At DuPont Electronic Materials, a range of thick-film resistor and overglaze compositions has been developed for use on stainless steel for high volume heating and other power applications.

One example of its use is in the external printed elements used in the latest generation of kettles, where the printed elements have replaced the more traditional resistance coils. Compared with conventional glazes, the high volume manufacturer can make considerable process savings.

The core of the new materials system is an insulating glaze which works on 430 and similar grades of stainless steel. The chemistry of the glaze gives a better match to the thermal expansion coefficient of steel than older glazes, thereby providing flatter substrates after firing, which in turn leads to easier printing of subsequent layers. It also results in reduced bowing during thermal cycling in use.

In order to meet the need for tight resistance tolerances and high yields in volume manufacturing, the thick film resistor and overglaze compositions come in a range with three different thermal coefficients of resistance (TCR). Two different pastes can be blended together to provide the desired TCR. The circuit designer is therefore able to choose the best materials for his layout and target resistance.

It is also possible to make fine adjustments to the resistance of the elements directly on the production line, improving yields, while the ability to co-fire different layers further speeds up the overall manufacturing process.

Figure 1: New glaze and resistor compositions for high volume heating and power applications

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