Near-IR sintering of conductive silver nanoparticle ink with in situ resistance measurement

Metal nanoparticle inks are excellent options for printing low-resistance metal conductors and electrical interconnects. However, after deposition, these inks require high-temperature annealing to sinter and increase conductivity. Infrared (IR) heaters are an efficient, roll-to-roll compatible method to apply thermal energy. Here, we characterize the effect of near-infrared (N-IR) heating on the structure and properties of printed silver nanoparticle ink (UTD Ag40x, UT Dots Inc.). A method was developed to measure the resistance and temperature of printed conductive inks as a function of exposure to the IR heater. The N-IR heater was found to sinter the Ag40x silver samples (lower the resistance of 7 mm printed lines to 1000 Ω) in 11.6 ± 1.5 min at maximum intensity with a large drop from the highest measured resistance (60 MΩ) to 1000 Ω in 1.2 ± 0.2 min. Decreasing the heater power increased the time to reach 1000 Ω (to 28.3 ± 2.0 min at 80%), but reducing from 60 MΩ to 1000 Ω still only took 1.9 ± 0.3 min. This suggests sintering progresses rapidly once initiated. SEM images of the ink before and after IR heating show microstructural changes associated with sintering and indicate the role of agglomerates and organic binders in impeding sintering.