Growth Of IMC Layer Research Articles

Effect of Sb and Ag Addition and Aging on the Microstructural Evolution, IMC Layer Growth, and Mechanical Properties of Near-Eutectic Sn-Bi Alloys

Effect of Sb and Ag Addition and Aging on the Microstructural Evolution, IMC Layer Growth, and Mechanical Properties of Near-Eutectic Sn-Bi Alloys

Mechanical properties degradation of Sn 37Pb solder joints caused by interfacial microstructure evolution under cryogenic temperature storage

The interfacial microstructure, shear property and fracture behaviors of Sn37Pb joints after cryogenic temperature storage for different durations were investigated in this study, storage test at room temperature (298 K) and thermal aging test at 423 K were also carried out as comparison. The morphology of interfacial Cu6Sn5 IMCs for the joints stored under 77 K and 173 K transformed from scallop-like to column-like, moreover, the IMC layer thickness slowly increased with prolonged storage time. The growth rate of Cu6Sn5 layer in Sn37Pb joint stored at 77 K was slightly faster as compared with that stored at 173 K. However, the morphology and thickness of Cu6Sn5 IMC layer still remained roughly unchanged after storage at 298 K for up to 40 days. The Cu6Sn5 IMC growth of Sn37Pb joint stored at 77 K and 173 K was expected to be caused by Cu atom diffusion from Cu pad towards Sn37Pb solder, which was induced by the stress gradient. Additionally, the shear force declined and fracture position changed from in Sn37Pb solder to primarily in Sn37Pb solder and partly along the interface with the prolonging of storage time at 77 K and 173 K, which were induced by IMC layer growth.

Quasi in-situ observation of Ni-plated solder from various fracture mechanism using EBSD

In this study, Electron Backscattered Diffraction (EBSD) was used to investigate the blocking effect of novel electroplated Ni in order to inhibit the growth of IMC layers in high density packaging technology. The diffusion of interfacial elements was analyzed as the main cause for compound growth after high temperature storage. The grain orientation tends to be consistent and the grain size increased with increasing time. And the blocking effect of Ni was calculated from the atomic diffusion level. Moreover, the mechanical properties showed an increasing and then decreasing change with time. In nanopush ball experiments, we observed three fracture modes. The fracture type shifted from Type I to Type II to Type III due to the increase of IMC thickness and the generation of Cu6Sn5.

Effects of Nanoparticle Addition on the Reliability of Sn-Based Pb-Free Solder Joints Under Various Conditions: A Review

In order to satisfy the needs of electronic industries for high-reliability joints, different kinds of nanoparticles were incorporated into conventional Pb-free solders to enhance the performance of solder joints by researchers for decades. It is reported that doping certain nanoparticles to the solder can promote the wettability and strength of the solder, refine the grain size of solder and intermetallic compounds, and inhibit IMC layer growth. In this paper, the effects and the corresponding mechanism of nanoparticle addition on the reliability of Sn-based Pb-free solder joints in various conditions are comprehensively analyzed and summarized such as under thermal aging, thermal cycling, thermal shock, electromigration and so on. In addition, directions for future study about the reliability of nanoparticles-doped solder joints were discussed, so as to provide theoretical support for developing high-reliability nanocomposite solder joints.

Interface reaction and properties of Sn3.5Ag0.5Cu-xNd solder joints subjected to isothermal aging

In this paper, rare earth Nd with various contents (0, 0.04 and 0.5 wt.%) was incorporated into Sn3.5Ag0.5Cu (SAC) solder. The influence of rare earth Nd on the interface reaction, microstructure development, mechanical behavior and wettability were investigated by scanning electron microscopy (SEM), joint strength measuring instrument, and wetting balance method. Adding a small amount of Nd can suppress the growth of interface IMC layer and subdivide the joint microstructure. The mechanical behavior and wettability were also improved efficiently. In the N2 atmosphere, the wettability of solder is better. In addition, the mechanical behavior of three kinds of solder joints decreases with increasing aging time, but the degree of decline of 0.04Nd solder joint is relatively slow.

Study of steel-aluminium joining under the influence of current waveforms using advanced CMT process variants

ABSTRACT In the conventional GMAW process, increasing weld deposition increases the heat input, which adversely affects the steel-aluminum joint performance due to the brittle IMC layer growth. In the present work, advanced CMT variants in AA6061-T6 and galvannealed steel joining were investigated. All Fe-Al joints are made at a constant joining speed and wire feed rate with CMT process variants, viz. CMT-Standard, CMT-Advanced, CMT-Pulsed, and CMT-Pulsed-Advanced. The influence of current and voltage characteristics of process variants on the thermal profile, joint profile, IMC layer morphology, and mechanical properties of the joint was studied. The welding arc and molten droplet transfer phenomena were explained using recorded welding current and voltage waveforms synchronized with welding arc images. The FE-SEM, EDS, and XRD analyses were performed to confirm the phases and morphology of the IMC layer. The results show that the localized heating due to positive current pulses in CMT-Pulsed and CMT-Pulsed-Advanced processes affects the IMC layer morphology and induces cracks at the Fe-Al joints’ root, leading to low shear tensile strength. The crack-free joints were observed with the CMT-Standard and CMT-Advanced processes. Also, with an increase in the positive CMT cycle in the CMT-Advanced process, heat input decreases and shear tensile strength increases.

Ultrasonic brazing of Zr-based bulk metallic glass and 1060 Al alloy using Zn-3Al filler metal

Ultrasonic brazing of Zr-based bulk metallic glasses (Zr-BMG) and 1060-Al alloy dissimilar was realized by using a Zn-3Al filler metal. A firm metallurgical bonding was obtained at the dissimilar joint interfaces. In the initial stage, a single-phased Zn50Al25Zr25 IMC layer was found on the Zr-BMG surface. Prolonging the brazing time, the excessive growth of the Zn50Al25Zr25 IMC layer inhibited the diffusion of Al from brazing seam to the reaction front, which induced the composition fluctuation of Al and thus the formation of Zn50Al25Zr25/Zn-rich phase composite layers on the Zr-BMG surface. The shear strength of joints was affected by the interfacial reaction phase, and the highest value obtained was 68 MPa.

Effect of Temperature Cycling on IMC Growth and Solder Joint Strength of SAC305 Solder Alloy and Low Silver Alloy REL61

This work deals with the comparison of the standard SAC305 (Sn 96.5 %; Ag 3 %; Cu 0.5 %) solder alloy with melting temperature between 217 - 220 °C and an alternative alloy REL61 (SnBiAgCu) with lower silver content and melting temperature in the range of 208 - 215 °C in terms of IMC layer growth during thermal cycling and its effect on the shear strength of the solder joints. The test PCBs were soldered using two different temperature profiles and the temperature cycling was performed under two different conditions. No negative effect of REL61 solder alloy on the growth of the IMC layer under thermal stress and on the subsequent shear strength of the solder joint was found. From this point of view, the REL61 solder alloy can be used as a replacement for the SAC305 solder alloy.

Structural, Thermal and Wetting Characteristics of Novel Low Bi-Low Ag Containing Sn–x.Ag–0.7Cu–1.0Bi (x = 0.5 to 1.5) Alloys for Electronic Application

Low drop failure tendency and reduced cost of low silver SAC alloys has provoked researchers to exploit their potential for portable electronics. Low Bi addition in near-eutectic SAC alloys has proven confinement of IMC layer. In order to exploit potential of Ag variation (0.5–1.5 wt%) on structural, thermal, wettability and IMCs layers growth during thermal aging in low Bi-low Ag, Sn–xAg–0.7Cu–1.0Bi alloys were investigated. The resulting microstructure were characterized by scanning electron microscopy, energy dispersive spectroscopy and X-ray diffraction. Furthermore, structure–property correlations were established. This study signifies that 1.5 wt% Ag is responsible for lower melting point (220.18 °C) and lower contact angle (33°) in low Bi-low Ag, Sn–xAg–0.7Cu–1.0Bi alloys. Moreover, increment in Ag content restricted the interfacial IMC layer growth during thermal aging making them reliable for use in portable electronics. The microstructural investigations inferred that 0.5 wt% Ag solder joint with Cu substrate had the highest growth rate (0.34 μm/h1/2) of IMC layer thickness while 1.5 wt% Ag solder joint had lowest growth rate (0.17 μm/h1/2).

Study on Hardness and Shear Strength with Microstructure Properties of Sn52Bi/Cu + 1% Al2O3 Nanoparticles

The Sn-58Bi (SB) lead-free solder was added with 1% nanoparticles (NP) of aluminium oxide (Al2O3) to investigate the shear strength based on microstructure and joint properties. The microstructures of the SB added with 1% Al2O3 NP containing Bi precipitation and β-Sn grains. The spacing between the lamellar structures of a SB solder alloy was narrower. Proper arrangement of the microstructure of β-Sn, Bi and with the presence of Al2O3 as discrete particles (dispersion strengthening) contributes to the increase on the shear strength and hardness value. The shear strength of the SB added with 1% Al2O3 NP solder joint was enhanced by 50% compared to the bare SB solder joint while there was a 33% increase in the microhardness as well. The shear test was conducted based on ASTM D1002 specification of single lap joint method. The presence of Al2O3 NP along the interface (Hall-Petch effect) contributes to the improvement in the shear strength by reducing the thickness of the IMC layer and retarding the growth of the Cu6Sn5 IMC layer. This study provides evident results for the enhancement of the mechanical properties of the 1% Al2O3 NP added SB solder.

Effects of Ni modified MWCNTs on the microstructural evolution and shear strength of Sn-3.0Ag-0.5Cu composite solder joints

A composite solder was prepared by adding different amount Ni modified multi-walled carbon nanotubes (MWCNTs) into the Sn-3.0Ag-0.5Cu (SAC305) solder. Experiments were conducted to investigate the thermal behavior, mechanical properties of composite solder alloys, shear fracture behavior of solder joints were evaluated as well. The modification process was carried out on the MWCNTs using electroless modification method to synthesis the Ni modified carbon nanotubes (Ni-CNTs), which was manually mixed into SAC305 solder powder with different amount. The melting point of the composite solder alloys was slightly increased with the increment of the amount of Ni-CNTs. The nanoindentation test results confirmed that the hardness and modulus of composite solder alloys were enhanced after the addition of Ni-CNTs. The aging experiment was implemented for the joints and the results indicated that the Ni-CNTs could effectively inhibit the growth of IMC layer as an additive in SAC305 solder. The shear strength of SAC305-xNi-CNTs/Cu (x = 0, 0.1 and 0.2 wt.%) joints was reinforced with the increment of Ni-CNTs amount. Furthermore, the SAC305-0Ni-CNTs/Cu and SAC305-0.1Ni-CNTs/Cu solder joints were broken partially between the solder and IMC, mostly between the solder matrix, and SAC305-0.2Ni-CNTs/Cu solder joint was broken completely inside solder matrix. It was suggested that the fracture mode of the solder joints changed from mix fracture mode to ductile fracture mode as the amount of Ni-CNTs increased.

Nanocomposite SAC solders: the effect of adding CoPd nanoparticles on the morphology and the shear strength of the Sn–3.0Ag–0.5Cu/Cu solder joints

The effect of bimetallic monodisperse CoPd nanoparticles on the microstructure and the shear strength of the Cu/ SAC305/Cu solder joint was investigated. The nanocomposite Sn–3.0Ag–0.5Cu (SAC305) solders with 0.1, 0.3, 0.5, and 1.0 wt% nanoCoPd were prepared through a paste mixing method. The employed bimetallic nanoparticles were produced via a modified oleylamine method. The microstructural analysis of as-solidified Cu/solder/Cu joints was performed by scanning electron microscopy. The results showed that initial additions of CoPd nanoparticles into the SAC305 solder promoted the growth of the interfacial planar-type Cu3Sn IMC layer; while the average thickness of the interfacial scallop-type Cu6Sn5 IMC layer slightly decreased. Further additions of the nanosized CoPd admixtures to the SAC305 solder paste lead to a significant increase of the average thickness of the Cu6Sn5 intermetallic compound layer up to 40%. The shear strength measurements were performed to investigate a relationship between the microstructure and mechanical properties of the investigated solder joints. The results indicated a decrease in the shear strength of the SAC305 solder joint by addition of 0.1 wt% CoPd NPs, while a difference in absolute values between solder joints with 0.3, 0.5, and 1.0 wt% nanoCoPd was practically insignificant.

Effect of Thermal Cycling on Interfacial Microstructure and Mechanical Properties of Sn-0.3Ag-0.7Cu-(α-Al2O3) Nanoparticles/Cu Low-Ag Solder Joints

The evolution of interfacial microstructures and mechanical properties of joints soldered with Sn-0.3Ag-0.7Cu (SAC0307) and SAC0307-0.12Al2O3 nanoparticles (NPs) subjected to thermal cycling were investigated. The joint soldered with SAC0307-0.12Al2O3 displayed an enhanced thermal cycling shear force with a ductile fracture mode when compared with the original alloy whose fracture mode showed a mixed feature of ductile and brittle. The enhanced thermal cycling shear force was attributed to a pinning effect by Al2O3 NPs on interfacial IMC grain growth. Even after 1200 thermal cycles, SAC0307-0.12Al2O3 solder was still structurally characterized by a much more refined microstructure than the non-reinforced solder alloy. Theoretical analysis on the growth of interfacial IMC layer showed that with the addition of Al2O3 NPs, the average growth coefficients of total interfacial IMCs (DT) and Cu3Sn IMCs (\( D_{{{\rm{Cu}}_{3} }} \)) were decreased from 9.2 × 10−11 cm2/h to 5.6 × 10−11 cm2/h, and from 6.9 × 10−11 cm2/h to 4.1 × 10−11 cm2/h, respectively. Hence, a much thinner IMC layer was produced at the SAC0307-0.12Al2O3/Cu interface, thus contributing to an enhanced shear resistance.

Isothermal aging and shear creep behavior of a novel lead-free solder joint with small additions of Bi, Sb and Ni

In this paper, we investigate the effects of isothermal aging on the microstructure and creep properties of a novel lead-free SAC387-3Bi-1.5Sb-0.15Ni (InnoLot)/Cu solder joints. Single-lap shear solder joints of the InnoLot solder were aged up to 1 year at 100 °C, and then loaded to failure in shear creep tests under different applied shear stresses and testing temperatures. The findings show that both aging time and temperature lead to the global increase of the interfacial IMC thickness significantly, but the growth of the Sn-rich IMC layer during aging remains limited in comparison with other solder materials due to the Ni content. In addition, shear creep tests reveal that the shear creep strength of the aged solder joint decreases initially before remaining dramatically stable in the long term. In terms of failure modes, shear creep tests at room and elevated temperatures show distinct rupture features. While rupture within the bulk solder happens at higher temperatures, rupture through the interface occurs at lower temperatures. When the specimens are exposed to isothermal aging, creep deformation becomes more predominant. The aged microstructure exhibits a brittle-to-ductile transition with occurrence of intergranular fracture due to the dynamic recrystallization inside the solder matrix. It is observed that the mechanical factor is of first-order importance in the formation of the new grain structure of the solder.

Coupling effects of rare-earth Pr and Al2O3 nanoparticles on the microstructure and properties of Sn-0.3Ag-0.7Cu low-Ag solder

Low-cost Al2O3 nanoparticles (NPs) are regularly incorporated into lead-free solder to improve its mechanical performance, but the poor wettability of Al2O3 NPs leads to weak Al2O3/solder interface bonding. In this work, a novel idea different from the common solution of pre-coating a metal layer on the surface of NPs was proposed to address the issue of weak interface bonding by simultaneously doping rare-earth (RE) Pr (0.06 wt%) and Al2O3 NPs (0–0.5 wt%) into Sn-0.3Ag-0.7Cu low-Ag solder. The coupling effects of RE Pr and Al2O3 NPs on the wettability, microstructures, shear force and creep resistance of prepared nanocomposite solder were systematically investigated. It was found that the coupling effects were concentration dependent. When the content of Al2O3 NPs was less than 0.06 wt%, a synergistic relationship between free Pr atoms and Al2O3 NPs was established. This is because the surface-active Pr atoms, acting as bridges between Al2O3 NPs and solder matrix, can be spontaneously adsorbed at the surfaces of Al2O3 NPs to in situ form Pr-coated Al2O3 NPs, which have much better wettability than the single Al2O3 NPs. However, increasing the doping content of Al2O3 NPs over 0.06 wt% led to a competitive relationship among free Pr atoms, Al2O3 NPs and Pr-coated Al2O3 NPs, which was probably caused by the emerged Al2O3 agglomerates occupying partial space of grain surfaces. The optimum doping content of Al2O3 NPs in SAC0307–0.06Pr solder was approximately 0.06 wt% and SAC0307–0.06Pr-0.06Al2O3 possessed the best wettability, a well-controlled growth of interfacial IMC layer, the highest shear force (∼61 N) and a superior room-temperature creep resistance with creep stress exponent (n) reaching approximately 11.7.

Bond strength evaluation of heat treated Cu-Al wire bonding

Bond strength evaluation of wire bonding in microchips is the key study in any wire bonding mechanism. The quality of the wire bond interconnection relates very closely to the reliability of the microchip during performance of its function in any application. In many reports, concerns regarding the reliability of the microchip are raised due to formation of void at the wire-bond pad bonding interface, predominantly after high temperature storage (HTS) annealing conditions. In this report, the quality of wire bonds prepared at different conditions, specifically annealed at different HTS durations are determined by measurements of the strength of the interface between the bond wire and the bond pad. The samples are tested in pull test and bond shear test. It was observed that the higher bonding temperature as well as the longer duration of HTS increased the bond strength. This is represented through the analysis of the measurements of ball shear strength. This is due to the fact that higher bonding temperature and longer HTS promoted better growth of the Cu-Al IMC layer. A transmission electron microscopy - energy dispersive X-ray analysis (TEM-EDX) has been carried out to observe the formation of the Cu-Al IMC layer in the sample.

Effect of alternating current (AC) stressing on the microstructure and mechanical properties of low-silver content solder interconnect

The low-cost low-silver-content solder is receiving high attention while its reliability is not well studied. In this work, a copper/tin-silver-copper/nickel (Cu/Sn0.3Ag0.7Cu/Ni) line-type solder interconnect was designed for investigation of the effect of alternating current (AC) on the microstructure and mechanical properties. Three dimensional (3D) X-ray microcomputed tomography tests showed voids and protruding IMCs formed in the solder/Ni and solder/Cu interface regions of the interconnect after prolonged AC stressing, respectively. The thickness growth of interfacial IMC layers followed linear laws with faster rates than those in thermal aged sample. Atomic migration of Cu atoms in Sn0.3Ag0.7Cu solder was estimated using mathematical models with a thermal gradient of 206.77 °C cm−1. Significant degradation in mechanical properties happened. Nano-indentation results showed the hardness and elastic modulus in different solder areas were in the following order: central solder > solder near solder/Ni interface > solder near solder/Cu interface. Four mechanisms can be used to explain these results of AC damages: 1) elevated temperature due to Joule heating, which enhanced grain coarsening and dislocations redistribution; 2) thermal fatigue due to cyclic loading, which damaged the interconnect strength by accumulated stress induced by mismatch in the coefficients of thermal expansion; 3) thermo-migration due to thermal gradient from Ni side to Cu side, which released the thermal stress at the solder/Ni interface and prevented further deterioration, while increasing the thermal stress at the solder/Cu interface and deteriorated the mechanical strength; 4) atomic migration due to chemical gradient, which induced the mass redistribution and contribute to the growth of IMCs layers.

Study on microstructure and properties of Zn–20Sn–0.2Ni–xRE solders

In the present work, 0.2 wt% Ni and 0.1–0.5 wt% RE (Ce and La mixed rare-earth) were added into Zn–20Sn high-temperature lead-free solders. The effects of Ni and RE additions on the microstructure and properties of the solder alloys were investigated. The results show that with the increase of RE content, the solidus temperature of the solder alloys does not change much, but the liquidus temperature decreases, and the wettability and microhardness of the solder alloys increase. Adding Ni or RE element individually does not change the IMC layer structure at the solder/copper interface, but it affects the growth of the IMC layer. That is, the addition of Ni inhibits the growth of the interface IMC layer, and the addition of RE promotes the growth of the IMC layer.

The effects of TiO2 nanoparticles addition on the thermal shock resistance, shear strength and IMC layer growth of SAC305 alloy

The present study explores the effect of nano-sized TiO2 ceramic particles on interfacial structure, creep and shear strength of eutectic Sn-3Ag-0.5Cu (SAC305 in wt.%) interconnect material under isothermal aging and thermal shock cycles. The study revealed that the non-reacting and non-coarsening TiO2 nanoparticles improved the creep, shear strength and thermal shock resistance through refined the structure. An interfacial microstructural analysis confirmed that a layer types Cu6Sn5 and Cu3Sn phases are grown at the interface of SAC305/Cu system. When SAC305 was in contact with the Au/Ni-plated Cu pad ball grid array (BGA) substrate, a ternary (Cu, Ni)-Sn phase was detected. The thickness of IMC phase is increased with the aging time. However, the growth of IMC layer as well as the IMC phases inside the matrix e.g., Ag3Sn, Cu6Sn5, and AuSn4 is slower in the composite interconnection systems than that of reference interconnection systems. Furthermore, during the thermal shock cycles some micro-cracks are found at the interface and matrix regions in the reference interconnection systems. The measured shear strength of composite interconnections exhibited higher values as compare to the reference interconnection systems. However, the thermal shock cycles degrades the shear strength of interconnection faster than the situation in isothermal aging.

Enhancement on the high-temperature joint reliability and corrosion resistance of Sn–0.3Ag–0.7Cu low-Ag solder contributed by Al2O3 Nanoparticles (0.12 wt%)

In this study, the evolution of interfacial microstructures and mechanical properties of the joints soldered with Sn–0.3Ag–0.7Cu (SAC0307) and SAC0307-0.12Al2O3 nanoparticles (NPs) aged at 150 °C for different hours (72–840 h) were investigated. It was found the joint soldered with SAC0307-0.12Al2O3 displayed a significantly enhanced high-temperature joint reliability, reflected in a higher shear force than that of the original. This enhancement in shear force primarily benefited from the refinement in solder microstructure contributed by Al2O3 NPs. As aging time reached 840 h, a controlled growth of interfaical IMC layer resulted from the pinning effect of Al2O3 NPs contributed to the increase in shear force. Theoretical analysis showed 0.12 wt% Al2O3 NPs effectively lowered the growth constant of total interfacial IMCs (DT) from 3.19 × 10−10 to 1.02 × 10−10 cm2 s−1. Moreover, comparative studies on the corrosion resistances of SAC0307 and SAC0307-0.12Al2O3 were also conducted by electrochemical test and analyzed by electrochemical impedance spectroscopy (EIS). The results revealed SAC0307-0.12 Al2O3 solder displayed a stronger corrosion resistance (Rt; ~ 3.1 kΩ cm2 vs ~ 7.1 kΩ cm2). This is also related with the tailored microstructure, which provides more grain boundaries for the initial nucleation of passive film.