Surface-mounted fuse device with conductive terminal pad layers and groove on side surfaces

• US 5,790,008 A
• Filed: 01/14/1997
• Issued: 08/04/1998
• Est. Priority Date: 05/27/1994
• Status: Expired due to Term

• Current Assignee: Littlefuse Incorporated
• Original Assignee: Littlefuse Incorporated
• Inventors: McGuire, Katherine M., Onken, Daniel B., Neuhalfen, Andrew J., Blecha, Vladimir
• Primary Examiner(s): Picard, Leo P.
• Assistant Examiner(s): Gandhi, Jayprakash N.
• Application Number:
  US08/813,230
• Time in Patent Office: 567 Days
• Field of Search: 337/152, 337/160, 337/227, 337/290, 337/295, 337/296, 337/297, 337/401, 337/413, 29/623
• US Class Current: 337/297
• CPC Class Codes: H01C 17/08 by vapour deposition
• CPC Class Codes: H01H 2085/0414 Surface mounted fuses
• CPC Class Codes: H01H 69/022 of printed circuit fuses
• CPC Class Codes: H01H 85/0411 Miniature fuses
• CPC Class Codes: H01H 85/046 Fuses formed as printed circuits
• CPC Class Codes: H01H 85/11 with applied local area of a metal which, on melting, forms a eutectic with the main material of the fusible member, i.e. M-effect devices
• CPC Class Codes: Y10T 29/49107 Fuse making

Abstract

A thin film surface-mount fuse having two material subassemblies. The first subassembly includes a fusible link, its supporting substrate with a groove on side surfaces and a plurality of conductive terminal pad layers. The second subassembly includes a protective layer which overlies the fusible link so as to provide protection from impacts and oxidation. The protective layer is preferably made of a polymeric material. The most preferred polymeric material is a polyurethane gel or paste. In addition, the most preferred supporting substrate is an FR-4 epoxy or a polyimide.

Claims

1. A thin film surface-mount fuse, said fuse comprising two material subassemblies:

a. the first subassembly comprising a fusible link, a supporting substrate and terminal pads, each of the terminal pads including a plurality of conductive terminal pad layers, the supporting substrate having an upper surface, lower surface and opposing side surfaces, each of the opposing side surfaces having a groove therein, a first of the plurality of conductive terminal pad layers and the fusible link formed as a single-continuous layer and extending across the upper surface of the supporting substrate, the first of the conductive terminal pad layers further extending over the grooves of the opposing side surfaces; and

,

b. the second subassembly comprising a single protective layer which overlies the fusible link so as to provide protection from impacts and oxidation, the protective layer having a substantially flat upper surface.

2. The surface-mount fuse of claim 1, wherein said protective layer is made of a polymeric material.

3. The surface-mount fuse of claim 2, wherein said polymeric material is clear and colored.

4. The surface-mount fuse of claim 1, wherein said protective layer is made of polyurethane.

5. The surface-mount fuse of claim 1, wherein said supporting substrate is made of an FR-4 epoxy or a polyimide.

6. The surface-mount fuse of claim 1, wherein said protective layer is clear and colorless.

7. The surface mount fuse of claim 1, wherein the first conductive layer terminates on the lower surface of the substrate.

8. The surface mount fuse of claim 1, wherein the first conductive layer terminates on the lower surface of the substrate.

9. The surface mount fuse of claim 1, wherein the fusible link has a central portion, the central portion having a tin-lead or tin spot thereon.

10. A method of protecting a thin film surface-mount fuse having a fusible link and terminal pads, the terminal pads having a plurality of conductive terminal pad layers and the substrate having a top, a bottom and opposing side surfaces, each of the opposing side surfaces having a groove therein, wherein a first of the plurality of conductive terminal pad layers and the fusible link form a single continuous film which extends across the top surface of the substrate, the first of the conductive terminal pad layers further extending over the grooves of the opposing side surfaces and terminating on the lower surface of the substrate, said method comprising placing a single protective layer over the entire top surface of the substrate, the single protective layer having a surface thereof which is applied as a gel and is smoothed across the upper surface of the supporting substrate and hardens with a substantially flat upper surface.

11. A thin film surface mount fuse comprising:

a. a substrate, having opposing side surfaces, each of the opposing side surfaces having a groove therein;

b. a fusible link and a first terminal pad layer formed as a single continuous layer disposed on the substrate, wherein the fusible link and the first terminal pad layer are made of a metal selected from a group consisting of copper, silver, nickel, titanium, aluminum and alloys thereof;

c. a second terminal pad layer disposed on the first terminal pad layer, wherein the second terminal pad is made of the same metal as the first layer;

d. a third terminal pad layer disposed on the second terminal pad layer, wherein the third terminal pad layer is made of nickel; and

,

e. a fourth terminal pad layer disposed on the third terminal pad layer, wherein the fourth terminal pad layer is made of tin-lead or tin.

12. The surface mount fuse of claim 11, wherein the fusible link has a central portion with a tin-lead spot being disposed on the central portion.

13. The surface mount fuse of claim 11, wherein a protective coating is applied over the fusible link, the protective coating having a substantially flat upper surface.

14. The surface mount fuse of claim 13, wherein the protective coating is also applied over a portion of the fourth terminal pad layer.

15. The surface mount fuse of claim 11, wherein the first, second, third and fourth conductive layers extend over the grooves of the opposing side surfaces of the substrate.

16. The surface mount fuse of claim 11, wherein the fusible link has a central portion, the central portion having a tin-lead or tin spot thereon.

17. A thin film surface-mount fuse, said fuse comprising:

a. a substrate, having opposing side surfaces, each of the opposing side surfaces having a groove therein;

b. a fusible link made of a first conductive metal deposited on the substrate;

c. a second conductive metal, other than the first conductive metal, deposited on the surface of the fusible link;

d. terminal pads electrically connected to the fusible link, the terminal pads having a plurality of conductive layers, wherein a first of the plurality of conductive layers and the fusible link form a single continuous film; and

e. a protective layer applied over the fusible link, the protective layer having a substantially flat upper surface.

18. The device of claim 17, wherein a second of the plurality of conductive layers is deposited on the first of the plurality of conductive layers and consists of the same metal as the first conductive metal.

19. The device of claim 18, wherein a third of the plurality of conductive layers is deposited on the second of the plurality of conductive layers and consists of nickel.

20. The device of claim 19, wherein a fourth of the plurality of conductive layers is deposited on the third of the plurality of conductive layers and consists of tin-lead or tin.

21. The surface-mount fuse of claim 17, wherein the first conductive metal is selected from the group including copper, silver, nickel, titanium, aluminum or alloys thereof.

22. The surface-mount fuse of claim 17, wherein the second conductive metal is a tin-lead alloy.

23. The surface-mount fuse of claim 22, wherein the second conductive metal is deposited onto the fusible link in the form of a rectangle.

24. The surface-mount fuse of claim 23, wherein the fusible link has a central portion and the rectangle is deposited along the central portion of said fusible link.