A metallic anti-biofouling surface with a hierarchical topography containing nanostructures on curved micro-riblets

Metallic surface finishes have been used in the anti-biofouling, but it is very difficult to produce surfaces with hierarchically ordered structures. In the present study, anti-biofouling metallic surfaces with nanostructures superimposed on curved micro-riblets were produced via top-down fabrication. According to the attachment theory, these surfaces feature few attachment points for organisms, the nanostructures prevent the attachment of bacteria and algal zoospores, while the micro-riblets prohibit the settlement of macrofoulers. Anodic oxidation was performed to induce superhydrophilicity. It forms a hydration layer on the surface, which physically blocks foulant adsorption along with the anti-biofouling topography. We characterized the surfaces via scanning electron and atomic force microscopy, contact-angle measurement, and wear-resistance testing. The contact angle of the hierarchical structures was less than 1°. Laboratory settlement assays verified that bacterial attachment was dramatically reduced by the nanostructures and/or the hydration layer, attributable to superhydrophilicity. The micro-riblets prohibited the settlement of macrofoulers. Over 77 days of static immersion in the sea during summer, the metallic surface showed significantly less biofouling compared to a surface painted with an anticorrosive coating.

Effect of Ni(P) Layer Thickness on Interface Reaction and Reliability of Ultrathin ENEPIG Surface Finish

Electroless Ni(P)/electroless Pd/immersion Au (ENEPIG) is a common surface finish in electronic packaging, while the Ni(P) layer increases the impedance of solder joints and leads to signal quality degradation in high-frequency circuits. Reducing the thickness of the Ni(P) layer can balance the high impedance and weldability. In this paper, the interfacial reaction process between ultrathin ENEPIG substrates with different Ni layer thicknesses (0.112 and 0.185 μm) and Sn–3.0Ag–0.5Cu (SAC305) solder during reflow and aging was studied. The bonding ability and reliability of solder joints with different surface finishes were evaluated based on solder ball shear test, drop test and temperature cycle test (TCT), and the failure mechanism was analyzed from the perspective of intermetallic compound (IMC) interface growth. The results showed that the Ni–Sn–P layer generated by ultrathin ENEPIG can inhibit the growth of brittle IMC so that the solder joints maintain high shear strength. Ultrathin ENEPIG with a Ni layer thickness of 0.185 μm had no failure cracks under thermal cycling and drop impact, which can meet actual reliability standards. Therefore, ultrathin ENEPIG has broad prospects and important significance in the field of high-frequency chip substrate design and manufacturing.

Electromigration and Flux Residues

Electromigration and its subcategory electrochemical migration is a serious problem in electronic industry working with printed circuit boards (PCB). Smaller equipment with high density of interconnection (HDI) is assembled with surface mounted devices (SMD) and through hole components (THC) Assembly techniques are realised mainly by soldering process with no clean fluxes. Result is not only a reliable solder joint, but also flux residues. The first part of the article after short theory is focused on gatering basic knowledge about fluxes and surface finishes by using cyclic voltammetry (CV) and electrochemical impedance spectrometry (EIS). The second part of the experiments is oriented on practical test with different fluxes for wave and reflow soldering. These tests are associated with the reduction of surface insulation resistance, corrosion, dendrite/fiber growth and the formation of subsequent short circuits. The acceleration of these electrochemical reactions is helped by higher working temperatures, higher humidity, and magnitude \ and frequency of electrical voltage between the conductors.

The Effect of Surface Finishes on Rising Damp in Oriented Strand Board

It is known that oriented strand board (OSB) is prone to water absorption. This characteristic of OSB is undesirable, it can have a negative impact on the physical and mechanical properties of the material and it can also make it prone to attack from wood-destroying insects, rot or mould. The research follows previous work of the authors related to optimisation of surface finishes for OSB in order to increase its moisture resistance. The aim of the research is to compare the rise of dampness in test specimens with different types of coating, spray, primer and waterproofing under predefined conditions. The paper contains a definition of the basic material, test specimens and test methods, and covers 8 different types of surface finish materials selected for application to the test specimens. The results include graphs showing rise of dampness in the test specimens for each day of observation. The results are also discussed and in the conclusion the results are evaluated. The results of the experiments confirm the assumption that the choice of surface finish has a significant effect on slowing down the rise of dampness in OSB.

Image-based goniometric appearance characterisation of bronze patinas

Patinas are a form of metal polychromy used to decorate metallic artworks. Due to the nature of the metallic surface, their colour and gloss is perceived differently when the illumination and viewing directions vary. Sparkle effect on surfaces is a physical phenomenom caused by micro-facets on the surface coating which are also perceived with changing viewing and illumination geometry. In this paper, a method designed for the measurement of sparkle is applied for the goniometric characterisation of bronze patinas. Using a set of six different patinas, in three colours and two surface finishes, it is found that these surfaces exhibit different appearance when illuminated and viewed at different angles. Moreover, the roughness of the patinas is measured and as expected, as the roughness increases the specular reflection peak decreases. The experiment is repeated at two different institutions with different sets of equipment to test its repeatability and robustness. The sparkle is presented as a function of the angle of tilting, and it is characterised by its maximum value and full-width halfmaximum. It is found that the maximum and the roughness have a negative exponential relationship whereas the full-width halfmaximum and the roughness have a linear relationship.