Deposition and application of electroless Ni–W–P under bump metallisation for high temperature lead-free solder interconnects

A reliable and robust diffusion barrier, commonly known as under bump metallisation (UBM), is indispensable in solder interconnects in order to retard the interfacial reaction rate, hence the growth of intermetallic compounds (IMCs). However, electroless Ni-P coatings are not adequate to inhibit interfacial reactions effectively since the formation of columnar structure and voids in the crystalline Ni3P layer in hybrid automotive devices (operating temperature above 300ºC) can significantly deteriorate the mechanical integrity of solder joints. In this thesis, electroless Ni-W-P coatings, as an effective UBM capable to serving under high temperature (up to 450ºC), are developed, characterised and subsequently applied onto the high temperature lead-free solder interconnects. [Continues.

Thermal stability of high temperature Pb-free solder interconnect characterised by in-situ electron microscopy

The present investigation aimed to use in-situ heating experiment in a transmission electron microscope (TEM) to live characterize the thermal stability of a Cu/Ni-W-P interlayer/ZnAl solder interconnect. It demonstrated the TEM was able to detect live intermetallic compounds (IMCs) growth during heating. In addition, stress building up was evidenced by the progressive evolving of the dislocations at the interface between NiW-P interlayer and the ZnAl Solder. However, due to the μm to nm scale of specimens' dimensions required for electron microscopy, the sample preparation and data interpretation remains a challenge

Retained ratio of reinforcement in SAC305 composite solder joints: effect of reinforcement type, processing and reflow cycle

Purpose This paper aims to systematically study the effect of reinforcement type, processing methods and reflow cycle on actual retained ratio of foreign reinforcement added in solder joints. Design/methodology/approach Two kinds of composite solders based on SAC305 (wt.%) alloys with reinforcements of 1 wt.% Ni and 1 wt.% TiC nano-particles were produced using powder metallurgy and mechanical blending method. The morphology of prepared composite solder powder and solder pastes was examined; retained ratios of reinforcement (RRoR) added in solder joints after different reflow cycles were analysed quantitatively using an Inductively Coupled Plasma optical system (ICP-OES Varian-720). The existence forms of reinforcement added in solder alloys during different processing stages were studied using scanning electron microscope, X-ray diffractometry and energy dispersive spectrometry. Findings The obtained experimental results indicated that the RRoR in composite solder joints decreased with the increase in the number of reflow cycles, but a loss ratio diminished gradually. It was also found that the RRoR which could react with the solder alloy were higher than that of the one that are unable to react with the solder. In addition, compared with mechanical blending, the RRoRs in the composite solders prepared using power metallurgy were relatively pronounced. Originality/value Present study offer a preliminary understanding on actual content and existence form of reinforcement added in a reflowed solder joint, which would also provide practical implications for choosing reinforcement and adjusting processing parameters in the manufacture of composite solders

Diffusion barrier property of electroless Ni-W-P coating in high temperature Zn-5Al/Cu solder interconnects

The operating temperature of high-temperature electronics can significantly promote the growth of intermetallic compounds (IMCs) at solder/substrate interfaces, particularly for low-cost Zn-based solders because of the rapid rate of reaction of Zn with Cu. Thus, a reliable and robust diffusion barrier is indispensable for suppressing the reactions between solder and substrate. In this work, a ternary Ni-W-P alloy was prepared via electroless plating. Its diffusion barrier property was evaluated by comparing the microstructures of IMC layers in Zn-5Al/Ni-W-P/Cu and Zn-5Al/Cu interconnects after liquid-solid reaction for prolonged durations. When the reaction lasted for 30 min, the thickness of the Al3Ni2 produced in the Zn-5Al/Ni-W-P/Cu solder interconnects was only 2.15 μm, whereas the thickness of the interfacial layer of Cu-Zn IMCs (CuZn4, Cu5Zn8 and CuZn) at the Zn-5Al/Cu interface was 94 μm. Because of the unbalanced growth of the IMCs in the Zn-5Al/Cu interconnects, notable numbers of Kirkendall voids were identified at the CuZn4/Cu5Zn8, Cu5Zn8/CuZn and CuZn/Cu interfaces after prolonged liquid-solid reaction. By contrast, the Al3Ni2 layer in the Zn-5Al/Ni-W-P/Cu solder joints remained intact, showing the potential to effectively enhance the mechanical reliability of electronic devices

Microstructural evolution of 96.5Sn–3Ag–0.5Cu lead free solder reinforced with nickel-coated graphene reinforcements under large temperature gradient

In this study, 96.5Sn–3Ag–0.5Cu (SAC305) lead-free composite solder containing graphene nanosheets (GNS) decorated with Ni nanoparticles (Ni-GNS) was prepared using a powder metallurgy method. A lab-made set-up and a corresponding Cu/solder/Cu sample design for assessing thermo-migration (TM) was established. The feasibility of this setup for TM stressing using an infrared thermal imaging method was verified; a temperature gradient in a solder joint was observed at 1240 K/cm. Microstructural evolution and diffusion of Cu in both plain and composite solder joints were then studied under TM stressing conditions. Compared to unreinforced SAC305 solder, the process of diffusion of Cu atoms in the composite solder joint was significantly reduced. The interfacial intermetallic compounds (IMCs) present in the composite solder joint also provide a more stable morphology after the TM test for 600 h. Furthermore, during the TM test, the Ni-GNS reinforcement affects the formation, migration and distribution of Ni–Cu–Sn and Cu–Sn IMCs by influencing the dissolution rate of Cu atoms

Interfacial reaction and microstructural evolution between Au-Ge solder and electroless Ni-W-P metallization in high temperature electronics interconnects

© 2017 IEEE. The elevated working temperature of high temperature electronics can inevitably cause potential excessive growth of interfacial intermetallic compounds (IMCs), which can significantly deteriorate the mechanical integrity of electronic devices. Therefore, a robust diffusion barrier that can operate reliably under elevated temperature is highly demanded to retard the interfacial reaction between solder and substrate. In this work, a ternary Ni-W-P alloy was deposited through electroless plating and applied as an Under Bump Metalisation (UBM) to Au-Ge solder joints. The interfacial reaction in Au-Ge/Ni-W-P solder joints after reflow and prolonged ageing durations was investigated. We found NiGe and Ni5Ge3 layers formed after reflow, however only NiGe was observed after 1000h aging at 300°C. The thickness of NiGe increases linearly with the square root of ageing time up to 1500h, indicating that the growth mechanism of NiGe is diffusion-control process when Ge atoms are sufficient. After ageing for 2000h, although Ge atoms from Au-Ge solder was fully consumed, the Ni-W-P coating remained stable and exhibited excellent diffusion barrier property. During various ageing durations, the top-view morphology of NiGe IMC grains changed from pyramid-like and polygon-like shape at as-built stage to granulate-like (up to 1500h), and finally a polygon-like shape (after 2000h)

Kropsla : voorjaarsteelt 1989 : rassenproef 1e beoordeling

Material was stained and analyzed by EM. VLP structures with variable shapes and sizes were detected.<p><b>Copyright information:</b></p><p>Taken from "Rift Valley fever virus structural proteins: expression, characterization and assembly of recombinant proteins"</p><p>http://www.virologyj.com/content/5/1/82</p><p>Virology Journal 2008;5():82-82.</p><p>Published online 18 Jul 2008</p><p>PMCID:PMC2488336.</p><p></p

Thermo-migration behavior of SAC305 lead-free solder reinforced with fullerene nanoparticles

In this work, SAC305 lead-free solder reinforced with 0.1 wt. % fullerene nanoparticles was prepared using a powder metallurgy method. A lab-made setup and a corresponding Cu/solder/Cu sample for thermo-migration (TM) test were designed and implemented. The feasibility of this setup for TM stressing was further verified with experimental and simulation methods; a temperature gradient in a solder seam was calculated as 1070 K/cm. Microstructural evolution and mechanical properties of both plain and composite solder alloys were then studied under the condition of TM stressing. It was shown that compared to unreinforced SAC305 solder, the process of diffusion of Cu atoms in the composite solder seam was remarkably suppressed. After the TM test for 600 h, Cu/solder interfaces in the composite solder seam were more stable and the inner structure remained more intact. Moreover, the addition of fullerene reinforcement can considerably affect a distribution of Cu6Sn5 formed as a result of dissolution of Cu atoms during the TM test. Hardness data across the solder seam were also found notably different because of the elemental redistribution caused by TM

Surface characterization, mechanical properties and corrosion behaviour of ternary based ZneZnOeSiO2composite coating of mild steel

Zinc coatings are obtained either from cyanide, non-cyanide alkaline or acid solutions. Because of the pollution and high cost associated with cyanide, deposition from other baths is gaining importance. In order to develop a bath with additive that could produce a quality coating is the motivation behind this present work which is surface modification of Zne8ZnOeSiO2 nano composite coating on mild steel surface by electrodeposition route. The influence of SiO2 on Zne8ZnO sulphate electrolyte on the properties and microstructure of the produced nano-coatings were investigated. The SiO2 was varied from 0 to 16wt%. The microstructure characteristics of these produced series composites coating were investigated using scanning electron microscopy couple with energy dispersive spectroscopy (SEM/EDS), X-ray diffraction and atomic force microscopy (AFM). The corrosion degradation properties in 3.65% NaCl medium were studied using potentiodynamic polarization technique and characterized by high resolution optical microscope (HR-OPM). The hardness and wear of the composite coating were measured with high diamond microhardness tester and dry abrasive MTR-300 testers respectively. The results showed that average hardness value of 142.5 and 251.2HV and corrosion rate of 0.13088 and 0.00122 mm/yr were obtained for the 0 and 16wt% SiO2 in Zne8ZnO. The work have established that upto 16% SiO2 in Zne8ZnO composite coating on mild steel can be used in improving the microhardness, wear loss and corrosion resistance of mild stee

From Design Changes to Lawsuits: An Exploratory Study Using Text Analytics Based on Legal Case Database

Design change is a major issue influencing construction productivity and if handled inappropriately, may lead to lawsuits in extreme cases. Canadian Legal Information Institute (CanLII) database is an open database that houses massive construction legal case document, each containing thousands of words detailing the judge’s deliberation that leads to the final decision. The study proposes a manual labelling method for legal documents and takes a Latent Dirichlet Allocation (LDA) modelling approach as the primary tool to provide fast and accurate categorization and identification of the legal cases. The study concludes that the LDA method can classify and identify legal cases. Exploratory in nature, this study nevertheless confirms the potential of the CanLII database for knowledge discovery in construction management research.</p