Sinter inks

Reported volume resistivities for printed patterns formed from commercial silver-based inks are higher than that of bulk silver. This occurrence reflects the fact that sintered ink patterns contain non-ideal defects such as incomplete particle-to-particle contact, incomplete sintering between contacting particles, residual porosity, and the presence of non-conductive additives. The morphology and extent of void formation in two representative sintered silver nanoparticle inkjet inks are illustrated in Fig. 1. 

The applications of the nanoparticles and structures that we have surveyed here have extended from various kinds of sensors and analytical devices, through spectrally selective coatings and sinter inks to medical diagnostics and therapeutics. Nanoscale gold must surely be one of the most versatile and valuable materials systems available ... 

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. 

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... 

Adhesion of the ink to the substrate is largely dependent on the substrate type and its surface treatment and it can also depend strongly on sintering or curing conditions. Maximal curing temperature is dictated by the resistance of the substrate to heat. Both the glass transition temperature (T ) and the melting characteristics of the substrate must be considered. 

Fig. 1. Morphology of nanosilver inks after sintering. High resolution scanning electron micrographs of cross-sections of inkjet printed features after sintering at 150°C for 60 minutes (a) Cima Nanotech ink, (b) Cabot ink.

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. 

Perelaer J, Gans BJ, and Schubert US. (2006) Ink-jet printing and microwave sintering of conductive silver tracks. Adv Mater 18 2101-2104. 

Suspensions or dispersions of particles in a liquid medium are ubiquitous. Blood, paint, ink, and cement are examples that hint at the diversity and technological importance of suspensions. Suspensions include drilling muds, foodstuffs, pharmaceuticals, ointments and cremes, and abrasive cleansers and are precursors of many manufactured goods, such as composites and ceramics. Control of the structure and flow properties of such suspensions is often vital to the commercial success of the product or of its manufacture. For example, in consumer products, such as toothpaste, the rheology of the suspension can often determine consumer satisfaction. In ceramic processing, dense suspensions are sometimes molded (Lange 1989) and then dried and sintered or fired into optical components, porcelin insulators, turbine blades, fuel cells, and bricks (Rice 1990 Simon 1993). Crucial to the success of the processing is the ability to transform a liquid, moldable suspension into a solid-like one that retains its shape when removed from the mold. These examples could be multiplied many times over. 

Y. Murata and R. Smoak in S. Somiya and S. Saito, eds., Proc. Ink Sjmp. of Factors in Densification and Sintering of Oxide and Nonoxide Ceramics, Gakujutsu Bunkeri Fukyu-Kai, Tokyo, 1979, p. 382. 

To overcome these difficulties, printable compositions were formulated. The printable sensor inks contained three major components the metal oxide, glass frit for adhesion, and organic vehicles that burn off during firing. A catalyst, in the form of a precious metal chloride, was applied and fired on the sintered metal oxide layer alternatively, precious metal resinate solutions were incorporated directly into the ink. Initial tests of these printable layers demonstrated sensor resistivities that changed rapidly and reversibly by as much as a factor of 14. The response time was a few seconds while recovery took about 1 min, although complete recovery was often longer than 16 h. 

Inks having a fluorocarbon base can be used to print stripe patterns on wire for identification. In practice a wheel coated with the desired color runs along the wire prior to the sintering step of the manufacturing process. For more than one stripe, additional wheels are needed. The ink is sintered at the same time as the insulation. PTFE and FEP dispersion have been used as the base to produce ink. Inorganic pigment that is stable under the sintering conditions of polytetrafluoroethylene must be used. 

For the preparation of a symmetrical cell, the composite LSM-YSZ was prepared on both sides of a 0.4 mm thick YSZ substrate, which was used as an electrolyte. For a fuel cell preparation, prior to cathode deposition Ni-YSZ powder ink (Ni 45 wt%) was screen printed on the YSZ substrate and sintered at 1,400°C for 1 h. 

---