M.A. Azmah Hanim

Effect of Reflow Profile on Intermetallic Compound Formation

Reflow soldering in a nitrogen atmosphere is a common process consideration in surface mount technology assembly. This is because the use of nitrogen in reflow equipment may benefit the process as well as the quality of the end product, where it can increase the reliability of the solder joint. So far, many papers have reported effects of cooling speed, type of solder pastes and solder fluxes on the reliability of lead-free solder joints. While the effects of reflow conditions on intermetallic compound (IMC) formation at the solder joint such as the atmosphere during the reflow process are still unclear. The present study investigated thoroughly the effect of different reflow soldering atmosphere, which is air and nitrogen on IMC formation and growth. Several techniques of materials characterization including optical, image analysis, scanning electron microscopy and energy dispersive X-ray analysis will be used to characterise the intermetallics in terms of composition, thickness and morphology. In addition, the effects of cooling rate and isothermal aging were also studied for the solder alloy Sn–4Ag–0.5Cu on electroless nickel/immersion gold (ENIG) surface finish. From the study, it was found that reflowing under nitrogen atmosphere had better effect on IMC formation and growth compared to reflowing under air. Besides, the cooling rate of solder during reflow also appears to have a significant effect on the final structure of the solder joint, and controlling the growth behaviour of the IMC during subsequent isothermal aging.

Effect of equal channel angular extrusion on Al-6063 bending fatigue characteristics

The purpose of this investigation was to refine the grains of annealed 6063 aluminum alloy and to improve its yield stress and ultimate strength. This was accomplished via the equal channel angular extrusion (ECAE) process at a temperature of 200°C using route A, with a constant ram speed of 30 mm/min through a die angle of 90° between the die channels for as many as 6 passes. The experiments were conducted on an Avery universal testing machine. The results showed that the grain diameter decreased from 45 μm to 2.8 μm after 6 extrusion passes. The results also indicated that the major improvement in fatigue resistance occurred after the first pass. The subsequent passes improved the fatigue life but at a considerably lower rate. A maximum increase of 1100% in the case of low applied stresses and an approximately 2200% increase in fatigue resistance in the case of high applied stresses were observed after 5 passes. The improvement of fatigue resistance is presumed to be due to (1) a reduction in the size and the number of Si crystals with increasing number of ECAE passes, (2) the aggregation of Cu during the ECAE process, (3) the formation and growth of CuAl2 grains, and (4) grain refinement of the Al-6063 alloy during the ECAE process.

Tensile and Flexural Behavior of Hybrid Banana Pseudostem/Glass Fibre Reinforced Polyester Composites

Natural fibre-based thermoset composites are generally lower in strength performance compared to synthetic thermoset composites. Hybridization with some amount of synthetic fibre enhanced the mechanical properties of the composites. This study focused on the performance of mechanical properties of hybrid banana/glass fibre reinforced polyester composites. Hybrid composites with different volume ratios of banana to glass fibre were prepared. The reinforcing effect of both fibres in polyester is also evaluated in various fibre loadings. Results showed that both flexural and tensile properties have been improved with the increasing level of overall fibre content loading. Tensile and flexural strength shows great enhancement by the introduction of a slight amount of glass fibre to the banana fibre polyester matrix.

Improvements in the microstructure and fatigue behavior of pure copper using equal channel angular extrusion

In this study, annealed pure copper was extruded using equal channel angular extrusion (ECAE) for a maximum of eight passes. The fatigue resistance of extruded specimens was evaluated for different passes and applied stresses using fatigue tests, fractography, and metallography. The mechanical properties of the extruded material were obtained at a tensile test velocity of 0.5 mm/min. It was found that the maximum increase in strength occurred after the 2nd pass. The total increase in ultimate strength after eight passes was 94%. The results of fatigue tests indicated that a significant improvement in fatigue life occurred after the 2nd pass. In subsequent passes, the fatigue life continued to improve but at a considerably lower rate. The improved fatigue life was dependent on the number of passes and applied stresses. For low stresses (or high-cycle fatigue), a maximum increase in fatigue resistance of approximately 500% was observed for the extruded material after eight passes, whereas a maximum fatigue resistance of 5000% was obtained for high-applied stresses (or low-cycle fatigue). Optical microscopic examinations revealed grain refinements in the range of 32 to 4 μm. A maximum increase in impact energy absorption of 100% was achieved after eight passes. Consistent results were obtained from fractography and metallography examinations of the extruded material during fatigue tests.

Mechanical properties of WC-based hardmetals bonded with iron alloys – a review

Growing concerns over the use of cobalt as binder for WC-based hardmetals has directed research efforts towards finding a suitable alternative binder offering comparable or even superior properties than those found in WC–Co hardmetals. Complete substitution of cobalt by iron alloys has been extensively explored in several studies with significant improvements in mechanical properties of WC bonded with Fe alloys when carbon content addition is strictly controlled in powder composition. Asides from the commonly studied hardness and fracture toughness properties, transverse rupture strength property of this composites has also been observed to hold future promise with further development in the microstructural parameters such as porosity during sintering. This article reviews the progress in the mechanical properties of WC–Fe alloys hardmetals.

The Effect of Commercial Rice Husk Ash Additives on the Porosity, Mechanical Properties, and Microstructure of Alumina Ceramics

A porous ceramic is made from composite materials which consist of alumina and commercial rice husk ash. This type of ceramics is obtained by mixing the commercial rice husk ash as a source of silica (SiO2) and a pore forming agent with alumina (Al2O3) powder. To obtain this type of ceramic, a solid-state technique is used with sintering at high temperature. This study also investigated the effects of the rice husk ash ratios on the mechanical properties, porosity, and microstructure. The results showed that, by increasing the content of the rice husk ash from 10 to 50 wt%, there is an increase in the porosity from 42.92% to 49.04%, while the mechanical properties decreased initially followed by an increase at 30 wt% and 50 wt%; the hardness at 20 wt% of the ash content was recorded at 101.90 HV1. When the ash content was increased to 30 wt% and 50 wt%, the hardness was raised to 150.92 HV1 and 158.93 HV1, respectively. The findings also revealed that the tensile and compressive strengths experienced a decrease at 10 wt% of the ash content and after that increase at 30 wt% and 50 wt% of rice husk ash. XRD analysis found multiple phases of ceramic formation after sintering for the different rice husk ash content.

Effect of reflow soldering profile on intermetallic compound formation

Reflow soldering in a nitrogen atmosphere is a common process in surface mount technology assembly since it can increase solder joint reliability. The present study investigated the effect of different reflow soldering atmospheres, either air or nitrogen, on intermetallic compound IMC formation and growth. Several techniques of materials characterisation including optical, image analysis, scanning electron microscopy and energy dispersive X-ray analysis were used to characterise the intermetallics. Besides, the effects of cooling rate and isothermal ageing were also studied. In summary, reflowing under nitrogen atmosphere had better effect on IMC formation and growth compared to reflowing under air. Besides, the cooling rate of solder during reflow also appears to have an effect on the final structure of the solder joint, and controlling the growth behaviour of the IMC during subsequent isothermal ageing. However, further research can be carried out to determine the solder joints strength produced by both reflow soldering profiles.

Effect of Isothermal Aging 2000 Hours on Intermetallics Formed between Ni-Pd-Au with Sn-4Ag-0.5Cu Solders

The present study investigated the effect of isothermal aging up to 2000 hours on the intermetallics formed between Sn-4Ag-0.5Cu lead free solder on electroless nickel electroless palladium immersion gold surface finish (Ni-Pd-Au). For all parameters, aging have an effect of changing the intermetallic morphology to coarser and dense structure. The intermetallic compound formed for the interconnection of the lead free solder changes with increased aging time from (Cu,Ni)6Sn5 compound to (Ni,Cu)3Sn4. At the end of the 2000 hours aging time, it changes to Ni3Sn4. This is the effect of Cu element availability during the intermetallics growth process. Starting from as reflow process, (Pd, Ni)Sn4 intermetallics formed near the interface of the solder joint. The formation of the (Pd, Ni)Sn4 intermetallics act like a diffusion barrier to slow down the growth of interface intermetallics. Lastly, Au element was detected in the Pd-Sn based intermetallic after aging more than 1000 hours.

Bismuth-Antimony as an Alternative for High Temperature Lead Free Solder

The development works on high temperature lead free solder are mostly discussed nowadays. To replace the current high temperature lead free solders, further research need to be done. A great deal of effort has been put into the development of lead free solder alloys. Bi (Bismuth) and Sb (Antimony) solder system proved as one of the promising candidates for electronic assembly. Melting temperature of three Bi-Sb solder alloys studied in this research enhanced their potential as the alternative solder candidates for high temperature lead free solder. At interface, Cu3Sb IMC layer was formed for 95Bi-5Sb solder alloy. Spallation of Cu3Sb IMC layer took placed with the results of Cu3Sb IMC also found in the solder bulk. Analysis of 97.5Bi-2.5Sb solder alloy classified as no metallurgical reaction at the interface and only the mechanical joining existed at the interface. The dissolution of Cu from subtrate affected the formation of Cu rich phase and the unstable Bi-Cu rich phase phenomena act as the isothermal product found in solder bulk. Mechanical grain boundary grooving observed in 98.5Bi-1.5Sb solder alloys at interface. Different compositions of Bi-Sb solder alloys resulted in different types of microstructures at interface and in solder bulk after reflow.

Effect of heat treatment parameters on the microstructure and microhardness of Ti-6Al-4V alloy

Ti-6Al-4V is a dual-phase (α+β) Ti-alloy which possesses potential series and complex microstructures. The coexistence of β-phase alongside α-phase in Ti-6Al-4V alloy enhances the heat treatment process. Precise adjustments of heat treatment parameters can lead to diversity of microstructures that can be transformed from equiaxed to fully lamellar to bi-modal. These microstructures have a critical impact on the mechanical properties. This work investigates the effect of altering the heat treatment parameters on both the microstructure and microhardness of Ti-6Al-4V alloy to elucidate alloy’s behaviour on the basis of microstructure - properties relations. Recrystallization annealing, solution treatment followed by aging, and β-annealing were performed on several samples to obtain various microstructures. The as-received sample exhibited fine equiaxed structure with a grain size of 1.78 µm. Recrystallization annealing of the fine equiaxed structure yielded considerable grain growth, resulting 7.29 µm larger globular grains. The bi-modal microstructure was obtained from the equiaxed structure through solution treatment followed by aging. The application of β-annealing treatment resulted in a lamellar microstructure. The microhardness readings were affected by variations in the heat treatment procedures. The highest and lowest hardness were 386.1Hv and 302.2 Hv for the lamellar and the equiaxed microstructures, respectively. The improvement in the microhardness was 27.8%. In comparison, the bi-modal microstructure demonstrated a balanced hardness.Ti-6Al-4V is a dual-phase (α+β) Ti-alloy which possesses potential series and complex microstructures. The coexistence of β-phase alongside α-phase in Ti-6Al-4V alloy enhances the heat treatment process. Precise adjustments of heat treatment parameters can lead to diversity of microstructures that can be transformed from equiaxed to fully lamellar to bi-modal. These microstructures have a critical impact on the mechanical properties. This work investigates the effect of altering the heat treatment parameters on both the microstructure and microhardness of Ti-6Al-4V alloy to elucidate alloy’s behaviour on the basis of microstructure - properties relations. Recrystallization annealing, solution treatment followed by aging, and β-annealing were performed on several samples to obtain various microstructures. The as-received sample exhibited fine equiaxed structure with a grain size of 1.78 µm. Recrystallization annealing of the fine equiaxed structure yielded considerable grain growth, resulting 7.29 µm large...