Thin film circuit
AssigneeRobert Bosch GmbH
InventorsHeiko Gruner, Georg Zimmermann
Life of this patent
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Abstract
To improve the adhesion of a nickel layer to a valve metal layer in a thin film electronic circuit, a boundary layer is created between the valve metal and the nickel layer. The boundary layer is created by oxidizing the valve metal surface and applying the nickel layer by cathode sputtering with sufficiently high energy to cause nickel-ion migration into the valve metal oxide layer. The so-formed boundary layer improves the mechanical adhesion of the nickel layer to the valve metal layer and also prevents penetration of solder to the valve metal layer since the boundary layer acts as a diffusion barrier.
Claims22
In an electronic thin film circuit comprising a substrate (1) of insulating material, a valve metal layer (2) covering a part of said substrate and forming a first (M.sub.1) and at least one further (M.sub.2, M.sub.3) pattern, said first pattern constituting electrically conductive connecting means, said second pattern constituting an electronic circuit element, and a nickel layer (5) positioned over said valve metal layer in said first pattern, and a soft solder layer (6) covering at least a part of said nickel layer (5) the improvement comprising a boundary layer (4) comprising said valve metal, an oxide of said valve metal, nickel, nickel oxide and mixed phases thereof integral with and between said valve metal layer and said nickel layer, said boundary layer having been formed by forming an oxide layer having a thickness between 3 and 10 nm on said valve metal, applying said nickel layer and applying sufficient energy to form said boundary layer of valve metal, valve metal oxide, nickel oxide, nickel and mixed phases thereof by diffusion either during or subsequent to applying said nickel layer.
A method for manufacturing an electronic thin film circuit on an insulating substrate (1), comprising the steps of depositing a valve metal layer (2) on said substrate by cathode sputtering;
- oxidizing said valve metal layer, thereby creating a valve metal oxide layer having a thickness between 3 and 10 nm on said valve metal;
- applying a nickel layer to said valve metal oxide layer by cathode sputtering, at a sputtering energy sufficiently high to cause an intermetallic diffusion of nickel atoms into said valve metal oxide layer to form a boundary layer (4) comprising said valve metal, an oxide of said valve metal, nickel, nickel oxide and mixed phases thereof, whereby a three-layer system is created on said substrate;
- and
- etching said three-layer system to create predetermined patterns constituting circuit elements of said thin film circuit.
Dependencies are inferred from the claim text.