The thick film technique is a very flexible and cost-effective technology for producing functional layers on green or fired ceramics. In this process viscous pastes are pressed through a structured screen or stencil and deposited on a ceramic substrate. The thickness of these layers can vary from 1 to 300 μm and line width from 100 μm to 1 or more millimeters. It is possible to print on both plane and tubular substrates.
These pastes are required for many different applications. The pastes are basically composed of functional powder containing all active ingredients, and an organic paint vehicle which is burned out in case of glass-bound pastes.
For screen printing the pastes must have the following properties which are determine by the interaction of the particles and the viscosity of the organic binder:
- Storage stability (no segregation, no sedimentation, no chemical alteration)
- Reduction of viscosity over many orders of magnitude until passing the screen
- Sufficient wetting of squeegee, screen and substrate
- Well defined relaxation during leveling
- Adhesion of dried layer on the substrate
The properties of the layer are determined by the functional powder, its concentration, grain size distribution, composition and distribution in the paste.
Thick film applications are mainly used in microelectronics, microwave technology, sensors and energy systems.