Conductive inks

Figure 12.8. A photograph of a traditional roto-gravure label press that has a web width of 4 in. The press consists of a single gravure head that can be used to apply conductive inks, such as nanoparticle silver suspensions, onto surface-treated polymer substrates to generate patterned interconnects and electrodes.

In conductive inks for continuous ink-jet printers salts such as lithium acetate and potassium cyanate are added to adjust the specific conductivity. 

It is interesting to note that a combined effect of surface tension gradients and evaporation may result in unique structures, namely ring structures. In the graphic arts this is usually a problematic phenomenon, but in functional printing it can be used to obtain interesting properties such as room temperahire conductivity obtained by drops of conductive inks. ... 

The basic formulation requirements and properties of conductive IJ inks are similar to those of standard IJ inks such as for graphics applications, with the major exception that formulations for conductive inks contain components that allow for the most important characteristic of the printed pattern, that is, its ability to conduct electric current. 

For the case of conductive inks, the ink must also conduct electricity after printing. This requirement typically dictates an additional sintering and/ or curing step after the usual IJ printing process. Most conductive ink formulations aim to achieve as low a resistance as possible and the narrowest printed lines possible. To achieve these goals, ink properties, substrate-ink interaction, and printer capabilities must be synchronized. 

Conductive inks may be based on aqueous (water-based) vehicles or on organic solvent systems. Typical solvents for non-aqueous conductive inks are similar to the solvent systems found in... 

Obviously, one of the major concerns in the preparation of the conductive ink is the need for low electrical resistivity. Commercial conductive IJ inks based on silver particles have metal loadings ranging from approximately 20% to 80% by weight. Resistance of a pattern printed from a single pass of a print head is thus expected to be lower for formulations with higher sohds content. However, another factor that influences resistivity is the non-conductive organic load in the ink and in the sintered pattern. Therefore, when choosing... 

One of the substrates that deserves special attention in our discussion is silicon (Si), and in particular Si wafers for producing solar cells. A variety of sirrface treatments are applied to Si in the solar cell industry Native Si vs. chemically protected (SiN, for example), pohshed versus unpohshed versus patterned to give surface texture, etc. In order to ensirre proper Si-metal contacts, careful control of the conductive ink composition is required. In addition, very high curing temperatures are usually employed in the manufacture of solar cells, thus there is a need for a suitable binding component. Special care is taken to avoid excessive diffusion of metal into the emitter layer, nevertheless, somewhat limited diffusion is desirable so that contact resistance is adequate. ... 

A conductive ink is coated or printed in a simple pattern having length L and width B and is then sintered according to manufacturer s specifications. 

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