Electronic module assembly

Electronics is the vital basis for innovations and the essential enabler for global trends like connectivity, electro mobility and renewable energies. These applications require high performance and reliability of the electronic modules. Their assembly combines very heterogeneous process chains like remarkable productive and diminutive surface mount technology (SMT), powerful and robust power electronic interconnection techniques, as well as pioneering reel-to-reel based organic electronic printing. After briefly outlining the enormous global economic impact of electronic modules, this paper presents the state of the art of electronic module assembly including substrate materials, electronic components, packaging and assembly processes as well as quality and reliability testing methods.     

Predicting Prostephanus truncatus (Horn) (Coleoptera: Bostrichidae) populations and associated grain damage in smallholder farmers’ maize stores: A machine learning approach

Prostephanus truncatus is a notorious pest of stored-maize grain and its spread throughout sub-Saharan Africa has led to increased levels of grain storage losses. The current study developed models to predict the level of P. truncatus infestation and associated damage of maize grain in smallholder farmer stores. Data were gathered from grain storage trials conducted in Hwedza and Mbire districts of Zimbabwe and correlated with weather data for each site. Insect counts of P. truncatus and other common stored grain insect pests had a strong correlation with time of year with highest recorded numbers from January to May. Correlation analysis showed insect-generated grain dust from boring and feeding activity to be the best indicator of P. truncatus presence in stores (r = 0.70), while a moderate correlation (r = 0.48) was found between P. truncatus numbers and storage insect parasitic wasps, and grain damage levels significantly correlated with the presence of Tribolium castaneum (r = 0.60). Models were developed for predicting P. truncatus infestation and grain damage using parameter selection algorithms and decision-tree machine learning algorithms with 10-fold cross-validation. The P. truncatus population size prediction model performance was weak (r = 0.43) due to the complicated sampling and detection of the pest and eight-week long period between sampling events. The grain damage prediction model had a stronger correlation coefficient (r = 0.93) and is a good estimator for in situ stored grain insect damage. The models were developed for use under southern African climatic conditions and can be improved with more input data to create more precise models for building decision-support tools for smallholder maize-based production systems.     

Hydrothermal synthesis and characterization of surface-modified δ-MnO2 with high Fenton-like catalytic activity

Surface-modified δ-MnO₂ with a hierarchical structure was synthesized via a hydrothermal redox reaction between toluene and KMnO₄. Toluene is oxidized to produce benzoic acid which rapidly adsorbs onto the surface of δ-MnO₂. The δ-MnO₂ sample prepared with toluene exhibited a much higher catalytic activity for the Fenton-like oxidation of methylene blue in aqueous solution than that prepared without toluene. The enhanced catalytic activity might be attributed to the surface-bound persistent free radicals produced from the electron transfer from the adsorbed C₆H₅–COO⁻ to Mn(IV).     

Multi-criteria environmental and economic impact assessment of wire arc additive manufacturing

Wire Arc Additive Manufacturing (WAAM) is a fusion- and wire-based additive manufacturing technology which has gained industrial interest for the production of medium-to-large components with high material deposition rates. However, in-depth studies on performance indicators that incorporate economic and environmental sustainability still have to be carried out. The first aim of the paper has been to quantify the performance metrics of WAAM-based manufacturing approaches, while varying the size and the deposited material of the component. The second aim has been to propose a multi-criteria decision-analysis mapping to compare the combined impacts of products manufactured by means of the WAAM-based approach and machining.     

Preparation and characterization of Cu/(WC-TiC-Co)/graphene nano-composites as a suitable material for heat sink by powder metallurgy method

Cu/WC-TiC-Co/GNs nano-composites were successfully prepared by the powder metallurgy technique. The predetermined weight percent value of WC-TiC-Co powder was mixed with 0.25, 0.5, 0.75, and 1 wt% of graphene nano-sheets for 3 h. by 1:2 powder to ball ratio. The mixed powders were coated with 90 wt% copper by the electro-less deposition technique. The composites were compacted at 900 MPa then sintered twice in a hydrogen atmosphere furnace once at 1000 °C and another at 1100 °C for 140 min. Sintering at 1000 °C proved to present the more suitable temperature. Both SEM and EDAX were used to investigate the microstructure and constituents of the sintered nano-composites. The relative density, hardness, electrical and thermal conductivity were studied. The microstructure refers to a good adhesion and homogeneous distribution of WC-TiC-Co and GNs in the copper metal matrix. The results showed that the relative density was increased up to 0.25 wt% GNs then decreased. In spite of the decreasing of the density after 0.25 wt% GNs, the hardness increased up to 1 wt% GNs. Because of the large surface area and the nano-size thickness of GNs, electrical and thermal conductivities got increased by its increasing up to 1 wt%.     

Precipitating spinel into precursor glass and its assistance in crystallization

The crystallization phenomena of spinel in CaO-MgO-Al₂O₃-SiO₂-Fe₂O₃ glass have received much attention due to the particular role in preparation of glass-ceramic materials, which represent an effective option to manage hazardous waste. In this study, both preliminary spinel and secondary spinel were precipitated in the precursor glass. The formation of these spinel was meticulously assessed by a combination of X-ray diffractometry and scanning electron microscopy. The structure of the microenvironment in the precursor glass was characterized by Raman spectrums. These advanced techniques highlight the potential for one-step crystallization of the glass. The investigation, which focused on one-step crystallization, demonstrated the growth of pyroxene on spinel accompanying a migration of chromium. The results also show the microstructure of the obtained glass-ceramic was very dependent on the heat-treat temperature. This study not only unambiguously reveals the precipitation mechanisms of spinel but also provides more documentation for one-step crystallization in the glass-ceramics field.