Intermetallic Compound Growth Rate Research Articles

Interface reaction between SnAgCu/SnAgCuCe solders and Cu substrate subjected to thermal cycling and isothermal aging

Trace amount of rare earth Ce (0.03 wt.%) was added into SnAgCu solder in order to reform the properties of the solder. In this study, interface reaction mechanism during thermal cycling and isothermal aging, was studied by studying the formation and growth of the intermetallic compound (IMC) at the solder (SnAgCu or SnAgCuCe)/Cu interface, and the growth kinetics which forming IMC in both systems (SnAgCu or SnAgCuCe) were also investigated under different aging conditions. The results show that the morphology of IMCs formed both at SnAgCu/Cu and SnAgCuCe/Cu interfaces was gradually changed from scallop-like to planar-like, and the thickness of different IMCs evolved with the increasing of aging time. The results also indicate that the growth rate of IMC at both interfaces during thermal cycling was higher than that during isothermal aging. Especially, the addition of amount of rare earth Ce into the SnAgCu solder can refine the microstructures; decrease the thickness of the intermetallic compound layer of SnAgCu solder alloys.

Microstructural evolutions of Cu(Ni)/AuSn/Ni joints during reflow

AbstractInterfacial reactions of the Ni/AuSn/Ni and Cu/AuSn/Ni joints are experimentally studied at 330 °C for various reflow times. The microstructures and mechanical properties of the as-solidified solder joints are examined. The as-solidified solder matrix of Ni/AuSn/Ni presents a typical eutectic ζ-(Au,Ni)5Sn+δ-(Au,Ni)Sn lamellar microstructure after reflow at 330 °C for 30 s. After reflow for 60 s, a thin and flat (Ni,Au)3Sn2 intermetallic compound (IMC) layer is formed, and some needle-like (Ni,Au)3Sn2 phases grow from the IMC layer into the solder matrix. On the other hand, a cellular-type ζ(Cu) layer is found at the upper AuSn/Cu interface in the Cu/AuSn/Ni joint after reflow for 30 s, and a (Ni,Au,Cu)3Sn2 IMC layer is also formed at the lower AuSn/Ni interface. For both joints the IMC layer grows significantly with the increase of reflow time, but the growth rate of (Ni,Au,Cu)3Sn2 IMC in the Cu/AuSn/Ni joint is smaller than that of the (Ni,Au)3Sn2 layer in the Ni/AuSn/Ni joint. The comparisons of the shear strength and fracture surface between the Ni/AuSn/Ni and Cu/AuSn/Ni joints suggest that the coupling effect of the Cu/AuSn/Ni sandwich joint is helpful to prevent the excessive growth of (Ni,Au)3Sn2, which in turn enhances the mechanical reliability of the solder joint.

Effect of high intensity magnetic field on intermetallic compounds growth in SnBi/Cu microelectronic interconnect

The growth kinetics of intermetallic compounds (IMCs) (Cu 6Sn 5 and Cu 3Sn) in eutectic Sn58 wt.%Bi/Cu joints were studied, after they were aged at 85, 100 and 120 °C for different times in 0, 12 Tesla (T) magnetic fields, respectively. The Cu is believed to be dominant species, when Cu and Sn inter-diffuse to form IMCs in the interconnect. When the solder joints were aged in the magnetic field, magnetic field direction (denoted by magnetic flux density B → ) was arranged to be parallel and anti-parallel as well as perpendicular to that of Cu diffusion. The results indicated that chemical compositions of the IMCs formed in magnetic fields were the same as those formed without magnetic field. The IMC growth rate in magnetic field was higher than that without magnetic field. And the activation energy for IMC growth in 12 T magnetic field was 43.29 kJ/mol, lower than 84.45 kJ/mol for IMC growth without magnetic field. The accelerated IMC growth was independent of magnetic field direction. The phenomenon resulted from promoted interfacial reaction by magnetic field.

Effect of intermetallic growth rate on spontaneous whisker growth from a tin coating on copper

Intermetallic compound (IMC) growth at the interface between a Sn coating and a Cu substrate with or without a Ni underlayer and its related stress state was evaluated by real-time measurements using the flexure beam method. For the Sn coating without a Ni underlayer, pyramid-shaped IMC grains of Cu6Sn5 grew along the grain boundaries of Sn from the Cu substrate, especially at the triple grain boundary junctions and the IMC grains rapidly increased their volume during the initial 3 days, During this time, the IMC growth rate was 2.3 μm3/day and the compressive stress in the Sn coating rapidly developed and became saturated at about −11 MPa. In contrast, platelet IMC grains of Ni3Sn4 formed at the surface of the Ni underlayer and the IMCs grew at a rate of 1.0 μm3/day for the Sn/Ni coating. In addition, the stress in the Sn coating with a Ni underlayer remained low, slightly tensile and no whiskers were formed on the Sn plating. Therefore, the IMC growth rate and shape are key factors that affect the mechanism of Sn whisker growth during room temperature storage.

Formation and Growth of Intermetallic Compound Layers at Interface of Solder/Copper Alloys for Lead Frame

The effect of chemical species of copper alloys on growth of intermetallic compounds (IMCs) at interface of solder/copper alloys for lead frame was investigated. The results have revealed that Cu is the main diffusing species during aging. After aged at 160°C for 300h, only a Cu6Sn5IMC layer is observed at SnPb/copper alloys interfaces. The growth rate of IMC on the Cu-Cr-Zr system alloys and Cu-Ni-Si alloys was much slower than that of IMC on the C19400 alloy. The Pb phase and voids were found to be inside the Cu6Sn5phase. Chromium, one of the alloying element in Cu-Cr-Zr-Zn alloys, has found to be segregated at the interface between the copper alloy/Cu6Sn5. Zn and Zr in the Cu-Cr-Zr-Zn system alloy are enriched in small amout inside the IMC. These observed results were discussed and analysed on the baisis of diffusion and growth kinetics.

Improving Low-Ag Pb-Free Solder Performance by Adding Bi, Ni Elements

In this study, some Ni, Bi elements were added into low-Ag (less than 1%) Sn-Ag-Cu (SAC) solder. The effect of these additive elements on the solderability, intermetallic compounds (IMCs), and electromigration performance of low-Ag SAC (LASAC) solder were investigated. With the increase of Bi content in LASAC-0.05Ni-xBi (x=0, 2.0, 2.5, 3.0, 3.5, 4.0) solders, the peak melting point decreases while the wetting area of solder alloy increases. With the addition of Ni, the IMC between Cu pad and LASAC solder transforms from Cu6Sn5 to (Cu1-xNix)6Sn5 and the morphology of the IMC turns from bulk-like to needle-like. Either the addition of Bi or Ni will slow down the IMCs growth rate during high temperature storage aging (HTS) at 180°C and has a positive effect on electromigration performance of LASAC soldering.

Effect of Cr additions on interfacial reaction between the Sn–Zn–Bi solder and Cu/electroplated Ni substrates

Intermetallic compounds (IMCs) growth on the Sn–8Zn–3Bi (–Cr) solder joints with Cu and electroplated Ni substrates was investigated after aging at 150 °C. It was found that the IMCs were the Cu 5Zn 8 and Ni 5Zn 21 at the solder/Cu and solder/Ni interface, respectively. The IMCs growth rate at the Sn–8Zn–3Bi–Cr/Cu and Ni interface was slower than that at Sn–8Zn–3Bi/Cu interface (about 1/2 times) and Sn–8Zn–3Bi/Ni interface (about 1/4 times) during aging. The reason may be that Cr reacts with Zn and forms the Sn–Zn–Cr phase which block the diffusion of Zn atom to the interface and slow down the IMCs growth rate.

Effect of Adding Er on Interfacial Reactions between Sn-3.0Ag-0.5Cu Solder and Cu Substrate

The formation and the growth of Cu-Sn intermetallic compound (IMC) layer at the interface between Sn-3.0Ag-0.5Cu-xEr(x=0, 0.1) solder and Cu substrate during soldering and aging were studied. The results show that Cu6Sn5 IMC is observed at the interface between solder and Cu substrate in all conditions. After aging for 120 h, the Cu3Sn IMC is then obtained. With increasing aging time, the scalloped Cu6Sn5 structure changes to a plate structure. The Cu3Sn film always forms with a relatively planar interface. By adding a small amount of the rare earth element Er (only 0.1%, mass fraction) into the Sn-3.0Ag-0.5Cu solder alloy, the growth rate of the Cu-Sn IMC at the interface of solder alloy system is decreased. When the time exponent is approximately 0.5, the growth of the IMC layer is mainly controlled by a diffusion over the studied time range.

Kinetics of Intermetallic Compound Formation at the Interface Between Sn-3.0Ag-0.5Cu Solder and Cu-Zn Alloy Substrates

The growth kinetics of an intermetallic compound (IMC) layer formed between Sn-3.5Ag-0.5Cu (SAC) solders and Cu-Zn alloy substrates was investigated for samples aged at different temperatures. Scallop-shaped Cu6Sn5 formed after soldering by dipping Cu or Cu-10 wt.%Zn wires into the molten solder at 260°C. Isothermal aging was performed at 120°C, 150°C, and 180°C for up to 2000 h. During the aging process, the morphology of Cu6Sn5 changed to a planar type in both specimens. Typical bilayer of Cu6Sn5 and Cu3Sn and numerous microvoids were formed at the SAC/Cu interfaces after aging, while Cu3Sn and microvoids were not observed at the SAC/Cu-Zn interfaces. IMC growth on the Cu substrate was controlled by volume diffusion in all conditions. In contrast, IMC growth on Cu-Zn specimens was controlled by interfacial reaction for a short aging time and volume diffusion kinetics for a long aging time. The growth rate of IMCs on Cu-Zn substrates was much slower due to the larger activation energy and the lower layer growth coefficient for the growth of Cu-Sn IMCs. This effect was more prominent at higher aging temperatures.

Dissolution and Interface Reactions between Palladium and Tin(Sn)-Based Solders: Part II. 63Sn-37Pb Alloy

The interface microstructures as well as the rate kinetics of dissolution and intermetallic compound (IMC) layer formation were investigated for couples formed between molten 63Sn-37Pb (wt pct) solder and 99.9 pct Pd sheet. The solder bath temperatures were 488 K to 593 K (215 °C to 320 °C), and the immersion times were 5, 15, 30, 60, 120, and 240 seconds. The predominant IMC phases were Pd(Sn, Pb)4, PdSn4, and PdSn3. The IMC layer microstructure contained these phases and varying amounts of solder Pb- and Sn-rich phases. Isolated Pd-Sn needles appeared in the solder field at temperatures and times of ≥563 K (290 °C) and ≥30 seconds, respectively. Palladium dissolution was largely monotonic as a function of time and solder temperature, except for a sharp decline at 593 K (320 °C). The dissolution rate kinetics over 488 K to 563 K (215 °C to 290 °C) were represented by the At n exp(−ΔH/RT) equation. The values of n and ΔH were 0.67 ± 0.19 and 48 ± 20 kJ/mol, respectively, suggesting that a combination of interface reaction and solid-state mass transport processes controlled dissolution. The IMC layer grew monotonically with time and solder temperature, except at 593 K (320 °C) where growth dropped off significantly. The IMC growth rate kinetics over 488 K to 563 K (215 °C to 290 °C) exhibited values of n and ΔH equal to 0.88 ± 0.10 and 64 ± 10 kJ/mol, respectively, indicating a combination of interface reaction and solid-state diffusion processes. The extents of Pd dissolution and IMC layer development were significantly greater for molten Sn-Pb solder than the Pb-free Sn-Ag-Cu solder (Part I study) at a given test temperature.

Intermetallic Compound Growth and Reliability of Cu Pillar Bumps Under Current Stressing

Fine-pitch Cu pillar bumps have been adopted for flip-chip bonding technology. Intermetallic compound (IMC) growth in Cu pillar bumps was investigated as a function of annealing or current stressing by in situ observation. The effect of IMC growth on the mechanical reliability of the Cu pillar bumps was also investigated. It is noteworthy that Sn exhaustion was observed after 240 h of annealing when current stressing was not applied, and IMC growth rates were changed remarkably. As the applied current densities increased, the time required for complete Sn consumption became shorter. In addition, Kirkendall voids, which would be detrimental to the mechanical reliability of Cu pillar bumps, were observed in both Cu3Sn/Cu pillars and Cu3Sn/Cu under-bump metallization interfaces. Die shear force was measured for Cu pillar samples prepared with various annealing times, and degradation of mechanical strength was observed.

Microstructure Evolution of Sn-2.5Ag-2.0Ni Solder Joint with Various Ni Platings on SiC<sub>p</sub>/Al Composites

A novel Sn-2.5Ag-2.0Ni alloy has been developed for soldering of SiCp/Al composites substrate with various types of Ni coatings. An investigation about electroplated Ni layer, electroless Ni-5 wt.% P, Ni-10wt.% P and Ni-B layers has been carried out. It is found that the solder joints possess a single intermetallic compound (IMC) Ni3Sn4, which coarsens with an increase in aging time. The formation of Ni2SnP has been observed to significantly affect the reliability of the solder joints. But the formation of Ni2SnP can be suppressed by lowering the P contents in as-deposited Ni coatings. It has been also found that the thermal stresses generated in solder joint increases with the decrease of P contents in Ni-P layer. Furthermore, the concentration of thermal stresses in the electroplated Ni solder joint is found to be higher than that in other three electroless Ni layers. Out of four as-deposited Ni coatings, the Ni-B layer exhibits good wettability with solder and low IMC growth rate during aging. Also, the shear strength of solder joint decreases with an increase in aging time and Ni-B solder joint demonstrates the highest shear strength after long term aging.

Wettability and interfacial reactions of Sn–Ag–Cu/Cu and Sn–Ag–Ni/Cu solder joints

The effects of Cu and Ni additions on the wettability and interfacial reaction of Sn–Ag solder with Cu substrate were investigated. The wettability of the Sn–3.0Ag–0.5Cu (or Ni) solder alloy was firstly measured by a wetting balance test. The formation and growth of intermetallic compounds (IMCs) between the Sn–Ag–Ni solder and Cu substrate were evaluated, and compared the results to the Sn–Ag–Cu/Cu system. In the wetting test, the Cu and Ni additions exerted positive and negative effects, respectively, on the wettability of the Sn–Ag solder. In the solid-state reaction of the Sn–Ag–Cu/Cu solder joint, two IMC layers, Cu 6Sn 5 and Cu 3Sn, grew with increasing aging temperature and time. The growth rate of the Cu 3Sn IMC was higher than that of the Cu 6Sn 5 IMC at the high aging temperatures of 150 and 170 °C. On the other hand, in the case of the Sn–Ag–Ni/Cu solder joint, thick (Cu,Ni) 6Sn 5 and thin Cu 3Sn IMCs formed and grew at the interface during isothermal aging. The addition of Ni to the Sn–Ag solder effectively suppressed the growth of the Cu 3Sn IMC but increased the amount of the (Cu,Ni) 6Sn 5 IMC at the interface.

Growth Behavior of Intermetallic Compounds at SnAgCu/Ni and Cu Interfaces

The growth behavior of reaction-formed intermetallic compounds (IMCs) at Sn3.5Ag0.5Cu/Ni and Cu interfaces under thermal-shear cycling conditions was investigated. The results show that the morphology of (CuxNi1–x)6Sn5 and Cu6Sn5 IMCs formed both at Sn3.5Ag0.5Cu/Ni and Cu interfaces gradually changed from scallop-like to chunk-like, and different IMC thicknesses developed with increasing thermal-shear cycling time. Furthermore, Cu6Sn5 IMC growth rate at the Sn3.5Ag0.5Cu/Cu interface was higher than that of (CuxNi1–x)6Sn5 IMC under thermal-shear cycling. Compared to isothermal aging, thermal-shear cycling led to only one Cu6Sn5 layer at the interface between SnAgCu solder and Cu substrate after 720 cycles. Moreover, Ag3Sn IMC was dispersed uniformly in the solder after reflow. The planar Ag3Sn formed near the interface changed remarkably and merged together to large platelets with increasing cycles. The mechanism of formation of Cu6Sn5, (CuxNi1–x)6Sn5 and Ag3Sn IMCs during thermal-shear cycling process was investigated.

IMC Growth Mechanisms of SAC305 Lead-Free Solder on Different Surface Finishes and Their Effects on Solder Joint Reliability of FCBGA Packages

Intermetallic compound (IMC) growth behavior of lead-free solder plays an important role in ball grid array (BGA) solder joint reliability for flip chip BGA (FCBGA) packaging applications. The growth mechanism of IMC is reported based on a diffusion model. Thermal treatment such as accelerated thermal cycling (ATC) and isothermal aging exposure also contribute to the growth rate and morphology of lead-free solder IMC. Among the lead-free solder alloys, Sn-3.0wt.%Ag-0.5wt.%Cu (SAC305) solder is a promising substitute for Sn-Pb because of its good mechanical properties and wettability with current surface finishes. After thermal exposure, BGA solder joint reliability is degraded due to IMC formation and growth. In this study, two different thermal treatments, ATC and isothermal aging, and two different pad surface finishes, solder on pad (SOP) and electroless Ni immersion gold (ENIG), are considered in terms of IMC growth rate and mechanical solder joint reliability. An SOP finished interface forms a thin ε-phase Cu3Sn layer and a scallop-like η-phase Cu6Sn5 layer. In contrast, the ENIG finished interface forms a thick (Cu,Ni)6Sn5 IMC layer and prevents overall IMC growth. Different surface finished test vehicles are evaluated in an ATC test in a 0°C to 100°C temperature range and the Ni diffusion layer shows a longer solder joint fatigue lifetime than the nondiffusion barrier interface based on the micro cross-section and dye penetration analysis results. In an isothermal aging test at 100°C and 150°C, the aging temperature and time are valid factors to decide mechanical shock reliability. Interfacial fractures are found in the 100°C aged test vehicle due to easier crack propagation at the interface between the thin Cu3Sn layer and the scallop-like Cu6Sn5 layer based on SEM microstructure analysis results. Finally, this investigation proposes how to improve solder joint reliability and prevent interfacial fracture for SAC305 lead-free application.

Effect of Electromigration on the Mechanical Performance of Sn-3.5Ag Solder Joints with Ni and Ni-P Metallizations

The effect of moderate electric current density (1 × 103 to 3 × 103 A/cm2) on the mechanical properties of Ni-P/Sn-3.5Ag/Ni-P and Ni/Sn-3.5Ag/Ni solder joints was investigated using a microtensile test. Thermal aging was carried out at 160°C for 100 h while the current was passed. The interfacial microstructure and intermetallic compound (IMC) growth were analyzed. It was found that, at these levels of current density, there were no observable voids or hillocks. Samples aged at 160°C without current stressing failed mostly inside the bulk solder with significant prior plastic deformation. The passage of current was found to cause brittle failure of the solder joints and this tendency for brittle failure increased with increasing current density. Fractographic analysis showed that, in most of the electrically stressed samples, fracture occurred at the interface region between the solder and the joining metals. The critical current density that caused brittle fracture was about 2 × 103 A/cm2. Once brittle fracture occurred, the tensile toughness, defined as the energy per unit fractured area, was usually lower than ~5 kJ/m2, compared with the case of ductile fracture where this value was typically greater than ~9 kJ/m2. When comparing the two types of joint, the brittle failure was found to be more severe with the Ni than with the Ni-P joint. This work also found that the passage of electric current affects the IMC growth rate more significantly in the Ni than in the Ni-P joint. In the case of the Ni joint, the Ni3Sn4 IMC at the anode side was appreciably thicker than that formed at the cathode side. However, in the case of electroless Ni-P metallization, this difference was much smaller.

Effect of adding Ce on interfacial reactions between Sn-3.0Ag-0.5Cu solder and Cu substrate

The formation and the growth of Cu-Sn intermetallic compound (IMC) layer at the interface between Sn-3.0Ag-0.5Cu-xCe solder and Cu substrate during soldering and aging were studied. The results show that Cu6Sn5 IMC is observed at the interface between solder and Cu substrate in all conditions. After aging for 120 h, the Cu3Sn IMC is then obtained. With increasing aging time, the scalloped Cu6Sn5 structure changes to a plate structure. The Cu3Sn film always forms with a relatively planar interface. By adding a small amount of the rare earth element Ce (only 0.1%, mass fraction) into the Sn-3.0Ag-0.5Cu solder alloy, the growth rate of the Cu-Sn IMC at the interface of solder alloy system is decreased. When the time exponent is approximately 0.5, the growth of the IMC layer is mainly controlled by a diffusion over the studied time range.

Solid-state and liquid-state interfacial reactions between Sn-based solders and single crystal Ag substrate

Growth kinetics and interfacial morphologies of the intermetallic compounds (IMCs) between single crystal Ag and Sn–4Ag, Sn–3Cu and Sn–37Pb solders were investigated by solid-state aging at 160 ◦ C and liquid-state aging at 260 ◦ C. Isothermal equation of chemical reaction and phase diagrams were used to explain the effects of Ag, Cu and Pb on the growth kinetics of IMCs under solid-state and liquid-state aging conditions. The diffusion coefficients for the three solder joints of Sn–4Ag/Ag, Sn–3Cu/Ag and Sn–37Pb/Ag were calculated after solid-state and liquid-state aging. It is found that Pb can effectively retard the growth of IMCs during liquid-state aging but has little influence on the growth rate of IMCs during the solid-state aging. Some local small cracks were frequently observed in the Cu6Sn5 particles near interfaces of the Sn–3Cu/Ag solder joints after solid-state aging for several days. However, there were no such local small cracks when solders or interfaces did not contain the Cu6Sn5 particles after the same aging time. © 2008 Elsevier B.V. All rights reserved.

Reliability of Electroplated Sn-37Pb Solder Bumps with Different Under Bump Metallizations (UBMs) during High Temperature Storage Test

The interfacial reactions and shear properties of Sn-37Pb (wt.%) solder bumps with two different under bump metallizations (UBMs), Cu and Ni, were investigated after high temperature storage (HTS) tests at 150 C for up to 65 days. Two different intermetallic compounds (IMCs), Cu6Sn5 and Cu3Sn, were formed at the bump/Cu interface, whereas only a Ni3Sn4 IMC layer was formed at the bump/Ni interface. The thicknesses of these IMCs increased linearly with the square root of duration time. The IMC growth rate at the bump/Cu UBM interface was much greater than that at the bump/Ni UBM interface. The shear properties of the bumps with the Cu UBM were greatly decreased with increasing duration time, compared with those with the Ni UBM.

Electromigration effect on intermetallic growth and Young’s modulus in SAC solder joint

Solid-state intermetallic compound (IMC) growth behavior plays and important role in solder joint reliability of electronic packaging assemblies. The directional impact of electromigration (EM) on the growth of interfacial IMCs in Ni/SAC/Ni, Cu/SAC/Ni single BGA ball solder joint, and fine pitch ball-grid-array (FPBGA) at the anode and cathode sides is reported in this study. When the solder joint was subjected to a current density of 5,000 A/cm2 at 125°C or 150°C, IMC layer growth on the anode interface was faster than that on the cathode interface, and both were faster than isothermal aging due to the Joule heating effect. The EM affects the IMC growth rate, as well as the composition and mechanical properties. The Young’s modulus and hardness were measured by the nanoindentation continuous stiffness measurement (CSM) from planar IMC surfaces after EM exposure. Different values were observed at the anode and cathode. The energy-dispersive x-ray (EDX) line scan analysis was conducted at the interface from the cathode to anode to study the presence of species; Ni was found in the anode IMC at SAC/Cu in the Ni/SAC/Cu joint, but not detected when the current was reverse. Electron-probe microanalysis (EPMA) measurement on the Ni/SAC/Ni specimen also confirmed the polarized Ni and Cu distributions in cathode and anode IMCs, which were (Ni0.57Cu0.43)3Sn4 and (Cu0.73Ni0.27)6Sn5, respectively. Thus, the Young’s moduli of the IMC are 141 and 175 GPa, respectively.