Patent Publication Number: US-2007119620-A1

Title: Flexible circuit shields

Description:
BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates in general to the field of flexible circuits, and more particularly to the field of shielding electrical components in flexible circuits.  
      2. Description of the Related Art  
      A flexible circuit includes a flexible material that has one or more metal circuit patterns. The flexible material may be single-layered or multi-layered, depending on the number of metal circuit patterns that are insulated from one another by flexible polymer films. The metal circuit patterns include electrical signal paths and ground planes that are embedded in the flexible material. The metal circuit patterns can be interconnected through vias. As is known in the art, a via refers to a metal-plated through hole that connects two or more metal circuit patterns, allowing signals to pass through the flexible material to the signal layers or the ground planes. Several electrical components that can be passive and/or active may be mounted on the flexible circuit. Passive components refer to devices that have a minimal impact on the electrical signals passing through them. Examples of passive components include, but are not limited to, resistors, capacitors and inductors. Active components refer to devices with gains, or which direct the flow of the current. Examples of active components include, but are not limited, to transistors and thyristors.  
      The electrical components used in the flexible circuits may produce electromagnetic interference (EMI) and radio frequency interference (RFI). Electromagnetic interference refers to interference caused by the electromagnetic radiation emitted by electrical devices. RFI refers to interference due to electromagnetic radiation in the radio frequency spectrum emitted by electrical devices. These interferences induce unwanted signals in other circuits, which may cause electronic failure and degrade the performance of the other circuits. Hence, shielding is required to block EMI and RFI in many electrical devices, including those that contain flexible circuits. Generally, these devices are positioned on printed circuit boards and are covered with metal shields. Because the shields are made of metal, a gap must be maintained between the shields and the components. This gap and the thickness of the shields and the PCB add to the overall height of a device housing them.  
     SUMMARY OF THE INVENTION  
      The present invention concerns a method for shielding at least one electrical component on a flexible shielding circuit. The electrical component may produce electromagnetic interference (EMI) or radio frequency interference (RFI). The flexible shielding circuit can include one or more signal layers that are separated by insulating layers and at least a first portion and a second portion.  
      The method can include the steps of mounting the electrical component on the first portion of the flexible shielding circuit, covering at least one exposed surface of the electrical component that is mounted on the first portion with the second portion of the flexible shielding circuit, and selectively securing the second portion to the first portion. In accordance with an embodiment of the inventive arrangements, the second portion can provide shielding for the electrical component.  
      In one arrangement, covering the exposed surface of the electrical component can include folding the second portion of the flexible shielding circuit over the electrical component. This folding process can include bending the second portion in a manner such that a loop can be formed by a part of the second portion. Selectively securing the second portion to the first portion can include joining the ends of the loop with a conductive adhesive.  
      In another arrangement, covering the exposed surface of the electrical component can include covering the exposed surface in a manner such that a gap can be formed between the exposed surface of the electrical component and the second portion covering the exposed surface. Also, covering the exposed surface can include securing the second portion covering the exposed surface to the exposed surface with an adhesive. Additionally, the method can also include the steps of mounting another electrical component on top of the second portion shielding the electrical component and routing signals from one part of the electrical component to another part of the electrical component, or another electrical component, through signal layers, without interfering with a ground plane in the first portion.  
      The present invention also concerns a flexible shielding circuit. The flexible shielding circuit can include at least one electrical component that may produce electromagnetic interference or radio frequency interference and a flexible circuit that may containing one or more signal layers. As an example, the flexible circuit can include a first portion and a second portion in which the electrical component can be mounted on the first portion. In addition, the second portion can cover at least one exposed surface of the electrical component and can be selectively secured to the first portion. As a result, the second portion may provide shielding for the electrical component.  
      In one arrangement, the second portion of the flexible circuit can be folded over the electrical component and bent in a manner such that a part of the second portion can form a loop. As an example, the ends of the loop can be joined by a conductive bond. The flexible shielding circuit may also include an adhesive that can secure the second portion to the exposed surface of the electrical component. In another arrangement, there may be a gap between the exposed surface of the electrical component and the second portion that can cover the exposed surface.  
      In yet another arrangement, signals may be routed from one part of the electrical component to another part of the electrical component or some other electrical component through the signal layer in the second portion. The first portion of the flexible circuit may include a ground plane, and the signals may be routed through the signal layer of the second portion without interfering with the ground plane in the first portion. The flexible shielding circuit can also include another electrical component mounted on top of the second portion of the flexible shielding circuit. As an example, the flexible shielding circuit can be part of a mobile communications unit having a transmitter or a receiver or both. At least a portion of the flexible circuit can include an outer, non-conductive layer that may surround the signal layers.  
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The features of the present invention, which are believed to be novel, are set forth with particularity in the appended claims. The invention, together with further objects and advantages thereof, may best be understood by reference to the following description, taken in conjunction with the accompanying drawings, in the several figures of which like reference numerals identify like elements, and in which:  
       FIG. 1  illustrates a side view of an example of an electrical component mounted on a flexible shielding circuit, in accordance with an embodiment of the inventive arrangements;  
       FIG. 2  illustrates a cross-sectional diagram of an example of a flexible shielding circuit used for shielding an electrical component, in accordance with an embodiment of the inventive arrangements;  
       FIG. 3  illustrates an isometric view of the flexible shielding circuit portrayed in  FIG. 2 , in accordance with an embodiment of the inventive arrangements;  
       FIG. 4  illustrates a cross-sectional diagram of an example of a multi-layered flexible shielding circuit used for shielding an electrical component, in accordance with an embodiment of the inventive arrangements;  
       FIG. 5  illustrates an isometric view of shielding portrayed in  FIG. 4 , in accordance with an embodiment of the inventive arrangements; and  
       FIG. 6  illustrates a flowchart of a method for shielding an electrical component using flexible shielding circuit, in accordance with an embodiment of the inventive arrangements.  
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      While the specification concludes with claims defining the features of the invention that are regarded as novel, it is believed that the invention will be better understood from a consideration of the following description in conjunction with the drawing figures, in which like reference numerals are carried forward.  
      As required, detailed embodiments of the present invention are disclosed herein. However, it is to be understood that the disclosed embodiments are merely exemplary of the invention, which can be embodied in various forms. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one skilled in the art to variously employ the present invention in virtually any appropriately detailed structure. Further, the terms and phrases used herein are not intended to be limiting, but rather to provide an understandable description of the invention.  
      The terms “a” or “an”, as used herein, are defined as one or more than one. The term “plurality”, as used herein, is defined as two or more than two. The term “another”, as used herein, is defined as at least a second or more. The terms “including” and/or “having”, as used herein, are defined as comprising (i.e., open language).  
      The invention concerns a method and system for shielding an electrical component by using a flexible shielding circuit. The electrical component may produce electromagnetic interference (EMI) or radio frequency interference (RFI). The flexible shielding circuit can include one or more signal layers. In one arrangement, the method can include the steps of mounting the electrical component on a first portion of the flexible shielding circuit, covering an exposed surface of the electrical component that is mounted on the first portion with a second portion of the flexible shielding circuit, and selectively securing the second portion to the first portion. This process can provide EMI and RFI shielding for the electrical component without substantially increasing the thickness of a device housing the electrical component and the flexible shielding circuit. As an example, the flexible shielding circuit can be part of a mobile communications unit having a transmitter or a receiver or both.  
      In one arrangement, the method can also include the steps of folding the second portion of the flexible shielding circuit over the electrical component, bending the second portion such that a loop is formed by a part of the second portion, and joining the ends of the loop with a conductive adhesive. In addition, the method can include the steps of mounting another electrical component on top of the second portion, and routing signals from one part of the electrical component to another part of the electrical component or some other electrical component, through signal layers in the second portion, without interfering with a ground plane in the first portion. As such, the invention can provide shielding for electrical components and can also pass electrical signals.  
      Referring to  FIG. 1 , a side view  100  of an electrical component  104 , mounted on a flexible shielding circuit  102 , is shown. It will be apparent to a person skilled in the art that the electrical component  104  can have various shapes. For example, the electrical component  104  can have the shape of a cube. In this case, the electrical component  104  has six faces or surfaces. In  FIG. 1 , only four surfaces  106 ,  108 ,  110  and  112  can be seen. The surface  106  of the electrical component  104  can be mounted on the flexible shielding circuit  102  and secured to the circuit  102  using any suitable means or process, such as through soldering. Surface  108 , surface  110 , and surface  112  are the exposed surfaces of the electrical component  104 . Surface  108  is the top exposed surface of the electrical component  104 . Any one of the exposed surfaces  108 , 110  and  112  and the surface  106  of the electrical component  104  may emanate electromagnetic radiation. As an example, the electrical component  104  may be an integrated circuit (IC), although other suitable components are within contemplation of the inventive arrangements.  
      Referring to  FIG. 2 , a cross-sectional diagram of a system  200  for shielding an electrical component  104  by using a flexible shielding circuit  102  is shown. In one arrangement, the system  200  can include a first portion  202  of the flexible shielding circuit  102 , a second portion  204  of the flexible shielding circuit  102 , the electrical component  104 , and a conductive adhesive  206 , which can help secure the second portion  204  to the first portion  202 . Examples of the conductive adhesive  206  can include, but are not limited to, solder and anisotropic conducting films (ACF), although any other suitable conductive adhesive may be used here.  
      The surface  106  of the electrical component  104  can be mounted on the first portion  202  in accordance with any suitable procedure for securing an electrical device to a flexible circuit. Both the first portion  202  and the second portion  204  may be part of the flexible shielding circuit  102 . In other words, the two portions of the flexible shielding circuit  102  may be in continuum, although they can also be separate parts joined together through any suitable process.  
      In one arrangement, the second portion  204  of the flexible shielding circuit  102  can be folded over the electrical component  104  to cover, for example, the exposed surfaces of the electrical component  104 . The electrical component  104  can then be shielded by securing the second portion  204  of the flexible shielding circuit  102  to the first portion  202  with the conductive adhesive  206 .  
      In one arrangement, the second portion  204 , covering the exposed surfaces of the electrical component  102 , can be selectively secured to the exposed surfaces by using an adhesive. In another arrangement, the second portion  204  can be merely positioned over the exposed surfaces of the electrical component  104  such that there may be a slight gap between the second portion  204  and the exposed surfaces.  
      Though the system  200  is shown to include only the electrical component  104 , the system  200  can include a plurality of electrical components that are shielded by the flexible shielding circuit  102 . For example, a plurality of electrical components  104  can be mounted next to one another on the first portion  202  of the flexible shielding circuit  102 , and second portions  204  can be used to shield these components  104 . Moreover, one or more electrical components  104  can be mounted on the top surface of the second portion  204 , and another second portion  204  can be folded over these components  104  and secured to the second portion  204  on which the components  104  are mounted. This process can allow for the stacking of electrical components  104 , and each of them can be shielded by a second portion  204 .  
      Referring to  FIG. 3 , an isometric view of the system  200 , discussed in  FIG. 2 , is shown. The second portion  204  extends from the first portion  202  and can cover the surfaces of the electrical component  104 . The second portion  204  can include one or more flaps  205 , each of which can be secured to the first portion  202 , such as with a conductive adhesive (see  FIG. 2 ). In view of this exemplary design, the second portion  204  can shield the top and the sides of the electrical component  104 .  
      Referring to  FIG. 4 , a cross-sectional diagram of a system  400  and a system  500  for shielding an electrical component  104  by using a flexible shielding circuit  102 , in accordance with another inventive arrangement of the present invention, is shown. In one arrangement, the flexible shielding circuit  102  of the system  400  and the system  500  can include multiple signal layers. In particular, the system  400  can have a two-layer flexible shielding circuit  102  and the system  500  can have a four-layer flexible shielding circuit  102 , although it is understood that the invention is in no way limited to these two examples.  
      As an example, in the flexible shielding circuit  102  of both systems  400 ,  500 , a first portion  202  and a second portion  204  can include one or more signal layers  402 , one or more insulating layers  404 , and one or more ground planes  406 . It is important to note that the invention is not limited to the layer layout that is illustrated here in  FIG. 4 , as other suitable arrangements are within contemplation of the invention. In one embodiment, the signal layers  402  can be selectively connected to each other and the ground plane(s)  406  through vias  408 .  
      While covering the electrical component  104 , the second portion  204  can be folded in a manner so that a loop  410  is formed, similar to what is shown in  FIG. 3 . As can be seen and as explained earlier, the second portion  204  can be secured to the first portion  202  with a conductive adhesive  206 . In addition to the vias  408  and as will be appreciated by those of skill in the art, the conductive adhesive  206  can be used to facilitate the transfer of electrical signals between the signals layers  402  and the ground plane(s)  406 . In view of the ground plane(s)  406 , the flexible shielding circuit  102  can serve as a suitable shield for the electrical component  104 .  
      The external layer of the flexible shielding circuit  102  can be an insulating layer  404  or material, which, as those of skill in the art can appreciate, can allow the second portion  204  to be secured to the top of the electrical component  104 , such as with an adhesive. Accordingly, there may be little or no space between the top of the component  104  and the circuit  102 . This can lower the overall height of the systems  400 ,  500 . As an alternative, the second portion  204  can be merely placed over the top of the electrical component  104 . In this arrangement, a small gap may exist between the top of the electrical component  104  and the circuit  102 . In either alternative, the overall height of the systems  400 ,  500  is reduced because the flexible shielding circuit  102  is thinner than a conventional metal shielding arrangement.  
      Although the flexible shielding circuit  102  may be mounted on a printed circuit board (PCB), it is not necessary to do so. That is, the flexible shielding circuit  102  may stand on its own. This feature can enable the circuit  102  to be implemented in electrical devices or portions of electrical devices that do not have a PCB, such as the flip portion of a cellular telephone.  
      In another arrangement, signals can be routed from one part of the electrical component  104  to, for example, another part of the electrical component  104  through the signal layers  402  without interfering with the ground plane  406 . Those of skill in the art can appreciate the utility of this feature. In addition, the vias  408  and the conductive adhesive  206  can assist in the routing of these signals.  
      Referring to  FIG. 5 , an isometric view of a system  600  is shown. This system  600  is similar to the embodiments previously described. Here, however, in contrast with the arrangement shown in  FIG. 2 , the loop  410  can be secured to the first portion  202 , such as with an adhesive, including the conductive adhesive  206  of  FIG. 2 . This process can eliminate or at least reduce the gaps that may be created when the loop  410  is formed, which can result in even better shielding for the electrical component  104 .  
      In one of the inventive arrangements, another electrical component  412  can be mounted on the second portion  204  of the flexible shielding circuit  102 , in a manner that is similar to the mounting discussed with reference to  FIG. 2 . This feature can allow for the stacking of electrical components  104  that can be properly shielded but without increasing the height of the stack beyond an unacceptable level.  
      The inventive arrangements discussed above can be implemented by using a method  600  for shielding an electrical component  104 , using the flexible shielding circuit  102 , as shown in  FIG. 6 . To describe the method  600 , reference will be made to  FIGS. 1-5 , although it is understood that the method  600  can be implemented with reference to any other suitable arrangement of the present invention. In addition, the method  600  can contain a greater or a fewer number of steps than shown in  FIG. 6 . Several suitable examples of method  600  will be presented below.  
      In one arrangement, the method  600  can include one or more method steps for shielding the electrical component  104  by using the flexible shielding circuit  102 . At step  602 , the method  600  can begin. At step  604 , the electrical component  104  can be mounted on the first portion  202  of the flexible shielding circuit  102 . At step  606 , the exposed surfaces of the electrical component  104 , mounted on the first portion  202  of the flexible shielding circuit  102 , can be covered with the second portion  204  of the flexible shielding circuit  102 . In another arrangement of the present invention, the second portion  204 , covering the exposed surfaces of the electrical component  104 , can be secured to the exposed surfaces with an adhesive. In yet another arrangement of the present invention, the electrical component  104  can be covered with the second portion  204 , such that a gap is formed between the exposed surfaces of the electrical component  104  and the second portion  204  that is covering the exposed surfaces of the electrical component  104 .  
      In another arrangement of the present invention, at step  606 , the second portion  204  can be folded to cover the exposed surfaces of the electrical component  104 . In yet another arrangement, at step  606 , while folding the second portion  204  for covering the electrical component  104  mounted on the ground plane  406  of the first portion  202  of the flexible shielding circuit  102 , the second portion  204  can be bent in a manner such that the loop  410  is formed. The ends of the loop  410  can be selectively secured to each other with the conductive adhesive  206 .  
      In yet another arrangement, the method  600  can include the step of mounting another electrical component  412  on top of the second portion  204  covering the electrical component  104  that is mounted on the first portion  202  of the flexible shielding circuit  102 . In still another arrangement, the method  600  can include the steps of routing signals from one part of the electrical component  104  to another part of the electrical component  104  or to the electrical component  412  through the signal layers  402  and the vias  408  connecting the signal layers of the second portion  204 , without interfering with the ground plane  406  of the first portion  202  of the flexible shielding circuit  102 .  
      At step  608 , in one arrangement of the invention, the second portion  204  can be selectively secured to the first portion- 202  with the conductive adhesive  206 . In another arrangement to the invention, at step  608 , the second portion  204  of the flexible shielding circuit can be selectively secured to the first portion  202  with the conductive adhesive  206 . In yet another arrangement, the electrical component  412  mounted on the second portion  204 , can be shielded by using the flexible shielding circuit  102  or some other flexible shielding circuit. At step  610 , the method  600  can end.  
      Therefore, it should be clear from the preceding disclosure that the present invention provides a system and a method for shielding at least one electrical component by using flexible shielding circuits that provide better flexibility and compact shielding. While the preferred embodiments of the invention have been illustrated and described, it will be clear that the invention is not so limited. Numerous modifications, changes, variations, substitutions and equivalents will occur to those skilled in the art without departing from the spirit and scope of the present invention as defined by the appended claims.