Fuse

Claim 1

A fuse comprising an elongated electric insulating substrate of cross section S, and elongated electric conductor of cross section S in the form of a thin film deposited on the surface of said elongated electric insulating substrate characterized in that the dimensions and materials of the substrate and conductor are selected such that for a rated current designated IN, a predetermined maximum temperature variation along the conductor designated ΔTmax, and a length of the electric conductor designated 2b, thermal equilibrium is obtained, when the said rated current flows along said conductor, when the relationship between the cross section S of the said electric conductor and the cross section S' of the substrate is approximately: S=ρ'.sub.th ·ρ.sub.e ·b.sup.2 ·IN.sup.2 /2S'·ΔTmax where ρ' th is the thermal resistivity of the substrate and ρ e is the electrical resistivity of said electric conductor and in that the said conductor has respective opposite end regions and the substrate has respective opposite end regions adjacent thereto and a medial region therebetween, and there is a thermal resistivity between ambient temperature and each said end region of the substrate which is <200° C./W whereas there is a thermal resistivity >500° C./W between the ambient temperature and said medial region of the said substrate, the value of ΔTmax being chosen sufficiently high that said thermal equilibrium is broken in <ls when the current flowing along said conductor reaches 2IN.

Claim 11

A method for manufacturing electrical circuit fuses having accurate high speed fusing characteristics over a range of rated currents IN from approximately 10 milliamperes to approximately 10 amperes, said method comprising the steps of: vapor-phase vacuum depositing a thin film of metal less than 10 μm thickness on an insulating substrate; and photoetching said thin film of metal to form an elongated electric conductor of length 2b and cross section S on an elongated insulating substrate of cross section S' wherein for a predetermined maximum temperature variation ΔTmax along the conductor at thermal equilibrium, the following relationship is at least approximately satisfied: S=ρ'.sub.th ·ρ.sub.e ·b.sup.2 ·IN.sup.2 /2S'·ΔTmax where ρ' th is the thermal resistivity of the substrate and ρ e is the electrical resistivity of the electric conductor, wherein there is a thermal resistivity of less than 200° C./W between ambient temperature and each end region of the substrate and a thermal resistivity of more than 500° C./W between ambient temperature and a medial region of said substrate, and wherein the value of ΔTmax is sufficiently high to break thermal equilibrium in less than one second when current flowing along said conductor reaches 2IN.

Claim 12

A method for manufacturing electrical circuit fuses having accurate high speed fusing characteristics over a range of rated currents IN from approximately 10 milliamperes to approximately 10 amperes, said method comprising the steps of: vapor-phase vacuum depositing a thin film of metal less than 10 μm thickness on an insulating substrate; and photoetching said thin film of metal to form an elongated electric conductor of length 2b and cross section S on an elongated insulating substrate of cross section S' wherein for a predetermined maximum temperature variation ΔTmax along the conductor at thermal equilibrium, the following relationship is at least approximately satisfied: S=ρ'.sub.th ·ρ.sub.e ·b.sup.2 ·IN.sup.2 /2S'·ΔTmax where ρ' th is the thermal resistivity of the substrate and ρ e is the electrical resistivity of the electric conductor, wherein there is a thermal resistivity of less than 200° C./W between ambient temperature and each end region of the substrate and a thermal resistivity of more than 500° C./W between ambient temperature and a medial region of said substrate, and wherein the value of ΔTmax is sufficiently high to break thermal equilibrium in less than one second when current flowing along said conductor reaches 2IN.