PATENT DOCUMENT

Publication Number: US-9596756-B2
Application Number: US-201314020059-A
Country: US
Kind Code: B2

Title: Electronic device with printed circuit board noise reduction using elastomeric damming and damping structures

Abstract:
An electronic device may be provided with integrated circuits and electrical components such as capacitors that are soldered to printed circuit boards. Liquid polymer adhesive such as encapsulant and underfill materials may be deposited on the printed circuit. Electrical components such as capacitors may be coated with the encapsulant. The underfill may be deposited adjacent to an integrated circuit, so that the underfill wicks into a gap between the integrated circuit and the printed circuit board. The encapsulant may be more viscous than the underfill and may therefore prevent the flowing underfill from reaching the electrical components. Some of the encapsulant may be located between the electrical components and the printed circuit board. The encapsulant can be cured to form an elastomeric material covering the electrical components that helps damp vibrations. The elastomeric material may be less stiff than the underfill.

Claims:
What is claimed is: 
     
       1. Apparatus, comprising:
 an electronic device housing; 
 a printed circuit board in the electronic device housing, wherein the printed circuit board has first and second opposing surfaces; 
 an integrated circuit mounted on the first surface of the printed circuit board; 
 an electrical component adjacent to the integrated circuit on the first surface of the printed circuit board; 
 underfill between the integrated circuit and the first surface of the printed circuit board; 
 elastomeric material between the underfill and the electrical component that prevents the underfill from reaching the electrical component; and 
 additional elastomeric material between the electronic device housing and the second surface of the printed circuit board, wherein the additional elastomeric material is in direct contact with the electronic device housing and the second surface of the printed circuit board. 
 
     
     
       2. Apparatus, comprising:
 a printed circuit board; 
 a capacitor soldered to the printed circuit board; 
 an integrated circuit soldered to the printed circuit board; 
 underfill having a portion that is between the integrated circuit and the printed circuit board that secures the integrated circuit to the printed circuit board; and 
 a material that is less stiff than the underfill that blocks the underfill from reaching the capacitor. 
 
     
     
       3. The apparatus defined in  claim 2  wherein the material comprises an elastomeric material. 
     
     
       4. The apparatus defined in  claim 3  wherein the elastomeric material comprises encapsulant that covers the capacitor. 
     
     
       5. The apparatus defined in  claim 4  wherein the elastomeric material has a portion that is located under the capacitor and between the capacitor and the printed circuit board. 
     
     
       6. The apparatus defined in  claim 5  wherein the underfill contacts the elastomeric material. 
     
     
       7. The apparatus defined in  claim 1 , wherein the additional elastomeric material between the electronic device housing and the second surface of the printed circuit board is formed in a gap between the electronic device housing and the printed circuit board and at least one additional electronic component is mounted in the gap. 
     
     
       8. The apparatus defined in  claim 7 , further comprising:
 a display mounted in the electronic device housing, wherein the electronic device housing has first and second opposing surfaces, the additional elastomeric material directly contacts the first surface of the electronic device housing, and the second surface of the electronic device housing forms an external surface of the apparatus.

Description:
BACKGROUND 
     This relates generally to electronic devices and, more particularly, to reducing noise generated by components within electronic devices. 
     Electronic devices such as computers, cellular telephones, and other electronic devices often include printed circuits. Electrical components such as integrated circuits and other devices can be interconnected using signal traces on the printed circuits. Components such as ceramic capacitors are often mounted adjacent to integrated circuits to reduce power supply noise. Components such as these may exhibit electromechanical characteristics such as piezoelectric characteristics or electrostrictive characteristics that cause them to vibrate during operation. Vibrations can be coupled into printed circuits, which can result in undesirable audible noise for a user of an electronic device. 
     It would therefore be desirable to be able to reduce noise from electrical components in electronic devices. 
     SUMMARY 
     An electronic device may be provided with integrated circuits and electrical components such as capacitors. The integrated circuits and capacitors may be soldered to printed circuit boards. During operation, time-varying signals may be applied to the electrical components. For example, decoupling capacitors near integrated circuits may experience power supply voltage variations. This can give rise to potential vibrations in the capacitors. If care is not taken, there is a potential for these vibrations to create undesired noise, particularly in situations in which underfill is present under the edges or bottom of the capacitors that increases coupling of electromechanical forces from the capacitors to a printed circuit board on which the capacitors are mounted. 
     Vibrations and undesired noise may be suppressed using elastomeric material that prevents underfill from wicking under the capacitors when the underfill is being used to secure the integrated circuits to the printed circuit boards. To be effective, the elastomeric material preferably has better transmission characteristics than the underfill. 
     A liquid polymer adhesive dispensing tool may have a computer-controlled positioner for dispensing liquid adhesive such as liquid underfill and liquid elastomeric encapsulant. Using the dispensing tool, encapsulant and underfill materials may be deposited on the printed circuit. Initially, electrical components such as capacitors may be coated with the encapsulant. The underfill may be deposited adjacent to an integrated circuit, so that the underfill wicks into a gap between the integrated circuit and the printed circuit board. The encapsulant may be more viscous than the underfill. By coating the capacitors with the encapsulant or otherwise forming a barrier to the flow of underfill using the encapsulant, the underfill may be prevented from reaching the electrical components that have been covered with the encapsulant. After curing, the elastomeric material of the encapsulant may be less stiff than the underfill to help reduce coupling between the capacitors and the printed circuit board on which the capacitors are mounted and thereby reduce vibrations and noise. Vibrations and noise may also be reduced by placing elastomeric material on other portions of a printed circuit board. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of an illustrative electronic device such as a handheld computing device or other electronic device in accordance with an embodiment. 
         FIG. 2  is a cross-sectional side view of an illustrative electronic device in accordance with an embodiment. 
         FIG. 3  is a cross-sectional side view of a component such as a capacitor mounted on a printed circuit board in accordance with an embodiment. 
         FIG. 4  is a cross-sectional side view of a portion of a printed circuit board showing how a component such as a capacitor may be encapsulated to prevent underfill from flowing under the capacitor in accordance with an embodiment. 
         FIG. 5  is a flow chart of illustrative steps involved in forming electronic devices containing printed circuit boards with reduced vibrational noise in accordance with an embodiment. 
         FIG. 6  is a top view of an illustrative printed circuit board on which encapsulant has been deposited prior to dispensing underfill to help prevent the underfill from flowing under vibrating components in accordance with an embodiment. 
         FIG. 7  is a top view of a printed circuit board on which a ring-shaped layer of encapsulant has been used to cover vibrating components to prevent underfill from flowing under the vibrating components in accordance with an embodiment. 
         FIG. 8  is a top view of a printed circuit board on which a ring of encapsulant has been formed to prevent underfill from flowing outward from inside an opening in the center of the ring and under vibrating components located outside of the ring in accordance with an embodiment. 
         FIG. 9  is a top view of an illustrative printed circuit board on which vibration reducing material such as elastomeric encapsulant material is being used to damp printed circuit board vibrations in accordance with an embodiment. 
         FIG. 10  is a cross-sectional side view of an illustrative electronic device in which vibration reducing material has been interposed between vibrating portions of a printed circuit board and nearby housing structures to reduce vibrations in the printed circuit board in accordance with an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     An electronic device may be provided with electronic components that are interconnected by conductive traces on printed circuits. The printed circuits may include rigid printed circuit boards formed from materials such as fiberglass-filled epoxy and flexible printed circuits formed from sheets of polyimide or other flexible polymer layers. The electrical components may include integrated circuits, discrete components such as resistors, capacitors, and inductors, switches, and other electrical components. 
     Some components may have a tendency to produce vibrations during normal operation. For example, ceramic capacitors may include materials that tend to vibrate when subjected to electrical signal fluctuations. Electrical signal fluctuations may occur at 60 Hz, for example, as a graphics processor or other integrated circuit renders frames of display data at a frame rate of 60 Hz. Waveform shape may include higher harmonic content. Natural modes of the system can be excited by the fundamental and higher order harmonics and create acoustic noise efficiently. The presence of vibrating components such as ceramic capacitors may therefore create undesirable audible buzzing noises. 
     Buzzing noises and other undesirable audible artifacts from vibrating components can be minimized by incorporating elastomeric encapsulant structures into a printed circuit. The elastomeric encapsulant can prevent hard underfill material from wicking under vibrating components such as capacitors. This can help reduce coupling between the vibrating component and the printed circuit board. Elastomeric material can also be deposited on portions of a printed circuit board that are subject to vibrations to help damp the vibrations. For example, elastomeric material may be placed in gaps between a printed circuit board and an electronic device housing. 
     An illustrative electronic device of the type that may be provided with printed circuits having structures for reducing vibrations from vibrating components is shown in  FIG. 1 . Device  10  may be a computing device such as a laptop computer, a computer monitor containing an embedded computer, a tablet computer, a cellular telephone, a media player, or other handheld or portable electronic device, a smaller device such as a wrist-watch device, a pendant device, a headphone or earpiece device, or other wearable or miniature device, a television, a computer display that does not contain an embedded computer, a gaming device, a navigation device, an embedded system such as a system in which electronic equipment is mounted in a kiosk or automobile, a router, a set-top box, equipment that implements the functionality of two or more of these devices, or other electronic equipment. In the illustrative configuration of  FIG. 1 , device  10  is a portable device such as a cellular telephone, media player, tablet computer, or other portable computing device. 
     Device  10  may have one or more displays such as display  14  mounted in housing structures such as housing  12 . Housing  12  may be formed of materials such as plastic, glass, ceramics, carbon-fiber composites and other fiber-based composites, metal (e.g., machined aluminum, stainless steel, or other metals), other materials, or a combination of these materials. If desired, openings may be formed in display  14  to accommodate components such as button  16  and speaker port  18  of  FIG. 1  (as examples). Buttons, connector ports, and other structures may also be accommodated using openings in housing  12 . 
       FIG. 2  is a cross-sectional side view of electronic device  10  of  FIG. 1  taken along line  20  and viewed in direction  22  of  FIG. 1 . As shown in  FIG. 2 , display  14  may be mounted in electronic device housing  12 . Display  14  may include display cover layer  24  (e.g., a sheet of clear glass or plastic) and display layers  26 . Display layers  26  may be associated with a liquid crystal display and may include structures such as a thin-film transistor layer, color filter layer, a layer of liquid crystal material, polarizer layers, and backlight structures. Other types of display technology may be used in forming display  14  if desired. 
     One or more printed circuits such as printed circuit  28  may be used to mount and interconnect electronic components in device  10 . Printed circuit  28  may be, for example, a rigid printed circuit board formed from fiberglass-filled epoxy. Flexible printed circuits formed from polyimide layers or other sheets of flexible polymer may also be used in device  10 , if desired. The amount of sound that is produced when vibrating components are mounted on rigid printed circuit boards tends to be greater than the amount of sound that is produced when vibrating components are mounted on flexible printed circuit boards, so sound minimizing techniques are sometimes described herein in the context of rigid printed circuit boards. 
     Electrical components such as components  30  and  32  may be mounted to printed circuit board  28  using solder or conductive adhesive. Components  30  and  32  may include integrated circuits, discrete components such as resistors, capacitors, and inductors, switches, sensors, connectors, audio components, etc. For example, components  30  may be integrated circuits such as graphics chips or other video processing circuits, microcontrollers, microprocessors, memory, application-specific integrated circuits, digital signal processors, or other integrated circuits. Components  32  may be components that are prone to vibration during operation such as ceramic capacitors or other components that exhibit piezoelectric and/or electrostrictive characteristics. For example, components  32  may be power supply decoupling capacitors that are mounted adjacent to integrated circuits  30 . 
     With one suitable layout, integrated circuit  30  has a rectangular footprint and capacitors  32  are mounted on printed circuit board  28  along one or more sides of integrated circuit  30  or in a ring surrounding integrated circuit  30 . There may be any suitable number of integrated circuits  30  on printed circuit board  28  (e.g., one or more, two or more, three or more, etc.) and there may be any suitable numbers of associated capacitors  32  (e.g., one or more, two or more, ten or more, fifty or more, etc.). Fasteners such as screws  34  may be used in attaching printed circuit  28  to housing  12 . There may be one or more printed circuits  28  in device  10 . 
     A cross-sectional side view of an illustrative capacitor of the type that may produce vibrations during operation is shown in  FIG. 3 . As shown in  FIG. 3 , capacitor  32  may have interleaved capacitor plates  36  mounted within housing  58 . A first set of the plates may be electrically connected to capacitor terminal  38  and associated metal contact  42 . A second set of the plates may be electrically connected to capacitor terminal  40  and associated metal contact  48 . Contacts (terminals)  42  and  48  may mounted to printed circuit board  28  using conductive adhesive, solder, or other conductive materials. For example, capacitor contact  42  may be soldered to pad  46  on printed circuit board  28  using solder  44  and capacitor contact  48  may be soldered to pad  52  using solder  48 . 
     The material that is used in forming capacitor plates  36  may move when signals are applied across terminals  42  and  48 . For example, in ceramic capacitors, capacitor plates  36  may be formed from piezoelectric or electrostrictive material that expands and contracts as a function of applied voltage. When time-varying electrical signals such as power supply voltage fluctuations are applied across terminals  42  and  48  in a scenario in which capacitor  32  contains piezoelectric and/or electrostrictive layers  36 , capacitor  32  will vibrate up in direction  54  and down in direction  56 . These movements of capacitor  32  may be coupled to printed circuit board  28  through solder joints  44  and  48 . 
     In conventional component mounting arrangements, thin liquid epoxy material commonly called underfill is used to secure integrated circuits to printed circuit boards. The underfill helps to prevent an integrated circuit from becoming detached from a printed circuit board in a drop event and to otherwise prevent integrated circuit connections from becoming damaged, cracked, disconnected, or detached during stress events. The underfill that is used to secure an integrated circuit to the printed circuit board may wick under nearby components such as ceramic capacitors. When cured, the underfill becomes stiff. The presence of stiff underfill between the underside of a vibrating capacitor and the upper surface of a printed circuit board may mechanically couple the capacitor to the underlying printed circuit board and thereby cause the printed circuit board to vibrate and produce noise. 
     To avoid undesired vibrational coupling effects of this type, the underfill may be prevented from flowing under capacitors such as capacitor  32 . With one illustrative embodiment, an elastomeric material may be used to encapsulate capacitor  32  and thereby block the underfill as the underfill wicks under a nearby integrated circuit. The underfill may flow into contact with the elastomeric material. The elastomeric material may be more viscous than the underfill that flows into contact with the elastomeric material to prevent mixing of the underfill and the elastomeric material. To ensure satisfactory curing of the underfill and elastomeric material even in the event that there is a small amount of mixing at the interface between the underfill and the elastomeric material, the underfill and elastomeric material may be based on similar chemistries (i.e., the underfill and the elastomeric material may both be epoxy-based polymers). Additives may be incorporated into the epoxy of the elastomeric material to ensure that the elastomeric material is more viscous than the underfill. After curing (e.g., using time and elevated temperature), the underfill that has flowed under the integrated circuit will harden and help secure the integrated circuit to the printed circuit board. The elastomeric material will cure to a state that is resilient, softer, and less stiff than the underfill. When capacitor  32  vibrates during operation, the elastomeric nature of the elastomeric material that is adjacent to capacitor  32  will tend to exhibit reduced mechanical coupling with printed circuit board  28  and will tend to damp vibrations in capacitor  32  and printed circuit board  28  and thereby reduce noise. 
       FIG. 4  is a cross-sectional side view of an illustrative printed circuit board  28  on which components such as ceramic capacitor  32  and integrated circuit  30  have been mounted using solder  70 . Liquid adhesive dispensing tool  60  may include computer-controlled positioner  62  and adhesive dispensing head  64 . Nozzle  66  of head  64  may be used to dispense liquids such as liquid adhesives (e.g., liquid epoxies or other liquid polymer adhesives). 
     Using positioner  62 , tool  60  may dispense liquid adhesive material onto various portions of the surface of printed circuit  28 . For example, tool  60  may initially be used to dispense elastomeric material  68  over capacitor  32 . The deposited elastomeric material may flow under capacitor  32 , as illustrated by elastomeric material portion  68 ′ in the  FIG. 4  example. Elastomeric material  68  may be cured using heat, application of ultraviolet light, or other techniques. After dispensing elastomeric material  68  (and preferably before elastomeric material  68  has cured by applying heat or ultraviolet light), positioner  62  may position tool head  64  and nozzle  66  (or a separate nozzle) at a position such as position P 1  (i.e., a position between integrated circuit  30  and capacitor  32  that is near the edge of integrated circuit  30 ) or position P 2  (i.e., a position on the far side of integrated circuit  30  from capacitor  32 . The use of underfill dispensing positions such as position P 2  may help prevent underfill from flowing under capacitor  32  and may be used in scenarios in which no elastomeric material  68  has been deposited prior to underfill dispensing, if desired. 
     In the example of  FIG. 4 , elastomeric material  68  has been deposited over capacitor  32  by tool  60  prior to deposition of underfill  72 . As a result, capacitor  32  is encapsulated and protected from underfill  72 . Underfill  72  is less viscous than elastomeric material  68  and has a propensity to spread out on the surface of printed circuit  28  and to wick into cracks such as the gap between underside  74  of integrated circuit  30  and upper surface  76  of printed circuit board  28 . Underfill  72  also tends to wick partway up the sidewalls of integrated circuit  30  (and, if not blocked by the presence of elastomeric material  68 , would tend to wick up the sides of capacitor  32  and other components). 
     After curing, underfill  72  will be relatively stiff and will hold integrated circuit  30  to surface  76  of printed circuit board  28  in the event that printed circuit board  28  is dropped, whereas elastomeric material  68  will be less stiff (i.e., material  68  will have a lower modulus of elasticity). The reduced stiffness of cured elastomeric material  68  (sometimes referred to as encapsulant) and the absence of stiff underfill  72  will help reduce mechanical coupling of vibrations from capacitor  32  to printed circuit  28 . The presence of elastomeric material  68  below and/or to the sides and/or above capacitor  32  and/or no printed circuit board  28  may also help damp vibrations. 
     Illustrative steps involved in forming and operating an electronic device having components such as one or more capacitors  32  (e.g., decoupling capacitors) mounted to a printed circuit board as described in connection with  FIG. 4  are shown in  FIG. 5 . At step  78 , electrical components may be mounted to printed circuit boards. For example, one or more integrated circuits  30  may be soldered to printed circuit board  28  and one or more capacitors  32  or other components that have the potential to vibrate during operation may be soldered to printed circuit board  28 . Components such as capacitors  32  (e.g., coupling capacitors) may be located adjacent to integrated circuits  30 . For example, there may be a rectangular ring of capacitors  32  surrounding each integrated circuit  30  or one or more rows of capacitors running along one or more edges of integrated circuit  30 . 
     At step  80 , elastomeric material  68  (sometimes referred to as encapsulant) may be deposited over capacitors  32  in liquid form using adhesive dispensing system  60 . The deposited elastomeric material  68  may be patterned to form a drop, a strip (i.e., a line of adhesive when viewed from above printed circuit  28 ), a rectangular shape, a circular ring or rectangular ring, or other suitable shape. 
     At step  82 , underfill  72  may be deposited by adhesive dispensing system  60  in liquid form. Underfill  72  may be deposited adjacent to capacitors  32  and integrated circuit  30 . Underfill  72  may be formed from a liquid polymer adhesive such as liquid epoxy that is thin and able to wick into the gap between lower surface  74  of integrated circuit  30  and upper surface  76  of printed circuit  28 . Uncured liquid elastomeric material  68  may be formed form a liquid polymer adhesive such as liquid epoxy with thickening additives that is more viscous than uncured liquid underfill  72 . Because elastomeric material  68  is more viscous than underfill  72 , underfill  72  will be prevented from wicking under capacitors  32 . Underfill  72  and elastomeric adhesive  68  may both be formed from epoxies or may both be formed using another type of adhesive chemistry. If desired, elastomeric material may be applied to portions of printed circuit board  28  that tend to vibrate (e.g., to serve as sound deadening material and/or to damp vibrations by providing a cushion between printed circuit board  28  and housing  12 ). 
     At step  84 , heat may be applied to printed circuit  28  to elevate the temperature of printed circuit  28 , underfill  72 , and elastomeric material  68  or ultraviolet light may be applied to cure elastomeric material  68 . The applied heat (or ultraviolet light) cures underfill  72  to form a relatively stiff solid bond between integrated circuit  30  and printed circuit  28  and cures elastomeric material  68  to form a cured elastomeric material that is softer and less stiff than cured underfill  72 . 
     At step  86 , printed circuit  28  and other components of device  10  may be assembled together to form device  10 . Device  10  may be operated by a user at step  86 . Due to the absence of stiff underfill beneath capacitor  32  and/or due to the damping presence of elastomeric material  68  on and/or below capacitor  32  and/or on other portions of printed circuit board  28 , vibrations from capacitor  32  will be only weakly coupled to printed circuit board  28  and/or will be damped by the vibration damping properties of elastomeric material  68 . The user of device  10  will therefore be exposed to minimized amounts of vibration-induced noise while operating device  10  at step  88 . 
       FIG. 6  is a top view of an illustrative layout for printed circuit board  28  on which two integrated circuits  30  have been mounted. In the upper left corner of printed circuit board  28 , elastomeric encapsulant  68  has been placed over capacitors  32  running along the right-hand edge of integrated circuit  30  before applying underfill  72  to attach integrated circuit  30  to printed circuit board  28 . In the lower right corner of printed circuit board  28 , elastomeric encapsulant  68  has been deposited in four strips over the capacitors  32  that run along each of the four sides of integrated circuit  30  before applying underfill  72 . 
       FIG. 7  shows how elastomeric material  68  may be deposited in the shape of a rectangular ring that surrounds integrated circuit  30 . In this configuration, elastomeric material  68  encapsulates vibrating components such as capacitors  32  while forming a ring-shaped barrier having a central opening that receives integrated circuit  30 . Underfill  72  may be dispensed at a location along the outer edge of integrated circuit  30  so that underfill  72  flows under integrated circuit  30 . Elastomeric material  68  surrounds and encloses underfill  72 , thereby preventing underfill  72  from flowing outward to encapsulated capacitors  32 . 
     If desired, elastomeric material  68  may form a barrier to underfill  72  without covering capacitors  32 . As shown in  FIG. 8 , for example, elastomeric material  68  may be deposited in a rectangular ring shape that runs along the four peripheral edges of integrated circuit  30  without covering capacitors  32 . When underfill  72  is deposited on the surface of printed circuit  28  within the inner opening of the ring of elastomeric material  68 , underfill  72  will wick under integrated circuit  30 , but will be prevented from flowing outwards to capacitors  32  due to the presence of the barrier formed by elastomeric ring  68 . 
     Elastomeric material  68  may be deposited on portions of printed circuit board  28  other than the regions of printed circuit board containing capacitors  32  that are adjacent to integrated circuits  30 .  FIG. 9  is a top view of an illustrative printed circuit that has been provided with this type of elastomeric material. As shown in  FIG. 9 , printed circuit  28  may be attached to the housing of electronic device using screws  90 . Some components such as capacitors  32  may be mounted adjacent to integrated circuits such as integrated circuit  30  (e.g., to serve as power supply decoupling capacitors). These capacitors may be coated with elastomeric material  68 - 1 , so that underfill  72  is prevented from reaching capacitors  32  and does not overlap capacitors  32 . In the example of  FIG. 9 , the portion of printed circuit  28  in the example of  FIG. 9  that is most prone to vibrations is located in the center of printed circuit  28 . To reduce vibrations in this area, elastomeric material  68 - 2  may be placed in the center of printed circuit board  28 . In this configuration, elastomeric material  68 - 2  may damp vibration resulting in less efficient noise generation from printed circuit  28 . If desired, elastomeric material  68 - 2  that is being used as vibration damping may optionally cover one or more electrical components such as components  92  (e.g., integrated circuits, etc.). Even if components  92  do not produce vibrations during operation, the presence of elastomeric material  68 - 2  may help damp vibration that has been imparted to printed circuit board by more distant components such as capacitors  32 . 
       FIG. 10  shows how printed circuit board  28  may be mounted to housing  12  using screws  90 . To reduce noise in this type of configuration, elastomeric material  68  may be deposited in one or more locations in gap  92  between lower surface  94  of printed circuit board  28  and upper (inner) surface  96  of housing  12  or elsewhere between printed circuit board  28  and housing  12 . As shown in  FIG. 10 , when elastomeric material is deposited in multiple portions of gap  92 , space may be made available for components  98 . For example, components  98  may be mounted in portion  92 ′ of gap  92  between elastomeric material  68 A and elastomeric material  68 B. Elastomeric material such as elastomeric material  68 A and  68 B forms a soft damping support structure between rigid device structures such as housing  12  and printed circuit board  28 , thereby damping vibrations in printed circuit board  28 . Elastomeric material may be placed against regions in printed circuit board  28  that are prone to vibrations (e.g., resonance locations) to maximize damping effectiveness. 
     The foregoing is merely illustrative and various modifications can be made by those skilled in the art without departing from the scope and spirit of the described embodiments. The foregoing embodiments may be implemented individually or in any combination.

Metadata:
Filing Date: 20130906
Publication Date: 20170314
Grant Date: 20170314
Priority Date: 20130906
Inventors: RAINER AMANDA R.
DUKE CONNOR R.
BILANSKI JAMES W.
THOMA JEFFREY M.
ENG MICHAEL
LI MINGZHE
YOO SUNG WOO
LARA-PENA MIGUEL ALEJANDRO
FOO WENG CHOY
POULAIN KIERAN
Assignee: APPLE INC
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Family ID: 52625391