Materials
Substrates
Substrates are supporting materials which carry printed circuits and discrete components. Several substrate materials, which distinguish themselves by their temperature stability, surface roughness, high electrical resistance, chemical resistance and low costs, are in use today. As an example of material, polyester can be named at this point. Polyester is processed with a standardised width of 350mm and run length of several hundred metres at plastic electronic.
Special substrate types are partially metallised substrates, which become conductive, when partially vacuum metallised with achievable coating thicknesses of a few microns of copper or aluminium.
Printing pastes
Printing pastes are used for producing conductive paths, resistors, capacitors, isolating layers or passivation, whereas the compatibility of the pastes as well as their consistency to each other is the main issue for their selection.
For the manufacturing of conductive traces silver, copper, carbon or graphite are preferred materials.
For transparent, conductive layers, PEDOT/PSS or nanoparticles are applied in our systems.
For printing of resistors, resistance-pastes, which show little variance and high stability in their electrical characteristics are integrated. Values of up to 1 MΩ/Square can be achieved. This enables the adaption of geometrical dimensions according to various requirements.
Pastes for overcrossings and multilayer circuits have the main function of isolating the circuit paths from each other; these do have a low dielectric constant, high isolating resistance and electrical breakdown strength.
To a certain extend also capacitors on base of special isolating pastes can be manufactured. (miniaturisation versus electric breakdown strength versus required capacity). These pastes mainly consist of polymers with ceramic particles and have a high dielectric constant in contrast to conventional isolating pastes. A drawback of printed capacitors is their sensitivity to humidity, which can however be decreased by an adequate passivation layer.
Passivation overprinting protect the layers underneath from abrasion and aggressive environments. In addition they can be applied in various colours and can therefore be used for the graphical product design. All pastes are printed on to the substrate and are cured thermally or via UV irradiation.
Special polymers
The competitiveness of special polymers (organic semiconductor materials) in the various areas of electronics arises from the widely known advantages of polymer materials compared to silicon and other inorganic semiconductors.
The advantages of using polymeric functional layers are the following:
- Energy saving and cost effective production
- Cost effective processing of very thin layers as well as on large areas
- Enormous potential for optimizing the electronic characteristics by selectively altering chemically the molecule structur
- Easily recyclable and environmentally friendly disposal
In particular, polymeric semiconductors have two performance limits, which can’t be resolved in short term:
- Relatively low charge carrier mobility with 10-5bis 10-1 cm2/VS
- No guaranty of long term stability can be given yet
The performance limit named first can mostly be avoided by working with very thin and fine structures. It is necessary to protect the polymeric electronic components from harming influences of oxygen and humidity via barrier layers in order to increase the long term stability.
