Synthesis and Application of Ceramic Paste for High-Temperature Electronic Packaging

This dissertation research focused on the synthesis and application of ceramic paste for high-temperature applications. An alumina paste material comprising aluminum dihydric phosphate and alumina powder was developed for high-temperature electronic packaging. Nano aluminum nitride and nano-silica powders were embedded to promote the paste curing process, limit the grain growth, and increase its bond shear strength. The chip-to-substrate bond strength was enhanced and met the MIL-STD requirements for die-attach assembly. Its encapsulation property was improved with fewer cracks compared to similar commercial ceramic encapsulants. The die-attach material and encapsulation properties tested at 500°C showed no defect or additional cracks. Thermal aging and thermal cycling were carried out on the synthesized paste. XPS analysis revealed a higher oxygen bonding percentage for the 10% nanosilica ceramic sample than other samples. XRD peak broadening is largest for the 10% nano-silica ceramic which indicated smaller crystallite sizes. The smaller crystallite size for the 10% nanosilica sample introduces a larger microstrain to the alumina crystal structure. FTIR revealed the presence of alumina-silicate bonds on these samples with the largest amount present in the 10% nanosilica samples. SEM and EDX results showed a uniform bond line for the 10% sample and uniform material distribution. An electronic packaging technology that survives the Venusian condition was developed. Alumina ceramic substrates and gold conductors on alumina were evaluated for electrical and mechanical performance. The most promising die-attach materials were found to be thick-film gold and alumina-based ceramic pastes. Alumina, sapphire, silicon, and silicon carbide dice were attached to the alumina substrates using these die-attach materials and exposed to the Venusian condition for 244 hours. The devices on the packaging substrates were encapsulated by a ceramic encapsulant with no significant increase in cracks and voids after the Venusian simulator test. Wire pull strength tests were conducted on the gold bond wire to evaluate mechanical durability before and after the Venusian simulator exposure test with about 30.8% decrease which satisfied the minimum requirement for the MIL-STD-885 method. The overall wire-bond daisy-chain resistance change was 0.47% after the Venus simulator test, indicating a promising wire bond integrity. A titanium package was fabricated to house the ceramic packaging substrate and a two-level metalized feedthrough was fabricated to provide electrical interfaces to the package. A double-layer ceramic electronic packaging technology that survives the Venusian surface condition was developed using a ceramic interlayer dielectric with gold conductors. A 60-µm ceramic interlayer dielectric served as the insulator between the top and bottom gold conductors on high-purity ceramic substrates. Test devices with AuPtPd metallization were attached to the top gold pads using a thick-film gold paste. Thermal aging for 115 hours at 500°C and thermal cycling from room temperature to 450°C were performed. Dielectric leakage tests of the interlayer ceramic layer between the top and bottom gold conductors revealed a leakage current density of less than 50 10-7 A/cm2 at 600V after thermal cycling. The die shear test showed a 33% decrease in die shear strength after thermal tests but still satisfies the MIL-STD method

A Study of the Effects of Mobile Technology Solutions on Effective Deployment of Mobile Learning in Medical Education Based on the Technology Acceptance Model

Background & Objective: Mobile learning, as a new stage of development in e-learning, provides opportunities for information transfer, and strengthening and improving lifelong learning in students of medical sciences. The present study was conducted to evaluate the effect of mobile technology solutions on effective deployment of mobile learning in medical education based on the Technology Acceptance Model (TAM). Methods: This was an objective-based applied research and, based on the method of data collection, a descriptive survey. The statistical population consisted of all faculty members of the Hamadan University of Medical Sciences in 2014. The sample size (n = 188) was determined using Cochran formula. Data were collected using the Mobile Technology Development Strategies Questionnaires and Davis’ TAM. Data analysis was performed using the correlation coefficient, t-test, confirmatory factor analysis, structural equation modeling, and path analysis and LISREL and SPSS software. Results: Instructional strategies, administrative-structural, managerial, and motivational–recreational, respectively, had the most significant effect (at the level of 0.01) on the teachers’ perception of the usefulness of mobile learning and the simplicity of its use. Based on TAM, these two components had positive effects on attitude toward using and deciding to use mobile technology. Thereby, they have significant positive effects on the application of mobile technology in teaching and learning by teachers (at the level of 0.01). Conclusion: Based on these results, TAM was approved according to the guidelines provided on mobile learning development in the study population, and thus, has deployment potential in the target population. Key Words: Mobile technology, Mobile learning, Technology Acceptance Model (TAM), Structural equation, Path analysi

Correlates of Alcohol Consumption and Drug Injection among Homeless Youth: A Case Study in the Southeast of Iran

Background: Alcohol use and drug injection are prevalent among homeless youths. The aim of this study wasto identify the associated factors of alcohol consumption and drug injection among homeless youths aged18-29 years.Methods: Data on 202 homeless youths (111 males and 91 females) were collected using a standardizedquestionnaire and face-to-face interview. Lasso logistic regression was applied to determine the impact ofassociated factors on alcohol consumption and drug injection.Findings: The mean age of the participants was 26.30 ± 3.19 years. Also, the prevalence of alcoholconsumption and drug injection was 33.0% [95% confidence interval (CI): 30-36] and 4.0% (95% CI: 0-8),respectively; 6 people (3.0%) consumed alcohol and injected drugs at the same time. Correlates of alcoholconsumption and drug injection were male sex [odds ratio (OR)Alc = 5.7], age (ORAlc = 0.96 and ORDI = 0.98),bachelor or higher education level (ORAlc = 1.34), non-Iranian nationality (ORAlc = 0.05 and ORDI = 0.18),food score (ORDI = 0.92), smoking (ORAlc = 2.05), substance use (ORAlc = 1.12), opposite sex relationship(ORAlc = 1.6), homosexual relationship (ORAlc = 3.56 and ORDI = 2.69), and mental disorder (ORAlc = 0.99).Conclusion: Based on our findings, it seems that the homeless youth are more desired to use alcohol and druginjection, whereas the prevalence of alcohol consumption and drug injection in homeless youth was higherthan general youth population in Iran. Therefore, some suitable solutions are needed to prevent thehomelessness. Also, the effective variables that were identified in this study for alcohol use and drug injectioncan help design and implement beneficial interventions

Barbarians at the British Museum: Anglo-Saxon Art, Race and Religion

A critical historiographical overview of art historical approaches to early medieval material culture, with a focus on the British Museum collections and their connections to religion

Prevalence of high-risk sexual behavior among Iranian young people: A systematic review and meta-analysis

Sex out of marriage is considered to be illegal, non-religious, immoral, and taboo in Iran. Risky sexual behaviors, such as condomless sex, multiple sexual partners, starting sex at an early age, adversely affect young people's health and expose them to sexually transmitted infections and unwanted pregnancy to females. These behaviors could lead to deleterious health, social and economic consequences. We conducted a systematic review to estimate the prevalence of extra/premarital sex and high-risk sexual behaviors among Iranian young people. We systematically searched seven databases to identify relevant studies up to 22nd of December 2019 and we found 28 eligible studies implemented in Iran. The pooled prevalence of life-time extra/premarital sex was estimated at 24 (95 CI: 17�30) overall, 33 (95 CI: 25�40) in male and 14 (95 CI: 8�19) in female. Moreover, the prevalence of high-risk sexual behaviors such as having condomless sex (12.8 to 89.6), multi-sex partners (7.7 to 62.9), sex in return for payment (1.3 to 7.0), and starting sexual activity at under 15 years (24.0 to 60.5) was varied between studies. These findings suggested relatively high extra/premarital sex and unsafe sex behaviors among young people and the need for targeted, appropriate sex education programs. © 2020 Elsevier Lt