DZP Technologies Ltd. , Future Business Centre, Kings Hedges Road , Cambridge CB4 2HY , U.K.
Advanced Technology Institute , University of Surrey , Guildford, Surrey GU2 7XH , U.K.
ACS Appl Mater Interfaces. 2018 Jun 27;10(25):21398-21410. doi: 10.1021/acsami.8b04157. Epub 2018 Jun 18.
Printing of highly conductive tracks at low cost is of primary importance for the emerging field of flexible, plastic, and large-area electronics. Commonly, this is achieved by printing of metallic conductive inks, often based on Ag or Cu nanoparticles dispersed in organic solvents. The solvents, which must be safely removed, have particular storage and handling requirements, thus increasing the process costs. By using water-based inks containing micron-sized silver flakes, both material and process costs can be reduced, making these inks attractive for industrial applications. However, the sintering of flake inks requires higher temperatures than nano-sized inks owing to the particles' smaller surface area-to-volume ratio, meaning that when cured thermally the conductivity of many flake inks is lower than nanoparticle alternatives. This problem can be addressed by the application of visible light photonic curing; however, the substrate must be protected and so process parameters must be defined for each material/substrate combination. Here, we report results of a large-scale trial of photonic curing of aqueous flake silver inks on poly(ethylene terephthalate) substrates in an industrial setting. The resistivity of printed patterns after an optimized photocuring regime matched those reported for typical nanoparticle inks; on the order of 100 μΩ cm depending on substrate and geometry. Scanning electron microscopy revealed evidence for structural changes within the printed films consistent with localized melting and necking between adjacent particles, leading to an improved percolation network. Furthermore, in the large-scale industrial trial employing screen-printed silver lines, the manufacturing yield of conductive lines was increased from 44% untreated to 80% after photocuring and reached 100% when photocuring was combined with thermal curing. We believe this to be the first reported observation of an increase in the yield of printed electronic structures following photocuring. We propose a crack-healing mechanism to explain these increases in yield and conductivity. We further report on the effects of the photonic curing on the mechanical bending stability of the printed conductors and discuss their suitability for wearable applications.
在新兴的柔性、塑料和大面积电子领域，以低成本打印高度导电的轨道至关重要。通常，这是通过印刷金属导电油墨来实现的，这些油墨通常基于分散在有机溶剂中的 Ag 或 Cu 纳米粒子。必须安全去除的溶剂具有特殊的储存和处理要求，从而增加了工艺成本。通过使用含有微米级银薄片的水基油墨，可以降低材料和工艺成本，使这些油墨对工业应用具有吸引力。然而，由于颗粒的表面积与体积比较小，片状油墨的烧结需要比纳米级油墨更高的温度，这意味着当热固化时，许多片状油墨的导电性低于纳米粒子替代品。这个问题可以通过应用可见光光子固化来解决；然而，基底必须得到保护，因此必须为每种材料/基底组合定义工艺参数。在这里，我们报告了在工业环境中对聚对苯二甲酸乙二醇酯基底上水性片状银油墨进行光子固化的大规模试验结果。优化光固化条件后，印刷图案的电阻率与典型纳米粒子油墨相当；根据基底和几何形状的不同，电阻率约为 100 μΩ cm。扫描电子显微镜显示，印刷薄膜内存在结构变化的证据，这与相邻颗粒之间的局部熔化和颈部形成一致，从而改善了渗流网络。此外，在采用丝网印刷银线的大规模工业试验中，未经光固化处理的导电线路的制造合格率从 44%提高到 80%，而光固化与热固化相结合时，合格率达到 100%。我们认为这是首次报道在光固化后印刷电子结构的产量增加的观察结果。我们提出了一种裂纹愈合机制来解释这些产量和电导率的提高。我们进一步报告了光子固化对印刷导体的机械弯曲稳定性的影响，并讨论了它们在可穿戴应用中的适用性。
