Morphology Of Interfacial Intermetallic Compounds Research Articles

Morphology evolution and grain orientations of intermetallic compounds during the formation of full Cu3Sn joint

The morphological evolution and grain orientations of intermetallic compounds (IMCs) were investigated during the formation of full Cu3Sn joints at two soldering temperatures (310 and 430 °C). The mechanical properties of both types of full Cu3Sn joints were then analyzed. The experimental results showed that the morphology of interfacial IMCs varied significantly at two temperatures. At 310 °C, scallop-like Cu6Sn5 grains became larger but were fewer in number and the top of the scallops became rough due to the grain ripening effect. With the increase in the soldering temperature to 430 °C, Cu3Sn no longer grew uniformly as observed during soldering at 310 °C, but exhibited various growth rates. Furthermore, some η-Cu6Sn5 transformed into η′-Cu6Sn5 during cooling, and the following orientation groups between η′-Cu6Sn5 and η-Cu6Sn5, i.e., {102}η′ and {112‾0}η, {112}η′ and {101‾0}η, and {2‾01}η′ and {0001}η, were found to be near-parallel. The Cu3Sn grains were preferably oriented with [203] and [100] crystal orientations parallel to transverse direction (TD) at both temperatures. Noteworthy, the Cu3Sn grains with [203]//TD and [010]//ND grew much faster than those with other orientations at 430 °C. Moreover, molecular dynamics simulation showed that the diffusion coefficients of atoms in Cu3Sn crystals along [203] direction were significantly greater than those in other low-index crystal directions. After soldering, two types of full Cu3Sn joints obtained at different temperatures exhibited different shear strength and fracture mechanisms.

Effects of Si contents in filling wires on microstructure evolution and properties of Al-steel dissimilar joint by laser welding-brazing

The overlap joints of 6061 aluminium alloy and galvanized DP590 steel were made by the laser welding-brazing technology. Effects of Si contents in filler wires on weld appearances, microstructure and mechanical properties of the welding-brazing joints were studied. The well-formed joints could be obtained under the optimized welding-brazing parameters. The interfacial intermetallic compounds (IMCs) could divided into five zones from the steel side to the Al side: the R-IMCs and G-IMCs mainly composed by Fe(Al,Si) phases, the S-IMCs mainly consisted of Fe2(Al,Si)5 phases, the P-IMCs mainly made up of Fe(Al,Si)3 phases and the Fe2Al8Si phases formed at edges of the P-IMCs. Various ranges and morphologies of IMCs within different zones were attributed to the element diffusion and microstructure evolution affected by thermal interactions. Formation of the Fe–Al–Si ternary compounds softened the hardness of interfacial zones compared to the Fe–Al binary compounds. Harness of the Fe2(Al,Si)5 phase was highest, followed by the Fe(Al,Si)3 phase and then the Fe(Al,Si) phase. Addition of Si element significantly improved tensile properties of the welding-brazing joints, optimal tensile strength and ductility could be achieved when the AlSi10 wire was adopted, owing to the dispersion strengthening of the soft G-IMCs distributed discretely within S-IMCs.

SY7-3. Trials of IT based-telemonitoring of blood pressure for pregnant women at higher risk: an overview of the BUMP trials

The overlap joints of 6061 aluminium alloy and galvanized DP590 steel were made by the laser welding-brazing technology. Effects of Si contents in filler wires on weld appearances, microstructure and mechanical properties of the welding-brazing joints were studied. The well-formed joints could be obtained under the optimized welding-brazing parameters. The interfacial intermetallic compounds (IMCs) could divided into five zones from the steel side to the Al side: the R-IMCs and G-IMCs mainly composed by Fe(Al,Si) phases, the S-IMCs mainly consisted of Fe2(Al,Si)5 phases, the P-IMCs mainly made up of Fe(Al,Si)3 phases and the Fe2Al8Si phases formed at edges of the P-IMCs. Various ranges and morphologies of IMCs within different zones were attributed to the element diffusion and microstructure evolution affected by thermal interactions. Formation of the Fe–Al–Si ternary compounds softened the hardness of interfacial zones compared to the Fe–Al binary compounds. Harness of the Fe2(Al,Si)5 phase was highest, followed by the Fe(Al,Si)3 phase and then the Fe(Al,Si) phase. Addition of Si element significantly improved tensile properties of the welding-brazing joints, optimal tensile strength and ductility could be achieved when the AlSi10 wire was adopted, owing to the dispersion strengthening of the soft G-IMCs distributed discretely within S-IMCs.

Effects of ultrasonic treatment on mechanical properties and microstructure evolution of the Cu/SAC305 solder joints

The effects of different ultrasonic treatment time on microstructure evolution and mechanical property of Cu/Sn-3.0Ag-0.5Cu (SAC305) solder joints were investigated. Experiments were set to obtain Cu/SAC305 solder joints, which were compared with solder joints without ultrasonic treatment. The application of short-term ultrasonic treatment on the solder joints would alter the morphology of interfacial intermetallic compound (IMC) layer, IMC thickness and grains size were reduced. Besides, ultrasonic treatment could significantly improve the shear strength of solder joints. In addition, the liquid solder would further flow along the direction of ultrasound, resulting in the reduction of contact angle. Due to the increase of ultrasonic time, the optimal growth direction of grains was changed after the ultrasonic treatment. However, excessive ultrasonic time would reduce the shear strength of solder joints and increase the IMC thickness, which would reduce the stability of solder joints.

Comparative study between the Sn–Ag–Cu/ENIG and Sn–Ag–Cu/ENEPIG solder joints under extreme temperature thermal shock

The interfacial reactions and the growth behavior of interfacial intermetallic compounds (IMCs), as well as their effects on the mechanical properties of the Sn-3.0Ag-0.5Cu (SAC305)/electroless nickel-electroless palladium-immersion gold (ENEPIG) solder joints under extreme temperature thermal shock between − 196 °C and + 150 °C were investigated, and compared with those of the SAC305/electroless nickel-immersion gold (ENIG) solder joints. The morphology of (Cu, Ni)6Sn5 IMCs formed at the SAC305/ENIG interface transformed from column-type to polygon-type during extreme temperature thermal shock, while the needle-type and thin-layer-type (Cu, Ni, Pd)6Sn5 IMCs at the SAC305/ENEPIG interface completely transformed to chunk-type. The growth rate of interfacial IMCs in the SAC305/ENEPIG joint was slower in contrast to that in the SAC305/ENIG joint, since the Pd(P) layer in the ENEPIG surface finish inhibited the formation and growth of interfacial IMCs. After thermal shock for 400 cycles, the shear force of the SAC305/ENIG and SAC305/ENEPIG joints decreased about 29.06% and 9.79%, respectively. Moreover, the shear force of the SAC305/ENEPIG joints was consistently higher than that of the SAC305/ENIG joints. The SAC305/ENEPIG joints always fractured in the solder matrix, regardless of thermal shock cycles, while the fracture location of the SAC305/ENIG joints transferred from inside the solder matrix to partially inside the solder matrix and partially at the solder/IMC layer interface with increasing thermal shock cycles.

A data-driven framework to predict the morphology of interfacial Cu6Sn5 IMC in SAC/Cu system during laser soldering

A data-driven approach combining together the experimental laser soldering, finite element analysis and machine learning, has been utilized to predict the morphology of interfacial intermetallic compound (IMC) in Sn-xAg-yCu/Cu (SAC/Cu) system. Six types of SAC solders with varying weight proportion of Ag and Cu, have been processed with fiber laser at different magnitudes of power (30−50 W) and scan speed (10−240 mm/min), and the resultant IMC morphologies characterized through scanning electron microscope are categorized as prismatic and scalloped ones. For the different alloy composition and laser parameters, finite element method (FEM) is employed to compute the transient distribution of temperature at the interface of solder and substrates. The FEM-generated datasets are supplied to a neural network that predicts the IMC morphology through the quantified values of temperature dependent Jackson parameter (αJ). The numerical value of αJ predicted from neural network is validated with experimental IMC morphologies. The critical scan speed for the morphology transition between prismatic and scalloped IMC is estimated for each solder composition at a given power. Sn-0.7Cu having the largest critical scan speed at 30 W and Sn-3.5Ag alloy having the largest critical scan speed at input power values of 40 W and 50 W, thus possessing the greatest likelihood of forming prismatic interfacial IMC during laser soldering, can be inferred as most suitable SAC solders in applications exposed to shear loads.

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.

Effect of laser beam models on laser welding–brazing Al to steel

Joining dissimilar metals Al to steel in butt configuration was successfully realized by laser welding–brazing process with different laser beam models (single laser beam, cross and in–line dual laser beams). Undercut occurred at the joint produced by single laser beam and satisfactory weld formations were obtained in the joints produced by cross and in–line dual laser beams. Dual laser beam was beneficial for the reduction of interfacial intermetallic compound (IMC) thickness and homogenization of interfacial IMC morphology. Numerical models were developed to calculate the thermal cycles along brazing interface. Calculation of interfacial thermal cycles revealed that lowest peak temperatures (1028 °C, 1036 °C and 990 °C respectively for top, middle and bottom regions), shortest time of interaction at high temperature (2.2 S) and smallest temperature gradients (1036–990 °C = 46 °C) were all obtained in the joint produced by cross dual laser beam and these all made contribution to its thinnest and most homogeneous interfacial IMC. Joint with the highest tensile strength was produced when the cross dual laser beam was adopted due to its satisfactory weld formation and most homogeneous of τ5.

Interfacial intermetallic compound growth in Sn-3Ag-0.5Cu/Cu solder joints induced by stress gradient at cryogenic temperatures

During deep space exploration, electronic devices will be inevitably exposed to cryogenic temperatures. The effects of cryogenic temperature storage on the interfacial microstructure and mechanical behaviors of Sn-3Ag-0.5Cu/Cu (SAC305/Cu) solder joints were systematically investigated. The thickness of interfacial intermetallic compounds (IMCs) in the joints stored at −196 °C and −100 °C was found to gradually increase with the prolonging of storage time, and the morphology of the interfacial IMCs transformed from scallop type to column type. The growth rate of interfacial IMCs in the joints stored at −196 °C was faster than that stored at −100 °C. The stress gradient in the solder joints induced by thermal expansion mismatch was the primary driving force for atomic diffusion and interfacial IMC growth at cryogenic temperatures. The stress gradient in solder joints stored at −196 °C was higher than that stored at −100 °C, leading to a faster growth rate of interfacial IMCs at −196 °C. During cryogenic temperature storage, the interfacial IMC growth caused a volume shrinkage and thus generated residual stresses around the interface. As a result, the shear strength of the solder joints stored at −196 °C and −100 °C declined and the fracture location shifted towards the solder/IMC layer interface with the increase of storage time.

Synchrotron radiation imaging study on the rapid IMC growth of Sn–xAg solders with Cu and Ni substrates during the heat preservation stage

Synchrotron radiation X-ray real-time imaging technology was used to study the interfacial reactions of Sn and Sn3.5Ag solders with Cu and Ni substrates during the heat preservation stage. This experiment allows us to in-situ observe the interfacial intermetallic compounds (IMCs) growth, provides a stage to distinctly separate their growth at isothermal reflow and cooling durations, and thus avoids the measurement errors for size and morphology of interfacial IMCs. The results show that the Cu6Sn5 morphology is scalloped at Sn–xAg/Cu interfaces, whereas (Cu,Ni)6Sn5 is wide-stripe shaped at Sn–xAg/Ni interface during the heat preservation stage. It is interesting to note that the grain boundary molten liquid gaps is observed at both of the Sn3.5Ag/Cu and Sn3.5Ag/Ni interfaces. Compared with pure Sn solder, Sn3.5Ag solders are observed with interfacial IMC of greater thickness, smaller base width, lower aspect ratio and more substrate consumption. In addition, it is confirmed that Ag3Sn grains appear in Sn3.5Ag solder, but not on the surface of existing interfacial Cu6Sn5 grains at Sn3.5Ag/Cu interface during the heat preservation stage. All of the growth kinetic index (n) for Sn–xAg/Cu is close to 1/3 indicating that grain boundary diffusion determines the interfacial reaction at the heat preservation stage. The mechanism by which Ag addition affects interfacial reaction and changes the mirostructure of solder matrix through creation of grain boundary gaps and decrease of the growth activation energy of IMC is also clarified. The knowledge for morphology and thickness control of interfacial IMCs by alloy elements addition as outlined by this study can be utilized to improve the reliability of solder joints in electronic packaging and solar photovoltaic (PV) cells array manufacturing sectors.

Cu–Al interfacial compounds and formation mechanism of copper cladding aluminum composites

Abstract Copper cladding aluminum (CCA) rods with the section dimensions of 12 mm in diameter and 2 mm in sheath thickness were fabricated by vertical core-filling continuous casting (VCFC) technology. The kinds and morphology of interfacial intermetallic compounds (IMCs) were investigated by SEM, XRD and TEM. The results showed that the interfacial structure of Cu/Al was mainly composed of layered γ1(Cu9Al4), cellular θ(CuAl2), and α(Al)+θ(CuAl2) phases. Moreover, residual acicular ɛ2(Cu3Al2+x) phase was observed at the Cu/Al interface. By comparing the driving force of formation for ɛ2(Cu3Al2+x) and γ1(Cu9Al4) phases, the conclusion was drawn that the ɛ2(Cu3Al2+x) formed firstly at the Cu/Al interface. In addition, the interfacial formation mechanism of copper cladding aluminum composites was revealed completely.

Effect of initial Cu concentration on the IMC size and grain aspect ratio in Sn–xCu solders during multiple reflows

The effect of initial Cu concentration in Sn–xCu solders, on grain size and morphology of interfacial intermetallic compound (IMC) during multiple reflow process, was investigated in this work. It was found that the initial Cu content in solders is closely related to the IMC nucleation and Cu migration behavior, which can govern the IMC crystal growth as well as grain aspect ratio evolution. In general, higher initial Cu in solder would lead to an increase in thickness of IMC, regardless of the reflow number. For Sn, Sn0.5Cu, Sn1.5Cu and Sn2.0Cu, the grain aspect ratios show decreased values with rising initial Cu percentage in solder; but for Sn0.7Cu, it has an even smaller aspect ratio than pure Sn. Moreover, Sn0.5Cu, Sn1.5Cu and Sn2.0Cu present a pronounced suppression of grain aspect ratio with reflow number, whereas this is not observed in context of pure Sn and Sn0.7Cu solders. Fine Cu6Sn5 nanoparticles on the surface of interfacial IMC grains in Sn0.7Cu alloy were observed in both isothermal heating and cooling, which may have served as the reason for its unique behavior of grain aspect ratio evolution. The relationship between Cu addition and IMC grain growth can be utilized in the reliability design of Pb-free solder materials.

Effect of P and Ge doping on microstructure of Sn-0.3Ag-0.7Cu/Ni-P solder joints

Purpose The purpose of this paper is to comparatively investigate the microstructure and interfacial intermetallic compound (IMC) layer of Cu/SACPG/Ni and Cu/SAC0307/Ni solder joints after thermal aging. Design/methodology/approach The specimens were thermally aged at 150°C for 0, 24, 168 and 500 h. The microstructure and morphology of the interface IMC layer were observed by means of scanning electron microscope. The IMCs and the solder bump surface were analyzed by EDS. Moreover, the thickness of IMC layer was measured by using the image analysis software. Findings The morphology of IMC of Cu/SAC0307/Ni solder joint was consistent with that of the Cu/SACPG/Ni joint, which indicates that the addition of P and Ge had little effect on the IMC formation. The needle-like (Cu,Ni)6Sn5 was formed at the interface of solder/Ni solder joints. Meanwhile, the tiny particles inferred as Ag3Sn phase attached to the surface of (Cu,Ni)6Sn5. The growth rate of IMC layer of the Cu/SACPG/Ni joint was smaller than that of Cu/SAC0307/Ni joint with aging time increasing, which means the addition of trace P and Ge can slightly suppress the diffusion rate of the interfacial IMC. Originality/value There are no previous studies on the formation mechanism of the IMC layer of SAC0307 solder alloys with P and Ge addition.

Microstructural evolution and joint strength of Sn-58Bi/Cu joints through minor Zn alloying substrate during isothermal aging

To improve the interfacial microstructure and mechanical behaviors of Sn-58Bi/Cu joint, minor Zn element was alloyed into Cu substrate. The interfacial intermetallic compound (IMC) growth and bending properties of Sn-58Bi/Cu and Sn-58Bi/Cu-2.29Zn were studied with the effect of isothermal liquid and solid aging. Although there was no significant change on the composition, thickness and morphology of interfacial IMC under liquid aging, the depressing of IMC growth at the interface between Sn-58Bi solder and substrate and the avoidance on formation of Cu3Sn IMC, Kirkendall voids and Bi segregation at the IMC/Cu interface were realized with Cu-Zn substrate under isothermal solid aging. Joint strength and fracture behavior were also improved by Cu-Zn substrate. There was no obvious decreasing on the joint strength and the fracture during bending was mainly occurred in the solder matrix with ductile fracture mode or along the solder/IMC interface with partly brittle fracture mode for Cu-Zn joint compared with the dramatically decreasing on joint strength and brittle fracture mode occurred along the interface between IMC and Cu for Sn-Bi/Cu joints after aging.

Isothermal Aging Affect to the Growth of Sn-Cu-Ni-1 wt.% TiO<sub>2</sub> Composite Solder Paste

This work investigated the effects of 1.0 wt. % TiO2 particles addition into Sn-Cu-Ni solder paste to the growth of the interfacial intermetallic compound (IMC) on Cu substrate after isothermal aging. Sn-Cu-Ni solder paste with TiO2 particles were mechanically mixed to fabricate the composite solder paste. The composite solder paste then reflowed in the reflow oven to form solder joint. The reflowed samples were then isothermally aged 75, 125 and 150 ° C for 24 and 240 h. It was found that the morphology of IMCs changed from scallop-shape to a more uniform planar shape in both Sn-Cu-Ni/Cu joints and Sn-Cu-Ni-TiO2 /Cu joint. Cu6Sn5 and Cu3Sn IMC were identified and grew after prolong aging time and temperature. The IMCs thickness and scallop diameter of composite solder paste were reduced and the growth of IMCs thickness after isothermal aging become slower as compared to unreinforced Sn-Cu-Ni solder paste. It is suggested that TiO2 particles have influenced the evolution and retarded the growth of interfacial IMCs.

Microstructure, elastic modulus and shear strength of alumina (Al2O3) nanoparticles-doped tin–silver–copper (Sn–Ag–Cu) solders on copper (Cu) and gold/nickel (Au/Ni)-plated Cu substrates

This paper investigates the influence of Al2O3 nanoparticles on the morphology of interfacial intermetallic compound (IMC) layer and material properties of Sn–3.0Ag–0.5Cu (wt%) solders on Cu and Au/Ni-plated Cu substrates. In the solder/Cu substrate systems, an island-shaped Cu6Sn5 IMC layer was found to be adhered at the interface in the initial reaction stage. However, a very thin Cu3Sn IMC layer was also observed between the Cu6Sn5 IMC layer and Cu substrate after long time reaction in all solder joints. On the other hand, a ternary scallop-shaped (Cu, Ni)–Sn IMC layer was found in both plain Sn–Ag–Cu solder joints and solder joints containing Al2O3 nanoparticles on Au/Ni-plated Cu substrates. These IMC layer thicknesses were increased with the reaction time. In the solder ball region, Ag3Sn, Cu6Sn5 IMCs were found to be uniformly distributed in the β-Sn matrix in both types of solder joints. However, after adding Al2O3 nanoparticles these IMCs appeared with fine microstructure. Furthermore, the elastic moduli and shear strength of composite solders containing Al2O3 nanoparticles exhibited consistently higher value than that of plain Sn–Ag–Cu solder joints by a second phase dispersion strengthening mechanism. The fracture surface of plain Sn–Ag–Cu solder joints appeared a brittle fracture mode with a smooth surface, while Sn–Ag–Cu solder joints containing Al2O3 nanoparticles showed semi-ductile failure characteristics with rough dimpled surfaces.

Deformation and fracture behaviour of electroplated Sn–Bi/Cu solder joints

This work utilizes the lap shear test to investigate the shear strength and fracture behaviour of electroplated and reflowed Sn–Bi/Cu lead-free solder joints. Particular emphasis is given on the effects of reflow temperature on the interrelationships among the interfacial intermetallic compound (IMC) morphology, shear strength and the fracture mechanism of the solder joints. Single-lap shear specimens are prepared by joining two commercially pure Cu substrates with electroplated Sn–Bi solder of about 50 µm thickness. The geometry of the lap shear specimen is designed to minimize the differences between far-field and actual responses of the solder. Three reflow temperatures (200, 230 and 260 °C) are used to investigate the effects of reflow temperature on the microstructure and shear strength of the solder. The specimens are loaded to failure at a strain rate of 4 × 10−4/s. Elemental mapping of the fracture surface is performed with field emission scanning electron microscope coupled with energy dispersive X-ray spectroscopy. A reflow temperature of 200 °C yields prism-like interfacial IMC morphology, while higher reflow temperatures of 230 and 260 °C yield scallop-like interfacial IMC morphology. The shear strength and elastic energy release, U, of the solder joints increase with increasing reflow temperature. Fractographs of the failed joints suggest that the fracture mechanism is dependent on the interfacial IMC morphology, where solder joints with prism-like interfacial IMC fail within the bulk solder and solder joints with scallop-like interfacial IMC failed with a mixture of bulk and interfacial fracture.

Diffusion wave model and growth kinetics of interfacial intermetallic compounds in Sn–3.0Ag–0.5Cu–xTiO2 solder joints

The growth kinetics of the interfacial intermetallic compounds (IMCs) between Sn–3.0Ag–0.5Cu–xTiO2 composite solder and Cu substrate during reflow process has been investigated in this work. Scanning electron microscope was adopted to observe the microstructure evolution of solder joints and measure the thickness of the interfacial IMC layer. The IMC phases were identified by energy-dispersive X-ray spectroscopy and X-ray diffractometry. Results show that both the reflow time and nano-TiO2 addition affects the microstructural morphology of IMCs. The thickness of Cu6Sn5 IMC was observed to increase with an increase in the reflow time, decrease with nano-TiO2 addition, and has a significant drop with the nano-TiO2 proportion of about 0.1 wt%. The growth of IMC layer was found to deviate the classical Fick’s diffusion law at the early stages of the IMC growth and then to approach the parabolic law. To explore the interfacial IMC growth kinetics, a diffusion wave model was proposed for predicting the IMC growth. Results show that the theoretical model was well consistent with the experimental data, which shows the feasibility of the model to predict the interfacial IMC growth for Sn–3.0Ag–0.5Cu–xTiO2 solder joints in the reflow process.

Effects of Microstructure and Loading on Fracture of Sn-3.8Ag-0.7Cu Joints on Cu Substrates with ENIG Surface Finish

When dropped, electronic packages often undergo failure by propagation of an interfacial crack in solder joints under a combination of tensile and shear loading. Hence, it is crucial to understand and predict the fracture behavior of solder joints under mixed-mode high-rate loading conditions. In this work, the effects of the loading conditions (strain rate and loading angle) and microstructure interfacial intermetallic compound (IMC) morphology and solder yield strength] on the mixed-mode fracture toughness of Sn-3.8 wt.%Ag-0.7 wt.%Cu solder joints sandwiched between two Cu substrates with electroless nickel immersion gold (ENIG) metallization have been studied, and compared with the fracture behavior of joints attached to bare Cu. Irrespective of the surface finish, the fracture toughness of the solder joints decreased monotonically with strain rate and mode-mixity, both resulting in increased fracture proportion through the interfacial IMC layer. Furthermore, the proportion of crack propagation through the interfacial IMC layer increased with increase in the thickness and the roughness of the interfacial IMC layer and the yield strength of the solder, resulting in a decrease in the fracture toughness of the joint. However, under most conditions, solder joints with ENIG finish showed higher resistance to fracture than joints attached directly to Cu substrates without ENIG metallization. Based on the experimental observations, a fracture mechanism map is constructed correlating the yield strength of the solder, the morphology and thickness of the interfacial IMC, and the fracture mechanisms as well as the fracture toughness values for different solder joints under mode I loading.

Formation behaviour of reaction layer in Sn-3.0Ag-0.5Cu solder joint with addition of porous Cu interlayer

The morphology and growth of interfacial intermetallic compound (IMC) between Sn-3.0Ag-0.5Cu solder alloy and Cu substrate metal of solder joint is reported. The IMC morphology and IMC thickness layer were observed at three different porosities of porous Cu interlayer. The results revealed that during soldering process, Cu6Sn5 compound with scallop like morphology was formed at the interface of both the solder alloy and Cu substrate and at solder alloy and porous Cu interlayer. By adding porous Cu interlayer at the solder joint, the IMC thickness increased with increasing soldering temperature and the number of pores in porous Cu interlayer. The effect of porosity on increasing the IMC layer was also due to the slower cooling rate during solidification of molten solder.