PATENT DOCUMENT

Publication Number: US-10431382-B2
Application Number: US-201514841387-A
Country: US
Kind Code: B2

Title: Printed circuit board assembly having a damping layer

Abstract:
A printed circuit board (PCB) assembly having several electronic components mounted on a PCB and a damping layer covering the electronic components, is disclosed. Embodiments of the PCB assembly include an overmold layer constraining the damping layer against the PCB. Embodiments of the PCB assembly include an interposer between a capacitor of the electronic components and the PCB. Other embodiments are also described and claimed.

Claims:
What is claimed is: 
     
       1. A printed circuit board assembly, comprising:
 a printed circuit board (PCB) having a first flexural modulus and a top surface; 
 a plurality of electronic components mounted on the top surface of the PCB; 
 a damping layer mounted on the top surface of the PCB, wherein the damping layer includes a continuous layer of viscoelastic material covering the plurality of electronic components, wherein the damping layer is attached to the top surface of the PCB at a plurality of locations around the plurality of electronic components, and wherein the damping layer includes a second flexural modulus lower than the first flexural modulus; and 
 an overmold layer mounted on the top surface of the PCB, wherein the overmold layer is a continuous layer of waterproof material covering the plurality of electronic components and the continuous layer of viscoelastic material, and wherein the overmold layer is in direct contact with the damping layer and is attached to the top surface of the PCB at a plurality of locations around the damping layer. 
 
     
     
       2. The printed circuit board assembly of  claim 1 , wherein the PCB includes a first density and the damping layer includes a second density, and wherein a first ratio of the first flexural modulus to the first density is greater than a second ratio of the second flexural modulus to the second density. 
     
     
       3. The printed circuit board assembly of  claim 1 , wherein the overmold layer constrains the damping layer against the PCB. 
     
     
       4. The printed circuit board assembly of  claim 3 , wherein the overmold layer includes a third flexural modulus higher than the second flexural modulus, and wherein the damping layer includes a first damping loss factor higher than a second damping loss factor of the overmold layer. 
     
     
       5. The printed circuit board assembly of  claim 4 , wherein the plurality of electronic components include a capacitor, and further comprising an encapsulation layer covering the capacitor and disposed between the damping layer and the PCB, wherein the encapsulation layer includes a fourth flexural modulus lower than the third flexural modulus. 
     
     
       6. The printed circuit board assembly of  claim 5 , wherein the encapsulation layer surrounds a periphery of the capacitor, and wherein the damping layer is in direct contact with and surrounds the encapsulation layer around the periphery. 
     
     
       7. The printed circuit board assembly of  claim 1 , wherein the plurality of electronic components include a capacitor, and further comprising
 an interposer between the capacitor and the PCB, wherein the interposer includes an upper contact electrically connected to the capacitor, a lower contact electrically connected to the PCB, and a via electrically connected with the upper contact and the lower contact and laterally offset from one or more of the upper contact or the lower contact. 
 
     
     
       8. The printed circuit board assembly of  claim 7 , wherein the capacitor includes a normal centerline perpendicular to the PCB, and wherein the normal centerline is nearer to the lower contact than the upper contact. 
     
     
       9. The printed circuit board assembly of  claim 7 , wherein the via includes a first via segment extending downward from a top face of the interposer and a second via segment extending upward from a bottom face of the interposer, and wherein the first via segment is laterally offset from the second via segment. 
     
     
       10. The printed circuit board assembly of  claim 9 , wherein the interposer includes at least two layers having one or more interface surfaces between the top face and the bottom face, and wherein the first via segment extends from the top face to an interface surface and the second via segment extends from the bottom face to the interface surface. 
     
     
       11. The printed circuit board assembly of  claim 10 , wherein the interposer includes a trace extending along the interface surface between the first via segment and the second via segment. 
     
     
       12. The printed circuit board assembly of  claim 10  further comprising an acoustic trap extending from the via along one of the one or more interface surfaces to trap vibrational acoustics of a predetermined wavelength, wherein the acoustic trap includes a trap length equal to one-quarter of the predetermined wavelength. 
     
     
       13. The printed circuit board assembly of  claim 7  further comprising an encapsulation layer covering the capacitor and disposed between the damping layer and the PCB, wherein the encapsulation layer includes a third flexural modulus lower than the second flexural modulus. 
     
     
       14. The printed circuit board assembly of  claim 13 , wherein the encapsulation layer surrounds a periphery of the capacitor, and wherein the damping layer is in direct contact with and surrounds the encapsulation layer around the periphery. 
     
     
       15. A method, comprising:
 mounting a plurality of electronic components on a top surface of a printed circuit board (PCB), wherein the PCB includes a first flexural modulus; 
 depositing a damping layer on the top surface of the PCB, wherein the damping layer includes a continuous layer of viscoelastic material over the plurality of electronic components, wherein the damping layer is attached to the top surface of the PCB at a plurality of locations around the plurality of electronic components, and wherein the damping layer includes a second flexural modulus lower than the first flexural modulus; and 
 depositing an overmold layer on the top surface of the PCB, wherein the overmold layer is a continuous layer of waterproof material over the plurality of electronic components and the continuous layer of viscoelastic material, and wherein the overmold layer is in direct contact with the damping layer and is attached to the top surface of the PCB at a plurality of locations around the damping layer and constrains the damping layer against the PCB. 
 
     
     
       16. The method of  claim 15 , wherein the overmold layer includes a third flexural modulus higher than the second flexural modulus. 
     
     
       17. The method of  claim 16 , wherein the plurality of electronic components include a capacitor, and further comprising depositing an encapsulation layer over the capacitor, wherein the encapsulation layer includes a fourth flexural modulus lower than the third flexural modulus. 
     
     
       18. The method of  claim 17 , wherein mounting the capacitor on the PCB includes:
 mounting the capacitor on an interposer, wherein the interposer includes an upper contact electrically connected to the capacitor; and 
 mounting the interposer on the PCB, wherein the interposer includes a lower contact electrically connected to the PCB, and wherein the interposer includes a via electrically connected with the upper contact and the lower contact, the via being laterally offset from one or more of the upper contact or the lower contact.

Description:
BACKGROUND 
     Field 
     Embodiments related to printed circuit board (PCB) assemblies are disclosed. More particularly, embodiments related to PCB assemblies having several electronic components mounted on a PCB are disclosed. 
     Background Information 
     An electronic device, such as a computer and/or a mobile device, may include a printed circuit board (PCB) assembly having electronic components, such as integrated circuits and capacitors, mounted on a PCB. The electronic components may be electrically connected through a printed circuit having vias and traces. The electronic components may deform when a voltage ripple occurs in a driving electrical signal delivered through the printed circuit. Furthermore, the deformation of the electronic components can transmit deforming loads to the PCB, which can cause the PCB to vibrate. Such vibration may lead to radiation of audible acoustic noise from the PCB and the electronic devices of the PCB assembly. 
     SUMMARY 
     A printed circuit board (PCB) assembly may include a waterproofing layer surrounding electronic components mounted on a PCB. The waterproofing layer may function to protect the electronic components from moisture. The waterproofing layer, however, is typically over-molded using a rigid epoxy, so although it may prevent ingress of moisture to the electronic components, it can actually exacerbate the radiation of acoustic noise from the PCB assembly. More particularly, the electronic components can force the rigid waterproofing layer to vibrate along with the PCB, which may lead to increased acoustic noise radiation. For example, experimental test results have indicated that a PCB assembly having a rigid waterproofing layer can be 10 dBA louder than a PCB assembly without a rigid waterproofing layer. This increased acoustic noise from the PCB assembly may be undesirable for a user of an electronic device that includes the waterproofed PCB assembly. 
     In an embodiment, a PCB assembly includes one or more mechanisms to waterproof electronic components without substantially increasing acoustic noise radiation from the PCB assembly. The PCB assembly may include a printed circuit board (PCB) having a flexural modulus, several electronic components mounted on the PCB, and a damping layer covering electronic components and attached to the PCB at several locations around the electronic components. The damping layer may include a flexural modulus lower than the flexural modulus of the PCB. Furthermore, the PCB may include a first density and the damping layer may include a second density, such that a first ratio of the first flexural modulus to the first density is greater than a second ratio of the second flexural modulus to the second density. Thus, the damping layer may modify the vibrational characteristics of the PCB assembly in a manner that reduces acoustic noise radiation from the PCB assembly. 
     In an embodiment of the PCB assembly, an overmold layer covers the damping layer and is attached to the PCB at several locations around the damping layer. Thus, the overmold layer may be rigidly secured to the PCB to sandwich the damping layer and constrain the damping layer against the PCB. The overmold layer may be a waterproof layer that includes a flexural modulus higher than the flexural modulus of the damping layer. Furthermore, the damping layer may include a first damping loss factor higher than a damping loss factor of the overmold layer. Thus, the overmold layer may prevent moisture from migrating into the damping layer, and the damping layer may modify the vibrational characteristics of the PCB assembly in a manner that reduces acoustic noise radiation from the PCB assembly. 
     In an embodiment, an encapsulated capacitor is mounted on the PCB of the PCB assembly. More particularly, an encapsulation layer may cover the capacitor and be disposed between the damping layer and the PCB. That is, the encapsulation layer may form a thin film around the capacitor, and another capacitor may also be surrounded by a respective encapsulation layer such that the damping layer fills a lateral space between the encapsulated capacitors. Each encapsulation layer may provide waterproofing protection for the capacitor that it encapsulates, and furthermore, the encapsulation may improve mechanical coupling between the capacitors and the PCB. That is, the encapsulation layer may surround a periphery of the capacitor, and the damping layer may surround the encapsulation layer around the periphery. In an embodiment, the encapsulation layer(s) include a flexural modulus that is lower than the flexural modulus of the overmold layer. Thus, the encapsulation layer(s) may modify the vibrational characteristics of the PCB assembly in a manner that reduces acoustic noise radiation from the PCB assembly. 
     Additional components may be used to reduce acoustic noise radiation from a PCB assembly. For example, in an embodiment, a PCB assembly includes a capacitor mounted on a PCB, and a damping layer covering the capacitor and attached to the PCB at several locations around the capacitor. Additionally, the PCB assembly may include an interposer between the capacitor and the PCB. For example, the interposer may include an upper contact electrically connected to the capacitor, a lower contact electrically connected to the PCB, and a via electrically connected with the upper contact and the lower contact. The via may be laterally offset from one or more of the upper contact or the lower contact, and thus, the interposer may deform more easily between the contacts to absorb energy and reduce the transmission of vibration between the capacitor and the PCB. 
     In an embodiment, the capacitor includes a normal centerline perpendicular to the PCB, and the normal centerline is nearer to the lower contact than the upper contact. For example, a via of the interposer may include a first via segment extending downward from an upper contact on a top face of the interposer, and a second via segment extending upward from a lower contact on a bottom face of the interposer. The contacts may be laterally offset from each other such that the first via segment is laterally offset from the second via segment, and the second via segment is closer to the normal centerline. 
     The interposer of the PCB assembly may include at least two layers having one or more interface surfaces between a top face and a bottom face of the interposer. Thus, the first via segment may extend from the top face to an interface surface and the second via segment may extend from the bottom face to the interface surface. In an embodiment, a trace extends along the interface surface between the first via segment and the second via segment to complete an electrical circuit between the upper contact and the lower contact. 
     The PCB assembly may include an acoustic trap to reflect acoustic waves emitted by an electronic component coupled to the PCB, and thus prevent the acoustic waves from propagating toward and exciting the PCB. The acoustic trap may extend from the via along one of the interface surfaces to trap vibrational acoustics of a predetermined wavelength. For example, the acoustic trap may include a trap length equal to one-quarter of the predetermined wavelength, and thus, the acoustic trap may block the passage of acoustic waves having the predetermined wavelength. 
     In an embodiment, the PCB assembly having the damping layer and the interposer may also include an overmold layer and/or an encapsulation layer. For example, an overmold layer may cover the damping layer and be attached to the PCB at several locations around the damping layer. Furthermore, an encapsulation layer may cover the capacitor and be disposed between the damping layer and the PCB. 
     A method of fabricating a PCB assembly is provided. In an embodiment, the method includes mounting several electronic components on a printed circuit board (PCB) and depositing a damping layer over the electronic components. The damping layer may be a continuous layer covering the electronic components, and may fill a lateral space between the components and be attached to the PCB. Accordingly, the damping layer may alter the vibrational characteristics of the PCB and reduce noise radiation from the PCB assembly. The method may also include depositing an overmold layer over the damping layer such that the overmold layer is attached to the PCB at several locations around the damping layer to constrain the damping layer against the PCB. Furthermore, the method may include depositing an encapsulation layer over at least one of the electronic components, e.g., a capacitor. As described above, several electronic components may be encapsulated by respective encapsulation layers such that the damping layer fills a lateral space between the encapsulated electronic components. 
     In an embodiment, mounting of the capacitor on the PCB includes mounting the capacitor on an interposer such that an upper contact of the interposer is electrically connected to the capacitor. The interposer may also be mounted on the PCB, such that a lower contact of the interposer is electrically connected to the PCB. Furthermore, the upper contact and the lower contact of the interposer may be electrically connected by a via having one or more via segments between different layers of the interposer. Accordingly, at least one of the via segments may be laterally offset from one or more of the upper contact or the lower contact to reduce the stiffness beneath the terminals of the capacitor, and accordingly, to reduce the transmission of excitatory vibrations from the capacitor to the PCB. 
     In an embodiment, an epoxy-coated capacitor is provided. The epoxy-coated capacitor may be mounted on a PCB and/or may be incorporated in a PCB assembly. For example, the epoxy-coated capacitor may be mounted directly on the PCB or it may be mounted on an interposer that is electrically connected to the PCB. In an embodiment, the capacitor includes a capacitor body having a top surface and a periphery. The periphery may include a first height, and a coating may cover the top surface and a portion of the periphery. For example, the coating may include an epoxy that covers a portion of the periphery having a second height that is less than the first height. By way of example, the second height may be between 0.8 and 0.99 of the first height. In an embodiment, the epoxy is a low modulus epoxy. For example, the epoxy may include a modulus less than 1.0 GPa and/or less than 0.5 GPa, e.g., between 0.2 and 0.5 GPa. Accordingly, the low modulus epoxy coating may dampen excitatory vibrations from the capacitor. 
     The above summary does not include an exhaustive list of all aspects of the present invention. It is contemplated that the invention includes all systems and methods that can be practiced from all suitable combinations of the various aspects summarized above, as well as those disclosed in the Detailed Description below and particularly pointed out in the claims filed with the application. Such combinations have particular advantages not specifically recited in the above summary. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a pictorial view of an electronic device in accordance with an embodiment. 
         FIG. 2  is a schematic view of an electronic device in accordance with an embodiment. 
         FIG. 3  is a sectional view, taken about line A-A of  FIG. 1 , of an electronic device having a printed circuit board (PCB) assembly in accordance with an embodiment. 
         FIG. 4  is a top view of a PCB assembly having a baffle covering a PCB in accordance with an embodiment. 
         FIG. 5  is a top view of a PCB assembly having a baffle covering a PCB in accordance with an embodiment. 
         FIG. 6  is a sectional view, taken about line B-B of  FIG. 3 , of a PCB assembly having a damping layer covering several electronic components in accordance with an embodiment. 
         FIG. 7  is a sectional view, taken about line B-B of  FIG. 3 , of a PCB assembly having an overmold layer and a damping layer covering several electronic components in accordance with an embodiment. 
         FIG. 8  is a sectional view, taken about line B-B of  FIG. 3 , of a PCB assembly having an overmold layer and a damping layer covering several electronic components, including at least one encapsulated capacitor, in accordance with an embodiment. 
         FIG. 9  is a sectional view, taken about line B-B of  FIG. 3 , of a PCB assembly having a damping layer covering several electronic components, including at least one encapsulated capacitor mounted on an interposer, in accordance with an embodiment. 
         FIG. 10  is a perspective view of an interposer in accordance with an embodiment. 
         FIG. 11  is a sectional view of an interposer having via segments laterally offset from electrical contacts in accordance with an embodiment. 
         FIG. 12  is a sectional view of an interposer having via segments and electrical contacts laterally offset from other electrical contacts in accordance with an embodiment. 
         FIG. 13  is a top view of an interposer having centrally located electrical contacts in accordance with an embodiment. 
         FIG. 14  is a sectional view of an interposer having an acoustic trap in accordance with an embodiment. 
         FIG. 15  is a sectional view, taken about line C-C of  FIG. 14 , of an interposer having an acoustic trap in accordance with an embodiment. 
         FIG. 16  is a flowchart of a method of making a PCB assembly having a baffle covering a PCB in accordance with an embodiment. 
         FIG. 17  is a perspective view of an epoxy-coated capacitor in accordance with an embodiment. 
         FIG. 18  is a sectional view, taken about line D-D of  FIG. 17 , of an epoxy-coated capacitor in accordance with an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments describe printed circuit board (PCB) assemblies having one or more mechanisms to waterproof electronic components without substantially increasing acoustic noise radiation from the PCB assembly, particularly for use in electronic device applications. Some embodiments are described with specific regard to integration within mobile devices such as mobile phones. The embodiments are not so limited, however, and certain embodiments may also be applicable to other uses. For example, a PCB assembly as described below may be incorporated into other devices and apparatuses, including desktop computers, laptop computers, or motor vehicles, to name only a few possible applications. 
     In various embodiments, description is made with reference to the figures. Certain embodiments, however, may be practiced without one or more of these specific details, or in combination with other known methods and configurations. In the following description, numerous specific details are set forth, such as specific configurations, dimensions, and processes, in order to provide a thorough understanding of the embodiments. In other instances, well-known processes and manufacturing techniques have not been described in particular detail in order to not unnecessarily obscure the description. Reference throughout this specification to “one embodiment,” “an embodiment,” or the like, means that a particular feature, structure, configuration, or characteristic described is included in at least one embodiment. Thus, the appearance of the phrase “one embodiment,” “an embodiment,” or the like, in various places throughout this specification are not necessarily referring to the same embodiment. Furthermore, the particular features, structures, configurations, or characteristics may be combined in any suitable manner in one or more embodiments. 
     The use of relative terms throughout the description, such as “upward” and “downward” may denote a relative position or direction. For example, an electrical connection may be described as extending “downward” from a top surface and “upward” may be opposite to the downward direction. Nonetheless, such terms are not intended to limit the use of a PCB assembly to a specific configuration described in the various embodiments below. For example, a PCB assembly may be oriented in any direction with respect to an external environment, including such that a PCB surface supporting electronic components is facing upward, downward, sideways, etc., relative to the ground. 
     There are several ways to reduce acoustic noise radiation from a PCB assembly. For example, quieter capacitors such as non-uniform dielectric layer capacitors or dummy layer capacitors may be used. Several manners of reducing noise radiation, without directly altering the electronic components mounted on a PCB of the PCB assembly, are described below. 
     In an aspect, an electronic device includes a PCB assembly having several electronic components mounted on a PCB, and a baffle covering the electronic components. The baffle includes one or more layers having waterproofing and/or noise reducing characteristics. For example, a damping layer may cover the electronic components to prevent the ingress of moisture into the electronic components. Furthermore, the damping layer may have a flexural modulus that is lower than a flexural modulus of the PCB, such that the flexural wave speed of the PCB assembly is decreased and acoustic noise radiation is reduced. 
     Referring to  FIG. 1 , a pictorial view of an electronic device is shown in accordance with an embodiment. Electronic device  100  may be a smartphone device. Alternatively, it could be any other portable or stationary device or apparatus, such as a laptop computer or a tablet computer. Electronic device  100  may include various capabilities to allow the user to access features involving, for example, calls, voicemail, music, e-mail, internet browsing, scheduling, or photos. Electronic device  100  may also include hardware to facilitate such capabilities. For example, a housing  102  may contain a microphone  104  to pick up the voice of a user during a call, and an audio speaker  106 , e.g., a micro speaker, to deliver a far-end voice to the near-end user during the call. Audio speaker  106  may also emit sounds associated with music files played by a music player application running on electronic device  100 . A display  108  may present the user with a graphical user interface to allow the user to interact with electronic device  100  and/or applications running on electronic device  100 . Other conventional features are not shown but may of course be included in electronic device  100 . 
     Referring to  FIG. 2 , a schematic view of an electronic device is shown in accordance with an embodiment. As described above, electronic device  100  may be one of several types of portable or stationary devices or apparatuses with circuitry suited to specific functionality. Accordingly, the diagrammed circuitry is provided by way of example and not limitation. Electronic device  100  may include a PCB assembly (not shown) having several integrated circuits and other electronic components mounted on a PCB. For example, one or more processors  202  may be mounted on the PCB to execute instructions to carry out the different functions and capabilities described above. Instructions executed by processor(s)  202  of electronic device  100  may be retrieved from a local memory  204 , and may be in the form of an operating system program having device drivers, as well as one or more application programs that run on top of the operating system. The instructions may cause electronic device  100  to perform the different functions introduced above, e.g., phone and/or music play back functions. To perform such functions, processor(s)  202  may directly or indirectly implement control loops and provide drive signals to other electronic components, such as one or more surface-mount capacitors (not shown). Voltage ripples in these drive signals may result in deformation of the capacitors and concomitant acoustic noise radiation from the PCB. 
     Referring to  FIG. 3 , a sectional view, taken about line A-A of  FIG. 1 , of an electronic device having a PCB assembly is shown in accordance with an embodiment. Electronic device  100  may include an enclosure that holds external device components such as display  108 , speaker  106 , and microphone  104 , and the enclosure may also surround internal device components such as a PCB assembly  302 . More particularly, housing components made from the same or different types of materials, e.g., plastic, ceramic, glass, or metal, may be mechanically coupled to form housing  102  surrounding an internal space. PCB assembly  302  may be enclosed in the internal space. For example, PCB assembly  302  may be mounted on a back surface of housing  102  to stabilize the assembly, and a front panel of housing  102  may cover the PCB assembly  302 . 
     In an embodiment, PCB assembly  302  includes a PCB  304  supporting several electronic components  306 , such as a capacitor  308  and processor  202 . PCB  304  includes one or more layers of non-conductive substrate supporting one or more conductive sheets, e.g., copper sheets. The conductive sheets may be patterned to form a printed circuit having conductive traces, conductive pads, conductive vias, and other conductive interconnections to electrically connect electronic components  306  such as processor  202  and capacitor  308 . Thus, electronic components  306  may be mounted on PCB  304  and electrically connected by the printed circuit to form a printed circuit assembly. 
     The printed circuit assembly of the PCB assembly  302  may be covered at least in part by a baffle  310 . Baffle  310  may deflect, check, or regulate the passage of a fluid or sound between PCB  304  and the internal space within housing  102 . More particularly, baffle  310  may cover at least a portion of the printed circuit assembly, including two or more electronic components  306  within that portion. Baffle  310  may cover and be attached to PCB  304  around the covered electronic components  306  to prevent the ingress of moisture and the egress of sound to/from the covered PCB portion. 
     Referring to  FIG. 4 , a top view of a PCB assembly having a baffle covering a PCB is shown in accordance with an embodiment. PCB assembly  302  may include the printed circuit assembly covered partially by baffle  310 . For example, PCB  304  may include a PCB perimeter  402  at an outer edge where a top surface of PCB  304  meets the sides of PCB  304 , i.e., around the top surface of the PCB  304 . Various electronic components  306  of the printed circuit assembly may be mounted on the top surface of PCB  304 , and thus, may reside laterally inward of PCB perimeter  402 . For example, in an embodiment, processor  202 , capacitors  308 , and one or more other electronic components  306 , e.g., diodes, transistors, integrated circuits, or optoelectronic devices, are mounted on the top surface. In an embodiment, two or more capacitors  308  form a subset of the electronic components  306  mounted on PCB  304 . The capacitors  308  may be surface-mount ceramic capacitors that deform when driven by an electrical signal having a voltage ripple. For example, ceramic capacitors may be Class I or Class II multilayer style (MLCC) ceramic capacitors. Each of the electronic components  306 , including the capacitors  308 , may be mechanically coupled to PCB  304  through a solder joint, e.g., by a high temperature solder connection, to electrically connect terminals of the electronic component  306  with respective conductive pads on the top surface of PCB  304 . 
     Baffle  310  may cover several electronic components  306 . Baffle  310  may be deposited over printed circuit assembly such that a baffle perimeter  404  defines the outer limits of baffle  310  in the lateral direction along the top surface of PCB  304 . Furthermore, baffle perimeter  404  may follow a path along the top surface around two or more electronic components  306 , e.g., several capacitors  308 . Thus, baffle  310  may cover not only capacitors  308 , but also the top surface of PCB  304  within the area defined by baffle perimeter  404 . By contrast, baffle perimeter  404  may be laterally inward of PCB perimeter  402 , and thus, other electronic components  306  (such as processor  202  shown in  FIG. 4 ) may reside laterally outside of baffle  310  and not be protected from moisture within the internal space of housing  102 . 
     Referring to  FIG. 5 , a top view of a PCB assembly having a baffle covering a PCB is shown in accordance with an embodiment. In an embodiment, PCB assembly  302  may include baffle  310  that covers an entire PCB  304 . For example, baffle  310  may extend over an entire top surface of PCB  304 , as well as across one or more of the sides of PCB  304  that define PCB perimeter  402 . In addition to covering one or more of the sides, baffle  310  may wrap around at least a portion of a bottom surface of PCB  304  and extend over some or all of the back surface. Thus, baffle  310  may cover an entire top surface of PCB  304 , an entire top surface and one or more sides of PCB  304 , and/or may encapsulate the entire PCB  304 . Baffle  310  may also cover electronic components  306  mounted on the covered portion (top or back) of PCB  304 . As shown in  FIG. 5 , when baffle  310  covers the entire top surface of printed circuit assembly, baffle perimeter  404  may extend laterally outside of PCB perimeter  402 . Thus, baffle  310  may prevent the ingress of moisture or the egress of sound to/from the entire top surface of PCB  304 . 
     Baffle  310  may be configured in numerous manners to waterproof PCB assembly  302  and/or to reduce the acoustic noise radiation from PCB assembly  302 . Several embodiments are presented below that describe baffle  310  as including one or more layers of material specifically suited to these functions. For example, the layers of baffle  310  may not only directly prevent the passage of sound from a vibrating electronic component  306 , but may also increase coupling between the electronic components  306  and PCB  304  to reduce overall board vibration, which has a noise reducing effect. Furthermore, baffle  310  may alter the bulk, i.e., composite, vibrational characteristics of PCB assembly  302 , which may also have a noise reducing effect. Thus, an understanding of the following description may lead to other embodiments of baffle  310  having alternative arrangements of the described layers to protect a printed circuit assembly of PCB assembly  302  from moisture while reducing acoustic noise radiation from PCB assembly  302 . 
     Referring to  FIG. 6 , a sectional view, taken about line B-B of  FIG. 3 , of a PCB assembly having a damping layer covering several electronic components is shown in accordance with an embodiment. In an embodiment, PCB assembly  302  includes at least one electronic component  306  mounted on PCB  304 . For example, electronic component  306  may be capacitor  308  that is mechanically coupled to PCB  304  at one or more terminals by solder  602  joints. Capacitor  308  may include a periphery  604  defined by the lateral sides of capacitor  308 . Capacitor  308  may also include a top surface and a bottom surface, and the bottom surface may be nearest to PCB  304 . Since solder  602  may have a thickness in the upward direction perpendicular to the top surface of PCB  304 , a gap  606  may be located between the bottom surface of capacitor  308  and the top surface of PCB  304 . 
     In an embodiment, baffle  310  includes a damping layer  608  covering capacitor  308  and/or at least one other electronic component  306 . That is, although only capacitor  308  is shown, damping layer  608  may be continuous over the top surface of PCB  304  to cover other electronic components  306  in an area broken out of  FIG. 6 . Damping layer  608  may be attached to the top surface of PCB  304  around the electronic components  306 . More particularly, damping layer  608  may be attached to PCB  304  around electronic components  306 , and may also be attached to PCB  304  at locations laterally between the electronic components  306 . Thus, damping layer  608  may substantially or entirely fill the space between respective peripheries  604  of laterally offset electronic components  306 . Furthermore, damping layer  608  may cover the top surfaces of the electronic components  306  such that the electronic components  306  are encapsulated between damping layer  608  and PCB  304 . For example, a thickness of damping layer  608  may be greater than a height of capacitor  308  (a distance between the top surface of capacitor  308  and the top surface of PCB  304 ). Furthermore, the thickness of damping layer  608  may be greater than a height of all the electronic components  306  that baffle  310  covers, such that damping layer  608  provides a minimum encapsulation of 0.2 mg of damping material over each electronic component  306 . In an embodiment, damping layer  608  may provide a minimum thickness of 0.1 mm of damping material over each electronic component  306 . Capacitor  308  may be considered to be encapsulated even though gap  606  may remain between the bottom surface of capacitor  308  and the top surface of PCB  304 . More particularly, damping layer  608  material may or may not fill gap  606  underneath capacitor  308 . Thus, capacitor  308  may be considered to be encapsulated when every side but the bottom is covered by damping layer  608 . In an embodiment, however, damping layer  608  fills gap  606  to form an underfill portion of damping layer  608  between capacitor  308  and PCB  304 . 
     A single damping layer  608  covering electronic components  306  and the PCB  304  surface on which the electronic components  306  are mounted may function as both a moisture barrier and an acoustic damping mechanism. In an embodiment, damping layer  608  may be formed from an epoxy, silicone, or other polymers having water resistant properties. For example, damping layer  608  may include an encapsulation material formulated from a low glass transition temperature material designed to provide a flexible encapsulation for components on PCB  304 . Thus, moisture in the housing cavity surrounding PCB assembly  302  may be unable to pass through damping layer  608  to capacitor  308  or other covered electronic components  306 . 
     In addition to waterproofing PCB assembly  302 , a single damping layer  608  may provide a damping effect by altering the bulk vibrational characteristics of PCB assembly  302 . For example, the composite structure of damping layer  608  attached to PCB  304  may reduce the flexural wave speed of PCB assembly  302 . Acoustic noise radiation is related to the flexural wave speed of the PCB assembly  302 , and more particularly, acoustic noise radiation of the PCB assembly  302  depends on the ratio of the flexural wave speed of damping layer  608  as compared to the flexural wave speed of PCB  304 . When damping layer  608  has a flexural wave speed that is less than the flexural wave speed of PCB  304 , the acoustic noise radiation from PCB assembly  302  may be reduced. Flexural wave speed of the assembly components depends on several parameters, and thus, the structure of these components may be manipulated in several manners to achieve the desired ratio and concomitant noise reduction. 
     The flexural wave speeds of PCB assembly components are directly proportional to their respective flexural modulus. Accordingly, in an embodiment, damping layer  608  includes a flexural modulus that is lower than a flexural modulus of PCB  304 . For example, PCB  304  may include a flexural modulus in a range of 3 to 30 GPa. By contrast, damping layer  608  may include a flexural modulus below that of PCB  304 . For example, the flexural modulus of damping layer  608  may be at least 20% lower than the flexural modulus of PCB  304 . By way of example, the flexural modulus of damping layer  608  may be in a range of 0.001 to 2.4 GPa. 
     Another critical parameter in determining the flexural wave speed of damping layer  608  and PCB  304  is the density of those PCB assembly components. More particularly, the flexural wave speed of damping layer  608  and the flexural wave speed of PCB  304  is inversely proportional to the density of the respective components. Accordingly, in an embodiment, damping layer  608  includes a density that is higher than a density of PCB  304 . For example, PCB  304  may include a density in a range of 0.5 to 3 g/cm 3 . By contrast, damping layer  608  may include a density above that of PCB  304 . For example, the density of damping layer  608  may be at least 10% higher than the density of PCB  304 . By way of example, the density of damping layer  608  may be in a range of 0.6 to 3.5 g/cm 3 . 
     In reality, the flexural wave speed of a PCB assembly component is determined by a complex relationship between not only density and flexural modulus, but also other parameters such as a thickness of the respective component. Thus, one skilled in the art would understand that particular relationships of these parameters may be critical to controlling the flexural wave speed. In an embodiment, a ratio of the flexural modulus to the density of each assembly component may be controlled to reduce acoustic radiation. For example, a ratio of the flexural modulus to the density of damping layer  608  may be lower than a ratio of the flexural modulus to the density of PCB  304  layer. For example, the predetermined ratio for PCB  304  may be in a range of 1 to 60 GPa/(g/cm 3 ). By contrast, the predetermined ratio for damping layer  608  may be at least 20% lower than the ratio for PCB  304 . By way of example, the predetermined ratio for damping layer  608  may be in a range of 0.0001 to 0.8 GPa/(g/cm 3 ). 
     Referring to  FIG. 7 , a sectional view, taken about line B-B of  FIG. 3 , of a PCB assembly having an overmold layer and a damping layer covering several electronic components is shown in accordance with an embodiment. Baffle  310  may include at least two layers of material covering one or more electronic components  306 . Baffle  310  may include damping layer  608  covering capacitor  308  and/or other electronic components  306 , as described above with respect to  FIG. 6 . In an embodiment, baffle  310  further includes an overmold layer  702  covering all or most of damping layer  608 . More particularly, overmold layer  702  may cover damping layer  608  and be attached to PCB  304  at one or more locations around a central portion of damping layer  608 , which covers several electronic components  306 . For example, overmold layer  702  may extend over a top surface of damping layer  608  and surround a damping layer periphery  704  to attach to PCB  304  at or near PCB perimeter  402 . 
     In an embodiment, overmold layer  702  provides waterproofing to prevent the ingress of moisture into damping layer  608  and electronic components  306  covered by damping layer  608 . Accordingly, overmold layer  702  may be formed from a silicone or epoxy material having water resistant properties. Given that overmold layer  702  fulfills a waterproofing function, damping layer  608  may be formed from a material that fulfills a noise reduction function, but not necessarily a waterproofing function. For example, damping layer  608  may be formed from a viscoelastic damping material that does or does not provide a barrier to water migration. More particularly, damping layer  608  material may be chosen based upon its effect of reducing vibrations of PCB assembly  302 , while overmold layer  702  material may be chosen based upon its ability to restrict the passage of moisture toward PCB  304 . 
     Overmold layer  702  may cover the entirety of damping layer  608 , and in addition, overmold layer  702  may cover an entire top surface of PCB  304  as shown in  FIG. 7 . In addition to covering damping layer  608 , however, overmold layer  702  may also constrain damping layer  608  against PCB  304 . For example, overmold layer  702  may be deposited directly onto damping layer  608  during a manufacturing process such that an inner (or bottom) surface of overmold layer  702  is in direct contact with an outer (or top) surface of damping layer  608 . Furthermore, as described above, overmold layer  702  may surround damping layer periphery  704  to attach directly to PCB  304  and form a shell around damping layer  608 . Thus, material strains such as expansions of damping layer  608  may be resisted by overmold layer  702 , which presses against damping layer  608  as it tries to expand. By constraining damping layer  608 , overmold layer  702  may further reduce acoustic radiation because it does not allow the damping material to expand, which may disrupt natural vibration modes in damping layer  608 . 
     In an embodiment, overmold layer  702  is formed from a more rigid material than damping layer  608  to facilitate the constraint of damping layer  608 . More particularly, overmold layer  702  may include a flexural modulus higher than the flexural modulus of damping layer  608 . For example, overmold layer  702  may include a flexural modulus in a range of 0.02 to 30 GPa. By contrast, damping layer  608  may include a flexural modulus less than that of overmold layer  702 . For example, the flexural modulus of damping layer  608  may be at least 10% lower than the flexural modulus of overmold layer  702 . By way of example, the flexural modulus of damping layer  608  may be in a range of 0.001 to 2.4 GPa. 
     As described above, damping layer  608  may be formed from a viscoelastic material. In fact, damping layer  608  may be formed from any material having the requisite damping properties. More particularly, in an embodiment, damping layer  608  is formed from a material having a damping loss factor that reduces acoustic noise radiation from PCB  304 . Damping layer  608  may include a damping loss factor of at least 0.01 over a frequency range of 20 Hz to 20 kHz. For example, damping loss may be in a range of 0.01 to 1. In an embodiment, the damping loss factor of damping layer  608  may be higher than a damping loss factor of overmold layer  702 , such that damping layer  608  provides more damping of acoustic noise radiation than overmold layer  702 . 
     Referring to  FIG. 8 , a sectional view, taken about line B-B of  FIG. 3 , of a PCB assembly having an overmold layer and a damping layer covering several electronic components, including at least one encapsulated capacitor, is shown in accordance with an embodiment. In addition to overmold layer  702  and/or damping layer  608  covering electronic components  306  mounted on PCB  304 , each electronic component  306  of PCB assembly  302  may also be covered by a respective encapsulation layer  802 . For example, encapsulation layer  802  may cover capacitor  308  and be disposed between damping layer  608  and PCB  304 . More particularly, encapsulation layer  802  may surround periphery  604  of capacitor  308  and/or cover the top surface of capacitor  308 . Encapsulation layer  802  may cover the entire capacitor  308 , such that capacitor  308  is encapsulated between encapsulation layer  802  and PCB  304 . Similar to the single damping layer  608  described above, however, encapsulation layer  802  may not fill gap  606  below capacitor  308 . In an embodiment, however, encapsulation layer  802  fills gap  606  and including an underfill portion between capacitor  308  and PCB  304 . 
     Encapsulation layer  802  may serve as a moisture barrier and may also serve as an energy absorber. More particularly, encapsulation layer  802  may be attached to the top surface of PCB  304  to form a shell around capacitor  308  similar to the manner in which overmold layer  702  forms a shell around damping layer  608 . As such, encapsulation layer  802  may constrain capacitor  308  by increasing a mechanical coupling between capacitor  308  and PCB  304 . Encapsulation layer  802  may itself be encapsulated within damping layer  608  and/or overmold layer  702 . That is, one or both of damping layer  608  or overmold layer  702  may surround the sides of encapsulation layer  802 , and as such, may also surround periphery  604  of capacitor  308 . 
     To avoid moisture capture, encapsulation layer  802  may be formed from a water barrier material. For example, encapsulation layer  802  may be formed from silicone, epoxy, or other materials having water resistant or waterproof properties. Encapsulation layer  802  may nonetheless be formed from a material that absorbs vibrational energy from electronic components  306 . In an embodiment, encapsulation layer  802  has a lower flexural modulus than the flexural modulus of PCB  304 . For example, PCB  304  may include a flexural modulus in a range of 3 to 30 GPa. By contrast, encapsulation layer  802  may include a flexural modulus less than that of PCB  304 . For example, the flexural modulus of encapsulation layer  802  may be at least 10% lower than the flexural modulus of PCB  304 . By way of example, the flexural modulus of encapsulation layer  802  may be in a range of 0.01 to 5 GPa. Accordingly, encapsulation layer  802  may have a lower flexural wave speed than PCB  304 , and a damping effect on acoustic noise radiation. 
     In an embodiment, encapsulation layer  802  has a lower flexural modulus than the flexural modulus of overmold layer  702 . For example, overmold may include a flexural modulus in a range of 0.02 to 30 GPa. By contrast, encapsulation layer  802  may include a flexural modulus less than that of overmold layer  702 . For example, the flexural modulus of encapsulation layer  802  may be at least 10% lower than the flexural modulus of overmold layer  702 . By way of example, the flexural modulus of encapsulation layer  802  may be in a range of 0.01 to 5 GPa. Accordingly, encapsulation layer  802  may have a lower flexural wave speed than overmold layer  702 . 
     Although not shown in  FIG. 8 , multiple electronic components  306 , e.g., multiple capacitors  308 , may be encapsulated by respective encapsulation layers  802 . For example, another capacitor  308  may be mounted on PCB  304  in the broken out section of  FIG. 8 , and another encapsulation layer  802  may form a thin encapsulation film around the other capacitor  308 . Thus, damping layer  608  may be disposed laterally between the multiple electronic components  306 , and more particularly, may be disposed in the lateral space between the respective encapsulation layers  802  that cover the electronic components  306 . 
     In an embodiment, overmold layer  702  does not surround one or more sides of damping layer  608 . Overmold layer  702  may nonetheless substantially constrain damping layer  608  against PCB  304 . For example, overmold layer  702  may cover all or most of the top surface of damping layer  608  and be attached to PCB  304  at several locations around the covered electronic components  306  to apply a constraining force to the top surface in a normal direction relative to PCB  304 . The constraining force may press downward on damping layer  608  over the covered electronic components  306 . 
     One or more bridging members  802  may provide an attachment between overmold layer  702  and PCB  304 . For example, bridging member  802  may be an elongated protrusion extending from the inner (or bottom) surface of overmold layer  702  to the top surface of PCB  304 . The protrusion may be attached to PCB  304  in a number of ways, including by adhesive bonds, mechanical couplings, or snap fit features. Thus, bridging members  802  may retain overmold layer  702  at a fixed distance from PCB  304 , even when damping layer  608  attempts to expand due to deformation of electronic components  306 . Accordingly, overmold layer  702  and PCB  304  essentially form an enclosure around damping layer  608  and electronic components  306 , albeit without necessarily surrounding the sides of damping layer  608 . That is, as shown in  FIG. 8 , damping layer  608  may extend laterally around bridging members  802  such that the sides of damping layer  608  meet with PCB perimeter  402  and bridging members  802  are encapsulated by damping layer  608  material between overmold layer  702  and PCB  304 . 
     Bridging members  802  may have several configurations. In an embodiment, bridging members  802  are integrally formed with overmold layer  702  such that bridging members  802  extend continuously from a bottom surface of overmold layer  702  toward PCB  304 . For example, bridging members  802  may be formed with overmold layer  702  in a same overmolding process operation. Alternatively, bridging members  802  may be separate components, including stanchions, posts, or other standoffs, that may be affixed to overmold layer  702  at one end and to PCB  304  at another end in order to fasten and physically connect those components together. 
     Referring to  FIG. 9 , a sectional view, taken about line B-B of  FIG. 3 , of a PCB assembly having a damping layer covering several electronic components, including at least one encapsulated capacitor mounted on an interposer, is shown in accordance with an embodiment. Baffle  310  having one or more layers, such as overmold layer  702 , damping layer  608 , or encapsulation layer  802 , may reduce acoustic noise radiation from PCB assembly  302  by preventing passage of acoustic waves from electronic components  306  and by modifying the bulk vibrational characteristics of PCB assembly  302  to reduce acoustic noise radiation. In particular, surrounding periphery  604  of capacitors  308  and constraining capacitors  308  against PCB  304 , while also lowering a flexural wave speed of PCB assembly  302 , provides a damping effect to PCB assembly  302 . In an embodiment, a damping effect is also achieved by reducing or eliminating vibration transmitted from capacitor  308  to PCB  304 . 
     In an embodiment, an interposer  902  is disposed in gap  606  between capacitor  308  and PCB  304 . More particularly, interposer  902  may include a structure that conveys electrical signals from PCB  304  to capacitor  308 , but is impervious or does not deform as much as capacitor  308 , when the electrical signals include voltage ripples. Interposer  902  may be rigidly attached to capacitor  308  and PCB  304  in numerous manners. For example, interposer  902  may be mechanically coupled to one or more PCB contacts  904  on PCB  304 , and may also be mechanically attached to electrical terminals of capacitor  308 . Attachments may include solder  602  joints to affix the components and to allow the components to communicate electrically with one another. In an embodiment, although the attachments between interposer  902  and capacitor  308  or PCB  304  may be rigid, interposer  902  may include a structure that nonetheless provides a damping effect and reduces the transmission of vibrations from a noisy capacitor  308  to PCB  304 . 
     Referring to  FIG. 10 , a perspective view of an interposer is shown in accordance with an embodiment. Interposer  902  may include one or more interposer layers  1002  arranged in an essentially flat configuration and laminated one on top of another. Interposer layers  1002  may be nonconductive, i.e., insulating. For example, interposer layers  1002  may be formed from glass fibers interwoven within an epoxy binder. In other words, interposer layers  1002  may have a similar structure to the insulating layers of PCB  304 . In an embodiment, interposer layers  1002  include an epoxy, however, no glass fibers are interwoven within the epoxy. Thus, interposer  902  and interposer layers  1002  may include a flexural modulus lower than the substrate of PCB  304 . By way of example, interposer layers  1002  may be formed from polyimide film, liquid photoimageable coverlay (LPI), acrylic, epoxy glass, or polyimide-glass. A flexural modulus of interposer layers  1002  may be in a range of 0.01-2.1 GPa. More particularly, the flexural modulus of interposer  902  may be at least 30% lower than the flexural modulus of PCB  304 . 
     In an embodiment, the flexural wave speed of interposer  902  may be less than the flexural wave speed of PCB  304 . Thus, as discussed above, other parameters besides flexural modulus may be modified to achieve this relationship. For example, a density of interposer  902  may be higher than the density of PCB  304 . Furthermore, a thickness of interposer  902  may be greater than a thickness of PCB  304 . Interposer  902  may have a specific thickness selected such that interposer  902  acts as a non-rigid acoustically insulating barrier between capacitor  308  and PCB  304 . The thickness of PCB  304  may typically be in a range of 0.005-inch to 0.038-inch, and thus, a thickness of interposer  902  may be in a range of 0.001-inch to 0.010-inch. 
     In addition to reducing transmission of mechanical vibrations from a noisy capacitor  308  to PCB  304 , interposer  902  may also provide an electrical connection between contacts on capacitor  308  and PCB  304 . In an embodiment, interposer  902  includes one or more upper contact  1004  on a top face. Upper contacts  1004  may be located on the top face to directly oppose terminals on capacitor  308 . Similarly, interposer  902  may include one or more lower contacts  1006  on a bottom face. Lower contacts  1006  may be located to directly oppose PCB contacts  904  on the top surface of PCB  304 . Upper contacts  1004  and lower contacts  1006  may be formed from conductive materials, such as copper foils that have not been etched away on the top and bottom faces in order to maintain an electrically conductive contact surface. 
     Each upper contact  1004  may be electrically connected to a respective lower contact  1006  through one or more electrical trace  1008  and/or electrical via  1010 . Such electrical connections are well-known in the art. For example, vias are commonly used to make electrical connections between layers in a printed circuit of a PCB, and traces are commonly used to make electrical connections and conduct signals along the planar surfaces of layers in a printed circuit of a PCB. Dimensions, including the width and thicknesses of traces  1008  and vias  1010 , may be varied depending on the electrical signals, power, or current that the electrical connections are required to carry. Traces  1008  and vias  1010  are formed from a metal, and thus, may be stiffer than materials used to form interposer layers  1002 . Nonetheless, the volume occupied by traces  1008  and vias  1010  may be less than a corresponding volume occupied by traces and vias in a portion of PCB  304  under interposer  902 . Furthermore, in an embodiment, vias  1010  and traces  1008  may be routed to help maximize the compressibility of interposer  902  to absorb vibrational energy from a noisy capacitor  308 . 
     Interposer  902  may include upper contact  1004  and lower contacts  1006  located laterally outward from vias  1010 . More particularly, vias  1010  may include two or more via segments  1102 , and at least one via segment may be located nearer to a center of interposer  902  than either upper contact  1004  or lower contact  1006 . As shown, vias  1010  may have segments that respectively drop through one or more interposer layers  1002 . Furthermore, the segments may be interconnected by traces  1008  such that the combination of segments of via  1010  drop from a top face of interposer  902  to a bottom face of interposer  902 . In an embodiment, the segments of via  1010  are located closer to a center of interposer  902  than upper contact  1004  and lower contacts  1006 . More particularly, the segments of via  1010  may be laterally offset from upper contact  1004  and lower contacts  1006  such that no segments reside directly between the contacts. A structural effect of this routing is to make the interposer  902  more rigid within its center region than at its lateral edges. More particularly, interposer  902  may be more compressible between upper contact  1004  and lower contact  1006  than between the upper face and the lower face at the central region having vias  1010  and traces  1008 . Accordingly, vibrations of a noisy capacitor  308  are absorbed by the interposer layer  1002  material between upper contacts  1004  and lower contacts  1006 . 
     Referring to  FIG. 11 , a sectional view of an interposer having via segments laterally offset from electrical contacts is shown in accordance with an embodiment. Referring now to the electrical connection between the top face and the bottom face of the left side of interposer  902  shown in  FIG. 11 , a first trace  1008  may be routed transversely from upper contact  1004  to an upper end of via segment  1102 , along the top face of interposer  902 . The upper end of via segment  1102  may be more centrally located than upper contact  1004 . Via segment  1102  may then drop down, e.g., through the top two interposer layers  1002 , to a lower end connected to a trace  1008  sandwiched between interposer layers  1002  within interposer  902 . The trace  1008  within interposer  902  may be routed laterally toward a side of interposer  902  away from the centrally located via segment  1102 . The laterally routed trace  1008  may terminate at another via segment  1102  located above the lower contact  1006 , and that via segment  1102  may drop down through one or more interposer layers  1002  to connect to lower contact  1006 . Thus, in the electrical connection shown in  FIG. 11 , at least one via segment  1102  may be located nearer to the center of interposer  902  than either upper contact  1004  or lower contact  1006 . 
     Referring to  FIG. 12 , a sectional view of an interposer having via segments and electrical contacts laterally offset from other electrical contacts is shown in accordance with an embodiment. In an embodiment, upper contact  1004  and lower contact  1006  of interposer  902  are laterally offset from one another. For example, upper contact  1004  may be located nearer to an outer limit, i.e., a periphery, of interposer  902 , while lower contact  1006  may be located nearer to a normal centerline  1202  extending in a direction perpendicular to the top face of interposer  902 . Furthermore, one via segment  1102  may extend from upper contact  1004  downward through one or more interface layer and another via segment  1102  may extend upward from lower contact  1006  through one or more interposer layers  1002 . Thus, the via segment  1102  extending from upper contact  1004  may be laterally offset from lower contact  1006 , and the via segment  1102  extending upward from lower contact  1006  may be laterally offset from upper contact  1004 . Likewise, the via segment  1102  extending downward from the top face of interposer  902  may be laterally offset from the via segment  1102  extending upward from the bottom face of interposer  902 . 
     Interposer layers  1002  may be laminated upon one another, and thus, one interposer layer  1002  may have a bottom surface facing a top surface of an adjacent interposer layer  1002 . More particularly, the facing surfaces may be in contact with an intermediate interface surface  1204 . Thus, in the case of interposer  902  having two interposer layers  1002 , a single interface surface  1204  may exist between the layers. Similarly, in an interposer  902  having four interposer layers  1002 , three interface surfaces  1204  may exist between the layers, as shown. In an embodiment, interface surfaces  1204  include a conductive material, e.g., a copper film, disposed on interposer layers  1002  to allow for electrical connections to be formed. That is, interface surfaces  1204  may be etched conductive film to form one or more trace  1008  extending along a surface of interposer layers  1002 . As shown, trace  1008  may extend along interface surface  1204  between via segment  1102  connected to upper contact  1004  and via segment  1102  connected to lower contact  1006 . Interface surfaces  1204  may be formed by etching to generate any desired printed circuit on respective interposer layers  1002 . Thus, interposer  902  may be formed with laterally offset via segments  1102 , i.e., via segments  1102  laterally offset from one another and/or via segments  1102  laterally offset from upper contacts  1004  or lower contacts  1006 . By staggering the via segments  1102  away from capacitor terminations, interposer  902  becomes more flexible such that interposer  902  material directly under the terminations can absorb energy and reduce the transmission of vibration from capacitor  308  to PCB  304 . 
     Referring to  FIG. 13 , a top view of an interposer having centrally located electrical contacts is shown in accordance with an embodiment. Interposer  902  may include vias  1010  laterally offset from upper contacts  1004  and capacitor terminations. Vias  1010  may be connected to lower contacts  1006  through traces  1008  such that lower contacts  1006  are as close as possible to a transverse centerline  1302  of interposer  902 . Referring to the leftmost upper contact  1004  shown, trace  1008  may extend laterally along the top face of interposer  902  from upper contact  1004  to transverse centerline  1302 , which may run along a plane extending transversely through a middle of interposer  902  and oriented perpendicular to the top face of interposer  902 . A via  1010  connected with the leftmost upper contact  1004  and a via  1010  connected with the rightmost upper contact  1004  may both be arranged along transverse centerline  1302 , however, the vias  1010  may be transversely offset near normal centerline  1202  passing perpendicular to the top face of interposer  902 . That is, one via  1010  may be transversely offset on one side of normal centerline  1202  and the other via  1010  may be transversely offset on another side of normal centerline  1202 . In an embodiment, the vias  1010  extend downward from a top face of interposer  902  through interposer layers  1002  to the bottom face of interposer  902 . Thus, each via  1010 , rather than having multiple via segments  1102 , may be a single connector in the direction perpendicular to the interposer  902  faces. A bottom end of the vias  1010  may be connected to respective lower contacts  1006  by traces  1008  (shown with hidden lines in  FIG. 13 ) running along the bottom face of interposer  902  in the transverse direction (in the direction of transverse centerline  1302 ). That is, trace  1008  may interconnect a bottom end of via  1010  with lower contact  1006  positioned at the middle of interposer  902  along transverse centerline  1302 . More particularly, lower contacts  1006  may reside at the middle of interposer  902 , which may also be a location that coincides with a middle of capacitor  308 . 
     Still referring to  FIG. 13 , a transverse separation distance between vias  1010  and or lower contacts  1006  along transverse centerline  1302  may be determined based on manufacturability. For example, lower contacts  1006  may be located adjacent to transverse edges of the lower face of interposer  902  such that the contacts are separated as much as possible along transverse centerline  1302 . In another embodiment, however, lower contacts  1006  may reside at the center of interposer  902  below the center of capacitor  308 , in a side-by-side configuration. That is, lower contacts  1006  may be located on the lower face of interposer  902  directly below vias  1010 , so long as lower contacts  1006  are separated by a distance to allow for reliable etching of the conductive films on interposer  902  and to prevent electrical shorting between the lower contacts  1006  and/or PCB contacts  904  to which the lower contacts  1006  connect. By making the final interconnection between lower contacts  1006  and PCB contacts  904  at a location near the middle of capacitor  308 , the final interconnections will be within a region exposed to the least acoustic noise, and thus may benefit from reduced mechanical strain and transmit less acoustic vibration to PCB  304 . 
     Referring to  FIG. 14 , a sectional view of an interposer having an acoustic trap is shown in accordance with an embodiment. As described above, interposer  902  may include electrical connections having upper contact  1004 , lower contact  1006 , via segments  1102 , or traces  1008 , to electrically connect capacitor  308  mounted on upper contacts  1004  to PCB  304  on which interposer  902  is mounted. The laterally offset contacts and/or via segments  1102  may reduce the transmission of vibration from capacitor  308  to PCB  304 , as discussed above. Vibrational acoustics, however, may nonetheless be generated by a noisy capacitor  308 , and more particularly, acoustic waves may radiate toward PCB  304  from capacitor  308 . To prevent these acoustic waves from reaching PCB  304 , interposer  902  may include an acoustic trap  1402  to trap and/or reflect the acoustic waves away from PCB  304 . Acoustic trap  1402  may be a quarter wave acoustic trap placed along a path of the electrical connection between upper contact  1004  and lower contact  1006 . More particularly, acoustic trap  1402  may be formed from one or more trace  1008  or via  1010  extending from via segment  1102  or trace  1008  between the interposer contacts. Although acoustic trap  1402  may be formed from conductive material such as copper film or metallic via material, acoustic trap  1402  may not form a circuit, and thus, acoustic trap  1402  may not interconnect electrical components of interposer  902 . That is, a first end (start location) of acoustic trap  1402  may be located at via segment  1102  or trace  1008 , but a second end of acoustic trap  1402  may be a dead end  1404 , i.e., may not be connected to a separate component. In an embodiment, the start location is also separated from the electrical connection running through interposer  902 . Thus, acoustic trap  1402  may be an acoustic element, not an electrical element. 
     Referring to  FIG. 15 , a sectional view, taken about line C-C of  FIG. 14 , of an interposer having an acoustic trap is shown in accordance with an embodiment. Acoustic trap  1402  may extend from trace  1008  or via segment  1102 , and thus, acoustic trap  1402  may include horizontal trace lengths (when acoustic trap  1402  extends from via segment  1102 ) or vertical via lengths (when acoustic trap  1402  extends from trace  1008 ). As shown, a start location  1504  of acoustic trap  1402  may be located at via segment  1102  and acoustic trap  1402  may follow a path along the interface surface  1204  over trap length  1502  to dead end  1404 . Acoustic trap  1402  may follow any path between start location  1504  and dead end  1404 . For example, acoustic trap  1402  may include one or more linear segments and/or one or more curvilinear segments, as shown. In addition to having bends formed by curvilinear segments, linear segments may meet at a right angle to form a bend, although this is not necessarily preferred. Therefore, acoustic trap  1402  may be patterned and/or etched on interface surface  1204  in any geometry having the requisite trap length  1502  to reflect the predetermined acoustic wavelengths. 
     Acoustic trap  1402  of interposer  902  may trap and/or reflect acoustic waves having a wavelength that is four times a trap length  1502 . Thus, trap length  1502  may be varied to prevent passage of acoustic waves having a predetermined wavelength. By way of example, capacitor  308  may emit noise predominantly at a given wavelength, such as 5 kHz, and the acoustic waves at that frequency may have a wavelength of 7 cm. Accordingly, to trap and/or reflect the acoustic waves, acoustic trap  1402  may be formed with a trap length  1502  of 1.75 cm, which is one quarter of the predetermined wavelength to be trapped. Of course, capacitor  308  may emit noise having a wide range of frequencies, and thus, interposer  902  may include one or more acoustic traps  1402  having respective trap lengths  1502  designed to reflect particular sound waves. That is, each acoustic trap  1402  may have a trap length  1502  to trap or reflect a respective predetermined wavelength. As such, the acoustic traps  1402  help ensure that multiple acoustic frequencies do not pass from capacitor  308  to PCB  304 , and thus, reduce excitation of PCB  304  by the predetermined vibrational acoustics. 
     Referring to  FIG. 16 , a flowchart of a method of making a PCB assembly having a baffle covering a PCB is shown in accordance with an embodiment. In an embodiment, PCB assembly  302  may include baffle  310  having one or more of overmold layer  702 , damping layer  608 , or encapsulation layer  802 , as well as interposer  902 , which may or may not include acoustic trap  1402 . A method of forming PCB assembly  302  having one or more of the above features may optionally begin at operation  1602 , by mounting capacitor  308  on interposer  902 . In an embodiment, capacitor  308  and interposer  902  may have profiles, i.e., outer peripheries viewed from above, that are the same. Alternatively, the profiles may differ and the profile of capacitor  308  may be larger than the profile of interposer  902 , or vice versa. As discussed above, terminals of capacitor  308  may be bonded to upper contact  1004  of interposer  902  using solder  602 . Additional joints may also be used to fasten capacitor  308  to interposer  902 , for example, epoxy joints may be formed between a bottom surface of capacitor  308  and an adjacent top face of interposer  902 . 
     At operation  1604 , interposer  902  may be mounted on PCB  304 . As discussed above, lower contacts  1006  of interposer  902  may be bonded to PCB contacts  904  using solder  602 . Additional joints may also be used to secure interposer  902 . For example, epoxy joints may be formed between a top surface of PCB  304  and an adjacent face of interposer  902 . PCB  304  may include a flexural modulus, which is a critical parameter in the flexural wave speed of PCB  304 . 
     In an embodiment, a method of making PCB assembly  302  may not include providing interposer  902  between capacitor  308  and PCB  304 . For example, capacitor  308  may instead be mounted directly on PCB  304  as discussed above. In such case, solder  602  and/or epoxy joints may be formed between capacitor  308  and PCB  304 . Furthermore, epoxy may be used to at least partially fill gap  606  between a bottom surface of capacitor  308  and a top surface of PCB  304 . 
     At operation  1606 , one or more additional electronic components  306  may be mounted on PCB  304 . Mounting of additional electronic components  306 , including processor  202 , may be performed in a similar manner as that described above with respect to capacitor  308 . For example, solder  602  joints may be formed between electronic components  306  and PCB contacts  904  to create a mechanical and electrical connection between electronic components  306  and PCB  304 . Gap  606  between the additional electronic components  306  and PCB  304  may be filled by an epoxy or other filler. 
     At operation  1608 , damping layer  608  may be deposited over several electronic components  306 . For example, damping layer  608  may be deposited as a continuous layer to cover an entire top surface of the printed circuit assembly such that damping layer  608  covers all electronic components  306  mounted on PCB  304 . Alternatively, a continuous damping layer  608  may cover a portion of the printed circuit assembly and include damping layer periphery  704  around capacitor  308  and several other electronic components  306 , but the damping layer periphery  704  may be laterally inward of PCB perimeter  402 . In an embodiment, damping layer  608  is formed from a viscoelastic material, such as an elastomeric material, having a viscosity that allows damping layer  608  to be flowed between electronic components  306  mounted on PCB  304 . For example, damping layer  608  material may have a viscosity in a range of 10,000 to 50,000 mPa*s at 25° C. (measured using a Brookfield CP51, 2 rpm). Accordingly, damping layer  608  material may be molded in an uncontrolled manner to encapsulate electronic components  306  on PCB  304  and fill the lateral spaces between the electronic components  306 . Alternatively, damping layer  608  material may be flowed over electronic components  306  using a controlled molding process, such as a dam and fill process, to form damping layer  608  and encapsulate electronic components  306  mounted on PCB  304 . It has been shown that encapsulating electronic components  306  with damping layer  608  applied by a controlled dam and fill molding process results in reduced acoustic noise radiation from PCB assembly  302 , however, other processes for depositing damping layer  608  onto the printed circuit assembly may be used. For example, damping layer  608  material may be deposited using injection molding, transfer molding, or spray processes to fabricate the damping layer  608  structures discussed above. Damping layer  608  may be deposited on only one side of PCB  304 , such as the top surface of PCB  304 . Alternatively, damping layer  608  may be deposited onto at least two sides of PCB  304 , such as on both the top surface and the bottom surface of PCB  304  to encapsulate electronic components  306  above and below PCB  304 . 
     The deposited damping layer  608  may be attached to PCB  304  around mounted electronic components  306 . As discussed above, damping layer  608  may include a flexural modulus lower than the flexural modulus of PCB  304 . Thus, damping layer  608  may alter the flexural wave speed of PCB assembly  302  and reduce acoustic noise radiation from PCB assembly  302 . Accordingly, damping layer  608  acts as a semi-rigid acoustically insulating barrier between capacitor  308  and the inner space within housing  102 . 
     At operation  1610 , overmold layer  702  may be deposited over damping layer  608 . Like damping layer  608 , overmold layer  702  may be deposited using a controlled or uncontrolled molding process. For example, a dam and fill molding process may be used to form overmold layer  702  over damping layer  608 . Overmold layer  702  may be attached to PCB  304  at several locations around electronic components  306  covered by damping layer  608 . For example, overmold layer  702  may surround damping layer periphery  704  to attach to PCB  304 , or bridge elements may extend from overmold layer  702  through a thickness of damping layer  608  to PCB  304  to form a mechanical coupling between the components. Thus, overmold layer  702  may be connected to PCB  304  at several locations around a central portion of damping layer  608 . Accordingly, overmold layer  702  may constrain damping layer  608  against PCB  304  to limit expansion of the deposited damping layer  608  material and thereby reduce noise radiation. As discussed above, overmold layer  702  may include a flexural modulus higher than the flexural modulus of damping layer  608 . Furthermore, the flexural modulus of overmold layer  702  may be the same or less than the flexural modulus of PCB  304 . The flexural modulus of overmold layer  702  may be varied through material choice, e.g., by choosing a molding material having an intrinsic flexural modulus and/or by incorporating filler material in the overmold layer  702  material to alter the intrinsic flexural modulus. For example, fused silica may be incorporated in overmold layer  702  material to increase the flexural modulus of overmold layer  702 . 
     Other operations may be performed to form the structural features described above. For example, in addition to depositing damping layer  608  and overmold layer  702  over the electronic components  306  on PCB  304 , encapsulation layer  802  may also be deposited over individual electronic components  306 . In an embodiment, encapsulation layer  802  is deposited directly on capacitor  308  to form a thin-film encapsulation around capacitor  308  and to constrain capacitor  308  against PCB  304 . Electronic components  306  may be encapsulated by encapsulation layer  802  prior to depositing damping layer  608 . Like damping layer  608  and overmold layer  702 , encapsulation layer  802  may be deposited using controlled or uncontrolled molding processes. For example, encapsulation layer  802  may be controllably deposited over several electronic components  306  without filling the lateral space between the electronic components  306  (such that damping layer  608  may fill that space instead). Thus a viscosity of encapsulation layer  802  may be chosen to allow encapsulation layer  802  to form a thin film around capacitor  308 . Furthermore, material properties such as the flexural modulus of encapsulation layer  802  and the viscosity of encapsulation layer  802  may be chosen to facilitate the molding process and to ensure that encapsulation layer  802  provides the desired waterproofing and/or noise reducing effects. 
     The structural features and manufacturing processes discussed above may be varied within the scope of this disclosure to achieve the desired noise reduction effect. For example, preliminary test and simulation results have shown that the noise reduction effects can be tuned and optimized by changing material properties, e.g., flexural modulus, density, or viscosity, of damping layer  608 , and also by adjusting coverage, i.e., an amount of the printed circuit assembly that is encapsulated by damping layer  608  or a surface area of PCB  304  that is covered by damping layer  608 . The above description provides the details necessary for one skilled in the art to perform such optimization. 
     Referring to  FIG. 17 , a perspective view of an epoxy-coated capacitor is shown in accordance with an embodiment. Electronic component  306  incorporated in any of the PCB assemblies  302  described above may include an epoxy-coated capacitor  308 . More particularly, an epoxy-coated capacitor  308  may be provided as an electronic component  306  that can be mounted directly on PCB  304 , or may be mounted on interposer  902  and subsequently attached to PCB  304 . 
     In an embodiment, an epoxy-coated capacitor  308  includes a capacitor body  1702  and a coating  1704  covering at least a portion of capacitor body  1702 . Coating  1704  may include an epoxy material, e.g., a low modulus epoxy, having material properties such as those described below. As shown, coating  1704  may cover capacitor body  1702  incompletely to provide a receded covering, i.e., to expose at least a portion of the bottom and lateral sides of capacitor body  1702 . 
     Referring to  FIG. 18 , a sectional view, taken about line D-D of  FIG. 17 , of an epoxy-coated capacitor is shown in accordance with an embodiment. Capacitor body  1702  may include known passive two-terminal capacitor parts, such as end terminations  1802  electrically connected with electrodes  1804 , which are separated by a dielectric material. Furthermore, capacitor body  1702  may have reference geometry to embodiments of capacitor  308  described above, i.e., capacitor body  1702  may include a top surface  1806 , periphery  604  defined by the lateral sides of capacitor body  1702 , and a bottom surface that faces PCB  304  when epoxy-coated capacitor  308  is incorporated in PCB assembly  302 . Capacitor body  1702 , and more particularly periphery  604  of capacitor body  1702 , may include a capacitor body height  1808 . For example, capacitor body height  1808  may be a distance along periphery  604  between top surface  1806  and the bottom surface of capacitor body  1702 . 
     In an embodiment, coating  1704  covers top surface  1806  and at least a portion of periphery  604  of capacitor body  1702 . For example, coating  1704  may form a cap over an upper portion of capacitor body  1702 . The cap may cover all or part of periphery  604 . In an embodiment, covering  1704  extends over the entirety of top surface  1806  and along a portion of periphery  604  having a coating height  1810  that is less than capacitor body height  1808 . For example, coating height may be between 50% and 99% of capacitor body height  1808 . In an embodiment, the height of an exposed portion of periphery  604 , i.e., the difference between capacitor body height  1808  and coating height  1810  is no more than 20% of capacitor body height  1808 . For example, coating height  1810  may be at least 90% of capacitor body height  1808 . 
     In an embodiment, coating  1704  includes a low modulus material such as a low modulus epoxy. A low modulus epoxy may be an epoxy have a modulus less than 1.0 GPa. For example, coating  1704  may include an epoxy having a modulus less than 0.5 GPa, e.g., between 0.2 to 0.5 GPa. Accordingly, the low modulus epoxy coating  1704  may provide both a moisture barrier and an acoustic damping mechanism to dampen excitatory vibrations from capacitor body  1702 . 
     One skilled in the art will appreciate that coating  1704  may be applied over capacitor body  1702  in numerous manners. For example, a manufacturer of capacitor body  1702  or a third-party manufacturer may dip capacitor body  1702  into a low modulus epoxy. The epoxy coating  1704  formed by dipping may be cured to form epoxy cap over the predetermined portions, e.g., top surface  1806  and a portion of periphery  604 . The epoxy-coated capacitor  308  may then be placed into a tape and reel. In an embodiment, the epoxy-coated capacitor  308  may be electrically and/or physically connected to an interposer  902 , e.g., via solder  602  joints, and the capacitor-interposer subassembly may then be placed into a tape and reel. Thus, the epoxy-coated capacitor  308  may be provided in tape and reel carriers as a finished product for use in fabricating PCB assemblies  302 . 
     As described above, the epoxy-coated capacitor  308  and/or the capacitor-interposer subassembly may be attached to PCB  304  via solder  602  joints. Subsequently, additional materials may be loaded over or under epoxy-coated capacitor  308 . For example, encapsulation layer  802 , damping layer  608 , and/or overmold layer  702  may be applied over coating  1704 . Similarly, in an embodiment, damping layer  608  fills gap  606  between PCB  304  and the bottom surface of epoxy-coated capacitor  308  and/or interposer  902  to form an underfill portion. 
     In the foregoing specification, the invention has been described with reference to specific exemplary embodiments thereof. It will be evident that various modifications may be made thereto without departing from the broader spirit and scope of the invention as set forth in the following claims. The specification and drawings are, accordingly, to be regarded in an illustrative sense rather than a restrictive sense.

Metadata:
Filing Date: 20150831
Publication Date: 20191001
Grant Date: 20191001
Priority Date: 20150831
Inventors: LI, GEMIN
MARTINEZ, PAUL
BARD, BENJAMIN A.
DUKE, CONNOR R.
GONG, ZHONG-QING
RICHARDSON, KEVIN R.
MEAD, CURTIS C.
POULAIN, KIERAN
YOO, SUNG WOO
KOTTKE, NELSON J.
Assignee: APPLE INC
CPC Classifications: [{"code": "H05K2201/2045", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K2203/1316", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K2201/2045", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K1/181", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01G2/06", "inventive": true, "first": false, "tree": "[]"}, {"code": "H05K3/284", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01G4/224", "inventive": true, "first": false, "tree": "[]"}, {"code": "H05K2201/049", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K2203/1316", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K2201/2045", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K1/181", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K2201/10227", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K1/141", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K2203/1322", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K1/18", "inventive": true, "first": false, "tree": "[]"}, {"code": "H05K2201/049", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K2201/10015", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01G2/06", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01G4/30", "inventive": true, "first": true, "tree": "[]"}, {"code": "H01G4/30", "inventive": true, "first": true, "tree": "[]"}, {"code": "H05K1/0271", "inventive": true, "first": true, "tree": "[]"}, {"code": "H05K1/141", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K2203/1322", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01G4/224", "inventive": true, "first": false, "tree": "[]"}, {"code": "H05K3/284", "inventive": true, "first": false, "tree": "[]"}, {"code": "H05K2201/04", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K2201/10015", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K2201/2045", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01G2/06", "inventive": true, "first": false, "tree": "[]"}, {"code": "H05K3/284", "inventive": true, "first": false, "tree": "[]"}, {"code": "H05K1/141", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01G4/224", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01G4/30", "inventive": true, "first": true, "tree": "[]"}, {"code": "H05K2201/10015", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K2201/049", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K1/181", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K2203/1316", "inventive": false, "first": false, "tree": "[]"}, {"code": "H05K2203/1322", "inventive": false, "first": false, "tree": "[]"}]
Family ID: 58097224