Line Patterning of Silver Nanoparticle via Nanosecond Pulsed Laser Ablation: the Influence of Pre-Sintering, Heat Affected Zone, and Substrate Thermal Properties

Abstract

In printed electronics, patterns can be manufactured by printing and sintering silver (Ag) nanoparticle(NP) inks. The pulsed laser ablation (PLA) process can be introduced in printed electronics for the purposes of assistant patterning or repairing of misprinted circuits. The nanosecond pulsed lasers have the advantages of cheap cost and better availability, but have the disadvantages of larger thermal influence. This work studies the influence of property variations of the sintering of Ag NP layer and the use of new substrate on the aspects of Ag NP layer ablation. The sintering process of the printed electronics manufacturing causes the Ag NPs to agglomerate and enhance the movement of electrons, thus achieving the electrical conductance required as an electronic circuit. The sintering process also causes characteristic changes in thermal and optical properties of Ag NP. When nanosecond (ns) pulsed laser ablation (PLA) is introduced into the printed electronics manufacturing process, the influence of such property variations must be considered because the ns PLA is essentially a thermal process. The effect of property variations would be more prominent in a line patterning process, as the laser beam irradiates on the spot that has been already irradiated by a previous laser beam. In Chapter 2, the influence of sintering on ablation aspects was investigated by studying the pulsed laser scanning ablation (PLSA) of pre-sintered Ag NP. The results showed that higher thermal conductivity of pre-sintered Ag NP layer with higher sintering temperature leads to wider Heat Affected Zone (HAZ) in the ablated line boundary edge and a higher ablation threshold fluence. The influence of sintering on the line patterning process was further studied in Chapter 3. The results showed that the ablation on a single spot does not guarantee the formation of an ablated line, and the “line ablation threshold” for line patterning was suggested. The line width at the line ablation threshold was similar regardless of the sintering temperature. In Chapter 4, the influence of the HAZ in the vicinity of the ablation crater on the line patterning process was studied in more detail. It was showed that unintended sintering of Ag NPs in the vicinity of ablated crater functioned adversely to the ablation process. When laser irradiation fails to ablate the Ag NPs, the transferred heat sinters the Ag NPs. As compared to the original Ag NPs, HAZ requires more energy for ablation. Also, due to the higher reflectivity, the energy required for HAZ ablation has to be transferred from the Ag NP layer in the vicinity. The failure of Ag NPs ablation due to this phenomenon and the required conditions to minimize such adversity have been introduced. In Chapter 5, the influence of the substrate thermal properties on the PLSA of Ag NP layer was discussed. A comparison on the ablation thresholds of polyimide (PI), glass, and silicon (Si) substrates were done. The difference between PI and glass substrates were not noticeable. The difference Si and the other substrates were noticeable for the Ag NP layers sintered at 150 and 200 °C. Analysis on the results were done based on the thermal properties of the Ag NP layer and the substrates. The results of this work can provide guidance on the influence of property variation of the Ag NP layer and substrate on the Ag NP PLSA process, and can aid future manufacturers to produce refined patterns on Ag NP layer with ns PLSA.