Ball Shear Test Research Articles

A new omnibus SPRT chart for monitoring process mean and variability based on the average number of observations to signal

The recent development of the omnibus sequential probability ratio test (OSPRT) chart marks a significant contribution to the advancement of joint monitoring schemes. As the OSPRT chart is a variable-sample-size control chart, practitioners often wish to understand its inspection efficiency, i.e. the number of observations it samples before producing a signal. In this article, we propose two enhanced optimization designs for the OSPRT chart based on the average number of observations of signal (ANOS) and expected value of the ANOS (EANOS) metrics under deterministic and unknown shift sizes, respectively. The ANOS metric is central to our design as it perfectly combines both the average run length (ARL) and the average sample number. A comparative analysis reveals that the OSPRT chart outperforms four benchmarking control charts in terms of the ANOS and EANOS metrics. Finally, an implementation of the OSPRT chart is presented with a ball shear test dataset.

Improving Reliability of Fan -Out Wafer Level Package Through Doping of Lead-Free Solder Balls

Embedded wafer level ball grid array (eWLB) or FO-WLP (Fan-out wafer-level packaging) is investigated as a package for MMICs (Monolithic Microwave Integrated Circuit) for automotive radar applications in the 77GHz range. Doping of Bi and/or Sb was applied to improve the resistance of lead-free SAC balls against thermal cycling stress. We have shown that by increasing the doping level the lifetime can be increased and determined the maximum doping level before extrinsic failure modes dominate. It is well-known from the literature that doping of Bi and/or Sb improves the resistance of lead-free SAC balls against thermal cycling stress. It was shown that lifetime of FC-BGA package can be multiplied using Bi and/or Sb doping. The lifetime gain is achieved by reduced creepage of the hardened balls caused by the doping. This reduced creepage increases the risk of causing other failures than ball cracks in the eWLB package or the PCB during thermal cycling stress. We have tested robustness of 7x8,5 mm^2 eWLB packages against thermal cycling stress T = -40 to 125 °C using SAC-balls with different Bi-doping content from 0% to 2,5% Bi concentration. As could be expected the solder ball fatigue mode is delayed more and more increasing the Bi content. We found other failure modes than solder ball fatigue emerging at doping around 1%. The fatigue modes are shifted towards cupper lines on PCB or into the package. Cu line cracks can be overcome by switching the PCB layout from NSMD (non solder-mask defined) to SMD (solder-mask defined) solder pads. In general there is a lifetime penalty when switching from NSMD to SMD, but by avoiding the Cu line cracks this lifetime loss is overcompensated using SMD pads for optimum performance. As input for simulations we have characterized the doped solder material using specimens produced in glass columns. We have also tested the components on PCBs with different top layer laminate with different CTE and elastic modulus to assess the influence of the PCB properties on the lifetime. It is a trend in automotive radar systems to use stiffer laminates which are cheaper but have negative influence on component lifetime. Solder ball shear tests were also carried out to characterize the influence of ball doping on other board-level reliability beyond thermal cycling performance. As expected ball shear force is increased with increased doping level. At increased shear-force the shearing is still done through the solder ball and does not lead to different shear-mode. Finally drop-tests were done to check influence of doping on board-level reliability performance other than thermal-cycling performance.

Effect of Sb Addition on Microstructure and Shear Strength of Sn-3.0Ag-0.5Cu Solder Ball Joints

The effect of a small amount of Sb addition to Sn-3.0Ag-0.5Cu (mass%) solder on microstructures and impact properties of the solder ball joint was investigated. Cross-sectional microstructural observation revealed that scalloped Cu6Sn5 is formed at the solder/Cu interface, and Cu3Sn is formed at the interface between Cu6Sn5 and Cu with aging. It was confirmed that the growth of the reaction layer is suppressed by the addition of Sb. Moreover, the result of the impact ball shear test showed that the decrease in impact properties with aging can be suppressed in Sn-3.0Ag-0.5Cu-1.5Sb (mass%). It was also suggested that the suppression of linear crack propagation at the Cu3Sn/Cu6Sn5 interface is effective to prevent the reduction of absorbed energy.

Bonding Property of Middle Temperature Sn-Ag-Cu Solder Ball Joint of Ball Grid Array Package

Alloying effects of Nickel and Bismuth in SAC solder to achieve mechanical and microstructural evolution were investigated by comparing three different chemical composition of solders. Sn-3.0Ag-0.5Cu (SAC305) is the most commonly used for Pb-free solder and solder balls are based on Sn-Ag-Cu alloy composition. Compositions of solder balls were Sn-3.0Ag-0.5Cu (SAC305), Sn-1.2Ag-0.5Cu-0.05Ni (SAC1205N) and Sn-Ag-Cu-Ni-Bi based solder (SACNB). Organic solderability preservative (OSP) surface finished substrate, ball grid array (BGA) package arranged by 300 ㎛ diameter solder ball and Type 4 solder paste were used. Solder ball shear test of the BGA package was conducted before the reflow soldering. Board level package bonding process was carried out by hot air reflow soldering. Void content of the BGA solder joint was investigated after soldering. The microstructure evolution before and after thermal cycle test (TCT) was observed using scanning eletron microscopy (SEM) and energy dispersive spectroscopy (EDS). After TCT, intermetallic compound (IMC) refinement and solid solution strengthening effects of Bi element addition were observed in the solder matrix, and also any segregation of Bi element was not founded. Based on these result, it was found that the solder joint reliability of the middle and low temperature solder joints was improved.

Effects of Process Parameters on Bond Properties of Ag-2.35Au-0.7Pd-0.2Pt-0.1Cu Alloy Wire.

Bond properties were performed on Ag-2.35Au-0.7Pd-0.2Pt-0.1Cu alloy wire with a diameter of 25 µm under different process parameters. The effects of electrical flaming off (EFO) current and EFO time on the deformability of the free air ball (FAB) were investigated using scanning electron microscopy (SEM), as well as the effects of ultrasonic power and bonding force on the bond characteristic. The experimental results show that FAB grows from a preheated tip to a small ball, a regular ball, and finally to a golf ball with increasing either the EFO current or the EFO time, and the FAB presents an optimal shape at 25 mA and 650 μs. Moreover, a nonlinear relationship between FAB diameter and EFO time is obtained at an EFO current of 25 mA, which could be expressed by a cubic equation. Further, at a constant bonding force, as the ultrasonic power increased, the mashed ball diameter grew larger and larger, the capillary hole imprint became more and more obvious, and the tail width also increased, and vice versa. The optimal ultrasonic power and bonding force are 70 mW and 45 gf for ball bonding and 90 mW and 75 gf for wedge bonding, respectively. Finally, for all the bonded wire samples prepared under optimal process parameters, no ball and wedge bond lifts happened after the destructive pull test, and full intermetallic compound coverage with perfect morphology occurred on the bond pad after the ball shear test, which meant that the bonded wire samples had high bond strength and hence improved the reliability of microelectronic products. It provided technical support for the reliability research of Pt-containing Ag-based bonding alloy wires.

Experimental and Statistical Study of the Fracture Mechanism of Sn96.5Ag3Cu0.5 Solder Joints via Ball Shear Test.

Ball shear testing is an efficient approach to investigate the mechanical reliability of solder joints at the structural level. In the present study, a series of low-speed ball shear tests were conducted to study the deformation and fracture characteristics of Sn96.5Ag3Cu0.5 solder joints at continuous speeds from 10 μm/s to 200 μm/s. In order to account for randomness, the quantity of tests was repeated for each shear rate. The relationship between mechanical properties and shear speeds was calculated in detail via effective statistical analysis. In addition, by utilizing SEM imaging and ingredient analysis the interfacial effect and fracture mechanism of solder balls were obtained and their fracture mode classified into two types, viz., bulk fracture and interface fracture. Furthermore, by means of statistical analysis and approximate calculation it was proven that bulk fracture balls have greater adhesive powers and reliability compared with interface fracture balls.

Effect of Ni(P) Layer Thickness on Interface Reaction and Reliability of Ultrathin ENEPIG Surface Finish.

Electroless Ni(P)/electroless Pd/immersion Au (ENEPIG) is a common surface finish in electronic packaging, while the Ni(P) layer increases the impedance of solder joints and leads to signal quality degradation in high-frequency circuits. Reducing the thickness of the Ni(P) layer can balance the high impedance and weldability. In this paper, the interfacial reaction process between ultrathin ENEPIG substrates with different Ni layer thicknesses (0.112 and 0.185 μm) and Sn–3.0Ag–0.5Cu (SAC305) solder during reflow and aging was studied. The bonding ability and reliability of solder joints with different surface finishes were evaluated based on solder ball shear test, drop test and temperature cycle test (TCT), and the failure mechanism was analyzed from the perspective of intermetallic compound (IMC) interface growth. The results showed that the Ni–Sn–P layer generated by ultrathin ENEPIG can inhibit the growth of brittle IMC so that the solder joints maintain high shear strength. Ultrathin ENEPIG with a Ni layer thickness of 0.185 μm had no failure cracks under thermal cycling and drop impact, which can meet actual reliability standards. Therefore, ultrathin ENEPIG has broad prospects and important significance in the field of high-frequency chip substrate design and manufacturing.

Ultrasonic Bonding Interface Degradation Characteristics of Gold-Coated Silver Wire for Semiconductor Packaging

Gold-coated silver wire was developed to alleviate the high cost of Au wire used in semiconductor packaging. Ball-bonding and stitch-bonding techniques were used to fabricate the dummy packaging material, comprising 97.3 % Ag, 97.3% Au-Coated Ag, and 99.99 %Au wires. The wire ball shear test (BST), the wire ball pull test (BPT), and the microstructural attributes of the ultrasonic bonding interfaces were compared with the initial properties, both before and after the highly accelerated stress test (HAST), conducted at 130 ℃ and 85% relative humidity (RH). The initial bonding strength for all the wire variants was ?23~24 gf. Following the HAST, the bonding strength of the Ag wire, the Au-coated Ag wire, and the Au wire decreased by approximately 75 %, 47 %, and 17 %, respectively. The microstructure analysis revealed that cracks developed and propagated at the ends of the interface and that the Au-rich Au-Al intermetallic compound (IMC) inhibited the propagation of the crack at the ACA/Au wire interface. Additionally, it was discovered that the presence of the Ag-Au-Al IMC at the interface of the ACA wire reduced Kirkendall voids, which act as a barrier to Au-Al interdiffusion.

Enhanced Ball Shear Testing Configuration For Substrate LGA Sensor Devices

Semiconductor assembly mass production environment has means of testing and verifying bond consistency and reliability during wire bonding. Common bond integrity assessment is ball shear testing (BST). This test enables analysis of the strength between the bond pad and a ball bond. This paper presents significant procedure on how ball shear testing parameters should be treated during wirebond integrity check. Device complexity in terms of performing ball shear testing specifically on sensor dice has different output responses. Frequent shearing on die resulted as bond pads are elevated by 30 µm (microns). To address manufacturing in-process controls challenges, shearing tool position, dage settings, and optical scopes are taken into consideration. Also, a study was performed on the execution correctness in combination with proper dage parameters was explored to meet good ball shear test process capability and break modes.

IMC microstructure modification and mechanical reinforcement of Sn–Ag–Cu/Cu microelectronic joints through an advanced surface finish technique

Intermetallic compound(s) (IMC) that nucleates at the interface between solder and Cu trace during a soldering reaction, is one of the most crucial factors for microelectronic packaging reliability. This study was conducted to modify the IMC microstructure and to reinforce the mechanical strength of Sn–Ag–Cu/Cu microelectronic joints through various surface finish coatings, including organic solderability preservative (OSP), immersion Ag (ImAg), immersion Sn (ImSn), Au/Pd (electroless palladium/immersion gold, EPIG), and Au/Pd/Au (IGEPIG) layer(s). We confirmed that the type of surface finish dominated the IMC growth morphology and mechanical characteristics of the Sn–Ag–Cu/Cu solder joints, even though these surface finishes were eliminated in a few seconds of the soldering process. A dense Cu6Sn5 layer with a scallop-like appearance was obtained for the traditional OSP case, while a prismatic, loose Cu6Sn5 microstructure was produced for the alternative cases (metal films). This loose Cu6Sn5 microstructure offered numerous molten solder channels for the in-diffusion of Sn to Cu, retarding undesired Cu3Sn growth at the Cu6Sn5/Cu interface; consequently, a brittle-to-ductile transition in the joint fracture mode with a high shear strength and fracture energy was obtained in the high-speed ball shear (HSBS) test. A significant mechanical reinforcement of the Sn–Ag–Cu/Cu microelectronic joints can be achieved with the replacement of the traditional OSP coating by the newly developed IGEPIG trilayer surface finish.

Nucleation and Morphology of Cu6Sn5 Intermetallic at the Interface between Molten Sn-0.7Cu-0.2Cr Solder and Cu Substrate

The nucleation kinetics and morphology of Cu6Sn5 IMCs at the interface between a Sn-0.7Cu-0.2Cr solder and Cu substrate were investigated in this study. A Sn-0.7Cu solder was utilized as a reference to elucidate the impact of Cr addition. The mechanical properties of the solder joints were determined via ball-shear tests. Cu coupons were dipped in the molten solders for 1 and 3 s at 240–300 °C, and the morphological analyses were conducted via electron microscopy. Both the solders contained scallop-like Cu6Sn5 IMCs. The smallest Cu6Sn5 IMCs were observed at 260 °C in both the solders, and the particle size increased at 280 and 300 °C. The IMCs in the Sn-0.7Cu-0.2Cr solder were smaller and thinner than those in the Sn-0.7Cu solder at all the reaction temperatures. The thickness of the IMCs increased as the reaction temperature increased. Inverse C-type nucleation curves were obtained, and the maximum nucleation rate was observed at an intermediate temperature. The shear strengths of the Sn-0.7Cu-0.2Cr solder joints were higher than those of the Sn-0.7Cu solder joints. This study will facilitate the application of lead-free solders, such as Sn-0.7Cu-0.2Cr, in automotive electrical components.

Multi-response optimization of wire bonding process for evaluating alternative wire material

Finding an alternative material to gold wire is important to cost reduction for the wire bonding process. The wire materials for laser diodes are required to pass ball shear test, wire pull test and several reliability tests, so that it can be used in production. This research employs the Multi-response Quality Test procedure that investigates the feasibility and optimal conditions of using silver alloy wire in the wire bonding process. The weighted Principal Components Analysis-based Taguchi method is used to determine the optimal parameter combination of the wire bonding process, which can minimize quality loss in multiple tests. The result shows that under the optimal parameter combination of the wire bonding process, silver alloy wire can outperform gold wire by having higher ball bond strength, higher wire strength, and smaller operation current changes after the reliability tests. Substituting gold wire with silver alloy wire can significantly reduce cost by 30% while improving wire bond quality.

The Fabrication of Ni-MWCNT Composite Solder and Its Reliability Under High Relative Humidity and Temperature

Ni decorated multi-walled carbon nanotube (Ni-MWCNT) composite solders have been fabricated using Ni-MWCNT composite materials and Sn58Bi solder alloys. Ni-MWCNT composite materials were synthesized with functionalization, reduction and electroless plating. The Ni-MWCNT composite solders were fabricated at various weight percentages (0, 0.05, 0.1 and 0.2 wt.%) of Ni-MWCNT. The mechanical properties of Ni-MWCNT composite solder were evaluated using ball shear tests. The shear strength and fracture energy were improved about 16.02% and 12.60%, respectively, by adding 0.1 wt.% of Ni-MWCNTs, which released the stress in the solder alloy. The environmental reliability was examined at 85°C with 85% relative humidity at various holding times. After environmental reliability testing, the microstructure was analyzed to characterize the grain and intermetallic layers. The growth of grains and intermetallic layer thickness were mitigated by Ni-MWCNTs in the solder matrix that affected the mechanical properties. The distribution of Ni-MWCNTs inside the solder joints was confirmed by EPMA and Raman spectroscopy.

Mechanical Properties and Microstructure of Cu Core Solder Ball (CCSB) Compared with SAC305 Solder for 2.5D and 3D Structure Package (PKG)

Package structures are continually becoming more complicated to achieve high-performance devices. Thus, the 2D structure of package needs to be modified to a 2.5D or 3D structure. Therefore, standoff properties at the solder joint are required to prevent Si chip damage and electrical shorts when the solder joint is located between the substrate and interposer. Cu-core solder balls (CCSB) are the most popular interconnection choice for a 2.5D package because they have better standoff properties than the general SAC solder. The mechanical properties of CCSBs were evaluated by ball shear tests and measuring bump height as compared with Sn–3.0 wt.%Ag–0.5 wt.% Cu solder. The bump heights of CCSBs and Sn–3.0 wt.%Ag–0.5 wt.% Cu were measured under several compressive pressure conditions at room temperature, 175 °C and 235 °C. The stand-off height of the CCSBs dramatically better than that of Sn–3.0 wt.%Ag–0.5 wt.% Cu solder under high pressure and temperature. The shear strength of the CCSBs was stronger than that of SAC solder at all multiple reflows due to the finer microstructure and higher stacking of dislocations at the interface of the Cu core ball surface.

Microstructures and Mechanical Properties of Sn-58 wt.% Bi Solder with Ag-Decorated Multiwalled Carbon Nanotubes Under 85°C/85% Relative Humidity Environmental Conditions

The mechanical properties of Sn-58 wt.% Bi solder with different amounts (0 wt.%, 0.05 wt.%, 0.1 wt.%, and 0.2 wt.%) of Ag-decorated multiwalled carbon nanotube (MWCNT) nanoparticles under 85°C/85% relative humidity environmental conditions for 0 h to 1000 h was investigated. Sn-58 wt.% Bi solder is a lead-free option for use in solder joints due to its low melting temperature and good creep resistance; however, it is brittle and has reliability issues. Ag-decorated MWCNT nanoparticles were used to improve these weaknesses of Sn-58 wt.% Bi solder. A ball shear test was performed using a bond tester to investigate the solder's mechanical properties. The microstructures of the solder joints and fracture mode were analyzed using a field-emission scanning electron microscope. The results demonstrated that the addition of Ag-decorated MWCNT nanoparticles to Sn-58 wt.% Bi increased the shear strength and fracture energy by approximately 15% and 14%, respectively, compared with Sn-58 wt.% Bi alone. After a high-temperature, high-humidity test for 1000 h, the shear strength and fracture energy of Sn-58 wt.% Bi with 0.1 wt.% Ag-decorated MWCNT nanoparticles were 13% and 21% greater than for Sn-58 wt.% Bi alone.

Strain Rate Sensitivity of Mixed SAC-SnBi Solder Joints

Abstract As the electronics industry continues to evolve a concerted effort has developed to implement lower melting point solders. The ability to minimize the thermal exposure that an assembly is subjected to affords significant benefits with respect to both the reliability and the materials that can be used. One of the most popular low melt solder alloys currently being investigated by the industry is the Bi-Sn eutectic system, which has a melting point of 139°C. The BiSn system itself is not particularly novel as it was posited as a SAC alternative during the initial shift from Pb based solders. While a body of knowledge currently exists regarding this system, and the near eutectic variant BiSnAg, there are still concerns regarding its ductility, especially as a function of thermal exposure and strain rate. Bismuth is widely acknowledged as a brittle element and its presence in such quantities raises concerns of not just Cu6Sn5 embrittlement but also solder fragility in high strain rate types of environments. A challenge with regards to near term implementation is that most packages are not available with BiSn solder bumps. Therefore, it will be necessary to use components already balled with SAC 305 solder. This means that the resulting solder interconnect, reflowed below conventional SAC reflow temperatures, will form a type of mixed hybrid microstructure. This non-equilibrium microstructure will be composed of two regions, one Bi-rich region which is well past saturation and a second region which is Bi-deficient. It is of specific industrial interest then to not just investigate the BiSn solder system but also within the context of a realistic mixed interconnect. Recent work by several researchers has shown that this hybrid microstructure is unstable and quite active with respect to the movement and localized concentration of the Bismuth. The degree of mixing of these two regions has been shown to be highly dependent upon reflow temperature and the paste to ball volume ratio. Mixed SAC-BiSn solder joints were formed by placing SAC 305 spheres on BiSn paste deposits for a paste to ball volume ratio of .18. These samples were then reflowed at either 175°C or 200°C. SAC 305 control samples were also made using a conventional Pb-free reflow profile with a peak temperature of 247°C. A 22 mil Cu-OSP pad on a 1.0 mm thick FR4 substrate was used for all samples. A selection of the solder joints were then isothermally aged at 90°C for 200 hours. Using a joint level micromechanical tester, ball shear tests were conducted at a range of strain rates for samples in the as-reflowed and aged state. Using this information, the strain rate sensitivity of the interconnects was mapped and correlated with the observed failure modes. Investigations into the fracture mechanisms were conducted by examining the shear fracture surface with optical and scanning electron microscopy. Additionally, the evolution of the microstructure was characterized. Results showed a clear transition from ductile solder failure to a brittle separation failure at the higher strain rates.

Study on the strength of diameter-reducing solder balls by shear and pull tests

Purpose The purpose of this paper is to study the variation of the mechanical strength and failure modes of solder balls with reducing diameters under conditions of multiple reflows. Design/methodology/approach The solder balls with diameters from 250 to 760 µm were mounted on the copper-clad laminate by 1-5 reflows. The strength of the solder balls was tested by the single ball shear test and pull test, respectively. The failure modes of tested samples were identified by combing morphologies of fracture surfaces and force-displacement curves. The stresses were revealed and the failure explanations were assisted by the finite element analysis for the shear test of single solder ball. Findings The average strength of a smaller solder ball (e.g. 250 µm in diameter) is higher than that of a larger one (e.g. 760 µm in diameter). The strength of smaller solder balls is more highly variable with multiple reflows than larger diameters balls, where the strength increased mostly with the number of reflows. According to load-displacement curves or fracture surface morphologies, the failure modes of solder ball in the shear and pull tests can be categorized into three kinds. Originality/value The strength of solder balls will not deteriorate when the diameter of solder ball is decreased with a reflow, but a smaller solder ball has a higher failure risk after multiple reflows. The failure modes for shear and pull tests can be identified quickly by the combination of force-displacement curves and the morphologies of fracture surfaces.

The Optimization of Ball Shear Strength Using a Computational Model

Nowadays, Ball Grid Array, BGA technologies are prevalent through the IC packaging industry. Among them are larger numbers of I/Os, leading to many advantages over conventional ones and low cost assemblies for mass production. BGA packages are compatible with surface mount technology (SMT). BGA uses solder joints as surface mount components (SMC). It is not only used for the conduction of electrical signals, power and ground. It also acts as mechanical support to hold the package in position on a printed circuit board (PCB). Thus, solder joint strength is a major concern for BGA packages. To evaluate the strength of the solder joint attached to the package and PCB, a popular method to use is the ball shear test. In this study, the focus of interest was on the size of the ball, the diameter of solder resistance opening, ball height and shear tool clearance by using finite element method. The experiment design aimed to find out the best conditions for the ball. The results were validated by other authors for suitable correlation. The standard deviation of the parameters concerning ball shear test value was also defined

Effect of Surface Finish on the Shear Properties of SnAgCu-Based Solder Alloys

The reliability of an electronic assembly is typically limited by the failure of one of the solder interconnections. One of the key factors that define the quality of solder interconnections is the strength of the solder joint attachment to the printed circuit board (PCB). The ball shear testing is commonly used as a quantitative approach to evaluate the integrity of the solder. Several factors control the shear strength and failure mechanism of solder joints, including the surface finish, solder alloy composition, and speed of shearing (shear strain rate). In this paper, the effect of surface finish on the shear properties of various “microalloyed” SnAgCu-based solder materials was investigated. Individual solder joints were fabricated on a PCB with a solder mask defined configuration. A series of shear testing was conducted at four different strain rates of 0.001, 0.01, 0.1, and 1 s−1. Shear stress–strain curves were recorded for each test, and both shear strength and shear energy were measured. Following the shear testing, fractured top surfaces and cross sections were inspected using SEM/EDS microscopy to characterize the failure mechanism. The results showed that both shear strength and shear energy increase with increasing shear strain rate due to the viscoplasticity of the solder materials. Failure mode analysis indicated the existence of three failure mechanisms, including ductile failure, brittle failure, and mixed failure. Higher occurrence of brittle failure was observed when the shear strain rate is high regardless of surface finish. It was also found that the combination of solder alloy with high silver (Ag) and bismuth (Bi) content and electroless Ni/immersion Au (ENIG) surface finish is more susceptible to brittle failure compared to the rest of solder alloy-surface finish combinations.

Wettability, Interfacial Behavior and Joint Properties of Sn-15Bi Solder

Sn-15Bi solid solution solder provides a potential replacement for Sn-40Pb solder due to lower cost and similar melting point. Sn-15Bi solder was compared with Sn-40Pb solder to assess the microstructure, wettability, bulk tensile properties, interfacial microstructures in solder joints with a Cu substrate, the interfacial evolution in joints during isothermal aging, and the shear strength on ball solder joints with the effect of aging conditions. The microstructure of Sn-15Bi bulk solder was composed of the primary β-Sn phase with Bi in solid solution and with precipitated Bi phases along the grain boundaries. The wettability of solder alloys was evaluated with wetting balance testing, and the results showed that Sn-15Bi solder had a lower wetting force and longer wetting time than Sn-40Pb solder. The poorer wettability of Sn-15Bi solder was not influenced by different types of soldering flux, but improved with increasing temperature. Tensile tests on bulk solder alloys indicated that Sn-15Bi solder had a higher tensile strength but lower elongation than Sn-40Pb solder. Also, the tensile strength of Sn-Bi solder decreased with decreasing strain rate and with increasing temperature, while the elongation of Sn-Bi solder was independent of the temperature and strain rate. In as-soldered joints, Sn-15Bi solder produced a thicker Cu6Sn5 layer than Sn-40Pb solder. Following isothermal aging, the thickness of the interfacial Cu-Sn intermetallic compound (IMC) increased with the aging time, and the growth rate of the IMC layer in Sn-15Bi solder joints was slightly higher than that in Sn-40Pb solder joints during aging. Ball shear test on solder joints illustrated that Sn-15Bi solder joint had a higher shear strength than Sn-40Pb solder joint, and that with increased aging time, the solder became stronger due to precipitation of Bi, leading to a change in the fracture mode from ductile failure in the solder to brittle fracture at the IMC interface.