Method and component for forming an embedded resistor in a multi-layer printed circuit

Abstract

A component for use in forming a multi-layer printed circuit comprised of a film substrate formed of a first polymeric material. At least one layer of a flash metal is applied to a first side of the film substrate, and at least one layer of copper is applied on the layer of flash metal. A discrete area of a resistive material is disposed on a second side of the film substrate.

Having described the invention, the following is claimed:  
     
         1 . A method of forming resistive elements in a multi-layer printed circuit, comprising the steps of: 
 a) forming an inner core from one or more printed circuit laminates, each of said printed circuit laminates having a core substrate and a first surface with at least one strip conductor disposed thereon,    b) forming at least one surface laminate, said surface laminate comprised of:    a film substrate formed of a first polymeric material;    at least one layer of a flash metal applied to a first side of said film substrate;    at least one layer of copper on said layer of flash metal; and    a discrete area of a resistive material formed on a second side of said film substrate;    c) applying an adhesive material between said surface laminate and said inner core,    d) compressing said inner core and said surface laminate together under conditions of heat and pressure to create a first multi-layer printed circuit, wherein said discrete area of resistive material is embedded within said first multilayer printed circuit between said film substrate and said adhesive layer;    e) circuitizing said layer of copper on said surface laminate to form at least one strip conductor thereon;    f) connecting an end of a first strip conductor with a first end of said resistive area by a through hole connection; and    g) connecting an end of a second strip conductor with a second end of said resistive area by a through hole connection.    
     
     
         2 . A method as defined in  claim 1 , wherein said at least one flash layer is comprised of a metal selected from the group consisting of nickel, chromium, titanium, aluminum, iron, vanadium, silicon and alloys thereof.  
     
     
         3 . A method as defined in  claim 2 , wherein said at least one flash layer has a thickness of about 50 Å to about 500Å.  
     
     
         4 . A method as defined in  claim 3 , wherein said at least one layer of copper has a thickness of about 1000 Å to about 35 μm.  
     
     
         5 . A method as defined in  claim 4 , wherein said first polymeric material is a polyimide.  
     
     
         6 . A method as defined in  claim 5 , wherein said adhesive layer is formed from a material selected from the group consisting of acrylics, epoxies, nitrile rubbers, phenolics, polyamides, polyarylene ethers, polybenzimidazoles, polyesters, polyimides, polyphenylquinoxalines, polyvinyl acetals, polyurethanes, silicones, vinyl-phenolics, urea-formaldehyde and combinations thereof.  
     
     
         7 . A method as defined in  claim 1 , wherein said resistive material is a metal or metal alloy having a resistivity greater than copper.  
     
     
         8 . A method as defined in  claim 7 , wherein said metal is selected from the group consisting of chromium, nickel, titanium, aluminum, vanadium, silicon, iron and alloys thereof.  
     
     
         9 . A method as defined in  claim 1 , wherein said resistive material is a polymer resistor ink.  
     
     
         10 . A multi-layer printed circuit, comprising: 
 a) an inner core formed from one or more printed circuit laminates, said printed circuit laminates comprised of a core substrate having a first surface with a strip conductor disposed thereon,    b) at least one surface component attached to said inner core, said surface component, comprised of: 
 a film substrate formed of a first polymeric material;  
 at least one layer of copper on one side of said polymeric material; and  
 a discrete area of a resistive material disposed on a second side of said film substrate, said surface laminate attached to said inner core with said discrete area of resistive material embedded within said multi-layer printed circuit between said core and said film substrate,  
   c) a first through hole connecting one end of said discrete area to a first circuit trace line of said multi-layer printed circuit; and    d) a second through hole connecting another end of said discrete area to a second trace line of said multi layer printed circuit.    
     
     
         11 . A multi-layer printed circuit as defined in  claim 10 , wherein said resistive material is a metal or metal alloy having a resistivity greater than copper.  
     
     
         12 . A multi-layer printed circuit as defined in  claim 11 , wherein said metal is selected from the group consisting of chromium, nickel, titanium, aluminum, vanadium, silicon, iron and alloys thereof.  
     
     
         13 . A multi-layer printed circuit as defined in  claim 10 , wherein said resistive material is a polymer resistor ink.  
     
     
         14 . A multi-layer printed circuit as defined in  claim 10 , wherein at least one layer of a flash metal is disposed between said polymeric material and said at least one layer of copper.  
     
     
         15 . A component for use in forming a multi-layer printed circuit comprised of: 
 a film substrate formed of a first polymeric material;    at least one layer of a flash metal applied to a first side of said film substrate;    at least one layer of copper on said layer of flash metal; and    a discrete area of a resistive material disposed on a second side of said film substrate.    
     
     
         16 . A component as defined in  claim 15 , further comprising a metal support substrate that constitutes a discardable element in the formation of a printed circuit board, one surface of said metal support substrate being essentially uncontaminated and engageable with said layer of copper, said support substrate attached to said layer of copper at its borders to define a substantially uncontaminated central zone of copper inwardly of the edges of the copper layer.  
     
     
         17 . A component as defined in  claim 15 , wherein said resistive material is a metal or metal alloy having a resistivity greater than copper.  
     
     
         18 . A component as defined in  claim 17 , wherein said metal is selected from the group consisting of chromium, nickel, titanium, aluminum, vanadium, silicon, iron and alloys thereof.  
     
     
         19 . A component as defined in  claim 15 , wherein said resistive material is a polymer resistor ink.  
     
     
         20 . A component as defined in  claim 15 , wherein said discrete area of resistive material is dimensioned to be attached to an inner core of a multi-layer printed circuit board with said discrete area of resistive material embedded within said multi-layer printed circuit between said core and said film substrate.