Intermetallic Compound Growth Rate Research Articles

Influence of the solubility range of intermetallic compounds on their growth behavior in hetero-junctions

The solubility range has a large effect on the growth rate of intermetallic compounds (IMCs) formed at hetero-junctions, however, is extremely difficult to determine accurately experimentally. In this work, it is studied for IMCs with a narrow solubility range how the thermodynamic properties affect their solubility and growth rate in hetero-junctions. Furthermore, a method is developed to estimate the solubility range of IMCs based on phase-field simulations combined with experimentally measured diffusion coefficients and steady-state growth rate coefficients. Application of the method to the phases ε-Cu3Sn and η-Cu6Sn5 of the Cu–Sn system at 453K, gives the solubility ranges of the order of Δxε=2.0×10−2 and Δxη=2.6×10−2 using the experimental growth rates kε=4.40×10−9 and kη=7.76×10−9ms−0.5 (Onishi and Fujibuchi, 1975) together with the diffusion coefficients D∼ε=3.62×10−16 and D∼η=1.01×10−15m2s−1 (Mei et al., 1992), respectively.

Interfacial reaction and intermetallic compound formation of Sn–1Ag/ENIG and Sn–1Ag/ENEPIG solder joints

Interfacial reactions and intermetallic compound (IMC) formation of Sn–1wt.%Ag solder with two different surface finishes, electroless nickel–immersion gold (ENIG) and electroless nickel–electroless palladium–immersion gold (ENEPIG), were evaluated during a reflow process. We first compared the interfacial reactions of the two solder joints and identified a relationship between the interfacial reaction behavior and solder/substrate compatibility. The Sn–1Ag/ENIG joint exhibited stable IMC growth and superior interfacial stability compared with the Sn–1Ag/ENEPIG joint. The growth rate of the interfacial IMC layer and consumption rate of the Ni(P) layer were closely related to the interfacial microstructure and morphology of the IMCs. The layer-type well-attached interfacial IMCs had advantages with respect to IMC growth rate and Ni(P) consumption rate. Compared to the previous Sn–3.0Ag–0.5Cu study, ENEPIG performed very well with Sn–Ag–Cu solder alloy. On the other hand, ENEPIG proved not to be a suitable surface finish for Sn–Ag solder alloy in this study.

Tensile properties of Cu/Sn–58Bi/Cu soldered joints subjected to isothermal aging

The effects of isothermal aging on the tensile properties of Cu/Sn–58Bi/Cu soldered joints were investigated. Experimental results show that the scallop-shaped Cu6Sn5 and planar Cu3Sn formed at the interface between solder and Cu substrate during reflowing and aging. The thickness of the intermetallic compounds (IMCs) increased almost linearly with the square root of aging time, and aging at 120 °C yielded a much faster growth of the IMCs layer than that of samples aged at 100 °C. The IMCs growth rate constants were 6.02 × 10−18 and 1.85 × 10−18 m2 s−1 for solder joints aged at 120 and 100 °C, respectively. The tensile strength of the Sn–58Bi/Cu soldered joints decreased slightly with the increasing aging time and temperature. The failure was dominated by the mixed fracturing in both the solder and the Cu6Sn5 grains irrespective of their thermal aging conditions. However, the fracture pattern tended to transform from ductile to brittle with increasing aging time and temperature. The Bi segregation and voids were observed around the Cu/Cu3Sn interface as the long term aging at high aging temperature was carried out, which resulted in reduction of tensile strength of solder joints.

Thermal Performance of Low-Melting-Temperature Alloy Thermal Interface Materials

Thermal resistance of low-melting-temperature alloy (LMTA) thermal interface materials (TIMs) was measured by laser flash method before and after different stages of heating. The results showed that the thermal performance of the LMTA TIMs was degraded during the heating process. It is suggested that the degradation may mainly be attributed to the interfacial reaction between the Cu and the molten LMTAs. Due to the fast growth rate of intermetallic compound (IMC) at the solid–liquid interface, a thick brittle IMC is layer formed at the interface, which makes cracks easy to initiate and expand. Otherwise, the losses of indium and tin contents in the LMTA during the interfacial reaction will make the melting point of the TIM layer increase, and so, the TIM layer will not melt at the operating temperature.

Effects of Bonding Wires and Epoxy Molding Compound on Gold and Copper Ball Bonds Intermetallic Growth Kinetics in Electronic Packaging

This paper discusses the influence of bonding wires and epoxy mold compounds (EMC) on intermetallic compound (IMC) diffusion kinetics and apparent activation energies (E aa) of CuAl and AuAl IMCs in a fineline ball grid array package. The objective of this study is to study the CuAl and AuAl IMC growth rates with different epoxy mold compounds and to determine the apparent activation energies of different combination of package bills of materials. IMC thickness measurement has been carried out to estimate the coefficient of diffusion (D o) and E aa various aging conditions of different EMCs and bonding wires. Apparent activation energies (E aa) of both wire types were investigated after high temperature storage life tests (HTSL) for both molding compounds. Au bonds were identified to have faster IMC formation, compared to slower IMC growth of Cu. The E aa obtained for CuAl IMC diffusion kinetics are 1.08 and 1.04 eV with EMC A and EMC B, respectively. For AuAl IMC diffusion kinetics, the E aa obtained are 1.04 and 0.98 eV, respectively, on EMC A and EMC B. These values are close to previous HTSL studies conducted on Au and Cu ball bonds and are in agreement to the theory of HTSL performance of Au and Cu bonding wires.Overall, EMC B shows slightly lower apparent activation energy (E aa) valueas in CuAl and AuAl IMCs. This proves that the different types of epoxy mold compounds have some influence on IMC growth rates.

Study of the Interfacial Reaction between the Sn-3.5Ag Solder and Electroless Ni-P Metallization

This work summarizes the interfacial reaction between lead-free solder Sn-3.5Ag and electrolessly plated Ni-P metallization in terms of morphology and growth kinetics of the intermetallic compounds (IMC). Comparison with pure Ni metallization is made in order to clarify the role of P in the solder reaction. During reflow, the IMCs formed with the Ni-P under-bump metallization (UBM) exist in chunky crystal blocks and small crystal agglomerates, while the ones with the sputtered Ni UBM exhibit uniformly scallop grains with faceted surfaces. The IMC thickness increases with reflow time following approximately a t^sup 1/3^ power law for both systems. The IMC growth rate is higher with the Ni-P UBM than the Ni UBM. The thickness of the Ni^sub 3^Sn^sub 4^ layer increases linearly with the square root of thermal aging time, indicating that the growth of the IMCs is a diffusion-controlled process. The activation energy for Ni^sub 3^Sn^sub 4^ growth in solid-state reaction is found to be 110 kJ/mol and 91 kJ/mol for the Ni-P and sputtered Ni UBMs, respectively. Kirkendall voids are detected inside the Ni^sub 3^P layer in the Sn-3.5AgTNi-P system. No such voids are found in the Sn-3.5AgTNi system.

The Influence of Sn Orientation on Intermetallic Compound Evolution in Idealized Sn-Ag-Cu 305 Interconnects: an Electron Backscatter Diffraction Study of Electromigration

Previous research showed the relationship between Sn grain orientation and the intermetallic growth rate in Sn-Ag-Cu (SAC)305 interconnects. Samples with the Sn c-axis aligned parallel to the current flow have an intermetallic compound growth rate significantly faster than samples with the c-axis perpendicular to the current flow. This study continues the previous research by investigating intermetallic growth in polygranular joints and in joints that have a thin Ni layer at the cathodic or anodic interface of the interconnect. Planar SAC305 interconnects were sandwiched between two Cu pads (sometimes incorporating a thin Ni layer at the interface) and subjected to uniaxial current. The crystallographic orientation of Sn in these samples was characterized with electron backscatter diffraction before and after electromigration testing. The results show that polycrystalline joints have relatively slow intermetallic growth rates, close to those found in single-crystal joints with the c-axis perpendicular to the current. When a Ni layer was present on the anode side, the intermetallic grew at a rate comparable to that in samples without a Ni layer. However, when the Ni layer was on the cathode side, the intermetallic growth was significantly retarded. The measured growth rates of the intermetallic, combined with literature values for the diffusion of Cu in Sn, were used to calculate values for the effective charge, z*, which is significantly smaller for samples with current parallel to the c-axis than for either polycrystalline samples or samples with the c-axis perpendicular to the electron flow.

Effect of isothermal aging and low density current on intermetallic compound growth rate in lead-free solder interface

This study investigated the effects of isothermal aging and low density current on intermetallic compound (IMC) growth rate and microstructural evolution of lead-free solder interface at a temperature of 398K. The results showed that the morphology of IMC layers under high temperature aging and current stressing was basically same. The growth rate of IMC at the anode was the fastest. That was because chemical diffusion force and electronic wind acted together to drive the growth of IMC at the anode. The current density was not high enough for obvious polarization effects and crack along the electron flow direction to be observed. Next the mean-time-to-failure analysis was used to calculate the lifetime of ball grid array solder joints stressed electrically. However, the calculated value was much shorter than the true value. Indicating that perhaps the equation needs to be modified when applied to Cu interconnects and flip chip solder joints.

Influence of POSS nano-particles on Sn–3.0Ag–0.5Cu–xPOSS/Cu composite solder joints during isothermal aging

Polyhedral oligomeric silsesquioxanes (POSS) nano-particles reinforced Sn–3.0Ag–0.5Cu–xPOSS (x = 1, 3, 5) composite solders were prepared and were reflowed on Cu substrates at 543 K. Then, the solder joints were isothermal aged at 393 K for 24 and 48 h, respectively. Microstructural evolution of the solder joints were observed by scanning electron microscopy and the influence of POSS nano-particles on the solder joint were investigated. The results showed that β-Sn primary phase was refined and the number of grain boundary increased with the addition of POSS nano-particles. The growth rates of intermetallic compounds (IMCs) layer were suppressed by the adsorption affection of POSS nano-particles to the IMCs layer during isothermal aging. Moreover, the dissolution process of the IMCs layer, which was accompanied by with the growth of the IMCs layer, changed the morphology of the IMCs layer. The growth rate and the dissolution rate of the IMCs layer in Sn–3.0Ag–0.5Cu–3POSS/Cu composite solder joint were the lowest.

The Effectiveness of Surface Coatings on Preventing Interfacial Reaction During Ultrasonic Welding of Aluminum to Magnesium

Abstract High power ultrasonic spot welding (USW) is a solid-state joining process that is advantageous for welding difficult dissimilar material couples, like magnesium to aluminum. USW is also a useful technique for testing methods of controlling interfacial reaction in welding as the interface is not greatly displaced by the process. However, the high strain rate deformation in USW has been found to accelerate intermetallic compound (IMC) formation and a thick Al12Mg17 and Al3Mg2 reaction layer forms after relatively short welding times. In this work, we have investigated the potential of two approaches for reducing the IMC reaction rate in dissimilar Al-Mg ultrasonic welds, both involving coatings on the Mg sheet surface to (i) separate the join line from the weld interface, using a 100-μm-thick Al cold spray coating, and (ii) provide a diffusion barrier layer, using a thin manganese physical vapor deposition (PVD) coating. Both methods were found to reduce the level of reaction and increase the failure energy of the welds, but their effectiveness was limited due to issues with coating attachment and survivability during the welding cycle. The effect of the coatings on the joint’s interface microstructure, and the fracture behavior have been investigated in detail. Kinetic modeling has been used to show that the benefit of the cold spray coating can be attributed to the reaction rate reverting to that expected under static conditions. This reduces the IMC growth rate by over 50 pct because at the weld line, the high strain rate dynamic deformation in USW normally enhances diffusion through the IMC layer. In comparison, the thin PVD barrier coating was found to rapidly break up early in USW and become dispersed throughout the deformation layer reducing its effectiveness.

Microstructural and mechanical analysis of Cu and Au interconnect on various bond pads

Effects of High Temperature Storage (HTS) and bonding toward microstructure change of intermetallic compound (IMC) at the wire bonding interface of 3 types of bond pad (Al, AlSiCu and NiPdAu) were presented in this paper. Optical and electron microscope analyses revealed that the IMC growth rate of samples under 175 and 200 °C HTS increased in the order of Al > AlSiCu > NiPdAu. Besides, higher HTS and bonding temperatures also promoted higher IMC thickness. The compositional study showed that higher HTS and bonding temperature developed rapid interdiffusion in bonding interface. In the mechanical ball shear test, a decrease of the shear force of Al and AlSiCu bond pads after 500 h HTS was believed due to poorly developed IMC at bonding interface. On the other hand, shear force degradation at 1000 h was due to excessive growth of IMC that in turn causes the formation of defects. For NiPdAu bond pad, increasing trend of shear force with HTS duration at 175 °C implied a good reliability of the Cu wire bonding. The rapid microscopic inspection on Cu wired Al bond pad under HTS 175 °C showed the IMC development from the periphery to the center of the ball bond. However, after 500 h voids started to develop until the crack was observed at 1000 h.

Effect of graphene doping on microstructural and mechanical properties of Sn–8Zn–3Bi solder joints together with electromigration analysis

Abstract In this study, various weight percentages (0, 0.05 and 0.1 wt.%) of graphene nanosheet doped lead-free Sn–8Zn–3Bi solder alloys were investigated in order to analyze the electromigration induced microstructural development and mechanical properties, such as the shear strength and microhardness, as well as the melting characteristics of the novel composite solders. The effect of electromigration on the solder joint was systematically studied by using a newly developed wire-type testing configuration. The samples were stressed under a current density of 5 × 10 3 A/cm 2 at 100 °C for different aging periods in order to study the electromigration induced reliability issues. For solders with and without the graphene, γ-Cu 5 Zn 8 intermetallic compounds (IMCs) were found at the solder and Cu pad interface. The majority of the added graphene nanosheets were proved to be uniformly distributed in the β-Sn matrix. After the graphene addition, needle-like Zn-rich phases with a finer microstructure were discovered in the solder matrix. The growth rate of the IMC layers of the graphene doped solder was slower in comparison to IMC layers in plain solder at the interfaces. With 0.1 wt.% graphene addition, the measured IMC growth rate was decreased from 30.9 × 10 −14 to 24.9 × 10 −14 cm 2 /s. The melting temperature of the doped solder measured by differential scanning calorimeter (DSC) showed little difference from that of the plain solder. The Vickers hardness, up to 29.9 Hv with 0.1 wt.% graphene addition, is 9.1% higher than that of plain solder. The graphene doped solder consistently demonstrated higher ball shear strength as a function of aging time. The ball shear strength value was increased by 10.2 ± 0.8% than that of plain solders during the whole aging period. The improvement was due to the dispersion-strengthening mechanism, refined microstructure and excellent intrinsic mechanical properties of graphene. Moreover, fracture occurred at the IMC interface of the doped samples showed a ductile fracture pattern with a large distribution of dimples on the rough surface.

리플로우 시간에 따른 Pb-free 솔더/Ni 및 Cu 기판 접합부의 전단강도 평가

Reflow soldering process is essential in electronic package. Reflow process for a long time results from the decrease of reliability because IMC is formed excessively. Solder alloys of Sn-37Pb and Sn-Ag with different kinds of Cu contents (0, 0.5 and 1 wt.%) as compared with Ni and Cu plate joints are investigated according to varying reflow time. The interfaces of solder joints are observed to analyze IMC (intermetallic compound) growth rate by scanning electron microscope (SEM). Shear test is also performed by using SP (Share-Punch) tester. The test results are compared with the solder joints of two different plates (Ni and Cu plate). IMCs are formed on Cu plate interfaces after reflows in all samples. Ni3Sn4 and IMCs are also formed on Ni plate interfaces. The IMC layer forms are affected by reflow time and contents of solder alloy. These results show that mechanical strength of solder joints strongly depends on thickness and shape of IMC.

Growth behaviors of intermetallic compound layers in Cu/Al joints brazed with Zn–22Al and Zn–22Al–0.05Ce filler metals

The structure development and growth rate of intermetallic compounds in Cu/Al brazed joint formed under aging treatment were investigated in this paper. Trace amount of rare earth Ce (0.05wt.%) was added into Zn–22Al filler metal in order to reform the properties of the Cu/Al joint. The interfacial morphology and constituent phases at the interface were examined by the scanning electron microscopes (SEM) and X-ray energy dispersion spectrometry (EDS), respectively. The growth kinetics of intermetallic compounds formed in both systems (Zn–22Al and Zn–22Al–0.05Ce) was also investigated under different aging conditions. The results indicated that interface structure of Cu/Al brazed joints changed from CuAl2/CuZn3 to CuAl2/CuAl/CuZn3 and finally to ε/CuAl2/CuAl/CuZn3 during aging. The growth rate of intermetallic compounds observed in the Zn–22Al system was higher than that in Zn–22Al–0.05Ce. Meanwhile, the activation energy of CuAl2 phase increased from 76.9kJ/mol to 87.6kJ/mol with the 0.05wt.% Ce addition. The results also revealed that the joint brazed with Zn–22Al–0.05Ce constantly possessed higher shear strength than that of Zn–22Al throughout the aging treatment. The addition of Ce into the Zn–22Al filler metal decreased the thickness of the intermetallic compound layer produced in the aging, resulting in higher fracture toughness.

The effect of intermetallic compound evolution on the fracture behavior of Au stud bumps joined with Sn-3.5Ag solder

The microstructure and joint properties of Au stud bumps joined with Sn-3.5Ag solder were investigated as functions of flip chip bonding temperature and aging time. Au stud bumps were bonded on solder-onpad (SOP) at bonding temperature of 260°C and 300°C for 10 s, respectively. Aging treatment was carried out at 150°C for 100 h, 300 h, and 500 h, respectively. After flip chip bonding, intermetallic compounds (IMCs) of AuSn, AuSn2, and AuSn4 were formed at the interface between the Au stud bump and Sn-3.5Ag solder. At a bonding temperature of 300°C, AuSn2 IMC clusters, which were surrounded by AuSn4 IMCs, were observed in the Sn-3.5Ag solder bump. After flip chip bonding, bonding strength was approximately 220.5mN/bump. As aging time increased, the bonding strength decreased. After 100 h of aging treatment, the bonding strength of the joint bonded at 300°C was lower than that bonded at 260°C due to the fast growth rate of the AuSn2 IMCs. The main failure modes were interface fractures between the AuSn2 IMCs and AuSn4 IMCs, fractures through the AuSn2 IMCs and pad lift. Initial joint microstructures after flip chip bonding strongly affected the bonding strengths of aged samples.

Influence of TiO2 nanoparticles on IMC growth in Sn–3.0Ag–0.5Cu–xTiO2 solder joints in reflow process

The influence of TiO2 nanoparticles on the growth kinetics of intermetallic compound (IMC) between Sn–3.0wt.% Ag–0.5wt.% Cu–xwt.%TiO2 (x=0, 0.02, 0.05, 0.1, 0.3, and 0.6) solder and copper substrate during reflow process has been investigated in this study. Scanning electron microscope (SEM) was applied to observe the microstructural evolution of the solder joints, to measure the thickness of the IMC layer, and to estimate the grain size of the IMC layer. The IMC phases were identified by energy-dispersive X-ray spectroscopy (EDX) and X-ray diffractometry (XRD). Results show that both the thickness and grain size of IMC decrease when TiO2 nanoparticles are added into the Sn–3.0Ag–0.5Cu solder system, and have a significant drop when the weight percentage of TiO2 nanoparticles is about 0.1wt.%. Beyond this amount, the thickness and grain size of IMC increase slightly. The growth exponents for both the IMC layers and grains are determined by curve-fitting to study the growth kinetics of IMC in the soldering reaction process. Results reveal that the growth exponents of the IMC layer range from 0.354 to 0.358, and those of the IMC grains range from 0.332 to 0.346, which suggests that the growth of the IMC layer is controlled by the combined kinetics process of atomic interdiffusion, interfacial reaction, and grain ripening. These data also show that Sn–3.0Ag–0.5Cu with about 0.1wt.% TiO2 nanoparticles solder system exhibits the smallest growth rate and gives the most prominent effect in suppressing IMC growth and refining IMC grain size. Based on the theory of adsorption, heterogeneous nucleation, and Ostwald ripening, a mechanism for retarding the IMC growth rate due to TiO2 nanoparticles addition is proposed.

Effects of Multiple Reworks on the Accelerated Thermal Cycling and Shock Performance of Lead-Free BGA Assemblies

In this paper, the effect of multiple rework cycles (up to 5×) on reliability of lead-free assemblies is investigated. The test vehicle is designed to capture the reliability impact of rework processes on interconnects of ball grid array (BGA) devices, the solder joints of its adjacent components, and BGA devices of clamshelled devices. The effects on high aspect ratio plated through hole (PTH) vias and microvias are also considered. A variety of BGA packages, such as flip-chip BGA, plastic BGA, and chip array BGA are selected to represent different package technologies and stress levels. The effect of multiple reworks on the behavior of lead-free solder joints during accelerated thermal cycling (ATC) and mechanical shock is extensively explored in this paper. The experimental and analytical findings showed that multiple reworks significantly degraded the ATC performance of the reworked assemblies by up to 50% in terms of characteristic life. It is also found that multiple reworks affect the PTH vias significantly. The combination of increased lead-free rework temperature excursions and high-end printed circuit board (PCB) aspect ratios may incur higher stresses in the PTH copper barrel. Early failures are observed post multiple reworks and the subsequent ATC test due to PTH barrel cracking. However, the effects of multiple reworks are less severe for devices with microvias compared to those with PTH vias. Multiple reworks also cause severe degradation of long-term performance of devices with clamshell designs. With proper control in rework process, multiple reworks have minimum effects on the adjacent BGA solder joints. In addition, failure analysis is performed in order to study the impact of multiple rework on the microstructure of SnAgCu solder joints. It is found that the intermetallic compounds (IMC) layer grows thicker as the number of reworks increases; however, the IMC growth rate and morphology are dependent on the surface finish of the package substrate. The failure mode and failure mechanism after ATC are also compared for different number of rework cycles. The implications of these results for the reliability of lead-free solder joints are discussed in this paper.

Effects of Ag particles content on properties of Sn0.7Cu solder

To improve properties of Sn0.7Cu solder, method of particles reinforced was employed. Effects of Ag particle contents (1, 3, 5, 7.5, and 10 vol.%) on spreadability, microstructure, shear strength and creep rupture life of Sn0.7Cu solders have been studied. The experimental results indicate that intermetallic compound (IMC) grows, Shear strength is increased and grains are fined with the increasing of Ag particles. When content of Ag particles is more than 5 vol.%, growth rate of IMC is increased significantly. When the content of Ag is 5 vol.%, the composite solder presents best spreadability and excellent creep rupture property which have maximum spreading area, minimum wetting angle and longest creep rupture life (about 22 times as long as that of Sn0.7Cu solder).

Influence of External Strain on the Growth of Interfacial Intermetallic Compounds Between Sn and Cu Substrates

This study used a four-point bending procedure to investigate the influence of compressive and tensile strain on the growth of an interfacial Cu-Sn intermetallic compound (IMC) layer. The test specimens were prepared by depositing 25 μm layers of matte or bright tin atop a copper substrate using electroplating. Samples were then placed in a furnace at 200°C, and external bending strain was applied through a strained substrate. Comparisons were made between samples undergoing tensile strain or compressive strain, and those without strain. We observed the influence of strain levels and aging time on the formation of the IMC. Both tensile and compressive strain influenced the formation of the Cu/Sn IMC. In matte tin samples, the IMC thickness increased under compressive strain and decreased under tensile strain. In contrast, in bright tin samples, the IMC thickness increased under both compressive and tensile strained substrate conditions. The growth rate of IMC was faster in strained bright tin samples than in strained matte tin samples. Moreover, the formation of IMC microscopic structures under external strain differed considerably according to the source of tin.

Effect of humidity on tin whisker growth from Sn3Nd intermetallic compound

Abstract