Interfacial Intermetallic Growth Research Articles

Evaluation of Solidification and Interfacial Reaction of Sn-Bi and Sn-Bi-In Solder Alloys in Copper and Nickel Interfaces

Although there are studies devoted to lower Indium (In) addition, Sn-Bi alloys containing 10 wt.% In or more have been barely investigated so far. Higher In contents may offer the potential for improved joint production, better control over the growth of interfacial layers, and enhanced mechanical strength. The present article focuses on the solidification, wettability, adhesion strength, and interfacial intermetallic growth in the Sn-40%Bi-10%In alloy soldered on Cu and Ni pads. SEM-EDS, wettability tests, and tensile tests were performed. The contact angles were measured in Cu and Ni as 24° and 26°, respectively. Indium addition promoted coarsening of the as-solidified microstructure due to an increase in the alloy solidification range. The Bi spacing was increased at least three times, with a strong segregation of Bi towards the interface. The formation and growth of alloy/Cu reaction layers were also evaluated under the different aging conditions of the as-soldered joints, simulating real service. A growth kinetics model of the reaction layer showed that In increases the activation energy, thereby reducing the layer growth. The adhesions of the formed intermetallics films in Cu and Ni were analyzed using tensile tests. It was observed that the alloy/Ni couple exhibited better adhesion. Premature fracturing appears to happen in the alloy/Cu joint due to the higher intermetallic compound’s (IMC) thickness, rough morphology, and coarser microstructure. Both ductile fracture features with dimples and cleavage zones associated with Bi, Cu6(Sn,In)5, and Ni3Sn4 intermetallics were observed.

Effects of Bi and Cu addition on mechanical properties of Sn9Zn alloy and interfacial intermetallic growth with Ni substrate

Sn9ZnxBixCu (x = 0, 1.0, 2.0, 3.0 and 4.0 wt%) solder alloys were prepared by adding different contents of Bi and Cu elements, and the effects of Bi and Cu addition on the mechanical properties, wettability, and interfacial intermetallic compound (IMC) layer were researched. The addition of Bi and Cu can significantly improve the mechanical properties and creep resistance of the alloy. When the addition of Bi and Cu reaches 2 wt%, small Bi phases are dispersed in the matrix, and moderate Cu5Zn8 phases appear, which strengthens the solder matrix. The ultimate tensile strength (UTS) of the Sn9Zn2Bi2Cu alloy reaches 51.01 MPa, which is 149.32% higher than that of the Sn9Zn alloy, and the elongation reaches 26.56%. Nanoindentation results show that the holding displacement of the Sn9Zn4Bi4Cu alloy decreased by 28.48% compared with that of the Sn9Zn alloy at a loading rate of 0.1 mN/s. In addition, proper addition of Bi and Cu can improve the wettability of the solder alloy and inhibit the growth of interfacial intermetallic compounds (IMCs) between the solder and Ni substrate. When the reflow time reaches 40 min (min), the interfacial IMC thickness of the Sn9Zn2Bi2Cu/Ni solder joint is 1.93 µm, which is 46.09% smaller than that of the Sn9Zn alloy. Moreover, the shear strength of the Sn9Zn2Bi2Cu/Ni solder joint increases by 33.3%, reaching the maximum value (38.76 MPa). When the Bi and Cu addition reaches 2 wt%, the wetting area reaches a larger value (13.525 mm2), which is 28.35% higher than that of Sn9Zn alloy.

Elimination of Intermetallic Coverage Over-etching on Aluminum Pad

Intermetallic coverage (IMC) is one of the critical wirebond output responses that is usually checked to ensure the ball to pad integrity. The success of wirebonding relies on the formation of an interfacial intermetallic growth of ball bond to ensure it can withstand reliability stresses. The challenging approach in IMC analysis detect as over-etching around IMC area that leads to inaccurate IMC data collection. To address the over-etching, we generate a new method which is backside polishing that results to a reliable IMC data collection and help reduced the cycle time of IMC data gathering.

Effect of Trace Addition of In on Sn-Cu Solder Joint Microstructure Under Electromigration

Recently In has been considered as an additional alloying element in Sn-rich solders primarily due to its abilities to decrease the solder melting temperature and to modify mechanical properties and microstructure. While In is an attractive candidate for addition to solder, its effect on solder microstructure is not well understood. In order to study the effect of minor In additions on Sn-rich solder alloys, solder joints were prepared using Sn-0.7 wt.% Cu and Sn-0.7 wt.% Cu- < 1 wt.% In alloys. Thermal aging and electromigration testing were done, followed by post-mortem microstructure characterization including composition, morphology, and grain structure. The addition of In did not appear to affect the microstructure under thermal aging conditions, but slowed interfacial intermetallic growth under electromigration, particularly of the compound Cu6Sn5. Transmission electron microscope analysis revealed the formation of Cu7In3 IMC nanoparticles, which were semicoherent with the surrounding Sn matrix.

Interfacial Reactions between Ga and Cu-10Ni Substrate at Low Temperature.

Ga alloys have been attracting significant renewed attention for low-temperature bonding applications in electronic packaging. This study systematically investigates the interfacial reaction between liquid Ga and Cu-10Ni substrates at 30 °C. In addition to CuGa2 formed from binary Ga/Cu couples, a layer of nanocrystalline Ga5Ni and CuGa2 formed between the Cu-10Ni substrate and the blocklike micrometer scale CuGa2 layer. The growth of interfacial intermetallics (IMCs) on the Cu-10Ni substrate was substantially accelerated compared to the IMC growth in binary Ga/Cu couples. Reaction kinetics study shows the IMC growth from the Cu-10Ni substrate was controlled by reaction and volume diffusion, while the IMC growth from the Cu substrate was controlled by volume diffusion. It is also found that the presence of Ni within the CuGa2 phase resulted in improved thermal stability and a smaller coefficient of thermal expansion during heating from 25 to 300 °C, using synchrotron XRD analysis. There was least thermal expansion anisotropy among most of the IMCs that form in conventional Sn-based solder alloys, including Cu6Sn5 and so forth. It is concluded that using a Cu-10Ni substrate as opposed to a Cu substrate could achieve sufficient metallurgical bonding within shorter processing time. The results have implications for broadening the application temperatures when using Ga as a low-temperature joining material.

Effect of nano-Ag3Sn additions on wettability, interfacial intermetallic growth and mechanical properties of Zn–30Sn–1Ge solders on Cu substrates

The influences of different addition (0, 0.2, 0.4, 0.6, 0.8, and 1.0 wt%) of Ag3Sn on the wettability, the morphology of interfacial intermetallic compounds (IMCs), and the mechanical properties of Zn30Sn1Ge (ZSG) solder on Cu substrate were investigated. The Ag3Sn nanoparticles with an average particle size of approximately 30–45 nm were dispersed in the α-Zn phase and IMC layer. The added Ag3Sn nanoparticles can remarkably improve the wettability of ZSG solder and inhibit the formation and growth of the interfacial IMCs between the nanocomposite solders and Cu substrates. The enhancement of wettability and inhibition of interfacial IMC increased with the increase of nano-Ag3Sn addition amount under low concentration. However, the excessive addition of Ag3Sn nanoparticles in ZSG solder will degrade the wettability and inhibition of interfacial IMCs. When the amount of Ag3Sn nanoparticles is 0.6 wt%, the ZSG–0.6Ag3Sn solders possess the best wettability. In addition, the ZSG–0.4Ag3Sn solder exhibits the most prominent effect in retarding the formation and growth of interfacial IMCs. Meanwhile, the addition of Ag3Sn nanoparticles increases the shear strength and Vickers hardness of the solder joint. When the amount of Ag3Sn nanoparticles is 0.4 wt%, the shear strength of the welded joint is increased by 13.3%. Moreover, the macroscopic hardness of ZSG–0.6Ag3Sn solder is 49.507 HV, which is 57.5% higher than that of the solder without added nanoparticles (31.38 HV). Results show that the addition of Ag3Sn nanoparticles plays an important role in the interfacial reaction and mechanical properties between the ZSG solder and Cu substrate.

Wettability, Interfacial Intermetallic Growth and Joint Shear Strength of Eutectic Sn–Cu Solder Reflowed on Bare and Nickel-Coated Copper Substrates

In the present study, wettability, interfacial intermetallic growth and shear strength of Sn–Cu eutectic solder solidified on bare as well as nickel-coated copper substrates were examined. Sn–0.7Cu solder was reflowed over the substrate for reflow times ranging from 10 to 500 s at 270 °C. Samples were cooled by quenching in water. The wetting behavior was similar on both the substrates. The corresponding time period to the end of gravity zone (Tgz) was measured from the relaxation curve obtained from wetting studies. Tgz was found to be 25 s for Sn–0.7Cu on bare and 50 s on Ni-coated copper substrates. The intermetallic compound layer thickness was fitted to a growth model to study the growth kinetics. The integrity of solder/substrate joint was assessed by performing ball as well as single-lap joint shear tests. The shear strength was found to be maximum at Tgz for all solder/substrate systems.

The effect of CNT and Cu on interfacial intermetallic growth of Sn-Ag-Cu solder

In this study, the effect of copper and carbon nanotubes (CNT) composition on interfacial growth of various Sn-Ag-Cu (SAC) solder joints were investigated. SAC is proven to have good reliability and mechanical properties but lacking in terms of melting point and wettability. Thus, Sn-4.0 wt%Ag-0.3wt%Cu (SAC403) and Sn-4.0 wt%Ag-0.7 wt%Cu (SAC407) were reinforced with CNT with various weight percentages of 0 to 0.1wt%. The wetting angle and intermetallic compound (IMC) thickness is measured using optical microscope (Olympus BX5/M) and Olympus Stream Essentials software. The high Cu content alloys formed a long Cu6Sn5 whisker which act as an obstacle to crack propagation. CNT improves wettability and IMC layer growth for both SAC403 and SAC407 by lowering the wetting angle and IMC thickness compared to the plain solder.

Formation and growth of interfacial intermetallics in Sn-0.3Ag-0.7Cu-xCeO2/Cu solder joints during the reflow process

The effects of adding CeO2 nanoparticles on the formation and growth of interfacial intermetallic compounds (IMCs) between Sn-0.3Ag-0.7Cu-xCeO2 (x = 0, 0.05, 0.1, 0.15, 0.2, 0.3 wt%) (SAC0307-xCeO2) solders and Cu substrates during reflow soldering were investigated. Scanning electron microscopy (SEM) was used to observe the microstructural evolution of the solder joints and measure the thickness and grain size of the intermetallic layers. The results show that the thicknesses and grain sizes of the IMCs decrease with CeO2 nanoparticle addition to the SAC0307 solder and that these parameters decrease significantly at a particle concentration of approximately 0.15 wt%. At higher concentrations, the thicknesses and grain sizes of the IMCs increase slightly. The growth exponents for the IMC layers and grains are determined by curve fitting to study the growth kinetics of the IMCs during reflow soldering. The results reveal that the growth exponents of the IMC layers range from 0.335 to 0.374 and those of the IMC grains range from 0.302 to 0.318, thus suggesting that the growth of the IMCs is controlled by the combined kinetic processes of atomic interdiffusion, interfacial reactions, and grain ripening. These data also show that among the tested solders, the SAC0307–0.15CeO2 solder joint has the smallest growth rate and exhibits the most significant effects in IMC growth suppression and grain size refinement. Based on the theories of heterogeneous nucleation and adsorption, a mechanism for reducing the IMC growth rate by the addition of CeO2 nanoparticles to the SAC0307 solder is proposed.

Effect of heat treatment on the interfacial microstructure and properties of Cu-Al joints

The purpose of this article is to study the effect of heat treatment on the interfacial microstructure and properties of the Cu-Al contact reaction brazed joint, and compare the results with a similar study performed on flash welding. The results show that the interfacial intermetallics in Cu-Al joint change from original two layers (Cu9Al4/CuAl2) to three layers (Cu9Al4/CuAl/CuAl2) both in contact reaction brazing and in flash welding. Some Kirkendall voids form during the growth of interfacial intermetallics. The voids in the contact reaction brazed joint form in the middle of interfacial intermetallic layer and lead a discontinuous crack after 500 h heat treatment. The voids in the flash welded joint form between copper and interfacial intermetallics and lead to a continuous crack after 500 h heat treatment. The growth rate of interfacial intermetallics conforms to the parabolic law for both joints. The relation between joint properties and the interfacial intermetallic thickness can be described by a linear function. The joint properties of contact reaction brazing are better than that of flash welding during the heat treatment. Therefore, contact reaction brazing is more preferred to maintain electrical stability and mechanical integrity of Cu-Al joint.

Phase Field Modeling of Joint Formation During Isothermal Solidification in 3DIC Micro Packaging

In this paper, a computational multi-phase field approach is utilized to study the formation of the Cu/Sn/Cu micro-joint in 3-Dimensional Integrated Circuits (3DICs). The method considers the evolution of the system during isothermal solidification at 250 °C for the case of two different interlayer thicknesses (5 and 10 µm). The Cu/Sn/Cu interconnection structure is important for the micro packaging in the 3DIC systems. The thermodynamics and kinetics of growth of η-Cu6Sn5 and ɛ-Cu3Sn interfacial intermetallics (IMCs) are investigated by coupling the multi-phase field method with CALPHAD approach. The interaction of the phases is addressed by assuming a metastable condition for the Cu/Sn reacting system. The simulations start with the nucleation and rapid growth of the η-Cu6Sn5 IMCs at the initial stage, the nucleation and growth of ɛ-Cu3Sn IMCs at the intermediate stage ending with the full consumption of Sn layer and the domination of ɛ-Cu3Sn IMCs at the later stages. In addition, comparing different diffusion rates through the grain boundary of η phases show that their morphology is the direct consequence of balance of kinetic forces. This work provides a valuable understanding of the dominant mechanisms for mass transport in the Cu/Sn/Cu low volume interconnections. The results show that the phase field modeling is successful in addressing the morphological evolution and growth of IMC layers in the 3DIC joint formation.

Effect of nano-Al addition on properties and microstructure of low-Ag content Sn–1Ag–0.5Cu solders

In this paper, Al nanoparticles were manually mixed into the Sn–1Ag–0.5Cu solder paste to prepare composite solder. The content of Al nanoparticles ranged from 0 to 0.4 wt% in the solders. The influences of Al nanoparticles on the melting characteristics, wettability, mechanical properties, microstructure and interfacial intermetallic growth of low-Ag Sn–1Ag–0.5Cu solders on copper substrate were investigated. Results show that added Al nanoparticles can not obviously change the melting point of the Sn–1Ag–0.5Cu solder, and improve the wettability and mechanical properties of plain Sn–1Ag–0.5Cu solder. However, excessive addition Al nanoparticles will reduce the wettability and mechanical properties of the solder. There is an optimum amount of Al nanoparticles in Sn–1Ag–0.5Cu solder, which is 0.1 wt%, and Sn–1Ag–0.5Cu–0.1Al nano-composite solder exhibit the best comprehensive properties. Based on the microstructure examination, it is found that adding Al nanoparticles can obviously refine the microstructure of Sn–1Ag–0.5Cu–xAl solder. In addition, the interfacial intermetallic compounds (IMC) layer thickness of the Sn–1Ag–0.5Cu–xAl solders are smaller than that of plain Sn–1Ag–0.5Cu solder, which indicates that Al nanoparticles can effectively suppress IMC formation and growth.

Phase segregation, interfacial intermetallic growth and electromigration-induced failure in Cu/In–48Sn/Cu solder interconnects under current stressing

The evolution of microstructure in Cu/In–48Sn/Cu solder bump interconnects at a current density of 0.7 × 104 A/cm2 and ambient temperature of 55 °C has been investigated. During electromigration, tin (Sn) atoms migrated from cathode to anode, while indium (In) atoms migrated from anode to cathode. As a result, the segregation of the Sn-rich phase and the In-rich phase occurred. A Sn-rich layer and an In-rich layer were formed at the anode and the cathode, respectively. The accumulation rate of the Sn-rich layer was 1.98 × 10−9 cm/s. The atomic flux of Sn was calculated to be approximately 1.83 × 1013 atoms/cm2s. The product of the diffusivity and the effective charge number of Sn was determined to be approximately 3.13 × 10−10 cm2/s. The In–48Sn/Cu IMC showed a two layer structure of Cu6(Sn,In)5, adjacent to the Cu, and Cu(In,Sn)2, adjacent to the solder. Both the cathode IMC and the anode IMC thickened with increasing electromigration time. The IMC evolution during electromigration was strongly influenced by the migration of Cu atoms from cathode to anode and the accumulation of Sn-rich and In-rich layers. During electromigration, the Cu(In,Sn)2 at the cathode interface thickened significantly, with a spalling characteristic, due to the accumulation of In-rich layer and the migration of Cu atoms - while the Cu(In,Sn)2 at the anode interface reduced obviously, due to the accumulation of Sn-rich layer. The mechanism of electromigration-induced failure in Cu/In–48Sn/Cu interconnects was the cathode Cu dissolution-induced solder melt, which led to the rapid consumption of Cu in the cathode pad during liquid-state electromigration and this finally led to the failure.

Effects of Cobalt Nanoparticles Addition on Shear Strength, Wettability and Interfacial Intermetallic Growth of Sn−3.0Ag−0.5Cu Solder during Thermal Cycling

In the present study, Cobalt nanoparticles were synthesized and mixed with Sn-3.0Ag-0.5Cu solder (SAC305). The effect of 0.05 wt.%, 0.2 wt.%, 0.5 wt.% and 1.0 wt.% Co nanoparticles on the wettability, the shear strength as well as the growth of intermetallic compounds (IMCs) at composite solder/Cu interface during thermal cycling were investigated. Results show that Co nanoparticle addition can considerably improve wettability, increase the shear strength and suppress the growth of interfacial IMCs. The addition amount of Co nanoparticles have the consistent relation with the improvement extent of the wettability, shear strength and the growth rate of interfacial IMCs. Slight addition (0.05 wt.% and 0.2 wt.%) can significantly improve the properties of nanocomposite solder in all the three aspects. However, with excessive addition amount (0.5 wt.% and 1.0 wt.%) of Co nanoparticles, the improvement extent will decline. The Cross-section images of the interface of nanocomposite solder/Cu joint show that Co can form reinforcement particles in the solder and can act as the sacrificial element to substitute Cu to react with Sn. Excessive Co nanoparticles would form large amount of hard and brittle intermetallics which leads to decreasing shear strength of the composite solder.

Effect of nano-Fe2O3 additions on wettability and interfacial intermetallic growth of low-Ag content Sn–Ag–Cu solders on Cu substrates

In the present study, Fe2O3 nanoparticles were synthesized and smelted with pure Sn, Ag, and Cu to prepare Sn–1.0Ag–0.7Cu–xFe2O3 nano-composite solders. The content of Fe2O3 nanoparticles ranged from 0 to 1wt.% in the solders. The influences of Fe2O3 nanoparticles on the wettability and the morphology of interfacial intermetallics compounds (IMCs) of low-Ag Sn–Ag–Cu solders on Cu substrate were investigated. Results show that added Fe2O3 nanoparticles can remarkably improve the wettability of Sn–1.0Ag–0.7Cu solder alloys and inhibit the formation and the growth of the interfacial IMCs between the nano-composite solders and Cu substrate. Meanwhile, not only the wettability of the nano-composite solders but also the formation and the growth of the interfacial IMCs, during reflow and aging, are identically relied on Fe2O3 weight percent in nano-composite solders. The enhancement of wettability improvement and interfacial IMC inhibition caused by nano-Fe2O3 addition increased with the addition amount under small concentration. However, excessive addition of Fe2O3 nanoparticles in the Sn–1.0Ag–0.7Cu solder alloys will degrade the wettability and the inhibition effect on the interfacial IMCs. There is an optimum amount of Fe2O3 nanoparticles in Sn–1.0Ag–0.7Cu solder alloys, which is 0.4wt.%, and Sn–1.0Ag–0.7Cu–0.4Fe2O3 solders possess the best wettability and the inhibition effect on the interfacial IMCs formation and growth. The reason for improving wettability and simultaneously inhibiting IMCs formation and growth due to Fe2O3 nanoparticles addition is explained.

Interfacial intermetallic growth and mechanical properties of carbon nanotubes reinforced Sn3.5Ag0.5Cu solder joint under current stressing

In this work, multi-walled carbon nanotubes (MWCNTs) with various weight percentages of 0.01wt%, 0.05wt%, 0.1wt% were incorporated into Sn3.5Ag0.5Cu (SAC) solder matrix by mechanical blending followed by reflow process. The microstructure with interfacial intermetallics (IMCs) growth were investigated after aging at 100°C and a current density of 1.2×104A/cm2 for 336h. CNTs were found to be homogeneously dispersed into the solder matrix by EDX analysis. Experimental results revealed that microporosities existed in some areas of doped solders, which retarded the formation of Ag3Sn IMCs. The growth of IMCs for CNTs reinforced solders was less significantly than that of the plain solder, because CNTs affected the reaction mechanisms of both Cu5Sn6 and Cu3Sn at the anode side and alleviated IMCs growth and solder dissolution into Cu substrate at the cathode side. A slight decrease in melting temperature for CNT reinforced solders was found compared to that of the plain solder. The CNT doped solders demonstrated promising improved shear strength and hardness.

Dependence of electromigration damage on Sn grain orientation in Sn–Ag–Cu solder joints

The relationship between the “polarity effect” of electromigration on interfacial intermetallic growth and the Sn grain orientation was investigated in Sn-Ag-Cu solder joints. The growth of the interfacial intermetallic compound was found to depend strongly on the Sn grain orientation. When the c-axes of the Sn grains were closely aligned to the current flow direction, a severe polarity effect was observed in which the anode interface was covered with a thick layer of Cu-Sn intermetallic while the intermetallic layer at the cathode interface was almost depleted. If the c-axes of the Sn grains were rotated away from the current direction, the polarity effect became less pronounced. When the c-axis was perpendicular to the current direction, the polarity effect essentially disappeared. The difference in the intermetallic layer thickness between the anode and the cathode, Δd, followed a parabolic function of the cosine of the angle, α, between the c-axis and the current direction. A kinetic model based on the highly anisotropic diffusion behavior of Cu in Sn was presented to explain the relationship between the electromigration polarity effect and Sn-grain orientation. The model showed good agreement with the experimental data.

Interfacial Intermetallic Growth and Strength of Composite Lead-Free Solder Alloy Through Isothermal Aging

The effects of particle reinforcement of Sn-4.0wt.%Ag-0.5wt.%Cu (SAC405) lead-free solder on interfacial intermetallic layer growth and strength of the ensuing joints through short-term isothermal aging (150°C) were studied. Composite solders were prepared by either incorporating 2 wt.% Cu (3 μm to 20 μm) or Cu2O (∼150 nm) particles into SAC405 paste. Aggressive flux had the effect of reducing the Cu2O nanoparticles into metallic Cu which subsequently reacted with the solder alloy to form the Cu6Sn5 intermetallic. While all solders had similar interfacial intermetallic growth upon reflow, both of the composite solders’ growth rates slowed through aging to reach a common growth rate exponent of approximately 0.38, considerably lower than that of the nonreinforced solder (n = 0.58). The nanoscale reinforced solder additionally exhibited the highest tensile strength in both the initial and aged conditions, behavior also attributed to its quick conversion to a stable microstructure.

Interfacial intermetallic growth and shear strength of lead-free composite solder joints

In the present study, varying weight percentages of carbon nanotubes (CNTs) were incorporated into Sn–Ag–Cu solder matrix, to form composite solders. Isothermal aging study was performed on solder joints, to investigate the formation and growth of the intermetallic compound (IMC) layer at the solder/metallization interface. Shear tests were also conducted on as-soldered and aged solder joints. Results revealed that after soldering, the initial interfacial IMC thickness of the unreinforced solder joint was comparable to that of the composite solder joints. However, after aging, the interfacial IMC layer of the unreinforced solder joint was observed to grow more significantly than that of the composite solder joints. Moreover, the composite solder joints also exhibited lower diffusion coefficient and this signified that the presence of CNTs was effective in retarding the growth of the IMC layer. Shear tests results revealed that as-soldered and aged composite solder joints had better shear strength than their monolithic counterparts and the shear strength of all aged solder joints decreased with increasing aging time.

Tensile fracture behaviors of solid-state-annealed eutectic SnPb and lead-free solder flip chip bumps

The tensile fracture behavior for solid-state-annealed eutectic SnPb and lead-free solder flip chip bumps was examined. The annealing temperatures were in the range of 125–170 °C for 500 h. Prior to solid state annealing, the eutectic Sn–37Pb (SnPb) and Sn–0.7Cu (SnCu) solders showed fracture through the bulk solder. Brittle interfacial fracture occurred in the Sn–3.5Ag (SnAg) solder. After solid-state annealing, the fracture behavior changed dramatically. For eutectic SnPb solder, the fracture modes gradually changed from cohesive solder failure to interfacial fracture with increasing annealing temperature. The fracture mode of the SnCu solder showed greater change than the SnPb and SnCu solders. After annealing at 125 °C, the SnAg solder had a ductile taffy pull fracture, but an increase in temperature resulted in brittle interfacial fracture again. The SnCu solder maintained the same ductile taffy pull mode up to170 °C annealing, independent of the under bump metallization (UBM) type. Microstructure analysis showed that the interfacial fracture of the SnPb and SnAg solder bumps was ascribed to Pb-rich layer formation and Ag embrittlement at the interface, respectively. The bulk solder fracture of SnAg annealed at 125 °C appeared to be a transient phenomenon due to the abrupt breakdown of the hard lamella structure. The eutectic SnCu solder bumps had no significant change in the interfacial structure, except for interfacial intermetallic growth.