Conventional tin-lead solder alloys have been widely used in electronics interconnection owing to their properties such as low melting temperature, good ductility and excellent wettability on copper and other substrates. However, due to the worldwide legislation addressing the concern over the toxicity of lead, the usage of lead-containing solders has been phased out, thus stimulating substantial efforts on lead-free alternatives, amongst which eutectic Sn-Ag and Sn-Cu, and particularly Sn-Ag-Cu alloys, are promising candidates as recommended by international parties. To meet the increasing demands of advanced electronic products, high levels of integration of electronic devices are being developed and employed, which is leading to a reduction in package size, but with more and more input/output connections. Flip chip technology is therefore seen as a promising technique for chip interconnection compared with wire bonding, enabling higher density, better heat dissipation and a smaller footprint. This thesis is intended to investigate lead-free (eutectic Sn-Ag, Sn-Cu and Sn-Ag-Cu) wafer level solder bumping through electrodeposition for flip chip interconnection, as well as electroplating lead-free solderable finishes on electronic components. The existing knowledge gap in the electrochemical processes as well as the fundamental understanding of the resultant tin-based lead-free alloys electrodeposits are also addressed. For the electrodeposition of the Sn-Cu solder alloys, a methanesulphonate based electrolyte was established, from which near-eutectic Sn-Cu alloys were achieved over a relatively wide process window of current density. The effects of methanesulphonic acid, thiourea and OPPE (iso-octyl phenoxy polyethoxy ethanol) as additives were investigated respectively by cathodic potentiodynamic polarisation curves, which illustrated the resultant electrochemical changes to the electrolyte. Phase identification by X-ray diffraction showed the electrodeposits had a biphasic structure (β-Sn and Cu6Sn5). Microstructures of the Sn-Cu electrodeposits were comprehensively characterised, which revealed a compact and crystalline surface morphology under the effects of additives, with cross-sectional observations showing a uniform distribution of Cu6Sn5 particles predominantly along β-Sn grain boundaries. The electrodeposition of Sn-Ag solder alloys was explored in another pyrophosphate based system, which was further extended to the application for Sn-Ag-Cu solder alloys. Cathodic potentiodynamic polarisation demonstrated the deposition of noble metals, Ag or Ag-Cu, commenced before the deposition potential of tin was reached. The co-deposition of Sn-Ag or Sn-Ag-Cu alloy was achieved with the noble metals electrodepositing at their limiting current densities. The synergetic effects of polyethylene glycol (PEG) 600 and formaldehyde, dependent on reaching the cathodic potential required, helped to achieve a bright surface, which consisted of fine tin grains (~200 nm) and uniformly distributed Ag3Sn particles for Sn-Ag alloys and Ag3Sn and Cu6Sn5 for Sn-Ag-Cu alloys, as characterised by microstructural observations. Near-eutectic Sn-Ag and Sn-Ag-Cu alloys were realised as confirmed by compositional analysis and thermal measurements. Near-eutectic lead-free solder bumps of 25 μm in diameter and 50 μm in pitch, consisting of Sn-Ag, Sn-Cu or Sn-Ag-Cu solder alloys depending on the process and electrolyte employed, were demonstrated on wafers through the electrolytic systems developed. Lead-free solder bumps were further characterised by material analytical techniques to justify the feasibility of the processes developed for lead-free wafer level solder bumping.

This PhD project is focused on three lead-free ferroelectric solid solutions, which are specifically Na0.5Bi0.5TiO3-KNbO3(NBT-KN), Na0.5Bi0.5TiO3-NaNbO3(NBT-NN) and Na0.5Bi0.5TiO3-BaTiO3(NBT-BT), to evaluate the effects of composition, electric field and temperature on structural and electrical properties. Novel observations of both reversible and irreversible electric field-induced phase switching were made in both NBT-KN and NBT-NN ceramics. The NBT-KN solid solution is the primary focus of this thesis. All compositions were observed to be cubic in the as-sintered, unpoled state. However, a well-defined ferroelectric hysteresis P-E loop was obtained for compositions with low KN contents, indicating that an irreversible phase transition from a weak-polar relaxor ferroelectric (RF) to a long-range ordered metastable ferroelectric (FE) state had occurred during the measurement procedure. Both the unpoled and poled ceramic powders were examined using high resolution synchrotron XRD. For the poled state, a rhombohedral R3c structure was identified for compositions with low KN content, confirming the occurrence of the irreversible electric field-induced structural transformation from cubic to rhombohedral. In contrast, a cubic structure was retained for high KN contents, giving rise to reversible phase switching evidenced by constricted P-E hysteresis loops. Similar behaviour was observed for NBT-NN system. An 'in-situ' electric field poling experiment was conducted using high energy synchrotron XRD. In certain NBT-KN compositions the structural transformation, from cubic to mixed phase cubic+rhombohedral and finally single phase rhombohedral, occurred progressively with increasing cycles of a bipolar electric field. Similar behaviour was observed for NBT-NN compositions having low NN contents. Furthermore, the distributions of domain orientation and lattice strain over a range of orientations relative to the poling direction were determined for NBT-KN, NBT-NN and NBT-BT ceramics exhibiting the rhombohedral phase. By combining the structural information with the results of dielectric and ferroelectric measurements, a phase diagram was constructed to illustrate the influence of temperature and composition on the stability of the metastable ferroelectric and relaxor ferroelectric states for the NBT-KN system. Furthermore, the phase transition temperatures obtained from dielectric measurements were correlated with the ferroelectric and thermal depolarisation characteristics for each of the NBT-KN, NBT-NN and NBT-BT systems.

Thesis (M.S.)--State University of New York at Binghamton, Department of Physics, 2006. / Includes bibliographical references.

<p>The directive of the European parliament and of the council on the Restriction of the use of certain Hazardous Substances (RoHS) in Electrical and Electronic Equipment (EEE) took effect in the European Union on July 1, 2006. Japan, California, China and Korea are all closed markets for exporters of components containing lead from July 1, 2007. Taiwan and Australia are working with similar directives. The RoHS directive is the reason why this thesis about the implementation of lead-free soldering in highly reliable applications is necessary.</p><p>The European Lead Free soldering NETwork (ELFNET) status survey from 2005 shows that the majority of the companies are well informed, but 20% are still not active in lead-free soldering. The Swedish industry is for the most part prepared and 95% of the components are lead-free. The transition to lead-free soldering will have a major affect on logistics and administration, because the RoHS directive is 90% about administration and logistics problems. Only 10% is technical problems.</p><p>The higher melting point in lead-free soldering affects every stage of the lead-free manufacturing, from assembly to testing and repair.</p><p>The major concern for highly reliable applications are that there are not enough data to understand to what grade lead-free solders will perform differently from lead based solders. Five different types of reliability testing were studied in this thesis; vibration, mechanical shock, thermal shock, thermal cycling and combined environments. Whiskers, voids, brittle fractures and mixed assembly problems were also studied. Individual tests alone should not be used to make definite decisions on lead-free soldering reliability. The lower reliability for lead-free solders in some tests does not necessarily mean that lead-free solders not can be used in highly reliable applications like defence electronics.</p><p>The most important conclusions from this thesis are:</p><p>• Update or change the logistic system and mark/label according to available standards.</p><p>• Secure a good board layout.</p><p>• Secure a good process control.</p><p>• Alternative surface board should be used. Tin-silver-copper (SAC) is the most reliable solder and Electroless Nickel/Immersion Gold (ENIG) is the most reliable surface finish.</p><p>• Remember that the higher temperature affects every stage of the manufacturing.</p><p>• No increased problems with whiskers or risk of high voiding levels.</p><p>• Mixed assembly is a risk. Compatibility and contamination risks must be taken seriously.</p><p>• Which environment will the applications be in? If it is not a highly vibrating and thermal cycling environment, lead-free soldering should be safe to use.</p> / <p>Europaparlamentets och rådets direktiv om begränsning av användningen av vissa farliga ämnen i elektriska och elektroniska produkter började gälla i Europeiska unionen 1 juli, 2006. Japan, Kalifornien, Kina och Korea är alla stängda marknader för exportörer av komponenter som innehåller bly från och med 1 juli, 2007. Taiwan och Australien arbetar med liknande direktiv. RoHS-direktivet är anledningen till varför detta examensarbete om implementeringen av blyfri lödning i högtillförlitliga applikationer är nödvändigt.</p><p>En undersökning från 2005 av ELFNET visar att majoriteten av företagen är väl informerade, men 20% är fortfarande i aktiva med blyfri lödning. Den svenska industrin är till största delen väl förberedd och 95% av komponenterna är blyfria. Övergången till blyfri lödning kommer att ha stor effekt på logistik och administration, därför att 90% är administrations- och logistikproblem i RoHS-direktivet. Bara 10% är tekniska problem.</p><p>Den högre smälttemperaturen i blyfri lödning påverkar varje steg av den blyfria tillverkningen, från montering till testning och reparation.</p><p>Den stora oron för högtillförlitliga applikationer är att det inte finns tillräckligt med data för att förstå i vilken grad som blyfria lod kommer att bete sig annorlunda jämfört med blybaserade lod. Fem olika typer av tillförlitlighetstester har undersökts i detta examensarbete; vibration, mekanisk chock, termisk chock, termisk cykling och kombinerade tester. Whiskers, voids, sprödbrott och blandad montering studerades också. Individuella tester ska inte användas för att ta några definitiva beslut om blyfri lödnings tillförlitlighet. Den lägre tillförlitligheten för blyfria lod i en del tester behöver nödvändigtvis inte betyda att blyfria lod inte kan användas i högtillförlitliga applikationer som försvarselektronik.</p><p>De viktigaste slutsatserna från detta examensarbete är:</p><p>• Uppdatera eller byt logistiskt system och märk enligt tillgängliga standarder.</p><p>• Säkerställ en bra kretskortsdesign.</p><p>• Säkerställ en bra processkontroll.</p><p>• Alternativa mönsterkort bör användas. SAC är det tillförlitligaste lodet och ENIG är den tillförlitligaste ytbehandlingen.</p><p>• Kom ihåg att den ökade temperaturen påverkar varje steg i tillverkningen.</p><p>• Inga ökade problem med whiskers eller stort antal voids.</p><p>• Blandmontage är riskfyllt. Kompatibilitet och risker med kontaminering måste tas på allvar.</p><p>• Vilken miljö kommer applikationen att befinna sig i? Är det inte en starkt vibrerande eller temperaturcyklisk miljö bör blyfri lödning vara säkert att använda.</p>

Joining of electronic components onto the circuit boards is done by soldering operation, during production of all electronic devices. In many countries, including Turkey, traditionally used tin-lead (Sn-Pb) solder alloys have been restricted to be used in consumer electronics appliances because of the toxic effects of lead (Pb) within these alloys. Tin-silver-copper (Sn-Ag-Cu) based alloys have been developed as the most promising candidate that can replace the Sn-Pb alloys. However, various problems have emerged with the increasing trend in use of Sn-Ag-Cu solder alloys in electronics industry, namely large intermetallic compound formation, low wettability and thermal shock resistance. Many researches have been done in the past decade to overcome these problems. The solutions are based on changing the undercooling of the solder alloy / which was determined to be done by either changing the composition of the solder alloy by micro-alloying or changing the cooling rate during soldering operation. In this thesis study Sn-3.5Ag-0.9Cu (wt. %) lead-free solder having the eutectic composition, was micro-alloyed with additions of aluminum (Al), iron (Fe) and titanium (Ti). Experimental results were compared with commercially available near-eutectic Sn-40Pb (wt. %) solder, a commercially available Sn-3.0Ag-0.5Cu (wt. %) solder and also eutectic Sn-3.5Ag.0.9Cu (wt. %) and near-eutectic Sn-3.7Ag-0.9Cu (wt. %) solders that were produced for this thesis study. In the first stage of the study, the effects of 0.05 wt. % of Al, Fe and Ti micro-alloying were investigated. When preliminary results of mechanical and thermal test were compared, Fe was found to make positive effect on shear strength and undercooling. Further research was carried out to establish a relationship between the Fe compositions and solder properties. Therefore, 0.01, 0.03, 0.07 and 0.1 wt. % Fe additions were also studied and results were reported. 0.01 wt. % and 0.07 wt. % Fe added solders were found to have a smaller undercooling, resulting with dispersed intermetallic compound (IMC) and thus has highest shear strength. Different cooling rates / 0.017, 0.17 and 1.7 &deg / C/sec were applied to solder-copper joints and microstructures were investigated. Large IMC-free microstructure was achieved by 0.01 wt. % Fe micro-alloyed solder, which was cooled with 1.7 &deg / C/sec rate. Wetting of copper substrate was found to be improved by additions of Al, Fe and Ti compared to alloy with eutectic composition of Sn-Ag-Cu alloy. Selected SAC+X alloys have been subjected to thermal shock experiments for crack formation analysis on the copper substrate-solder joints. The results showed that SAC+0.05Al solder has the higher thermal shock resistance, which no cracks were observed after 1500 cycles of thermal shock. In order to understand the insights of SAC performance, some of the lead-free solders were applied onto printed circuit boards for thermal shock resistance test. These results have indicate that the cracking may occur after thermal shock cycles due to process conditions of soldering operation (i.e. cooing rate), independent of the solder alloy composition.

The directive of the European parliament and of the council on the Restriction of the use of certain Hazardous Substances (RoHS) in Electrical and Electronic Equipment (EEE) took effect in the European Union on July 1, 2006. Japan, California, China and Korea are all closed markets for exporters of components containing lead from July 1, 2007. Taiwan and Australia are working with similar directives. The RoHS directive is the reason why this thesis about the implementation of lead-free soldering in highly reliable applications is necessary. The European Lead Free soldering NETwork (ELFNET) status survey from 2005 shows that the majority of the companies are well informed, but 20% are still not active in lead-free soldering. The Swedish industry is for the most part prepared and 95% of the components are lead-free. The transition to lead-free soldering will have a major affect on logistics and administration, because the RoHS directive is 90% about administration and logistics problems. Only 10% is technical problems. The higher melting point in lead-free soldering affects every stage of the lead-free manufacturing, from assembly to testing and repair. The major concern for highly reliable applications are that there are not enough data to understand to what grade lead-free solders will perform differently from lead based solders. Five different types of reliability testing were studied in this thesis; vibration, mechanical shock, thermal shock, thermal cycling and combined environments. Whiskers, voids, brittle fractures and mixed assembly problems were also studied. Individual tests alone should not be used to make definite decisions on lead-free soldering reliability. The lower reliability for lead-free solders in some tests does not necessarily mean that lead-free solders not can be used in highly reliable applications like defence electronics. The most important conclusions from this thesis are: • Update or change the logistic system and mark/label according to available standards. • Secure a good board layout. • Secure a good process control. • Alternative surface board should be used. Tin-silver-copper (SAC) is the most reliable solder and Electroless Nickel/Immersion Gold (ENIG) is the most reliable surface finish. • Remember that the higher temperature affects every stage of the manufacturing. • No increased problems with whiskers or risk of high voiding levels. • Mixed assembly is a risk. Compatibility and contamination risks must be taken seriously. • Which environment will the applications be in? If it is not a highly vibrating and thermal cycling environment, lead-free soldering should be safe to use. / Europaparlamentets och rådets direktiv om begränsning av användningen av vissa farliga ämnen i elektriska och elektroniska produkter började gälla i Europeiska unionen 1 juli, 2006. Japan, Kalifornien, Kina och Korea är alla stängda marknader för exportörer av komponenter som innehåller bly från och med 1 juli, 2007. Taiwan och Australien arbetar med liknande direktiv. RoHS-direktivet är anledningen till varför detta examensarbete om implementeringen av blyfri lödning i högtillförlitliga applikationer är nödvändigt. En undersökning från 2005 av ELFNET visar att majoriteten av företagen är väl informerade, men 20% är fortfarande i aktiva med blyfri lödning. Den svenska industrin är till största delen väl förberedd och 95% av komponenterna är blyfria. Övergången till blyfri lödning kommer att ha stor effekt på logistik och administration, därför att 90% är administrations- och logistikproblem i RoHS-direktivet. Bara 10% är tekniska problem. Den högre smälttemperaturen i blyfri lödning påverkar varje steg av den blyfria tillverkningen, från montering till testning och reparation. Den stora oron för högtillförlitliga applikationer är att det inte finns tillräckligt med data för att förstå i vilken grad som blyfria lod kommer att bete sig annorlunda jämfört med blybaserade lod. Fem olika typer av tillförlitlighetstester har undersökts i detta examensarbete; vibration, mekanisk chock, termisk chock, termisk cykling och kombinerade tester. Whiskers, voids, sprödbrott och blandad montering studerades också. Individuella tester ska inte användas för att ta några definitiva beslut om blyfri lödnings tillförlitlighet. Den lägre tillförlitligheten för blyfria lod i en del tester behöver nödvändigtvis inte betyda att blyfria lod inte kan användas i högtillförlitliga applikationer som försvarselektronik. De viktigaste slutsatserna från detta examensarbete är: • Uppdatera eller byt logistiskt system och märk enligt tillgängliga standarder. • Säkerställ en bra kretskortsdesign. • Säkerställ en bra processkontroll. • Alternativa mönsterkort bör användas. SAC är det tillförlitligaste lodet och ENIG är den tillförlitligaste ytbehandlingen. • Kom ihåg att den ökade temperaturen påverkar varje steg i tillverkningen. • Inga ökade problem med whiskers eller stort antal voids. • Blandmontage är riskfyllt. Kompatibilitet och risker med kontaminering måste tas på allvar. • Vilken miljö kommer applikationen att befinna sig i? Är det inte en starkt vibrerande eller temperaturcyklisk miljö bör blyfri lödning vara säkert att använda.

As the world moves towards eliminating lead from consumer products, the microelectronics industry has put effort into developing lead-free solder paste. The major drawback of lead-free solder is the problems caused by its high reflow temperature. Variable frequency microwave (VFM) processing has been shown to allow some materials to be processed at lower temperatures. Issues addressed in this study include using VFM to reduce the solder reflow temperature, comparing the heating rate of different size solder particles, and comparing the reliability of VFM reflowed solder versus conventionally reflowed solder. Results comparing the effect of particle size on the heating rate of solder showed that the differences were negligible. This is due in part to the particle sizes overlapping. Many lead-free solder pastes reflow around 250℃. Results indicate that when using the VFM, lead-free solder paste will reflow at 220℃. The reliability of solder that was reflowed using the VFM at the reduced temperature was found to be comparable to solder reflowed in a conventional manner. Based on these findings, VFM processing can eliminate the major obstacles to making lead-free solder paste a more attractive option for use in the microelectronics industry.

Thesis (M.S.)--State University of New York at Binghamton, Thomas J. Watson School of Engineering and Applied Science, Department of Systems Science and Industrial Engineering, 2009. / Includes bibliographical references.

The disturbed state concept (DSC) based constitutive model is the focus of this research. It is applied for characterizing two problems; thermomechanical reliability analysis of electronic packages, and prediction of glacial motion. A new procedure for construction of static yield surface for materials is proposed. Further, a modified DSC model to include effect of rate of loading on material behavior is proposed.The DSC is applied to characterize the behavior of Sn-3.9Ag-0.6Cu (SAC) lead free solder alloy used in electronic packages. Proposed procedure of construction of static curve and rate dependent DSC model is applied for prediction of creep and rate dependent behavior of the SAC alloy. Laboratory test data is adopted from the literature and material parameters are determined. The DSC model is validated using the derived material parameters. A finite element analysis of the BGA 225 package is performed under cyclic thermomechanical loading. Analysis results are compared with available test data. A failure criterion for prediction of number of cycles to failure for BGA 225 is then derived.The second application of DSC discussed in this work is prediction of glacial motion. Mechanical behavior of glacial till and its contribution to overall ice movement is characterized using DSC. Two regionally significant tills are chosen and samples are collected from field. A series of laboratory tests are conducted on samples. Tests results are used for model calibration and validation. A numerical simulation of an idealized ice - till system under gravity loading is performed. Two such analyses are performed with DSC and Mohr Coulomb models and the results are compared.The DSC predicts failure when a significant portion of the material reaches a critical disturbance whereas the Mohr Coulomb model predicts failure based on peak stress. DSC predicts a gradual progression to failure whereas the Mohr Coulomb model predicts early catastrophic failure. According to DSC, the material undergoes considerable plastic strains before it reaches failure whereas the Mohr Coulomb predicts failure at very low elastic strains. In general the DSC is considered to provide a more realistic and general constitutive model for glacial tills.

The objective of this study is to understand the effect of surface roughness of the Cu substrate on the wetting of molten solder alloys. Eutectic Sn-Pb, pure Sn and eutectic Sn-Cu solder alloys and Cu substrates with different surface finish viz., highly polished surface, polished surface and unpolished surface were used in this work. Highly polished surface was prepared in Metallography lab, University of Kentucky while other two substrates were obtained from a vendor. Surface roughness properties of each substrate were measured using an optical profilometer. Highly polished surface was found to be of least surface roughness, while unpolished surface was the roughest. Hot-stage microscopy experiments were conducted to promote the wetting behavior of each solder on different Cu substrates. Still digital images extracted from the movies of spreading recorded during hot-stage experiments were analyzed and data was used to generate the plots of relative area of spread of solder versus time. The study of plots showed that surface roughness of the Cu substrate had major influence on spreading characteristics of eutectic Sn-Pb solder alloy. Solder showed better spreading on the Cu substrate with least surface roughness than the substrates with more roughness. No significant influence of surface roughness was observed on the wetting behavior of lead free solders (pure Sn and eutectic Sn-Cu).