Thin film resistor fabricated on header

Abstract

An igniter assembly for a gas generator used to inflate air bags or activate seat belt tensioners includes a header having a bridge element fabricated on a surface of the header. A pyrotechnic charge is applied to the bridge element so that delivering energy to the header heats the bridge thereby igniting the pyrotechnic material. The header includes metal sections separated by a insulating section of low thermal conductivity. A resistive film is applied to the header, across the metal sections and the insulating section. The bridge element is formed by laser cutting a kerf into the resistive film and thereby directing all current between the metal sections through a section of the film which comprises a resistor.

I claim:  
     
         1 . A bridge-header assembly comprising 
 a header providing first and second electrically conductive sections separated by an electrically insulating section having a thermal conductivity less than about .04 watts/centimeter-K; and    a resistive thin film layer on the conductive sections and the insulating section and providing 
 a kerf in the film intersecting the electrically insulating section and separating the film into a first film section in electrical contact with the first conductive section, a second film section in electrical contact with the second conductive section and a third film section bonded to the insulating section providing a resistor through which current between the first and second conductive sections passes.  
   
     
     
         2 . The assembly of  claim 1  further comprising a pyrotechnic charge abutting the resistor.  
     
     
         3 . The assembly of  claim 1  wherein the kerf is a laser cut.  
     
     
         4 . The assembly of  claim 1  wherein the first film section covers substantially the entire first conductive section and part of the insulating section.  
     
     
         5 . The assembly of  claim 4  wherein the second film section covers substantially the entire second conductive section and part of the insulating section.  
     
     
         6 . The assembly of  claim 1  wherein the first conductive section comprises a metal pin and the insulating section comprises a sleeve around the pin, the pin comprising a mechanical and electrical connection to an adjacent part.  
     
     
         7 . The assembly of  claim 6  wherein the second conductive section comprises a sleeve around the insulating section, the sleeve comprising a mechanical and electrical connection to the adjacent part.  
     
     
         8 . The assembly of  claim 7  wherein the header comprises a central axis and the pin lies on the axis.  
     
     
         9 . The assembly of  claim 6  wherein the second conductive section comprises a second metal pin offset relative to the first pin, the second pin comprising a mechanical and electrical connection to the adjacent part.  
     
     
         10 . The assembly of  claim 1  wherein there is only one resistor and all current between the first section and the second section must pass through the resistor.  
     
     
         11 . The assembly of  claim 1  wherein the resistor is of rectilinear shape.  
     
     
         12 . The assembly of  claim 1  wherein the kerf provides a pair of parallel segments defining opposite edges of the resistor.  
     
     
         13 . The assembly of  claim 12  wherein the kerf provides an end segment perpendicular to and intersecting each of the parallel segments.  
     
     
         14 . The assembly of  claim 1  wherein the insulating section has a thermal conductivity less than .03 watts/centimeter-K.  
     
     
         15 . The assembly of  claim 14  wherein the insulating section is a glass.  
     
     
         16 . The assembly of  claim 1  wherein the header provides a flat surface on which the first and second electrically conductive sections and the electrically insulating section are exposed and the resistive thin film layer is on the flat surface.  
     
     
         17 . A bridge-header assembly comprising 
 a header providing first and second metal pins for connection to a control device, the pins being assembled in a rigid unit having a flat top perpendicular to the pins, the flat top providing a first metal section in electrical communication with the first pin and a second metal section in electrical communication with the second pin and an electrically insulating section of low thermal conductivity electrically separating the first and second metal sections; and    a resistive thin film layer on the metal sections and the insulating section and providing 
 a kerf in the film intersecting the electrically insulating section and separating the film into a first film section in electrical contact with the first metal section, a second film section in electrical contact with the second metal section and a third film section bonded to the insulating section providing a resistor through which current between the first and second metal sections passes.  
   
     
     
         18 . A method of making a bridge-header assembly for a gas generator comprising the steps of 
 providing a header having first and second electrically conductive sections each having at least one pin providing an electrical connection to a control device, the electrically conductive sections being separated by an electrically insulating section of low thermal conductivity;    depositing a resistive thin film layer on the conductive sections and the insulating section; and    cutting a kerf in the film intersecting the insulating section and separating the film into a first film section in electrical contact with the first conductive section, a second film section in electrical contact with the second conductive section and a third film section bonded to the insulating section providing a resistor of predetermined area through which current between the first and second conductive sections passes.    
     
     
         19 . The method of  claim 18  wherein the header comprises a metal pin providing the first conductive section, an insulating sleeve around the pin providing the insulating section and an annular metal member around the insulating sleeve providing the second conductive section and wherein the step of cutting a kerf in the film comprises cutting an arc in the film around and spaced from the pin leaving the third film section between ends of the arc.  
     
     
         20 . The method of  claim 18  wherein the header provides a flat surface on which the first and second electrically conductive sections and the electrically insulating section are exposed and the depositing step comprises applying the film to the flat surface.  
     
     
         21 . The method of  claim 18  wherein the header comprises a pair of spaced metal pins providing the first and second conductive sections, an insulating sleeve around and separating the pins and providing the insulating section and wherein the step of cutting a kerf in the film comprises cutting at least one segment in the film between the pins.  
     
     
         22 . The method of  claim 21  wherein the step of cutting a kerf in the film comprises cutting a pair of segments in the film between the pins, the segments having a pair of parallel adjacent sections providing edges of the resistor.