Development of novel nano-coating applied on metal stencils used in the manufacture of printed circuit boards and similar products.

Abstract

The tenacious desire to obtain a mechanically improved, tribologically enhanced, and hydrophobic surface has driven extensive research into advanced coating techniques and materials. This will enhance the application of the surfaces in various automobile and structural applications. This enhancement will not only help reduce material wastage but also improve energy efficiency. It is well-known that surface topography and roughness are efficacious in improving tribological properties. For improving the surface properties various coatings are admitted on the surface. Electrodeposition is one such coating method which copes with all these applications. The elements used in electrodeposition and physical-chemical parameters of coating can be modified to improve the properties of the coating for specific applications. Combined with surface topography, coating can be instrumental in improving the tribological properties of surfaces. Electrodeposition coating is one of the traditional techniques which can be varied in physical and chemical parameters. Therefore the selection of parameters is one of the important steps in the electrodeposition coating technique which can help to select the best coating according to its applications. The Electronics industry is evolving every day, thereby in need of an improved coating in the moving parts, such as hard drives, stencils, etc. Stencil boards which are used in the application of solder paste into circuit boards have been a focus wherein an improved tribological performance along with an improved hydrophobic property is essential. Ni-Co is a seemingly competent candidate in the electronics industry due to its astonishing ferromagnetic properties. The limited literature on coating with Ni-Co calls for in-depth research on the said coating. In this context influence of the roughness parameter over the nanotribological and contact angle of Ni- Co pulse electrodeposition coating is imminent. Therefore, in the current work, Ni-Co pulse electrodeposition coating with various reinforcing nanocomposites is performed. The physical parameters, duty cycle and current density of Ni-Co coating are varied in order to obtain the optimum properties. The duty cycle is varied from 20% to 100% with 20% increment and current density 3 A/dm2 to 9 A/dm2 with an increment of 3 A/dm2. The other physical parameters, including frequency, temperature, stir speed, and pH were kept constant. The grain size was seen to decrease with the increase in duty cycle and current density. The change in duty cycle was mainly associated with the lower duty cycle, where the current OFF time is high allowing more particles to adhere to substrate. Similarly, with an increased current density, the overpotential leads to the increase in the grain size of coating. With these, initiation of grain growth increases leading to a decrease in grain size. This further led to an increase in nanohardness of the coating, which subsequently helped in improving the nanotribological properties of coating at lower duty cycle and current density. The improvement in tribological properties is due to the synergistic effect of lower grain size and higher hardness of coating surface. The change in contact angle was associated with varied roughness parameters. The influence of reinforcing nanocomposites was explored, with Al2O3, SiC, ZrO2 and PTFE as reinforcing nanocomposites. The optimized physical parameters obtained earlier were utilized with reinforcing nanocomposites varied. The grain size was seen to decrease further with the addition of reinforcing nanocomposite. The change in grain size was characterized by reinforcing nanocomposites, which inhibited grain growth at substrate, leading to increased grain growth sites and lower grain size. The nanohardness of reinforcing nanocomposite coatings was seen to improve more than Ni-Co coating, which was due to the synergistic effect of lower grain size and dispersion strengthening. The increase in hardness and lower grain size further influenced nanotribological properties, which were seen to improve with the addition of nanocomposites. The water contact angle of coatings were also analyzed, which was greatly influenced by roughness of surfaces. PTFE was found to be the optimum candidate with improvement in nanotribological and contact angle properties. To understand the optimum reinforcing nanocomposite required for improved properties, PTFE content was varied from 10 g/L to 30 g/L in Ni-Co coating. Saccharin was added to improve aesthetics of coating with CTAB for improving the zeta potential. The additives caused an improvement in the coating which was best observed at 20 g/l of PTFE. The EDS confirmed presence of PTFE. The nanohardness was seen to decrease with increase in PTFE, corresponding decrease in reduced modulus was also observed. Regardless of decrease in nanohardness, improvement in nanotribological properties was obtained for 20 g/L of PTFE when compared to Ni-Co nanocoating, which was due to the lower reduced modulus. The contact angle was also seen to improve with increase in PTFE content, which was due to the synergistic effect of PTFE and Svk/Sk ratio. Svk/Sk ratio is seen to have a higher influence on contact angle rather than surface roughness, which creates air pockets reducing sagging of water into the coating, making coating surface hydrophobic. To further improve the hydrophobic nature of coatings, post-process functionalization was performed with stearic acid and mystic acid. The contact angle was seen to increase with functionalization, due to the hydrophobic effect of functionalization and Svk/Sk roughness ratio. Mystic acid functionalization was observed to have a better hydrophobic and nanotribological properties, which makes it the optimum coating candidate for the coating.