PATENT DOCUMENT

Publication Number: US-10211663-B2
Application Number: US-201615082935-A
Country: US
Kind Code: B2

Title: 3D shaped inductive charging coil and method of making the same

Abstract:
A three-dimensional inductive charging coil assembly and a method of making the same. The method can include patterning a first conductive layer affixed to a first surface of an insulating layer to form a coil configured to transmit or receive power, patterning a second conductive layer affixed to a second surface of the insulating layer opposite the first surface to form a conductive trace element, and electrically coupling the coil and the conductive trace element. The coil, insulating layer, and conductive trace element can be molded (e.g., simultaneously) into a three dimensional shape. In some embodiment, the molding can include a thermoforming process such as compression molding, vacuum forming, or the like.

Claims:
What is claimed is: 
     
       1. An inductive charging component for wireless charging comprising:
 a curved charging surface; 
 an inductive coil assembly proximate the curved charging surface, the inductive coil assembly comprising:
 an insulating layer comprising a first surface and a second surface opposite the first surface; 
 a conductive multi-turn coil arranged in a spiral pattern on the first surface of the insulating layer; and 
 a conductive trace element affixed to the second surface of the insulating layer, wherein the conductive multi-turn coil and the conductive trace element are electrically coupled, the conductive multi-turn coil, the conductive trace element and the insulating layer having a curvature corresponding to the curved charging surface. 
 
 
     
     
       2. The inductive charging component of  claim 1  wherein the conductive multi-turn coil, the insulating layer, and the conductive trace element have a non-planar geometry. 
     
     
       3. The inductive charging component of  claim 1  wherein the conductive multi-turn coil and the conductive trace element are electrically coupled by a via formed through the insulating layer. 
     
     
       4. The inductive charging component of  claim 2  further comprising a laminate layer disposed on the multi-turn coil, wherein the laminate layer has a non-planar geometry. 
     
     
       5. An inductive charging component comprising:
 a curved charging surface; and 
 an inductive coil assembly adjacent to the curved charging surface, wherein the inductive coil assembly comprises:
 a polymer layer comprising a first surface and a second surface opposite the first surface, the polymer layer having a curvature corresponding to the curved charging surface; 
 a multi-turn coil coupled to the first surface of the polymer layer and configured to transmit or receive power; 
 a conductive trace element adhesive coupled to the second surface of the polymer layer; and 
 a via formed through the polymer layer that electrically couples the multi-turn coil and the conductive trace element. 
 
 
     
     
       6. The inductive charging component of  claim 5  wherein the polymer layer is non-planar, and wherein the inductive coil assembly is characterized by a three-dimensional shape such that it conforms to a contour of the curved charging surface. 
     
     
       7. The inductive charging component of  claim 5  wherein the inductive coil assembly further comprises:
 a laminate layer disposed on the multi-turn coil. 
 
     
     
       8. The inductive charging component of  claim 5  wherein the inductive coil assembly further comprises:
 a ferrite layer disposed on the conductive trace element. 
 
     
     
       9. The inductive charging component of  claim 5 , wherein the multi-turn coil is formed by patterning a metal layer affixed to the first surface of the polymer layer.

Description:
CROSS-REFERENCES TO RELATED APPLICATION 
     This application claims priority to U.S. Provisional Patent Application No. 62/208,451 filed Aug. 21, 2015, which is incorporated by reference herein in its entirety for all purposes. 
    
    
     FIELD 
     The present invention relates generally to wireless charging. More particularly, some embodiments of the invention relate to inductive coil assemblies, and methods of making inductive coil assemblies, configured to wirelessly transmit and/or receive power and characterized by a three-dimensional shape. 
     BACKGROUND 
     Wireless charging uses an electromagnetic field to transfer energy from a charging device (such as a charging station) to an inductively coupled electronic device (such as a wearable device, smart phone, or the like). Typically, an inductive coil within the charging device (a “transmitter”) generates a time-varying electromagnetic field from, for example, an alternating current (AC) flowing through the coil. This field generates a corresponding time-varying current within a second inductive coil in the electronic device (a “receiver”) by way of electromagnetic induction, and the electronic device can use this generated current to charge its battery. The transmitter and receiver inductive coils in proximity to each other effectively form an electrical transformer. Generally, the inductive coils must be in close proximity for power to be transferred. As the distance between the coils increases, power transfer becomes less efficient. 
     The proximity requirement can be especially problematic for electronic devices and their charging stations having three-dimensional (e.g., curved) charging surfaces. Inductive charging coils generally have a planar geometry. Thus, when a conventional coil is disposed along a non-planar charging surface of an electronic device or charging station, portions of the coil may be positioned some distance from the surface. This increases the distance between portions of the transmitter and receiver coils, thereby reducing wireless charging efficiency. 
     In one existing solution, wound coils have been designed where a wire is physically wound about an object having the desired three-dimensional geometry. Such processes, however, are time consuming and are associated with low precision of coil geometry and wire spacing, thereby resulting in undesirable losses in charging efficiency. 
     SUMMARY 
     Some embodiments of the invention pertain to methods of making three-dimensional inductive coil assemblies used for wireless charging. Other embodiments pertain to three-dimensional inductive coil assemblies used for wireless charging, and some other embodiments pertain to inductive chargers comprising such three-dimensional inductive coil assemblies. The three-dimensional inductive coil assemblies in accordance with embodiments of the present invention can be used in wearable electronic devices with curved charging surfaces (such as the Apple WATCH), but embodiments of the invention are not limited to such applications. 
     In some embodiments, a method of making a three-dimensional inductive coil assembly for wireless charging can include patterning (e.g., by etching) a first conductive layer affixed to a first surface of an insulating layer. The patterning can form a coil configured to wirelessly transmit or receive power. A second conductive layer affixed to a second surface of the insulating layer opposite the first surface can be patterned (e.g., by etching) to form a conductive trace element. In some embodiments, the first and second conductive layers can comprise a metal, and the insulating layer can comprise a polymer. The coil and the conductive trace element can be electrically coupled (e.g., by forming a via through the insulating layer). 
     The multi-layered structure comprising the coil, the insulating layer, and the trace element, can be molded into a three-dimensional shape. In some embodiments, the molding can include a compression molding process. In some other embodiments, the molding can include a vacuum forming process. In some embodiments, the method can further include laminating the coil and an exposed region of the first surface of the insulating layer prior to molding. In further embodiments, the method can include depositing a ferromagnetic layer (e.g., ferrite) onto the conductive trace element and an exposed region of the second surface of the insulating layer prior to molding. In some embodiments, the multi-layered structure comprising the coil, the insulating layer, and the trace element can be molded simultaneously. 
     In some embodiments, a three-dimensional inductive coil assembly is provided that can be used for wireless charging, either as a transmitter or a receiver. The three-dimensional coil assembly can include an insulating layer comprising a first surface and a second surface opposite the first surface, a first conductive layer affixed to the first surface of the insulating layer and patterned to form a coil configured to transmit or receive power, and a second conductive layer affixed to the second surface of the insulating layer and patterned to form a conductive trace element. In some embodiments, the first and second conducive layers can comprise a metal, and the insulating layer can comprise a polymer. The coil and the conductive trace element can be electrically coupled (e.g., by way of a via formed through the insulating layer). The first conductive layer, the insulating layer, and the second conductive layer can be characterized by a three-dimensional shape. 
     In some embodiments, the coil assembly can further include a laminate layer disposed on the first conductive layer and characterized by the three-dimensional shape. In further embodiments, the coil assembly can include a ferrite layer disposed on the second conductive layer and characterized by the three-dimensional shape. 
     In some embodiments, an inductive charger is provided that can include a charging surface and an inductive coil assembly adjacent to the charging surface. The coil assembly can include a polymer layer comprising a first surface and a second surface opposite the first surface, a first metal layer adhesively coupled to the first surface of the polymer layer and patterned to form a coil configured to transmit or receive power, and a second metal layer adhesively coupled to the second surface of the insulating layer and patterned to form a conductive trace element. The coil assembly can further include a via formed through the polymer layer that electrically couples the coil and the conductive trace element. In some embodiments, the charging surface can be nonplanar, and the inductive coil assembly can be characterized by a three-dimensional shape such that it conforms to a contour of the nonplanar charging surface. In some further embodiments, the coil assembly can further include a laminate layer disposed on the first metal layer. 
     The following detailed description together with the accompanying drawings in which the same reference numerals are sometimes used in multiple figures to designate similar or identical structures structural elements, provide a better understanding of the nature and advantages of the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a simplified view of an example electronic device (i.e. a watch) and corresponding charging station which can each incorporate a three-dimensional inductive coil assembly in accordance with some embodiments of the invention; 
         FIG. 2  is a simplified cross-sectional view of a planar inductive receiver coil disposed above a curved charging surface of an electronic device, and a simplified cross-sectional view of a corresponding planar inductive transmitter coil disposed under a curved charging surface of a charging station; 
         FIG. 3  shows a multi-layered structure usable to form a three-dimensional inductive coil assembly according to some embodiments of the invention; 
         FIG. 4  is a flowchart of a method of making a three-dimensional inductive coil assembly for wireless charging according to some embodiments of the invention; 
         FIG. 5A  is a simplified cross-sectional view of a multi-layered coil assembly prior to molding according to some embodiments of the invention; 
         FIG. 5B  is a simplified cross-sectional view of another multi-layered coil assembly prior to molding according to some embodiments of the invention; 
         FIG. 6A  and  FIG. 6B  are simplified diagrams illustrating a compression molding process according to some embodiments of the invention; 
         FIG. 7A  and  FIG. 7B  are simplified diagrams illustrating a vacuum forming process according to some embodiments of the invention; 
         FIG. 8A  and  FIG. 8B  are top and bottom views of a three-dimensional inductive coil assembly according to some embodiments of the invention; 
         FIG. 9  shows a wound coil that has been formed into a three-dimensional inductive coil assembly according to some embodiments of the invention; 
         FIG. 10  is a simplified cross-sectional view of an example electronic device (i.e. a watch) and charging station including three-dimensional inductive coil assemblies according to some embodiments of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     Some embodiments of the invention pertain to methods of making a three-dimensional inductive coil assembly configured to transmit or receive power in an electronic device or charging station. As described in further detail below, the methods can include patterning and molding a multi-layered coil structure to form a coil assembly having the desired three-dimensional shape. The described methods can provide a number of advantages over existing solutions, including enhanced coil shape control, improved precision of coil dimensions, the ability to form thinner coils occupying less space, scalability, and more efficient and low-cost manufacturing processes. Moreover, the three-dimensional shape of the formed coil assemblies can precisely conform to the contours of the charging surface of an electronic device or charging station. Such a configuration can reduce the distance between transmitter and receiver coils when an electronic device is “docked” in the charging station, thereby improving power transfer efficiency. 
     Embodiments of the invention may operate with one or more inductive charging components such as electronic devices and chargers. An example is shown in  FIG. 1 . As shown, a wearable electronic device  100  (i.e. a watch) includes a casing  102  that houses a display  104  and various input devices including a dial  106  and a button  108 . 
     Device  100  may be worn on a user&#39;s wrist and secured thereto by a band  110 . Band  110  includes lugs  112   a,    112   b  at opposing ends of band  110  that fit within respective recesses or apertures  114   a,    114   b  of casing  102  and allow band  110  to be removably attached to casing  102 . Lugs  112   a,    112   b  may be part of band  110  or may be separable (and/or separate) from the band. Generally, lugs  112   a,    112   b  may lock into recesses  114   a,    114   b  and thereby maintain connection between band  110  and casing  102 . Casing  102  can include electronic circuitry (not shown), including a processor, communication circuitry, and sensors that enable device  100  to perform a variety of functions. 
     A battery (not shown) internal to casing  102  powers device  100 . The battery can be recharged by an external power source, and device  100  can include circuitry configured to operate as a receiver in a wireless power transfer system. For example, the circuitry can include a receiver coil configured for inductive charging, such that a current is generated within the coil in response to an externally applied time-varying magnetic field. The receiver coil can be disposed within casing  102  and, in particular, above a curved charging surface  116  shown in  FIG. 1 . 
       FIG. 1  also shows a “charger” or charging station  100 ′. Charger  100 ′ includes a curved charging surface  116 ′ that is designed to conform to surface  116  of device  100 . Charger  100 ′ can be connected to an external power supply through a cable (not shown), and can also include a power-transmitting component such as an inductive transmitter coil to transmit power wirelessly to device  100 . For example, when device  100  is docked in charger  100 ′ with surface  116  resting on surface  116 ′, a transmitter coil disposed below surface  116 ′ can generate a time-varying magnetic field (e.g., by way of AC flowing through the transmitter coil). The generated field can then induce a corresponding time-varying current in the receiver coil disposed above surface  116  of device  100 . Device  100  can utilize the generated current (e.g., by rectification into DC) to power its battery. Device  100  and charger  100 ′ are examples of inductive charging components. 
       FIG. 2  is an expanded, simplified, cross-sectional view of surface  116  of device  100  showing an inductive charger receiver coil  202  disposed above surface  116 . As shown, receiver coil  202  is a conventional flat coil. As a result of the planar geometry, coil  202  is disposed close to surface  116  but does not precisely conform to it, thereby creating a gap  204 . 
     Also shown in  FIG. 2  is an expanded, simplified, cross-sectional view of surface  116 ′ of charger  100 ′. Similar to receiver coil  202 , charger  100 ′ includes a conventional flat transmitter coil  202 ′ disposed below surface  116 ′. Transmitter coil  202 ′ is disposed close to surface  116 ′ but does not conform to surface  116 ′ due to its planar geometry, thereby creating a gap  204 ′. As a result of gaps  204 ,  204 ′, there is an undesirable spacing between coils  202 ,  202 ′ when device  100  is docked in charger  100 ′, as this spacing can reduce power transfer efficiency from charger  100 ′ to device  100 . 
     In embodiments of the present invention, methods are provided for making three-dimensional inductive coil assemblies that can better conform to the charging surfaces of electronic devices and charging stations, thereby reducing or eliminating gaps (e.g., gaps  204 ,  204 ′) and improving charging efficiency. In some embodiments, methods can include patterning and molding a multi-layered structure to form a coil assembly having the desired geometry. 
       FIG. 3  shows a multi-layered structure  300  usable to form a three-dimensional inductive coil assembly according to some embodiments of the invention. In the example shown in  FIG. 3 , structure  300  comprises a plurality of layers including a first conductive layer  302 , an insulating layer  306 , and a second conductive layer  310 . 
     First conductive layer  302  and second conductive layer  310  can comprise any suitable electrically conductive material including, but not limited to, metals (e.g., copper, gold, silver, etc.), alloys, semiconductors, conductive ceramics, conductive polymers, and the like. Insulating layer  306  can comprise any suitable electrically insulating material compatible with molding processes such as the thermoforming processes described herein. For example, in some embodiments, insulating layer can comprise a polymer such as polyimide, PET, and other thermoformable materials. 
     As shown in  FIG. 3 , first conductive layer  302  can be affixed to a first surface of insulating layer  306  by a first adhesive layer  304  which can comprise, for example, epoxy, acrylic, or the like. Similarly, second conductive layer  310  can be affixed to a second surface of insulating layer  306  by a second adhesive layer  308  which can also comprise, for example, epoxy, polyimide, or acrylic. 
     Starting with multi-layered structure  300 , a number of processes can be performed in accordance with various embodiments of the present invention to form an inductive coil assembly having a three-dimensional shape. For example, as described in further detail below with regard to the method of  FIG. 4 , first conductive layer  302  can be patterned (e.g., by etching) to form a coil configured to transmit or receive power. Second conductive layer  310  can also be patterned to form a conductive trace element. The coil and conductive trace element can be electrically coupled by, for example, forming a via through the insulating layer. In some embodiments, the resulting structure comprising the coil, insulator layer, and trace element can then be molded into a desired three-dimensional shape using a thermoforming process such as compression molding, vacuum forming, or the like. 
     It should be noted that the particular configuration of structure  300  shown in  FIG. 3  is not intended to be limiting. For example, although structure  300  is depicted as including one insulating layer disposed between two conductive layers, any suitable number of conductive and insulating layers can be utilized in accordance with various embodiments of the invention. 
       FIG. 4  is a flowchart of a method  400  of making a three-dimensional inductive coil assembly according to some embodiments of the invention. In some embodiments, method  400  can incorporate a multi-layered structure such as structure  300  described above and shown in  FIG. 3 . For simplicity of discussion, method  400  is described below with reference to the various layers of structure  300 . 
     At block  402 , a first conductive layer (i.e. layer  302 ) affixed to a first surface of an insulating layer (i.e. layer  306 ) is patterned to form a coil configured to transmit or receive power. In some embodiments, the coil can be patterned from first conductive layer  302  using an etching process where regions of first conductive layer  302  are removed by a chemical etchant with the portions of first conductive layer  302  left behind forming the coil. For example, in some embodiments, a mask that is resistant to the etchant and includes the desired coil design (e.g., a spiral) can be affixed to the surface of first conductive layer  302  exposed to the etchant, the mask being removed at the end of the patterning process. 
     In some embodiments, photolithography techniques can be used to generate the mask having the desired coil design. In such processes, a layer of photoresist can be applied to first conductive layer  302  and exposed to light (e.g., UV) in the desired geometric pattern. Upon application of a developer solution that dissolves the regions of the photoresist exposed to the light (or that dissolves the un-exposed regions), the remaining photoresist can act as the mask that forms the coil design in first conductive layer  302  after etching. 
     Any suitable etchant can be used in embodiments of the invention so long as the selected etchant dissolves the exposed regions of first conductive layer  302  but does not dissolve (or dissolves at a slower rate) the mask material. Suitable etchants can include, but are not limited to, hydrofluoric acid, phosphoric acid, hydrochloric acid, nitric acid, sodium hydroxide, SC-1 solution, organic solvents, plasma etchants, and the like. Coils having very intricate patterns can be precisely formed according to embodiments of the present invention. 
     In some other embodiments, first conductive layer  302  can be printed or otherwise deposited onto insulating layer  306  in the desired coil pattern using known printing or deposition techniques. Depending on the feature size required for the coil, solid ink printers can be used to print the coil and/or to print the mask prior to etching. 
     At block  404 , a second conductive layer (i.e. layer  310 ) affixed to a second surface of insulating layer  306  opposite the first surface is patterned to form a conductive trace element. As with the coil patterned at block  404 , the conductive trace element can be patterned from second conductive layer  310  using an etching process where regions of second conductive layer  310  are removed by a chemical etchant with the portions of second conductive layer  310  left behind forming the conductive trace element. For example, in some embodiments, a mask that is resistant to the etchant and includes the desired trace element design (e.g., a flat wire) can be affixed to the surface of second conductive layer  310  exposed to the etchant, the mask being removed at the end of the patterning process. 
     In some embodiments, photolithography techniques can be used to generate the mask having the desired trace element design. In such processes, a layer of photoresist can be applied to second conductive layer  310  and exposed to light (e.g., UV) in the desired geometric pattern. Upon application of a developer solution that dissolves the regions of the photoresist exposed to the light (or dissolves the un-exposed regions), the remaining photoresist can act as the mask that leaves behind the conductive trace element in second conductive layer  310  after etching. 
     Any suitable etchant can be used in embodiments of the invention so long as the selected etchant dissolves the exposed regions of second conductive layer  310  but does not dissolve (or dissolves at a slower rate) the mask material. Suitable etchants can include, but are not limited to, hydrofluoric acid, phosphoric acid, hydrochloric acid, nitric acid, sodium hydroxide, SC-1 solution, organic solvents, plasma etchants, and the like. In some other embodiments, second conductive layer  310  can be printed or otherwise deposited onto insulating layer  306  in the desired pattern using known printing or deposition techniques. 
     At block  406 , the coil formed from patterning first conductive layer  302 , and the conductive trace element formed from patterning second conductive layer  310  can be electrically coupled. In some embodiments, this coupling can be achieved by way of a via that extends through insulating layer  306 , and through adhesive layers  304 ,  308 . For example, a hole can be punched through the patterned multi-layered structure and then filled with an electrically conductive material (e.g., a metal) that contacts both the coil and the trace element, thereby forming the via electrically coupling the coil and trace element. In some embodiments, the conductive material in the via, first conductive layer  302 , and second conductive layer  310  can be the same material (e.g., copper). 
     Additional processing can be performed on the multi-layered structure formed at blocks  402 - 406 . In some embodiments, method  400  can further include laminating the coil and an exposed region of the first surface of insulating layer  306 . In further embodiments, method  400  can further include depositing a ferromagnetic layer onto the conductive trace element and an exposed region of the second surface of insulating layer  306 . In some other embodiments, the ferromagnetic layer can be deposited onto the coil and the exposed region of the first surface of insulating layer  306 , and laminating can be performed on the conductive trace element and the exposed region of the second surface of insulating layer  306 . The ferromagnetic material can comprise ferrite (i.e. a material comprising Fe 2 O 3 ) in some embodiments. The laminate can comprise any suitable electrically insulating material including, for example, an epoxy resin, in some embodiments. 
       FIG. 5A  is a simplified cross-sectional view of a multi-layered coil assembly  500  prior to molding (i.e. prior to block  408  of method  400 ) according to some embodiments of the invention. As shown in  FIG. 5A , assembly  500  can include laminate layer  502 , patterned coil  504 , insulating layer  306 , conductive trace element  508 , and ferromagnetic layer  510 . In some embodiments, adhesive layers (e.g., layers  304 ,  308  in  FIG. 3 ) may be present between patterned coil  504  and insulating layer  306  and between insulating layer  306  and conductive trace element  508 . Laminate layer  502  can serve the function of electrically insulating the final coil assembly from nearby components or metallic surfaces of an electronic device or charging station in which the coil assembly is installed. Ferromagnetic layer  510  can serve the function of containing and concentrating magnetic fields within the coil assembly during wireless charging, thereby improving the efficiency of power transfer. In some embodiments, ferromagnetic layer  510  can comprise a composite of polymer and ferrite characterized by a ductility suitable for thermoforming processes. The polymer, such as an acrylic polymer in some embodiments, may act as a binder for small ferrite particles. Such a composite may be designed to not crack during subsequent thermoforming processes due to its ductility at high temperatures. 
       FIG. 5B  is a simplified cross sectional view of multi-layered coil assembly  550  prior to molding according to some embodiments of the invention. As shown in  FIG. 5B , assembly  550  can include more than one patterned coil. Assembly  550  can include laminate layer  502 , patterned coil  504 , insulating layer  306 , a second patterned coil  505 , a second insulating layer  306 , conductive trace element  508 , and ferromagnetic layer  510 . In some embodiments, patterned coil  505  can be patterned differently from patterned coil  504 . In some embodiments, an insulating layer between second patterned coil  505  and conductive trace element  508  can be made of a different material from the insulating layer between first patterned coil  504  and second patterned coil  505 . Although assembly  550  includes two patterned coil layers, other embodiments can include three or more patterned coil layers separated by insulating layers. 
     In some other embodiments, not shown in  FIGS. 5A-5B , laminate layer  502  and ferromagnetic layer  510  can be added to assembly  500  after block  408  in  FIG. 4 . For example, when laminate layer  502  and/or ferromagnetic layer  510  are not ductile enough for thermoforming processes, one or both of these layers can be applied in one or more separate processes. 
     At block  408 , assembly  500  can be subjected to a molding process to form a three-dimensional shape. In some embodiments, the assembly that is molded comprises patterned coil  504 , insulating layer  306 , and conductive trace element  508 . In some embodiments, as shown in  FIGS. 5A-5B , the assembly that is molded further comprises laminate layer  502  and ferromagnetic layer  510 . In some embodiments, at block  408 , the assembly can be molded into the three-dimensional shape by way of a thermoforming process where pressure and heat are applied simultaneously. Exemplary thermoforming processes are described in further detail below with reference to  FIGS. 6A-7B . 
       FIGS. 6A and 6B  are simplified diagrams illustrating a compression molding process according to some embodiments of the invention. In  FIGS. 6A-6B , the compression molding process is illustrated in two parts,  600   a,    600   b  for simplicity of discussion. As shown in  FIG. 6A , multi-layered coil assembly  500  from  FIG. 5A  is placed on a mold  604 . Mold  604  can have a cavity having a shape that corresponds to the final three-dimensional target shape of coil assembly  500 . In  FIG. 6A , this target shape has a concave bowl-like geometry. In other embodiments, the cavity shape of mold  604  can correspond to any other suitable geometry designed to conform to the contours of a charging surface of an electronic device or charging station. 
     In some embodiments, the cavity shape of mold  604  can be slightly different than the final target shape of coil assembly  500  to account for elastic deformation. In such embodiments, the cavity shape of mold  604  can be calculated to account for “spring-back” effects after molding. By taking such factors into account, the final three-dimensional shape of coil assembly  500  can precisely conform to a charging surface of the intended electronic device or charging station. 
     As shown  FIG. 6A , a plug member  602  can have a shape that corresponds to the shape of the cavity of mold  604 . For example, in this non-limiting illustration, plug member  602  has a convex shape that corresponds to the concave shape of the cavity of mold  604 . Appropriate force can be applied through the movement of plug member  602  towards the cavity of mold  604  (or vice versa), thereby contacting and deforming coil assembly  500  in the process. As force (i.e. pressure) is applied, a heating element  606  can provide the appropriate temperature to soften coil assembly  500  thereby improving the ductility of the constituent layers. For example, heating can be provided through infra-red (IR) heating, radio frequency (RF) heating, hot air heating, and the like. In some embodiments, the heat and pressure can be maintained until insulating layer  306  (e.g., polyimide) has cured. In some embodiments, a temperature of 100-250° C. can be used. The length of time during which heat and pressure are applied can vary depending on, for example, the shape and size of coil assembly  500 . 
       FIG. 6B  shows coil assembly  500  in mold  604  after heat and pressure have been applied. As seen in  FIG. 6B , coil assembly  500  can take the shape of the space between mold  604  and plug member  602 . In some embodiments, coil assembly  500 , in this shape, can conform to a charging surface of an electronic device or charging station and can represent the final shape of the coil assembly. In some other embodiments, the shape of coil assembly  500  may change upon removing of the pressure and/or cooling, owing to a spring-back effect. In such embodiments, the shape of the coil assembly after spring-back may conform to the desired charging surface. 
     At the end of molding, and after cooling, the final multi-layered coil assembly having the three-dimensional shape may be rigid. According to some embodiments, a trimming or cutting of excess material can be performed prior to installing the coil assembly of the desired shape and dimensions in an electronic device or charging station. 
       FIGS. 7A and 7B  are simplified diagrams illustrating a vacuum forming process according to some embodiments of the invention. In  FIGS. 7A-7B , the vacuum forming process is illustrated in two parts,  700   a,    700   b  for simplicity of discussion. As shown in  FIG. 7A , multi-layered coil assembly  500  from  FIG. 5A  is placed on a mold  702 . Mold  702  can have a cavity characterized by a shape that corresponds to the final three-dimensional target shape of coil assembly  500 . In  FIG. 7A , this target shape has a concave bowl-like geometry. In other embodiments, the cavity shape of mold  702  can correspond to any other suitable geometry designed to conform to the contours of a charging surface of an electronic device or charging station. 
     In some embodiments, the cavity shape of mold  702  can be slightly different than the final target shape of coil assembly  500  to account for elastic deformation. In such embodiments, the cavity shape of mold  702  can be calculated to account for “spring-back” effects after molding. By taking such factors into account, the final three-dimensional shape of coil assembly  500  can precisely conform to a charging surface of the intended electronic device or charging station. 
     As shown  FIG. 7A , pressure is applied to coil assembly  500  by means of a vacuum through outlet  704  in mold  702 . In evacuating the air from a cavity region  708 , the air pressure inside cavity region  708  becomes lower than the pressure outside cavity region  708  (i.e. on the upper surface pf coil assembly  500 ). This results in a suction force that “pulls” coil assembly  500  towards the cavity surface of mold  702 . As the vacuum is applied, a heating element  706  can provide the appropriate temperature to soften coil assembly  500  thereby improving the ductility of the constituent layers. For example, heating can be provided through infra-red (IR) heating, radio frequency (RF) heating, hot air heating, and the like. In some embodiments, the heat and pressure can be maintained until insulating layer  306  (e.g., polyimide) has cured. In some embodiments, a temperature of 100-250° C. can be used. The length of time during which heat and pressure are applied can vary depending on, for example, the shape and size of coil assembly  500 . 
     The vacuum forming process shown in  FIGS. 7A-7B  for forming the three-dimensional shape of coil assembly  500  can provide several advantages. For example, in the vacuum forming process, no force need be directly applied to the top surface of coil assembly  500 . Such a configuration can minimize cracks or fractures otherwise caused by contact forces (i.e. from a plug member) during molding. 
       FIG. 7B  shows coil assembly  500  in mold  702  after heat and pressure have been applied. As seen in  FIG. 7B , coil assembly  500  can take the shape of mold  702 . In some embodiments, coil assembly  500 , in this shape, can conform to a charging surface of an electronic device or charging station and can represent the final shape of the coil assembly. In some other embodiments, the shape of coil assembly  500  may change upon removing the vacuum and/or cooling, owing to a spring-back effect. In such embodiments, the shape of the final coil assembly after spring-back may conform to the desired charging surface. 
     At the end of molding, and after cooling, the final multi-layered coil assembly having the three-dimensional shape may be rigid. According to some embodiments, a trimming or cutting of excess material can be performed prior to introducing the coil assembly of the desired shape and dimensions into an electronic device or charging station. 
     Although the layers of coil assembly  500  are depicted in  FIGS. 6A-7B  as being molded simultaneously, in some embodiments, one or more layers of coil assembly  500  can be formed and molded separately. Each layer can be molded using any suitable process described herein such as, for example, a compression molding and/or vacuum forming process. Separately molded layers having a three-dimensional shape may be assembled (e.g., using an adhesive) to form the final multi-layered coil assembly characterized by the three-dimensional shape. 
       FIGS. 8A and 8B  are top and bottom views  800   a,    800   b  of a three-dimensional inductive coil assembly according to some embodiments of the invention. It should be noted that the terms “top view” and “bottom view” are used for simplicity of discussion, and that inductive coil assemblies in accordance with embodiments of the invention can be positioned within an electronic device or charging station in any suitable orientation. The coil assembly shown in  FIGS. 8A-8B  can be formed in accordance with the methods described herein (i.e. method  400 ) and using any suitable molding process such as compression molding (as shown in  FIGS. 6A-6B ), vacuum forming (as shown in  FIGS. 7A-7B ), or other suitable molding process. In other words,  FIGS. 8A and 8B  illustrate the result of forming and thermoforming multi-layered coil assembly  500  in some embodiments. 
     As seen in  FIG. 8A , a patterned coil  802  is disposed on insulating layer  804  and has a three-dimensional helical shape. In some embodiments, patterned coil  802  may be coated or otherwise covered with a ferromagnetic (e.g., ferrite) layer (not shown in  FIG. 8A ). The coil assembly also includes a conductive trace element  806  on the opposite surface of insulating layer  804 . Patterned coil  802  can include an end  810  that is electrically coupled to trace element  806  by, for example, a via that extends through insulating layer  804 . Conductive trace element  806  can be electrically coupled to a wire  808   a,  and patterned coil  802  can be electrically coupled to a wire  808   b.    
     If the coil assembly is a transmitter (e.g., in a charging station), time-varying electrical current can flow through wire  808   a,  trace element  806 , patterned coil  802 , and wire  808   b,  to generate a time-varying magnetic field. If the coil assembly is a receiver (e.g., in an electronic device), a time-varying magnetic field generated by a proximate transmitter coil can induce a current that flows through wire  808   a,  trace element  806 , patterned coil  802 , and wire  808   b,  the induced current being usable to charge a battery. 
     In the top view  800   b  of the coil assembly shown in  FIG. 8B , the coil assembly further includes a laminate layer  812  under which conductive trace element  806  is disposed. As further shown in  FIG. 8B , an outline of patterned coil  802  can also be seen through laminate layer  812  as a result of the molding process deforming insulating layer  804 . 
     In some embodiments, instead of patterning and molding multi-layered structure  300  described above, a wound coil can be used as a starting structure and then molded into the desired three-dimensional shape by way of, for example, the thermoforming processed described above with regard to  FIGS. 6A-7B . Use of wound coils in place of a multi-layered structure can provide advantages in a wireless power transfer system. For example, the dimensions of a wound coil and the amount of conductive material contained therein can be greater than that of a coil formed by the patterning techniques described herein. This can provide for lower impedance at target AC frequencies and increased inductance. The quality factor (Q) of the coil, which is a measure of efficiency, is thereby increased as it represents the ratio of inductive reactance to coil resistance at a selected frequency. 
     In some embodiments, an insulated metal (e.g., copper) wire can be mechanically wound into the desired spiral shape to form the coil. For example, the wire can be wound about an object having a circular cross section such a solid or hollow tube. The shape of the wound coil can be fixed by way of a suitable bonding material. In some embodiments, the insulator on the wire comprises an epoxy resin such as polyurethane or a polyester compound. A bonding agent such as polyimide, a rubber, nitrile or other heat-sensitive material can also be used. Upon heating the wound coil to a critical temperature determined by the selected organic materials, the wound insulated wire can be bonded into place to form a “resin-potted” wound coil. In some embodiments, the wound coil can have a planar geometry. The wound coil can then be molded into the desired three-dimensional shape using any suitable molding process including, for example, the thermoforming processes described above with respect to  FIGS. 6A-7B . 
       FIG. 9  shows a wound coil that has been formed into a three-dimensional inductive coil assembly  900  according to some embodiments of the invention. As shown in  FIG. 9 , assembly  900  comprises the wound coil  904  having a plurality of windings of insulated wire. The wire in wound coil  904  can comprise any suitable conductive metal such as copper, gold, silver, or the like. In some other embodiments, the wire can comprise another type of conductive material such as an alloy, semiconductor, conductive ceramic, conductive polymer, or the like. 
     As further shown in  FIG. 9 , wound coil  904  can be bonded in a resin. The resin can comprise polyurethane, polyester, or other suitable resin, and can further comprise a bonding agent such as a polyimide, rubber, nitrile, or the like. A conductive trace element  902  can be electrically coupled to the “beginning” and “end” of wound coil  904  to allow electrical current from a power source to flow through wound coil  904 . Assembly  900 , as shown in  FIG. 9 , has been molded into a three-dimensional shape using a thermoforming process such as compression molding ( FIGS. 6A-6B ), vacuum forming ( FIGS. 7A-7B ), or other suitable molding process. 
       FIG. 10  is a simplified cross-sectional view of an example electronic device  1000  (i.e. a watch) and charging station  1000 ′ including three-dimensional inductive coil assemblies according to some embodiments of the invention. Electronic device  1000  and charging station  1000 ′ are examples of inductive charging components. As shown in  FIG. 10 , a receiver coil assembly  1004 , formed according to embodiments of the invention, may be disposed adjacent to a non-planar (e.g., curved) charging surface  1002  of device  1000 . In some embodiments, receiver coil assembly  1004  may be attached to surface  1002  by means of a pressure sensitive adhesive (PSA). The PSA can form a bond between the surface and the coil assembly when pressure is applied, without the need for a solvent, heat, or water to activate the PSA. Device  1000  can further include circuitry (not shown) configured to utilize current generated in receiver coil assembly  1004  to charge a battery. 
     Likewise, charging station  1000 ′ can comprise a corresponding transmitter coil assembly  1004 ′ formed according to embodiments of the invention. Transmitter coil assembly  1004 ′ may be disposed adjacent to a non-planar (e.g., curved) charging surface  1002 ′ of charging station  1000 ′. As seen in  FIG. 10 , charging surface  1002 ′ may be contoured to conform to charging surface  1002  of device  1000  when device  1000  is docked in charging station  1000 ′. In some embodiments, transmitter coil assembly  1004 ′ may also be attached to charging surface  1002 ′ by means of a pressure sensitive adhesive (PSA). Charging station  1000 ′ may be connected to a source of power through a power input  1006 . The power source for the charging station  1000 ′ can be a replaceable battery, rechargeable battery, external power supply, or the like. Charging station  1000 ′ can further include circuitry (not shown) configured to generate time-varying current (e.g., AC) in transmitter coil assembly  1004 ′ for wireless power transfer to device  1000 . 
     In some embodiments, coil assemblies  1004  and  1004 ′ can be identical. In some other embodiments, coil assemblies  1004  and  1004 ′ can have different coil dimensions, numbers of windings, numbers of layers, etc. For example, transmitter coil assembly  1004 ′ can have a greater number of turnings and/or thicker wire, and thus effectively more metal. Such a configuration can account for ohmic and other losses that may occur during wireless power transmission. In some embodiments where a wound coil such as coil  900  is used for the transmitter and receiver coil assemblies, the diameter of the transmitter coil can be greater than the diameter of the receiver coil. 
     During a charging operation, power may be transferred wirelessly from transmitter coil assembly  1004 ′ to receiver coil assembly  1004 . During such an operation, device  1000  can be docked in charging station  1000 ′ with charging surfaces  1002  and  1002 ′ adjacent to each other. In such a configuration, transmitter coil assembly  1004 ′ may be aligned with receiver coil assembly  1004  along a shared axis in some embodiments. 
     The patterned coil of transmitter coil assembly  1004 ′ can produce a time-varying electromagnetic flux to induce a current within the patterned coil of receiver coil assembly  1004 . The patterned coil transmitter coil assembly  1004 ′ may transmit power at a selected frequency or band of frequencies. In some embodiments, the transmit frequency is substantially fixed, although this is not required. For example, the transmit frequency may be adjusted to improve power transfer efficiency for particular operational conditions. More particularly, a high transmit frequency may be selected if more power is required by device  1000  and a low transmit frequency may be selected if less power is required. In some other embodiments, patterned coil of transmitter coil assembly  1004 ′ may produce a static electromagnetic field and may physically move, shift, or otherwise change its position to produce a spatially-varying electromagnetic flux to induce a current within the patterned coil of receiver coil assembly  1004 . 
     As shown in  FIG. 10 , the patterned coils of transmitter coil assembly  1004 ′ and receiver coil assembly  1004  are disposed close together with very little or no gap between the coils and the surfaces. This arrangement can reduce leakage flux, thereby minimizing loss during transfer of power, improving charging efficiency, and allowing for faster charging. 
     Device  1000  may include a processor (not shown) that can be used to control the operation of or coordinate one or more functions of charging station  1000 ′. In some embodiments, charging station  1000 ′ may include one or more sensors to determine whether device  1000  is present and ready to receive power from charging station  1000 ′. For example, charging station  1000 ′ may include an optical sensor, such as an infrared proximity sensor. When charging station  1000 ′ is attached to or brought within the proximity of device  1000 , the infrared proximity sensor may produce a signal that the processor in device  1000  may use to determine the presence of charging station  1000 ′. Examples of other sensors that may be suitable to detect or verify the presence of device  1000  may include a mass sensor, a mechanical interlock, switch, button or the like, a Hall effect sensor, or other electronic sensor. 
     As previously mentioned, although embodiments described in the drawings and specification relate to coil assemblies as used in a personal wearable electronic devices such as a watch, embodiments of the invention can be used in a variety of wearable or non-wearable electronic devices in addition to the particular wrist-worn electronic devices discussed above. For example, embodiments of the invention may be used in Bluetooth headsets, smartphones, electronic glasses, wearable medical devices, and wearable fitness devices. 
     The foregoing description, for purposes of explanation, used specific nomenclature to provide a thorough understanding of the described embodiments. However, it will be apparent to one skilled in the art that the specific details are not required in order to practice the described embodiments. For example, while several specific embodiments of the invention described above use inductive coupling to wireless transmit power to a wearable electronic device, the invention is not limited to any particular wireless power transfer technique and other near-field or non-radiative wireless power transfer techniques as well as radiative wireless power transfer techniques can be used in some embodiments. Thus, the foregoing descriptions of the specific embodiments described herein are presented for purposes of illustration and description. They are not target to be exhaustive or to limit the embodiments to the precise forms disclosed. It will be apparent to one of ordinary skill in the art that many modifications and variations are possible in view of the above teachings.

Metadata:
Filing Date: 20160328
Publication Date: 20190219
Grant Date: 20190219
Priority Date: 20150821
Inventors: MATSUYUKI, NAOTO
GRAHAM, Christopher S.
BRZEZINSKI, MAKIKO K.
Assignee: APPLE INC
CPC Classifications: [{"code": "H02J50/005", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J50/10", "inventive": false, "first": false, "tree": "[]"}, {"code": "H02J7/025", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01F2038/143", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01F2027/2809", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01F41/127", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01F41/046", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01F38/14", "inventive": true, "first": true, "tree": "[]"}, {"code": "H01F27/327", "inventive": true, "first": true, "tree": "[]"}, {"code": "H01F27/2871", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01F2027/2809", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01F27/2804", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J50/10", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01F38/14", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01F38/14", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01L23/5226", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01L23/5227", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01F2027/2809", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01F41/127", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01F27/2871", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01F27/327", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01F2027/2809", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01F41/127", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J50/10", "inventive": false, "first": false, "tree": "[]"}, {"code": "H02J7/025", "inventive": true, "first": true, "tree": "[]"}, {"code": "H01L23/5227", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01F38/14", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01F27/2871", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L23/5226", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J5/005", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01F27/327", "inventive": true, "first": true, "tree": "[]"}, {"code": "H02J50/005", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 56561208