Inkjet printing is an excellent printing technique and an attractive alternative to conventional technologies for the production of flexible, low-cost microelectronic devices. Among many parameters that have a significant impact on the correctness of the printing process, the most important is ink viscosity. During the printing process, the ink is influenced by different strains and forces, which significantly change the printing results. The authors present a model and calculations referring to the shear rate of ink in an inkjet printer nozzle. Supporting experiments were conducted, proving the model assumptions for two different ink formulations: initial ink and with the addition of a dispersing agent. The most important findings are summarized by the process window regime of parameters, which is much broader for the inks with a dispersing agent. Such inks exhibit preferable viscosity, better print-ability, and higher path quality with lower resistivity. Presented results allow stating that proper, stable graphene inks adjusted for inkjet technique rheology must contain modifiers such as dispersing agents to be effectively printed.

Immersion tin is widely used as a lead free surface finish in the printed circuit board technology. Tin prevents the underlying copper from corrosion and preserves its solderability during a long storage and lead-free assembly processes. Investigated immersion tin coatings were deposited on copper foil from thiourea-type baths with hydrochloric acid addition (SnHCl coatings) or methanesulfonic acid addition (SnMSA coatings). Obtained coatings were investigated in the as deposited state and after aging (4 h at 155 8C, in air). The scanning electron microscopy studies revealed differences in structure of tin samples deposited from different baths. Results of polarization and impedance investigations indicated that as deposited SnHCl coatings had better corrosion resistance in 0.5 M NaCl solution than SnMSA coatings. The aging resulted in the improvement of the corrosion resistance of thinner coatings (0.2 and 0.5 mm thick SnHCl and 0.3 mm thick SnMSA), which were thoroughly converted into Sn-Cu intermetallic (IMC) phases. In contrary, thicker coatings exhibited some worsening of the corrosion resistance upon aging. The solderability of all as-deposited tin coatings was acceptable, but decreased after aging, especially for thinner coatings, showing the through conversion into Sn-Cu IMC phases.

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