Saab Microwave Systems, SMW is a supplier of radar systems. The circuit boards that are operating in their radars have components which solder joints contains lead. However, the EU directive RoHs and WEEE are causing SMW to prepare for a transition to lead free solder joints. The objective of this thesis is to gain deeper knowledge of lead free solder joints. Brittle fractures in solder joints is a type of failure that might increase in a transition to lead free solder joints. The brittle fractures are induced by the creation of the intermetallic phases which are formed during soldering. The amount and composition of the intermetallics affects the mechanical strength of the joint. An intermetallic layer is thickened during heat exposure as during soldering, thermal aging and rework. The focus of this thesis was to investigate how rework affect the brittleness of the lead free solder joint and thereby how the intermetallic layers change depending on chemical composition, design and reflow cycles. Two types of components and two types of solder materials (SnPb and SAC305) were studied. To study the mechanical properties of the joint a shear testing device was used. This is a way of measuring the reliability of the joint when subjected to mechanical shock. The intermetallic layers were examined in a Scanning Electron Microscope and the fracture surfaces were studied in a optical microscope, a scanning electron microscope and a stereomicroscope. The heat spread over the board where examined by soldering thermocouples to the board and plotting the values of time and temperature. The results showed that the rework process did not have any significant impact of the intermetallic growth. The adjecent and distant components were not damaged during rework. A lead free rework process can therefor be preformed successfully at SMW. The intermetallic layers formed at the interface between the a lead free solder and a nickel finish grew faster than an intermetallic layer formed between a leaded solder and a nickel finish. The presence of nickel could therefore have a more negative effect on the intermetallic growth rate for the lead free material compared to the leaded.

<p>Saab Microwave Systems, SMW is a supplier of radar systems. The circuit boards that are operating in their radars have components which solder joints contains lead. However, the EU directive RoHs and WEEE are causing SMW to prepare for a transition to lead free solder joints. The objective of this thesis is to gain deeper knowledge of lead free solder joints.</p><p>Brittle fractures in solder joints is a type of failure that might increase in a transition to lead free solder joints. The brittle fractures are induced by the creation of the intermetallic phases which are formed during soldering. The amount and composition of the intermetallics affects the mechanical strength of the joint. An intermetallic layer is thickened during heat exposure as during soldering, thermal aging and rework.</p><p>The focus of this thesis was to investigate how rework affect the brittleness of the lead free solder joint and thereby how the intermetallic layers change depending on chemical composition, design and reflow cycles. Two types of components and two types of solder materials (SnPb and SAC305) were studied.</p><p>To study the mechanical properties of the joint a shear testing device was used. This is a way of measuring the reliability of the joint when subjected to mechanical shock. The intermetallic layers were examined in a Scanning Electron Microscope and the fracture surfaces were studied in a optical microscope, a scanning electron microscope and a stereomicroscope. The heat spread over the board where examined by soldering thermocouples to the board and plotting the values of time and temperature.</p><p>The results showed that the rework process did not have any significant impact of the intermetallic growth. The adjecent and distant components were not damaged during rework. A lead free rework process can therefor be preformed successfully at SMW. The intermetallic layers formed at the interface between the a lead free solder and a nickel finish grew faster than an intermetallic layer formed between a leaded solder and a nickel finish. The presence of nickel could therefore have a more negative effect on the intermetallic growth rate for the lead free material compared to the leaded.</p>

Made available in DSpace on 2016-04-18T21:36:00Z (GMT). No. of bitstreams: 4 Danieli Cristina Pedroso1.pdf: 893786 bytes, checksum: 0b49df9c67021da69e5f47f5170c5703 (MD5) Danieli Cristina Pedroso2.pdf: 3031650 bytes, checksum: bbf4b2dc04de906b1c5596adb5c76bb8 (MD5) Danieli Cristina Pedroso3.pdf: 2597659 bytes, checksum: 1a3e7d52a670d6eb3f003b1583e76702 (MD5) Danieli Cristina Pedroso4.pdf: 198943 bytes, checksum: 16b69ef67e7c298a9fc35b695825e236 (MD5) Previous issue date: 2009-08-17 / In this work the causes of rejection of lots of artifacts from the company Produto para Linhas Preformados, PLP, were analyzed which are made of steel SAE 1010 and SAE 1020 and zinc coated by hot-dip galvanizing. Lots of samples from different manufacturers were selected, with different chemical composition and geometry, but belonging to rejected lots and approved lots in accordance with usual market standards. The rejections are due to problems related to the adhesion of the layer of zinc. The samples were submitted to optical microscopy test, scanning electron microscopy and X-ray diffractions for comparative checking of between the structures of zinc formed layers by hot -dip galvanizing. To verify the corrosion in coating failure, corrosion tests were performed in three different environments: urban environment considered to be low-polluted; environment simulating sea water, salt spray. There is no failure evidence between the zinc coating and the substrate structure; irregular coatings and not very well defined phases were found in the rejected parts. In regions with failures, the results show a behavior similar to the literature with the rapid formation of rust at the beginning of the exposure followed by a show oxidation. / Neste trabalho foram analisadas as causas da rejeição de lotes de artefatos da empresa Produto para Linhas Preformados, PLP, fabricados com aços SAE 1010 e SAE 1020 e zincados por imersão a quente. Foram selecionadas amostras de lotes de fabricantes diferentes, com composição química e geometrias distintas, pertencentes a lotes rejeitados e a lotes aprovados de acordo com normas usuais de mercado. As rejeições se devem a problemas relacionados a aderência da camada de zinco. As amostras foram submetidas a exames por microscopia óptica, microscopia de varredura e análises por difração de raio-X para verificação comparativa entre as estruturas das camadas de zinco formadas no processo zincagem por imersão a quente. Para verificar a corrosão nas falhas de revestimento de zinco, foram realizados ensaios de corrosão em três ambientes diferentes: ambiente considerado urbano de baixa poluição; ambiente simulando água do mar; câmara de névoa salina. Não há indício de relação entre a falha nos revestimentos de zinco e a estrutura do substrato; revestimentos irregulares e com fases não muito bem definidas foram encontrados nas peças rejeitadas. Nas regiões com falha, os resultados evidenciam um comportamento semelhante ao da literatura, com formação rápida de ferrugem no início da exposição das peças seguida por uma oxidação lenta.