U.S. Philips Corporation

Wolfgang E Schnitker

Michael P Nover

Kay Appel

Ernst Klein

Heinz Scholz

The invention relates to a method of forming a thick-film circuit arrangement having an electronic circuit which is constructed on a surface (17) of a ceramic substrate plate (3) and which consists of conductor paths (5), resistors, capacitors and components, in particular integrated switching circuits without a housing, formed according to thick-film technique, in this structure has between the electrically conductive structures (5) a sintered, non-conductive paste substantially filling the intermediate spaces between them and both the structures and the interposed pastes are covered by a sintered insulating paste. For concealing the thick-film circuit arrangement from unauthorized access, the following covering construction is carried out:

Method of manufacturing a thick-film circuit arrangement

The invention relates to a thick-film circuit arrangement having an electronic circuit which is constructed on a surface (17) of a ceramic substrate plate (3) and which consists of conductor paths (5), resistors, capacitors and components, in particular integrated switching circuits without a housing, formed according to thick-film technique. This structure has between the electrically conductive structures (5) a sintered, nonconductive paste substantially filling the intermediate spaces between them and both the structures and the interposed pastes are covered by a sintered insulating paste. For concealing the thick-film circuit arrangement from unauthorized access, the following covering construction is carried out:

Thick-film circuit arrangement having a ceramic substrate plate

A suspension of a poorly water-soluble iron (II) containing compound in a liquid which consists substantially of water and is preferably alkaline is oxidized, to form goethite crystals and particles. The crystals and particles are filtered off, washed and dried. From a thermodynamic point of view, 'more monoenergetic' particles are obtained than particles manufactured according to conventional production processes, when electrolytic oxidation processes are used, in particular, when the oxidation to goethite occurs entirely or partly by a (preferably periodic) electrolysis process. The electrolysis process may be combined with oxidation by an oxidation agent, preferably an oxidizing gas or gas mixture. Furthermore, it is possible to first oxidize the iron (II) containing compound completely to goethite by an oxidation agent, preferably an oxidizing gas or gas mixture, and to then subject the resulting suspension to an electrolytic oxidation after-treatment which preferably occurs periodically.

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Krefeld, Germany

Wolfgang E Schnitker