ALBERT

Notes: In the present study, Functionally gradient HA-ZrO2-Ti coatings (FGC) on Ti6Al4V wereprepared by the plasma spraying process. The residual stress and surfacial morphology of coatingwere studied by X-ray diffraction and scanning electron microscopy with an energy dispersivespectroscopy. The results showed that: (1) the residual stress of FGC is 72.1Mpa, much lower thanthat of single HA coating, (2) The surfacial morphology of the FGC showed typical characteristics ofplasma-sprayed coating, no microcracks was observed because of its the thermal expansion matchedbetween the gradient coating and substrate

Notes: The PCL plates hydrolyzed by NaOH aqueous solutions and carboxylate groups wereintroduced onto the surfaces of specimen. Specimens were treated by CaCl2 and K2HPO4⋅3H2O underthe normal-pressure condition and low-pressure of 103 Pa condition for 30min separately. Dense anduniform bone-like layers could be formed on the surface of specimens after mineralizing for less than24h in simulated body fluids (SBF). The low-pressure condition could accelerate the formation ofapatite layer

Notes: In this article, a multilayer tissue engineering scaffold has been fabricated. The uppermost layeris consisted by the collagen and the downmost layer is consisted by the collagen/hydroxyapatide.Between the two layers, there have several continues changed collagen/HA layers at different ratio. Thesegradient scaffolds have been made by the freeze dried method. The morphology of the multiphasescaffold has been observed by the SEM. The chondrocytes from New Zealand rabbit knee joint wereseparated, harvested and cultured on the top layer of the scaffold. The histological and the immunohistochemicaltesting show that the chondrocytes keep its normal type in the 2 culture weeks

Notes: In this study, the bioactive composites based on β-tricalcium phosphate (β-TCP),bioglass (BG) and poly lactic acid (PLA) were prepared. The microstructure, degradability andreaction products of the scaffold soaked in a simulated body fluid (SBF) at 36.5℃ for different dayswere characterized through scanning electron microscopy (SEM), energy-dispersive X-ray analysis(EDS), X-ray diffraction (XRD), Fourier transformed infrared spectroscopy (FT-IR) and inducedcoupled plasma spectroscopy (ICP). The weight loss and strength decrease with the time were tested.The results showed that at the same porosity, the degradability of the scaffold samples decreased asfollowed: β-TCP/BG/PLA〉β－TCP/BG〉β－TCP.The materials had highly bioactive responseability to the Simulate Body Fluid (SBF) and promptly induced a bone like HA layer on the surfaceof the scaffolds when immersed in the SBF

Notes: In the present study, bioactive functional gradient coatings were prepared using net-energycontrolled plasma spraying technology. The microstructure and phases of the bioactive functional gradientcoating were examined by means of transmission electron microscope, scanning electron microscopyand X-ray diffraction. The results revealed that: (1) as-sprayed coatings contained a large amount ofamorphous phases and some nano-sized HA crystals formed during rapid solidification, (2) surface of thecoating was very rough with different-sized micropores, and the gradient layer was much denser whichfirmly bonded to the substrate without gaps and obvious interface between the coating and the substrate

Notes: A reflow profile is proposed which is engineered to optimize soldering performance based on defect mechanism analysis. In general, a slow ramp-up rate is desired in order to minimize hot slump, bridging, tombstoning, skewing, wicking, opens, solder beading, solder balling, and components cracking. A minimized soaking zone reduces voiding, poor wetting, solder balling, and opens. Use of a low peak temperature lessens charring, delamination, intermetallics, leaching, dewetting, and voiding. A rapid cooling rate helps to reduce grain size as well as intermetallic growth, charring, leaching and dewetting. However, a slow cooling rate reduces solder or pad detachment. The optimized profile favors that the temperature ramps up slowly until reaching about 180°C. Implementation of the optimized profile requires the support of a heating-efficient reflow technology with a controllable heating rate. Emergence of the forced air convection reflow provides a controllable heating rate. In addition, it is not sensitive to variation in parts' features, thus allows the realization of the optimized profile.

Notes: Two new electrolytically plated lead-free surface finishes are evaluated for their wettability, bond strength, and voiding performance, and are compared with electrolytic nickel gold and an OSP. The results indicate that Ni–Sn achieve the highest wettability, one of the highest lap shear strengths, and the lowest levels of voiding. It also performs better under a long reflow profile. Under most instances, the soldering performance is comparable with, or better than, the reference OSP and Ni–Au surface finishes. Ni–PdCo–Au was found to give a poor wettability, fairly low lap shear strength, and have high levels of voiding. However, it is fairly stable, and its soldering performance is not sensitive to the reflow profile length or atmosphere, aging treatment, or flux chemistry. OSP was found to be the poorest in terms of wettability, but one of the best for lap shear strength. It also performs best under long profile, is not sensitive to reflow atmosphere, is slightly sensitive to alloy type, but is very sensitive to aging and flux chemistry.

Notes: Purpose - Tombstoning and voiding have been plaguing the surface mount assembly industry for decades. The recent global move toward lead-free soldering and the extensive adoption of microvia technology further aggravate the problems. The present study investigates the impact of SnAgCu (SAC) alloy composition on these important issues. Design/methodology/approach - In this study, tombstoning and voiding at microvias are studied for a series of SAC lead-free solders, with an attempt to identify a possible "composition window" for controlling these problems. Properties which may be related to these problems, such as alloy surface tension, alloy melting pattern, and solder wetting behaviour, were investigated in order to assess the critical characteristics required to control these problems. Findings - The results indicate that the tombstoning of SAC alloys is greatly influenced by the solder composition. Both the wetting force and the wetting time at a temperature well above the melting point have no correlation with the tombstoning frequencies. Because the tombstoning is caused by imbalanced wetting forces, the results suggest that the tombstoning may be controlled by the wetting at the onset of the paste melting stage. A maximum tombstoning incidence was observed for the 95.5Sn3.5Ag1Cu alloy. The tombstoning rate decreased with increasing deviation in Ag content from this composition. A differential scanning calorimetry (DSC) study indicated that this was mainly due to the increasing presence of the pasty phase in the solders, which result in a slower wetting speed at the onset of solder paste melting stage. Surface tension plays a minor role, with lower surface tension correlating with a higher tombstoning rate. The voiding rate at the microvias was studied by employing simulated microvias. The voiding level was lowest for the 95.5Sn3.8Ag0.7Cu and 95.5Sn3.5Ag1Cu alloys, and increases with a further decrease in the Ag content. The results indicate that voiding at microvias is governed by the via filling and the exclusion of fluxes. The voiding rate decreased with decreasing surface tension and increasing wetting force, which in turn is dictated by the solder wetting or spreading. Both low surface tension and high solder wetting prevents the flux from being entrapped within a microvia. A fast wetting speed may also facilitate reducing voiding. However, this factor is considered not as important as the final solder coverage area. Research limitations/implications - In general, compositions which deviate from the ternary eutectic SAC in Ag content, particularly with a Ag content lower than 3.5Ag, exhibit a greater solid fraction at the onset of melting, resulting in a lower tombstoning rate, presumably due to a slower wetting speed. The SAC compositions with an Ag content lower than 3.5 per cent, such as 2.5Ag, resulted in a lower tombstoning rate with minimal risk of forming Ag3Sn intermetallic platelets. On the other hand, ternary eutectic SAC exhibits a lower surface tension resulting in an easier solder spread or solder wetting, and consequently exhibit a higher tombstoning frequency and a lower incidence of voiding. Practical implications - Provides a solution to the tombstoning problem in lead-free soldering. Originality/value - The present study provided a solution to the tombstoning problem encountered in lead free soldering by controlling the SAC solder alloy compositions.

Notes: The rheology of solder paste significantly affects the qualities of stencil printing, tack and slump performance. This paper describes a series of tests performed on solder paste to investigate and determine the rheological properties of a group of solder pastes and fluxes, and the correlation of those properties with paste performance prior to reflow. Data indicate that: the incidence of print defects are proportional to the material's compliant qualities (J1 and J2) and are inversely proportional to the elastic properties (G¢/G¢¢ and recovery) and meta-rigidity (yield stress); slump resistance is proportional to elastic properties (recovery), solid characteristics (stress [G¢ = G¢¢]), and rigidity (|G*|); and that high elastic properties (recovery), low compliance (J1 and J2), and low solid characteristics (stress [G¢ = G¢¢]) are required in order to achieve high tack value. Good correlation between fluxes and solder pastes were observed for yield stress and recovery only, suggesting that those two properties are primarily dictated by fluxes.