Cu3Sn Interfacial Intermetallic Compound Research Articles

Study on Ni-GNSs enhanced Sn2.5Ag0.7Cu0.1RE/Cu solder joints β-Sn grain orientation and interfacial IMC growth kinetics under constant temperature thermomigration

Aiming at the thermomigration problem caused by the large temperature gradient (TG) of micro-soldering joints, a constant temperature thermomigration device with temperature control function was designed and manufactured. This paper studied the polarity phenomenon, crystallographic characteristics, and interfacial intermetallic compound (IMC) growth kinetics of Ni-GNSs reinforced Sn2.5Ag0.7Cu0.1RE/Cu solder joints under thermomigration. The results indicate that Ni-GNSs reinforced Sn2.5Ag0.7Cu0.1RE/Cu solder joints exhibited a significant thermomigration polarity phenomenon under the conditions of TG ≥ 1000 °C/cm and θ ≤ 43.5° between the c-axis and TG of β-Sn grains. At the cold end of the solder joint, the Cu6Sn5 phase at the interface gradually thickens and forms Cu3Sn phase on the substrate side, while microcracks expanded and gradually developed into macrocracks. At the hot end of the interface, the Cu6Sn5 phase gradually dissolved. The growth of the Cu3Sn phase was accompanied by “Kirkendall voids” that formed cracks at the interface between the joint and the solder until a “fully IMC solder joint” was formed. The growth of Cu6Sn5 IMC at the solder joint interface came before that of Cu3Sn IMC. The average temperature and temperature gradient of the solder joint were correlated with the growth of Cu3Sn IMC, leading to the formation of interface Cu3Sn IMC due to the oversaturation of Cu atoms. The addition of 0.05 wt% Ni-GNSs refines the grain structure and increases the activation energy for the growth of Cu6Sn5 and Cu3Sn IMC at the cold end of the solder joint, suppressing the thermomigration polarity phenomenon.

Performance of Sn-3.0Ag-0.5Cu Composite Solder with Kaolin Geopolymer Ceramic Reinforcement on Microstructure and Mechanical Properties under Isothermal Ageing.

This paper elucidates the effect of isothermal ageing at temperature of 85 °C, 125 °C and 150 °C for 100, 500 and 1000 h on Sn-3.0Ag-0.5Cu (SAC305) lead-free solder with the addition of 1 wt% kaolin geopolymer ceramic (KGC) reinforcement particles. SAC305-KGC composite solders were fabricated through powder metallurgy using a hybrid microwave sintering method and reflowed on copper substrate printed circuit board with an organic solderability preservative surface finish. The results revealed that, the addition of KGC was beneficial in improving the total thickness of interfacial intermetallic compound (IMC) layer. At higher isothermal ageing of 150 °C and 1000 h, the IMC layer in SAC305-KGC composite solder was towards a planar-type morphology. Moreover, the growth of total interfacial IMC layer and Cu3Sn layer during isothermal ageing was found to be controlled by bulk diffusion and grain-boundary process, respectively. The activation energy possessed by SAC305-KGC composite solder for total interfacial IMC layer and Cu3Sn IMC was 74 kJ/mol and 104 kJ/mol, respectively. Based on a lap shear test, the shear strength of SAC305-KGC composite solder exhibited higher shear strength than non-reinforced SAC305 solder. Meanwhile, the solder joints failure mode after shear testing was a combination of brittle and ductile modes at higher ageing temperature and time for SAC305-KGC composite solder.

Dynamic Observation of Interfacial IMC Evolution and Fracture Mechanism of Sn2.5Ag0.7Cu0.1RE/Cu Lead-Free Solder Joints during Isothermal Aging.

Dynamic observation of the microstructure evolution of Sn2.5Ag0.7Cu0.1RE/Cu solder joints and the relationship between the interfacial intermetallic compound (IMC) and the mechanical properties of the solder joints were investigated during isothermal aging. The results showed that the original single scallop-type Cu6Sn5 IMC gradually evolved into a planar double-layer IMC consisting of Cu6Sn5 and Cu3Sn IMCs with isothermal aging. In particular, the Cu3Sn IMC grew towards the Cu substrate and the solder seam sides; growth toward the Cu substrate side was dominant during the isothermal aging process. The growth of Cu3Sn IMC depended on the accumulated time at a certain temperature, where the growth rate of Cu3Sn was higher than that of Cu6Sn5. Additionally, the growth of the interfacial IMC was mainly controlled by bulk diffusion mechanism, where the activation energies of Cu6Sn5 and Cu3Sn were 74.7 and 86.6 kJ/mol, respectively. The growth rate of Cu3Sn was slightly faster than that of Cu6Sn5 during isothermal aging. With increasing isothermal aging time, the shear strength of the solder joints decreased and showed a linear relationship with the thickness of Cu3Sn. The fracture mechanism of the solder joints changed from ductile fracture to brittle fracture, and the fracture pathway transferred from the solder seam to the interfacial IMC layer.

Influence of Interfacial Intermetallic Growth on the Mechanical Properties of Sn-37Pb Solder Joints under Extreme Temperature Thermal Shock

Solder joints in thermally uncontrolled microelectronic assemblies have to be exposed to extreme temperature environments during deep space exploration. In this study, extreme temperature thermal shock test from −196 °C to 150 °C was performed on quad flat package (QFP) assembled with Sn-37Pb solder joints to investigate the evolution and growth behavior of interfacial intermetallic compounds (IMCs) and their effect on the pull strength and fracture behavior of Sn-37Pb solder joints under extreme temperature environment. Both the scallop-type (Cu, Ni)6Sn5 IMCs at the Cu lead side and the needle-type (Ni, Cu)3Sn4 IMCs at the Ni-P layer side changed to plane-type IMCs during extreme temperature thermal shock. A thin layer of Cu3Sn IMCs was formed between the Cu lead and (Cu, Ni)6Sn5 IMC layer after 150 cycles. The growth of the interfacial IMCs at the lead side and the Ni-P layer side was dominated by bulk diffusion and grain-boundary diffusion, respectively. The pull strength was reduced about 31.54% after 300 cycles. With increasing thermal shock cycles, the fracture mechanism changed from ductile fracture to mixed ductile–brittle fracture, which can be attributed to the thickening of the interfacial IMCs, and the stress concentration near the interface caused by interfacial IMC growth.

Interfacial microstructure evolution and shear strength of Sn0.7Cu–xNi/Cu solder joints

The microstructure and growth behaviors of interfacial intermetallic compounds (IMCs) between the Sn–0.7Cu–xNi (x = 0, 0.1, 0.25, 0.5, and 1.0 mass%) solder alloys and copper pad were explored to reveal the influence of the Ni addition into the Sn–0.7Cu based solder on the formation of interfacial IMCs and shear strength of the solder joints in the present study. The impacts of adding different Ni on the growth behavior and total thickness of Cu6Sn5/(Cu, Ni)6Sn5 and Cu3Sn IMCs layers were compared and discussed after reflowing at 533 K for 600 s and aging at 423 K for various aging durations. The thickness of interfacial IMC layers increased drastically with addition of small amount of Ni into the Sn0.7Cu solder alloy, however, the particle sizes of the IMC grains obviously decreased with the addition of Ni into the solder, compared to the Sn0.7Cu/Cu system. The results indicated that, Cu6Sn5 turned into (Cu, Ni)6Sn5 due to the addition of Ni element and would enhance the growth rate of interfacial IMC resulted from more Ni added. It is quite obvious that 1 wt% Ni addition to the Sn–0.7Cu solder alloy extremely enhance growth and formation of the IMC in Sn–0.7Cu–xNi/Cu joints. In addition, the single-lap shear tests were also carried out to evaluate the mechanical properties of the as-reflowed Sn0.7Cu–xNi/Cu solder joints. The results of shear tests indicated that the shear stress of Sn–0.7Cu–xNi/Cu solder joints gradually increased with the increase of Ni concentration, and the maximum shear strength was reached with 1 wt% Ni addition. Besides, doping Ni element into the Sn–0.7Cu solder changed the shear fractures morphology of Sn–0.7Cu/Cu joints, which were revealed to be ductile essentially with the moderate strain rate (3.33 × 10−3 s−1) and mainly occurred in the solder matrix rather than through the IMCs layer.

Effect of Mn Nanoparticles on Interfacial Intermetallic Compound Growth in Low-Ag Sn-0.3Ag-0.7Cu-xMn Solder Joints

Interfacial intermetallic compound (IMC) growth between Cu substrates and low-Ag Sn-0.3Ag-0.7Cu-xMn (x = 0 wt.%, 0.02 wt.%, 0.05 wt.%, 0.1 wt.%, and 0.15 wt.%) (SAC0307-xMn) solders was investigated under different isothermal aging temperatures of 100°C, 150°C, and 190°C. Scanning electron microscopy (SEM) was employed to observe the microstructural evolution of the solder joints and measure the IMC layer thickness. The IMC phases were identified by energy-dispersive x-ray spectroscopy and x-ray diffraction. The results showed that a Cu6Sn5 IMC layer formed in the as-soldered solder joints, while a duplex structure consisting of a Cu6Sn5 IMC layer near the solder matrix and a Cu3Sn IMC layer was observed after isothermal aging. A considerable drop in the IMC layer thickness was observed when 0.1 wt.% Mn nanoparticles were added. Beyond this amount, the thickness of the IMC layer only slightly increases. Adding Mn nanoparticles can increase the activation energy and thus reduce the interdiffusion rates of the Sn and Cu atoms, which suppresses excessive IMC growth. The solder joint containing 0.1 wt.% Mn nanoparticles has the highest activation energy. SEM images revealed that the number of small particles precipitated in the channels between the Cu6Sn5 IMC layers increases with an increasing proportion of Mn nanoparticles. Based on the microstructural evolution of the solder joints, this study revealed that grain boundary pinning is one of the most important mechanisms for IMC growth inhibition when Mn nanoparticles are added.

The growth behavior of interfacial intermetallic compound between Sn–3.5Ag–0.5Cu solder and Cu substrate under different thermal-aged conditions

The interfacial reaction, morphology, activation energies and growth behavior of interfacial intermetallic compounds (IMCs) between the Sn–3Ag–0.5Cu (in wt%) solder and Cu substrate during reflow at 280 °C for 10 min and aging at different temperatures for up to 360 h were investigated, and the growth kinetics of the interfacial Cu–Sn binary IMC layers were monitored during the isothermal aging. The results showed that the thickness of IMCs increased linearly with square root of aging time, and the diffusion coefficient related to the Cu–Sn IMC layer increased with increasing aging temperature. During aging at medium temperature (180 °C), the scallop-like Cu6Sn5 IMC layer at the SAC305/Cu interface gradually transformed into planar type with prolonged aging time. Nevertheless, in the case of high temperature (200 °C) aging, the solder/Cu6Sn5 interface became uneven because the Cu atoms came from the bulk solder would accumulate on the Cu6Sn5 IMC surface to directly thicken the existed IMC layer. Beside, the Kirkendall voids within Cu3Sn layer and the neighborhood of the Cu3Sn/Cu interface almost aggregated into continuous regions to formed micro-voids. The activation energies of the total Cu–Sn, Cu6Sn5 and Cu3Sn IMCs were obtained by plotting the diffusion constants (D) as a function of the aging temperature (1/T), and were 115.2, 122 and 98 kJ/mol, respectively.

Effects of Metallic Nanoparticles on Interfacial Intermetallic Compounds in Tin-Based Solders for Microelectronic Packaging

Tin (Sn)-based solders have established themselves as the main alternative to the traditional lead (Pb)-based solders in many applications. However, the reliability of the Sn-based solders continues to be a concern. In order to make Sn-based solders microstructurally more stable and hence more reliable, researchers are showing great interest in investigating the effects of the incorporation of different nanoparticles into them. This paper gives an overview of the influence of metallic nanoparticles on the characteristics of interfacial intermetallic compounds (IMCs) in Sn-based solder joints on copper substrates during reflow and thermal aging. Nanocomposite solders were prepared by mechanically blending nanoparticles of nickel (Ni), cobalt (Co), zinc (Zn), molybdenum (Mo), manganese (Mn) and titanium (Ti) with Sn-3.8Ag-0.7Cu and Sn-3.5Ag solder pastes. The composite solders were then reflowed and their wetting characteristics and interfacial microstructural evolution were investigated. Through the paste mixing route, Ni, Co, Zn and Mo nanoparticles alter the morphology and thickness of the IMCs in beneficial ways for the performance of solder joints. The thickness of Cu3Sn IMC is decreased with the addition of Ni, Co and Zn nanoparticles. The thickness of total IMC layer is decreased with the addition of Zn and Mo nanoparticles in the solder. The metallic nanoparticles can be divided into two groups. Ni, Co, and Zn nanoparticles undergo reactive dissolution during solder reflow, causing in situ alloying and therefore offering an alternative route of alloy additions to solders. Mo nanoparticles remain intact during reflow and impart their influence as discrete particles. Mechanisms of interactions between different types of metallic nanoparticles and solder are discussed.

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.

Effect of Cooling Rate on the Microstructure and Mechanical Properties of Sn-1.0Ag-0.5Cu–0.2BaTiO3 Composite Solder

The microstructure, interfacial intermetallic compound (IMC) layer, microhardness, tensile properties, and fracture surfaces of Sn-1.0Ag-0.5Cu–0.2BaTiO3 composite solder were explored under three different cooling conditions (water-, air-, and furnace-cooled) during solidification. The average grain size was refined and the volume fraction of primary β-Sn dendrites increased with increasing cooling rate. The thickness of the IMC layer increased as the cooling rate was decreased, and the morphology also transformed from scallop shaped, for a rapid cooling rate, to irregular shaped for slower cooling; a Cu3Sn IMC layer was detected between the Cu6Sn5 IMC and copper substrate under the furnace-cooled condition, but not in water- or air-cooled specimens. The mechanical properties, including the microhardness and tensile properties, improved with rapid solidification due to the combined effects of grain refinement and a secondary strengthening mechanism. Fracture surfaces after tensile tests showed that the amount of dimples decreased and a cleavage-like pattern increased as the cooling rate was decreased from the water-cooled to furnace-cooled condition, so the fracture process transformed from ductile to mixed-mode fracture. A refined microstructure and excellent mechanical properties were obtained for the rapidly cooled sample.

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.

Improved drop reliability of Sn–Ag–Cu solder joints by Zn addition to a Cu wetting layer

Cu–20 wt% Zn solder wetting layers were fabricated by electroplating in cyanide and non-cyanide solutions, and board-level drop impact reliability was evaluated for Sn–Ag–Cu (SAC) solder joints formed on Cu–Zn layers. Adding Zn to the Cu wetting layer suppressed the formation of a large Ag3Sn plate in the solder and delayed interfacial intermetallic compound (IMC) growth in the solder/Cu–Zn interfaces. Formation of Cu3Sn IMC and microvoids was not observed in the Cu6Sn5/Cu–Zn interface during thermal aging. The drop impact reliability of the Cu–Zn/SAC/Cu–Zn solder joints was superior to that of Cu/SAC/Cu solder joints, both before and after aging. The drop impact performance of the Cu–Zn specimens was similar whether their Cu–Zn layers were electroplated in cyanide or non-cyanide solution. Drop impact reliability of both Cu and Cu–Zn specimens decreased after aging due to IMC growth and/or microvoid formation in the solder interfaces. Interfacial microstructure influenced the failure mode of the solder joints. For Cu specimens, the dominant failure sites were a Cu6Sn5/Cu interface before aging and a Cu3Sn/Cu interface after aging. The formation of a large Ag3Sn plate facilitated crack growth. For Cu–Zn specimens, the crack always propagated inside the Cu6Sn5 layer. Microstructural changes in the solder interfaces arising from the addition of Zn contributed to the improvement of drop impact reliability of SAC solder joints.

Effect of thermomigration on evolution of interfacial intermetallic compounds in Cu/Sn/Cu and Cu/Sn0.7Cu/Cu solder joints

The growth behaviors of the interfacial intermetallic compounds (IMCs) in Cu/Sn/Cu and Cu/Sn0.7Cu/Cu solder joints were systematically investigated under a temperature gradient of 1046 °C/cm for 250, 500, and 750 h, respectively. Thermomigration (TM) caused the interfacial IMCs accumulation at the cold end and disintegration at the hot end, and the evolution rate in Cu/Sn0.7Cu/Cu solder joint was faster than that in Cu/Sn/Cu solder joint. In addition, it was observed that both Cu6Sn5 and Cu3Sn IMC at the cold end grew with TM time in Cu/Sn0.7Cu/Cu solder joint, and the Cu3Sn at the hot end grew faster than at the cold end. However, no obvious change was observed in Cu/Sn/Cu solder joint. Therefore, we conclude that Cu/Sn0.7Cu/Cu solder joint has a more serious TM damage compared with Cu/Sn/Cu solder joint. The microhardness detection indicates that TM can cause microhardness reduction in the two solders, and the microhardness gradually increased from the hot end to the cold end, which was attributed to grain coarsening and higher vacancy concentration at the hot end.

In situ study on the effect of thermomigration on intermetallic compounds growth in liquid-solid interfacial reaction

Synchrotron radiation real-time imaging technology was carried out in situ to observe and characterize the effect of thermomigration on the growth behavior of interfacial intermetallic compounds (IMCs) in Cu/Sn/Cu solder joint during soldering. The thermomigration resulted in asymmetrical formation and growth of the interfacial IMCs. Cu6Sn5 and Cu3Sn IMCs formed at the cold end and grew rapidly during the whole soldering process. However, only Cu6Sn5 IMC formed at the hot end and remained relatively thin until solidification. The IMCs at the cold end were nearly seven times thicker than that at the hot end after solidification. The Cu dissolution at the cold end was significantly restrained, while that at the hot end was promoted, which supplied Cu atoms to diffuse toward the cold end under thermomigration to feed the rapid IMC growth. Moreover, the thermomigration also caused asymmetrical morphology of the interfacial IMCs at the cooling stage, i.e., the Cu6Sn5 IMC at the cold end transformed into facet structure, while that at the hot end remained scallop-type. The asymmetrical growth behavior of the interfacial IMCs was analyzed from the view point of kinetics.

Formation and growth of interfacial intermetallic layers in eutectic Sn-Ag solder and its composite solder joints

Single shear lap joints were made by soldering two Cu substrates with eutectic Sn-Ag solder, and its composite solders containing FeSn/FeSn2 or Ni3Sn2 intermetallic particles introduced by an in-situ method. Ageing of solder joints was performed at 70, 100, 120, 150, 180 °C for 1400 h. The growth of the interfacial intermetallic compound (IMC) layers was characterized assuming diffusion-controlled growth kinetics. Effects of such FeSn/FeSn2 and Ni3Sn4 particulates on the IMC layer growth rate were extensively characterized. Composite solder joints in the fabricated condition formed thinner IMC layers compared to the corresponding non-composite solder joints. The Cu6Sn5 IMC layer grew faster at temperatures above 120 °C (T/T m=0.8), while growing slower at temperatures below 120 °C in composite solder joints. In-situ introduced FeSn/FeSn2 and Ni3Sn4 particle reinforcements in composite solder joints proved effective in reducing the overall growth of the interfacial Cu6Sn5 IMC layer only at lower temperatures. Composite solder joints exhibited slower growth of the Cu3Sn layer during ageing at all temperatures used in this study. Two different regions having different activation energies depending on the temperature were identified for the growth of Cu6Sn5 and Cu3Sn IMC layers. © 2000 Kluwer Academic Publishers