Conductive inks sintering

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... 

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. 

Grouchko, M., Kamyshny, A., Florentina Mihailescu, C., Florin Anghel, D., Magdassi, S., 2011. Conductive inks with a brult-in mechanism that enables sintering at room temperature. ACS Nano 5 (4), 3354-3359. 

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. 

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

Pure AIN powders are sintered with sintering agents, typically oxides of yttrium or calcium. These additions degrade the thermal conductivity. In addition, moisture and many chemicals attack pure AIN substrates. As protection against these elements, and to promote adhesion to thick-fihn inks, a thin oxide layer is usually grown on the surface. Consequently, the thermal conductivity of AIN can vary widely from its maximum value, reported to be 320 W/(m and is typically in the range of 170 to 200 W/(m K). B. B. Poole of... 

It is standard practice to cure the printed circuits in a drying oven or reflow-soldering oven. There is a direct relationship between dwell time and curing temperature. Low temperatures necessitate long curing times to permit the ink to cure. This is the method of choice for substrates with low thermal durability. The dwell times for silver inks, for example, can be anything from 15 minutes up to 2 hours. The relationship between dwell time and temperature is also reflected in electrical conductivity, which tends to increase with sinter temperature. 

Perelaer, J. et al Plasma and Microwave Flash Sintering of a Tailored Silver Nanoparticle Ink, Yielding 60% Bulk Conductivity on Cost-Effective Polymer Foils. In Journal of Advanced Material, Vol. 24, Issue 29 (2012), pp. 3993-3998. 

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