SnPb Solder Research Articles

A study on the quantitative recrystallization of cold deformed copper affected by tin-lead solder

It has been observed that the fractional recrystallization characteristics of commercially pure copper is affected by the presence of individual or both the constituent elements of the Sn-Pb solder alloy. In order to design the experiment, commercially pure Cu, binary copper alloys (Cu-Sn and Cu-Pb) and ternary copper alloy, Cu-Sn-Pb are investigated. Cast alloys are homogenized, solution treated, and then quenched to complete the thermal treatment. In order to recrystallize, alloys are cold rolled to a 75% thickness and then annealed at 700°K isothermally for varying durations, up to 3600 seconds. In this experiment, the fractional recrystallization of annealed samples is evaluated as the normalized difference in microhardness recorded at various time steps. Additionally, in an attempt to verify the experimental results, the well-known Johnson-Mehl-Avrami-Kolmogorov equation is also used to predict the associated recrystallization behavior. From the study, it can be inferred that the presence of Sn-Pb solder-alloy elements have a positive impact on the recrystallization behavior of pure copper due to the solid solution strengthening, in which the effect of tin is greater than that of lead. Quantitative analysis indicates that recrystallization of pure Cu, Cu-Sn, Cu-Pb, and Cu-Sn-Pb alloys attains 99.4%, 95.4%, 98.4%, and 89.5%, respectively. Sn forms intermetallic with Cu but Pb does not. Additionally, Sn forms different intermetallic with impurities and has a BCC crystal structure dissimilar to the FCC of Cu and Pb. As a result, the formation of GP zones and the intermetallic phases during annealing show greater differences in the recrystallization behavior between the two approaches. By combination, microstructural studies of the cold-rolled alloys reveal the elongated grains of the second phases, and the alloys almost completely re-crystallized after 1800 seconds of annealing at 700°K.

Solid/solid state interfacial reactions in the lead-free solders/Cu- 2.3%wt. Fe alloy (C194) couples

BackgroundLead-free solders (LFSs) involve incorporating trace elements into Sn, resulting in alloys like Sn-3.0 wt.% Ag-0.5 wt.% Cu (SAC) and Sn-0.7 wt.% Cu (SC). These solder have similar properities to Sn-Pb solders. C194, renowned for its exceptional corrosion resistance, high strength, and good weldability, serves as a preferred lead-frame material in electronic packaging. In this study, we investigated the solid/solid state interfacial reactions between the LFS and Cu-2.3 wt.% Fe alloy (C194). MethodsThree LFS including Sn, SAC, and SC were first reflowed with C194 to form the LFS/C194 couple. Then the LSF/C194 couples were aged at 125–175 ℃ for 100–2000 h. Significant findingsThe results revealed that only the (Cu, Fe)6Sn5 phase was formed in the Sn/C194 couple aged at 125 ℃. At higher temperatures and longer aging times, the (Cu, Fe)3Sn phase was formed in all three couples. The Fe addition into Cu could inhibit the (Cu, Fe)3Sn phase growth. Kirkendall voids in this study occur more frequently with the increase in aging temperatures and times, but the intensity varies in each system. Meanwhile, the thickness of total intermetallic compound (IMC) was increased with the increase in aging times and temperatures in these three couples. The IMC growth mechanism is diffusion controlled in all LFSs/C194 couples.

Anomalous field-temperature phase diagram of superconductivity in Sn–Pb solder

Sn–Pb solders are superconducting materials whose Sn and Pb are perfectly phase-separated. Recently, anomalous magnetic-flux trapping in a Sn45–Pb55 solder has been revealed, where the magnetic fluxes are selectively trapped in the Sn regions due to the supercurrents in the surrounding Pb regions. Here, we report on the observation of the anomalous critical field (Hc)-temperature (T) phase diagram of superconductivity in the Sn45–Pb55 solder. Although the Hc(T) for the Pb regions decreases with increasing field as in normal type-I superconductors and is consistent with the conventional trend with Hc(0) ∼ 800 Oe, the Hc(T) for the Sn regions exhibits anomalous behaviors. The most noticeable trend was observed in the field-cooled (under 1500 Oe) solder. The Hc-T phase diagram for the Sn regions largely varies when the applied external field is reversed, and Tc increases with increasing field amplitude when H < 0 Oe is applied. On the basis of the flux trapping and the observed anomalous Hc-T phase diagrams, we propose that the field-robust superconductivity in the Sn regions is related to the ferromagnetically aligned magnetic fluxes (or formation of vortices) in the Sn regions of the Sn45–Pb55 solder.

Improvement of solder interconnections applied on back contact solar cells with low-temperature copper paste busbars

This work addresses the solderability and the reliability of n-type IBC ZEBRA cells with screen printed copper paste busbars. Improvement of the solderability by Sn60Pb40 solder alloy coated PV ribbon using an industrial automated IR stringer is reported. For qualification of the module reliability, climate chamber thermal cycling (TC) and damp heat tests (DH) were performed on mini modules with variations in material combinations: low temperature silver and copper pastes, each of them demanding dedicated soldering process parameters and two different encapsulation materials: polyolefin elastomers (POE) and ethylene vinyl acetate (EVA). All tested modules passed 3 x IEC TC and 2 x IEC DH, while the modules with EVA encapsulant passed DH 3000 as well. The copper paste metallized modules with EVA encapsulant showed no degradation in pseudo fill factor (pFF) and open circuit voltage (VOC), proving the statement that no copper diffuses into the silicon bulk.

Research on Processability and Transmission Performance of Low Temperature Co-Fired Ceramic Ball Grid Array Packaging Based on Electroless Plating Surface Modification for Microwave Transceiver Circuits.

A microwave transmitter/receiver using the low-temperature co-fired ceramic substrate and ball grid array packaging demonstrates superior properties, including high integration, miniaturization, and high electromagnetic shielding. However, it holds limitations of inadequate hermeticity (that is, gas or moist impermeability), high cost, and low reproducibility. In this work, we aim to overcome these difficulties by introducing a new packing technique. The packaging utilizes an electroless plated Ni/Pd/Au surface, resulting in a significant enhancement of the packaging hermeticity by orders of magnitude, approaching the level of <5 × 10-9 Pa·m3/s. Both Sn63Pb37 and Au80Sn20 solder alloys demonstrate exceptional solderability, attributed to Pd atoms diffusing to the Au layer during soldering at 310 °C. A reliability test of the packaging shows that the shear strength of the solder balls drops after thermal shocks but negligibly affects the hermeticity of the packaging. Furthermore, a meticulously designed internal vertical interconnect structure and I/O interconnections were engineered in the ball grid array packaging, showcasing excellent transmission characteristics within the 10-40 GHz frequency range while ensuring effective isolation between ports.

Equilibrium phase diagram design and structural optimization of SAC/Sn-Pb composite structure solder joint for preferable stress distribution

The Package-on-Package (PoP) technology is an efficient knowhow to increase the efficiency of electronic components, hence to secure the continuation of the validity of Moore's law. This novel form of packaging technology with bottom stackable narrow pitch Ball Grid Array (BGA) contributes to the integrity of the package. However, the high solder joint density introduces a great challenge on the packaging reliability. Therefore, more stringent requirements must be put forward for achieving the increased performance. That can be achieved by using composite solder joints. In this study, a novel composite SAC (Sn-3Ag-0.5Cu)/Sn-Pb (Sn37Pb) solder joint was designed for improving the stress distribution and its overall mechanical integrity. The formation process and a phase distribution of composite solder joint were investigated, indicating that the phase distribution mainly depends on the reflow temperature. The dissolution ratio of SAC into the composite solder at different temperatures was estimated by the phase diagram. The predicted values were consistent with the experimental results. A review of mechanical property test results, the best performance solder joint could be obtained at 200 °C for the dwell time of 60 s if the composite includes 10 wt% SnPb. The stress distribution of composite solder joint was analyzed by finite element simulation. By actively concentrating the stress in the middle area of the solder joint, the maximum stress in the composite solder reduced for up to 29% when compared to full SAC solder joint.

Early wetting and interfacial behavior of Sn-based solder on copper substrates with different roughness

Purpose This paper aims to investigate the effect of solder composition and roughness on early wetting behavior and interfacial reaction under atmospheric conditions. Design/methodology/approach High-speed photography is used to observe the early wetting and spreading process of the solder on the substrate in real time. The morphology of intermetallic compounds (IMCs) was observed by scanning electron microscopy, and the composition of IMCs micro bumps was determined by energy dispersive spectroscopy. Findings With a roughness range of 0.320–0.539 µm, the solder is distributed in an elliptical trilinear pattern along the grinding direction. With a roughness range of 0.029–0.031 µm, the solder spreads in the direction of grinding and perpendicular, forming a perfect circle (except in the case of Sn63Pb37 solder). The effect of three types of solder on early wettability is Sn63Pb37 &gt; Sn96.5Ag3Cu0.5 &gt; Sn. The wetting behavior is consistent with the Rn∼t model. The rapid spreading stage (Stage I) is controlled by the interfacial reaction with n1 values between 2.4 and 4. The slow spreading stage (stage II) is controlled by diffusion with n2 values between 4 and 6.7. The size of Cu6Sn5 formed on a rough substrate is greater than that produced on a smooth substrate. Originality/value Investigating the effect of solder composition and roughness on early wettability. This will provide a powerful guide in the field of soft brazing.

The Microstructural, Mechanical and Electrical Properties of Pb-Sn and Lead-Free SC0.7 Solders Containing Sub Micron Active Carbon Particles

Soldering is performed in order to easily assemble electronic components and also to provide electrical conductivity. The strengths, hardness, physical properties and electronic properties of the solders, i.e. reduced energy loss, hardness, melting point and longer service life, can be achieved when their usage is improvised by the help of necessary alloying or neutral additions. In this study, the effect of the addition of sub micron sized activated carbon on the mechanical, physical and electrical properties of industrially used solders, i.e. Pb-Sn and lead free SC0.7 solder was investigated.The thermal studies showed that the melting point of Pb-Sn was lowered against lead free solders with increasing amount of activated carbon. The tensile shear strength of both solders did not improve with increasing amount of activated carbon. In lead-free solders, the electrical resistance values decrease with respect to increasing active carbon ratio, however, the resistance of Pb-Sn solders increased. The addition of active particles have positively affected the microstructure of Pb-Sn solders, resulting in a finer grains, whereas, the addition of active carbon particles have no effect on the grain structures of lead free solder.

Use of Sn60Pb40 Solder in Resistance Element Soldering Technology

This work presents a new technology for joining dissimilar materials, Resistance Element Soldering (RES). This technology is fundamentally based on Resistance Element Welding (REW) technology; the difference is that the presented RES uses a bimetallic element composed of a hard Cu shell and a core made of Sn60Pb40 solder. The RES technology using the Cu/Sn60Pb40 bimetallic element was tested when joining a galvanized steel sheet (HX220BD-100MBO) to a thermoplastic (PMMA). The effect of the process parameters on the volume of the melted solder, the deformation of the element, and the structure of the soldered joint was investigated on the joints made. The final criterion for assessing the influence of the process parameters was the joint strength. Due to the low strength of PPMA, the maximum joint strength was determined on RES joints of galvanized steel sheet and aluminum. The results showed that, to ensure the joint strength at the level of the strength of the Sn60Pb40 solder used, a heat input of 952 J and a clamping force of 623 N are required. The mentioned parameters ensure the necessary conditions for the creation of a soldered joint with a galvanized steel sheet as well as the deformation of the bimetallic element to create a form-fit effect in the opening of the PMMA to create a mechanical connection.

The microstructure evolution and failure mechanism of Sn37Pb solder joints under the coupling effects of extreme temperature variation and electromigration

The effect of electromigration and thermal shock on the microstructure evolution and failure mechanism in the Sn37Pb/Cu solder joints were investigated in this study. With increasing thermal shock cycles, Pb atoms acted as the dominant effective charge carrier, which migrated with the electron flow and accumulated at the anode side. As the number of thermal shocks extended to 20 cycles, the dissolution of Cu trace was found at the corner positions where the current was crowded in the solder joints. High and low temperature thermal shock demonstrated the acceleration of solder failure that accompanies an increase in peak temperature and shock frequency during electromigration process. Combining the extreme temperature thermal shock (–196 to 120 °C) with the current density of 2.0 × 104 A/cm2, the cracks were prone to initiate at the corner and then propagate along the IMC layers with thermal shock cycles. The high thermal stress caused by the thermal expansion mismatch between Sn37Pb solder and Cu pad with the large temperature variation (ΔT = 316 °C) significantly aggravated the crack propagation, which induced the failure of Sn37Pb solder joints after 22 cycles.

Mechanical properties degradation of Sn 37Pb solder joints caused by interfacial microstructure evolution under cryogenic temperature storage

The interfacial microstructure, shear property and fracture behaviors of Sn37Pb joints after cryogenic temperature storage for different durations were investigated in this study, storage test at room temperature (298 K) and thermal aging test at 423 K were also carried out as comparison. The morphology of interfacial Cu6Sn5 IMCs for the joints stored under 77 K and 173 K transformed from scallop-like to column-like, moreover, the IMC layer thickness slowly increased with prolonged storage time. The growth rate of Cu6Sn5 layer in Sn37Pb joint stored at 77 K was slightly faster as compared with that stored at 173 K. However, the morphology and thickness of Cu6Sn5 IMC layer still remained roughly unchanged after storage at 298 K for up to 40 days. The Cu6Sn5 IMC growth of Sn37Pb joint stored at 77 K and 173 K was expected to be caused by Cu atom diffusion from Cu pad towards Sn37Pb solder, which was induced by the stress gradient. Additionally, the shear force declined and fracture position changed from in Sn37Pb solder to primarily in Sn37Pb solder and partly along the interface with the prolonging of storage time at 77 K and 173 K, which were induced by IMC layer growth.

Effect of Au thin films thickness on the wetting characteristics of eutectic Pb-Sn solder on Ni/Ag solder bath

Wetting of Pb-Sn solder on Au/Ni surface is experimentally studied as a function of the thickness of Au coating on Ni buffer layer. While Au coating is known to increase the wettability of Pb-Sn solder on Ni surface, the effect of Au layer thickness was not examined systematically. This study shows that i) an increase in Au layer thickness from 0.15 to 0.3 µm decreases the surface coverage (spread) of the solder and ii) there is a compositional change in Pb-Sn solder on Au/Ni surface due to formation of a Sn rich region at the solder - Ni interface during a reflow process of the solder. The thickness of Sn rich region near the interface increases with increasing the Au layer thickness. A driving force for the formation of the Sn rich phase is explained using the negative mixing enthalpy of Au-Sn. Since an increase in the Sn content of Pb-Sn solder increases the surface energy and viscosity of the solder melt, an increase in the thickness of the Sn rich region at the solder-Ni interface suppressed the wetting of the solder.

Effect of Nanosized Ni Reinforcements on the Structure of the Sn-3.0Ag-0.5Cu Alloy in Liquid and After-Reflow Solid States

The Sn-Ag-Cu (SAC) alloy family is commonly used in lead-free solders employed in the electronics industry, for instance, SAC305, SAC387, SAC405, etc. However, the trend in manufacturing small electronic products and device miniaturization faces some disadvantages in terms of mechanical properties and their higher melting temperatures compared to Pb-Sn solders, prompting new research relating to the reinforcement of existing SAC solders. The current study presents structural features of nanocomposite (Sn-3.0Ag-0.5Cu)100−x(nanoNi)x solders with 0.5 wt.%, 1.0 wt.%, and 2.0 wt.% Ni. Structural analysis of the investigated samples were performed by means of X-ray diffraction in a liquid state and scanning electron microscopy (SEM). SEM showed the mutual substitution of Ni and Cu atoms in the Cu6Sn5 and Ni3Sn4 phases, respectively. The performed structural studies in liquid and solid states provided essential information concerning the structural transformations of liquid Sn-3.0Ag-0.5Cu alloys caused by minor additions of nanosized Ni powder. The melting point and degree of undercooling of the samples were investigated by DTA analysis.

Mechanical properties of Sn–Pb based solder joints and fatigue life prediction of PBGA package structure

Solder joints are generally the weakest part in electronic packaging structure whose fatigue life depends to a large extent on the durability of solder joints. In pursuit of a balance between environmental protection and soldering performance, commonly used Sn–Pb solder should be modified by adding other chemical elements to reduce Pb content. This work aims to investigate the performance of different solder materials and explore the impact of different electronic package structures. Firstly, tensile experiments are performed on three kinds of solders (Sn–Pb, Sn–Pb–In, Sn–Pb–Bi) to obtain their mechanical behavior, and then the constitutive laws of them are calibrated by Anand model. Additionally, finite element method (FEM) is used simulate the response of plastic ball grid array (PBGA) package structure under thermal cycles, and mechanical variables including deformation, equivalent stress, and equivalent strain are analyzed. Finally, Coffin-Manson and Engelmaier equations are adopted to predict the fatigue life of package structures and the effects of various factors such as solder materials, dimensions of components, and welding quality are further investigated. Results reveal that adding Bi into Sn–Pb solder can make the solder joints have better performance. From the perspective of optimum fatigue life, the plastic package thickness is recommended in the range of 0.8 mm–0.9 mm, the chip thickness is recommended as 0.35 mm, the substrate thickness is recommended to be less than 0.34 mm, and the ratio of stand-off height to solder ball diameter should be controlled between 0.6 and 0.7. According to the prediction, the solder ball diameter is suggested to be 0.54 mm so that fatigue life could reach 194 cycles, and the stand-off height for this package structure is suggested to be 0.36 mm so that fatigue life could reach 123 cycles.

Effect of temperature on the low cycle fatigue properties of BGA solder joints

Since the restriction of hazardous substances (RoHS) directive, lead-free soldering has been widely broad adopted. In many applications, lead-free alloys have been substituted for conventional SnPb (Tin-Lead) solder. Among lead-free alloys, SAC305(Sn-3.0Ag-0.5Cu) has gained the highest acceptance as a solder alloy. The fatigue performance of solder joints has become an essential reliability assessment criterion due to the transition to more reliable lead-free alloys from highly predictable lead-based alloys. This study examines the shear fatigue characteristics of sandwich test vehicles for SnPb and SAC305 at different temperatures using both Organic Solderability Preservative (OSP) and Electroless Nickel-Immersion Silver (ENIG) surface finishes. The fatigue experiments were performed using an Instron micromechanical tester at a constant strain rate, and microstructural analysis was carried out using Scanning Electron Microscopy (SEM) to identify the Intermetallic Compound (IMC) morphology and failure mode. The stress-strain (hysteresis) loops of SnPb and SAC305 were measured, and the fatigue life of the specimens was estimated using the strain-life equation at various temperatures. SAC305 was observed to have a better fatigue life than SnPb, particularly at higher strain levels or testing temperatures. The OSP surface finish demonstrated superior fatigue properties compared to the ENIG surface finish. Additionally, elevated testing temperatures were found to accelerate fatigue failure in solder joints. The Arrhenius model was utilized to develop a general empirical model that predicts the fatigue life of SAC305 and SnPb solder alloys with OSP and ENIG surface finishes as a function of the strain level and testing temperature.

Acceleration Factors for Combined‐Accelerated Stress Testing of Photovoltaic Modules

Combined‐accelerated stress testing (C‐AST) is developed to establish the durability of photovoltaic (PV) products, including for degradation modes that are not a priori known or examined in standardized tests. C‐AST aims to comprehensively represent the sample, stress factors, and their combinations using levels at the statistical tails of the natural environment. Acceleration factors for relevant climate sequences within the C‐AST cycle with respect to the Florida USA climate are estimated for selected degradation mechanisms. It is found that for degradation of the outer backsheet polymer layer, the acceleration factor of the tropical climate sequence (the longest of the climate sequences) isf(T,G) = 17.3 with ultraviolet photodegradation; for polyethylene terephthalate hydrolysis (backsheets),f(T,RH) = 426; for electrochemical corrosion (PV cell),f(I) = 14.1; and for PbSn solder fatiguef(ΔT,r(T)) = 17.3. Here,Tis the module temperature,Gis the broadband spectrum irradiance on the plane of array of the module,RHis the relative humidity on the module surface,Iis the leakage current through the module packaging, andr(T), the number of temperature reversals. The methods discussed herein are generally applicable for evaluating acceleration factors in other accelerated test methods.

Study on IMC Growth Law of Solder Joints in Aerospace Electronic Products and Its Influence on Reliability

In order to better understand the influence degree of temperature curve parameters on the growth characteristics of intermetallic compounds (IMC) in solder joints during reflux welding, the influence of different temperature curve parameters on the thickness of IMC in Sn63Pb37 solder joints was explored based on the orthogonal test method. A multiple regression model was established for each parameter and the thickness of IMC. In addition, the results show that: (1) The influence degree of temperature curve parameters on IMC thickness in descending order is the highest temperature, liquidus time, cooling time and cooling rate. (2) The coefficient of the established multiple regression model is R2=0.70391. In this model, the IMC thickness increases with the increase of the maximum reflow temperature and liquidus time and decreases with the increase of the cooling time. (3) When the thickness of IMC is 1 μm- 4 μm, the thermal shock reliability of solder joints decreases with the increase of IMC thickness.

Characterising Solder Materials from Random Vibration Response of Their Interconnects in BGA Packaging

Solder interconnection in electronic packaging is the weakest link, thus driving the reliability of electronic modules and systems. Improving interconnection integrity in safety-critical applications is vital in enhancing application reliability. This investigation qualifies the random vibration response of five essential solder compositions in ball grid array (BGA) solder joints used in safety-critical applications. The solder compositions are eutectic Sn63Pb37 and SnAgCu (SAC) 305, 387, 396, and 405. Computer-aided engineering (CAE) employing ANSYS finite element analysis and SolidWorks software is implemented in this investigation. The solder Sn63Pb37 deformed least at 0.43 µm, followed by SAC396 at 0.58 µm, while SAC405 deformed highest at 0.88 µm. Further analysis demonstrates that the possession of a higher elastic modulus and mass density culminates in lower solder joint deformation. Stress is concentrated at the periphery of the solder joints in contact with a printed circuit board (PCB). The SAC396 solder accumulates the lowest stress of 14.1 MPa, followed by SAC405 at 17.9 MPa, while eutectic Sn63Pb37 accrues the highest at 34.6 MPa. Similarly, strain concentration is found at the interface between the solder joint and copper pad on a PCB. SAC405 acquires the lowest elastic strain magnitude of 0.0011 mm/mm, while SAC305 records the highest strain of 0.002 mm/mm. These results demonstrate that SAC405 solder has maximum and SAC387 solder has minimum fatigue lives.

Fabrication and Performance of 300-mm Wafer-Scale Silicon Microchannel Cooler

This paper describes the design, fabrication, and thermal performance of 300 mm diameter wafer-scale Si microchannel coolers that demonstrated a junction temperature rise of less than 18°C when dissipating about 14 kW of power. A thermal test wafer, which included hot-spot regions to mimic high-power compute cores, was attached to the wafer-scale microchannel cooler with Pb-Sn solder. Glass manifold layers were attached to the microchannel wafer using a frit material. The average apparent heat transfer coefficient, h <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">app</sub> , was about 104,000 W/(K-m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ).

Effect of Graphene Nanosheets on the Microstructure and Mechanical Properties of Sn-20Bi Solder.

The application of Sn-Bi series solder is limited due to the brittleness of Bi phase. Sn-20Bi solder with less Bi element content has great research prospects, but it needs modification to make it a substitute for traditional Sn-Pb solder. In this article, we mixed graphene nanosheets with nanometer Sn powder by means of ultrasonic oscillation, and Sn-20Bi-qGNS (q = 0.01, 0.02, 0.04, 0.06, and 0.1 wt.%) solder alloys were prepared by the melt-casting method. The effects of graphene nanosheets (GNSs) on the microstructure, physical properties, mechanical properties, and corrosion resistance of solder alloys were investigated. Scanning electron microscopy, energy dispersive spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy were used to determine the microstructural morphology and composition. The results showed that the melting point, density, and wettability of the solder decreased slightly with the addition of GNSs. The addition of GNSs as a second phase refined the solder structure and improved the tensile strength of the molten Sn-20Bi composite solder to 99.6 MPa, while elongation decreased with the addition of GNSs. Furthermore, GNSs prevented the MC Sn-20Bi-qGNSs/Cu intermetallic compound layers' growth by interfering with atomic diffusion and grain boundary movement. In addition, the addition of 0.02 wt.% GNSs enhanced the shear strength of MC Sn-20Bi solder joints to 46.3 MPa. The electrochemical experimental results show that the surface corrosion products of MC Sn-20Bi-qGNSs under 3.5% NaCl solution were Sn3O(OH)2Cl2, with MC Sn-20Bi-0.01GNSs exhibiting the best corrosion resistance.