1,721,014 research outputs found
Effect of Cooling Rate on the Microstructures and Mechanical Properties of Sn-Ag-Cu Lead-free Solder Joints on Cu Substrate
No full textThermodynamic issues of lead-free soldering in electronic packaging
No full textNew boundary conditions are foreseen which require alternative lead-free solder materials to Pb-Sn alloys in soldering of electronic packaging due to increasing environmental and health concerns over the use of lead. The reliability of soldered devices is related to wettability of the solder to the substrate and to microstructural evolution of the joint during soldering operation or in use. The reliability of the solder joint is strongly affected by type and extent of the interfacial reaction between solders and substrates. Accordingly, the solder-substrate interaction is increasingly important and a deeper understanding of the interfacial reaction between solder and substrate is necessary. A thermodynamic methodology to predict the intermetallic compound (IMC) phase, which forms first at the substrate/solder interface during the soldering process, has been suggested. By comparing the activation energy for nucleation of individual IMC phases, which is a function of the interfacial energy and the driving force for formation, the IMC phase that forms first is predicted as the one with the smallest activation energy. Additionally, the grain morphology of IMC at the solder joint has been explained through the energy-based calculations. The Jackson's parameter of the IMC grain with a rough surface is smaller than 2 while it is larger than 2 for faceted grains.This study was supported by the KOSEF(Korea Science and Engineering Foundation) through the Center for Electronic Packaging Materials (CEPM)
A thermodynamic study of phase equilibria in the Au-Sb-Sn solder system
No full textTo design and develop high-temperature solder alloys, the thermodynamic calculations of phase equilibria have been performed on the binary Au-Sb and ternary Au-Sb-Sn systems over the entire composition range. The Gibbs free energy of individual phases has been approximated using a subregular-solution model, and the thermodynamic parameters for each phase have been evaluated using available experimental information on phase boundaries and other related thermodynamic properties. The calculated phase diagrams and thermodynamic quantities of the Au-Sb binary system show good agreement with experimental data, and the liquidus projection and the vertical sections in the Au-Sb-Sn ternary system are well reproduced using assessed thermodynamic parameters derived in this work.This study has been supported by the Center for
Electronic Packaging Materials of the Korea Science
and Engineering Foundation
Effect of cooling rate on growth of the intermetallic compound and fracture mode of near-eutectic Sn-Ag-Cu/Cu pad: Before and after aging
No full textSeveral near-eutectic solders of (1) Sn-3.5Ag, (2) Sn-3.0Ag-0.7Cu, (3) Sn-3.0Ag1.5Cu, (4) Sn-3.7Ag-0.9Cu, and (5) Sn-6.0Ag-0.5Cu (in wt.% unless specified otherwise) were cooled at different rates after reflow soldering on the Cu pad above 250degreesC for 60 sec. Three different media of cooling were used to control cooling rates: fast water quenching, medium cooling on an aluminum block, and slow cooling in furnace. Both the solder composition and cooling rate after reflow have a significant effect on the intermetallic compound (IMC) thickness (mainly Cu6Sn5). Under fixed cooling condition, alloys (1), (3), and (5) revealed larger IMC thicknesses than that of alloys (2) and (4). Slow cooling produced an IMC buildup of thicker than 10 mum, while medium and fast cooling produced a thickness of thinner than 5 pm. The inverse relationship between IMC thickness and shear strength was confirmed. All the fast- and medium-cooled joints revealed a ductile mode (fracture surface was composed of the beta-Sn phase), while the slow-cooled joints were fractured in a brittle mode (fracture surface was composed Of Cu6Sn5 and Cu3Sn phases). The effect of isothermal aging at 130degreesC on the growth of the IMC, shear strength, and fracture mode is also reported.This study has been supported by the Center for
Electronic Packaging Materials of the Korea Science
and Engineering Foundation
Abnormal grain growth of Ni3Sn4 at Sn-33Ag/Ni interface
No full textBy the reaction of molten solder alloy with compositions of 96.5Sn-3.5Ag (compositions are all in weight percent unless specified otherwise) with either the thick Cu or the thick Ni substrate at 250degreesC, the rounded Cu6Sn5 grains formed over Cu and the faceted Ni3Sn4 grains precipitated over Ni. As the soldering time changed from 1 min to 60 min, normal grain growth occurred for rounded Cu6Sn5 grains while abnormal grain growth (AGG) mode was observed for faceted Ni3Sn4 grains. The measured grain size distributions also confirmed the difference between normal grain growth and abnormal grain growth.This study has been supported by the CEPM (Center for Electronic Packaging Materials) of the KOSEF (Korea Science and Engineering Foundation). Many discussions with Profs. S.-J. L. Kang and D. Y. Yoon at KAIST are gratefully acknowledged
Interfacial microstructure and joint strength of Sn-3.5Ag-X (X = Cu, In, Ni) solder joint
No full textInterfacial phase and microstructure, solder hardness. and joint strength of Sn-3.5Ag-X (X = Cu. In, Ni; compositions are all in wt% unless specified otherwise) solder alloys were investigated. Considering the melting behavior and the mechanical properties, five compositions of Sn-3.5Ag-X solder alloys were selected. To examine the joint characteristics, they were soldered on under bump metallurgy isothermally at 250 degreesC for 60 s. Aging and thermal cycling (T/C) were also performed on the solder joint. The interfacial microstructure of the joint was observed by scanning electron microscopy. X-ray diffraction and energy dispersive x-ray analyses were made to identify the type of solder phase and to measure compositions. Excessive growth of an inter-facial intermetallic layer in the Sn-3.5Ag-6.5 In solder joint led to a brittle fracture. In the other four solder joints, ductile fractures occurred through the solder region and the solder hardness was closely related with the joint strength.This study has been supported by the Center for Electronic Packaging Materials (CEPM) of the Korea Science and Engineering Foundation (KOSEF)
Morphological transition of interfacial Ni3Sn4 grains at the Sn-3.5Ag/Ni joint
No full textThe transition in morphology of Ni3Sn4 grains that formed at the interface between liquid Sn-3.5Ag (numbers are in wt.% unless specified otherwise) solder and Ni substrate has been observed at 250-650 degreesC. The morphological transition of Ni3Sn4 is due to the decrease of entropy of formation of the Ni3Sn4 phase and has been explained well by the change of Jackson's parameter with temperature. According to the variation of solder joint strength with temperature, it decreased rapidly between 350 degreesC and 450 degreesC, where the thickness of the Ni3Sn4 intermetallic compound (IMC) layer was around 6.5 mum. However, the solder joint strength decreased slowly with an increase of soldering time without a significant drop, although the thickness of the IMC was larger than 6.5 mum. The notable drop of solder joint strength and the fracture mode transition with increase of soldering temperature appears to come from excessive lateral growth of IMC grains between 350 degreesC and 450 degreesC.This study has been supported by the Center for
Electronic Packaging Materials of the Korea Science
and Engineering Foundation
Effect of under bump metallurgy and reflows on shear strength and microstructure of joint between Cu substrate and Sn-36Pb-2Ag solder alloy
No full textThe interfacial reaction between Sn-36Pb-2Ag (numbers are all in mass% unless specified otherwise) solder balls and Ni, Ag and Ni/Ag electroplated on a Cu substrate was investigated and the joint bonding strength was measured using a ball shear tester. The intermetallic Ag(3)Sn was observed at the interface of the Cu/Ag/solder joint and Ni(3)Sn(4) was found at the Cu/Ni/solder joint. In the case of Cu/Ni/Ag substrate, the layer sequence was observed to be Cu/Ni/Ni(3)Sn(4)/Ag(3)Sn/solder. The Ag layer was completely consumed by formation of Ag(3)Sn but the Ni layer remained. Environmental tests showed that the Cu/Ni/Ag substrate retained better solder joint reliability than either Ni or Ag single plated Cu substrate. Two types of reflow profiles were tested and the specimen reflowed by a higher temperature profile showed a higher solder joint strength. Solder joint strength and microstructural change were observed with several reflow cycles in considering the real board mounting conditions. There was significant evolution of solder and joint microstructures with reflow cycles and it explained well the change of solder joint strength.This study has been supported by the CEPM (Center for Electronic Packaging Materials) of the KOSEF (Korea Science and Engineering Foundation)
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