Before making the thick film heating element, it is necessary to perform a pretreatment on the stainless steel substrate to remove oil stains, impurities, fingerprints, etc. on the stainless steel substrate. When touching the substrate, you should wear latex gloves. First of all, we need to select the material for screen printing according to the parameters of the paste we want to screen. After the mesh is stretched, the photosensitive adhesive is applied. The thickness of the photosensitive adhesive also needs to be selected according to the parameters of the slurry. After drying, exposure and development are performed.
After the pretreatment, enter the screen printing process. The printing sequence of the paste is to print the insulating medium layer first, then the conductor. If the PTC protection resistor needs to be printed, the PTC protection resistor is printed after the conductor is printed (PTC protection resistor is used to detect heat generation. body surface temperature), then print the heating resistor, and finally print the surface medium. Generally, the surface medium and the insulating medium are the same paste. The printing thickness is determined according to the paste specification. Generally, the thickness of the insulating layer is more than 80 microns, the heating resistance is 20 microns, and the conductive paste is more than 10 microns.
The paste is dried and sintered after printing, and each paste has different drying and sintering temperature and time, which all need to be determined according to the parameters of the selected paste.
After the sintering is completed, it is necessary to carry out appearance inspection to find defective sintered products, such as blisters and voids. Then conduct electrical performance testing, including insulation resistance, withstand voltage, leakage current, resistance value and other tests. According to household appliances, the insulation resistance of the heating body is required to be more than 100M, the withstand voltage is 1500V/1min/10mA, and the leakage current is less than 0.75mA
