Lead-free Solder Research Articles

A novel multi-information fusion CNN for defect detection in laser soldering of SAC305

Identification of laser soldering of lead-free solder Sn-3.0Ag-0.5Cu (SAC305) in electronic packaging was still an enormous challenge. It was difficult to detect defects in large-scale production. This work proposed an identification model based on multi-information fusion convolutional neural network (MIFCNN) for inspecting laser soldering process. In this method, the forty images in chronological order and the temperature data were combined as the input to be utilized in detecting defects. The results demonstrated that MIFCNN had best accuracy for three types of joints with accuracy of 98.28 % due to the combination of images and temperature information. The ICNN and TCNN had poor recognition accuracy for the warpage defect with 73.9 % and the poor wetting defect with 66.5 %, respectively. This was because the images and temperature information were the key to identifying the poor wetting defects and warpage defects, respectively. The poor wetting defect could be recognized by difference of contact angle, while the warpage defect could be significantly detected by maximum temperature. This work could help detecting defects of laser soldering in the actual production and widen the application of MIFCNN in the field of laser soldering.

Comparison of the Young’s modulus of the lead free solder alloy Sn-Ag3.8-Cu0.7 determined by hot tensile tests, ultrasonic measurements and [formula omitted]-Sn single crystal calculations

Sn-based solders are known for their tendency to form coarse grained microstructures. In combination with the high elastic anisotropy of β-Sn, the overall elastic properties and their interpretation require a careful discussion of the structure–property-relationship as elastic constants are often important input parameters for creep or fatigue models. This study therefore investigates the influence of microstructure and testing method on the Young’s modulus E for the widespread lead free solder alloy Sn-Ag3.8-Cu0.7 (SAC387) using bulk specimens. Due to its already high homologous temperature at room temperature (Thom≈ 0.6 = T/Tm for Tm being the melting temperature), hot tensile tests generally bear the risk of superimposed creep deformation. Mechanical testing becomes even more challenging, since yield strengths are usually low for these alloys. Consequently, in addition to the hot tensile tests executed for the engineering strain rate ϵ̇e=1⋅10−3 s−1, two supplemental methods are used to determine the Young’s modulus comprising of the dynamic resonance frequency measurement and the calculation of the Young’s modulus based on single crystal compliance data of the majority phase β-Sn.Young’s moduli yielded from dynamic resonance frequency measurement and calculations based on single crystal compliance data showed comparable results of (E35 °C≈ 55 GPa, E80 °C≈ 51 GPa and E125 °C≈ 48 GPa). Hot tensile tests showed similar data with the largest deviation at 80 °C, where E80 °C≈ 53 GPa was determined. These absolute values and their temperature dependence can be attributed to the microstructure of the cast specimens which show a general preferred orientation of β-Sn grains close to <110> after analysis via electron backscattered diffraction (EBSD). A comparison with literature data revealed significant differences in the Young’s moduli which are likely to be attributed to differences in the preferred orientation of β-Sn grains.

The Effect of Bi Addition on the Electromigration Properties of Sn-3.0Ag-0.5Cu Lead-Free Solder

As electronic packaging technology advances towards miniaturization and integration, the issue of electromigration (EM) in lead-free solder joints has become a significant factor affecting solder joint reliability. In this study, a Sn-3.0Ag-0.5Cu (SAC305) alloy was used as the base, and different Bi content alloys, SAC305-xBi (x = 0, 0.5, 0.75, 1.0 wt.%), were prepared for tensile strength, hardness, and wetting tests. Copper wire was used to prepare EM test samples, which were subjected to EM tests at a current density of approximately 0.6 × 104 A/cm2 for varying durations. The interface microstructure of the SAC305-xBi alloys after the EM test was observed using an optical microscope. The results showed that the 0.5 wt.% Bi alloy exhibited the highest ultimate tensile strength and microhardness, improving by 33.3% and 11.8% compared to SAC305, respectively, with similar fracture strain. This alloy also displayed enhanced wettability. EM tests revealed the formation of Cu6Sn5 and Cu3Sn intermetallic compounds (IMCs) at both the cathode and anode interfaces of the solder alloy. The addition of Bi inhibited the diffusion rate of Sn in Cu6Sn5, resulting in similar total IMC thickness at the anode interface across different Bi contents under the same test conditions. However, the total IMC thickness at the cathode interface decreased and stabilized with increasing EM time, with the SAC305-0.75Bi alloy demonstrating the best resistance to EM.

Microstructural Evolution of Intermetallic Compound Between SN100C Solder and ENIMAG Substrate During Isothermal Ageing

SN100C alloy emerges as a promising candidate when introducing lead-free solder alternativesdue to its mechanical properties and solderability. The study aims to explore interfacial reactions between SN100C solder and ENIMAG surface finish. Methods involve preparingENIMAG substrates, solder paste application, and reflow processes following JEDEC standards. Isothermal ageing treatments were conducted, and interfacial reactions were characterized using top surface and cross-section analyses via Optical Microscope (OM), Scanning Electron Microscope (SEM), and Energy Dispersive X-ray (EDX). Post-reflow, distinct IMC layers formed at the SN100C/ENIMAG solder joint's interface, evolving with ageing. Further analysis via cross-section confirms the initial formation of (Ni, Cu)3Sn4 layer followed by (Cu, Ni)6Sn5, each exhibiting varying appearance and thicknesses. Isothermal ageing increases IMC thickness, which is particularly influenced by Cu diffusion and exposure to high temperatures, and itfacilitates the growth rate of IMCs.

Understanding the deformation creep and role of intermetallic compound-microstructure in Sn-Ag-Cu solders

Tin-based alloys are commonly used in lead-free solder joints in electronic interconnection applications, where creep can limit joint reliability. In this work, directionally solidified bulk solder alloys of different compositions (pure tin, SAC105 and SAC305) are mechanically tested under a constant load for each composition at room temperature to understand mechanical creep performance and quantify the role of different content of Ag3Sn and Cu6Sn5 intermetallic compounds (IMCs) in terms of secondary creep strain rate, microstructural evolution, and total amount of accumulated strain. In this work, microstructures are fabricated using directional solidification to promote a systematic variation in IMC sizes, shapes, and distributions within similar crystal orientations of the primary β-Sn matrix. Analysis of creep data indicates that secondary creep is dominated by obstacle-controlled dislocation motion. This is further confirmed by electron backscatter diffraction (EBSD) analysis, which reveals that the formation of subgrains and internal structure, correlating to the initial microstructure of the sample, i.e. changes in secondary dendrite arm spacing (λ2) and eutectic intermetallic spacing (λe). The experimental observations are supported further by crystal plasticity simulations that explicitly model the presence of IMCs within the Sn-based samples and show the dependence of the secondary creep rate upon the IMC content, and therefore be beneficial for the possible future composition design in solders.

Effect of Composition on Structural, Mechanical, and Wetting Properties of Sn-40Bi-xAg Lead-Free Solder Alloys for Green Electronics

Effect of Composition on Structural, Mechanical, and Wetting Properties of Sn-40Bi-xAg Lead-Free Solder Alloys for Green Electronics

Effects of Bi Doping on Zn-Rich Phase Evolution and Physical and Chemical Properties of Sn-6.5Zn Lead-Free Solder Alloy

Effects of Bi Doping on Zn-Rich Phase Evolution and Physical and Chemical Properties of Sn-6.5Zn Lead-Free Solder Alloy

Analysis of BGA Lead-Free solder joints failure behavior based on thermal shock testing

The interconnected solder joints within automotive electronic components are the most vulnerable parts of the structure, and their reliability is crucial for the development of new energy vehicles. This study focuses on automotive ADAS (Advanced Driver Assistance System) devices, analyzing the failure behavior of internal BGA (Ball Grid Array) lead-free solder joints under thermal shock conditions.Through thermal shock testing from −40℃ to 95℃, it was observed that microcracks first appeared in the upper intermetallic compound (IMC) layer of corner solder joints after 1600 cycles. As the number of thermal shock cycles increased, the net-like β-Sn phase in the solder joints gradually transformed into block and dot-like structures. Due to the relatively weak strength between the IMC layer and the Ag-Sn compound region, cracks typically propagated along the boundaries of these areas. Recrystallization occurred in the interface between the solder joint and the upper pad, with the proportion of high-angle grain boundaries increasing from 10.74% to 72.43%. The crack propagation mode changed from initial intergranular to transgranular fracture. Throughout the thermal shock test, the upper IMC layer remained thicker than the lower one, with the lower IMC layer thickness showing a minimum point at 750 cycles.The average thrust force between the solder joints and the substrate decreased more rapidly with thermal shock cycles, indicating that non-solder mask defined pads are more effective in improving structural strength.

Interfacial IMC growth behavior of Sn-3Ag-3Sb-xIn solder on Cu substrate

PurposeThe reliability of solder joints is closely related to the growth of an intermetallic compound (IMC) layer between the lead-free solder and substrate interface. This paper aims to investigate the growth behavior of the interfacial IMC layer during isothermal aging at 125°C for Sn-3Ag-3Sb-xIn/Cu (x = 0, 1, 2, 3, 4, 5 Wt.%) solder joints with different In contents and commercial Sn-3Ag-0.5Cu/Cu solder joints.Design/methodology/approachIn this paper, Sn-3Ag-3Sb-xIn/Cu (x = 0, 1, 2, 3, 4, 5 Wt.%) and commercial Sn-3Ag-0.5Cu/Cu solder were prepared for bonding Cu substrate. Then these samples were subjected to isothermal aging for 0, 2, 8, 14, 25 and 45 days. Scanning electron microscopy and transmission electron microscopy were used to analyze the soldering interface reaction and the difference in IMC growth behavior during the isothermal aging process.FindingsWhen the concentration of In in the Sn-3Ag-3Sb-xIn/Cu solder joints exceeded 2 Wt.%, a substantial amount of InSb particles were produced. These particles acted as a diffusion barrier, impeding the growth of the IMC layer at the interface. The growth of the Cu3Sn layer during the aging process was strongly correlated with the presence of In. The growth rate of the Cu3Sn layer was significantly reduced when the In concentration exceeded 3 Wt.%.Originality/valueThe addition of In promotes the formation of InSb particles in Sn-3Ag-3Sb-xIn/Cu solder joints. These particles limit the growth of the total IMC layer, while a higher In content also slows the growth of the Cu3Sn layer. This study is significant for designing alloy compositions for new high-reliability solders.

Influence of alloying elements on microstructure, mechanical properties and corrosion behaviour of hypoeutectic Sn-6.5wt%Zn-0.5 wt%X (X = Ag, Al, Cu) lead-free solders

Lead-free solders are promising candidates for the replacement of Sn–Pb solders due to their environmental friendly, good thermal properties and wettability which render them suitable for this application. In this study, a set of lead-free solders Sn-6.5 wt. and Sn-6.5 wt% Zn-0.5 wt% X (X = Ag, Al, Cu) were studied by metallography, mechanical and electrochemical techniques. The results show that the addition of the alloying elements Ag, Al and Cu modifies the amount of the eutectic phase and promotes the formation of intermetallic compounds (IMCs). The corrosion resistance of the samples also modified, showing that the formation of IMCs can have detrimental effects with higher current densities in saline media, as determined for the Ag and Al alloyed solders. The corrosion resistance is higher for the unalloyed and the Sn-6.5 wt%Zn-0.5 wt% Cu alloy. However, the addition of Cu not only stabilizes the corrosion products thus increasing the protective properties of the alloy, but also modifies the mechanical behaviour of the lead-free solders and so enhancing the UTS values and ductility. Furthermore, the surface morphology is influenced by the alloying elements showing a smooth surface (Sn-Zn, Cu) or a highly corroded appearance with round aggregates (Ag and Al). These new lead-free solders have a lower melting point with higher ductility than the commercial SAC 305. Therefore, these alternatives have high potential in applications in mechanical engineering.

EBSD characterization of Ag3Sn phase transformation in Sn–Ag lead-free solder alloys: a comparative study before and after heat treatment

EBSD characterization of Ag3Sn phase transformation in Sn–Ag lead-free solder alloys: a comparative study before and after heat treatment

Investigation of the mechanical properties of lead-free Sn-58Bi solder alloy with cobalt addition through flux doping

PurposeThis study aims to investigate the effect of incorporating cobalt (Co) into Sn-58Bi alloy on its phase composition, tensile properties, hardness and thermal aging performances. The fracture morphologies of tensile-tested solders are also investigated to correlate the microstructural changes with tensile properties of the solder alloys. Then, the thermal aging performances of the solder alloys are investigated in terms of their intermetallic compound (IMC) layer morphology and thickness.Design/methodology/approachThe Sn-58Bi and Sn-58Bi-xCo, where x = 1.0, 1.5 and 2.0 Wt.%, were prepared using the flux doping technique. X-ray diffraction (XRD) is used to study the phase composition of the solder alloys, whereas scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) are used to investigate the microstructure, fractography and compositions of the solders. Tensile properties such as ultimate tensile strength (UTS), Young’s modulus and elongation are tested using the tensile test, whereas the microhardness value is gained from the micro-Vickers hardness test. The morphology and thickness of the IMC layer at the solder’s joints are investigated by varying the thermally aging duration up to 56 days at 80°C.FindingsXRD analysis shows the presence of Co3Sn2 phase and confirms that Co was successfully incorporated via the flux doping technique. The microstructure of all Sn-58Bi-xCo solders did not differ significantly from Sn-58Bi solders. Sn-58Bi-2.0Co solder exhibited optimum properties among all compositions, with the highest UTS (87.89 ± 2.55 MPa) at 0.01 s−1 strain rate and the lowest IMC layer thickness at the interface after being thermally aged for 56 days (3.84 ± 0.67 µm).Originality/valueThe originality and value of this research lie in its novel exploration of the flux doping technique to introduce minor alloying of Co into Sn-58Bi solder alloys, providing new insights into enhancing the properties and performance of these solders. This new Sn-Bi-Co alloy has the potential to replace lead-containing solder alloy in low-temperature soldering.

Accelerated discovery of lead-free solder alloys with enhanced creep resistance via complementary machine learning strategy

Minor alloying is an effective method to improve the performance of lead-free solder alloys. In this study, we propose a complementary Machine Learning (ML) strategy for minor alloying to design solder alloys with enhanced creep resistance. Two ML models, leveraging compositional and knowledge-aware features, respectively, were constructed to predict the creep stress exponent of Sn–Ag–Cu (SAC)-based solder alloys. Five new solder alloys were designed and experimentally evaluated by screening the virtual sample space consisting of the critical elements, including Bi, In, and Ni, affecting the creep resistance of SAC solder alloys with the ML model. The creep resistance of the designed alloys was characterized using nanoindentation tests. Notably, the creep stress exponent of SAC387-3 wt % Bi-0.4 wt% Ni was determined to be 12.82 at room temperature, indicating a significant 33.9% decrease in creep strain rate compared to the SAC387 alloy. This study demonstrates the potential of the ML approach to design solder alloys with enhanced creep resistance.

Effects of TiC nanoparticle addition on microstructures and mechanical properties of Sn-58Bi solder joints

The Sn58Bi solder has gained significant attention in the electronic packaging industry owing to its low melting temperature and excellent mechanical properties. However, the brittleness of Sn58Bi solder presents challenges in practical applications. This study investigates the effect of adding titanium carbide (TiC) nanoparticles on the mechanical properties of Sn58Bi solder joints. The study examines the melting behavior, spreadability, microstructure, and mechanical properties of Sn58Bi-xTiC (x = 0, 0.05, 0.1, 0.2 wt%) composite solders. The results indicate that adding TiC nanoparticles has merely a minor effect on the melting point of the Sn58Bi solder. However, the presence of TiC nanoparticles refined the solder’s microstructure, reduced the thickness of the intermetallic compounds, and enhanced the spreadability and mechanical properties. The Sn58Bi-0.1TiC composite solder exhibits the most favorable properties, including a 28.6 % increase in fracture energy compared with that of Sn58Bi solder. Consequently, incorporating TiC nanoparticles enhances the performance of the Sn58Bi solder by improving its spreadability and reducing its brittleness. These results hold great potential for advancing the development of lead-free solders with improved reliability and performance in electronic applications. The findings of this study could pave the way for the practical and widespread use of Sn58Bi-xTiC composite solders, offering a viable alternative to lead-containing solders while maintaining excellent mechanical characteristics.

Investigation of the Impacts of Solder Alloy Composition and Temperature Profile on Fatigue Life of Ball Grid Array Solder Joints Under Accelerated Thermal Cycling

Abstract This study investigated the thermal fatigue reliability of ball grid array (BGA) solder joints under accelerated thermal cycling, considering the impacts of solder alloy and temperature profile. Applying the Darveaux solder joint reliability assessment, simulations consider lead-based (63Sn37Pb and 62Sn36Pb2Ag) and lead-free (SAC105, SAC305, and SAC405) solder alloys under temperature profiles: 0°C (Tmin) to 100°C (Tmax), −40°C to 85 °C, −40 °C to 125 °C, and −40 °C to 150 °C. Results indicate that SAC305 exhibited the highest equivalent stress, while 63Sn37Pb demonstrated the highest plastic strain and creep strain energy density. SAC105 displayed the lowest stress and strain parameters. Moreover, increasing the thermal cycling temperature range intensifies stress, strain, and damage parameters, with −40 °C to 150 °C showing the highest magnitudes. SAC405 exhibited superior thermal fatigue life compared to other alloys, with its cycles to failure outperforming 63Sn37Pb, SAC105, 63Sn36Pb2Ag, and SAC305 by 16832, 11992, 6218, and 3601 cycles, respectively. Lower temperature ranges enhance thermal fatigue life, with 0 °C to 100 °C recording 8%, 33%, and 53% higher life than −40 °C to 85 °C, −40 °C to 125 °C, and −40 °C to 150 °C, respectively. Notably, higher silver content and lower temperature ranges were associated with increased thermal fatigue life, providing valuable insights for BGA solder joint reliability enhancement.

Effect of Bi on the Tensile and Viscoplastic Behavior of Sn-Ag-Cu-Bi Alloys Used for Microelectronics Applications

Sn-Ag-Cu-Bi (SAC-Bi) alloys are gaining popularity as a potential replacement for current lead-free solder alloys in microelectronic packages. In this study, the tensile and viscoplastic behaviors of eight SAC-Bi alloys with 0, 1 wt.%, 2 wt.%, and 3 wt.% Bi content were investigated. The samples of these eight alloys were cast, aged at room temperature, 75 °C and 125 °C, and tensile-tested at rates of 0.1/s, 0.01/s, and 0.001/s in ambient and elevated temperature environments to facilitate the quantification of viscoplasticity using the Anand viscoplastic model. The Anand parameters of all eight alloys in the as-cast and aged conditions were determined. Tensile strength was found to increase with the addition of Bi. Additionally, alloys containing 2 and 3 wt.% Bi showed a 5 to 10% increase in tensile strength after isothermal aging of 90 days at 125 °C. On the contrary, the tensile strength of alloys with up to 1 wt.% Bi decreased by 22 to 48% after such aging. Using a Scanning Electron Microscope (SEM) and energy dispersive spectroscopy (EDS), the microstructure of the alloys was characterized. The aging-induced property changes in the samples were correlated to strengthening by Bi solute atoms for alloys with 1 wt.% Bi and the formation of Bi precipitation for alloys with 2 wt.% and 3 wt.% Bi.

Effects of soldering temperature and preheating temperature on the properties of Sn–Zn solder alloys using wave soldering

Purpose This study aims to address the problem of low-temperature wave soldering in industry production with Sn-9Zn-2.5 Bi-1.5In alloys and develop qualified process parameters. Sn–Zn eutectic alloys are lead-free solders applied in consumer electronics due to their low melting point, high strength, and low cost. In the electronic assembly industry, Sn–Zn eutectic alloys have great potential for use. Design/methodology/approach This paper explored developing and implementing process parameters for low-temperature wave soldering of Sn–Zn alloys (SN-9ZN-2.5BI-1.5 In). A two-factor, three-level design of the experiments experiment was designed to simulate various conditions parameters encountered in Sn–Zn soldering, developed the nitrogen protection device of waving soldering and proposed the optimal process parameters to realize mass production of low-temperature wave soldering on Sn–Zn alloys. Findings The Sn-9Zn-2.5 Bi-1.5In alloy can overcome the Zn oxidation problem, achieve low-temperature wave soldering and meet IPC standards, but requires the development of nitrogen protection devices and the optimization of a series of process parameters. The design experiment reveals that preheating temperature, soldering temperature and flux affect failure phenomena. Finally, combined with the process test results, an effective method to support mass production. Research limitations/implications In term of overcome Zn’s oxidation characteristics, anti-oxidation wave welding device needs to be studied. Various process parameters need to be developed to achieve a welding process with lower temperature than that of lead solder(Sn–Pb) and lead-free SAC(Sn-0.3Ag-0.7Cu). The process window of Sn–Zn series alloy (Sn-9Zn-2.5 Bi-1.5In alloy) is narrow. A more stringent quality control chart is required to make mass production. Practical implications In this research, the soldering temperature of Sn-9Zn-2.5 Bi-1.5In is 5 °C and 25 °C lower than Sn–Pb and Sn-0.3Ag-0.7Cu(SAC0307). To the best of the authors’ knowledge, this work was the first time to apply Sn–Zn solder alloy under actual production conditions on wave soldering, which was of great significance for the study of wave soldering of the same kind of solder alloy. Social implications Low-temperature wave soldering can supported green manufacturing widely, offering a new path to achieve carbon emissions for many factories and also combat to international climate change. Originality/value There are many research papers on Sn–Zn alloys, but methods of achieving low-temperature wave soldering to meet IPC standards are infrequent. Especially the process control method that can be mass-produced is more challenging. In addition, the metal storage is very high and the cost is relatively low, which is of great help to provide enterprise competitiveness and can also support the development of green manufacturing, which has a good role in promoting the broader development of the Sn–Zn series.

Simulation and Prediction of Creep Rate, Activation Energy, and Rupture Time of Sn94Sb5Ag1 Lead-Free Solder Alloy Using Artificial Neural Network Modeling

Simulation and Prediction of Creep Rate, Activation Energy, and Rupture Time of Sn94Sb5Ag1 Lead-Free Solder Alloy Using Artificial Neural Network Modeling

Finite element method and experimental study on life prediction of lead-free BGA solder joints using an energy-based approach

Finite element method and experimental study on life prediction of lead-free BGA solder joints using an energy-based approach

Comprehensive investigation of oxidation behavior on ternary In–Zn–Sn lead-free solder electronic materials

Comprehensive investigation of oxidation behavior on ternary In–Zn–Sn lead-free solder electronic materials