Lead Tin Research Articles

Microanalytical identification of Pb-Sb-Sn yellow pigment in historical European paintings and its differentiation from lead tin and Naples yellows

The work is focused on identification of lead tin yellow types I and II, Naples yellow, and also on discrimination of a less common, distinct yellow pigment, the ternary Pb-Sb-Sn oxide. The knowledge about all those Pb-based yellows was in fact forgotten after introduction of modern synthetic yellows in 19th century. As late as in the last decade of the 20th century, the existence of Pb-Sb-Sn yellow and its production have been rediscovered, and only then it has been identified in colour layer of artworks. Pb-Sb-Sn yellow has recently been identified in colour layer of 17th century Italian paintings by Sandalinas and Ruiz-Moreno [C. Sandalinas, S. Ruiz-Moreno, Lead tin-antimony yellow, historical manufacture, molecular characterization and identification in seventeenth-century Italian paintings, Stud. Conserv. 49 (2003) 41–52], and here we report the finding of this pigment in Mid-European painting of the 18th and 19th centuries. Lead tin yellows, lead antimony yellow (Naples yellow), and lead antimony tin yellow were synthesized in laboratory following historical recipes, their colour was analyzed, and their structure was confirmed to provide a basis for their routine identification in microsamples of artworks by X-ray microdiffraction. Unequivocal identification of Pb-based yellows could help in authentication of traditional European paintings, because their use was temporally and also geographically specific. Combination of elemental microanalysis (X-ray fluorescence electron microanalysis) and X-ray powder microdiffraction were found very efficient in the microanalysis of colour layers of artworks with Pb-based yellows and their unequivocal identification.

Torsion test applied for reballing and solder paste volume evaluation

Electronic second level interconnect reliability characterization by accelerated thermal-cycling (ATC) test for long-term mission profile is costly and high time consuming. In order to reduce test duration, the torsion test was applied using some specific test parameters to reproduce the same failure modes found in accelerated thermal cycling (ATC) test and in the field. In this paper, we present the torsion test parameters definition and two demonstrations of torsion test application to accelerate reliability characterization of second level interconnect. The first application is the comparison between full SnPb (tin–lead) and reballed LF (lead-free) packages using SnPb balls. In the second the reliability of ceramic BGA solder joints using different solder paste volume was evaluated. In both cases, ATC test results were used as reference. The results suggest that torsion test is a valuable test method and can be applied to evaluate the impact of design and process variations in very short time.

Relieving Sn whisker growth driven by oxidation on Cu leadframe by annealing and reflowing treatments

Owing to environmental concern, Pb-free solders are replacing eutectic tin lead in electronic packaging industry. Thus, whisker growth becomes a serious reliability issue for Sn finishes. In this study, the mechanism of whisker growth from Sn finish on Cu leadframe was investigated under the temperature/humidity storage test. It is found that oxidation of the Sn finish was the driving force behind the whisker growth. Thermal treatments including annealing at 220 °C and reflowing at 260 °C were employed to mitigate the whisker growth. It is found that both heat treatments can significantly reduce the whisker growth rate. It is speculated that the heat treatments can relieve the residual stress in the Sn finishes and can modify their grain structure, resulting in a slower oxidation rate. Thus, they can slow down the grow rate of Sn whiskers. In addition, reflowing treatment can change the columnar grain structure of the Sn film to the equiaxed grain structure in some of its regions, resulting in a lower grain boundary diffusion rate of Sn. Therefore, the reflowed sample had the lowest growth rate of Sn whiskers.

Electrical and thermal conductivities and thermopower of some lead free solders (LFS) in the liquid and solid state

We have measured the electrical resistivity and thermopower of industrial liquid and solid lead–tin alloys and of several lead free solders (Sn–Ag; Sn–Cu; Sn–Sb; Sn–Ag–Cu), and have deduced the thermal conductivity as a function of the temperature by using the relations between the electronic transport coefficients. The resistivity of lead free solders are smaller than those of lead–tin alloys, which is desired. Similarly the algebraic value of the thermopower is increased in the liquid. From an electronic and thermal point of view, lead free solders have better properties than lead–tin alloys. Calculated values are compared to our experimental ones and give good results for the alloys. It is shown that the best lead free solders have an increased thermal conductivity up to 30% in liquid and solid state.

EDXRF and micro-EDXRF studies of Late Bronze Age metallurgical productions from Canedotes (Portugal)

Metallurgical production in Central Portugal during the Late Bronze Age was primarily based on copper–tin alloys, despite influences from the Atlantic area where copper–tin–lead alloys are common. Metallic artefacts from archaeological site of Canedotes (Central Portugal) were analysed by EDXRF to establish the type of alloys present. Polished spots in selected artefacts were also analysed by micro-EDXRF to determine the major and minor elemental composition of the original alloys. The collection constitutes 18 copper–tin artefacts and one unalloyed copper artefact with tin and arsenic as minor constituents. Artefacts that require a thermomechanical finishing process, such as tools and weapons, seem to have improved control over the tin content. The composition of two buttons, one cramp and one metallic droplet suggest that some of the copper sources were rich in arsenic. Finally, the low iron content of the artefacts seems to agree well with the smelting of copper ores in crucible furnaces, a smelting process used in certain areas of the Iberian Peninsula until pre-Roman times.

Superplastic power-law creep of Sn–40%Pb–2.5%Sb peritectic alloy

The power law-creep behavior of superplastic Sn–40Pb–2.5Sb alloys with different grain sizes has been investigated at room temperature. Stress exponent values for these alloys have been determined by indentation creep, conventional creep and uniaxial tension tests in order to evaluate the correspondence of indentation creep results with conventional tests. In all cases, the indentation results were in good agreement with each other and with those of the tensile and conventional creep tests. The average stress exponent values of about 2.6 and 3.0 corresponding to the strain rate sensitivity (SRS) indices of 0.33–0.39, depending on the grain size of the materials, indicate that the grain boundary sliding is the possible mechanism during creep deformation of Sn–Pb–Sb alloys. Within limits, the indentation tests are thus considered useful to acquire information on the creep behavior of small specimens of these soft tin–lead–antimony alloys at room temperature. It is also demonstrated that the indentation creep test provides a convenient method to measure SRS and thereby to assess the ability of a material to undergo superplastic deformation.

Leaded electronic waste is a possible source material for lead-contaminated jewelry

Highly leaded jewelry, often imported from China, remains widely available in the United States. Leaded electronic waste is exported from the United States to several Asian countries where solder is recovered and circuit boards are stripped of parts in small workshops. To assess whether electronic waste is being recycled into the jewelry, lead, tin and copper content of highly leaded jewelry samples were determined by atomic absorption spectrometry. Sixteen jewelry items previously determined to contain 20–80% lead by weight were analyzed. Samples were digested in nitric acid for analysis of lead and copper, and in aqua regia for analysis of tin. Six samples contained significant amounts of tin, from 20.8% to 29.9% by weight. In addition, copper was a significant minor component of five of these samples (up to 4% by weight). Copper (present at 10–40% by weight in circuit boards) was shown to rapidly move into heated lead–tin solder. The combined lead–tin–copper content of these six items ranges from 93.5% to 100%, suggestive of a solder-based source material. These results are consistent with the hypothesis that recycled circuit board solders are being used to produce some of the heavily leaded imported jewelry sold in the United States. Should this hypothesis be substantiated, it suggests that environmental policies to protect children’s health must address both proper recycling of source materials as well as restrictions of the lead content in consumer goods.

Evolution of mechanical and electrical properties of tin–lead and lead free solder to copper joint interface

Cu–(Sn37Pb) and Cu–(Sn3.5Ag0.5Cu) solder joints were prepared at the same reflow temperature of 230 °C. The microstructural observation of the solder assemblies in scanning and transmission electron microscopes confirmed the presence of η-Cu 6Sn 5 in case of the former, and Cu 3Sn + η-Cu 6Sn 5 for the latter in the reaction zone. The findings are correlated with the electrical and mechanical properties of the joints. Lead free solder-Cu joint exhibited lower reaction zone thickness and improved electrical conductivity (0.28 × 10 6Ω − 1 cm − 1 ) and shear strength ∼ 68MPa compared to conventional lead–tin solder-Cu joint. The latter showed electrical conductivity and shear strength of 0.22 × 10 6Ω − 1 cm − 1 and ∼ 55 MPa, respectively. The difference in reaction zone thickness is explained on the basis of melt superheat, with Sn being the primary diffusing species in the intermetallic layer.

A quasi two-dimensional benchmark experiment for the solidification of a tin–lead binary alloy

A horizontal solidification benchmark experiment with pure tin and a binary alloy of Sn-10 wt.%Pb is proposed. The experiment consists in solidifying a rectangular sample using two lateral heat exchangers which allow the application a controlled horizontal temperature difference. An array of fifty thermocouples placed on the lateral wall permits the determination of the instantaneous temperature distribution. The cases with the temperature gradient G = 0 , and the cooling rates equal to 0.02 and 0.04 K/s are studied. The time evolution of the interfacial total heat flux and the temperature field are recorded and analyzed. This allows us to evaluate heat transfer evolution due to natural convection, as well as its influence on the solidification macrostructure. To cite this article: X.D. Wang et al., C. R. Mecanique 335 (2007).

Impression creep of monolithic and composite lead free solders

Even though several EMS (Electronic manufacturing services) companies are currently producing “lead free” products, a general notion of apprehension still exists in the industry, primarily due to the lack of sufficient mechanical reliability data supporting the use of lead free alloys. The current study was an effort to generate an understanding of the mechanisms of creep deformation in monolithic and composite (Ag and Cu reinforced) Sn–3.5Ag and Sn–3.0Ag–0.5Cu lead free alloys in the high stress high temperature regime. Small volume solder samples were reflowed using a custom built computer controlled resistance furnace. Impression creep testing was employed to determine the activation energy and stress exponent. A careful analysis of the collected data revealed the underlying creep mechanisms and the following conclusions could be made. Both Sn–3.5Ag and Sn–3.0Ag–0.5Cu exhibited higher creep resistance as compared to the eutectic tin–lead solder under all tested conditions, with the ternary lead free alloy marginally outperforming the binary lead free alloy. Composite solders performed better as compared to monolithic solders. Furthermore, Cu reinforced solders demonstrated higher creep resistance as compared to Ag reinforced solders.

Annealing Effects on Powder Metallurgy Based Pb<sub>1-x</sub>Sn<sub>x</sub>Te Materials for Thermoelectric Applications

Lead tin telluride based alloys are known p-type materials for thermoelectric applications, in the 50-600oC temperature range. These alloys combine desired features of mechanical and thermoelectric properties. The electronic transport properties of PbTe and Pb1-xSnxTe materials may be strongly dependent on the preparation technique. Powder metallurgy process is known to introduce defects and strains, that may alter carrier concentration. Under such non-equilibrium conditions the thermoelectric properties are instable at the operating temperature. An appropriate annealing treatment can eliminate this effect.. The present communication describes the annealing treatment applied to cold compacted and sintered Pb1-xSnxTe materials.

In-doped Pb 0.5Sn 0.5Te p-type samples prepared by powder metallurgical processing for thermoelectric applications

Lead tin telluride-based alloys are appropriate p-type materials for thermoelectric applications in the 50–600 °C temperature range. Optimization of the thermoelectric performance in different temperature ranges can be achieved by varying the composition ( x values) in Pb 1− x Sn x Te alloys. An alternative approach for controlling the carrier concentration can be attained by indium doping the Pb 1− x Sn x Te alloys at a fixed composition. This second approach allows attaining a controlled energy gap and a specific lattice thermal conductivity. The present communication focuses on the development of Pb 0.5Sn 0.5Te alloys doped to different levels of indium concentration. The preparation techniques included preparation of master alloys with the desired composition, comminuting to appropriate powder particle size, cold compaction, sintering and annealing. The samples were examined by transport properties measurements. Thermoelectric figures of merit, Z, of ∼0.6–0.7×10 −3 K −1 were obtained for Pb 0.5Sn 0.5Te samples doped to levels of 0.5, 0.1 and 0.03 at% indium for the ∼100–300, 300–400 and 400–500 °C temperature ranges, respectively.

Isothermal aging effects on flex cracking of multilayer ceramic capacitors with standard and flexible terminations

Multilayer ceramic capacitors (MLCCs) are known to experience flex cracking when subjected to bending stresses. An experimental study was conducted to determine the susceptibility to flex cracking of flexible- and standard-termination surface mount MLCCs assembled with lead-free or tin–lead solders and aged at two different temperatures for 200 h. Experimental results showed that MLCCs mounted on printed circuit boards with lead-free solder are less susceptible to flex cracking compared with MLCCs mounted on boards with eutectic tin–lead solder. Two factors which make capacitors assembled with lead-free solder less susceptible to flex cracking were discussed: the lower tensile stresses inside the capacitor body which are a result of the differing elastic–plastic mechanical properties of the solder, and the higher residual compressive stresses after solder reflow assembly which are a result of the higher solidification temperature for the Sn3.0Ag0.5Cu lead-free solder. Flexible-termination MLCCs showed much more resistance to flex cracking in comparison to standard-termination MLCCs assembled with both lead-free and tin–lead solders. Aging at elevated temperatures had little effect on flex cracking susceptibility of MLCCs assembled with tin–lead solder. For MLCCs assembled with lead-free solder, aging at 150 °C increased the susceptibility to flex cracking in comparison with un-aged MLCCs.

A numerical investigation on the influence of liquid properties and interfacial heat transfer during microdroplet deposition onto a glass substrate

This work investigates the impingement of a liquid microdroplet onto a glass substrate at different temperatures. A finite-element model is applied to simulate the transient fluid dynamics and heat transfer during the process. Results for impingement under both isothermal and non-isothermal conditions are presented for four liquids: isopropanol, water, dielectric fluid (FC-72) and eutectic tin–lead solder (63Sn–37Pb). The objective of the work is to select liquids for a combined numerical and experimental study involving a high resolution, laser-based interfacial temperature measurement to measure interfacial heat transfer during microdroplet deposition. Applications include spray cooling, micro-manufacturing and coating processes, and electronics packaging. The initial droplet diameter and impact velocity are 80 μm and 5 m/s, respectively. For isothermal impact, our simulations with water and isopropanol show very good agreement with experiments. The magnitude and rates of spreading for all four liquids are shown and compared. For non-isothermal impacts, the transient drop and substrate temperatures are expressed in a non-dimensional way. The influence of imperfect thermal contact at the interface between the drop and the substrate is assessed for a realistic range of interfacial Biot numbers. We discuss the coupled influence of interfacial Biot numbers and hydrodynamics on the initiation of phase change.

Self-organization of PbTe and SnTe nanostructures on the van der Walls GaSe(0001) surface

The formation of nanodimensional defects on the van der Waals (0001) surface of a gallium selenide (GaSe) layered crystal and the growth of lead telluride (PbTe) and tin telluride (SnTe) nanostructures by deposition on this surface from the vapor phase has been studied. It is established that linear defects of various shapes and nanodimensional cavities (nanocavities) are formed on the van der Waals surface of a GaSe crystal as a result of plastic deformation. The nucleation and growth of PbTe and SnTe nanostructures on the flat van der Waals surface and in the nanocavities proceeds according to different mechanisms. It is demonstrated that selective growth of lead and tin chalcogenide nanostructures is possible on the van der Waals surfaces with nanocavities formed as a result of self-organization in the uppermost (less than 1 nm thick) layer of a GaSe crystal.

The combined use of lead–tin yellow type I and II on a canvas painting by Pietro Perugino

This article reports the first occurrence of the combined use of lead and tin yellow type I and type II identified on the same paint layer. The two forms have been identified by Raman microscopy on a green layer from the background of the painting Gonfalone della Giustizia (confraternity of Justice banner) executed at Perugia around 1496 by Pietro Perugino.

Powder metallurgical processing of functionally graded p-Pb 1−xSn xTe materials for thermoelectric applications

Lead tin telluride-based compounds are p-type materials for thermoelectric applications, in the 50–600 °C temperature range. The electronic transport properties of PbTe and Pb 1− x Sn x Te materials are strongly dependent on the processing approach. Powder metallurgy is a suitable approach for the preparation of Functionally graded materials (FGMs) but its effects on the electronic properties have to be carefully checked. Powder metallurgical processing may introduce atomic defects and local strains into the material and, thereby, alter the carrier concentration. Such material may be in non-equilibrium conditions at the operating temperature with unstable thermoelectric properties. This effect can be reduced and eliminated by appropriate annealing procedures. In FGMs, annealing up to the stabilization of the thermoelectric properties is mandatory for achieving the desired carrier concentration profile along the sample. The design procedures of the FGMs, as well as the annealing effects on cold compacted and sintered Pb 1− x Sn x Te samples are described in details.

Re‐calibration of Engelmaier's Model for Leadless, Lead‐free Solder Attachments

AbstractIn this paper, the solder attachment fatigue model created by Werner Engelmaier is re‐calibrated in order to make it applicable in conjunction with leadless, lead‐free solder attachments. Sn3.8Ag0.7Cu solder attached ball‐grid‐array components are addressed to three thermal cycling test profiles. Based on the results, both physical and statistical parameters are obtained and compared with the values relevant to tin–lead solder assemblies. The validity of the statistical distribution selection (two‐parameter Weibull) is studied. Acceleration factors correlating different test profiles are obtained, and they are found to be only weakly dependent on the test vehicle type. Copyright © 2006 John Wiley & Sons, Ltd.

Time‐dependent density functional theory studies of the electronic absorption spectra of metallophthalocyanines of group IVA

AbstractTime‐dependent density functional theory (TD‐DFT) calculations were carried out in a comparative study of the electronic absorption spectra of lead(II) phthalocyaninate (PbPc), tin(II) phthalocyaninate (SnPc), tin(IV) dichlorophalocyaninate (PcSnCl2), germanium(II) phthalocyaninate (GePc), and germanium (IV) dichlorophalocyaninate (PcGeCl2) with the B3LYP method and LANL2DZ basis set. Our calculated bands correspond well with the experimental results. The electronic natures of all the bands in the absorption spectra are assigned and analyzed comparatively according to the calculated electronic transition contributions. With the increase of the dielectric constant from CHCl3 to DMSO, all the electronic absorption bands are somewhat red shift, consistent with the shift rules measured experimentally. The radius of the central metals has great influence to the absorption spectra, especially for the B bands. The influence of the radius of the central metals to the absorption spectra of PcSnCl2 and PcGeCl2 is smaller than to the spectra of the nonplanar MPcs (M = Pb, Sn, and Ge). Axial ligands also greatly changed the electronic absorption spectra due to the change of the orbital energy level and the molecular symmetry. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007

CCGA packages for space applications

Commercial-off-the-shelf (COTS) area array packaging technologies in high reliability versions are now being considered for applications, including use in a number of NASA electronic systems being utilized for both the Space Shuttle and Mars Rover missions. Indeed, recently a ceramic package version specifically tailored for high reliability applications was used to provide the processing power required for the Spirit and Opportunity Mars Rovers built by NASA-JPL. Both Rovers successfully completed their 3-months mission requirements and continued exploring the Martian surface for many more moths, providing amazing new information on previous environmental conditions of Mars and strong evidence that water exists on Mars. Understanding process, reliability, and quality assurance (QA) indicators for reliability are important for low risk insertion of these newly available packages in high reliability applications. In a previous investigation, thermal cycle test results for a non-functional daisy-chained peripheral ceramic column grid array (CCGA) and its plastic ball grid array (PBGA) version, both having 560 I/Os, were gathered and are presented here. Test results included environmental data for three different thermal cycle regimes (−55/125 °C, −55/100 °C, and −50/75 °C). Detailed information on these—especially failure type for assemblies with high and low solder volumes—are presented. The thermal cycle test procedure followed those recommended by IPC-9701 for tin–lead solder joint assemblies. Its revision A covers guideline thermal cycle requirements for Pb-free solder joints. Key points on this specification are also discussed. In a recent investigation a fully populated CCGA with 717 I/Os was considered for assembly reliability evaluation. The functional package is a field-programmable gate array that has much higher processing power than its previous version. This new package is smaller in dimension, has no interposer, and has a thinner column wrapped with copper for reliability improvement. This paper will also present thermal cycle test results for assemblies of this and its plastic package version with 728 I/Os, both of which were exposed to four different cycle regimes. Two of these cycle profiles are specified by IPC-9701A for tin–lead, namely, −55 to 100 °C and −55 to 125 °C. One is a cycle profile specified by Mil-Std-883, namely, −65/150 °C, generally used for ceramic hybrid packages screening and qualification. The last cycle is in the range of −120 to 85 °C, a representative of electronic systems directly exposed to the Martian environment without use in a thermal control enclosure. Per IPC-9701A, test vehicles were built using daisy chain packages and were continuously monitored and/or manually checked for opens at intervals. The effects of many process and assembly variables—including corner staking commonly used for improving resistance to mechanical loading such as drop and vibration loads—were also considered as part of the test matrix. Optical photomicrographs were taken at various thermal cycle intervals to document damage progress and behavior. Representative samples of these are presented along with cross-sectional photomicrographs at higher magnification taken by scanning electron microscopy (SEM) to determine crack propagation and failure analyses for packages.