Fusing resistor

Abstract

A layer of material is disposed over at least a portion of a resistive film of a resistor. The material having a melting point lower than the melting point of the resistive film and when melted, chemically reacts with the resistive film to render at least a portion of the film non-conductive.

What is claimed is: 
     
       1. A resistor comprising: a non-conductive substrate,   a resistive tin oxide based film on said substrate,   a layer of glass frit material disposed on at least a portion of said resistive tin oxide based film having a melting point below the melting point of said resistive film which when melted chemically reacts with said film to render said portion thereof non-conductive,   metallic caps disposed at opposed ends of said substrate and overlying said film,   electrical leads coupled to said end caps, and   an insulative cover substantially surrounding said film and said caps.   
     
     
       2. A resistor according to claim 1 wherein said glass frit is a soda-lime glass. 
     
     
       3. A resistor according to claim 1 wherein said layer is centrally disposed in said resistor and is continuous around its entire periphery. 
     
     
       4. A resistor according to claim 1 wherein said layer is a spot. 
     
     
       5. A resistor according to claim 3 wherein there are spiral grooves in said resistive film providing a resistor path of a predetermined length. 
     
     
       6. A resistor according to claim 4 wherein there are spiral grooves in said resistive film providing a resistive path of a predetermined length and said spot extends across said resistive path. 
     
     
       7. In a tin oxide resistor wherein a tin oxide based film is carried on a non-conductive substrate, the improvement comprising providing a layer of glass frit material over at least a portion of said tin oxide based film which has a melting point below that of said tin oxide film and which when melted reacts chemically with said tin oxide film to render at least a portion thereof non-conductive. 
     
     
       8. A method of open circuiting a tin oxide thin film resistor which comprises providing a layer of glass frit material over at least a portion of said tin oxide thin film having a melting point below said thin film which when melted chemically reacts with said thin film to render it non-conductive, and melting said glass frit material upon overloading said resistor. .Iadd. 
     
     
       9.  An electrical resistor comprising a substrate of electrically insulating material, a thin film of resistance material of a metal oxide coated on said substrate, glass applied on only a portion of said thin film, conducting terminals provided at two ends of said resistor and lead wires soldered to said ends, respectively, and a protective coating formed over the entire surface of said coated substrate, whereby upon receipt of severe load said glass is fused by heat evolved by said resistor film to destroy said thin film thereby permitting the resistor to open circuit in which said resistor is inserted. .Iaddend. .Iadd.10. An electrical resistor as claimed in claim 9, wherein said thin film of resistance material is provided with a plurality of grooves determinant of the resistance of the resultant resistor. .Iaddend. .Iadd.11. An electrical resistor comprising a substrate of electrically insulating material, a thin film of resistance material of a metal oxide coated on said substrate, a plurality of grooves formed in said thin film on said substrate, glass applied on only a portion of said thin film, conducting terminals provided at two ends of said resistor and lead wire soldered to said ends, respectively, and a protective coating formed over the entire surface of said coated substrate, whereby upon receipt of severe load said glass is fused by heat evolved by said thin film to destroy said thin film thereby permitting the resistor to open a circuit in which said resistor 
     
     
        is inserted. .Iaddend. .Iadd.12.  An electrical resistor as claimed in claim 11, wherein the body of said glass applied on the thin film of resistance material on the substrate extends in parallel relation to the longitudinal axis of said substrate crossing a plurality of the grooves. .Iaddend. .Iadd.13. An electrical resistor as claimed in claim 11, wherein the body of said glass applied on the thin film of resistance material on the substrate extends in the form of a ring and located at a substantially intermediate portion of said substrate.