Electrical circuit on porcelain coated metal substrates

• US 4,365,168 A
• Filed: 07/14/1980
• Issued: 12/21/1982
• Est. Priority Date: 07/14/1980
• Status: Expired due to Term

• Current Assignee: Nortel Networks Limited (Nortel Networks Corporation)
• Original Assignee: Northern Telecom Limited (Nortel Networks Corporation)
• Inventors: Sich, Edward M., Chaput, Guy J.
• Primary Examiner(s): Rubinson, G. Z.
• Assistant Examiner(s): Dwyer, James L.
• Application Number:
  US06/167,734
• Time in Patent Office: 890 Days
• Field of Search: 361/274, 361/331, 361/301, 361/402, 307/115, 340/365 C, 200/5 A, 200/292
• US Class Current: 307/115
• CPC Class Codes: H01H 13/702 with contacts carried by or formed from layers in a multilayer structure, e.g. membrane switches
• CPC Class Codes: H01H 13/785 characterised by the material of the contacts, e.g. conductive polymers
• CPC Class Codes: H01H 2201/024 precious
• CPC Class Codes: H01H 2205/032 Several contacts formed in one plate or layer
• CPC Class Codes: H01H 2209/026 metallic
• CPC Class Codes: H01H 2221/002 integral with membrane
• CPC Class Codes: H01H 2229/002 Screen printing
• CPC Class Codes: H01H 2239/004 High frequency adaptation or shielding
• CPC Class Codes: H01H 2239/01 combined with other elements on the same substrate
• CPC Class Codes: H05K 1/0215 Grounding of printed circuits by connection to external grounding means
• CPC Class Codes: H05K 1/053 the metal substrate being covered by an inorganic insulating layer
• CPC Class Codes: H05K 1/162 incorporating printed capacitors
• CPC Class Codes: H05K 2201/09318 Core having one signal plane and one power plane

Abstract

A porcelain coated metal substrate bearing a printed circuit and in which a capacitive coupling is created between the substrate and the circuit to eliminate unwanted frequencies. This coupling is formed by the inclusion of a conductive element on the porcelain. The conductive element is out of direct electrical contact with the printed circuit and has a means to connect the element to ground. Connection to ground provides the desired capacitive coupling and another capacitive coupling from the metal substrate to the conductive element, the two couplings being in series.

Claims

1. A circuit board comprising an electrically conductive metal substrate having a porcelain layer on at least one of its surfaces, a printed electrical circuit on said porcelain layer, a conductive element carried by the porcelain layer and spaced from the metal substrate by the porcelain layer, the conductive element and the printed electrical circuit not being directly electrically connected together, and means to connect the conductive element to ground to provide one capacitive coupling from the printed circuit to the metal substrate and another capacitive coupling from the metal substrate to the conductive element and in series with said one capacitive coupling, the value of said one capacitive coupling being determined by the area of contact between the printed circuit and the porcelain layer and by the thickness of the porcelain layer.

3. A circuit board according to claim 1 wherein the printed circuit has at least one conductor which is printed with large and small width portions to give the desired area of contact with the porcelain layer.

4. A circuit board according to claim 1 provided with at least one resistor connecting portions of the conductor in series, the resistor formed by printing techniques and providing a capacitance effect with the metal substrate.

5. A circuit board according to claim 1 having an integrated circuit carried upon the porcelain and electrically connected to the printed circuit.

2. A pushbutton switch assembly for telecommunications apparatus comprising pushbutton means and a switch contact circuit associated with the pushbutton means so as to have contact areas connected by operation of the pushbutton means, and a circuit board according to claim 11, the printed circuit being connected to the switch contact circuit to transmit an audio signal to a desired destination upon connection of said contact areas and said conductive element connected to ground potential.