Abstract:
A multilayer printed circuit board provides both physical and electrical attributes necessary for creating an inductive touch sensor panel. Inductive sense coils are formed on a surface of first layer of the multilayer printed circuit board. A second layer is used as a spacer between the first layer and a third layer. The first, second and third layers of the multilayer printed circuit board form chambers in which the inductive sense coils are disposed therein. When a force is applied to a portion of the third layer proximate to an inductive sense coil, a metal target on a face of the third layer is biased toward the inductive sense coil and thereby changes the inductance value thereof.

Description:
RELATED PATENT APPLICATION 
       [0001]    This application claims priority to commonly owned U.S. Provisional Patent Application Ser. No. 61/249,816; filed Oct. 8, 2009; entitled “Laminated Printed Circuit Board Inductive Sensor,” by Keith Curtis, Stephen Porter and John Charais; and is hereby incorporated by reference herein for all purposes. 
     
    
     TECHNICAL FIELD 
       [0002]    The present disclosure relates to inductive touch sensors, and more particularly, to a laminated printed circuit board inductive touch sensor. 
       BACKGROUND 
       [0003]    Inductive touch sensor technology may be used as an alternative to capacitive touch sensor technology. An inductive touch sensor comprises a target (surface being touched or pressed), a spacer and an inductance coil. When the target is actuated (e.g., touched) the coil inductance changes value. Detection of this change in the inductance value of the coil indicates actuation of the inductive touch sensor. Manufacture of an inductive touch panel, comprising a plurality of inductive touch sensors, requires assembly of a sensor sandwich on a printed circuit board (PCB), generally at final assembly of a product. The spacer must be placed between the PCB which contains the inductance coils, one for each key or button, and the targets for each key or button. Current manufacturing technologies consist of producing the PCB, the spacer, laminating the spacer to the PCB and then mounting the PCB/Spacer assembly to the target panel. 
         [0004]    The spacer which is required for inductive touch system needs to be made from an insulating material which will not compress when the target is pressed. Currently all designs today consist of a spacer that is made independently of the PCB. This causes additional process steps where the spacer, and inductance coils on the PCB are manufactured separately then in another step laminated together. 
       SUMMARY 
       [0005]    What is needed is a simplified way to manufacture an inductive touch system. According to the teachings of this disclosure, a spacer may be designed directly onto a printed circuit board (PCB) to eliminate having to manufacture the spacer and PCB separately then having to laminate the spacer onto the PCB. This results in a significant simplification of the manufacture of an inductive touch system by eliminating the assembly of the sensor sandwich at final assembly. By building the stack as part of the PCB means that this assembly can be pre-built, allowing, for example but not limited to, a simple peel and stick operation at final assembly. 
         [0006]    PCBs are made by using multiple layers of an insulating material having conductors laminated to their surfaces. As the PCBs become more complicated, more layers are required. Some of the insulating materials used by the PCB manufacturers have the same characteristics that are required by the spacer of an inductive touch sensor, e.g., substantially incompressible. Integrating the spacer with the PCB during design thereof, from a PCB manufacturing standpoint, results in minimal additional work since the spacer can now be considered as just an additional PCB layer(s). 
         [0007]    The material required for the spacer must be non-conductive and non-compressing. Therefore, only some of the insulating materials used in PCB manufacturing meet this criteria. Also the geometries required for the spacer are not typical for a PCB. For example, a typical drilled hole needed for the spacer to surround an inductance coil is about 1-1.5 inches in diameter, whereas for mounting components onto a PCB the largest hole is typically about ⅜ inch or smaller. 
         [0008]    PCB&#39;s are not often viewed as a physical structure of an application but rather they are designed to fit the electronic circuits into an existing space. The spacer is a critical physical element for an inductive touch sensor system, since without it the inductive touch sensor system would not work. Having the spacer as part of the PCB takes advantage of the physical structure of the PCB for providing economical inductive touch sensors as well as a space for the electronic components associated therewith. 
         [0009]    According to a specific example embodiment of this disclosure, an inductive touch sensor multilayer printed circuit board comprises: a first nonconductive layer of a multilayer printed circuit board, the first nonconductive layer having a printed circuit inductor on a first face thereof, printed circuit conductors on a second face thereof, the second face printed circuit conductors adapted for connection to electronic devices, whereby the printed circuit inductor and the electronic devices are electrically connected together; a second nonconductive layer laminated to the first nonconductive layer of the multilayer printed circuit board, the second nonconductive layer having an opening around the printed circuit inductor; and a third layer laminated to the second nonconductive layer of the multilayer printed circuit board, whereby a chamber is formed around the printed circuit inductor by the first and second nonconductive layers and the third layer, the third layer having an inductance value influencing property, wherein when a portion of the third layer located over the chamber is biased toward the printed circuit inductor an inductance value thereof changes. 
         [0010]    According to another specific example embodiment of this disclosure, an inductive touch sensor panel multilayer printed circuit board comprises: a first nonconductive layer of a multilayer printed circuit board, the first nonconductive layer having a plurality of printed circuit inductors on a first face thereof, printed circuit conductors on a second face thereof, the second face printed circuit conductors adapted for connection to electronic devices, whereby the plurality of printed circuit inductors and the electronic devices are electrically connected together; a second nonconductive layer laminated to the first nonconductive layer of the multilayer printed circuit board, the second nonconductive layer having openings around each of the plurality of printed circuit inductors; and a third layer laminated to the second nonconductive layer of the multilayer printed circuit board, whereby chambers are formed around each of the plurality of printed circuit inductors by the first and second nonconductive layers and the third layer, the third layer having an inductance value influencing property, wherein when a portion of the third layer located over a one of the chambers is biased toward a respective one of the plurality of printed circuit inductors an inductance value thereof changes. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    A more complete understanding of the present disclosure thereof may be acquired by referring to the following description taken in conjunction with the accompanying drawings wherein: 
           [0012]      FIG. 1  is a schematic block diagram of an electronic system having an inductive touch keypad, an inductive touch analog front end and a digital processor, according to the teachings of this disclosure; 
           [0013]      FIG. 2  is a schematic frontal view of the inductive touch keypad of  FIG. 1  showing an inductive sense coil that is typical for all keys of the keypad; 
           [0014]      FIG. 3  is a schematic cutaway view of an inductive touch key formed with a multilayer printed circuit board, according to a specific example embodiment of this disclosure; 
           [0015]      FIG. 4  is a schematic cutaway view of the inductive touch key shown in  FIG. 3  being actuated by an external force, according to the teachings of this disclosure; and 
           [0016]      FIG. 5  is a schematic elevational view of a portion of the printed circuit board comprising an inductive touch sensor, according to a specific example embodiment for one of the touch keys shown in  FIGS. 2 and 3 . 
       
    
    
       [0017]    While the present disclosure is susceptible to various modifications and alternative forms, specific example embodiments thereof have been shown in the drawings and are herein described in detail. It should be understood, however, that the description herein of specific example embodiments is not intended to limit the disclosure to the particular forms disclosed herein, but on the contrary, this disclosure is to cover all modifications and equivalents as defined by the appended claims. 
       DETAILED DESCRIPTION 
       [0018]    Referring now to the drawings, the details of an example embodiment is schematically illustrated. Like elements in the drawings will be represented by like numbers, and similar elements will be represented by like numbers with a different lower case letter suffix. 
         [0019]    Referring to  FIG. 1 , depicted is a schematic block diagram of an electronic system having an inductive touch keypad, an inductive touch analog front end and a digital processor, according to the teachings of this disclosure. A digital processor  106 , e.g., a microprocessor, microcomputer, digital signal processor (DSP), application specific integrated circuit (ASIC), programmable logic array (PLA), etc., is coupled to an inductive touch analog front end (AFE)  104  and a matrix of inductive touch sensor keys  102 , e.g., pushbuttons, targets, etc. The digital processor  106  and AFE  104  may be part of a mixed signal (analog and digital circuits) integrated circuit device. 
         [0020]    The inductive touch AFE  104  facilitates, with a single low-cost integrated circuit device, all active functions used in determining when there is actuation of inductive sensors, e.g., by pressing and deflecting a target key that changes the inductance value of an associated inductive sensor. The inductive touch AFE  104  measures the inductance value of each sensor of the matrix of inductive touch sensor keys  102  and converts the inductance values into respective analog direct current (dc) voltages that are read and converted into digital values by the digital processor  106 . 
         [0021]    The digital processor  106  supplies clock and control functions to the inductive touch AFE  104 , reads the analog voltage detector output of the inductive touch AFE  104 , and selects each key of the matrix of inductive touch sensor keys  102 . When actuation of a key of the matrix of inductive touch sensor keys  102  is determined, the digital processor  106  will take an appropriate action. 
         [0022]    Referring to  FIG. 2 , depicted is a schematic frontal view of the inductive touch keypad of  FIG. 1  showing an inductive sense coil that is typical for all keys of the keypad. The keypad  200  of the matrix of inductive touch sensor keys  102  comprises a plurality of inductive touch sensors  206 . In each one of the plurality of inductive touch sensors  206  is a coil  204  having an inductance value that changes when an inductance affecting material, e.g., metal, changes position in relation to the coil  204 , as more fully described hereinafter. 
         [0023]      FIG. 3  is a schematic cutaway view of an inductive touch key formed with a multilayer printed circuit board, according to a specific example embodiment of this disclosure. The plurality of inductive touch sensors  206  may be fabricated from a single multilayer printed circuit board that also may be used to interconnect electronic components, e.g., the digital processor  106  and AFE  104  to each of the plurality of inductive touch sensors  206  (see  FIG. 5 ). The coil  204  is formed on a first printed circuit board layer  306 . A second printed circuit board layer  308  having an opening for each of the coils  204  is used as a spacer. A third printed circuit board layer  310  covers the second printed circuit board layer  308  and the openings around each of the coils  204 . The second printed circuit board layer  308  is substantially non-deformable. The third printed circuit board layer  310  is deformable at each of the openings over the coils  204 . A legend  314  may be placed on an front surface area of the third printed circuit board layer  310  for each of key of the matrix of inductive touch sensor keys  102  ( FIG. 2 ) for indicating the purpose or function of that key, e.g., 1, 2, 3, 4, start, stop, dry, warm, toast, etc. 
         [0024]      FIG. 4  is a schematic cutaway view of the inductive touch key shown in  FIG. 3  being actuated by an external force, according to the teachings of this disclosure. When a force  312 , e.g., a finger, presses on a portion of the third printed circuit board layer  310  located over a coil  204 , that portion of the third printed circuit board layer  310  moves toward the coil  204 . Since the second printed circuit board layer  308  is substantially non-deformable, only the coil  204  having the force  312  to the third printed circuit board layer  310  applied directly over that the coil  204  will have a change in inductance value. The other coils  204  of the plurality of inductive touch sensors  206  will not be affected. 
         [0025]      FIG. 5  is a schematic elevational view of a portion of the printed circuit board comprising an inductive touch sensor, according to a specific example embodiment for one of the touch keys shown in  FIGS. 2 and 3 . Each of the plurality of inductive touch sensors  206  ( FIG. 2 ) is fabricated in a single multi-layer printed circuit board, generally represented by the numeral  550 , and comprises the first printed circuit board layer  306 , second printed circuit board layer  308  and third printed circuit board layer  310 . One or more of the printed circuit board layers  306 ,  308  and/or  310  may have conductive foil arranged in patterns or as a solid conductive surface(s) on one or both sides thereof. In addition, interconnections between these conductive foils of the printed circuit board layers may be accomplished with plated through hole vias  536  as is well known to one skilled in the art of printed circuit board fabrication and having the benefit of this disclosure. 
         [0026]    The coil  204  may be formed in the conductive foil on an inside face of the first printed circuit board layer  306 . The beginning  520  and end  522  of the coil  204  conductive foil is connected to other circuits through vias  536   b  and  536   c , and conducts  530 ,  526  and  538 . Electronic components  528 , e.g., digital processor  106  and AFE  104  in an integrated circuit package(s) may be attached mechanically and electrically to foil patterns  530  on a face of the first printed circuit board layer  306  by, e.g., surface mount soldering. 
         [0027]    A chamber  524  is formed by the intersections of the first printed circuit board layer  306 , the second printed circuit board layer  308 , and the third printed circuit board layer  310 . Within this chamber  524 , a portion of the third printed circuit board layer  310  defects toward the coil  204  when the force  312  is applied thereto. 
         [0028]    A conductive surface  518  on a face of the third printed circuit board layer  310  proximate to the coil  204  may be used as a target that influences the inductance value of the coil  204 . When the third printed circuit board layer  310  is biased toward the coil  204  (e.g., displacement  534 ) by force  312  being applied to a portion thereof, the inductance value of the coil  204  will change. This change in inductance value is detected by the AFE  104 . The conductive surface  518  may be grounded through plated through hole via  536   a . Similarly, the coil  204  may be electrically connected to the electronic components  528  with vias  536   b  and  536   c , and conducts  530 ,  526  and  538 . 
         [0029]    A metal fascia may be used in place of the third printed circuit board layer  310  and conductive surface  518 , and may be fabricated with the other printed circuit board layers  306  and  308  during manufacture of the printed circuit board comprising the matrix of inductive touch sensor keys  102 . It is contemplated and within the scope of this disclosure that more than two or three printed circuit board layers may be used as required by the application design. 
         [0030]    Many different materials may be used for the first, second and third layers so long as the physical and electrical properties required herein are met. One having ordinary skill in the art of multilayer printed circuit board fabrication would know what materials would be appropriate by having knowledge of this disclosure. Some dielectrics that may be used, but not limited to, are as follows: polytetrafluoroethylene (Teflon), FR-4, FR-1, CEM-1 or CEM-3. In addition, well known prepreg materials used in the PCB industry are FR-2 (phenolic cotton paper), FR-3 (cotton paper and epoxy), FR-4 (woven glass and epoxy), FR-5 (woven glass and epoxy), FR-6 (matte glass and polyester), G-10 (woven glass and epoxy), CEM-1 (cotton paper and epoxy), CEM-2 (cotton paper and epoxy), CEM-3 (woven glass and epoxy), CEM-4 (woven glass and epoxy), and CEM-5 (woven glass and polyester). 
         [0031]    While embodiments of this disclosure have been depicted, described, and are defined by reference to example embodiments of the disclosure, such references do not imply a limitation on the disclosure, and no such limitation is to be inferred. The subject matter disclosed is capable of considerable modification, alteration, and equivalents in form and function, as will occur to those ordinarily skilled in the pertinent art and having the benefit of this disclosure. The depicted and described embodiments of this disclosure are examples only, and are not exhaustive of the scope of the disclosure.