Patent Publication Number: US-6906273-B2

Title: Switch assembly

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of the filing date of U.S. Provisional Application Ser. No. 60/402,504, filed Aug. 9, 2002, the teachings of which are incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to electrical switches, and in one embodiment, to electrical switches for automotive use. 
     BACKGROUND OF THE INVENTION 
     Common user actuated switches utilize rocker or push button style actuators to close contacts on a printed circuit board (PCB) or contact unit. The two most common methods to make this contact closure are to use microswitches or rubber domes, but rubber domes are susceptible to contamination. 
     Microswitches used for customer actuated switch (CAS) applications are typically sealed from contamination and rated for automotive use to assume proper function in extreme conditions and high cycle life. Depending on switch design, the microswitch might also have a preload stroke to absorb the manufacturing tolerances of the components and eliminate any buzz, squeak, or rattle conditions. The actuation force of the microswitch from excessive forces that can occur after contact closure is made. Unfortunately, these microswitches are generally cost prohibitive. 
     One alternative is to use an elastomer pad with integral buttons, also referred to as rubber dome pad or mat. With this design, a carbon or plated (Au or Ag) disk-shaped contact is insert molded inside each contact dome on the mat. The mat is placed over the surface of a PCB and the dome contacts align with the contact closures on the PCB surface. The switch actuator, either rocker or push button, collapses the rubber dome and the contact disk makes a connection across the contact closure on the PCB. Tactile force and stroke can be controlled by the design of the rubber dome. Although this design is less expensive than sealed microswitches, contamination is an inherent problem. The elastomer pad is not sealed to the PCB, and there is a tendency for the contamination to be drawn in the contact area as the dome returns to the open position. 
     Accordingly, there is a need for a switch assembly that is sealed from contamination, can meet specified tactile requirements for a CAS, i.e. force and tactile feel, and is cost effective and reliable. 
     BRIEF SUMMARY OF THE INVENTION 
     A switch assembly movable between a closed and open position consistent with the invention includes a multilayer circuit and an actuator. The multilayer circuit includes a first layer having a first conductive material disposed thereon, a second layer having a second conductive material disposed thereon, and a third layer disposed between the first and second layer, the third layer having an opening therein to permit contact between the first conductive material and the second conductive material when the switch assembly is in the closed position. The actuator is configured to provide force to the first layer to permit the first conductive material and the second conductive material to contact in the closed position and to enable separation of the first conductive material and the second conductive material in the open position. 
     In another embodiment consistent with the invention, a multilayer circuit switch assembly having an open and closed position is provided. The multilayer circuit includes: a first layer first layer having a first conductive material disposed thereon; a second layer having a second conductive material disposed thereon; and a third layer disposed between the first and second layer, the third layer having an opening therein to permit contact between the first conductive material and the second conductive material when the multiple layer circuit is in a closed position. 
     In yet another embodiment consistent with the invention, a method of making electrical contact is provided. The method includes: providing a first layer having a first conductive material disposed thereon; providing a second layer having a second conductive material disposed thereon; providing a third layer disposed between the first and second layer, the third layer having an opening therein; positioning the first layer proximate to the second layer; and applying force to the first layer so pass the first conductive material through the opening in the third layer to contact the second conductive material. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Advantages of the present invention will be apparent from the following detailed description of exemplary embodiments thereof, which description should be considered in conjunction with the accompanying drawings, in which: 
         FIG. 1  is an exploded view of an exemplary switch assembly consistent with the invention; 
         FIG. 2A  is a sectional view of an exemplary switch assembly consistent with the invention showing the switch in an open position; and 
         FIG. 2B  is a sectional view of and exemplary switch assembly consistent with the invention showing the switch in a closed position. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  illustrates a switch assembly  100  consistent with the invention. In general, the switch assembly  100  includes an upper housing  104 , lower housing  102 , multilayer circuit  106 , and actuator portion  108 . An exemplary switch assembly consistent with the invention may be constructed from polymer thick film (PTF) techniques. PTF technology employs screen printing to deposit or coat insulators, conductive tracks, and resistors onto a thermoplastic film substrate. The PTF inks that are screen printed are basically pastes that contain a functional phase dispersed in an organic solvent that, when cured, provides the desired cohesion for the printed ink and adhesion to the polymer substrate. 
     Turning to  FIG. 2A  a cross sectional view of a switch assembly consistent with  FIG. 1  is illustrate revealing more details of the switch assembly and, in particular the multilayer circuit  106 . The cross sectional view of  FIG. 2A  illustrates the switch assembly in an open position while the cross sectional view of  FIG. 2B  illustrates the switch assembly in a closed position. 
     The multilayer circuit  106  may include a top layer  202  having a conductive material  207  disposed thereon and a bottom layer  206  also having a conductive material  209  disposed thereon in a position relative to the first conductive material. In between the top layer  202  and bottom layer  204  may be an insulation layer  204  including an opening  214 . The opening  214  may be any variety of sizes large enough to permit the passage there through of the first conductive material  207  so that the first conductive material  207  may contact the second conductive material  209  when the switch assembly is in a closed position as illustrated in FIG.  2 B. The conductive materials  207 ,  209  electrically connect in this closed position of FIG.  2 A. 
     The top  202  and bottom  206  layers may be formed using PTF techniques and include the layer being a thermoplastic film substrate. The insulating layer  204  may be an unprinted layer. This multilayer circuit assembly  106  can be hermetically sealed by applying pressure sensitive adhesive around the perimeter between two adjacent layers. This multilayer circuit assembly  106  may withstand 100,000 or more cycles at extreme temperatures. 
     To meet tactile feel requirements, an exemplary switch consistent with present invention combines the multilayer circuit  106  with an actuator  114 . The actuator  114  is provided to meet the tactile requirements, so it does not require conductive disks. The actuator may be a rubber dome mat in one embodiment. When the rubber dome mat is combined with a multilayer circuit  106  consistent with the invention, it is less expensive than the rubber dome/PCB technology, and is not subject to contamination. Other means of meeting the tactile feel criteria, such as molded-in-spring features, compression springs, eyelet assemblies, plunger bumpers, etc., may be used. 
     In operation, a user of the customer activated switch assembly  100  would engage the actuator  114  with a force. In turn, the actuator  114  would provide a force to the top layer  202  of the multilayer circuit  106 . The top layer  202  may also have a protrusion  110  or similar mechanical feature to permit enhanced mechanical coupling between the actuator  114  and the top layer  202 . The top layer  202  including the conductive material  207  disposed thereon is forced towards the conductive material  209  on the bottom layer  206 . Advantageously, the insulating layer  204  has an opening  214  large enough to permit the passage of the conductive material  207  through the opening  214 . When proper electrical contact is made between the conductive material  207  of the top layer  202  and the conductive material  209  of the bottom layer  206 , the switch is in the closed position of FIG.  2 B. 
     When the operator engages the actuator again to open the switch, the force provided by the actuator against the top layer  202  is removed. The top layer  202  may be made of a resilient material such that when the force applied by the actuator  114  is removed, the top layer  202  returns to its undeformed position of  FIG. 2A  or the open position. Alternatively, the top layer  202  may return to its position of  FIG. 2A  by applying a force to the top layer. In the position of  FIG. 2A , a sufficient separation distance is maintained between the conductive material  207  and the conductive material  209  such that the there is no electrical coupling between the conductive materials  207  and  209 . 
     It is to be understood that the embodiments that have been described herein are but some of the several which utilize this invention and are set forth here by way of illustration, but not of limitation. It is obvious that many other embodiments, which will be readily apparent to those skilled in the art may be made without departing materially from the spirit and scope of the invention.