SnPb Solder Research Articles

Micro‐Particle Induced X‐ray Emission Study of Lead‐Free and Lead‐Based Solders and Interactions with Copper Wires

Pb‐free electrical solders, such as Cu–Sn alloys, work well for reflow soldering under tightly controlled conditions. Hand soldering, however, often results in poor quality joints compared to conventional Pb–Sn solders. To investigate this under realistic workshop conditions, micro‐particle induced X‐ray emission (micro‐PIXE) with 2 MeV protons has been employed. Commercial flux‐cored Cu–Sn and Pb–Sn solder wires are studied. Solder blobs under two cooling conditions as well as tinning Restriction of Hazardous Substances (RoHS)‐compliant and legacy component wires are investigated. The results show that the long heating and slow cooling of Cu–Sn solder blobs lead to formation of an acicular precipitate that can be ascribed to Cu6 Sn5. Pb–Sn solder under the same conditions shows phase separation with regions of high Sn and regions with high Pb. In the case of rapidly cooled blobs where a shiny surface is produced, no phase separation in either solder is observed. Tinning of RoHS‐compliant and legacy Cu component wires with the two solders produce significantly different interfacial depth profiles with varying degrees of grading, indicative of intermetallic phase formation.

FORMING OF A BIMETALLIC ELEMENT FOR THE RESISTANCE ELEMENT SOLDERING METHOD

The joining of sheet metal parts produced in the material combination of Fe-Fe, Fe-Al as well as Fe-thermoplastic and Al-thermoplastic can be realized by the Resistance Element Soldering (RES). Extruded bimetallic elements were used to form the overlap joint. The semi-finished product for extrusions was a Cu 99.9 tube with dimensions φ6 × 0.5 mm and length 9 mm, filled with Sn60Pb40 solder. “T” shaped overprints were produced in two ways. Simulation in the ANSYS software environment was chosen to optimize, select the appropriate forming process, and design the geometry of the functional parts of the forming tool, allowing to use only one extrusion forming operation. The results of the simulations are the magnitudes of stresses and strains, and different head shape geometries of the bimetallic element extrusions of the three proposed forming methods. The task was to achieve extrusions without defects of the Cu tube shell, such as corrugations and wrinkles. The geometry was observed and compared by macroanalysis of extrusion sections made on a laboratory forming tool.

Effects of Zn Addition on Dendritic/Cellular Growth, Phase Formation, and Hardness of a Sn–3.5 wt% Ag Solder Alloy

Sn–Ag‐based alloys are considered good alternatives to soldering operations as compared with the traditional Sn–Pb solder alloys. Herein, the effects of 0.5 and 1.0 wt% Zn additions to a Sn–3.5 wt% Ag eutectic alloy on cooling and growth rates, microstructure, and microhardness along the length of directionally solidified (DS) castings are examined. Characterization techniques such as optical microscopy (OM), scanning electron microscopy (SEM), X‐ray fluorescence (XRF), X‐ray diffraction (XRD), and Vickers microhardness are used to examine different samples extracted along the length of the DS castings. The Sn–3.5 wt% Ag alloy is shown to have a fully dendritic microstructure, characterized by a Sn‐rich matrix with the eutectic mixture located in the interdendritic regions. On the other hand, the alloy modified with 1 wt% Zn exhibits a microstructure entirely formed by β‐Sn cells, with a mixture of β‐Sn, ε‐Ag3Sn, and ζ‐AgZn phases in the intercellular regions. The DS Sn–3.5 wt% Ag–0.5 wt% Zn alloy casting exhibits a cellular/dendritic transition at a critical cooling rate of 8.5 °C s−1. The 0.5 wt% and 1 wt% Zn additions to the Sn–3.5 wt% Ag alloy improve hardness by 42.6% and 47.5%, respectively.

Reliability and Lifetime Prediction Model of Sintered Silver Under High-Temperature Cycling

Although excellent reliability has been reported for sintered silver as a die-attach material under both thermal and power cycling loads in power electronics applications, the promise of this material as a large-area attachment at temperatures beyond 200 °C needs to be investigated. This article presents insights into the thermomechanical behavior and reliability of sintered silver under extreme thermal cycling conditions. In this study, we bonded sintered silver samples and subjected it to a thermal cycling profile of −40 °C to 200 °C with high ramp rates. We periodically monitored samples under thermal cycling to detect the presence of any failure mechanisms using a scanning acoustic microscope. We also included 95Pb5Sn solder in the study to obtain reference data. Results show the occurrence of cracks in sintered silver followed by a rapid rate of crack growth that exceeded the failure criterion in just 50 cycles. The predominant failure mechanism we observed was adhesive failure. As a large-area attachment, solder exhibited a higher reliability than sintered silver but failed within 100 cycles. Finally, we performed thermomechanical modeling to compute strain energy density values and correlated these with the experimentally observed crack growth rates to formulate a lifetime prediction model for sintered silver.

Investigation of properties and structure of alloys of the lead-stibium system

Annotation. Problem. The problem is to obtain a database on the structure and properties of Pb-Sn solders, which are widely used in radio engineering. Target. The purpose of this work was to study the influence of the chemical composition of low-melting solders of the Pb-Sn system on the main mechanical properties and structure. Method. To achieve this goal, a complex of metallographic, mechanical and analytical studies of samples in the initial state was carried out. Results. The hardness of POS-40 and POS-61 solders turned out to be significantly higher compared to the hardness of the pure components from which they are formed. Mechanical studies have shown that the strength characteristics in POS-40 solder are lower, and ductility is higher than in POS-61. Both alloys had approximately the same relaxation properties and within 100 seconds the stress decreased by 70-80%. These data testify to the high ability of the materials that were studied to relieve stresses arising in the junction. Metallographic studies have shown that the structural state of the alloys that have been studied corresponds to the Pb-Sn diagram. The data obtained as a result of research on the properties and structure of POS-40 and POS-61 solders can be used in practice.

Interface Embrittlement Between 63Sn-37Pb Solder and Au Layer—Part 1: Physical Metallurgy of Liquid-State and Solid-State Reactions

Interface Embrittlement Between 63Sn-37Pb Solder and Au Layer—Part 1: Physical Metallurgy of Liquid-State and Solid-State Reactions

Anthropocene Geochemical and Technological Signatures of an Experimental Landfill Bioreactor in the Central Valley of California

The geochemical signatures of a 12-year-old experimental bioreactor at a California landfill are used to identify elemental concentrations and ratios that characterize the landfill and relate it to the age and state of technology of the deposited waste. The bioreactor was constructed and sealed with a synthetic liner during 2001–2002 and operated and monitored as an anaerobic digester to enhance methane production. In 2013, the bioreactor was sampled and trace element concentrations of the extracted fine fractions were determined. The concentrations normalized to a regional soil composition, reveal systematic peaks for transition metals, alkali metals, heavy metals, and various metalloids and non-metals. A group of potential solder elements (Cu, Zn, Cd, In, Sn, Pb, Bi, and Sb) shows moderate to strong co-variations and is largely attributed to household electronic components and other similar products, while elements that correlated well with rare-earth and other elements are related to the diluting effect of a soil component used as cover. Batteries show modest to little effects on the overall concentrations. Circulating fluids (recycled leachate) in the controlled reactor did not completely redistribute and homogenize the elemental signatures within the time frame of the bioreactor. It is concluded that the present experimental landfill defines an Anthropocene marker identifiable by building material (plaster), PVC plastic, and household electronic components (Pb–Sn solder). These marker elements and ratios are variably diluted by soil components identified by alkali metals, rare-earths, and high field-strength elements (Hf, Zr, Nb, and Ta).

Effect of Various Parameters on the Shear Strength of Solid-State Nanoporous Cu Bonding in Cu–Cu Disks for Power Device Packaging

Nanoparticle sintering is considered a promising alternative bonding method to Pb-based soldering for the attachment of components in high-temperature electronic devices. However, the technology still poses certain challenges, such as the difficulty in controlling the joint thickness and the generation of voids owing to solvent evaporation. In this study, a solid-state (solvent-free), nanoporous-Cu (NPC) bonding method was examined. The purpose of this study was to find the effect of the bonding temperature (200–400°C) and atmosphere (N2 or formic acid) on the shear strength of the joints formed between the NPC sheets and bare Cu disks for the replacement of the Pb–5Sn solder joint for high-temperature applications (> 300°C). The NPC/Cu joints were investigated by scanning electron microscopy, x-ray diffraction, and transmission electron microscopy. It was shown that the bondability of NPC under a N2 atmosphere is closely related to the oxide layer formed on the NPC surface that impairs the diffusion of Cu atoms between the NPC and Cu substrate. Furthermore, the densification of the NPC microstructure under a formic acid atmosphere at ≥ 350°C owing to the rapid diffusion of Cu atoms and accompanying plastic deformation induced by surface stress enhances the shear strength of the resulting NPC/Cu joint. The shear strength of the NPC/Cu joints formed under a formic acid atmosphere increased from 14.1 MPa to 35.9 MPa with an increasing bonding temperature. These results suggest that the NPC/Cu joints are a good alternative to Pb–5Sn solder joints. Based on the results of the investigation, a mechanism was proposed to explain the superiority of the Cu–Cu joints achieved using this method.

Investigation on the Influence of Nickel Contamination of Plated Through Hole (PTH) Solder Joint Integrity

An investigation was conducted to examine the validity of current industry maximum nickel contamination limits, which are established to ensure plated through hole solder joint integrity, for SnPb and SAC305 solder baths. Test vehicles were processed using three levels of nickel contamination for each solder: 0.01 wt.%, 0.02 wt.%, 0.05 wt.% for SnPb solder and 0.05 wt.%, 0.07 wt. %, 0.10 wt.% for SAC305 solder. The test vehicles were subjected to thermal cycle testing in accordance with the IPC-9701 specification. Based on this testing, the authors recommend that the allowable nickel contamination levels listed in the IPC-J-STD-001 specification (Table 3-1, Maximum Limits of Solder Bath Contaminant) be 0.05 wt.% for SnPb Assembly, 0.05 wt.% for SnPb Preconditioning, and 0.10 wt.% for SAC305 Pb-free Assembly.

Morphological and Structural Properties of Sn-Bi Lead-Free Solder in 6 M Potassium Hydroxide

Sn-based lead-free solder alloys have been explored extensively as an alternative to the conventional Sn–Pb solder alloys. While the miniaturization of electronic devices and the growth of appliance area, the corrosion resistance of solder alloys play a crucial element in the reliability of electronic devices in a prolonged period of service. This paper determines the corrosion effect of Sn-Bi solder lead-free solder, particularly immersed in alkaline solution which is potassium hydroxide. Morphological and elemental analyses reveal the formation of oxides on the surface after immersion after using a scanning electron microscope, dispersive energy X-ray and X-ray diffraction. The result of morphology reveals that the Sn matrix in plateau indicated dark contrast while Bi-rich in the lamellar eutectic structure indicated in light contrast appearance. In addition, phase and elemental analyses revealed the formation of mixed corrosion products of SnO, SnO2 and Bi2O3 on the surface after testing. It is hoped that this finding will provide some helpful evidence in clarifying the corrosion progress of lead-free solder alloys. Furthermore, the remaining corrosion potential and current of Sn-Bi in 6 M potassium hydroxide solutions in this research are proposed.

Three-dimensional interface and property of SnPb solder joint under extreme thermal shocking

To meet the demand of cryogenic reliability on the electronic packaging for deep space satellite, the three-dimensional interfacial morphology and property of eutectic SnPb solder joint under an extreme thermal shocking of 77–423 K were investigated. After thermal shocking, Cu-Sn IMC layers coarsened in the cross-sectional observation and micro-cracks formed in Cu6Sn5 layer. The rough Cu6Sn5 layer in the top view gradually smoothed, with broken Cu6Sn5 particles and exposed Cu3Sn. In the bottom-view observation, the Cu6Sn5 layer of as-soldered joint was overlapped by Cu3Sn layer. But no defects were generated in Cu3Sn layer. The shear force of solder joint was greatly reduced due to broken Cu6Sn5 with the changing fracture characteristics from the solder-controlled mode to the solder/IMC mixed mode.

Mixed Assembly of Lead-free Solder Joint: A Short Review

The transition from lead (Pb) to Pb-free solder has arisen the need for the development of the reliability of mixed assemblies solder joint research. Mixed assemblies are defined as solder joints that joint together with different compositions or solder forms for example Ball Grid Array (BGA) and solder paste. During the transition period of solder materials, mixed assemblies are still used in electronic packaging. In addition, Pb-free manufacturing has been forced to release some of the product categories since legislation banning the use of lead solder in electronic assemblies. This phenomenon causes health and environmental concern of the Pb solder used in electronic assembly. Hence, some electronic assemblies will continue to use traditional eutectic Sn–Pb solder paste while others will use Pb-free solder paste. This situation indicates that the use of mixed assemblies in electronics manufacturing is still inevitable. This paper presents a projection of the reliability of mixed assembly’s Pb-free solder joint.

Geometry Influence on Fracture Behavior of Lap-Shear Solder Joints

Single lap-shear (SLS) specimens of 63Sn37Pb solder joints were prepared with three different adherend thicknesses at three varying joint lengths. The fracture force was measured at a shear strain rate of 0.01 s <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−1</sup> for different geometries. The elastic–plastic fracture mechanics (EPFM) theory was used to find the energy dissipated in each case using a finite element model (FEM), and the fracture energy was obtained by cohesive zone modeling (CZM). Both 2-D and 3-D models were used to explain the variations in fracture energy by the level of constraint on the joint. Also, the plastic zone area and stress distribution along the solder layer were calculated at the moment of fracture. A phase angle definition was proposed and compared in different solder lengths to show its influence on fracture energy. It was concluded that the fracture energy was influenced by the local phase angle and plastic zone area at the moment of fracture. The effect of adherend thickness on fracture load was significant especially for long joints (i.e., lengths of 6.35 and 12.7 mm). The observations on the crack path showed that the crack was initiated near one of the adherends and tended to propagate within the intermetallic compound (IMC) layer. Also, the planar fracture surface was observed in all the specimens except for the short solder joints (i.e., with the length of 2.54 mm).

Microstructure, shear properties and corrosion resistance of Cu/Cu-In/Cu solder joints

Transient liquid phase sintering can successfully fabricate reliable high-temperature solder joints at a relatively low joining temperature by forming intermetallic compounds. In this work, microstructure, shear properties and corrosion resistance of Cu/Cu-In/Cu solder joints prepared by TLPS process were investigated. The shear strength of the Cu-In solder joints significantly increased during the initial aging period and then slightly decreased due to the increase of pores after continuous 24 h aging. The corresponding microstructure is that part of the Cu2In in the Cu-In solder joints transforms to Cu7In3 in the meanwhile. After continuous aging, the interfacial microstructure remained stable and contributed to good shear strength that exceeds 20 MPa after 96 h aging at 250 °C and 350 °C, which was 20.8 MPa and 23.4 MPa, respectively. Regarding corrosion resistance, the Cu-In interfacial layer (−0.24 V) has similar corrosion resistance to Cu substrate (−0.22 V) and shows superior to the commonly used Sn63Pb37 solder (-0.40 V) and Sn95.5Ag3.8Cu0.7 solder (−0.42 V).

Reliability and Characterization of Nanosilver Joints Prepared by a Time-Reduced Sintering Process

This study investigates the power cycling reliability of nanosilver sintered joints formed by a time-reduced sintering process, designed for use on a die bonder. A range of sintering parameters, reflecting different levels of manufacturability, were used to produce sintered joints in respect of shear strength and porosity, within a process cycle time of a few seconds. The reliability of the sintered attachments were evaluated against Pb5Sn solder joints under constant temperature swing power cycling conditions over the range 50 to 200 °C. The thermal performance and microstructural changes of the sintered joints were monitored and evaluated non-destructively at regular intervals using transient thermal impedance and X-ray computed tomography. The results show that sintered joints with higher shear strengths (>50 MPa) and lower porosities (<25 %) tend to maintain their thermal performance up to ~100k power cycles before gradual degradation occurs. Sintered joints with intermediate shear strengths (20 to 40 MPa) and with corresponding analogous porosities (35 to 51 %) also demonstrated comparable power cycling behavior; exhibiting a progressive decrease in effective thermal conductivity with increasing cycles. The evaluated lifetime of sintered joints with the highest shear strengths were found to be at least double those for the lower shear strength joints, and up to fourteen times those of a Pb5Sn solder die attachment. Even the most porous sintered joints exhibited lifetimes appreciably longer than a Pb5Sn die attachment. Degradation in thermal resistance was seen to correlate with observed microstructural changes, with a dependence on initial sintering parameters.

Thermal and Mechanical Properties of Sn-8Zn-3Bi Solder Alloy

Thermal and mechanical properties of Sn-8Zn-3Bi solder alloy on copper substrate were evaluated via measuring the melting temperature, the coefficient of thermal expansion (CTE), the tensile and shear strength of the solder joint. The measured properties of the alloy were then compared to the properties of the traditional and widely used eutectic Sn-37Pb solder alloy. The results show that the melting (liquidus) temperature of Sn-8Zn-3Bi was 195 °C, the CTE of Sn-8Zn-3Bi was 22.2´10-6 K-1 in the temperature range of 30-130 °C. At the same testing condition, both tensile and shear strength of Sn-8Zn-3Bi joints were higher than those of Sn-37Pb. The stress-strain curve indicated that the Sn-8Zn-3Bi joints were brittle whilst the Sn-37Pb joints were ductile.

Effect of temperature on the corrosion behavior of lead-free solders under polyvinyl chloride fire smoke atmosphere

Fire smoke could induce serious corrosion damage to electronic equipment away from the fire, causing significant economic losses. And lead-free solders used for chip package is the key to ensure the reliability of electronic equipment, which is vulnerable to corrosion. Therefore, it is very important to explore the corrosion hazard of fire smoke on lead-free solders for evaluating the reliability of electronic equipment after a fire. In this work, the effect of temperature on corrosion behavior of SAC305, Sn-0.7Cu, and Sn-37Pb solders under polyvinyl chloride fire smoke atmosphere was performed with the weight-loss method. The corrosion kinetics, corrosion morphology, and corrosion products were analyzed in the temperature range of 10 °C–50 °C. The corrosion kinetics results showed that the corrosion degree of all three solders aggravated linearly with rising temperature in that order: SAC305 > Sn-0.7Cu > Sn-37Pb. The corrosion of lead-free solder was more susceptible to temperature variation, and Sn-0.7Cu solder was the most serious. The corrosion morphology analysis exhibited that obvious corrosion traces had presented at 10 °C, and a great deal of large and thick corrosion products appeared at 50 °C. All solders presented galvanic corrosion under polyvinyl chloride fire smoke atmosphere. The corrosion products of lead-free solders were Sn21Cl16(OH)14O6, SnO, and SnO2, but those of Sn-37Pb solder contained Sn21Cl16(OH)14O6, PbCl2, SnO, and SnO2. The results could guide the formulation and implementation of rescue measures for electronic equipment post-fire.

Work of adhesion and reactive wetting in SnPb/Cu,Ni and SnBi/Cu,Ni soldering systems

Low contact angles in reactive wetting are often used as an indicator for strong solder connections. However, from a physical point of view, the so-called work of adhesion is the more justified measure, for which quantitative data are rare. Here, we present measurements for SnPb and SnBi solders on Cu and Ni base metallization. Surface tension and wetting angles are determined by the sessile drop method over the whole composition range of the solders. Provided comparable measurement conditions, the Young-Dupre equation is applied to determine interfacial energies and the work of adhesion. They reveal a characteristic dependence on the intermetallics formed in contact with the liquid solder, clearly supporting the concept of Eustathopoulos which assumes wetting angles are always in contact with the intermetallic of highest possible Sn content. The concentration dependence of the work of adhesion indicates significant segregation of Sn to the liquid-solid interface which significantly affects the bonding strength.

Reliability modeling and assessment of solder joints of electronic assemblies under mixed exposure to mechanical loads

PurposeIn this paper, a lifetime estimation model for the solder joint is proposed which is capable of considering both severe and running mechanical shocks which is the real case in electric converters in the automotive and aerospace applications. This paper aims to asses the reliability of the solder joint under mixed exposure of mechanical loads.Design/methodology/approachMechanical failure process may put at risk the perfect performance of any kinds of electronic systems regardless of the applications they are prepared for. Observation of solder joint health in an electronic assembly under simultaneous exposure of severe and running shocks is an open problem. Three commonly used soldering compositions are considered while the electronic assembly is exposed to three well-known driving cycles.FindingsThe results show that the best performance is achieved using SAC405 soldering alloy in comparison with Sn63Pb37 and SAC387 solder alloy. Consideration of mixed exposure to the mechanical loads leads to much more accurate lifetime estimation of the solder joint in the electronic assemblies.Originality/valueThe originality of the paper is confirmed.

Experimental Investigation of Microstructural Effects in Sn-Pb Solder Accumulated During Ten Years of Service Life

Aim: Solder joints of microelectronic devices are subjected to a wide range of loadings. They affect the microstructural evolution of the alloy. Long term investigations are commonly performed under thermally accelerated conditions, but are not available for real-life environmental conditions in literature yet. Therefore, the solder bumps of ten-year-old graphic cards are inspected here. Objectives: The primary objective of this study was the investigation of long-term accumulated effects in solder bumps. We classified the solder concerning its prior electrical functionality and analyzed theproperties of the microstructure. Methods: The image reconstruction is based on component identification, scratch elimination, and image stitching. Additionally, environmental scanning electron micrographs are employed to investigate the microstructure of the lead-rich phases. Results: Power supplying solder has the widest circularity distribution as a result of anisotropic diffusion and phase decomposition. On average, a bump with a cross-section of 0.12 mm2 contains 800 Pbrich phase islands. In the central region of the solder, broad Pb-rich platelets are present. Such platelets are typically perpendicular to the electric current flow and affected by the mechanical deformation of the bump. Additional electron-microscopy shows several micro-porous Pb-rich phase islands, which are induced by an uncalibrated diffusion of tin. Conclusion: We found the phase islands’ circularity to be the best indicator for the bulk dynamics. We conclude that device operation at normal working conditions leads to no hints for functional limitations at the end of the designed life span.