Low frequency shield solutions with sputtered/sprayed absorber materials and/or absorber materials mixed in mold compound

An electronic device includes an electromagnetic interference shield having a layer of conductive material covering at least a portion of the electronic device and having a skin depth of less than 2 μm for electromagnetic signals having frequencies in a kilohertz range.

BACKGROUND

Technical Field

Embodiments of this disclosure relate to multi-component microelectronic devices and structures and methods of mitigating electromagnetic cross-talk in same.

Description of Related Technology

Modern electronic devices may include modules or packages housing multiple components, for example, power amplifiers, low noise amplifiers, voltage-controlled oscillators, switches, filters, and other components that operate utilizing alternating current. Market forces continue to demand electronic devices having increasingly smaller form factors and that are lighter and less expensive, but have greater functionality, for example, in electronic communication devices, the ability to support multiple frequency bands. As a result, the circuit density in many electronic devices continues to become greater with each new product iteration. Electromagnetic interference (EMI) or cross-talk between the components in a common electronic device module or between components in an electronic device module and external sources may degrade overall performance or cause failure of an electronic device.

SUMMARY

In accordance with one aspect, there is provided an electronic device. The electronic device comprises an electromagnetic interference shield including a layer of conductive material covering at least a portion of the electronic device and having a skin depth of less than 2 μm for electromagnetic signals having frequencies in a kilohertz range.

In some embodiments, the electronic device is covered in a molding material and the electromagnetic interference shield is disposed on the molding material. The molding material may include a filler material that retards propagation of electromagnetic signals. The filler material may have a skin depth of less than 2 μm for electromagnetic signals having frequencies in the kilohertz range. The filler material may include a magnetic ceramic ferrite. The filler material may include an iron containing alloy. The filler material may be non-conductive. The filler material may include conductive particles surrounded by non-conductive material.

In some embodiments, a component of the electronic device is configured to emit an electromagnetic signal at a frequency within one or more of a hertz range, a kilohertz range, or a megahertz range.

In some embodiments, the layer of conductive material includes a magnetic ceramic ferrite.

In some embodiments, the layer of conductive material includes an iron containing alloy.

In some embodiments, the layer of conductive material has a thickness of less than 30 μm. The layer of conductive material may have a thickness of less than 20 μm.

In some embodiments, the electronic device further comprises a radio frequency filter. The electronic device may be included in an electronics module.

In accordance with another aspect, there is provided and electronic device. The electronic device comprises a molding material covering at least a portion of the electronic device and including a filler material having a skin depth of less than 2 μm for electromagnetic signals having frequencies in a kilohertz range.

In some embodiments, the filler material includes a magnetic ceramic ferrite.

In some embodiments, the filler material includes an iron containing alloy.

In some embodiments, the filler material is non-conductive.

In some embodiments, the filler material includes conductive particles covered by non-conductive material.

In some embodiments, a component of the electronic device is configured to emit an electromagnetic signal at a frequency within one or more of a hertz range, a kilohertz range, or a megahertz range.

In some embodiments, the electronic device further comprises an electromagnetic interference shield including a layer of conductive material having a skin depth of less than 2 μm for electromagnetic signals having frequencies in a kilohertz range disposed on the molding material. The layer of conductive material may include a magnetic ceramic ferrite. The layer of conductive material may include an iron containing alloy. The layer of conductive material may have a thickness of less than 30 μm. The layer of conductive material may have a thickness of less than 20 μm.

In some embodiments, the electronic device further comprises a radio frequency filter. The electronic device may be included in an electronics module.

In accordance with another aspect, there is provided a method of forming an electromagnetic interference shield on an electronic device. The method comprises depositing a molding material including a filler material having a skin depth of less than 2 μm for electromagnetic signals having frequencies in a kilohertz range on a surface of the electronic device.

In some embodiments, the method further comprises depositing a layer of conductive material having a skin depth of less than 2 μm for electromagnetic signals having frequencies in the kilohertz range on the molding material.

In accordance with another aspect, there is provided a method of forming an electromagnetic interference shield on an electronic device. The method comprises depositing a molding material on a surface of the electronic device; and depositing a layer of conductive material having a skin depth of less than 2 μm for electromagnetic signals having frequencies in a kilohertz range on the molding material.

DETAILED DESCRIPTION OF CERTAIN EMBODIMENTS

Modern electronic devices, for example, communications devices such as cellular telephones may include multiple components that operate at frequencies in the GHz range. Electromagnetic shielding for devices operating at frequencies in the GHz range may be accomplished using films or layers of conductive material disposed between devices one wishes to electromagnetically isolate from one another to prevent cross-talk. At such high frequencies, electromagnetic signals do not penetrate deeply into layers of conductive material, so electromagnetic shielding between devices operating at frequencies in the GHz range may be accomplished using thin films of conductive material, for example, metal films with thicknesses of 3 μm or less. At lower frequencies, for example, in the MHz, kHz, or Hz ranges electromagnetic signals propagate more deeply into layers of conductive material than do signals at frequencies in the GHz range. Shielding that may be useful for isolating devices operating in the GHz range may thus be inadequate for electromagnetically isolating devices operating at low frequencies—electromagnetic signals generated by components operating at low frequencies may pass through shielding designed to suppress cross-talk between devices operating at frequencies in the GHz range and may cause interference or cross-talk between other nearby devices. The degree to which electromagnetic signals penetrate into a conductor may be referred to as electromagnetic “skin depth.” The skin depth is a measure of the depth at which the intensity of electromagnetic radiation in a conductor falls to 1/e of its value near the surface of the conductor and is dependent on the frequency of the electromagnetic signal and material properties of the conductive material. One formula for skin depth δ is:

δ=ρμ*f*π
where ρ is resistivity (μΩ·cm) of the conductive material, f is frequency (MHz), and μ is permeability of the conductive material

The skin depth of copper, silver, and nickel at various frequencies is illustrated in Table 1 below:

TABLE 1Selected Material Skin Depths (μm)FrequencyCopperSilverNickel100kHz206.2200.517.05MHz29.128.32.4100MHz6.526.340.53500MHz2.932.870.421GHz2.072.030.302GHz1.461.440.215GHz0.930.910.1310GHz0.650.640.09100GHz0.210.200.03

As can be seen in Table 1 above, a film of copper of only a few microns in thickness may be sufficient to shield an electronic component against electromagnetic interference at frequencies in the GHz range, but to shield the component against electromagnetic interference at frequencies in the kHz range, the copper film should be a few hundreds of microns thick. Such thick shielding would typically not be practical or cost effective in typical electronic device fabrication processes.

One option for providing thin shielding against electromagnetic interference for EMI-sensitive devices is to utilize an EMI absorber material that has a higher permeability and is a better absorber of electromagnetic energy than copper, silver, or nickel. Such materials may include magnetic ceramic ferrites or iron containing alloys, for example, NiFe, CuNiFe/CZT (CZT=cadmium zinc telluride. For high frequency implementation in the GHZ range Cu may make up the majority of the material. For low frequency implementation or implementations in the kHz range NiFe may make up the majority of the material) or MCFS magnetic shielding film, available from EMR Shielding solutions and having a formula Co69Fe4Mo4NbSi16B7. A film of one or more of these materials may be deposited, for example, by sputtering, spraying, or printing on a packaged device or module before or after mounting the packaged device or module onto a carrier, for example, a printed circuit board. The deposited film thickness may range between about 5 μm and about 30 μm, or in some embodiments between 0 μm and about 20 μm. The EMI absorber material may have a skin depth of less than 3 μm, less than 2 μm, less than 1 μm, less than 0.5 μm, or less than 0.1 μm, for electromagnetic signals in the GHz range (1 GHz to 1,000 GHz), the MHz range (1 MHz to 1 GHz), the kHz range (1 kHz to 1 MHz), or the Hz range (1 Hz to 1 kHz) or skin depths less than that of copper, silver, or nickel at the respective frequencies illustrated in Table 1.

FIGS. 1A and 1Bcompare the effect of suppression of EMI from a power amplifier module (Skyworks Solutions, Inc. model SKY78140-22) operating at 127.7 kHz utilizing a 3 μm thick conformally deposited copper film vs. the same copper film covered device with an additional 20 μm thick film of MCFS placed over the device, respectively. InFIGS. 1A and 1Bthe location of the device beneath the respective films is indicated by the outline100. The Cu film suppressed EMI from the device by 63.6 dBm, while the Cu film with the additional MCFS film suppressed the EMI from the device by 90.1 dBm, a 26.5 dBm improvement.

FIG. 2schematically illustrates an electronic device, for example, a multi-chip module200disposed on a circuit board205, covered by a molding material210and further covered by a layer of highly absorbing EMI shield material215that has been deposited by, for example, sputtering or spraying. The molding material210may be or may include any typical electronic device molding material, for example, an epoxy or epoxy-based material.

One disadvantage of the EMI shielding method described above and illustrated inFIG. 2is that although EMI interference between adjacent packaged devices or modules may be suppressed or eliminated, the possibility still exists for electromagnetic interference or cross-talk to occur between different discreet components within the packaged module. A further embodiment, which may at least partially address this problem, includes incorporating an EMI absorber material into molding compound that is deposited on a device or module. The molding compound may be the same or similar type of molding compound that is typically used to seal and protect a packaged device or module, for example, epoxy or an epoxy-based material, but with the addition of the EMI absorber material. Particles or a powder of the EMI absorber material, which may be or may include one or more of the magnetic ceramic ferrites or iron containing alloys discussed above may be mixed or blended into a typical packaged module molding material. The particles may have characteristic dimensions, for example, radii that are at least as large as the skin depth of the material of the particles at a frequency of interest, for example, at a frequency of electromagnetic interference that the device is expected to generate or which the device may be sensitive to. The particles may have characteristic dimensions of between about 10 μm and about 100 μm. The molding material including the EMI absorber material may then be deposited on the device or module using conventional methods, or directly on a die including components to be shielded. The EMI absorber material filler or particles may be non-conductive or conductive with non-conductive coatings to help avoid shorts between exposed leads of the device or module. The molding material including the EMI absorber material may be deposited with a typical thickness for molding materials used in the industry, for example, between 350 μm and 1000 μm. The greater thickness of the molding material including the EMI absorber material as compared to a sputtered film (for example, 3 μm to 20 μm thick) may provide for greater EMI shielding than a sputtered film of EMI absorbing material. The greater thickness of the molding material vs. a sputtered film may also provide for the use of a lesser absorbing and less expensive EMI absorbing material to achieve equivalent EMI suppression performance as a thinner sputtered or sprayed layer of a higher absorbing but more expensive EMI absorbing material. Incorporating the EMI absorbing material into the molding material may also eliminate the need for any special steps to be performed to deposit the EMI absorbing material.

FIG. 3schematically illustrates an electronic device, for example, a multi-chip module300disposed on a circuit board305, covered by a molding material310including EMI absorbing material.

It should be appreciated that the embodiment illustrated inFIG. 2may be combined with that illustrated inFIG. 3. For example, the molding material210ofFIG. 2may include EMI shielding material, resulting in the structure illustrated inFIG. 4.

The devices discussed herein can be implemented in a variety of packaged modules. Some example packaged modules will now be discussed in which any suitable principles and advantages of the devices discussed herein can be implemented.FIGS. 5, 6, and 7are schematic block diagrams of illustrative packaged modules and devices according to certain embodiments.

Embodiments of the devices disclosed herein may include, for example, filters. In turn, a filter using one or more of the devices disclosed herein may be incorporated into and packaged as a module that may ultimately be used in an electronic device, such as a wireless communications device, for example.FIG. 5is a block diagram illustrating one example of a module400including a filter410. The filter410may be implemented on one or more die(s)420including one or more connection pads422. For example, the filter410may include a connection pad422that corresponds to an input contact for the filter and another connection pad422that corresponds to an output contact for the filter. The packaged module400includes a packaging substrate430that is configured to receive a plurality of components, including the die420. A plurality of connection pads432can be disposed on the packaging substrate430, and the various connection pads422of the filter die420can be connected to the connection pads432on the packaging substrate430via electrical connectors434, which can be solder bumps or wirebonds, for example, to allow for passing of various signals to and from the filter410. The module400may optionally further include other circuitry die440, such as, for example one or more additional filter(s), amplifiers, pre-filters, modulators, demodulators, down converters, and the like, as would be known to one of skill in the art of semiconductor fabrication in view of the disclosure herein. In some embodiments, the module400can also include one or more packaging structures to, for example, provide protection and facilitate easier handling of the module400. Such a packaging structure can include an overmold formed over the packaging substrate430and dimensioned to substantially encapsulate the various circuits and components thereon. The overmold may include a filler including examples of the EMI absorbing materials disclosed herein.

Various examples and embodiments of the filter410can be used in a wide variety of electronic devices. For example, the filter410can be used in an antenna duplexer, which itself can be incorporated into a variety of electronic devices, such as RF front-end modules and communication devices.

Referring toFIG. 6, there is illustrated a block diagram of one example of a front-end module500, which may be used in an electronic device such as a wireless communications device (e.g., a mobile phone) for example. The front-end module500includes an antenna duplexer510having a common node502, an input node504, and an output node506. An antenna610is connected to the common node502.

The antenna duplexer510may include one or more transmission filters512connected between the input node504and the common node502, and one or more reception filters514connected between the common node502and the output node506. The passband(s) of the transmission filter(s) are different from the passband(s) of the reception filters. Examples of the filter410can be used to form the transmission filter(s)512and/or the reception filter(s)514. An inductor or other matching component520may be connected at the common node502.

The front-end module500further includes a transmitter circuit532connected to the input node504of the duplexer510and a receiver circuit534connected to the output node506of the duplexer510. The transmitter circuit532can generate signals for transmission via the antenna610, and the receiver circuit534can receive and process signals received via the antenna610. In some embodiments, the receiver and transmitter circuits are implemented as separate components, as shown inFIG. 6, however in other embodiments these components may be integrated into a common transceiver circuit or module. As will be appreciated by those skilled in the art, the front-end module500may include other components that are not illustrated inFIG. 6including, but not limited to, switches, electromagnetic couplers, amplifiers, processors, and the like.

FIG. 7is a block diagram of one example of a wireless device600including the antenna duplexer510shown inFIG. 6. The wireless device600can be a cellular phone, smart phone, tablet, modem, communication network or any other portable or non-portable device configured for voice or data communication. The wireless device600can receive and transmit signals from the antenna610. The wireless device includes an embodiment of a front-end module500similar to that discussed above with reference toFIG. 6. The front-end module500includes the duplexer510, as discussed above. In the example shown inFIG. 7the front-end module500further includes an antenna switch540, which can be configured to switch between different frequency bands or modes, such as transmit and receive modes, for example. In the example illustrated inFIG. 7, the antenna switch540is positioned between the duplexer510and the antenna610; however, in other examples the duplexer510can be positioned between the antenna switch540and the antenna610. In other examples the antenna switch540and the duplexer510can be integrated into a single component.

The front-end module500includes a transceiver530that is configured to generate signals for transmission or to process received signals. The transceiver530can include the transmitter circuit532, which can be connected to the input node504of the duplexer510, and the receiver circuit534, which can be connected to the output node506of the duplexer510, as shown in the example ofFIG. 6.

Signals generated for transmission by the transmitter circuit532are received by a power amplifier (PA) module550, which amplifies the generated signals from the transceiver530. The power amplifier module550can include one or more power amplifiers. The power amplifier module550can be used to amplify a wide variety of RF or other frequency-band transmission signals. For example, the power amplifier module550can receive an enable signal that can be used to pulse the output of the power amplifier to aid in transmitting a wireless local area network (WLAN) signal or any other suitable pulsed signal. The power amplifier module550can be configured to amplify any of a variety of types of signal, including, for example, a Global System for Mobile (GSM) signal, a code division multiple access (CDMA) signal, a W-CDMA signal, a Long-Term Evolution (LTE) signal, or an EDGE signal. In certain embodiments, the power amplifier module550and associated components including switches and the like can be fabricated on gallium arsenide (GaAs) substrates using, for example, high-electron mobility transistors (pHEMT) or insulated-gate bipolar transistors (BiFET), or on a Silicon substrate using complementary metal-oxide semiconductor (CMOS) field effect transistors.

Still referring toFIG. 7, the front-end module500may further include a low noise amplifier module560, which amplifies received signals from the antenna610and provides the amplified signals to the receiver circuit534of the transceiver530.

The wireless device600ofFIG. 7further includes a power management sub-system620that is connected to the transceiver530and manages the power for the operation of the wireless device600. The power management system620can also control the operation of a baseband sub-system630and various other components of the wireless device600. The power management system620can include, or can be connected to, a battery (not shown) that supplies power for the various components of the wireless device600. The power management system620can further include one or more processors or controllers that can control the transmission of signals, for example. In one embodiment, the baseband sub-system630is connected to a user interface640to facilitate various input and output of voice and/or data provided to and received from the user. The baseband sub-system630can also be connected to memory650that is configured to store data and/or instructions to facilitate the operation of the wireless device, and/or to provide storage of information for the user. Any of the embodiments described above can be implemented in association with mobile devices such as cellular handsets. The principles and advantages of the embodiments can be used for any systems or apparatus, such as any uplink wireless communication device, that could benefit from any of the embodiments described herein. The teachings herein are applicable to a variety of systems. Although this disclosure includes some example embodiments, the teachings described herein can be applied to a variety of structures. Any of the principles and advantages discussed herein can be implemented in association with RF circuits configured to process signals in a range from about 30 kHz to 300 GHz, such as in a range from about 450 MHz to 6 GHz.

Aspects of this disclosure can be implemented in various electronic devices. Examples of the electronic devices can include, but are not limited to, consumer electronic products, parts of the consumer electronic products such as packaged radio frequency modules, uplink wireless communication devices, wireless communication infrastructure, electronic test equipment, etc. Examples of the electronic devices can include, but are not limited to, a mobile phone such as a smart phone, a wearable computing device such as a smart watch or an ear piece, a telephone, a television, a computer monitor, a computer, a modem, a hand-held computer, a laptop computer, a tablet computer, a microwave, a refrigerator, a vehicular electronics system such as an automotive electronics system, a stereo system, a digital music player, a radio, a camera such as a digital camera, a portable memory chip, a washer, a dryer, a washer/dryer, a copier, a facsimile machine, a scanner, a multi-functional peripheral device, a wrist watch, a clock, etc. Further, the electronic devices can include unfinished products.