Effective Solder for Improved Thermo-Mechanical Reliability of Solder Joints in a Ball Grid Array (BGA) Soldered on Printed Circuit Board (PCB)

Ball grid array (BGA) packages have increasing applications in mobile phones, disk drives, LC displays and automotive engine controllers. However, the thermo-mechanical reliability of the BGA solder joints challenges the device functionality amidst component and system miniaturisation as well as wider adoption of lead-free solders. This investigation determines the effective BGA solders for improved thermo-mechanical reliability of the devices. It utilised a conducted study on creep response of a lead-based eutectic Sn63Pb37 and four lead-free Tin-Silver-Copper (SnAgCu) [SAC305, SAC387, SAC396 and SAC405] solders subjected to thermal cycling loadings and isothermal ageing. The solders form the joints between the BGAs and printed circuit boards (PCBs). ANSYS R19.0 package is used to simulate isothermal ageing of some of the assemblies at -40℃, 25℃, 75℃ and 150℃ temperatures for 45 days and model the thermal cycling history of the other assemblies from 22℃ ambient temperature for six cycles. The response of the solders is simulated using Garofalo-Arrhenius creep model. Under thermal ageing, SAC396 solder joints demonstrate possession of least strain energy density, deformation and von-Mises stress in comparison to the other solders. Under thermal cycle loading conditions, SAC405 acquired the lowest amount of the damage parameters in comparison. Lead-free SAC405 and SAC387 joints accumulated the lowest and highest energy dissipation per cycle, respectively. It is concluded that SAC405 and SAC396 are the most effective solders for BGA in devices experiencing isothermal ageing and temperature cycling during operation, respectively. They are proposed as the suitable replacement of eutectic Sn63Pb37 solder for the various conditions.University of Derb

CO2 fixation by seaweeds and their role in De-acidifying Ocean - An experimental approach

CO2 fixation by seaweeds and their role in De-acidifying Ocean - An experimental approac

Perceived influence of economic recession and psychological adjustment on students' learning among undergraduate students of University of Calabar

The study investigated the perceived influence of economic recession and psychological adjustment on students’ learning among year two undergraduate students of the Faculty Education, University of Calabar, Cross River State. In carrying out the study, 200 respondents were randomly selected from a population of 2000. That is 10% of the total population of900 males and 1100females. Two research questions -were posed while two hypotheses were formulated. A researcher designed instrument titled “Economic Recession and Psychological Adjustment Questionnaire for Undergraduate Students” (ERPAQUS) was used for data collection. The instrument was subjected to face validity by experts in Educational Psychology and measurement and evaluation of the University of Calabar. The reliability estimate of the instrument was established using the Cronbach Alpha reliability method to determined the internal reliability index. The data collected were analyzed using independent t-test and Pearson Product Moment correlation analysis. The study indicated that there is a significant relationship among economic recession, psychological adjustment and undergraduate students of the University of Calabar, Cross River State. It also indicated various ways the students have adopted to tackle the excruciating pains posed by the economic down turn in the country. However, the government, parents and school authority were advised to help in alleviating the sufferings of the students by providing good policy initiative to assist the students in school

Spirituality and Mindfulness Practices of Early Childhood and Elementary Preservice Teachers: A Snapshot

This paper describes the results of a research survey that interpreted the patterns of mindfulness and spirituality within a convenience sample of preservice teachers at a Midwest teacher education institution.  Mindfulness and spiritualty represent topics of developing interest in teacher education that serve to increase candidate focus and revision of practice.  Respondents completed a survey as part of a semester’s project that interpreted the results of a semester-long mindfulness intervention on student mindfulness and spiritual attitudes and practices. The findings determined that participants had senses of mindfulness and self the emphasized themselves, and their external worlds, let weak connection with a higher spiritual entity.  Significant differences were observed between early childhood and elementary majors

Creep-Fatigue Behaviours of Sn-Ag-Cu Solder Joints in Microelectronics Applications

Electronic manufacturing is one of the dynamic industries in the world in terms of leading in technological advancements. At the heart of electronic assembly lies the 'soldering technology' and the 'solder joints' between electronic components and substrate. During the operation of electronic products, solder joints experience harsh environmental conditions in terms of cyclic change of temperature and vibration and exposure to moisture and chemicals. Due to the cyclic application of loads and higher operational temperature, solder joints fail primarily through creep and fatigue failures. This paper presents the creep-fatigue behaviours of solder joints in a ball grid array (BGA), soldered on a printed circuit board (PCB). Using finite element (FE) simulation, the solder joints were subjected to thermal cycling and isothermal ageing. Accelerated thermal cycling (ATC) was carried out using a temperate range from 40℃ to 150℃, and isothermal ageing was done at -40,25,75 and 150℃ temperatures for 45 days (64,800 mins). The solders studied are lead-based eutectic Sn63Pb37 and lead-free SAC305, SAC387, SAC396 and SAC405. The results were analysed using the failure criterion of equivalent stress, strain rate, deformation rate, and the solders' strain energy density. The SAC405 and SAC396 are found to possess the least stress magnitude, strain rate, deformation rate, and strain energy density damage than the lead-based eutectic Sn63Pb37 solder; they have the highest fatigue lives based on the damage mechanisms. This research provides a technique for determining the preventive maintenance time of BGA components in mission-critical systems. Furthermore, it proposes developing a new life prediction model based on a combination of the damage parameters for improved prediction.N/

Generating temperature cycle profile from in-situ climatic condition for accurate prediction of thermo-mechanical degradation of c-Si photovoltaic module

The use of climate specific temperature-cycling profile is critical to precisely quantifying the degradation rate and accurately determining the service fatigue life of crystalline silicon photovoltaic (c-Si PV) module operating in various climates. A reliable in-situ outdoor weathering database is pivotal to generating the required climate specific temperature cycle profile. This research utilizes high-resolution data obtained at five minutes interval from installed c-Si PV modules to generate a temperature cycle profile that is representative of a test site in sub-Saharan Africa climate. The study collected a three-year data from 2012 to 2014 on weathering of c-Si PV module located at College of Engineering, KNUST Ghana. The data site is on latitude 6° 40″ N and longitude 1° 37″ W at an elevation of 250 m above sea level. Analysis of the data on temperature variation and thermally induced stresses demonstrates that the region has a profile with a ramp rate of 8.996 °C/h, a hot dwell time of 228 min, cold dwell time of 369 min. Maximum and minimum module temperatures of 58.9 °C and 23.7 °C, respectively; and a cycle time of 86400 s. Comparison with the IEC 61215 standards for terrestrial PV modules qualification reveals percentage changes of – 91%, 2180%, 3590%, 747% for the ramp rate, dwell (hot and cold) and cycle times, respectively. The generated in-situ temperature cycle profile predicts to qualify accurately, c-Si PV modules operating in the sub-Saharan African test site. The systematic technique employed in this study to generate the in-situ temperature cycle profile would be useful to the thermo-mechanical reliability research community. In addition, photovoltaic design and manufacturing engineers may harness the information to create climate specific robust c-Si PV module. Keywords: Temperature cycling, Ramp rates, Temperature gradient, Accelerated Thermal Cycling (ATC), Co-efficient of Thermal Expansion (CTE), Rainflow counting, In-situ data generatio

Role of seaweeds in neutralizing the impact of seawater acidification- A laboratory study with beached shells of certain bivalves and spines of a sea urchin

Ocean acidification is one of the major impacts of climate change in sea which is manifested by the decrease in hydrogen ion concentration (pH) of seawater mainly due to increased uptake of CO2 and reduction in carbonate ions. This is a report on the dissolution rate of dead shells of four marine bivalves and spines of a sea urchin when treated with different levels of CO2 dissolved in seawater for 48 hours which was measured gravimetrically. Dissolution of dead shells expressed as reduction in shell weight was directly proportional to the concentration of dissolved CO2. Live thallus of green seaweed Chaetomorpha antennina did reduce the magnitude of dissolution rates (P<0.05) of all the shells and spines considerably as well as the change in pH of ambient seawater due to the addition of CO2. The remedial property of seaweeds was more effective at lower concentrations of dissolved CO2. The induced change in pH was restored by green seaweed only at concentrations above 250 ppm. Although we noticed strong impact of dissolved CO2 on the dead shells of Mactrinula plicataria even at 100 ppm level, the remedial action by the green seaweed was maximum in Siliqua radiata followed by Perna viridis. Results of this laboratory study shows the positive role of seaweeds in neutralizing the acidification impacts

Enhancing the low temperature hydrogen sensitivity of nanocrystalline SnO2 as a function of trivalent dopants

The effect of different indium doping concentrations on the room temperature hydrogen sensitivity of nano-SnO2 is investigated. The role of calcination temperature on the surface morphology, phase transformation, and subsequent impact on the gas sensing behavior of nanocrystalline doped SnO2 is presented. Differences in grain growth with varying doping amount give an explanation for enhanced sensing that is not always so obvious. Variation in the charge carrier density for indium doped nanocrystalline SnO2 is calculated as a function of indium concentration in the tin oxide lattice structure. The charge carrier density is correlated to the involved surface species of doped nanocrystalline SnO2 upon hydrogen gas exposure using Fourier transform infrared spectroscopy

Critical skills needs and challenges for STEM/STEAM graduates increased employability and entrepreneurship in the solar energy sector

Energy produced by photovoltaic module (PVM) is poised to deliver the UN Sustainable Development Goal 7 (SDG-7) by 2030 and Net-Zero by 2050 but not until ample graduates with adequate Solar Energy Technology (SET) skills are produced by Higher education institutions (HEIs). Although PVM has witnessed significant penetration globally, the sustainability of the growth of the sector is challenged by attendant monotonic skilled labour shortages. The evolving growth imbalance is critical in the European Union (EU), limits her global competitiveness and necessitates the need to create wider awareness on the green technology to stimulate more production of solar energy sector (SES) specific skills graduates. Discussing the mismatch between the skills Europe needs and has in the SES, the study outlines key critical skills Science, Technology, Engineering and Mathematics (STEM) cum Arts (STEAM) graduates ought to possess to secure sector employment and the challenges limiting them from acquiring the competencies. The review is conducted via extensive study of relevant literature, analysis of interviews and observations. Academic, industrial, and entrepreneurial skills are identified as critical SES needs. Designing and running educational modules/curricula that embed the identified solar technology specialist skills on students and learners are proposed as vehicle to increase their employability and entrepreneurship. This study profiles trends and developments in the SES for stakeholders’ increased awareness while presenting the specialist skills in-demand for employment in the sector. The adoption of SET Training (SETechTra) curricula/modules by the EIs will substantially increase the production of industry-ready graduates whilst decreasing the SES skills gap

Physical Properties of the Mountain Soils of Cross River State, Nigeria

The mountain soils of Cross River State, Oban hills and Obudu mountains have the following properties. The sand contents in Oban hills ranged from 34 to 82% while in Obudu plateau from 40 to 78 %. The silt contents of the soils in both Oban hills and Obudu plateau fluctuated with depth. At Oban hills the range was between 6 and 36 %, and 10 and 26 % at Obudu plateau. Clay contents at Oban hills ranged from 6 to 42 % while it ranged from 10 to 44 % at Obudu plateau. The bulk density values for both study sites increased with soil depth. The range of values at Oban hills top soils was 0.67 to 1.87 g/cm3, with the mean of 1.38 g/cm3 while values for subsoil horizon ranged from 1.64 to 2.33 g/cm3 with mean of 2.02 g/cm3.The range of bulk density values from the Obudu mountains was from 0.74 to 2.16 g/cm3. The soil surface values ranged from 0.74 to 1.75 g/cm3, with the mean of 1.2 g/cm. The total porosity values of Oban hills for top soil horizons ranged from 29.43 to 74.72%, with the mean of 47.93%. The subsurface horizon values ranged from 12.08 to 40.38%, with a mean of 22.54%. The surface soil horizon values at the Obudu mountains ranged between 33.96 and 70.08%, giving a mean of 50.63% while the subsurface values ranged from 19.62 to 55.47%, with the mean of 29.08%. Oban hills and Obudu mountain soils are rated good soils based on their total porosity values. The hydraulic conductivity values in the Oban hills ranged from 0.74 to 103.87 cm/hr. At the surface horizons, the conductivity values ranged from 7.56 to 103.87 cm/hr with the mean of 34.42 cm/hr. The subsurface horizon values ranged from 0.74 to 42.83 cm/hr, with the mean of 10.13 cm/hr. Hydraulic conductivity values at the Obudu mountains ranged from 0.05 to 78.99 cm/hr. The surface values ranged between 0.52 and 78.99 cm/hr, with the mean of 31.16 cm/hr. The subsurface horizon values range was from 0.05 to 42.13 cm/hr with the mean of 14.94 cm/hr. The conductivity values were high.Keywords: Texture, hydraulic conductivity, bulk density, porosity