TOP SIDE COOLING FOR POWER AMPLIFIER MODULE

Systems and methods for top side cooling for a power amplifier module are disclosed. The power amplifier module may be part of a system in a package that may be considered inverted relative to a normal orientation. A power amplifier die (and other elements) may be mounted on a metallization layer. Wire bond connections may communicatively couple the “top” of the power amplifier die to the metallization layer. A plated heat sink (PHS) laminate may be positioned “beneath” the power amplifier die in the metallization layer. The metallization layer may communicatively couple to vias that extend “up” and “above” the power amplifier die to a connection pad. The entire package is then inverted such that the connection pads may couple to a printed circuit board in a downward direction, and the PHS is now facing upward so that it may be coupled to a heat sink.

BACKGROUND

I. Field of the Disclosure

The technology of the disclosure relates generally to cooling a power amplifier module using top side cooling.

Computing devices abound in modern society, and more particularly, mobile communication devices have become increasingly common. The prevalence of these mobile communication devices is driven in part by the many functions that are now enabled on such devices. Increased processing capabilities in such devices means that mobile communication devices have evolved from pure communication tools into sophisticated mobile entertainment centers, thus enabling enhanced user experiences. With the advent of the myriad functions available to such devices, there has been an evolution in the wireless protocols used to convey information to and from the mobile communication devices. The new protocols have placed new demands on transceivers and particularly power amplifiers used by transceivers to send wireless signals. These increased demands mean that many of the power amplifiers are generating waste heat. Removing this waste heat before it damages components in the mobile communication device provides room for innovation.

SUMMARY

Aspects disclosed in the detailed description include systems and methods for top side cooling for a power amplifier module. In particular, the power amplifier module may be part of a system in a package that may be considered inverted relative to a normal orientation. In this regard, before inversion, a power amplifier die (and other elements) may be mounted on a metallization layer. Wire bond connections may communicatively couple the “top” of the power amplifier die to the metallization layer. A plated heat sink (PHS) laminate may be positioned “beneath” the power amplifier die in the metallization layer. The metallization layer may communicatively couple to vias that extend “up” and “above” the power amplifier die to a connection pad. The entire package is then inverted such that the connection pads may couple to a printed circuit board or other substrate in a downward direction, and the PHS is now facing upward so that it may be coupled to a heat sink or fan element. Thus, the signal paths now go “down,” and the heat dissipation paths now go “up.” By separating the signal paths from the heat dissipation paths, performance is improved. Additionally, heat-related failures are reduced, resulting in a longer device lifetime.

In an exemplary aspect, a package is disclosed. The package includes a metallization layer comprising a PHS configured to be coupled to an external heat sink through a first surface and a plurality of interior metal layers electrically isolated from the PHS. The metallization layer further comprising a plurality of vias coupling different ones of the plurality of interior metal layers and a die positioned adjacent to the PHS at a second surface opposite the first surface, the die coupled to at least one of the interior metal layers through a wire bond connection. The package further includes an external via configured to couple the metallization layer to an exterior surface opposite the first surface.

In another exemplary aspect, a method of routing signals to a die in a package is disclosed. The method includes generating a signal in a die mounted on a plated heat sink (PHS), passing the signal through a wire bond from the die to an interior metal layer within a metallization layer, and passing the signal from the interior metal layer to an external via that routes the signal to an exterior surface opposite the PHS.

In another exemplary aspect, a device is disclosed. The device includes a transceiver comprising a package comprising a metallization layer. The metallization layer includes a PHS configured to be coupled to an external heat sink through a first surface, a plurality of interior metal layers electrically isolated from the PHS, and a plurality of vias coupling different ones of the plurality of interior metal layers. The device further includes a die positioned adjacent to the PHS at a second surface opposite the first surface, the die coupled to at least one of the interior metal layers through a wire bond connection and an external via configured to couple the metallization layer to an exterior surface opposite the first surface.

DETAILED DESCRIPTION

In keeping with the above admonition about definitions, the present disclosure uses transceiver in a broad manner. Current industry literature uses “transceiver” both broadly to refer to a plurality of circuits that send and receive signals or narrowly to refer to a specific conversion circuit within the plurality of circuits. In the broad sense, the transceiver may include a baseband processor, an up/down conversion circuit, filters, amplifiers, couplers, and the like coupled to one or more antennas. Alternatively, for the narrow sense, some authors in the industry literature use “transceiver” to refer to a single circuit positioned between a baseband processor and a power amplifier circuit. This intermediate circuit may include the up/down conversion circuits, mixers, oscillators, filters, and the like, but generally does not include the power amplifiers. As used herein, the term transceiver is used in the first sense. Where relevant to distinguish between the two definitions, the terms “transceiver chain” and “transceiver circuit” are used respectively.

Further, the term approximately, as used herein, means within five percent (5%).

Aspects disclosed in the detailed description include systems and methods for top side cooling for a power amplifier module. In particular, the power amplifier module may be part of a system in a package that may be considered inverted relative to a normal orientation. In this regard, before inversion, a power amplifier die (and other elements) may be mounted on a metallization layer. Wire bond connections may communicatively couple the “top” of the power amplifier die to the metallization layer. A plated heat sink (PHS) laminate may be positioned “beneath” the power amplifier die in the metallization layer. The metallization layer may communicatively couple to vias that extend “up” and “above” the power amplifier die to a connection pad. The entire package is then inverted such that the connection pads may couple to a printed circuit board or other substrate in a downward direction and the PHS is now facing upward so that it may be coupled to a heat sink or fan element. Thus, the signal paths now go “down,” and the heat dissipation paths now go “up.” By separating the signal paths from the heat dissipation paths, performance is improved. Additionally, heat-related failures are reduced, resulting in a longer device lifetime.

Before addressing exemplary aspects of the present disclosure, an overview of a conventional approach is provided to assist in seeing the benefits of the present disclosure. In this regard, a conventional transceiver may include a power amplifier module or die that generates waste heat during signal amplification. This waste heat may, if unchecked, damage components in the power amplifier module (e.g., remelting solder, melting plastic mold material, or the like). Recognizing this risk, designers have tried to create a thermal path through which the waste heat may dissipate. Since the power amplifier module is attached to a material such as a printed circuit board (PCB), the common approach is to route the waste heat through the PCB. The PCB also serves as a structure through which signaling conductors pass. The juxtaposition of the signaling conductors and the thermal path imposes contradictory design constraints on the designers, adding to the complexity and sometimes resulting in a compromise in performance. One such compromise is that materials such as a PCB are generally poor thermal paths, resulting in less efficient heat transfer.

Exemplary aspects of the present disclosure provide for a bifurcated routing of the waste heat path and the signaling conductors. Specifically, heat may be transferred through the top of a package containing a heat-generating element, such as a power amplifier. Signaling conductors are routed from the die, through a metallization layer, and down through a mold compound to signaling paths in the PCB. Conversely, signals from the PCB pass through vias in the mold compound up to the metallization layer, and then to the die.

In this regard,FIG.1Atop-down view of a package100before mold is applied thereto.FIG.1Bis the same package100taken along line1B-1B ofFIG.1A. More specifically, the package100begins with a metallization layer102, which may sometimes be referred to as a substrate or a laminate. In an exemplary aspect, the metallization layer102will include one or more metal layers104(1)-104(M) (seeFIG.1B) therewithin connected with internal vias106that provide interconnections in the z-axis while the metal layers104(1)-104(M) provide connections in the x-y plane. Relevantly, the metal layers104(1)-104(M) are within the metallization layer102and do not lie on either exterior surface aside from contact points that couple to vias106that couple to the top metal layer. The metallization layer102may also have a plated heat sink (PHS)108therewithin. The PHS108may be made from a good thermal conductor such as copper and may be electrically isolated from electrical conductors (e.g., metal layers104(1)-104(M) and vias106) in the metallization layer102. Heat-producing dies110(1)-110(P) are positioned on top (i.e., in the z-axis) of the PHS108and secured thereto with, for example, a high thermal sintered material112. A plurality of dies may also be referred to herein as “dice.” Additionally, the dice110(1)-110(P) may be coupled to metal layers104(1)-104(M) by wire bond connections111. In an exemplary aspect, the dice110(1)-110(P) may be power amplifier dice including, for example, gallium nitride (GaN) power amplifiers. Additional elements such as surface-mounted devices (SMD)114(1)-114(Q) (generically114) may also be mounted on the metallization layer102and connected to metal layers104(1)-104(M) as is well understood.

The package100may further include an e-bar interposer116. In a first aspect, the e-bar interposer116surrounds the PHS108(in the x-y directions) and may be made from a plastic material with external vias118(as opposed to internal vias106) extending from a first surface120adjacent to the metallization layer102to a second surface122(i.e., in the z-axis) spaced from the metallization layer102. As better illustrated inFIG.4, there is no strict requirement to surround the PHS108. An overmold material119(also referred to as a mold compound) may fill the space between the metallization layer102to the height (approximately) (z-axis) of the e-bar interposer116.

The package100may be mounted on a PCB124, such as through a solder ball or other conductive coupling that couples the vias118to conductors (not shown) in the PCB124. This coupling may be referred to as communicatively coupling with the electrical connections forming a path that communicatively couples elements in the dice110(1)-110(P) to the conductors in the PCB124to allow signals to pass therethrough. In exemplary aspects, the signals may contain clock information, data, power, or the like. On the other side of the package100(as illustrated, towards the “top” in the z-axis), the PHS108may couple to a thermal interface material (TIM)126. The TIM126may couple to a heat sink128, which may be a metal material, have a fan mounted thereon, or the like. It should be appreciated that the TIM126and heat sink128are applied during installation in a final product and are not central to the present disclosure. Rather, of greater interest is the ability to route heat through a PHS108to a top side and route signal paths through a bottom side (e.g., through the e-bar interposer116) thereby creating separate signal and heat paths. Thus, the top side (e.g., the PHS108and a top side of the metallization layer102) is configured to couple to a heat sink128, such as through TIM126. Likewise, the bottom side is configured to couple to a PCB124or other mounting material. As explained above, this notion of “top” and “bottom” are used to help provide explanation of relative positions and not intended to be strictly limited.

FIGS.2A and2Bprovide additional details about the e-bar interposer116and vias118. The e-bar interposer116may be formed from a plastic material200and have channels202drilled therethrough. While drilling is specifically contemplated, other techniques may be used to form the channels202without departing from the present disclosure. The channels202are plated with a conductive material204(e.g., copper, aluminum, gold, etc.) and may be filled with a plug material206.

FIG.3provides a flowchart of a process300for making a package according to exemplary aspects of the present disclosure. The process300begins with forming a metallization layer102with a PHS108therein (block302). The dies110(1)-110(P) are placed on the PHS108(block304). SMDs114(1)-114(Q) are then mounted on the metallization layer102(block306). The e-bar interposer116is attached (block308). Note that blocks304,306, and308may be switched temporally or done concurrently with the same pick-and-place machinery if desired. The power amplifiers (PAs) (or more generally the dies110(1)-110(P)) are then wire bond attached to the metallization layer102(block310). Again, this step may be done earlier in the process if desired.

When the basic structures are in place, an overmold material119is then applied (block312). Various ways of doing applying overmold material119are set forth with reference toFIGS.5-9below. Packages may be singulated to finish the process300(block314).

Instead of an e-bar interposer116that surrounds the PHS108, the interposers may be non-continuous, discrete elements, as is better seen inFIG.4. Specifically, interposer modules400may be used. In an exemplary aspect, interposer modules400include two rows of vias402, where each row has three to six (although more are possible) vias402. One module400may be positioned on each side of the package100, with one row in a first package and the other row in a second package. During singulation, the rows are split such that a single row from four modules400is present in each package. The use of the initial double-row arrangement may promote stability, such as during solder reflow. Note that whileFIG.4contemplates a module400on each side of the package, fewer modules may be used (i.e., on two or three sides only). Likewise, while shown as centered on a side, the modules400may be off center if needed or desired. Still further, the present disclosure contemplates that more than one module400may be on a given side. Placement of the modules400may be rearranged to facilitate routing through metallization layer102, provide additional vias402to provide connections for pins on the dies110(1)-110(P) and/or pins on the SMD114, or the like.

FIGS.5-9illustrate various ways that the overmold material119may be applied for the package. The precise details are not central to the present disclosure, and any of these methods or variations thereon may be used without departing from the present disclosure.

In this regard,FIG.5illustrates a first overmold technique. Specifically, a film may be placed on a plane extending between surfaces500,502of the interposer116. Overmold material119may be injected from the sides (e.g., at points504A,504B), filling the space over the dice110(1)-110(P) and the SMDs114.

FIG.6contemplates a glob top approach to the overmold material119. In this approach, a needle dispenses overmold material119in layers over the dice110(1)-110(P) and SMD114. This approach may allow the height (z-axis) of the overmold material119to be controlled more readily.

FIG.7contemplates a compression mold approach where the package100is pressed down (see arrow700in z-axis) into an uncured volume of overmold compound, cured, and then ground down to expose the interposer116while leaving overmold material119over the dice110(1)-110(P) and SMD114.

FIG.8contemplates adding the overmold material119initially in a pattern that leaves room for the interposer116, which is added subsequently. This approach may leave a channel800between the overmold material119and the interposer116.

FIG.9uses vertical wire bonds900that are not specifically in an interposer116. The overmold material119flows around and encloses the wire bonds900to hold them in position and allow for interconnection of conductors in the metallization layer102to the PCB. Note that, as used herein the term external via also includes these vertical wire bonds900.

Another approach that may be used in isolation or with one of the techniques ofFIGS.5-9uses laser ablating to shape the overmold material119. Specifically, the overmold material119is applied through any appropriate technique and then ablated to expose the external vias118or otherwise expose sufficient metal to form a communicative coupling. A solder ball may then be attached to the freshly exposed metal of the external vias118. In an exemplary aspect, each external via118may have its own respective solder ball. The solder ball may then be used to attach to a complementary contact pad on the PCB124.

The systems and methods for top side cooling of a power amplifier module, according to aspects disclosed herein, may be provided in or integrated into any processor-based device. Examples, without limitation, include a set-top box, an entertainment unit, a navigation device, a communications device, a fixed location data unit, a mobile location data unit, a global positioning system (GPS) device, a mobile phone, a cellular phone, a smartphone, a session initiation protocol (SIP) phone, a tablet, a phablet, a server, a computer, a portable computer, a mobile computing device, a wearable computing device (e.g., a smartwatch, a health or fitness tracker, eyewear, etc.), a desktop computer, a personal digital assistant (PDA), a monitor, a computer monitor, a television, a tuner, a radio, a satellite radio, a music player, a digital music player, a portable music player, a digital video player, a video player, a digital video disc (DVD) player, a portable digital video player, an automobile, a vehicle component, avionics systems, a drone, and a multicopter.

With reference toFIG.10, the concepts described above may be implemented in various types of user elements1000, such as those listed in the previous paragraph. The user elements1000will generally include a control system1002, a baseband processor1004, transmit circuitry1006, which may include the power amplifier module ofFIGS.1A-6, receive circuitry1008, antenna switching circuitry1010, multiple antennas1012, and user interface circuitry1014. In a non-limiting example, the control system1002can be a field-programmable gate array (FPGA) or an application-specific integrated circuit (ASIC), as an example. In this regard, the control system1002can include at least a microprocessor(s), an embedded memory circuit(s), and a communication bus interface(s). The receive circuitry1008receives radio frequency signals via the antennas1012and through the antenna switching circuitry1010from one or more base stations. A low noise amplifier and a filter of the receive circuitry1008cooperate to amplify and remove broadband interference from the received signal for processing. Downconversion and digitization circuitry (not shown) will then downconvert the filtered, received signal to an intermediate or baseband frequency signal, which is then digitized into one or more digital streams using an analog-to-digital converter(s) (ADC).

The baseband processor1004processes the digitized received signal to extract the information or data bits conveyed in the received signal. This processing typically comprises demodulation, decoding, and error correction operations. The baseband processor1004is generally implemented in one or more digital signal processors (DSPs) and ASICs.

For transmission, the baseband processor1004receives digitized data, which may represent voice, data, or control information, from the control system1002, which it encodes for transmission. The encoded data is output to the transmit circuitry1006, where a digital-to-analog converter(s) (DAC) converts the digitally encoded data into an analog signal, and a modulator modulates the analog signal onto a carrier signal that is at a desired transmit frequency or frequencies. A power amplifier within a power amplifier module of the present disclosure will amplify the modulated carrier signal to a level appropriate for transmission and deliver the modulated carrier signal to the antennas1012through the antenna switching circuitry1010to the antennas1012. The multiple antennas1012and the replicated transmit and receive circuitries1006,1008may provide spatial diversity. Modulation and processing details will be understood by those skilled in the art.