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It is difficult to correlate the rheological data collected under very controlled conditions with a printing process. The printing speed, scale, geometry, press setting, substrate, chemical contaminants etc. make it difficult to analyze the exact working conditions. Shear rates can be significantly higher in printing processes than in a rheometer. Thus indirect correlation is sometimes necessary to deduce projected behavior when transitioning from lab to press. Properties of the dry ink are also important to the functionality of a device constructed from electronic inks. Tests like adhesion, rub resistance and solvent resistance provide an indication of the robustness of the printed materials. However, due to variability in processes, applications and substrates, there are no well defined standard ranges for such properties [23].
Most commercially available conductive inks are comprised of finely dispersed conductive particles in a non-conductive resin matrix which bind the particles. The particles may be metallic copper, silver or aluminum or non-metallic conductive carbon blacks. The volume fraction of the conductive particles is generally maintained above the percolation threshold, the minimum volume fraction required for inter-particle connectivity. The inks may be used to produce conductive patterns on flexible and rigid substrates. The flexo/gravure inks are generally water-based and the litho inks are oilbased. Conductive inks are compatible with a variety of blankets, plates and substrates These inks have low volatile organic chemical content and are considered to be environmentally-friendly. Line resolution of 50 microns (2 mil) are achievable with the flexo/gravure inks, and 40 microns (1 mil) with the litho inks. The inks have sheet resistance as low as 100 / at a film thickness of approximately 8 microns. For printedresistors, ink formulations can be tuned to cover a wide range of sheet resistance (100/ – 500/) at a film thickness of 2 microns or less. [24]
The conductivity in a given ink formulation is governed by the printing process, drying method, substrate etc. The conductivity measurements are typically analyzed in terms of sheet resistivity (s)
s = (resistance of a rectangular region of the printed conductor)*(width of region) (length of region)
The length of the conductive region pided by the width implies number of equal sided squares being measured. Hence sheet resistivity is reported in ohms per square (/). Lithographic inks: These are highly viscous inks (paste inks). The tack or splitting of the ink between 2 rolls is an important property to be considered in multi-impression printing. Lithographic conductive inks must be designed such that they do not chemically dissolve in image or non-image areas on the printing plate. A common problem with lithographic inks is that splitting of ink filaments can lead to uneven texture. Inks should exhibit the phenomenon of “trapping”. In this phenomenon, the first layer printed onto the substrate shows the ability to become more receptive to subsequent printed layers. Flexographic inks: These are relatively low viscosity inks (fluid inks). Low viscosity is necessary because the ink needs to flow into the cells of the anilox rolls of the press. The inks must be designed to be readily re-dispersible over the lifetime of the product. Various dispersing agents and binders may be used to obtain optimum properties. [23]
采用光刻的角度来看概述的常规模式的电子模式的电子以获得特定的设计可能常规进行在硅晶片上。这是一个将映像和模式从面具转移到硅晶片的表面的过程。光刻工艺中通常所涉及的步骤是 ︰ 硅片清洗、 屏障层的形成、 光刻胶中的应用、 软烘烤、 掩模版对准、 暴露和发展和硬烘烤。
硅晶片首先用化学处理以去除颗粒物、 有机污染物和离子和金属杂质。接下来,在整个晶圆片表面种植被动硅氧化物阻挡层。任何积极或消极的抗蚀剂层然后采用旋涂法。软烤照片成像中扮演非常关键的作用。在软烘烤步骤中，从光致抗蚀剂涂层去除，用到大部分的溶剂。这一光致抗蚀剂层然后满合适的面罩和暴露在光化性辐射。后照片曝光和职位曝光烘烤，抵抗被开发的选择性溶剂，揭示面具上的图案正面的或负面的形象。(积极 ︰ 暴露的材料是被去除，消极 ︰ 移除未曝光的材料)。在最后一步，该晶片是烤硬的残余溶剂去除光刻胶，提高对硅片表面光致抗蚀剂的附着力。抵制保护晶片的表面，并允许选择性蚀刻、 掺杂、 ionimplantation 或金属。最近的改进和技术进步的光刻技术领域作出可能获得附近纳米尺寸的电路。[1]。