This paper describes fabrication of a nano-textured surface on a fluorocarbon thin film using atmospheric-pressure microplasma (μ-AP; NU-Eco Engineering). Results show that a textured surface with vertical bumps of several tens of nanometers can be fabricated on a fluorocarbon 1.0-μm-thick thin film coated onto a steel substrate when argon gas is supplied with a 4.0 dm3 min−1 flow rate. The plasma-treated surface roughness decreased concomitantly with increased processing distance. Moreover, the horizontal intervals of the bumps are influenced by annealing treatment conditions. From measurement results obtained using atomic force microscopy (AFM), results show that non-uniformity of fluorocarbon polymer orientation, which is detectable as fluctuations in friction force, in the coating film before the plasma treatment is correlated with the number density of bumps fabricated by the plasma treatment, indicating that well-oriented fluorocarbon polymers are difficult to etch using plasma treatment. Furthermore, chemical bond components of C1s were analyzed using X-ray photoelectron spectroscopy (XPS) before and after treatment. Results show that C-H and C-C bonds are fewer after the plasma treatment, but C-O and C=O bonds are more numerous. The oil contact angles changed concomitantly with the change in surface morphology and chemical bond components according to the plasma treatment.
This study investigated the effects of a corrosive atmosphere on whisker growth of a Sn film and a Sn/Cu film that were electrodeposited onto a 42 alloy substrate. No whiskers were generated on the Sn single layer. However, numerous whiskers with length exceeding 100 μm were generated on the Sn/Cu double layer during 7000 hr in an ambient atmosphere. The whisker generation and growth of both the Sn single layer and the Sn/Cu double layer changed remarkably during 7000 hr under a corrosive atmosphere. This whisker growth behavior that occurred in the corrosive atmosphere was attributed to both the change of the Cu6Sn5 compound based on the mutual diffusion and the state transition of oxide film, depending on corrosion of the Sn film at the surface side.
With increasing thickness of electroless gold films (greater than 0.5 μm) as a top layer, Au/Ni film shows good wire bondability. However, we confirmed that the deposited nickel structure influences wire bondability for thinner (less than 0.5 μm) electroless gold plating after heat treatment because of the different diffusion behavior of gold on the deposited nickel used as an underlayer. In this study, two types of electroless nickel plating structure with columnar and layered structure were observed and bondability was evaluated. Auto-catalytic gold of 0.2 μm thickness on the layered nickel deposits shows good wire bondability after heat treatment because the gold was deposited uniformly. In contrast, for a columnar structure, the gold on the Ni films shows poor wire bondability after heat treatment because of local corrosion occurring at the initial stage of gold immersion and because the subsequent auto-catalytic gold is not evenly distributed.