Switch assembly

A switch assembly movable between a closed position and open position includes a multilayer circuit. 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 the second layer, the third layer having an opening therein to permit contact between said first conductive material and said second conductive material when the switch assembly is in the closed position. An actuator such as a rubber dome enables a customer to provide a force to move the switch assembly between closed and open positions. The actuator also meets tactile feel requirements for customer actuated switch applications.

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.

DETAILED DESCRIPTION

FIG. 1illustrates a switch assembly100consistent with the invention. In general, the switch assembly100includes an upper housing104, lower housing102, multilayer circuit106, and actuator portion108. 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 toFIG. 2Aa cross sectional view of a switch assembly consistent withFIG. 1is illustrate revealing more details of the switch assembly and, in particular the multilayer circuit106. The cross sectional view ofFIG. 2Aillustrates the switch assembly in an open position while the cross sectional view ofFIG. 2Billustrates the switch assembly in a closed position.

The multilayer circuit106may include a top layer202having a conductive material207disposed thereon and a bottom layer206also having a conductive material209disposed thereon in a position relative to the first conductive material. In between the top layer202and bottom layer204may be an insulation layer204including an opening214. The opening214may be any variety of sizes large enough to permit the passage there through of the first conductive material207so that the first conductive material207may contact the second conductive material209when the switch assembly is in a closed position as illustrated in FIG.2B. The conductive materials207,209electrically connect in this closed position of FIG.2A.

The top202and bottom206layers may be formed using PTF techniques and include the layer being a thermoplastic film substrate. The insulating layer204may be an unprinted layer. This multilayer circuit assembly106can be hermetically sealed by applying pressure sensitive adhesive around the perimeter between two adjacent layers. This multilayer circuit assembly106may withstand 100,000 or more cycles at extreme temperatures.

To meet tactile feel requirements, an exemplary switch consistent with present invention combines the multilayer circuit106with an actuator114. The actuator114is 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 circuit106consistent 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 assembly100would engage the actuator114with a force. In turn, the actuator114would provide a force to the top layer202of the multilayer circuit106. The top layer202may also have a protrusion110or similar mechanical feature to permit enhanced mechanical coupling between the actuator114and the top layer202. The top layer202including the conductive material207disposed thereon is forced towards the conductive material209on the bottom layer206. Advantageously, the insulating layer204has an opening214large enough to permit the passage of the conductive material207through the opening214. When proper electrical contact is made between the conductive material207of the top layer202and the conductive material209of the bottom layer206, the switch is in the closed position of FIG.2B.

When the operator engages the actuator again to open the switch, the force provided by the actuator against the top layer202is removed. The top layer202may be made of a resilient material such that when the force applied by the actuator114is removed, the top layer202returns to its undeformed position ofFIG. 2Aor the open position. Alternatively, the top layer202may return to its position ofFIG. 2Aby applying a force to the top layer. In the position ofFIG. 2A, a sufficient separation distance is maintained between the conductive material207and the conductive material209such that the there is no electrical coupling between the conductive materials207and209.

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.