With the continuous improvement of safety standards, metal film fuse resistors have been widely used in the power circuits of household appliances such as TV CD players. The metal film fuse resistor is a dual-function element. First, it has the function of an ordinary resistor; second, when the circuit suddenly fails and exceeds the multiple of its specified rated power, it will open within the specified time, thereby protecting the circuit and preventing failure Expanded and caused a fire.

The fuse principle of metal film fuse resistor

The metal film fuse resistor is made by chemical deposition method, a layer of Ni-P conductive film is formed on the ceramic substrate, and then the surface of the conductive film is coated with a low-melting glass fuse composed of metal oxide Pb0, etc. The resistor has fusing performance.

Effect of heat treatment conditions on the microstructure of nickel coating

The heat treatment is performed under the action of N2 air flow of 300 0 ~ temperature, and then heat preservation for 3 hours. The nickel coating that is heat-treated under this moss is a mixture of amorphous and crystalline although it has been partially crystallized. At the same time, the diffraction peaks of the Ni3P crystal phase are also beginning to protrude, indicating that the dispersed Ni3P phase has begun to crystallize. When under the action of airflow and 4000~temperature, keep heat for 1.5h for heat treatment. Heat treatment under this condition has made the crystallization of the nickel plating quite complete. The diffraction peaks of the nickel crystal plane become sharp, and the diffraction peaks of the Ni3P crystal phase are also more protruding and sharp. From the above differential thermal analysis IX ray diffraction analysis results, it can be seen that the best heat treatment condition for the electroless nickel coating is to heat it in a furnace at 400°C and cool it naturally to room temperature.

The fuse principle of metal film fuse resistor

When the metal film resistor is under normal load, its temperature rise is lower than the heat treatment temperature. At this time, the Ni3P phase basically does not precipitate, and its film structure and various properties are basically unchanged. When the metal film fuse resistor is overloaded, the temperature rise on it will be higher than the heat treatment temperature. At this time, the Ni3P phase continues to precipitate, the conductivity rises, and the resistance value decreases. At this time, the load on the resistor will increase. The temperature rise of the resistor will rise again, the amount of Ni3P precipitation will be more, and the resistance value of the resistor will become smaller. In a very short time, the temperature rise of the resistor will reach 900 GIX, and the resistor film will overheat and melt, causing the resistance The device is blown.