Sn-Ag-Cu Research Articles

Effect of aluminum addition on the electrochemical corrosion behavior of Sn–3Ag–0.5Cu solder alloy in 3.5 wt% NaCl solution

The ternary eutectic Sn–Ag–Cu (SAC) solder alloys has become the most promising Pb-containing solders for the application in electronic packaging. The effect of Aluminum on the electrochemical corrosion behavior of Sn–3.0Ag–0.5Cu (SAC 305) solder alloy was investigated in 3.5 wt% NaCl solution in terms of potentiodynamic polarization and electrochemical impedance spectroscopy. Scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD) and atomic force microscopy (AFM) were used to characterize the samples after the electrochemical tests. Polarization studies indicated that an addition of 0.1 and 0.5 wt% Al in the Sn–3.0Ag–0.5Cu solder alloy shifted the corrosion potential (Ecorr) towards more negative values. The Impedance results revealed that the addition of Al with Sn–3.0Ag–0.5Cu solder alloy led to a lower corrosion resistance in terms of impedance values and the capacitance. The SEM images revealed existence of openings and pores in the corrosion product of solders containing Al. EDX and XRD analysis confirmed that the oxides and hydroxides of Sn and Al were the major corrosion products. AFM images exhibited that the surface becomes more rough and non-uniform with Al addition to SAC 305 solder alloy.

Effect of Solder-Joint Geometry on the Low-Cycle Fatigue Behavior of Sn-xAg-0.7Cu

Low-cycle fatigue tests of Sn-Ag-Cu (SAC) Pb-free solder joints under fixed displacement were performed to evaluate the influence of Ag content (0–3 wt.%) and solder-joint geometry (barrel and hourglass types) on solder-joint fatigue behavior and reliability. The solder joints were composed of fine particles of Ag3Sn and Cu6Sn5, which aggregated as an eutectic constituent at grain boundaries of the primary β-Sn phase and formed a dense network structure. A decrease in the Ag content resulted in coarsening of the β-Sn and eutectic phases, which, in turn, decreased the strength of the joint and caused earlier failure. Solder joints in the hourglass form exhibited better fatigue performance with longer life than barrel-type joints. The sharp contact angle formed between the solder and the Cu substrate by the barrel-type joints concentrated stress, which compromised fatigue reliability. The addition of Ag to the solder, however, enhanced fatigue performance because of strengthening caused by Ag3Sn formation. The cracks of the barrel-type SAC solder joints originated mostly at the contact corner and propagated along the interfacial layer between the interfacial intermetallic compound (IMC) and solder matrix. Hourglass-type solder joints, however, demonstrated both crack initiation and propagation in the solder matrix (solder mode). The addition of 1.5–2.0 wt.% Ag to SAC solder appears to enhance the fatigue performance of solder joints while maintaining sufficient strength.

Effect of nano Co reinforcements on the structure of the Sn-3.0Ag-0.5Cu solder in liquid and after reflow solid states

Sn-Ag-Cu (SAC) alloys are commonly recognized as lead-free solders employed in the electronics industry. However, some disadvantages in mechanical properties and their higher melting temperatures compared to Pb-Sn solders prompt new research relating to reinforcement of existing SAC solders. One of the ways to reinforce these solder materials is the formation of composites with nanoparticles as filler materials. Accordingly, this study presents structural features of nanocomposite (Sn-3.0Ag-0.5Cu)100−x(nanoCo)x solders with up to 0.8 wt% nano Co. The effect of nano-sized Co particles was investigated by means of differential thermal analysis (DTA), X-ray diffraction (XRD) in both liquid and solid states, and scanning electron microscopy (SEM). The experimental data of DTA are compared with available literature data for bulk Sn-3.0Ag-0.5Cu alloy to check the capability of minor nano-inclusions to decrease the melting temperature of the SAC solder. The combination of structural data in liquid and solid states provides important information about the structural transformations of liquid Sn-3.0Ag-0.5Cu alloys caused by minor Co additions and the phase formation during crystallization. Furthermore, scanning electron microscopy has shown the mutual substitution of Co and Cu atoms in the Cu6Sn5 and CoSn3 phases, respectively.

Creep Constitutive Models Suitable for Solder Alloys in Electronic Assemblies

Most solders used in electronic systems have low-melting temperature and hence experience significant amount of creep deformation throughout their life-cycle because typical operational and test conditions represent high homologous temperature. Phenomenological and mechanistic models used in the literature for predicting creep response of both bulk and grain scale specimens are reviewed in this paper. The phenomenological models reviewed in this paper are based on purely empirical observations of the creep deformation behavior or derived from qualitative interpretation of the underlying microscale mechanisms. These models have some intrinsic disadvantages since they do not have explicit mechanistic dependence on microstructural features. Therefore, the constitutive relations derived using the above models are difficult to extrapolate beyond the test conditions. This paper also reviews how some of the above limitations can be mitigated by using mechanistic or microstructurally motivated models. Mechanistic models are capable of estimating the material creep response based on the detailed physics of the underlying mechanisms and microstructure. The microstructure and constitutive response of the most popular family of lead-free solders, namely, SnAgCu (SAC) solders, are significantly different from those of previously used eutectic Sn37Pb solder. The creep deformation in Sn37Pb solder occurs primarily through diffusion-assisted grain-boundary sliding. In SAC solder joints, dislocation-based creep deformation mechanisms such as glide, climb, detachment, and cross-slip appear to be the dominant mechanisms in coarse-grained joints. Mechanistic creep models are therefore based on the deformation mechanisms listed above.

Mechanical and Physical Properties of In-Zn-Ga Lead-Free Solder Alloy for Low Energy Consumption

Due to the demand in the use of electronics devices in industry, the usage of solder connections has increased. Concerning with the toxicity of lead in Sn-37Pb solder alloy, developing lead free solder alloy with low melting temperature is one of the most important issues in electronic industry. Previously, researchers found out that the most promising candidate of lead free solder alloy is Sn-3.0Ag-0.5Cu (SAC). However, the melting temperature of this solder alloy is 217°C, 34°C higher than Sn-37Pb. This can lead to high energy consumption in electronic industry. In this paper, In-Zn-Ga solder alloy was investigated as a potential candidate replacing SAC. This study covers on the physical and mechanical properties of the solder alloy. Differential Scanning Calorimetry (DSC) testing shows that this solder alloy gave low melting temperature as low as 141.31°C. The addition of Ga in In-Zn solder alloy lowered the melting temperature compared to SAC and Sn-37Pb. From coefficient of thermal expansion (CTE) analysis, the In-Zn-Ga solder alloy gives good expansion properties and able to avoid the mismatch between the solder and copper substrates. The density of In-Zn-Ga solder alloy is 6.801g/cm3, lower than SAC and Sn-37Pb. For the strength, single lap shear testing was conducted on the In-Zn-Ga solder alloy and the results is near to the strength of SAC.

Sn-Ag-Cu Nanosolders: Solder Joints Integrity and Strength

Although considerable research has been dedicated to the synthesis and characterization of lead-free nanoparticle solder alloys, only very little has been reported on the reliability of the respective joints. In fact, the merit of nanoparticle solders with depressed melting temperatures close to the Sn-Pb eutectic temperature has always been challenged when compared with conventional solder joints, especially in terms of inferior solderability due to the oxide shell commonly present on the nanoparticles, as well as due to compatibility problems with common fluxing agents. Correspondingly, in the current study, Sn-Ag-Cu (SAC) nanoparticle alloys were combined with a proper fluxing vehicle to produce prototype nanosolder pastes. The reliability of the solder joints was successively investigated by means of electron microscopy and mechanical tests. As a result, the optimized condition for employing nanoparticles as a competent nanopaste and a novel procedure for surface treatment of the SAC nanoparticles to diminish the oxide shell prior to soldering are being proposed.

Design and performance of Ag nanoparticle-modified graphene/SnAgCu lead-free solders

In this study, various weight percentages of Ag-nanoparticle-modified graphene (Ag-GNSs) were incorporated into Pb-free Sn-Ag-Cu (SAC) solder matrices via ball milling and mechanical mixing methods to form composite solders. Up to 0.2wt% of the Ag-GNSs particles was successfully incorporated into the composite solders, and the microstructures and mechanical properties of the solders were investigated. The experimental results demonstrated that as the Ag-GNSs content increased, the number of intermetallic particles gradually decreased in size. In addition, the uniformity of the interfacial structure increased compared to that of the pure SAC solder. Furthermore, the melting points of the SAC/Ag-GNSs composite solders were unchanged compared to that of the pure SAC solder. The experimental results also revealed that the wettability of the composite solders on Cu substrates was greatly improved. Thermomechanical measurements showed that the thermal stability of the composite solders was also improved. In addition, tensile tests showed that the ultimate tensile strength of the composite solders was enhanced compared to that of the pure SAC solder, but the ductility of the composite solders was reduced. In particular, the tensile strength of the composite solders with low Ag-GNSs contents was increased, but the tensile strength then decreased once a critical Ag-GNSs content was reached. For the ball-milled solders, the reinforcement provided by the addition of Ag-GNSs particles was much better than that provided by unmodified graphene. By comparing the properties of solders fabricated with different preparation methods, it was determined that the ball-milled solders were superior to the mechanically mixed solders.

Mechanistic Prediction of the Effect of Microstructural Coarsening on Creep Response of SnAgCu Solder Joints

Mechanistic microstructural models have been developed to capture the effect of isothermal aging on time dependent viscoplastic response of Sn3.0Ag0.5Cu (SAC305) solders. SnAgCu (SAC) solders undergo continuous microstructural coarsening during both storage and service because of their high homologous temperature. The microstructures of these low melting point alloys continuously evolve during service. This results in evolution of creep properties of the joint over time, thereby influencing the long term reliability of microelectronic packages. It is well documented that isothermal aging degrades the creep resistance of SAC solder. SAC305 alloy is aged for (24–1000) h at (25–100)°C (~0.6–0.8 × Tmelt). Cross-sectioning and image processing techniques were used to periodically quantify the effect of isothermal aging on phase coarsening and evolution. The parameters monitored during isothermal aging include size, area fraction, and inter-particle spacing of nanoscale Ag3Sn intermetallic compounds (IMCs) and the volume fraction of micronscale Cu6Sn5 IMCs, as well as the area fraction of pure tin dendrites. Effects of microstructural evolution on secondary creep constitutive response of SAC305 solder joints were then modeled using a mechanistic multiscale creep model. The mechanistic phenomena modeled include: (1) dispersion strengthening by coarsened nanoscale Ag3Sn IMCs in the eutectic phase; and (2) load sharing between pro-eutectic Sn dendrites and the surrounding coarsened eutectic Sn-Ag phase and microscale Cu6Sn5 IMCs. The coarse-grained polycrystalline Sn microstructure in SAC305 solder was not captured in the above model because isothermal aging does not cause any significant change in the initial grain size and orientation of SAC305 solder joints. The above mechanistic model can successfully capture the drop in creep resistance due to the influence of isothermal aging on SAC305 single crystals. Contribution of grain boundary sliding to the creep strain of coarse grained joints has not been modeled in this study.

마이크로솔더링을 이용한 정전류다이오드 회로 자외선 LED 광원모듈 제작

The improvement of irradiation intensity and irradiation uniformity is essential for large area and high power UVA light source application. In this study, large number of chips bonded by micro soldering technique were driven by low current, and current limiting diodes were configured to supply constant current to parallel circuits consisting of large number of series strings. The dimension of light source module circuit board was 350 × 90 mm 2 and 16,650 numbers of 385 nm flip chip LEDs were used with a configuration of 90 parallel and 185 series strings. The space between LEDs in parallel and series strings were maintained at 1.9 mm and 1.0 mm distance, respectively. The size of the flip chip was 750 × 750 µm 2 were used with contact pads of 260 × 669 µm 2 size, and SAC (96.5 Sn/3.0 Ag/0.5 Cu) solder was used for flip chip bonding. The fabricated light source module with 7.5 m A supply current showed temperature rise of 66℃, whereas irradiation was measured to be 300 mW/cm 2 . Inaddition, 0.23% variation of the constant current in each series string was demonstrated.

Effects of Ag content on the interfacial reactions between liquid Sn–Ag–Cu solders and Cu substrates during soldering

The effects of Ag content on the interfacial reactions between Sn–Ag–Cu (SAC) solders and Cu substrates during soldering were studied based on an experiment in which the liquid solder is removed after a long exposure time. This removal of the solder allows for the capture and visualization of the interfacial IMCs formed during soldering and avoids the influence of Cu6Sn5 precipitated from the solder matrix during cooling. The results showed that a Cu6Sn5 scallop type layer with round grains having a strong texture was formed at the interface of the SAC solders/Cu systems. The addition of Ag decreased the IMC/liquid SAC solder interfacial energy and improved the wettability of the solder on the Cu. In addition to the reaction energy, the interfacial microstructure also affected the interfacial IMC growth extent. By changing the growth environment near the interface, Ag affected the orientation of Cu6Sn5 grains formed at the interface, leading to the evolution of a microstructure that generates more Cu6Sn5 grain boundaries at the interface. Consequently, under the same reflow conditions, SAC solders with a higher Ag content in contact with the Cu substrate form thicker IMCs interfacial layers.

Multiscale modeling of the anisotropic transient creep response of heterogeneous single crystal SnAgCu solder

The lack of statistical homogeneity in functional SnAgCu (SAC) solder joints due to their coarse grained microstructure, in conjunction with the severe anisotropy exhibited by single crystal Sn, renders each joint unique in terms of mechanical behavior. A mechanistic multi-scale modeling framework is proposed in this study to predict the influence of composition and microstructure on the anisotropic transient creep response of single crystal SnAgCu (SAC) solder. Tier I consist of single-crystal eutectic Sn–Ag alloy, with nanoscale Ag3Sn particles embedded in a single-crystal Sn matrix. Tier II consists of single crystal SAC solder which is composed of Sn dendrites surrounded by the eutectic Sn–Ag phase of Tier I. The Tier I anisotropic transient creep model is based on dislocation mechanics. The Tier II model uses the results of Tier I as an input and is based on anisotropic composite micro-mechanics.In Tier I, creep deformation is governed by dislocation impediment and recovery at nanoscale Ag3Sn particles, with recovery being the rate controlling mechanism. Dislocation climb and dislocation detachment at the Ag3Sn particles are proposed to be the competing rate controlling recovery mechanisms. Line tension and mobility of dislocations in dominant slip systems of single crystal Sn are estimated based on the elastic crystal anisotropy of body centered tetragonal (BCT) Sn. The anisotropic transient creep rate of the eutectic Sn–Ag phase of Tier I is then modeled using above inputs and the evolving dislocation density calculated for dominant glide systems during the transient stage of creep. The dominant slip systems are determined based on the dislocation mobility and on the orientation angle between the crystal principal axes and the loading direction. The creep response of the eutectic phase (from Tier 1) is combined with the creep response of Sn lobes at Tier 2, using the anisotropic Mori-Tanaka homogenization theory, to obtain the transient creep response of a SAC305 single crystal along global specimen directions. This model has been calibrated using experimentally obtained transient creep response of a SAC305 single crystal specimen. The above multiscale calibrated model is then used to predict (i) the transient creep response of another SAC305 single crystal specimen and (ii) the effect of orientation (by changing one of the Euler angles) on the transient creep response of SAC305 single crystal. The grain orientation of above two SAC single crystal specimens (with respect to loading direction) were identified with orientation image mapping and then utilized in the model to estimate the resolved shear stress along the dominant slip directions. Parametric studies have also been conducted to predict the effects of the volume fraction, aspect ratio, and orientation of ellipsoidal Sn inclusions on the anisotropic transient creep response of SAC single crystals.

Electromigration of composite Sn-Ag-Cu solder bumps

This study investigates the electromigration (EM) behavior of lead free Sn-Ag-Cu (SAC) solder alloys that were reinforced with different types of nanoparticles [Copper-coated carbon nanotubes (Cu/CNT), La2O3, Graphene, SiC, and ZrO2]. The composite solders were bumped on a Cu substrate at 220°C, and the resistance of the bumped solders was measured using a four wire setup. Current aging was carried out for 4 hours at a temperature of 160°C, and an increase in resistance was noted during this time. Of all the composite solders that were studied, La2O3 and SiC reinforced SAC solders exhibited the smallest resistances after current aging. However, the rate of change in the resistance at room temperature was lower for the SiC-reinforced SAC solder. The SAC and Graphene reinforced SAC solder bumps completely failed within 15 - 20 min of these tests. The SiC nanoparticles were reported to possibly entrap the SAC atoms better than other nanoparticles with a lower rate of EM.

Effect of Graphene Nanoplatelets on Wetting, Microstructure, and Tensile Characteristics of Sn-3.0Ag-0.5Cu (SAC) Alloy

The effect of graphene nanoplatelets (GNPs) on the wettability, microstructure, and tensile properties of Sn-3.0Ag-0.5Cu (SAC 305) was studied using melting and casting route. The microstructure of the bulk solder is observed with a scanning electron microscope and transmission electron microscope, and the intermetallic compound (IMC) phases are identified by electron probe micro-analyzer. The solderability of the samples is assessed by spreading and wetting tests on a Cu substrate. The experimental results indicate that an addition of 0.05 wt pct GNPs in Sn-3Ag-0.5Cu solder improves the spreading and wettability significantly compared to monolithic SAC. It is also revealed that the thickness of the Ag3Sn IMCs is reduced as compared to the monolithic SAC alloy. Tensile results show that the composite solder exhibits the 13.9 pct elongation and 17 pct increase in the ultimate tensile strength when 0.05 wt pct GNPs in Sn-3Ag-0.5Cu alloy are added. This may be due to the refinement of the IMCs in composite solders compared to the same in Sn-3Ag-0.5Cu alloy brought about by the uniform dispersion of graphene nanoplatelets. It is suggested in this study that the amount of GNPs in Sn-3Ag-0.5Cu alloy should not exceed 0.05 wt pct as it may degrade the desired properties due to the agglomeration of GNPs.

Microstructure and mechanical properties of Pb-free Sn–3.0Ag–0.5Cu solder pastes added with NiO nanoparticles after reflow soldering process

Incorporating various types of ceramic type nanoparticles into Pb-free solder pastes produces unique nanocomposite solder pastes. In this study, Sn–Ag–Cu (SAC) 305 solder alloys were mixed with 0.5, 1.5, and 2.5wt.% NiO ceramic nano-elements to produce a new set of nanocomposite solder pastes. The displacement phenomenon of NiO nanoparticles during reflow soldering process may contribute efficient idea in the field of microelectronic industries. The reinforcement of reactive nanoparticles in SAC 305 solder paste caused 50% changes in the intermetallic layer thickness and hardness of plain solder. Top-view microstructural analysis wherein dimple surfaces were magnified showed that the combination of SAC 305–2.5wt.% NiO nanopaste exceeded the limits of alloy addition.

Aging resistance and mechanical properties of Sn3.0Ag0.5Cu solder bump joints with different bump shapes

The effects of bump shape on the aging resistance and mechanical properties of Sn3.0Ag0.5Cu (SAC) solder bump joints were investigated by high-temperature aging test and shear test. Three different SAC solder bump joints with barrel type, cylinder type, and hourglass type, respectively, were provided by controlling solder process. The results indicate that as the bump volume decreases from barrel bump to hourglass bump in the reflow, the thickness growth rate of intermetallic compounds (IMCs) between different solder joints and Cu substrates in the isothermal aging of 150 °C decreases. And the change of shear strength of hourglass interconnection solder joint with the increase in temperature is the minimum in the three interconnection solder joints. Thus, as the solder dosage decreases properly, hourglass interconnection solder joint is obtained, which is avail to enhance the solder joint reliability at the high-temperature aging and the ability to adapt to the change of environment temperature suddenly.

Individual Phase Mechanical Properties at Different Temperatures of Sn–Ag–Cu Lead-Free Solders Incorporating Special Pileup Effects Using Nanoindentation

Sn–Ag–Cu (SAC) alloys are considered as good replacements of Sn–Pb alloys which are banned due to the toxic nature of Pb. But, SAC alloys have a coarse microstructure that consists of β-Sn rich and eutectic phases. Nanoindentation is a useful technique to evaluate the mechanical properties at very small length scale. In this work, continuous stiffness measurement (CSM) nanoindentation setup (CSM Instruments SA, Peseux, Switzerland) is used to determine the individual phase mechanical properties like Young's modulus and hardness at high temperatures. It is demonstrated that these properties are a function of temperature for both β-Sn rich and eutectic phases. Loadings starting from 500 μN up to 5000 μN are used with 500 μN steps and average values are presented for Young's modulus and hardness. The loading rates applied are twice that of the loadings. High temperatures result in a higher creep deformation and therefore, to avoid it, different dwell times are used at peak loads. The special pileup effect, which is more significant at elevated temperatures, is determined and incorporated into the results. A better agreement is found with the previous studies.

Effects of graphene nanosheets on interfacial reaction of Sn–Ag–Cu solder joints

In this work, varying amount of graphene nanosheets (GNSs) were introduced as reinforcements into Sn–Ag–Cu (SAC) solder to get composite solders. Then, the formation and growth kinetics of the intermetallic compounds (IMC) were investigated during the liquid–solid reactions and solid-state aging. Experimental results demonstrated that the morphologies of the interfacial IMC were transformed from scalloped to platelike after liquid–solid reactions and solid-state aging. The IMC thickness of composite solder joints was thinner than that of the unreinforced solder joints. The calculations revealed that the growth rate constant of composite solder was lower than that of bulk SAC solder. It's worth to mention that the composite solder joints exhibited lower diffusion coefficients (ranging from 0.6 × 10−12 m2/s to 1.07 × 10−12 m2/s) than that of the SAC solder joints (1.81 × 10−12 m2/s) after liquid–solid reactions and the composite solder joints also exhibited lower diffusion coefficients (ranging from 1.42 × 10−12 m2/s to 1.78 × 10−12 m2/s), as compared to that of the monolithic SAC solder joint (2.46 × 10−12 m2/s) after aging studies. It indicates that the addition of GNSs can effectively suppress the growth of the overall IMC layers, which can also hinder the IMC's growth and enhance solder joints' reliability.

Effect of current load on corrosion induced tin whisker growth from SnAgCu solder alloys

The effect of current load was investigated on corrosion induced tin whisker growth from SnAgCu (SAC) solder alloys. Three alloys were studied: two low Ag content micro-alloyed SAC and the widely used SAC305. The solder joints were loaded with six different DC current levels between 0 and 1.5A and they were aged in corrosive environment (85°C/85RH%) for 3000h. The morphology of the whiskers and the micro-structural changes of the solder joints were examined by scanning electron microscope. It was shown that the current load can decrease the corrosion of the solder joints and consequentially it can decrease whiskering as well.

Reliability Comparison of Aged SAC Fine-Pitch Ball Grid Array Packages Versus Surface Finishes

Pb-free solder joints exposed to elevated isothermal temperatures for prolonged periods of time undergo microstructural and mechanical evolution, which degrades the joint electrical performance. We report the effect of isothermal aging on the reliability of Sn–Ag–Cu (SAC) assemblies on three different surface finishes [immersion Ag (ImAg), electroless Ni/immersion Au (ENIG), and electroless Ni/electroless Pd/immersion Au (ENEPIG)]. The characteristic life for SAC alloys in 10- and 15-mm ball grid array packages on ImAg degraded over 40% after an 85 °C/12 months aging and over 50% during a 125 °C/12 months aging. ENIG and ENEPIG outperformed ImAg for all aging treatments. For passive components (2512 resistors) on ImAg, the reliability performance degraded 16.7%/28.1% after a 1-year aging at 85 °C/125 °C. Failure analysis showed dramatic intermetallic binary Cu–Sn and ternary Ni–Cu–Sn film growth at the bottom of the solder joint interfaces for ImAg and ENIG/ENEPIG. For 125 °C-aged samples, the cracks appeared at the corners of both package and board sides of the solder ball and propagated along (near) the intermetallic compound location. For the case of aged fine-pitch packages, the failures tended to start at the component side solder ball corner and then propagate along an angled path downward into the bulk solder.

Improved drop reliability of Sn–Ag–Cu solder joints by Zn addition to a Cu wetting layer

Cu–20 wt% Zn solder wetting layers were fabricated by electroplating in cyanide and non-cyanide solutions, and board-level drop impact reliability was evaluated for Sn–Ag–Cu (SAC) solder joints formed on Cu–Zn layers. Adding Zn to the Cu wetting layer suppressed the formation of a large Ag3Sn plate in the solder and delayed interfacial intermetallic compound (IMC) growth in the solder/Cu–Zn interfaces. Formation of Cu3Sn IMC and microvoids was not observed in the Cu6Sn5/Cu–Zn interface during thermal aging. The drop impact reliability of the Cu–Zn/SAC/Cu–Zn solder joints was superior to that of Cu/SAC/Cu solder joints, both before and after aging. The drop impact performance of the Cu–Zn specimens was similar whether their Cu–Zn layers were electroplated in cyanide or non-cyanide solution. Drop impact reliability of both Cu and Cu–Zn specimens decreased after aging due to IMC growth and/or microvoid formation in the solder interfaces. Interfacial microstructure influenced the failure mode of the solder joints. For Cu specimens, the dominant failure sites were a Cu6Sn5/Cu interface before aging and a Cu3Sn/Cu interface after aging. The formation of a large Ag3Sn plate facilitated crack growth. For Cu–Zn specimens, the crack always propagated inside the Cu6Sn5 layer. Microstructural changes in the solder interfaces arising from the addition of Zn contributed to the improvement of drop impact reliability of SAC solder joints.