Patent Publication Number: US-2009231300-A1

Title: Methods and apparatus for improved electrical connection for touch screen display devices

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to improved touch screen displays. More particularly, the invention relates to an arrangement for providing improved electrical interconnection for touch screen sensors. 
     BACKGROUND OF THE INVENTION 
     Touch screen display devices have long been employed in a wide variety of applications, such as employee assisted and self service retail checkouts, medical kiosks, automotive devices, such as global positioning systems, for example, and numerous other applications. A touch screen device typically involves a control circuit, mounted on a printed circuit board along with a display device such as a liquid crystal display (LCD), and a touch screen sensor electrically connected to the control circuit. A touch screen device may typically comprise a glass or other insulating substrate coated with a conductive material configured so that current flows are established in the conductive material and a touch by a user causes current flows through the conductive material. Typically, the touch is to a protective covering layer rather than the conductive material itself. The display device employs a touch screen controller to sense and respond to these current flows. 
     A touch screen device typically includes traces that carry currents from selected areas of the touch screen, such as the corners of the touch areas, to selected points chosen for providing contact to the touch screen controller. The currents are conducted along the top side of the glass substrate, that is, the side facing the user. The controller is typically deployed on the underside of the substrate, that is, the side facing away from the user In such a configuration, the current flows must be conveyed from the top side of the glass substrate to the controller on its underside in order for the currents to provide information to the controller. 
     SUMMARY OF THE INVENTION 
     A system according to one aspect of the invention addresses these issues, as well as others, by providing for a connector for a touch screen sensor that is integrated into the substrate itself suitable for providing electrical contact with a connector on a touch screen controller, such as an elastomeric connector. A sensor includes a substrate of glass or other suitable material, with the substrate including a plurality of vias. The substrate suitably includes a conductive coating on its top side, that is, the side that is to face a user, and traces are placed on the substrate, with a trace running to each via. Connecting pins are secured in the vias, so that connectivity is provided from the top side to the underside by way of the connecting pins. A protective layer is suitably laminated to the top side of the touch sensor, over the conductive layer, and a similar protective layer may also suitably be laminated to the underside of the touch sensor. The touch sensor is mounted so that the pins contact a connector, such as an elastomeric connector that is positioned at the underside of the substrate when the touch screen sensor is in use. The connector is in turn connected to a touch screen controller attached to a printed circuit board providing a mounting for the controller and supporting other devices, such as a liquid crystal display (LCD). 
     A more complete understanding of the present invention, as well as further features and advantages of the invention, will be apparent from the following Detailed Description and the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a view of a touch screen including electrically conductive elements carrying current along a top surface of the touch screen according to an aspect of the present invention; 
         FIG. 2  illustrates a detailed view of selected elements of the touch screen of  FIG. 1 ; 
         FIGS. 3  illustrates an additional view of elements of the touch screen of  FIG. 1 , showing pins oriented for insertion into the touch screen; 
         FIG. 4  illustrates a pin for insertion into a via of a touch screen for providing electrical contact to a touch screen controller; 
         FIG. 5  illustrates a side view of a pin inserted into a touch screen; 
         FIG. 6  illustrates a view of a touch screen device according to an aspect of the present invention; and 
         FIG. 7  illustrates a process of touch screen sensor connection according to an aspect of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  illustrates a touch screen sensor  100  according to an aspect of the present invention. The sensor  100  comprises a glass substrate  102 , which may suitably be coated with a transparent conductive material which is not visible here, but which may suitably be an antimony-tin oxide coating or another appropriate coating material of the type normally used in touch screen sensors. If desired, the back of substrate  102  may also be coated with a conductive material, so as to provide for reduction in electrical noise. When the user touches the sensor  100  in a touch sensitive area  103 , a current flow is established through the coating. Portions of the current are conducted by traces  104 A- 104 D to contact points  106 A- 106 D. The contact points  106 A- 106 D are shown more clearly in  FIG. 2  and discussed in greater detail below. The contact points  106 A- 106 D take the form of vias through the substrate  102 , surrounded by annular rings, The rings provide for electrical connectivity between the traces  104 A- 104 D and pins that may be placed in the vias. The pins suitably provide for an electrical connection between the traces at the front of the substrate  102  to elements, such as a touch screen controller, that may be placed at the back of the substrate  102 , so that the current flow through the vias is passed through the substrate  102  to the elements at the back of the substrate  102  by way of the pins. An additional optional contact point  106 E is also shown here. The contact point  106 E is used if a rear coating for noise reduction is employed, and provides electrical contact between front and rear conductive coatings on the substrate  102 . 
       FIG. 2  illustrates additional details of a portion of the touch screen  100 , showing the contact points  106 A- 106 D, as well as the optional contact point  106 E. Portions of the traces  104 A- 104 D can also be seen. The contact points comprise vias  108 A- 108 D, surrounded by annular rings  110 A- 110 D respectively. The annular rings  110 A- 110 D are connected to the traces  104 A- 104 D, respectively. The optional contact point  106 E can also be seen, comprising an optional via  106 E. There is no visible annular ring surrounding the optional via  108 E, because an annular ring surrounds the via  108 E at the rear of the substrate  102 . A conductive pin may be inserted in each of the vias  108 A- 108 D, so that a portion of the pin comes in contact with the ring surrounding the via in which the pin is placed. In this way, current flowing through the trace is conveyed to the pin placed in the via surrounded by the annular ring connected to that trace. In addition, a conductive pin may be placed in the via  108 E, providing a contact between the front and back coating. 
       FIG. 3  illustrates a portion of the touch screen  100 , showing portions of the traces  104 A- 104 D, the vias  108 A- 108 D, the annular rings  110 A- 110 D, and pins  112 A- 112 D in a process of insertion into the vias  108 A- 108 D. In addition,  FIG. 3  illustrates the optional via  108 E, and the optional pin  112 E. The pins  112 A- 1121 E may suitably be pressed into the vias  108 A- 108 E from the back side of the substrate  102 , and secured in place with a small amount of adhesive. The pins  112 A- 112 D may then be soldered to the annular rings  108 A- 108 D, and the pin  112 E soldered to an annular ring placed on the rear of the touch screen  100 , surrounding the via  108 E. An electrical connection is thus achieved through each of the traces  104 A- 104 D, to the respective annular rings  110 A- 110 D, and through the respective pins  112 A- 112 D, so as to create electrically conductive paths from the corners of the touch screen sensor  100  to the reverse side of the sensor  100 . In addition, a contact may be made through the pin  112 E between the front and rear coatings. Once the pins have been secured, a protective layer may be laminated so as to cover the substrate  102 . 
       FIG. 4  illustrates further details of the pin  112 A, which may suitably be similar to the pins  112 B- 112 D. The pin  112 A, as well as the pins  112 B- 112 D, may suitably be a gold plated beryllium copper pin. The particular design and composition of the pin  112 A is exemplary, and other pin designs and compositions may be used. 
       FIG. 5  illustrates a side view of a portion of the substrate  102 , showing the pin  112 A in place. A thick film pattern  502 , comprising a portion of the trace  104 A, as well as the annular ring  104 A, can be seen on the top side of the substrate  104 . A portion  504  of a thin film coating can be seen on the underside of the substrate  102   502  and  504  can be seen on the top side and the underside of the substrate  102 , respectively. The pin  112 A extends from the underside to the top side of the substrate  102 , and may suitably be placed so that it extends 1 mil beyond the substrate  102  in each direction. 
       FIG. 6  illustrates a partial side view of a touch screen display device  600  incorporating the touch screen sensor  100 . The sensor  100  includes the substrate  102 . The thick film pattern  502  and the rear coating  504  can be seen on the front and rear surfaces, respectively, of the substrate  102 , and the pin  112 A can be seen extending through the via  108 A. The rear coating  504  is clear of the pin  112 A, because the rear coating  504  is applied so as to be clear of the vias  108 A- 108 D and to surround only the via  108 E. A front coating  602  can also be seen. The front coating  602  is clear of the pin  112 A, because the front coating  602  is typically used only in the actual touch area of the sensor  100 , while the thick film pattern  502  extends to the pin  112 A. 
     The via  108 A cannot be clearly seen from the perspective shown here in  FIG. 6 , but is more clearly visible in  FIGS. 1 ,  2 ,  3 , and  5 . A plastic frame  604  can be seen beneath the substrate  102 . The frame  604  suitably surrounds or is placed along an outer perimeter of the substrate  102 , to provide added rigidity to the touch screen  100 . The frame  604  suitably includes an opening to allow contact between the connector  606 , which may suitably be an elastomeric connector, and the pin  112 A and similar pins. One advantageous implementation of the connector  606  is as a zebra strip elastomeric connector. The frame  604  provides a guide for positioning the elastomeric connector  606  in contact with the pins  112 A and similar pins, with the connector being guided along the opening of the frame  604  to the pins. The frame  604  also provides for convenient placement of attachment points for attachment of the sensor  100  in the display device  600 . 
     The connector  606  provides electrical connectivity between the conductive pins, that is, the pins  112 A visible here and the other pins, and a touch screen controller  608 , here implemented in the form of a printed circuit board supporting appropriate electronic components and connections between the components. A display device, such as a liquid crystal display screen  610 , is suitably mounted on and supported by the touch screen controller  608 . When a user touches the sensor  100  in the touch area, suitably in response to a prompt displayed on the LCD  610 , a current flow is created in the conductive coating  602 . This current flow causes current flows in the traces  104 A- 104 D, and these current flows are conducted to the annular rings  110 A- 110 D surrounding the vias  10 SA- 108 D. The current flows are further conducted through the substrate  102  by the pins  112 A- 12 D. In the perspective presented in  FIG. 6 , as noted above, the pin  112 A can be seen to be in contact with the elastomeric connector  606 , and the remaining pins  112 B- 112 D are also in contact with the connector  606  when the sensor  100  is installed in the display device  600 . Thus, all the current flows are conducted to the connector  606  and to the controller  608  via the connector  606 . The controller  608  is thus able to detect the current flows in the pins  112 A- 112 D. Because the current flows depend on the location at which the sensor  100  is touched, the controller  608  is able to determine when and where a touch has occurred and to respond appropriately. 
     The connection provided by the integrated assembly illustrated here and in the previous drawings allows for a clean and attractive appearance, and thinner borders at the edge of the touch sensor because there is no need to accommodate a wiring harness. A flat sealed front surface is possible, without any gaps that might allow for leakage, and provides for higher reliability and easier serviceability. 
       FIG. 7  illustrates the steps of a process  700  of touch sensor fabrication and connection according to an aspect of the present invention. The process  700  is discussed here in connection with a single sensor, but it will be recognized that most of the process steps are undertaken simultaneously as part of a mass production process for fabrication of a number of sensors. At step  702 , a suitable substrate, such as glass substrate, for a touch sensor is fabricated, with a plurality of vias passing through the substrate at a desired location or locations, such as at a lower edge. The substrate may suitably be a glass lite, with a plurality of substrates being formed by cutting a sheet of an appropriate glass material, such as raw soda lime float glass, into individual sections, grinding the edges according to desired specifications, and drilling vias at appropriate locations. At step  704 , the substrate is washed and transported to a clean room. At step  706 , the substrate is mask printed on a screen printer to form tin antimony deletion areas. At step  708 , the masked substrate is passed through a tin antimony sputtering reactor. At step  710 , the substrate is passed through a lehr so as to oxidize the tin antimony deposition to form tin antimony oxide. At step  712 , the masking is mechanically removed, for example, through an abrasive wash with detergent. At step  714 , the substrate is washed. At step  716 , conductive elements are applied to the substrate, through thick film screen printing of an electrode pattern, conductors, and pads, with the electrodes and conductors suitably being silver frit traces. The conductive elements include a trace from each corner of the area to be used as the touch area of the touch screen to a corresponding via, with an annular ring surrounding the via and connected to the trace. At step  718 , the substrate is passed through a lehr to cure the thick film elements. At step  720 , the substrate is washed. At step  722 , the annular rings are burnished. At step  724 , a pin is inserted into and secured in each via, and soldered to the annular ring surrounding the via. At step  726 , a protective front surface cover is prepared and laminated to the substrate. At step  728 , the substrate and cover are mounted to a plastic frame. At step  730 , the substrate and cover, which may now be referred as a sensor, are mounted to a plastic frame. At step  732 , the touch sensor is suitably secured to a display device in such a way that the pins make electrical contact with an elastomeric connector secured to the display device, with the elastomeric connector providing electrical connectivity between the pins and a touch screen controller. Mounting of the touch sensor so as to achieve contact between the pins and the elastomeric connector is assisted by registration and alignment features of the plastic frame. At step  734 , the display device is suitably mounted in an appropriate terminal or other device for use.