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Since 2001, 3D microfabrication based on two‐photon polymerization (TPP) has drawn extensive attention and interest in biology, optics, photonics, material science, and high‐energy physics. The in‐volume fabrication capability due to the threshold behavior of two‐photon absorption enables TPP higher flexibility compared with other nanofabrication techniques. However, as determined by the in‐volume fabrication feature as well as various reaction dynamics, the writing characteristics of TPP, such as throughput, accuracy, surface quality, and fabrication capability, are still limited. Herein, a comprehensive study is performed on the spatiotemporal behavior of reaction dynamics during TPP fabrication, mainly focusing on spatiotemporal characteristics of radical diffusion, photothermal effect, microscale mechanics, and voxel stacking process. Based on the study, a nonsequential fabrication method is established to simultaneously improve key writing characteristics of TPP and realize sharp features, high speeds, large overhang structure, and smooth surfaces. The method established in this work can be applied to improve the performance of functional devices for various fields. [ABSTRACT FROM AUTHOR]

Injection moulding (IM) is a manufacturing technique used to produce intricately detailed plastic components with various surface finishes, enabling the production of high-tolerance functional parts at scale. Conversely, stereolithography (SLA) three-dimensional (3D) printing offers an alternative method for fabricating moulds with shorter lead times and reduced costs compared to conventional manufacturing. However, fabrication in a layer-by-layer fashion results in anisotropic properties and noticeable layer lines, known as the stair-step effect. This study investigates post-processing techniques for plaques with contrasting stair-step effects fabricated from commercially available SLA high-temperature resin, aiming to assess their suitability for IM applications. The results reveal that annealing significantly enhances part hardness and heat deflection temperature (HDT), albeit with a trade-off involving reduced flexural strength. Experimental findings indicate that the optimal stage for abrasive surface treatment is after UV curing and before annealing. Plaques exhibiting contrasting stair-step effects are characterized and evaluated for weight loss, dimensional accuracy, and surface roughness. The results demonstrate that abrasive blasting effectively removes the stair-step effect without compromising geometry while achieving polished surface finishes with roughness average (RA) values of 0.1 μm through sanding. Overall, a combination of abrasive blasting and sanding proves capable of precisely defining surface roughness without significant geometry loss, offering a viable approach to achieving traditional IM finishes suitable for both functional and aesthetic purposes. [ABSTRACT FROM AUTHOR]

Injection moulding (IM) is a manufacturing technique used to produce intricately detailed plastic components with various surface finishes, enabling the production of high-tolerance functional parts at scale. Conversely, stereolithography (SLA) three-dimensional (3D) printing offers an alternative method for fabricating moulds with shorter lead times and reduced costs compared to conventional manufacturing. However, fabrication in a layer-by-layer fashion results in anisotropic properties and noticeable layer lines, known as the stair-step effect. This study investigates post-processing techniques for plaques with contrasting stair-step effects fabricated from commercially available SLA high-temperature resin, aiming to assess their suitability for IM applications. The results reveal that annealing significantly enhances part hardness and heat deflection temperature (HDT), albeit with a trade-off involving reduced flexural strength. Experimental findings indicate that the optimal stage for abrasive surface treatment is after UV curing and before annealing. Plaques exhibiting contrasting stair-step effects are characterized and evaluated for weight loss, dimensional accuracy, and surface roughness. The results demonstrate that abrasive blasting effectively removes the stair-step effect without compromising geometry while achieving polished surface finishes with roughness average (RA) values of 0.1 μm through sanding. Overall, a combination of abrasive blasting and sanding proves capable of precisely defining surface roughness without significant geometry loss, offering a viable approach to achieving traditional IM finishes suitable for both functional and aesthetic purposes.

This paper deals with the design of an experimental circular channel model specially adapted for particle image velocimetry (PIV) measurements of airflow. The goal is to find a simple, fast, and functional approach for creating experimental models. The issue of the required PIV signal quality is defined, and the limits of acquiring relevant PIV data in the interior of circular channels are described, primarily as reflections of direct and scattered laser light caused by light passage through the cylindrical wall. As part of the experiment, measurements of reflections were made on differently coated surfaces of a plexiglass plate. Samples of various combinations of black matt spray, Rhodamine 6G coating, and roughened surface were created. From the presented results, a combination of black matt spray with a layer of Rhodamine 6G spray paint was chosen. The selected modification was further used for the internal modification of the experimental channel surface. Furthermore, a geometry modification to prevent light spread through the tube material is described. Data obtained from measurements before and after channel modification are presented and explained. [ABSTRACT FROM AUTHOR]

The surface finish (SF) becomes a part of the solder joint during assembly and improves the component's reliability. Furthermore, the SF influences the solder joint's reliability by affecting the thickness of the intermetallic compound (IMC) layer at the solder interface and copper pads. In this experiment, five different alloys are used and compared with the SAC305 alloy, two of which, Innolot and SAC-Bi, are bi-based solder alloys. This study includes three common SFs: electroless nickel immersion gold (ENIG), immersion silver (ImAg), and organic solderability preserve (OSP). The performance of three surface finishes is examined in terms of component characteristic life. All of the boards were isothermally aged for twelve months at 125 °C. The boards were then exposed to 5000 cycles of thermal cycling at temperatures ranging from −40–+125 °C. Most of the current research considers only one or two factors affecting the reliability of the electronic package. This study combines the effect of multiple factors, including solder paste content, SF, isothermal aging, and thermal cycling, to ensure that the test conditions represent real-world applications. In addition, the electronics packages are assembled using commercialized alloys. The current study focuses on a high-performance alloy already present in the electronic market. The failure data were analyzed statistically using the Weibull distribution and design of experiments (DOE) analysis of variance (ANOVA) techniques. The findings reveal that the micro and uniformly distributed precipitates in solder microstructures are critical for high-reliability solder joints. Re-crystallization of the thermally cycled solder joints promotes the local formation of numerous new grains in stress-concentrated zones. As the fracture spreads along these grain boundaries and eventually fails, these new grains participate in crack propagation. Aging significantly worsens this situation. Finally, although the ENIG surface finish with its Ni layer outperforms other SFs, this does not imply that ENIG is more reliable in all solder paste/sphere/finish combinations. [ABSTRACT FROM AUTHOR]

This paper introduces a Balanced Antipodal Vivaldi Antenna for microwave imaging applications and studies the impacts of immersion tin (ISn) and electroless nickel immersion gold (ENIG) surface finishes on the performance of the antenna. It proposes triple-scale apertures on conductor boundaries and uses partially carved substrate. Microstrip to stripline transition with via holes is used to accommodate the feeding. The design operates in 2 - 12 GHz frequency band with return loss less than - 10 dB. The proposed antenna achieves a maximum gain of 14.25 dBi at 12 GHz. The overall dimension of the antenna reaches 80 × 28 × 0.508mm 3 . The radiation characteristics of the final design are numerically and experimentally assessed and validated. Effects of ISn and ENIG finishes are analyzed for radiation properties. [ABSTRACT FROM AUTHOR]

This paper investigated the melting point and surface oxide thickness of Sn58Bi clean solder (non-flux-coated solder with a clean surface). The surface morphology, spreadability, voidage, and interfacial reaction of Sn58Bi clean solder and flux-coated solder welded with three different surface finishes were studied during vacuum welding and atmospheric reflow welding. The surface finishes consisted of pure copper, matte tin, and gold plating. The results indicated that the optimal welding surface finish of Sn58Bi clean solder was gold plating, and the interfacial reaction was sufficient and the average voidage was 7.69%. The interfacial intermetallic compound (IMC) was approximately 0.6-1 um thick, uneven and discontinuous. As for flux-coated solder, the preferable surface finish was matte tin, which had good welding surface morphology and formed a continuous smooth IMC layer with a thickness of about 0.4-0.8 um; spreading ratio and average voidage were 101.64% and 4.03%, respectively. An unknown particle-shaped Au-Sn-Bi phase ɑ with Au:Sn:Bi (wt.%) ≈ 18.5:56.2:24.2 (Au15Sn68Bi17 (at.%)) was discovered in the welding interface of Sn58Bi solder and gold-plated substrate. In addition, another Au-Sn-Bi ternary compound β with Au:Sn:Bi (wt.%) ≈ 27.8:65.5:6.7 (Au19Sn76Bi5 (at.%)) was found in Au18.5Sn56.2Bi24.2 (wt.%) alloy which prepared by smelting. (Au15Sn68Bi17 (at.%) named ɑ and Au19Sn76Bi5 (at.%) named β in the present work). [ABSTRACT FROM AUTHOR]

This paper deals with the design of an experimental circular channel model specially adapted for particle image velocimetry (PIV) measurements of airflow. The goal is to find a simple, fast, and functional approach for creating experimental models. The issue of the required PIV signal quality is defined, and the limits of acquiring relevant PIV data in the interior of circular channels are described, primarily as reflections of direct and scattered laser light caused by light passage through the cylindrical wall. As part of the experiment, measurements of reflections were made on differently coated surfaces of a plexiglass plate. Samples of various combinations of black matt spray, Rhodamine 6G coating, and roughened surface were created. From the presented results, a combination of black matt spray with a layer of Rhodamine 6G spray paint was chosen. The selected modification was further used for the internal modification of the experimental channel surface. Furthermore, a geometry modification to prevent light spread through the tube material is described. Data obtained from measurements before and after channel modification are presented and explained.

The surface finish (SF) becomes a part of the solder joint during assembly and improves the component’s reliability. Furthermore, the SF influences the solder joint’s reliability by affecting the thickness of the intermetallic compound (IMC) layer at the solder interface and copper pads. In this experiment, five different alloys are used and compared with the SAC305 alloy, two of which, Innolot and SAC-Bi, are bi-based solder alloys. This study includes three common SFs: electroless nickel immersion gold (ENIG), immersion silver (ImAg), and organic solderability preserve (OSP). The performance of three surface finishes is examined in terms of component characteristic life. All of the boards were isothermally aged for twelve months at 125 °C. The boards were then exposed to 5000 cycles of thermal cycling at temperatures ranging from −40–+125 °C. Most of the current research considers only one or two factors affecting the reliability of the electronic package. This study combines the effect of multiple factors, including solder paste content, SF, isothermal aging, and thermal cycling, to ensure that the test conditions represent real-world applications. In addition, the electronics packages are assembled using commercialized alloys. The current study focuses on a high-performance alloy already present in the electronic market. The failure data were analyzed statistically using the Weibull distribution and design of experiments (DOE) analysis of variance (ANOVA) techniques. The findings reveal that the micro and uniformly distributed precipitates in solder microstructures are critical for high-reliability solder joints. Re-crystallization of the thermally cycled solder joints promotes the local formation of numerous new grains in stress-concentrated zones. As the fracture spreads along these grain boundaries and eventually fails, these new grains participate in crack propagation. Aging significantly worsens this situation. Finally, although the ENIG surface finish with its Ni layer outperforms other SFs, this does not imply that ENIG is more reliable in all solder paste/sphere/finish combinations.

Natural stone has long been used as a building material because of its physical-mechanical resistance and its esthetic appeal. However, over the last century increasing industrial activity has produced more acidic environments, such as polluted urban areas, that can cause serious damage to many buildings and historic monuments, and in particular those made with carbonate rocks, which are most prone to decay. In order to mitigate the physicochemical processes that degrade these buildings, a number of phosphate-based consolidants have been developed, which are highly compatible with the carbonated substrate. Research about the role of the surface and its different possible finishes in the transmission of the agents that damage or protect the stone would therefore be very useful, both when choosing the most suitable stone for new constructions and when restoring historic buildings. The main objective of this research was to determine whether the roughness of three types of surface finish (saw-cut, honed and bush-hammered) influences the durability of four types of natural stone (two calcarenites, one travertine and one sandstone) widely used in Andalusia (Spain). The efficacy of a calcium phosphate-based consolidant as a mitigator of deterioration in polluted urban environments was also studied and to this end the physical properties of untreated and treated samples were measured and compared. The samples were exposed to artificial atmospheres with SO2 pollution in order to assess the damage caused to each surface finish. The results indicate that all the surface finishes were vulnerable to the decay caused by acidic atmospheres, although the saw-cut finish was less affected, perhaps because it did not require additional industrial processing. The mineral composition and texture of the rocks were critical factors in terms of the amount and type of decay they suffered, and the travertine and sandstone were more resistant to deterioration than the calcarenites. Similarly, the pore system of each rock was decisive in the penetration of the consolidant. Application of the consolidant improved the behavior of the treated samples by making them more resistant to acid attack without significantly altering the water vapor permeability, the color or the roughness of the surface.

In the 1920s, the improved concrete technology and growing acceptance of concrete as an aesthetical material resulted in an increased application of coloured concrete. This includes the use of organic and inorganic pigments, ground natural stone, consciously chosen coarse aggregates, and also a new technique: metallisation. This rare, yet internationally applied, technique was patented in the Netherlands in 1917 and allowed a colour change of the hardened concrete by applying metal salts on its surface. In conservation practice, there are misconceptions with respect to the period of application of exposed concrete and, in particular, of coloured concrete. The application of exposed concrete during the Interwar period (1918–1930s) is often not considered during inspections; this impacts the quality of value assessments, diagnosis of damage causes and choice of conservation strategies. Besides limited knowledge of the varieties of coloured concrete, the fact that many historic concrete buildings have since been plastered or painted impedes its correct identification. This poses a challenge, as the deviating properties of historic concrete, both due to production methods and use of unproved constituents, can affect the durability of concrete. This paper focuses on the characteristics which can be encountered during visual inspections, an early and influential phase within the conservation process.

The implant’s surface is responsible for direct interaction with the human body. For cases where osseointegration must be favored and the risk of bacteria proliferation is lower, rough surfaces are more suitable, while for implants where the risks are higher, a reduced surface roughness is required. This study aimed to analyze and produce different surface finishes on samples of Ti-6Al-4V alloy produced by additive manufacturing technique of Direct Metal Laser Sintering (DMLS). Surfaces of the samples were analyzed in the as-built condition, after blasting, after chemical etching, after electropolishing and two different combinations of these methods. The surfaces were studied using the technique of scanning electron microscopy, and surface roughness and mass measurements. The lower roughness value was obtained after a combination of blasting and chemical etching. Blasting results in a surface with uniform roughness while chemical etching cleans the surface and reduces its roughness.

This study illustrates test results and comparative literature data on the influence of isothermal aging and thermal cycling associated with Sn-1.0Ag-0.5Cu (SAC105) and Sn-3.0Ag-0.5Cu (SAC305) ball grid array (BGA) solder joints finished with ENIG and ENEPIG on the board side and ENIG on the package side compared with ImAg plating on both sides. The resulting degradation data suggests that the main concern for 0.4 mm pitch 10 mm package size BGA is package side surface finish, not board side. That is, ENIG performs better than immersion Ag for applications involving long-term isothermal aging. SAC305, with a higher relative fraction of Ag3Sn IMC within the solder, performs better than SAC105. SEM and polarized light microscope analysis show cracks propagated from the corners to the center or even to solder bulk, which eventually causes fatigue failure. Three factors are discussed: IMC, grain structure, and Ag3Sn particle. The continuous growth of Cu-Sn intermetallic compounds (IMC) and grains increase the risk of failure, while Ag3Sn particles seem helpful in blocking the crack propagation. [ABSTRACT FROM AUTHOR]

Two types of ornamental stones, namely granite (Blanco Rafaela or Zarzalejo Granite) and microcrystalline limestone (marble known commercially as Gris Pulpis), treated for different surface finishes, were tested for suitability as paving slabs. The finishes tested in both stones were polishing, hammering, honing and flaming, while acid treatment and abrasion were applied to limestone only and sawn finishes were only studied in granite. The stones were tested for the three physical properties that determine suitability for use as paving slabs; flexural strength under a concentrated load, and abrasion and slip resistance. Laboratory freeze-thaw cycle ageing tests were also conducted and flexural strength subsequently evaluated. Stone water sorption proved to be substantially unaltered by the type of finish employed. Finish barely affected flexural strength, except in the case of limestone flaming, where it was lower. Hammering was found to provide good slip resistance in both stones. The best slip performance for granite, however, was found for flamed specimens. Finish was shown to have no effect on abrasion resistance in either of the stone materials. Polished limestone suffered the least damage in freeze-thaw cycles, whereas freeze-thaw resistance was similar in all the granite specimens, regardless of the finish used.

The surface finishes have an important role on the energy requirements of the buildings. This paper presents a new factor denominated “outside coating factor” (OCF) for an air-conditioned building and for a building without summer thermal control. It synthetically describes the climate of the location considered and can be useful for building planners for choosing the optimal outside surface finishes from thermal and energetic point of view. This factor depends on the cooling/heating degrees-day and solar radiation. For positive values of the OCF (0, +2.5), the optimal choice falls on the high solar reflectance and high infrared emissivity surface finishes, while the opposite occurs for negative values of the OCF. [ABSTRACT FROM AUTHOR]

A great portion of the global energy consumption depends on existing buildings. So, energy saving and related CO2 emission reduction are important measures. This paper analyses the incidence of innovative surface finishes on the cooling and heating energy demand of existing buildings. These easy and cheap measures preserve the little living spaces, limited height and the architectural/chromatic characteristics. The analysis is conducted for various European cities, by using a dynamic energy simulation software. The primary energy required by the HVAC systems on seasonal and annual basis is evaluated and relevant energy saving (up to 21% on annual basis) is obtained. Finally, a technical-economic analysis is performed and interesting payback values are obtained (2.5-11 years in the best cases; 2-10 years, when a tax deduction of 35% is considered). [ABSTRACT FROM AUTHOR]

In historical centres, the buildings are characterized by pitched roofs, sometimes not insulated, with low thermal inertia and coated in brick tiles with low solar reflection factor. So, the attics show high energy costs for heating and cooling. This paper analyses the energy saving obtainable by applying innovative surface finishes on interior and exterior surfaces of opaque envelope components of existing buildings. This simple and inexpensive retrofit action determines energy cost reductions for heating and cooling, but also benefits regarding indoor thermal comfort and useful life of buildings, because condensation problems and thermal shock are reduced; moreover, it preserves the architectural and chromatic characteristics of the building envelope. The analysis is performed by means of a building energy simulation code, considering typical HVAC systems for various Italian and European cities. A technical-economic and environmental investigation is also performed. Thermal energy needs of buildings for summer cooling can be reduced up to 60% by applying “cool paints” on the external surface of walls and roof, while internal low infrared emissivity coatings can reduce winter thermal requirements up to 12.5%. Significant primary energy savings for heating and cooling and reductions of greenhouse gas emissions (up to 60%) can be obtained, as well as a payback value of few years in most cases. [ABSTRACT FROM AUTHOR]

Surface finishes are used to protect exposed copper metallization in printed circuit boards from oxidation and to provide a solderable surface on which to mount electronic components. While it is true that some people have called electroless nickel electroless palladium immersion gold (ENEPIG) a 'universal finish' for a wide range of applications from wire bonding to solder interconnects, this paper provides a review of the current literature on ENEPIG and assesses its overall capabilities compared to other surface finishes. Gaps in understanding the performance of ENEPIG as a printed wiring board surface finish are identified and further testing is recommended. [ABSTRACT FROM AUTHOR]

Highlights: [•] We studied the failure behavior induced by EM test on the Sn–Bi solder joint. [•] We evaluated the EM reliability of Sn–Bi solder joint on various surface finishes. [•] The Bi was segregated from cathode to anode side. [•] The OSP surface finish showed longer time to failure than others. [ABSTRACT FROM AUTHOR]

The degradation mechanisms of glass in a buried context result in surfaces that have been depleted in various elements. The stability of the glass is primarily affected by the burial environment and the glass composition. However, in all archaeological glasses, the corroded layer that is formed on the surface tends to be low in alkalis, high in silica and lacking in cohesion. The extent to which the material has degraded, along with the physical nature of the corrosion, has a profound effect upon a wide range of factors affecting the stability of artefacts, as well as the choice of conservation techniques to be employed. This study has a number of objectives: determination of the morphology of the surface of the leached layer in glasses of two different compositions with different surface finishes; examination of the transition between the corroded material and the unaffected substrate; and investigation of concentration profile of different elements within the surface layers, as a function of depth. The study uses two glasses, fabricated under laboratory conditions, to replicate two common glass types found in the historical environment; a soda-lime-silica glass typical of those found in the Roman period throughout the Mediterranean and northwestern Europe, and high-lime-potash glasses typical of those of Western Europe in the late medieval period. Three different surfaces have been prepared to mimic alternative manufacturing techniques such as blown, cast and ground surfaces for each composition. The glasses have been corroded under controlled laboratory conditions to replicate the buried environment. Imaging and chemical information is obtained using SEM-EDX and morphological information using IFM to produce 3-D mapping from topographical surfaces. [ABSTRACT FROM AUTHOR]

The effects of surface finishes on the in situ interfacial reaction characteristics of ball grid array (BGA) Sn-3.0Ag-0.5Cu lead-free solder bumps were investigated under annealing and electromigration (EM) test conditions of 130°C to 175°C with 5.0 × 10 A/cm. During reflow and annealing, (Cu,Ni)Sn intermetallic compound (IMC) formed at the interface of electroless nickel immersion gold (ENIG) finish. In the case of both immersion Sn and organic solderability preservative (OSP) finishes, CuSn and CuSn IMCs formed. Overall, the IMC growth velocity of ENIG was much lower than that of the other finishes. The activation energies of total IMCs were found to be 0.52 eV for ENIG, 0.78 eV for immersion Sn, and 0.72 eV for OSP. The ENIG finish appeared to present an effective diffusion barrier between the Cu substrate and the solder, which leads to better EM reliability in comparison with Cu-based pad systems. The failure mechanisms were explored in detail via in situ EM tests. [ABSTRACT FROM AUTHOR]

In this paper, the concept of a defect phase diagram is introduced which quantifies the effects of Cu and Pb additions to electrodeposited Sn films on surface defect formation, including but not limited to the formation of Sn whiskers. Transitions were observed in both the defect densities and the morphologies of hillocks and whiskers as Cu and Pb film compositions were systematically varied. Changes in crystallographic texture were also reported for a subset of the Sn–Cu–Pb alloys examined. The transitions between different defect types and the coexistence of certain defect types help to interpret the role of grain boundary pinning in hillock and whisker formation. [ABSTRACT FROM PUBLISHER]

Several types of surface finishes have been applied on Cu substrates in an effort to facilitate bonding and improve the reliability of lead-free solder joints. In the current research, the effects of printed circuit board surface finishes on the reliability of the solder joints were investigated by examining the morphology and growth behavior of the intermetallic compounds (IMCs) between Sn-based solders and different surface finishes on Cu. Three types of Cu substrates with different surface finishes were fabricated in this study: organic solderability preservative (OSP)/Cu, Ni/Cu, and electroless nickel immersion gold (ENIG)/Cu. Sn-3.5Ag and Sn-3.0Ag-0.5Cu were used as the solders. In the experiment, the solder joint specimens were aged isothermally at 150°C for up to 1000 h. Experimental results revealed that the OSP surface finish promoted the interdiffusion between Cu and Sn during soldering. The composition and morphology of the IMC layer at the solder/Ni/Cu interface were sensitive to the Cu concentration in the solder. Meanwhile, the solder joints with different morphological features of the IMCs exhibited significant differences in shear strengths. The Au-containing ENIG surface finish affected the shear strength of the solder joint significantly at the initial stage of isothermal aging. [ABSTRACT FROM AUTHOR]

The International Electronics Manufacturing Initiative (iNEMI) proposed a set of tests that were subsequently standardized by the Joint Electron Device Engineering Council (JEDEC) Solid State Technology Association as JESD22A121. However, further optimization was needed to validate and verify proposed iNEMI tests to determine whether these test methods could differentiate between component surface finishes, to investigate the connection between short-term and long-term tests, and to determine optimal inspection intervals and test durations. In the current work, 15 surface finishes were evaluated using iNEMI's three proposed environmental test conditions. These finishes were evaluated for whisker presence and length using a scanning electron microscope (SEM) every 1000 h or 500 accelerated thermal cycles for a total of at least 9000 h of isothermal testing or 3000 accelerated thermal cycles. Test results showed that thermal cycling and high-temperature/humidity testing could grow whiskers for all Pb-free Sn-based finishes, while only a few finishes exhibited whiskers after 10 000 h in an air-conditioned office environment. The results described in this paper were used to change the JEDEC tin whisker test method from the original iNEMI proposal by decreasing the humidity of the high-temperature humidity test, controlling the ambient test condition to 30 degC and 60% relative humidity (RH), and increasing the number of leads per sample and number of samples (sample size) for inspection [ABSTRACT FROM PUBLISHER]

Environmental and health concerns, due to the leaching of lead from landfills into ground water, have necessitated legislation that restricts the use of lead in electronics. The transition from the eutectic tin-lead composition used in electronic solders to lead-free solder is imminent. Understanding the impact of this transition on lead-free wave soldering is crucial because a large segment of printed circuit boards (PCBs) used in electronic home appliances are wave soldered. The usage of volatile organic compound (VOC)-free flux chemistry is expected to gather momentum in conjunction with lead-free wave soldering because of process requirements and environmental considerations. A thorough review of published literature indicated that there is limited information available on the application of water-soluble VOC-free flux chemistries for lead-free wave soldering. Consequently, the objectives of this research were to select a preferred VOC-free water-soluble flux chemistry, understand the process window of wave soldering using a 96.5Sn/3.0Ag/0.5Cu lead-free alloy, and study the impact of the lead-free wave soldering process on different surface finishes. Many of the earlier process recommendations were based on a solder pot temperature of 260 degC and higher. However, the packaging of through hole components may not withstand the higher pot temperature and longer contact time. Hence, assembly at a lower solder pot temperature and shorter contact time are highly desired. Consequently, experiments were conducted to verify the feasibility of reducing the solder pot temperature (250 degC) and the contact time (2 s). Three VOC-free fluxes, from three different vendors, were evaluated and the best flux chosen was used to establish the process window. It was demonstrated through this study that it is possible to wave solder, using a lead-free solder with low silver content, different surface finishes with a wide process window. The effect of lead-free process temperatures - - on the cleaning of the VOC-free water-soluble flux residues was evaluated. Residues were washed and cleaned using the existing equipment sets without any change in the process parameters. The process developed based on the initial set of experiments has been validated by the successful assembly of a number of lead-free prototype assemblies [ABSTRACT FROM PUBLISHER]

In the present work the effect of different surface conditions on the plasma nitriding response of AISI M2 high-speed steel was investigated. Samples and drills were prepared to different surface finishes prior to plasma nitriding: ground and sandblasted. Polished samples were used as a reference surface state. The plasma nitriding was performed at temperatures of 400 and 500 °C for two gas mixtures: 5 and 76 vol.% N2 in hydrogen. The surfaces were characterized before and after plasma nitriding concerning the microstructure, roughness, microhardness, chemical composition, phase composition and residual stress states. Machining tests were carried out with drills, during which drilling forces and flank wear were measured. A significant effect of the surface state prior to nitriding on the residual stress states and properties of the nitrided layer and untreated core has been observed. Thinner nitrided layers on ground and sandblasted samples were attributed to high compressive residual stress states and a stress-affected diffusion of nitrogen and carbon. In the machining tests, sandblasted drills exhibited the best performance. Lower nitrogen concentrations in the gas atmosphere gave the lowest drill flank wear for sandblasted surfaces, while higher nitrogen concentrations led to a reduction in drilling forces and torque. [Copyright &y& Elsevier]