The use of aluminum nitride as a substrate material for microelectronics is examined. A brief look at thermal, mechanical, and electrical properties of aluminum nitride show that it is a viable alternative material for this use. A study of the interfaces between aluminum nitride and several thick film pastes (palladium silver conductor, ruthenium oxide resistor, and gold conductor) was performed with optical microscopy, scanning electron microscopy, and energy dispersive spectroscopy. Results of this investigation showed that the contaminants in the substrate material that affect thermal conductivity do not affect the adhesion of the thick film pastes. However, it was found that the lack of certain elements in the binder of the thick film paste could lead to weaker adhesion, and severe degradation of the thick film's adhesion during thermal cycling.

Made available in DSpace on 2014-08-20T14:30:09Z (GMT). No. of bitstreams: 1 Dissertacao_hugo_ramalho.pdf: 1163967 bytes, checksum: 5735b7a46397cc9fceb1883f7a66141c (MD5) Previous issue date: 2013-03-18 / This study was composed by two phases that evaluated two gingival displacement (GD) techniques, conventional and cordless: 1- a in vitro study which assess cytoxicity/genotoxicity, and pH of AlCl3-based agents; and 2- a randomized clinical which evaluated the efficacy of these techniques. For in vitro phase, eluates were obtained by dilution of AlCl3-based into culture medium for 1h, 4h, and 24h. pH values were measured by digital pHmeter, cytotoxicity by MTT test and genotoxicity by Micronuclei test. A crossover, double-blind, randomized clinical trial was designed to evaluate clinical, immunologic and individual factors before and after GD by two techniques, conventional (gingival cord + astringent gel) and cordless (astringent-based paste). These factors were evaluated on incisors prepared for metal-ceramic dental crowns before, 1 day post-GD and 10 day post-GD. Interleukin 1&#946;, Interleukin 6 and Tumor Necrosis Factor &#945; concentrations were evaluated on gingival crevicular fluid collected before (control) and 1 day post-GD. In vitro data were analyzed by two-way ANOVA and Tukey test. Clinical data were analyzed by One-way Repeated Measures ANOVA and Tukey test (immunologic factor), Friedman test (periodontal parameters), and Fisher Exact or Qui-square test (pain, stress, and unpleasant flavor during GD). All test were realized considering p<0.05. Mean pH values were statistically higher for Viscostat than Expasyl. Both astringents were non-cytotoxic at 1h. Expasyl was more cytotoxic than Viscostat at 4h and 24h. Expasyl genotoxicity was not different from control group. Neither of the two evaluated techniques resulted in worse periodontal indices. Conventional technique was statistically more stressing than cordless, and similar considering pain and unpleasant taste. GD by the both 11 treatments evaluated led to statistically higher mean concentrations of the three interleukins evaluated. Conventional GD technique resulted in the highest interleukins levels. In vitro, AlCl3-based astringents presented acceptable biological activity with no genotoxic difference between Expasyl and control group. In vivo, cordless technique was less stressful and resulted in lower cytokines levels after GD / Este estudo foi composto por duas fases que avaliaram duas técnicas para afastamento gingival (AG), convencional e sem fio: 1- um estudo in vitro que avaliou acitotoxicidade/genotoxicidade, e o pH de agentes à base de AlCl3; e 2- um ensaio clínico randomizado que avaliou a eficácia destas técnicas. Na fase in vitro, eludatos foram obtidos pela diluição dos eluates agentes à base de AlCl3 em meio de cultura por 1h, 4h e 24h. Os valores de pH foram aferidos por pHmetro digital, citotoxicidade pelo teste MTT e genotoxicidade pelo teste do Micronúcleo. Um ensaio clínico randomizado, cruzado, duplo-cego foi concebido para avaliar fatores clínicos, imunológicos e individuais antes e após AG por duas técnicas, convencional (C: fio gengival + gel adstringente) e sem fio (SF: pasta à base de adstringente). Estes fatores foram avaliados em incisivos preparados para coroas metalo-cerâmicas antes, 1 dia e 10 dias após AG. As concentrações de Interleucina 1&#946;, Interleucina 6 e Fator de Necrose Tumoral &#945; foram avaliadas no fluido gengival crevicular coletado antes (controle) e 1 dia após AG. Os dados do estudo in vitro foram analisados por ANOVA 2-fatores e teste de Tukey. Os dados do ensaio clínico foram analiados por ANOVA para medidas repetidas e teste de Tukey (fator imunológico), teste de Friedman (parâmetros periodontais), e Exato de Fisher ou teste Qui-quadrado (dor, estresse e sabor desagradável). Todos os testes consideraram p<0.05. Os valores médios de pH foram estatísticamente superiores para C que para SF. As técnicas não foram citotóxicas no tempo de 1h. SF foi mais citotóxica que C em 4h e 24h. A genotoxicidade SF foi semelhante à do grupo controle. Nenhuma das técnicas avaliadas resultou em piora nos indices periodontais. Atétnica C foi mais estressante 9 que a SF, e semelhantes considerando dor e sabor desagradável. AG realizado por ambas as técnicas levou a maiores concentrações médias das três citocinas avaliadas. C resultou nos maiores níveis de interleucinas. In vitro, os adstringentes apresentaram atividade biológica aceitável, sem diferença na genotoxicidade entre as técnicas. In vivo, SF foi menos estressante e resultou em menores níveis de citocinas após AG

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