Growth Of Interfacial Interfacial Intermetallic Compound Research Articles

Influence behavior and mechanism of crystal orientation of Cu6Sn5 coating on interfacial intermetallic compounds growth in Sn-0.7Cu/Cu solder joint

Herein, the Cu6Sn5 coatings with principal crystal orientations were prepared on the Cu substrate using magnetron sputtering to inhibit the growth of interfacial intermetallic compounds (IMCs) in Sn-0.7Cu/Cu solder joint. The effect of sputtering parameter on the principal crystal orientation of Cu6Sn5 coating was researched firstly, followed by the investigation on the influence of Cu6Sn5 coating principal orientation on the interfacial IMCs growth kinetics. The influence mechanisms were studied using molecular dynamics simulations and first-principles calculations. The results revealed that the increasing sputtering power from 40 W to 60 W and 80 W can not only improve the bonding property between the prepared Cu6Sn5 coating and Cu substrate, but also promote the transformation of the coating principal orientation from (132) to (132)/(22-1) and (132)/(22-1)/(42-2). Moreover, the three prepared Cu6Sn5 coatings can inhibit IMC growth at SC07/Cu solder joint, and the Cu6Sn5 coatings with (132)/(22-1) and (132)/(22-1)/(42-2) principal orientations exhibit more significant inhibitory effects on IMC growth than that with (132) principal orientation. It can be proved in this work that the growth of interfacial IMCs in Sn-0.7Cu/Cu solder joint at aging stage is mainly caused by the diffusion of Cu from Cu substrate toward Cu6Sn5 phase. The difference in the growth behavior of IMCs can be attributed to the fact that when the Cu atoms diffuse across Cu6Sn5 (22-1) and Cu6Sn5 (42-2), the bonding strength between the Cu atom at the saddle point and its surrounding atoms is significantly larger than when diffusing across Cu6Sn5 (132), leading to the smaller diffusion coefficients and a slower interfacial IMCs growth rate.

Improved shear property of Sn-3.0Ag-0.5Cu/Ni micro solder joints under thermal shock between 77 K and 423 K by adding TiO2 nanoparticles

The rapid development of space exploration technology was intensifying the desire for lead-free solders with high performance and reliability under extreme temperature environments. In this study, the influence of TiO2 nanoparticle addition on the microstructure, growth behavior of interfacial intermetallic compounds (IMCs) and shear property of Sn-3.0Ag-0.5Cu (SAC305)/Ni micro solder joints under thermal shock from 77 K to 423 K was systematically investigated. The results indicated that the grain size of β-Sn, IMC (Ag3Sn and (Cu,Ni)6Sn5) particles inside the solder was refined by adding 0.05 and 0.1 wt% TiO2 nanoparticles. Due to the spalling of interfacial IMCs into the solder occurring in all micro joints during thermal shock, the thickness of interfacial IMCs did not show a monotony increasing trend with increasing thermal cycles. However, the micro composite solder joint added with 0.05 and 0.1 wt% TiO2 nanoparticles always exhibited thinner interfacial IMC thickness and higher shear force compared with the plain micro joints during thermal shock. The inhibiting effect of TiO2 nanoparticles on the interfacial IMC growth could be explained by the adsorption theory and grain boundary pinning theory. The improvement in shear property of micro composite solder joints was primarily induced by the refinement of IMC particles in the solder and the reduced growth rate of interfacial IMCs by adding TiO2 nanoparticles.

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.

Growth behavior and reliability of interfacial IMC for Sn58Bi/Cu and Sn58Bi–AlN/Cu solder joints applied in IGBT modules

The IMC (interfacial intermetallic compound) produced by the metallurgical reaction between the solder and the Cu plate enables the packaging of IGBT (insulated gate bipolar transistor) modules. In this paper, the growth behavior of IMCs of Sn58Bi/Cu and Sn58Bi-0.05AlN/Cu at different times (10, 30 and 60 min) and temperatures (200, 250 and 300 °C) was investigated, which can provide a reference for the connection of IGBT. It was shown that the interfacial IMC thickness of both solders increased with time and temperature, but the growth of interfacial IMC was suppressed for Sn58Bi solder containing 0.05 wt% AlN. The effect of AlN on the inhibition of grain growth was also observed by EBSD testing. Because of the adsorption effect of AlN nanoparticles, they can adhere to the surface of IMC layer and decrease the effective the diffusion path of unreacted Cu atoms, thereby inhibiting the growth of interfacial IMC. And the effect of AlN particles on interfacial IMC was analyzed via phase field simulation. In addition, under the heating conditions with high temperature and long time, there were fewer cracks in the solder joints containing AlN particles, compared to the Sn58Bi solder. Therefore, AlN nanoparticles can enhance the reliability of Sn58Bi/Cu solder joints.

Enhancement of structure and properties of Sn58Bi solder by AlN ceramic particles

The Sn58Bi composite solders reinforced by AlN ceramic particles was prepared by mechanical mixing method. The melting characteristics, wettability, microstructure, interfacial intermetallic compounds (IMC) layer, and mechanical properties of Sn58Bi-xAlN (x = 0, 0.03, 0.05, 0.07, 0.1, 0.2 wt.%) composite solders were systematically investigated, and influence mechanism of AlN ceramic particles on the Sn58Bi solder was analyzed. The experimental results show that the wetting area and shear strength of Sn58Bi–AlN composite solders present a trend of first increasing and then decreasing. At the AlN ceramic particles content of 0.05 wt.%, the wettability and mechanical properties of the Sn58Bi are enhanced considerably. However, the wettability, mechanical properties of Sn58Bi are reduced when the content of AlN ceramic particles is high. The melting temperature of Sn58Bi-0.07AlN composite solder is increased slightly. The addition of AlN particles can inhibit the growth of interfacial IMC, where the inhibition effect is more obvious for AlN content of 0.05 wt.% and 0.07 wt.%. Therefore, the addition of an appropriate amount of AlN ceramic particles can improve the comprehensive performance of Sn58Bi solder to a certain extent.

Microstructure and shear properties of ultrasonic-assisted Sn2.5Ag0.7Cu0.1RExNi/Cu solder joints under thermal cycling

Through ultrasonic wave assisted Sn2.5Ag0.7Cu0.1RExNi/Cu (x = 0, 0.05, 0.1) soldering test and − 40 to 125 °C thermal shock test, the microstructure and shear properties of Sn2.5Ag0.7Cu0.1RExNi/Cu solder joints under thermal cycling were studied by the SEM, EDS and XRD. The results show that the Sn2.5Ag0.7Cu0.1RExNi/Cu solder joints with high quality and high reliability can be obtained by ultrasonic assistance. When the ultrasonic vibration power is 88 W, the ultrasonic-assisted Sn2.5Ag0.7Cu0.1RE0.05Ni/Cu solder joints exhibits the optimized performance. During the thermal cycling process, the shear strength of ultrasonic-assisted Sn2.5Ag0.7Cu0.1RExNi/Cu solder joints had a linear relationship with the thickness of interfacial intermetallic compound (IMC). Under the thermal cycling, the interfacial IMC layer of ultrasonic-assisted Sn2.5Ag0.7Cu0.1RExNi/Cu solder joints consisted of (Cu,Ni)6Sn5 and Cu3Sn. The thickness of interfacial IMC of ultrasonic-assisted Sn2.5Ag0.7Cu0.1RExNi/Cu solder joints was linearly related to the square root of equivalent time. The growth of interfacial IMC of ultrasonic-assisted Sn2.5Ag0.7Cu0.1RExNi/Cu solder joints had an incubation period, and the growth of IMC was slow within 300 cycles. And after 300 cycles, the IMC grew rapidly, the granular IMC began to merge, and the thickness and roughness of IMC increased obviously, which led to a sharp decrease in the shear strength of the solder joints. The 0.05 wt% Ni could inhibit the excessive growth of IMC, improve the shear strength of solder joints and improve the reliability of solder joints. The fracture mechanism of ultrasonic-assisted Sn2.5Ag0.7Cu0.1RExNi/Cu solder joints changed from the ductile–brittle mixed fracture in the solder/IMC transition zone to the brittle fracture in the interfacial IMC.

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

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

Effect of nano-Ag3Sn additions on wettability, interfacial intermetallic growth and mechanical properties of Zn–30Sn–1Ge solders on Cu substrates

The influences of different addition (0, 0.2, 0.4, 0.6, 0.8, and 1.0 wt%) of Ag3Sn on the wettability, the morphology of interfacial intermetallic compounds (IMCs), and the mechanical properties of Zn30Sn1Ge (ZSG) solder on Cu substrate were investigated. The Ag3Sn nanoparticles with an average particle size of approximately 30–45 nm were dispersed in the α-Zn phase and IMC layer. The added Ag3Sn nanoparticles can remarkably improve the wettability of ZSG solder and inhibit the formation and growth of the interfacial IMCs between the nanocomposite solders and Cu substrates. The enhancement of wettability and inhibition of interfacial IMC increased with the increase of nano-Ag3Sn addition amount under low concentration. However, the excessive addition of Ag3Sn nanoparticles in ZSG solder will degrade the wettability and inhibition of interfacial IMCs. When the amount of Ag3Sn nanoparticles is 0.6 wt%, the ZSG–0.6Ag3Sn solders possess the best wettability. In addition, the ZSG–0.4Ag3Sn solder exhibits the most prominent effect in retarding the formation and growth of interfacial IMCs. Meanwhile, the addition of Ag3Sn nanoparticles increases the shear strength and Vickers hardness of the solder joint. When the amount of Ag3Sn nanoparticles is 0.4 wt%, the shear strength of the welded joint is increased by 13.3%. Moreover, the macroscopic hardness of ZSG–0.6Ag3Sn solder is 49.507 HV, which is 57.5% higher than that of the solder without added nanoparticles (31.38 HV). Results show that the addition of Ag3Sn nanoparticles plays an important role in the interfacial reaction and mechanical properties between the ZSG solder and Cu substrate.

Interfacial IMC Growth and Nanomechanical Characterizations of Solder in Sn-16Sb/Cu Joints during Solid-state Aging

The effects of aging time and temperature on the formation and growth behavior of interfacial intermetallic compound (IMC) of Sn-16Sb/Cu(wt%) solder joints prepared by using dip soldering were investigated. The results show that the major IMCs between Sn-16Sb solder and Cu substrate after thermal aging are Cu3Sn and Cu6Sn5. The thickness of the interfacial IMC in Sn-16Sb/Cu is linearly against the square root of aging time, which indicates that the growth of IMC is mainly controlled by diffusion between Cu and Sn atoms. By using linear regression method, the growth rate constants of interfacial IMC layers are 1.254×10-18, 8.821×10-18 and 1.22×10-17 m2s-1 for Sn-16Sb/Cu joints aged at 120, 150 and 170 °C, respectively. Besides, the activation energy of the interfacial IMC growth was also calculated to be 68.27 kJ/mol. The IMC grain diameters after aging treatment increase with the increasing aging time, with i e, d = 0.492t0.106, d = 0.543t0.143 and d = 0.290t0.263 for aging temperatures of 120, 150 and 170 °C, respectively. Besides, by using nanoindentation, the softening of Sn-16Sb solder was found during aging treatment. Moreover, the U-shape evolution of the values in hardness and Young's moduli was found in this work.

Effect of Cu6Sn5 nanoparticles size on the properties of Sn0.3Ag0.7Cu nano-composite solders and joints

The effect of different-sized Cu6Sn5 nanoparticles on thermal behavior and interfacial reaction with Cu substrate of Sn–0.3Ag–0.7Cu solder was evaluated. The results showed that 30 nm and 70 nm Cu6Sn5 nanoparticles were successfully synthesized by using the method of different reductants, attributed to the difference of reductive ability. Under condition of the same heating parameters, 30 nm Cu6Sn5 nanoparticle owned lower sintering temperature than that of 70 nm Cu6Sn5 nanoparticle. The thermal behavior was revealed that the composite solders with the addition of different-sized Cu6Sn5 nanoparticles had slightly lower melting point and higher undercooling value, compared with original Sn–0.3Ag–0.7Cu solder alloy. The highest undercooling value occurred with 30 nm Cu6Sn5 nanoparticle addition. Moreover, the interfacial reactions between Cu substrate and Sn–0.3Ag–0.7Cu solders mixed with different-sized Cu6Sn5 nanoparticles have produced after reflowing at 250 °C and aging at 150 °C for different interval time. It was clearly found that comparing to the initial Sn–0.3Ag–0.7Cu/Cu solder joint, the thickness of interfacial intermetallic compound (IMC) layer on solder joint with adding nanoparticle was thinner and the growth rate was slower. The growth of interfacial IMC was suppressed with the addition of Cu6Sn5 nanoparticle, and 30 nm Cu6Sn5 nanoparticle had the strongest inhibition effect on the growth of IMC, as well as the growth of IMC grains.

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

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

Unique interfacial reaction and so-induced change in mechanical performance of Sn–3.0Ag–0.5Cu/Cu solder joints formed during undercooled and eutectic liquid soldering processes

A novel technique is proposed to prepare Sn–3.0Ag–0.5Cu/Cu joints at three different processing temperatures, which are called undercooled liquid (UL, 213.0 °C), eutectic liquid (EL, 217.0 °C) and normal liquid (NL, 231.0 °C) soldering temperatures correspondingly, and each of them is lower than, equal to and higher than Sn–3.0Ag–0.5Cu solder’s melting point (217.0 °C), respectively. The interfacial reaction, intermetallic compound growth and mechanical performance of Sn–3.0Ag–0.5Cu/Cu joints formed during UL, EL and NL soldering processes were investigated systematically. Results show that for Sn–3.0Ag–0.5Cu solder as the undercooled liquid melt or eutectic liquid melt or normal liquid melt in the formation of joints, the thickness of interfacial intermetallic compound (IMC) layer in the joints increases with prolonging dwelling time. For three different liquid soldering processes, the change tendency of the interfacial IMC layer thickness is distinct. For joints formed at UL and EL temperatures, the excessive growth of primary Cu6Sn5 and interfacial IMC (mainly Cu6Sn5) can be suppressed during isothermally dwelling in the liquid state for more than 5 min. Ball shear test results show that solder joints formed at UL and EL temperatures have lower value of the maximum shear force (MSF) than those formed during the NL soldering process. For UL and EL types of joints, the fracture occurs either by shear slide fracture totally along the shear tool tip movement plane (i.e., in-plane shear slide fracture) or by shear slide fracture initially along the shear tool tip movement plane and afterwards shear deformation fracture in the solder matrix under the plane (i.e., out-of-plane shear slide and deformation mixed-mode fracture), while the fracture takes place in NL joints only by in-plane shear slide fracture mode.

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 reaction and IMC growth between Sn-37 Pb and heterogeneous dual-phase substrate

This paper described microstructure evolution of interfacial intermetallic compound (IMC) layers in a series of Sn-37Pb/Cu-Co systems (the different amount of Co additions was a variable in this experiment, and we represented it with Cu-xCo in the rest of this article). With the same aging temperature (150 °C), the addition of Co significantly influenced the interfacial reaction between Sn-37 Pb solder and Cu-Co substrate. Through analyses of these changes, we found that Co addition was an important strategy to control IMC thickness and improve the interfacial wettability. Additionally, correlations between the thickness of IMC layers and aging time were established, and successfully fitted into linear functions, and this relationship corresponded to the characteristics of growth mechanism controlled by volume diffusion. Unfortunately, Kirkendall voids and microcracks were still inevitable in the current study, which could severely degrade the performance of solder joint, so further methods to improve these defects need to be explored.

Interfacial Reaction and IMC Growth of an Ultrasonically Soldered Cu/SAC305/Cu Structure during Isothermal Aging.

In order to accelerate the growth of interfacial intermetallic compound (IMC) layers in a soldering structure, Cu/SAC305/Cu was first ultrasonically spot soldered and then subjected to isothermal aging. Relatively short vibration times, i.e., 400 ms and 800 ms, were used for the ultrasonic soldering. The isothermal aging was conducted at 150 °C for 0, 120, 240, and 360 h. The evolution of microstructure, the IMC layer growth mechanism during aging, and the shear strength of the joints after aging were systemically investigated. Results showed the following. (i) Formation of intermetallic compounds was accelerated by ultrasonic cavitation and streaming effects, the thickness of the interfacial Cu6Sn5 layer increased with aging time, and a thin Cu3Sn layer was identified after aging for 360 h. (ii) The growth of the interfacial IMC layer of the ultrasonically soldered Cu/SAC305/Cu joints followed a linear function of the square root of the aging time, revealing a diffusion-controlled mechanism. (iii) The tensile shear strength of the joint decreased to a small extent with increasing aging time, owing to the combined effects of IMC grain coarsening and the increase of the interfacial IMC. (iv) Finally, although the fracture surfaces and failure locations of the joint soldered with 400 ms and 800 ms vibration times show similar characteristics, they are influenced by the aging time.

Influence of SnO2 Nanoparticles Addition on Microstructure, Thermal Analysis, and Interfacial IMC Growth of Sn1.0Ag0.7Cu Solder

A new lead-free Sn-1.0Ag-0.7Cu-xSnO2 composite solder was smelted in a vacuum arc furnace at 900°C for 30 min. This paper investigated the influence of SnO2 nanoparticles on the microstructure, melting properties and growth of interfacial intermetallic compounds (IMCs) at the interface between Cu and the composite solder during isothermal aging. The results indicated that SnO2 particles effectively refined the β-Sn grains and reduced the size of Cu6Sn5. The thermal analysis data showed that nano-sized SnO2 decreased the pasty range and melting temperature. In addition, the additional nanoparticles reduced the diffusion coefficient and impeded the growth of intermetallic compounds during soldering and aging. The effect of nanoparticles on solder is closely associated with the added amount of nano-SnO2 particles. When the SnO2 concentration was 1.0 wt.%, the composite solder possessed an excellent microstructure, suitable melting properties and obvious inhibition effect on the interfacial IMCs. However, excessive addition of SnO2 particles in the solder alloys decreased the inhibition effect of the interfacial IMCs.

Effects of Ag addition on solid–state interfacial reactions between Sn–Ag–Cu solder and Cu substrate

Low–Ag–content Sn–Ag–Cu (SAC) solders have attracted much recent attention in electronic packaging for their low cost. To reasonably reduce the Ag content in Pb–free solders, a deep understanding of the basic influence of Ag on the SAC solder/Cu substrate interfacial reaction is essential. Previous studies have discussed the influence of Ag on the interfacial intermetallic compound (IMC) thickness. However, because IMC growth is the joint result of multiple factors, such characterizations do not reveal the actual role of Ag. In this study, changes in interfacial IMCs after Ag introduction were systemically and quantitatively characterized in terms of coarsening behaviors, orientation evolution, and growth kinetics. The results show that Ag in the solder alloy affects the coarsening behavior, accelerates the orientation concentration, and inhibits the growth of interfacial IMCs during solid–state aging. The inhibition mechanism was quantitatively discussed considering the individual diffusion behaviors of Cu and Sn atoms, revealing that Ag inhibits interfacial IMC growth primarily by slowing the diffusion of Cu atoms through the interface.

Comparative study on the wettability and interfacial structure in Sn–xZn/Cu and Sn/Cu–xZn system

Zn is the common used alloying element in Pb-free solder to depress the growth of interfacial intermetallic compound (IMC) in solder joints, but is also an oxidation preferred element to decrease the wettability of solder. This paper provides a potential replacement on the Zn-contained solder with small amount of Zn alloyed Cu substrate to avoid the deterioration on wettability but keep the depressing effect on growth of IMC through the comparative study on Sn–xZn/Cu and Sn/Cu–xZn. To systematically study the effect of Zn alloying, 0.2–0.8 wt% content of Zn was added into pure Sn solder and 2.29 and 4.89 wt% content of Zn was alloyed into Cu substrate. The wettability, interfacial reaction during soldering and interfacial IMC growth of Sn–xZn/Cu and Sn/Cu–xZn during isothermal aging were studied and compared with Sn/Cu system. Zn alloyed into Cu substrate exhibited a far better wettability than Zn alloyed into solder. Although there was no significant change on the composition, morphology and thickness of interfacial of IMC in Zn-contained system during soldering, Zn alloyed into Cu substrate or Sn solder obviously depressed the formation of Cu3Sn and the growth of IMC layers during isothermal aging compared with Sn/Cu system. The depressing effect and calculated activation energy on the growth of IMC increased with the content of Zn in Cu or in Sn, and can be attributed to the CuZn solid solution existed at the interface because it decreased the driving force on formation of Cu3Sn and the diffusion rate of Cu atoms. Compared Sn/Cu–xZn with Sn–xZn/Cu, Cu–4.89Zn substrate provided a similar depressing effect on IMC growth but an exceeding wettability compared with Sn–Zn solder, and can be offered as an alternative under bump metallurgy (UBM) in solder joints.

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.

Performance of Sn–3.0Ag–0.5Cu composite solder with TiC reinforcement: Physical properties, solderability and microstructural evolution under isothermal ageing

This paper is focused on the effect of TiC nano-reinforcement that was successfully introduced into a SAC305 lead-free solder alloy with different weight fractions (0, 0.05, 0.1 and 0.2 wt%) through a powder-metallurgy route. Actual retained ratios of TiC reinforcement in composite solder billets and solder joints were quantitatively analysed. The obtained SAC/TiC solders were also studied extensively with regard to their coefficient of thermal expansion (CTE), wettability and thermal properties. In addition, evolution of interfacial intermetallic compounds (IMCs) and corresponding changes in mechanical properties under thermal ageing were investigated. Only about 10%–30% of initial TiC nanoparticles added were found retained in the final composite solder joints. With an appropriate addition amount of TiC nanoparticles, the composite solders exhibited an improvement in their wettability. A negligible change in their melting point and a widened melting range were found in composite solders containing TiC reinforcement. Also, the CTE of composite solder alloys was effectively decreased when compared with the plain SAC solder alloy. In addition, a growth of interfacial IMCs in composite solder joints was notably suppressed under isothermal ageing condition, while their corresponding mechanical properties of composite solder joints significantly outperformed those of non-reinforced solder joints throughout the ageing period.