Coating processes – Electrical product produced – Metallic compound coating
Patent
1993-12-28
1995-10-17
Utech, Benjamin
Coating processes
Electrical product produced
Metallic compound coating
427331, 4273761, 4273762, B05D 512
Patent
active
054589118
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a method for producing a self-supporting thick-film structure on a substrate over a recess in this substrate.
2. Description of the Related Art
Thick-film circuits are preferably produced on ceramic, plate-like substrates by means of printing on a paste whose active material comprises metal powders, glass and glass-ceramic powders or mixtures of glass and metal oxides. Subsequent to firing these printed-on pastes at temperatures around approximately 850.degree. C., metallic layers, glass and glass-ceramic layers or resistance layers are produced, depending on the pastes used in each case. The entire surface of these layers bonds during firing with the surface of the substrate on which they subsequently form a firmly adhering substance.
These types of thick-film circuits find application in many fields of technology.
Some cases require that the layer including the active substance does not contact the entire substrate surface, but that bulging creates cavities in which, for example, conductor paths, elevations or other circuit components are arranged. Attention is directed, for example, to DE-OS (German Unexamined Published Patent Application) DE-OS 3,015,356, DE-OS 3,008,572 and DE-OS 2,829,195. However, these closed bubbles have the disadvantage that the air cushion in the bubble has certain undesirable effects on the circuit and the circuit components. Thus, a heat flow which still occurs through the air cushion worsens, for example, the dynamic characteristics of a sensor inside the closed bubble. This is why it might be desirable in some cases that, although a cavity is formed, this cavity not be closed on all sides. In that case, a recess, through which the cavity remains open, would need to be present in the substrate, with the cavity itself, however, being covered by the thick-film structure.
SUMMARY OF THE INVENTION
According to the method of the present invention, a bulge or a self-supporting dome is produced above the recess such that no closed bubble is formed below it. To this end, the layer has a thermal expansion coefficient which is less than that of the substrate. This means that during firing of the latter with the layer placed on it, the substrate expands further in the recess than the active layer and thus the latter forms a bulge over the recess.
Moreover, a dielectric material which can be fired is used for the layer, while the substrate may be made of ceramics, insulated high temperature steel or glass.
What is essential above all is the method step for producing the active layer and its preparation, respectively. It is understandable that this layer cannot be directly applied to the actual substrate, because otherwise it would fall into this recess. According to the invention, an auxiliary substrate is therefore used, and the actual substrate is not connected to the layer until after the layer is produced on this auxiliary substrate. It is preferable to initially print a glass-ceramic layer onto the auxiliary substrate on a glass-ceramic layer, with a hole, whose purpose will be explained below, remaining open in this layer. In any case, the diameter of the hole should correspond to approximately one half the diameter of the thick-film structure which is later to be of a self-supporting configuration. This layer is then fired at approximately 850.degree. C. in air.
Now a filler substance, which may, for example, be carbon, is printed onto the fired layer. The function of this filler substance is primarily to facilitate the subsequent detachment of the active layer as soon as the latter contacts the actual substrate. This is why the outer diameter of the filler substance layer and its outer contours, respectively, are greater than those of the active layer. This filler substance layer is then sintered down also at approximately 850.degree. C. in a nitrogen atmosphere.
Now the actual dielectric layer, which can be fired in a nitrogen atmosphere, is printed on, with the firing of this layer, which also ta
REFERENCES:
patent: 4382247 (1983-05-01), Stecher et al.
patent: 4816200 (1989-03-01), Stecher et al.
patent: 5097386 (1992-03-01), Byell et al.
Stecher Guenther
Zimmermann Herbert
Robert & Bosch GmbH
Utech Benjamin
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