The common failures of thick film heater mainly include pressure resistance breakdown, thick film circuit burning, electrical contact point burning, etc., and thick film circuit burning is the most important, but also the largest proportion of failures., the failure mechanism of the thick film heater is roughly summarized as follows.
1. Pressure withstand breakdown
Pressure withstand breakdown mainly appears in the production of thick film elements, and the main reasons for pressure withstand breakdown are as follows:
(1) The influence of the substrate material, the gold structure, composition and surface roughness of the substrate have an important effect on the insulation effect of the insulating medium, where the gold structure and chemical composition affect the corrosion resistance of stainless steel, and the composition of stainless steel determines the expansion coefficient.
(2) Influence of sintering process and sintering equipment. Each slurry has a specific sintering curve, and the sintering temperature and time are usually determined by the nature of the slurry. On one hand, the sintering equipment requires high accuracy, on the other hand, the sintering process must meet the sintering curve, whether there will be emptiness and other phenomena, all these will affect the insulation performance.
(3) Impact of the production environment. The ambient temperature, humidity and air dryness will affect the insulation performance of the product, and the production process must be controlled by the environmental factors.
(4) Insufficient creepage distance during the use of the product due to liquid leakage or moisture attached to the heating body surface will also cause the breakdown phenomenon.
Thick film circuit burning mainly occurs in the use stage of the product, and the main reasons for this phenomenon are as follows:
(1) The heating resistance thickness is uneven. Silk printing and sintering process will affect the thickness uniformity of the thick film resistance. When the thick film is uneven, the weak link resistance is large, the heat is also large, that easy to form hot spots and finally burn off.
(2) The surface temperature distribution of the heater is uneven. Usually,, in the walking mode of the heater surface, the structure of the product affects more greatly on the temperature field distribution. When the temperature field distribution is not uniform, the substrate and the heating filament expansion coefficient can damage the circuit. The uniformity of the temperature field is one of the most important indicators when designing a thick waist heating body.
(3) Temperature controller is not timely. When the appliance is in dry burning or other abnormal temperature increases, the heating body will be protected at 100℃ per second or even in time, which will eventually lead to damage to the heating resistance. So the choice of the protector is crucial for the life span of the thick film heating body.
(4) High power density or current density. Usually, the power or current density of the thick film heater should have sufficient surplus. Or will result in the failure of the thick resistance under the time accumulation or other abnormal circumstances.
(5) Substrate deformation. If the substrate material or structure design is not reasonable, or if the substrate is deformed by other structural reasons, the heating resistance attached to it will also be damaged by a phase change.
Due to the large working current of the thick film heater, the electrical contact point is also a weak part of the heating body. In the heating environment when hot and cold alternately, moisture environment, which are easy lead to oxidation and burn down, usually when design of thick film conductor material thickness and area, should leave a surplus. contact thickness and silver content should meet the actual use requirements.