Electricity: electrical systems and devices – Safety and protection of systems and devices – Circuit interruption by thermal sensing
Reexamination Certificate
1999-06-04
2001-03-13
Sherry, Michael J. (Department: 2836)
Electricity: electrical systems and devices
Safety and protection of systems and devices
Circuit interruption by thermal sensing
C361S124000, C361S093800, C337S297000
Reexamination Certificate
active
06201679
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electrical overload protection device that is integrated directly on the underlying structure of an electronic device. More particularly, the device which functions as a thermal fuse, is integrated directly on the substrate of a semiconductor device, and serves to protect associated system elements from electrical overstress conditions, thus insuring a failsafe mode of operation.
2. Description of Prior Art
A variety of fuses and breaker switches exist to protect electrical circuits or devices from overstress conditions. Such overstress conditions might include, for example, a lightning strike, a power surge, or more simply an overload condition being supplied at the power input terminal of the circuit or device. When such an overload condition exists, the electrical resistance of the device produces heat. While heat dissipation devices can be used (e.g., fans, heatsinks, and the like), they are generally not adequate to compensate for extreme overload conditions. If the overload condition persists, then the heat buildup may become great enough to melt and/or destroy key components, or the entire electrical circuit. Fires might even result in one component or device, and the fire can then spread and destroy an entire system.
In the past, thermal fuses have been used to guard against overstress conditions. A thermal fuse uses the heat generated by the electrical resistance and overload condition to break the electrical connection between two points on the circuit. This is usually accomplished by the overload condition heat causing an electrical contact point to melt, thereby severing the contact. In the past, such thermal fuses have been incorporated, as separate devices between the power input and an electrical device to be protected.
Several drawbacks exist, however, to the use of separate and distinct thermal fusing components. By way of example, and not limited to such, these drawbacks might include; first, thermal fuses are generally large components, and may be hard to incorporate in smaller electrical packages, particularly semiconductor packages; second, the thermal fuse might, under certain conditions, explode or expel byproducts, thereby damaging neighboring components or devices which the fuse was ultimately slated to protect; and third, the contact point material, which melts during an overstress condition, might drip or flow over neighboring components. Such hot, dripping material might thereafter cause short circuits, further overheating, fires, and/or other related damage to the neighboring components. Ultimately the entire system into which the components were incorporated might fail or be damaged. Moreover, separate thermal fuse components are generally not an integral part of the circuit which is generating heat due to the overstress condition. As a result, it is difficult for the fuse and the circuit to be at the same temperature. It is therefore possible that the device may overheat sufficiently before the separate fuse component opens, thereby causing a possible hazardous failure condition. One such condition would be where the device connections meet (or short out) and the resulting failure causes the device to fall off the printed circuit board to which it was soldered. This wayward part could thereby result in a possible short circuit or fire hazard in surrounding boards, or system-wide.
Accordingly, what is needed in the field is a thermal fuse which exists, or can be formed, integrally with an overall circuit, or collection of components. In particular, the thermal fuse should be capable of achieving a very small size, and yet still provide adequate overstress condition protection. The fuse should be integrated in the foundational material of the underlying device. Incorporation into a semiconductor circuit substrate would prove to be most useful. The fuse should also operate without jeopardizing neighboring components with dripping contact material, expulsions, or the like.
SUMMARY OF THE INVENTION
The present invention provides a thermal fuse device which can be formed integrally on an electrical circuit with other components. In particular, the thermal fuse device can be integrally formed, in many different shapes and/or sizes, on the underlying structural or foundational material which comprises the electrical circuit. A monolithic structure would include formation of the thermal fuse device according to its process steps. This provides a thermal fuse which is intimately linked with the various components of the circuit. In operation, the fuse is normally closed, and will sever an electrical contact according to overstress and/or heating conditions which are common to both the fuse and the underlying components with which the fuse is integrated.
According to one aspect of the present invention, the thermal fuse device includes first and second formed electrical contact areas which are separated by a gap. The contact areas are coated with underbump metallurgy (UBM) materials, and then a wettable material thereafter. The gap area is kept free from such wettable material. A solder bump is then formed (e.g., plated, screened, etc.) in the center of the formation, thereby spanning the gap and forming a bridge between the first and second contact areas. A flux is applied to the solder. When an electrical overstress condition is imposed between the contacts, the solder bump is heated to the point of melting. The wicking effect of the wettable material on the contact areas draws the molten solder out of the gap and onto the contact areas. Once the solder is completely melted and wicked away from the gap, then the electrical connection between the contact areas is severed, and the overload condition is isolated from the remainder of the components. The solder is also relatively contained on the wettable areas of the contact areas, and will not generally drip or flow elsewhere.
According to another aspect of the present invention, the present method of forming the thermal fuse is particularly adaptable to implementation directly on a semiconductor substrate according to standard manufacturing techniques, or process steps. Example steps include, in relevant part, but are not limited to the following: Forming conductive contact areas on an oxide layer which in turn is formed on an underlying substrate material. UBM layers are sputtered, as needed, thereafter. A photoresist mask is then applied to define the wetting area. A wettable material such as gold is plated on the defined contact areas, and the photoresist is stripped off. A photoresist mask is next applied to isolate the gap area between the contact areas. The UBM material is etched away from the gap area and the photoresist is stripped away. A photoresist mask is next applied to define the solder bridge area. A solder bump is formed on this defined area, and the photoresist is stripped away. A flux is thereafter applied to the solder area. The incoming power to the overall substrate devices can be connected through this integrated thermal fuse which, according to its design, will melt and wick away the solder, thereby severing the electrical connection if an overload condition occurs.
The thermal fuse, and in particular the electrical contact areas and gap therebetween can be designed according to many different shapes, sizes, and configurations. By varying certain parameters such as the contact area size, the gap width and depth, and the melting point of the solder material that bridges the contact areas, the fuse can be sized and designed to respond successfully to a variety of different overload conditions. The present invention is intended to include both the integrated thermal fuse, and the method for its formation.
These and other advantages of the present invention will become apparent upon reading the following detailed descriptions and studying the various figures of the drawings.
REFERENCES:
patent: 4652848 (1987-03-01), Hundrieser
patent: 4862134 (1989-08-01), Poerschke et al.
patent: 5097247 (1992-0
Beyer Weaver & Thomas LLP
California Micro Devices Corporation
Sherry Michael J.
LandOfFree
Integrated electrical overload protection device and method... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Integrated electrical overload protection device and method..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Integrated electrical overload protection device and method... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2461261