Preformed thermal fuse

• US 5,939,969 A
• Filed: 08/29/1997
• Issued: 08/17/1999
• Est. Priority Date: 08/29/1997
• Status: Expired due to Fees

• Current Assignee: MMC Bidding, Inc.
• Original Assignee: Microelectronic Modules Corporation (Bourns Incorporated)
• Inventors: Pathammavong, Keck C., Krachenfels, Kurt M., Doerrwaechter, Bernhard E.
• Primary Examiner(s): Picard, Leo P.
• Assistant Examiner(s): Vortman, Anatoly
• Application Number:
  US08/920,916
• Time in Patent Office: 718 Days
• Field of Search: 337/297, 337/158, 337/268, 337/159, 337/290, 337/401, 337/413-416, 337/152, 337/232
• US Class Current: 337/297
• CPC Class Codes: H01H 2037/046 being soldered on the printed circuit to be protected
• CPC Class Codes: H01H 2037/768 characterised by the composition of the fusible material
• CPC Class Codes: H01H 37/761 with a fusible element forming part of the switched circuit H01H37/767 takes precedence
• CPC Class Codes: H02H 9/042 comprising means to limit the absorbed power or indicate damaged over-voltage protection device
• 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 1/092 Dispersed materials, e.g. conductive pastes or inks
• CPC Class Codes: H05K 2201/0305 Solder used for other purposes than connections between PCB or components, e.g. for filling vias or for programmable patterns
• CPC Class Codes: H05K 2201/10181 Fuse
• CPC Class Codes: H05K 2201/10992 Using different connection materials, e.g. different solders, for the same connection
• CPC Class Codes: H05K 3/3463 Solder compositions in relation to features of the printed circuit board or the mounting process

Abstract

A preformed thermal fuse comprising two electrodes, first and second layers of solder, and a conductive bridge comprising a non-paste solder material is disclosed. The conductive bridge has a melting temperature which is substantially equivalent to the predetermined actuation temperature of the fuse. The melting temperatures of the first and second layers of solder are selected to allow reflow soldering of the device.

Claims

1. An apparatus comprising a heat actuated fuse which opens at a predetermined actuation temperature, said fuse comprising:

an electrically insulating substrate;

first and second electrodes disposed on a surface of said substrate in a spaced apart relationship to define a gap there between, each of said electrodes comprising a layer of electrically conductive material;

a first layer of solder disposed on each of the first and second electrodes;

a second layer of solder disposed on at least a portion of each of the first and second electrodes; and

a conductive link formed of a non-paste solder material having a melting temperature substantially corresponding to said predetermined actuation temperature extending across said gap and disposed on said portion of each of said first and second electrodes, wherein the second layer couples the conductive link to the electrodes.

2. The apparatus of claim 1 wherein said conductive link is a preformed chip.

3. The apparatus of claim 2 wherein said chip is a Sn/Pb/Ag solder alloy.

4. The application of claim 1 further including a flux material disposed in contact with at least a portion of said conductive link.

5. The apparatus of claim 4 further including a damage protective covering over at least said flux material.

6. The apparatus of claim 1 further including a resistive device positioned for effective heating of said fuse responsive to passage of an electric current through said resistive device.

7. The apparatus of claim 6 wherein said fuse and said resistive device are on the same substrate.

8. The apparatus of claim 7 wherein the resistive device is disposed proximate to said fuse.

9. The apparatus of claim 6 wherein said resistive device comprises a thick film resistor.

10. A heat actuated fuse for opening at a predetermined actuation temperature, said fuse compromising:

an electrically insulating substrate;

first and second electrodes disposed on a surface of said substrate in a spaced apart relationship to define a gap therebetween, each of said electrodes comprising a layer of electrically conductive material;

a layer of solder formed on each of the first and second electrodes;

a layer of a solder paste material disposed on at least a portion of each of the first and second electrodes, said solder paste having a melting temperature lower than both the melting temperature of the layer of solder and the predetermined actuation temperature of the fuse;

a conductive link extending across said gap and disposed on said portion of each of said first and second electrodes, said conductive link formed of a non-paste solder material having a melting temperature which substantially corresponds to said predetermined actuation temperature.

11. The fuse of claim 10 wherein said conductive link is a preformed chip.

12. The fuse of claim 11 wherein said chip is a Sn/Pb/Ag solder alloy.

13. The fuse of claim 10 further including a solder resist material disposed in contact with at least a portion of said first layer of solder.

14. The fuse of claim 13 further including a damage protective covering over at least said flux material.