximately 2 mm on each side, the diaphragm of acoustic device 110 has a diameter of 540-743 μm, and through hole 112 has a diameter of 410-613 μm.
Operationally, in some embodiments, acoustic device 110 may operate as a transmitting acoustic transducer to receive an electrical signal and to produce therefrom a corresponding acoustic signal or wave which is transmitted. In other embodiments, acoustic device 110 may operate as a receiving acoustic transducer to receive an acoustic signal or wave and to produce therefrom a corresponding electrical signal which is received. In still other embodiments, acoustic device may operate as both a transmitting acoustic transducer and a receiving acoustic transducer.
For illustration purposes only, in one embodiment semiconductor die 200 has dimensions of approximately 2 mm on each side, the diaphragms of acoustic devices 210 each have a diameter of 525-779 μm, and through hole 212 has a diameter of 395-649 μm.
For illustration purposes only, in one embodiment semiconductor die 300 has dimensions of approximately 2 mm on each side, the diaphragms of acoustic devices 310 each have a diameter of 525-779 μm, and through hole 112 has a diameter of 395-649 μm.
Packaged acoustic device 400 also includes a substrate 420 which includes one or more electronic devices (e.g., an amplifier) for operating with the acoustic transducer(s) of semiconductor die 200. However, it should be understood that in some embodiments, the substrate and the electronic devices may be omitted from the packaged acoustic device. Accordingly, packaged acoustic device 400 may be seen to represent a general embodiment that includes various features that may or may not be included in other embodiments.
Lead frame 510 and terminal leads 430 are formed from an electrically conductive material, such as various metals and metal alloys, including copper, nickel, aluminum, brass, copper/zinc alloys, and the like, or a combination thereof, for example. The material may be etched to form separate conductors and terminal leads 430, as well as other features, such as aperture 520 and pads 435. Lead frame 510 may also be plated for wirebonding, for example, using an optimized plating material, such as nickel and/or gold, to permit gold or aluminum wirebond attachment.
As shown in
Housing 410 further includes a base portion 415. The base portion 415 of housing 410 has an aperture 417 aligned with aperture 520.
In some embodiments, semiconductor die 200 is mounted on lead frame 510, for example by an adhesive 530 such as an epoxy. In other embodiments, particularly where aperture 417 is the same or nearly the same size as aperture 520, semiconductor die 200 is mounted or attached to a portion of housing 410 that surrounds aperture 417. Other arrangements are possible.
In some embodiments, housing 410 is formed from a non-conductive material, such as various plastics or polymers, including liquid crystal polymer (LCP), polybutylene terephthalate (PBT), polypropylene (PP), polyphthalamide (PPA), and the like, for example.
In a beneficial embodiment, housing 410 includes an acoustic horn (not shown in
Substrate 420 is mounted on base portion 415 of housing 410, for example by means of an adhesive 540 such as an epoxy. In the illustrated embodiment, substrate 420 is a printed circuit board. Beneficially, substrate 420 may be a ceramic or alumina ceramic substrate with electrically conductive pads and traces formed thereon, for example by a thick film printing metallization process.
Substrate 420 has mounted thereon an amplifier, which may be an operational amplifier. In the illustrated embodiment, the amplifier includes an integrated circuit device 422 with active elements, and one or more external components 424 (e.g., resistor(s), capacitor(s), etc.) for setting at least one operating parameters (e.g., gain, bandwidth, etc.) of the amplifier, and/or for filtering one or more supply voltages provided to the amplifier. In the illustrated example, integrated circuit device 422 is a packaged semiconductor die with leads connected to metal traces on substrate 420. However in other embodiments, integrated circuit device 422 may comprise an unpackaged semiconductor die. In some embodiments, the parameter-setting resistor(s)/capacitor(s) may be incorporated within the semiconductor die.
Bond wires 440 electrically and operationally connect the amplifier to the acoustic transducer(s) of semiconductor die 200, directly and/or via intermediate connections to pads 435 of lead frame 510. Also, bond wires 440 connect the amplifier of substrate 420 to one or more supply voltages, including an electrical ground, supplied via terminal leads 430. Such connections may be made via one or more pads 435.
Again, as noted above, it should be appreciated that some embodiments do not include substrate 420 or its associated electronics within the packaged acoustic device.
As shown in
In a beneficial arrangement, lid 550 provides shielding of acoustic transducer device(s) of semiconductor die 200 from exposure to externally-generated electromagnetic radiation that can interfere with the proper operation of the acoustic transducer, i.e., shielding from electromagnetic interference (EMI). In some embodiments, one of the terminal leads 430 is a ground lead that is configured to be connected to an electrical ground for the packaged acoustic device 400, and lid 550 is formed of an electrically conductive material, such as a metal, and is directly connected to the ground lead 430, for example by conductive epoxy 570 as shown in
Packaged acoustic device 600 includes a housing 610, a plurality of terminal leads 630, a semiconductor die 200 having one or more (e.g., three) acoustic transducers, and an electrically-conductive lid 650. Of course in other embodiments, other semiconductor dies, for example semiconductor dies 100 or 300, having different numbers and/or configurations of acoustic transducers could be employed instead of semiconductor die 200.
Terminal leads 630 and a lead frame to which they are attached are formed from an electrically conductive material, such as various metals and metal alloys, including copper, nickel, aluminum, brass, copper/zinc alloys, and the like, or a combination thereof, for example. The material may be etched to form separate conductors and terminal leads 630, as well as other features, such as aperture 620. The lead frame may also be plated for wirebonding, for example, using an optimized plating material, such as nickel and/or gold, to permit gold or aluminum wirebond attachment.
As shown in
Housing 610 further includes a base portion having an aperture 617 aligned with aperture 620 in the lead frame.
In some embodiments, semiconductor die 200 is mounted on the lead frame, for example by an adhesive such as an epoxy. In other embodiments, particularly where aperture 617 is the same or nearly the same size as aperture 620, semiconductor die 200 is mounted or attached to a portion of housing 610 that surrounds aperture 617. Other arrangements are possible.
In some embodiments, housing 610 is formed from a non-conductive material, such as various plastics or polymers, including liquid crystal polymer (LCP), polybutylene terephthalate (PBT), polypropylene (PP), polyphthalamide (PPA), and the like, for example.
As shown in
In a beneficial arrangement, lid 650 provides shielding of acoustic transducer device(s) of semiconductor die 200 from exposure to externally-generated electromagnetic radiation that can interfere with the proper operation of the acoustic transducer, i.e., shielding from electromagnetic interference (EMI). In some embodiments, one of the terminal leads 630 is a ground lead that is configured to be connected to an electrical ground for the packaged acoustic device 600. Lid 650 is formed of an electrically conductive material, such as a metal, and as shown in
In a beneficial embodiment, housing 610 includes an acoustic horn 611 provided on an opposite side of the lead frame from semiconductor die 200 for coupling acoustic waves between the ambient air atmosphere and the acoustic transducer(s) of semiconductor die 200. Generally, horns may be used to amplify acoustic signals, making them louder, as indicated by the incorporation of horns in various musical instruments and early hearing aids, for example. Horns may also be used to manipulate radiation patterns of acoustic emitters, generally referred to as beam forming or beam shaping, thus affecting dispersion of the acoustic signals. In addition, horns may provide impedance matching, rendering an acoustic transducer more compatible with the medium through which the acoustic signals travel.
In the depicted embodiment, acoustic horn 611 is integral with housing 610 and comprises a protruding portion that extends from the base portion of housing 610 along a center axis in a direction substantially perpendicular to the lead frame. In a representative embodiment, housing 610 including acoustic horn 611 is formed from plastic transfer molded to the lead frame, as discussed below.
In one embodiment, acoustic horn 611 has a flared cross-sectional shape (e.g., hyperbolic or exponential), such that an inner dimension of acoustic horn 611 extends outwardly from an inner aperture or throat 612 to a flared outer aperture or mouth 614. For example, the throat 612 may be circular with a diameter of about 2 mm and the mouth 614 may likewise be circular with a diameter of about 8 mm. However, the sizes and shapes of acoustic horn 611 and corresponding throat 612 and mouth 614, as well as the respective configurations of the base portion and the protruding portion of housing 610 may vary to provide unique benefits for any particular situation or to meet application specific design requirements of various implementations. For example, the cross-sectional shape of the protruding portion of acoustic horn 611 may be substantially conical, tubular, rectangular or trapezoidal, without departing from the scope of the present teachings.
Acoustic horn 610 may be molded in the shape depicted, for example, in
Device 600 further includes a protective mesh or barrier screen 616 that covers mouth 614 of acoustic horn 611. Beneficially, screen 616 may include a pattern of apertures for communicating acoustic signals between the acoustic transducer(s) of semiconductor die 200 and the exterior of packaged acoustic device 600. For example, each of the apertures of screen 616 may be substantially smaller than the size of aperture 620 in the lead frame. Screen 616 may include acoustically transparent solid material to allow acoustic signals to exit and/or enter aperture 620, but limiting debris, contaminants and/or moisture that can enter aperture 620. In an embodiment, screen 616 is positioned directly in mouth 612 of the protruding portion of acoustic horn 610. Screen 616 may be applied after assembling the packaged acoustic device 400, including attachment of lid 650.
In some embodiments, screen 616 provides EMI shielding for the acoustic transducer(s) of semiconductor die 200. In particular, screen 616 may comprise an electrically conductive material, for example a metal. In that case, in some embodiments screen 616 may be electrically connected to the ground lead 630 of device 600, for example through lid 650, or by some other connection.
In an example embodiment, a molding operation is performed on lead frame 510. The molding operation includes placing lead frame 510 in a transfer mold previously formed to define the shape of housing 410, including for example base portion 415 and acoustic horn 610. A polymer, e.g., LCP, PBT, PP, or PPA, is then transfer molded, for example, to encapsulate lead frame 510 and to simultaneously form housing 410, for example including an acoustic horn that is on the bottom of device 400 in the views of
Although not specifically shown in
While example embodiments are disclosed herein, one of ordinary skill in the art appreciates that many variations that are in accordance with the present teachings are possible that remain within the scope of the appended claims. The embodiments therefore are not to be restricted except within the scope of the appended claims.
