Method and a device for protecting a printed circuit board against overcurrents

• US 5,543,774 A
• Filed: 05/27/1994
• Issued: 08/06/1996
• Est. Priority Date: 05/28/1993
• Status: Expired due to Term

• Current Assignee: Telefonaktiebolaget LM Ericsson
• Original Assignee: Telefonaktiebolaget LM Ericsson
• Inventors: Lof, C. Stefan L.
• Primary Examiner(s): Picard, Leo P.
• Assistant Examiner(s): RYAN, STEPHEN
• Application Number:
  US08/249,987
• Time in Patent Office: 802 Days
• Field of Search: 337/186, 337/152, 337/159, 337/297, 337/290, 337/295, 29/623
• US Class Current: 337/297
• CPC Class Codes: H01H 69/022 of printed circuit fuses
• CPC Class Codes: H01H 85/046 Fuses formed as printed circuits
• CPC Class Codes: H05K 1/0209 External configuration of printed circuit board adapted for heat dissipation, e.g. lay-out of conductors, coatings
• CPC Class Codes: H05K 1/0293 Individual printed conductors which are adapted for modification, e.g. fusable or breakable conductors, printed switches
• CPC Class Codes: H05K 1/167 incorporating printed resistors
• CPC Class Codes: H05K 2201/0347 Overplating, e.g. for reinforcing conductors or bumps; Plating over filled vias
• CPC Class Codes: H05K 2201/09727 Varying width along a single conductor; Conductors or pads having different widths
• CPC Class Codes: H05K 2201/09781 Dummy conductors, i.e. not used for normal transport of current; Dummy electrodes of components
• CPC Class Codes: H05K 2201/10181 Fuse
• CPC Class Codes: Y10T 29/49107 Fuse making

Abstract

In order to reduce the costs of assembled printed circuit boards, a printed board fuse functions with great reliability at low manufacturing costs. By coating a large area of a printed board with metal, for example, by plating, a well-defined thickness of a metal layer may be achieved in which a fuse has been separated. The well-defined thickness also allows well-defined geometry of the fuse cross-sectional area and fuse length to be achieved and therefore its resistance and interruption characteristics will also be very accurately defined. In case of a temperature rise, the metal layer surrounding the fuse will have a heat dissipating effect on the fuse, providing a substantially reduced risk of board fire.

Claims

1. A method for manufacturing a printed board fuse to protect a printed board against overcurrents, comprising the step of depositing a heat dissipating metal layer having a substantially uniform thickness on a first area of the printed board and forming at least one fuse conductor in at least one second area of the printed board upon which the heat dissipating metal layer is not deposited, the fuse conductor and the heat dissipating metal layer each having a predetermined geometry and thickness selected to provide known resistance and interruption characteristics to the fuse conductor, and the first area substantially surrounding the at least one second area.

2. The method of claim 1, wherein the heat dissipating metal layer is copper and the layer is deposited by plating.

3. A printed board fuse for protecting a primed board against overcurrents, comprising at least one fuse conductor having a predetermined geometry and thickness selected to provide known resistance and interruption characteristics to the fuse conductor, wherein the at least one fuse conductor is formed by depositing a heat dissipating metal layer of a substantially uniform thickness on the printed board in a first area of the printed board substantially surrounding at least one second area of the printed board upon which the heat dissipating metal layer is not deposited, and forming the at least one fuse conductor on the at least one second area.

4. The printed board fuse of claim 3, wherein the fuse conductor is plated copper.

5. The printed board fuse of claim 3, wherein the fuse conductor has a square-wave shape and a section of reduced width.