The influence of slurry or paste selection on thick film heater

- Jul 31, 2020-

The slurry for making thick film heater can be divided into dielectric paste, resistance paste and conductor paste. The dielectric paste is directly printed on the stainless steel plate to form an insulating dielectric layer, while the resistance paste and conductor paste are printed directly on the insulating dielectric layer. The resistance paste is used for heating, while the conductor paste is used for the connection of external power supply. The size generally consists of three parts: functional phase, binder phase and organic carrier.The size generally contains three parts: functional phase, junction phase, and organic carrier, of which the organic carrier is mainly dispersed functional phase and binding phase, so that the size has a fixed viscosity suitable for screen printing. It usually contains solvent plasticizers and additives (such as thixotropic agents, surfactants, etc.). The organic carrier should have the following characteristics:

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Moderate viscosity, to ensure that the size has a certain liquidity suitable for screen printing; Thixotropy, after printing can make the paste keep good shape; Wettability, uniform dispersive bond phase and functional phase without agglomeration and precipitation; Volatile, characterized by gradation rather than concentration in a temperature range to avoid pores or cracks. The volatilization characteristic of solvent determines the volatilization characteristic of organic carrier, and the volatilization characteristic of organic carrier directly determines the quality of film layer. Solvent volatilization is too fast, when printing paste viscosity increases easy to plug screen, solvent volatilization is too concentrated, after drying and sintering is easy to form holes and micro-cracks on the surface of the film; The solvent volatilizes too slowly, and it is not easy to dry after screen printing, resulting in defects after sintering.

At the same time, the volatilization characteristic of the carrier is also an important factor affecting the stability and storage time of the slurry

It can be seen that the quality of paste directly affects the quality of thick film heating material. In the electronic paste industry, well-known manufacturers include EsL and DuPont from the United States, Heracus from Germany, and JAYE from China, etc. Paste selection mainly depends on the substrate material, because different substrate has different thermal expansion coefficient (TCE) and paste performance, if the substrate and paste do not match the quality of the product can be imagined. Some parameters related to slurry mainly include rheological ability, viscosity, mesh number, leveling time, drying temperature, sintering temperature, sintering thickness, coating rate, square resistance, temperature expansion coefficient TCE, etc

During paste printing, sintering and calculation, it is necessary to operate according to the parameter requirements in the paste Datasheet, otherwise the quality of heating element will be seriously affected.