Patent Application
20240120321
Embodiments of the present disclosure relate to power amplifier packages having air cavities enclosed by electrically-routed lids and to methods for fabricating such power amplifier packages.
A power amplifier (PA) module or package contains at least one semiconductor die bearing a transistor integrated circuit, which is utilized for radio frequency (RF) signal or power amplification purposes. In the case of a Doherty power amplifier package, for example, at least one carrier RF power die and at least one peaking RF power die are contained within the body of the PA package. The PA package may be mounted to a system-level substrate, such as a printed circuit board, supporting other discrete microelectronic components included in a larger PA circuit. In certain cases, the PA package may include a cover piece or lid enclosing an air cavity; the term “air cavity” referring to a sealed, gas-containing cavity by industry convention. In other instances, a PA package may be fabricated to lack such an air cavity and, instead, to contain an essentially void-free encapsulant body in which the RF power die or dies, as well as any other microelectronic components, are embedded. PA packages of this latter type are commonly referred to as “encapsulated,” “overmolded,” or “plastic” packages. Relative to fully encapsulated packages, PA packages having air cavity constructions typically provide superior electrical performance with certain tradeoffs including more costly and complex manufacture.
At least one example of the present invention will hereinafter be described in conjunction with the following figures, wherein like numerals denote like elements, and:
For simplicity and clarity of illustration, descriptions and details of well-known features and techniques may be omitted to avoid unnecessarily obscuring the example and non-limiting embodiments of the invention described in the subsequent Detailed Description. It should further be understood that features or elements appearing in the accompanying figures are not necessarily drawn to scale unless otherwise stated. For example, the dimensions of certain elements or regions in the figures may be exaggerated relative to other elements or regions to improve understanding of embodiments of the invention.
Embodiments of the present disclosure are shown in the accompanying figures of the drawings described briefly above. Various modifications to the example embodiments may be contemplated by one of skill in the art without departing from the scope of the present invention, as set-forth the appended claims. The term “exemplary,” as appearing throughout this document, is synonymous with the term “example” and is utilized repeatedly below to emphasize that the following description provides only multiple non-limiting examples of the invention and should not be construed to restrict the scope of the invention, as set-out in the Claims, in any respect.
The term “air cavity package,” as appearing herein, refers to a microelectronic package or module including a sealed cavity filled with a gas, regardless of the internal pressure within the cavity. The “air cavity” of the air cavity package will often be enclosed in an open air environment and, thus, contain air at approximately 1 atmosphere (atm) pressure with slight variations depending upon elevation and processing temperatures during package manufacture. In other implementations, the “air cavity” of the air cavity package may be enclosed in a partially evacuated chamber or a chamber containing an inert gas, such as argon, during manufacture and, thus, may not contain pure air in all instances. The term “air cavity,” then, should be understood as referring to a gas-containing cavity, which may or may not be partially evacuated and which is sealed from the ambient environment. Additionally, the seal formed between the air cavity and the ambient environment may not be hermetic, as strictly defined, but rather may be a low leakage seal having a gross leakage rate falling within acceptable parameters. For example, in certain contexts, a cavity may be considered “sealed” when little to no leakage (bubbles) is observed from the cavity's exterior when the cavity is filled with air or another gas and the air cavity package is immersed in a liquid (e.g., perfluoropolyether) at approximately 125 degrees Celsius (°). Finally, as further appearing herein, the term “package” is defined to be synonymous with and is utilized interchangeably with the term “module.”
Overview
Certain power amplifier (PA) packages, such as PA packages containing radio frequency (RF) semiconductor dies fabricated utilized power dense die technologies or operated at higher radio frequencies (e.g., frequencies approaching or exceeding approximately 2.1 gigahertz), are commonly prone to excess heat generation during package operation. In the absence of an adequate thermal solution for extracting and dissipating heat from the package interior, elevated local temperatures or “hot spots” can develop within the PA package limiting package performance. Thermal solutions traditionally implemented by manufacturers often rely upon increasing the metal content within a die supporting region of the package substrate; e.g., by forming bar vias within the package substrate or by installing a prefabricated metal body, such as a copper (Cu) coin, within a substrate cavity under the RF die or dies housed within the package. Such an embedded thermal dissipation structure (e.g., a metal slug or via farm) may form or help form a low thermal resistance heat transfer path extending from the RF circuitry (e.g., RF power dies) within the PA package to a thermal interface availed on the package exterior, such as an exposed surface of an embedded metal coin or a backmetal layer formed on the package bottomside. PA packages of this type may be imparted with a leaded formfactor or a flat no lead formfactor, such as a dual flat no lead (DFN) or a quad flat no lead (QFN) formfactor. When imparted with a flat no lead formfactor, the PA packages may include contacts, such as land grid array (LGA) pads, on the package bottomside surface forming an input/output (I/O) interface. The LGA pads are commonly arranged in multiple rows, which extend along an outer peripheral region of the package bottomside surface and flank the package's thermal interface. When the PA package is mechanically and electrically attached to a system level substrate (e.g., by soldering to a motherboard or other system-level printed circuit board (PCB)), conductive heat flow and electrical signals are both routed through the package bottomside during PA package operation.
More recently, dual-sided PA package architectures have been developed in which the thermal interface and the package I/O interface are provided on opposing principal surfaces of the package. Specifically, in such package architectures, the package I/O interface may be provided along the package topside surface, while the package thermal interface is availed along the package bottomside surface. PA packages of this type are referred to herein as “high thermal performance” or “HTP” packages. Such PA packages, when imparted with HTP architectures or designs, benefit from enhanced heat dissipation to limit peak operational temperatures occurring within the PA package, particularly when operated at higher power levels and frequencies or containing RF power dies having relatively high power densities. This, in turn, may improve the package electrical performance and operational lifespan relative to more conventional PA packages lacking HTP designs. These benefits notwithstanding, presently-suggested approaches for fabricating or constructing HTP packages present certain challenges. For example, in one one approach for fabricating HTP PA packages, one or more interposer pieces are initially bonded to a PCB serving as the package substrate. The interposer pieces may be PCB blocks or electrically-routed ceramic pieces, which are soldered to the populated side of the package substrate and extend upwardly therefrom. In certain instances, a single ring-shaped interposer piece may be bonded to the populated side of the package substrate; while, in other cases, multiple block-shaped interposer pieces may be spaced around the populate side of the PCB and so bonded. Following component population (e.g., RF die attach) and wirebonding, the interposer piece or pieces, the RF power dies, and any other packaged components contained in the circuit layout may be overmolded with a dielectric mold compound (e.g., utilizing a film assisted molding technique) to yield an encapsulant body in which the RF circuitry and interposer pieces are embedded. The upper surface of the encapsulant body may define the package topside surface along which the package topside I/O array is located, as well as provide a flat surface facilitating pick-and-place operations during package manufacture. A thermal interface may be provided on the opposing package backside, with a primary heat extraction path extending from the thermal interface, through one or more thermal dissipation structures (e.g., embedded Cu coins), and to the RF power die or dies within the PA package to complete the HTP package architecture.
While enhancing thermal performance attributes, molded HTP PA packages of the type just described remain limited in certain respects. Many of these limitations pertain to the presence of the overmold or encapsulant material itself, which inherently possesses a higher dielectric constant than does a gas-filled cavity; e.g., many thermoplastics or mold compounds utilized for encapsulation purposes have a dielectric constant ranging from about 3.5 to about 3.8 relative to a dielectric constant of essentially 1 in the case of air. Thus, the presence of the encapsulant material may also increase cross coupling between wirebond arrays, matching elements, and the I/O terminals of the package. In contrast to the gas-filled space within a PA package having a sealed air cavity, the dielectric encapsulant within an overmolded PA package can shift or otherwise alter the electrical performance parameters (e.g., gain and efficiency) of the PA package. While some fraction of the resulting performance detriment may be recovered through iterative post-mold tuning, some of this performance loss remains non-recoverable. Moreover, iterative post-mold tuning adds further design cycles, with post-mold tuning typically entailing the time-intensive and highly manual process of excavating overmolded matching components to allow such components to be modified or swapped with other components to allow additional testing and design iterations. As a further issue, the overmolding process employed to form the encapsulant body may be prone to mold flash, which may extend onto the contacts of the PA package and interfere with bonding of the PA package to a system-level substrate. Still other issues associated with overmolded or plastic HTP PA package designs can arise from the incorporation of the interposer piece or pieces into the molded package body. Geometric irregularities or coplanarity issues can occur across I/O plane of the PA package due to varying interposer heights and solder joint thicknesses, undesired solder extrusion can occur from the interposer joints, and moisture can become trapped beneath (or potentially ingress into) small voids between the interposer pieces and the package substrate, depending upon manufacturing tolerances and other factors. Any or all of these issues may negatively impact the structural integrity or performance of the PA package to vary degrees.
Considering the above, there exists an ongoing industrial demand for PA packages capable of overcoming most, if not all of the aforementioned limitations, while remaining readily adaptable to the incorporation of HTP architectures and amenable to cost effective manufacture. HTP PA packages having such attributes are described herein, as are methods for fabricating such PA packages in bulk or at scale to achieve increased process efficiencies and manufacturing cost reductions. As described in greater detail below, embodiments of the presently-disclosed PA packages contain air cavities, which are sealingly enclosed utilizing specialized, electrically-routed lids; the term “electrically-routed lid,” as appearing herein, referring to a cover piece or lid containing vias extending within one or more of the peripheral lid sidewalls to provide electrical connections between an I/O interface (e.g., a topside I/O interface) of the PA package and RF circuitry contained within the package interior. Such vias are described as “sidewall-embedded vias” and may be wholly or entirely embedded within a given lid sidewall or may instead be partially embedded in a lid sidewall (e.g., such that the via can be seen from the package interior or exterior). The sidewall-embedded vias provide electrical connection between terminals (e.g., electrically-conductive pads) in the topside I/O interface of the PA package and contacts spaced along an underside edge or surface of the electrically-routed lid. The sidewall-embedded vias can include or assume the form of any structure extending within the lid sidewalls in an essentially vertical or package height direction and providing electrically-conductive paths from the substrate-facing lid contacts to the topside I/O terminals provided on the lid topside. Such vias may be produced utilizing embedded metal structures, such as metallic columns or rods provided as discrete pieces or initially provided as a physically-interconnected array or structure and subsequently singulated during the manufacturing process. In other instances, the sidewall-embedded vias may be formed as through holes or vertical notches backfilled with an electrically-conductive material, such as an electrically-conductive epoxy or a sintered metallic material. As a still further example, in embodiments, the sidewall-embedded vias may be formed as plated through holes, which are produced by drilling holes through the dielectric cover body, plated, backfilled with a conductive or non-conductive material, and then capped (e.g., through formation of topside bondpads serving as terminals in the topside I/O interface).
Continuing the foregoing paragraph, the contacts present on the underside edge or surface of the electrically-routed lid are referred to herein as “substrate-facing lid contacts” and may assume the form of bondpads spaced in rows vertically overlapping or aligning with the terminals of the topside I/O interface; the term “vertical” referring to an axis orthogonal to the package topside surface and synonymous with the term “package height direction” herein. A corresponding set of contacts (herein, “lid-facing contacts”) may be provided on the populated side of the package substrate and electrically interconnected to the substrate-facing lid contacts. RF circuitry, which may include one or more power RF dies and any practical number of other microelectronic components (e.g., surface mount device (SMD) capacitors, resistors, or inductors), is further attached to the populated side (lid-facing side) of the package substrate and electrically interconnected with the topside I/O interface through lid-facing contacts, through the substrate-facing lid contacts, and through the sidewall-embedded vias. A robust electrical routing scheme is consequently provided for interconnecting the RF circuitry with the topside I/O interface without reliance upon the inclusion of overmolded interposer pieces within the package body. Additionally, in at least some embodiments, a unique bond layer system may be utilized to attach the electrically-routed lid to the package substrate, while providing a high integrity, 360° seal bounding the air cavity at lid-substrate interface. In at least some realizations, such a bond layer system may be formed to contain a dielectric bond layer and electrically-conductive bodies, which are distributed in the dielectric bond layer at locations between corresponding pairs of lid-facing and substrate-facing lid contacts. Furthermore, in certain implementations, the dielectric bond layer may be applied as a B-stage epoxy initially dispensed in a wet state (e.g., as a paste), which undergoes (e.g., second stage) curing during the lid attach process to create the desired seal about the lid-substrate juncture and sealingly enclose the package air cavity.
In the above-described manner, HTP PA packages can be fabricated possessing air cavity constructions to enhance the electrical performance characteristics of the PA packages, while optimal thermal performance is achieved by virtue of the package's dual-sided HTP architecture. Additionally, relative to comparable overmolded or plastic PA packages containing encapsulated components and interposer pieces, the presently-disclosed PA packages are less susceptible to coplanarity issues along the package mount plane and avoid challenges involving interposer piece attachment and overmolding. Such benefits may be optimized when an epoxy attach process is utilized to bond the electrically-routed lid to the package substrate; e.g., noting that cured epoxy materials are generally impervious to, or at least less prone to, reflow issues observed with some solder materials. As a still further advantage, embodiments of the presently-disclosed HTP PA packages are amenable to fabrication at scale or in larger numbers by processing a presingulated package substrate array to which a presingulated lid array (containing a plurality of physically-connected, electrically-routed lids) is attached. This may be accomplished utilizing, for example, an epoxy attach process of the type further discussed below; e.g., by screen printing or otherwise dispensing a wet state epoxy at the appropriate locations between the substrate and lid arrays to simultaneously enclose multiple air cavities during lid attach and epoxy curing stages. Example fabrication processes carried-out on a large (panel- or strip-level) scale to concurrently produce multiple (e.g., several dozen) PA packages in parallel are further discussed herein in connection with
Example Power Amplifier Package with Electrically-Routed Lid
PA package 10 is imparted with a dual-sided HTP architecture in the illustrated embodiment. In this regard, and as shown most clearly in
Referring now to
As indicated by the term “electrically-routed,” lid 22 is fabricated to contain certain internal electrically-conductive features, which help provide electrical interconnection between RF circuitry contained in air cavity 26 and topside I/O interface 18 of PA package 10. Specifically, and as shown most clearly in
The body or bulk of electrically-routed lid 22 may be composed of a dielectric resin material of the type utilized in PCB fabrication, a ceramic, or a thermoplastic material, such as a liquid crystal polymer (LCP) material, to list but a few examples. In certain embodiments, the dielectric body of electrically-routed lid 22 may be formed around pre-existing or premanufactured metal pieces (or other electrically-conductive structures) to produce sidewall-embedded vias 38 during lid fabrication. For example, in such cases, the electrically-conductive pieces serving as vias 38 may assume the form of structurally-separate or discrete electrically-conductive pieces (e.g., metal blocks or rods), which are arranged in a desired spatial layout or positioning utilizing a specialized fixture. Overmolding may then be performed, and the fixture removed following embedment of the metal (or other electrically-conductive pieces) within the lid. In other instances, such electrically-conductive pieces may be initially interconnected or physically tied together in some manner, overmolded, and then physically separated and electrically isolated post overmolding; e.g., by sawing during the singulation process. In still other manufacturing approaches, the dielectric lid body may be initially produced (e.g., via molding of a thermoplastic or by machining of a dielectric blank) to include unfilled through holes or tunnels in which sidewall-embedded vias 38 are ultimately formed. In this latter instance, the through holes may be formed as part of the molding process (when applicable); or, instead, produced subsequent to molding utilizing a suitable material removal process, such as mechanical drilling. Following this, discrete metallic pieces can be inserted or press-fit into the through holes and bonded to any existing contact pads, as appropriate. Alternatively, an electrically-conductive material can be deposited or dispensed into the through holes in sufficient quantity to provide the desired electrical connection between corresponding sets of LGA pads 18 and substrate-facing lid contacts 34, which may be subsequently produced depending upon the manufacturing approach employed. In the latter regard, an electrically-conductive wet state material can be dispensed or backfilled into the through holes and cured. Materials suitable for this purpose include electrically-conductive epoxies and metal particle-containing pastes, which may be sintered to form metallic (e.g., sintered Cu or silver (Ag)) bodies within the through holes to provide the desired electrical connections.
As a still further possibility, sidewall-embedded vias 38 can be formed as plated through holes and are depicted as such in
Discussing now
Bond layer system 24 may include any number of bond layers having varying compositions suitable for providing a high integrity, 360° seal around (bounding a perimeter of) air cavity 26 at the lid-substrate interface, while also providing robust electrical connection between corresponding pairs of substrate-facing lid contacts 34 on the lower edge of lid 22 and lid-facing contacts 76, 78, 80, 82 (
As depicted most clearly in
In the illustrated embodiment, uppermost metal layer 68 of package substrate 20 is patterned to define a number of electrically-conductive bondpads 76, 78, 80 (
Package substrate 20 may further contain one or more thermal dissipation (heat transfer) structures 97, which extend between surfaces 31, 50 of package substrate 20. When so provided, IC dies 52, 54, 56, 58 may be physically and electrically coupled to the uppermost surfaces of thermal dissipation structures 97 exposed at populated surface 50 of package substrate 20. Bottom surfaces 98 of thermal dissipation structures 97 may be exposed at non-populated surface 31 of package substrate 20, or bottom surfaces 98 of thermal dissipation structures 97 may be covered with bottommost metal layer 28, as shown in
The terminals or contacts included in topside I/O interface 18 of PA package 10 include an RF input terminal 76 and an RF output terminal 78 (identified in
The first output of power splitter 99 is electrically coupled to a carrier amplification path extending within PA package 10, while the second output of power splitter 99 is electrically coupled to a peaking amplification path within PA package 10. The RF signal produced at the second output of splitter 99 may be delayed by about 90° from the RF signal produced at the first power splitter output. Stated differently, the RF signal provided to the peaking amplification path may be delayed by about 90 degrees from the RF signal provided to the carrier amplification path. Due to this arrangement, the first RF signal generated by power splitter 99 is amplified through the carrier amplification path, while the second RF signal produced by power splitter 99 is amplified through the peaking amplification path. In the depicted embodiment, each of the carrier and peaking amplification paths extends through a two-stage power amplifier section in which a driver-stage transistor 90, 94 is implemented on a driver-stage die 52, 56, while a final-stage transistor 92, 96 is implemented on a separate final-stage die 54, 58. For example, each of transistors 90, 92, 94, 96 may be field effect transistors (FETs), such as laterally-diffused metal oxide semiconductor (LDMOS) FETs or high electron mobility transistors (HEMTs). The description and claims may refer to each transistor as including a control terminal and two current-conducting terminals. For example, utilizing terminology associated with FETs, a “control terminal” refers to a gate terminal of a transistor, and first and second current-conducting terminals refer to drain and source terminals (or vice versa) of a transistor. Although the below description may use terminology commonly used in conjunction with FET devices, the various embodiments are not limited to implementations the utilize FET devices, and instead are meant to apply also to implementations that utilize bipolar junction transistors (BIT) devices or other suitable types of transistors.
In the illustrated example, carrier amplifier section 100 of PA package 10 includes a silicon driver-stage die 52 and a gallium nitride (GaN) final-stage die 54; while peaking amplifier section 102 likewise includes a silicon driver-stage die 56 and a GaN final-stage die 58. In other embodiments, each of carrier and peaking amplifier sections 100, 102 may include a two-stage power amplifier implemented on a single die, or each of carrier and peaking amplifier sections 100, 102 may include a single-stage power amplifier implemented on a single die. In still other implementations, each of carrier and peaking amplifier section 100, 102 may include a two-stage power amplifier implemented on separate driver and final-stage dies, but the driver and final-stage dies may be formed utilizing the same semiconductor technology (e.g., both the driver and final-stage dies are silicon dies or GaN dies), or the driver and/or final-stage dies may be formed utilizing different semiconductor technologies than those described above (e.g., the driver and/or final-stage dies may be formed from silicon germanium (SiGe) and/or gallium arsenide (GaAs) die).
With continued reference to
The peaking amplification path includes the above-mentioned driver-stage die 56 and final-stage die 58. Driver-stage die 56 and final-stage die 58 of the peaking amplification path are electrically coupled together in a cascade arrangement between an input terminal 116 of driver-stage die 56 (corresponding to a peaking amplifier input) and an output terminal 120 of final-stage die 58 (corresponding to a peaking amplifier output). Driver-stage die 56 may include a plurality of ICs. In an embodiment, the integrated circuitry of die 56 includes a series-coupled arrangement of input terminal 116, an input impedance matching circuit (not numbered), a silicon power transistor 94, an integrated portion of an interstage impedance matching circuit (not numbered), and an output terminal not numbered, in an embodiment In particular, the gate of transistor 94 is electrically coupled through the input impedance matching circuit to input terminal 116, and the drain of transistor 94 is electrically coupled through the output-side impedance matching circuit to the output terminal of die 56. The source of transistor 94 is electrically coupled to a patterned metal layer on a bottom surface of die 56, and the bottom patterned metal layer is physically, electrically, and thermally coupled to the exposed top surface of a thermal dissipation structure 97. The output terminal of driver-stage die 56 is electrically coupled to the input terminal of final-stage die 58 through a wirebond array (not numbered) or another type of electrical connection. Final-stage die 58 also includes a plurality of integrated circuits. In an embodiment, the integrated circuitry of die 58 includes a series-coupled arrangement of an input terminal (not numbered), a GaN power transistor 96, and an output terminal 120. More specifically, the gate of transistor 96 is electrically coupled to the input terminal of die 58, and the drain of transistor 96 is electrically coupled to output terminal 120 of die 58. The source of transistor 96 is electrically coupled to a patterned metal layer on a bottom surface of die 58, and the bottom patterned metal layer is physically, electrically, and thermally coupled to the exposed top surface of a thermal dissipation structure.
To ensure proper Doherty operation, the carrier amplifier may be biased to operate in a class AB mode, and the peaking amplifier may be biased to operate in a class C mode. To accomplish this biasing, a plurality of gate and drain bias voltages may be provided by external bias voltage sources. In embodiments, the bias voltages are provided through the bias terminals and electrically-routed lid 22. Specifically, gate bias voltages for driver-stage transistors 90, 94 may be provided through driver gate bias terminals, drain bias voltages for driver-stage transistors 90, 94 may be provided through driver drain bias terminals, and gate bias voltages for final-stage transistors 92, 96 may be provided through gate bias terminals. Each of the terminals has a proximal end coupled to conductive structures (e.g., pads and traces) of patterned metal layer 68, and the conductive structures are electrically coupled (e.g., through wirebonds, as shown) to bias pads on the driver- and final-stage dies. In the illustrated embodiment, the gate and drain bias pads for both driver- and final-stage transistors 90, 92, 94, 96 are located on driver-stage dies 52, 56, and the gate bias voltage for final-stage dies 54, 58 “hops” from driver-stage dies 52, 56 to final-stage dies 54, 58 through wirebond connections, as shown. Returning again to the operation of PA package 10, an amplified carrier signal is produced at output terminal 122 of final-stage die 54, and an amplified peaking signal is produced at output terminal 120 of final-stage die 58, which also functions as combining node 104 for the amplifier. According to an embodiment, output terminal 122 of carrier final-stage die 54 is electrically coupled (e.g., through wirebonds (not numbered) or another type of electrical connection) to a first end of the phase shift and impedance inversion element 118, and output terminal 120 of peaking final-stage die 58 is electrically coupled (e.g., through wirebonds or another interconnect feature) to a second end of the phase shift and impedance inversion element 118.
In embodiments, phase shift and impedance inversion element 118 may be implemented with a quarter-wavelength or lambda/4 (λ/4) or shorter transmission line (e.g., a microstrip transmission line with an electrical length up to about 90°) formed from a portion of patterned metal layer 68. As utilized herein, lambda denotes the wavelength of an RF signal at the fundamental frequency of operation of PA package 10; e.g., a frequency in a range of about 600 megahertz (MHz) to about 10 gigahertz (GHz) or higher. The combination of the phase shift and impedance inversion element 118 and the wirebond (or other) connections to output terminals 122, 120 of dies 54, 58 may impart about a 90° relative phase shift to the amplified carrier signal as the signal travels from output terminal 122 to output terminal 120/combining node 104. When the various phase shifts imparted separately on the carrier and peaking RF signals through the carrier and peaking paths, respectively, are substantially equal, the amplified carrier and peaking RF signals combine substantially in phase at output terminal 120/combining node 104. Output terminal 120/combining node 104 is electrically coupled (e.g., through wirebonds or another type of electrical connection) through an output-side impedance matching network 106 to the RF output terminal. As previously noted, various other SMDs may also be mounted to populated frontside surface 50 of package substrate 20 to complete the circuitry of PA package 10, with an example of one such SMD 124 (e.g., a chip cap) shown in
Advancing to
Thermally-conductive bond layer 136 can be composed of any thermally-conductive bonding material, such as a sintered bond layer or another bonding material (whether electrically conductive or dielectric) having a relatively low thermal resistance. In other embodiments, assembly-level heatsink 134 may be thermally coupled to bottomside thermal interface 28 in a less direct manner. For example, in other instances, assembly-level heatsink 134 may be spatially separated from PA package 10 and a thermal conduit, such as a metallic body or an elongated heat pipe, may be thermally coupled between heatsink 134 and bottomside thermal interface 28. Regardless of its particular location relative to PA package 10, assembly-level heatsink 134 can be any thermally-conductive structure or device suitable for absorbing excess heat extracted from PA package 10 through the bottomside thermal interface. For example, in embodiments, assembly-level heatsink 134 may be a metal chassis, a fin structure (e.g., a pin-fin array), or another thermally-conductive body external to PA package 10. Assembly-level heatsink 134 may be convectively cooled by releasing heat to the ambient environment; and, in certain embodiments, a fan may direct airflow against assembly-level heatsink 134 to promote convective heat transfer to the impinging airflow. Generally, then, assembly-level heatsink 134 can assume different forms and configurations depending upon the characteristics of electronic assembly 126. It is also possible for PA package 10 to be installed within a larger electronic system or assembly, while bottomside thermal interface 28 is left exposed (and thus not directly thermally coupled to a heatsink) if such an arrangement provides sufficient heat dissipation from PA package 10 in certain applications.
By virtue of its dual-sided, high thermal performance architecture, PA package 10 provides a primary thermal conduction path extending from the RF power die or dies housed within package 10, through package substrate 20, through backmetal layer 28, through the thermally-conductive bond layer and bottomside surface 14, and ultimately to assembly-level heatsink 134. This primary thermal conduction path is non-tortuous and volumetrically robust, and may have a high metallic content or density to provide highly efficient heat flow from the packaged RF dies to assembly-level heatsink 134 in a direction opposite topside I/O interface 18 and assembly-level substrate 128. The heat dissipation capabilities of PA package 10 are boosted as a result to limit peak temperatures within package 10 during PA package operation. This, in combination with the air cavity construction of PA package 10, allow both the electrical and thermal performance characteristics of package 10 to be optimized relative to encapsulated packages having HTP architectures, air cavity packages lacking HTP architectures, and more conventional PA packages. Additionally, and as noted above, embodiments of PA package 10 are amenable to highly repeatable, reliable, and cost effective fabrication processes; while further mitigating issues encountered in connection with the fabrication of overmolded HTP PA packages containing interposer pieces. As a still further advantage, embodiments of HTP PA package 10 (and other PA packages produced in accordance with the present teachings) can be fabricated in parallel to lower manufacturing costs and durations. An example fabrication process for producing a relatively large number (e.g., several dozen) of HTP PA packages in parallel, with each PA package having an air cavity enclosed by an electrically-routed lid, will now be described in connection with
Initially referencing
In the depicted embodiment, package fabrication method 140 is divided into three process stages or blocks 142, 144, 146. To initiate method 140 (STAGE 142), an interconnected package substrate array is obtained, whether by independent fabrication, by purchase from a supplier, or in another manner. Here, the presingulated package substrate array obtained during STAGE 142 assumes the form of an elongated substrate strip 148 containing a relatively large number of interconnected LGA substrates arranged in two grid layouts 150. In other embodiments, the package substrate array may have various other formfactors. Next, during stage 144 of method 140, die attach is performed (step 152) to bond one or more RF power dies, and possibly other surface mount components (e.g., SMD capacitors, resistors, inductors, or the like), to the appropriate locations on the package substrates. A pick-and-place tool 154 may be employed for this purpose. Additionally, in keeping with the foregoing description, the presingulated package substrate array (elongated substrate strip 148) may include embedded thermal dissipation structures (analogous to structures 97 shown in
Next, at STEP 160, a presingulated lid array 162 is bonded to presingulated package substrate array 148 to enclose the RF power dies in sealed air cavities and produce a plurality of presingulated PA packages. Presingulated lid array 162 is positioned over presingulated package substrate array 148 to precisely align saw lanes of the lid array 162 (e.g., saw lanes 164, described below) with matching saw lanes of presingulated package substrate array 148, with fiducials potentially provided on presingulated lid array 162 to assist in the alignment process. Prior to positioning of presingulated lid array 162 over and onto package substrate array 148, a dielectric bond material is applied to lower surfaces of the presingulated lid array and/or onto the populated surfaces of the presingulated package substrate array; e.g., an epoxy paste may be screen printed, applied by fine needle dispense, or otherwise applied to the appropriate surfaces, or a preformed epoxy film may be positioned against the appropriate surfaces and captured between arrays 148, 162 prior to curing. So too may the electrically-conductive bond material (forming electrically-conductive bond layer portions 57,
Lastly, at STAGE 146 of method 140, the presingulated HTP PA packages are singulated to yield a plurality of singulated PA packages. A few instances of such PA packages are shown in the lower portion of
There has thus been provided HTP PA packages containing air cavities enclosed by specialized, electrically-routed lids, as well as methods for fabricating such PA packages in bulk. Due, at least in substantial part, to the unique, dual-sided, high thermal performance architecture and air cavity construction of the presently-disclosed PA packages, the PA packages are capable of achieving both optimal thermal and electrical performance characteristics, while remaining structurally robust or durable. Further, relative to comparable overmolded or plastic PA packages containing encapsulated components and interposer pieces, the presently-disclosed PA packages are less susceptible to coplanarity issues along the package mount plane and avoid or mitigate various challenges associated with interposer piece attachment and overmolding. As further discussed above, embodiments of the PA package are amenable to fabrication at scale (that is, in larger numbers) for increased process efficiencies and reduced manufacturing costs. Other benefits are also achieved by embodiments of the PA packages described herein, and the associated manufacturing techniques, as will be appreciated by one of ordinary skill in the relevant industry given the benefit of the present disclosure.
In embodiments, the presently-disclosed PA package includes a package body having a package topside surface and a package bottomside surface, which is located opposite the package topside surface in a package height direction. The package body is defined, at least in part, by a package substrate and an electrically-routed lid bonded to a populated side of the package substrate to sealingly enclose an air cavity. The electrically-routed lid includes, in turn, an upper lid wall at least partially defining the package topside surface, peripheral lid sidewalls joined to the upper lid wall and bounding a periphery of the air cavity, and sidewall-embedded vias contained in the peripheral lid sidewalls and each extending essentially in the package height direction. RF circuitry is attached to the populated side of the package substrate and located within the air cavity, while a topside I/O interface is supported by or otherwise provided on the upper lid wall and electrically interconnected with the RF circuitry through the sidewall-embedded vias of the electrically-routed lid. Further, in at least some instances, the peripheral lid sidewalls may include a first peripheral lid sidewall and a second peripheral lid sidewall, while the topside I/O interface includes an RF input terminal and an RF output terminal. In such instances, the sidewall-embedded vias may further include: (i) a first sidewall-embedded via electrically coupled to the RF input terminal and extending within the first peripheral lid sidewall from the RF input terminal toward the package substrate; and (ii) a second sidewall-embedded via electrically coupled to the RF output terminal and extending within the second peripheral lid sidewall from the RF output terminal toward the package substrate. The first peripheral lid sidewall may be located opposite the second peripheral lid sidewall as taken along an axis perpendicular to the package height direction, while an RF power die included in the RF circuitry may be located between the first peripheral lid sidewall and the second peripheral lid sidewall as further taken along the axis.
Embodiments of a method for fabricating a plurality of PA packages in parallel or as a batch have been further disclosed. In embodiments, the method includes the steps or processes of attaching RF power dies (and possibly other microelectronic components) to a presingulated package substrate array, electrically interconnecting the RF power dies to routing features of the interconnected package substrates (e.g., using wirebonding or another interconnection technique), and obtaining (e.g., independently fabricating or purchasing from a supplier) a presingulated lid array comprised of a plurality of electrically-routed lids. Each electrically-routed lid in the presingulated lid array may include: (i) an upper lid wall at least partially defining the package topside surface; (ii) peripheral lid sidewalls joined to the upper lid wall (e.g., to form an open box-like structure); (iii) sidewall-embedded vias extending in the peripheral lid sidewalls, and (iv) a topside I/O interface or array formed on the upper lid wall and electrically coupled to the sidewall-embedded vias. Embodiments of the fabrication method further includes bonding the presingulated lid array to the presingulated package substrate array to produce presingulated or physically-interconnected PA packages. The presingulated PA packages are then singulated (e.g., utilizing a dicing saw directed along saw lanes of the presingulated lid array) to yield a plurality of singulated PA packages. Each of the PA packages may include at least one RF power die located in an air cavity and electrically coupled to the topside I/O array through the sidewall-embedded vias.
Continuing the example from the foregoing paragraph, in certain implementations, the step or process of bonding may entail forming a bond layer system attaching the presingulated lid array to the presingulated package substrate array and electrically coupling bond pads on the presingulated package substrate array to substrate-facing lid contacts of the electrically-routed lid, which are electrically coupled to the sidewall-embedded vias (e.g., the substrate-facing lid contacts may electrically contact and may align with the sidewall-embedded vias as taken along axes extending in a package height direction). Additionally, in embodiments, the step or process of forming may further entail (i) applying a dielectric bond material (e.g., by dispensing a wet state material, such as an epoxy paste, or by positioning a bond layer film) on lower surfaces of the presingulated lid array or on populated surfaces of the presingulated package substrate array; (ii) positioning the presingulated lid array over the presingulated package substrate array such that the dielectric bond material contacts the presingulated lid array and the presingulated package substrate array; and (iii) curing the dielectric bond material to form a dielectric bond layer bonding the presingulated lid array to the presingulated package substrate array, while sealingly enclosing an air cavity within each of the singulated power amplifier packages. Electrically-conductive bond layer portions (e.g., composed of a dielectric epoxy) may also be formed in the dielectric bond layer (e.g., composed of an electrically-conductive epoxy), while the substrate-facing lid contacts are electrically coupled to lid-facing contacts on the presingulated package substrate array through the electrically-conductive bond layer portions.
While at least one example embodiment has been presented in the foregoing Detailed Description, it should be appreciated that a vast number of variations exist. It should also be appreciated that the example embodiment or example embodiments are only examples, and are not intended to limit the scope, applicability, or configuration of the invention in any way. Rather, the foregoing Detailed Description will provide those skilled in the art with a convenient road map for implementing an example embodiment of the invention, it being understood that various changes may be made in the function and arrangement of elements described in an example embodiment without departing from the scope of the invention as set forth in the appended claims. Numerical identifiers, such as “first,” “second,” “third,” and the like have been used above in accordance with the order in which certain elements were introduced during the course of the foregoing Detailed Description. Such numerical identifiers may also be used in the subsequent Claims to indicate order of introduction in the Claims. Accordingly, such numerical identifiers may vary between the Detailed Description and the subsequent Claims to reflect differences in the order of introduction of elements.
