A device for protection of a semiconductor device comprises a metallic wire and means for connecting said wire to the output of said semiconductor device, said metallic wire having a characteristic that when a current a little lower than the current that destroys said semiconductor device flows through said wire, said wire is melted in as short a period of time as possible.
This application is a continuation/application based on prior copending application Ser. No. 183,365, filed Sept. 2, 1980, "DEVICE FOR PROTECTION OF A SEMICONDUCTOR DEVICE"-Applicant: Yoshio Yamauchi; now abandoned.
This invention relates to a device for protecting semiconductor devices such as power transistors, power integrated circuits and the like, and also a protective element used in the protective device.
When a load is being driven by the output of a semiconductor device such as a power transistor or a power IC, if the load is short-circuited, an overcurrent flows through the semiconductor device to break the device. Repair or replacement of the broken device requires cost, time and labor and causes a great loss.
To protect a semiconductor device against breakdown due to overcurrent, it has been proposed to provide the semiconductor device with a protective circuit which operates in response to overcurrent to prevent it from flowing through the device. However, provision of such a protective circuit in the semiconductor device increases the cost of the device itself and erroneous operation is likely to occur so that proper protection cannot be expected.
Accordingly, it is one object of the present invention to effectively protect semiconductor devices against breakdown due to overcurrent.
Another object of the invention is to accomplish the protection of semiconductor devices from overcurrent by a simple arrangement.
In accordance with the invention, when an overcurrent flows through a load connected to a semiconductor device, the output terminal of the semiconductor device is disconnected from the load. To effect such disconnection a protective element is provided between the load and the semiconductor device to be protected. The protective element comprises a wire made of a metal which is melted and cut when a smaller amount of overcurrent than the amount that destroys the semiconductor device to be protected flows through the wire.
The wire is connected between an opposite pair of leads just as in the case of such semiconductor devices as diodes, transistors and the like. Connection of the wire with the leads may be made by the wire bonding method which is widely used in various semiconductor devices.
The wire and the leads are then packaged in synthetic resin by molding. The resins that can be used for packaging must be incombustible or non-inflammable since heat is produced when the wire is melted and severed or broken. Silicone resins are suitable for the purpose.
The package formed by molding resin to enclose the elements therein may be replaced by a box, a can or a frame having an interior space in which the opposed end portions of a pair of leads and the metallic wire connected therebetween are enclosed.
A fuse is commonly used to break a circuit when overcurrent flows therethrough. Ordinary fuses for low voltages are so standardized that they are melted within two minutes by a current of twice the rated amount. With such a fuse used in connection with a semiconductor device for protection, a current of twice the rated amount can flow through the semiconductor device continuously for a maximum of two minutes, so that the semiconductor device will be destroyed before the fuse is melted.
Furthermore, common fuses, especially those made of alloys having low melting points have great resistances, so that a great power loss is caused by the fuse, with resulting decrease in the power to be supplied to the load. In addition, the resistance and consequently the melting characteristics of the conventional fuses vary widely so that exact breaking operation cannot be expected. For example, a fuse rated to 1 amp. may be used to break a circuit when a current of 2 amp. flows therethrough. The average resistance of the fuses rated to 1 amp. is 0.25 ohm, with a variation (the standard deviation) of 90 milliohms. Such fuses are unstable in melting characteristics and cause a great output loss.
In accordance with the present invention, metals having lower specific resistances, such as gold, silver, copper, etc. are used for the wire. The thin wires made of these metals are used as inner leads in semiconductor devices and have resistances so small that the load loss caused thereby is negligible. The wires made of these metals are melted and severed in a short period of time, preferably within 0.5 second, when a current a little smaller than the excess current that will break the semiconductor device flows through the wires.
An electrical component has a plurality of paired contacts with spaced inner contact sections bridged by a fuse element. The paired contacts have outer contact sections enabling mounting to a circuit panel to complete circuit paths thereon. The component is used as a fuse component to protect the circuit panel by preventing overload of a circuit path by the respective fuse element. When the circuit paths have different design in-service currents and different levels of excessive electrical currents, the corresponding fuse elements can have correspondingly different in-service current-carrying capabilities and different melting points, in the same component. The component can be surface mountable and can have DIP configuration.
An electrical component has a plurality of paired contacts with spaced inner contact sections bridged by a fuse element. The paired contacts have outer contact sections enabling mounting to a circuit panel to complete circuit paths thereon. The component can be used as a shunt for programming the circuit panel by programming the component prior to in-service use of the panel, by the method of deliberately opening the respective fuse element between one or more selected pairs of contacts by an electrical programming current thereon, leaving other fuse elements intact for in-service path connection of their respective circuit paths. The component can be surface mountable and can have DIP configuration.
A microfuse (10) with a ceramic chip (12), thick film pads (14), fusible wire (16), attached to pads (14) without solder or flux, ceramic coating (18) and plastic body (20). External lead (24) configuration can be axial, radial or surface mount. The method of manufacturing the fuse (10) is improved by utilizing a wire bonding technique in order to improve the quality of the manufacturing process and increase the reliability in performance of the fuse and reduce manufacturing cost.
A microfuse (10) with a ceramic chip (12), thick film pads (14), fusible wire (16), attached to pads (14) without solder or flux, in an insulating enclosure or fuse tube (40). Ferrules (42) are attached to metallized areas (14) with solder (44). Performance and manufacturing of fuse (10) is improved by utilizing a wire bonding technique to improve the quality of the manufacturing process and increase the reliability of the fuse, and to reduce manufacturing cost.
Gold, copper, silver, palladium or aluminum and their alloys, but preferably gold or gold alloy, which may be in the form a wire, has deposited thereon or contained within the wire, a material such as metals or metal alloys which diffuse into the gold or into the other listed metals. With the passage of time and exposure to temperature the deposited metal or metal alloy continues to diffuse into the gold forming intermetallics with the gold and thereby causing the resistivity of the gold to increase and causing the gold to become progressively more brittle until such time as the gold wire ruptures at a stress point. At a given temperature the elapsed time until rupture takes place depends upon the metal or metal alloys deposited on or contained within the gold. Lead, indium, gallium, tin, bismuth and aluminum and the alloys of these metals diffuse into and form intermetallics with the gold. The time rate of embrittlement of the gold and the other soft metals listed is a function of the metal or metal alloy and the temperature. Gold wires so treated with the metal or metal alloys may be used as time temperature dependent fuses. For example such fuses may be useful for the protection of integrated circuits or systems of integrated circuits wherein the gold wires so treated are used as connections within the circuit or system.
