Interfacial Intermetallic Compound Growth Research Articles

An Innovative High-Entropy Alloy Solder for High-reliability Low-Temperature Bonding in 3D Electronic Packaging——Based on nano InSnBiZnAg particles

To address the demand for multilevel package, a low-melting-point high entropy alloy (HEA) solder was developed. It consists of 43In28Sn14Bi9Zn6Ag micro- and nanoparticles with a melting point of about 62.80 °C. We obtained 43In28Sn14Bi9Zn6Ag nanoparticles by combining ultrasonic heating interaction with a "hot shock" process. Upon reflowing at 115 °C for 5 min, a Cu/Zn/Ag ternary intermetallic compound (IMC) formed at the interface between the solder and the copper substrate, leading to a shear strength of 40 MPa. The microstructure of this joint exhibits a complex composition with at least three phases, including Bi3In5 phase, Ag5Zn8 phase, and In0.2Sn0.8 solid solution. The stable Ag5Zn8 phase not only enhances the overall strength of the alloy matrix but also impedes the diffusion of In and Bi atoms, thereby preventing the segregation of the Bi3In5 phase. The high mixing entropy and pronounced lattice distortion in this high entropy alloy hinder the diffusion of elements within the solder matrix, mitigating the issue of excessive interfacial IMC growth. Consequently, the solder joints exhibit little degradation even after a high-temperature aging test. This high-entropy alloy solder has promising potential for multi-level chip stacking in 3D packaging.

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.

Insight into the influence of Cu6Sn5/Cu micro-interface configuration on growth behavior of Cu-Sn interfacial intermetallic compounds in Sn/Cu solder joint

Herein, the behavior and mechanism of Cu atom diffusing across Cu6Sn5/Cu interface was researched for analyzing the influence of Cu6Sn5/Cu micro-interface configuration on growth behavior of Cu-Sn interfacial intermetallic compounds (IMCs) in Sn/Cu solder joint. The results indicate that, during Cu atoms diffusing across Cu6Sn5 (001)/Cu (110), Cu6Sn5 (110)/Cu (001), Cu6Sn5 (110)/Cu (111) interfaces, VA2→VA3 stage, VA2→VA3 stage and IA→VA1 stage are the decisive stages, respectively. At those diffusion decisive stages, the difference of average Mulliken population between Cu atom at saddle point and initial state with the surrounding atoms for Cu6Sn5 (110)/Cu (111) interface is 0.62, much greater than that for Cu6Sn5 (001)/Cu (110) and Cu6Sn5 (110)/Cu (001) interfaces with average Mulliken population difference of 0.29 and 0.20. Therefore, when Cu atom diffusing across Cu6Sn5 (110)/Cu (111) interface, the magnitude of increase in bonding strength between Cu atoms and the surrounding atoms is the largest, leading that the diffusion rate of Cu atom across Cu6Sn5 (110)/Cu (111) interface is several orders of magnitude smaller than the Cu6Sn5 (001)/Cu (110) and Cu6Sn5 (110)/Cu (001) interfaces. As a result, Cu6Sn5 (110)/Cu (111) interface shows the strongest ability for inhibiting Cu atom diffusion, and has the smallest IMC growth rate.

Interfacial intermetallic compounds growth kinetics and mechanical characteristics of Ga-Cu interconnects prepared via transient liquid phase bonding

Driven by continuous miniaturization, higher performance, and functional robustness in three-dimensional (3D) embodiments of electronic devices, Ga which possesses a low melting point (29.8°C) has shown its potential uses in electronics packaging and integration. The use of Ga metal as a solder material to achieve low-temperature transient liquid phase bonding (TLPB) has emerged as a viable solution for reliable interconnections of future-generation products. This study investigates the interfacial intermetallic compounds (IMCs) structure, growth kinetics, and mechanical characteristics of Ga-Cu TLPB joints in the temperature range of 150–220°C. The Cu9Ga4 phase were observed and the growth rate of Ga-Cu IMCs has been investigated. The research findings indicate that the growth mechanism of interface IMCs is primarily diffusion-controlled, with CuGa2 grains exhibiting anisotropic growth. Their shear strength has reached 23.8 MPa, with a porosity of 1.82±0.07%. Furthermore, the fracture interface is presented and correlated with the experimental observations.

Enhancement of SAC105 solder for vacuum soldering with Cu substrates through incorporation of activated Ti nanoparticles

This study incorporated activated Ti nanoparticles (Ti NPs) into Sn1·0Ag0·5Cu (SAC105) solder for vacuum soldering with Cu substrates. The wettability, microstructure, interfacial, and mechanical properties of SAC105-xTi (x = 0.1, 0.2, 0.3, 0.4, 0.5 wt%) composite solder were systematically investigated. The results showed that adding Ti NPs improved the wettability of SAC105 solder, in which the wetting angle of SAC105-0.3Ti solder was 19.51°. Additionally, Ti NPs helped to refine the microstructure and inhibited the growth of interfacial intermetallic compounds (IMC). The shear strength of SAC105/Cu joints increased and then decreased with increasing Ti NPs content, and the optimum shear strength was obtained for SAC105-0.3Ti/Cu joints at 27.98 MPa. The strength of the solder matrix and the IMC layer was altered by adding Ti NPs, resulting in a modification of the fracture path of the joint, bringing it closer to the IMC layer. Excessive addition of Ti NPs could lead to their agglomeration within the joints and result in damage to the mechanical properties of the joints. Furthermore, adding Ti NPs increased the microhardness of SAC105 solder.

Reliability improvement of SnAgCu interconnections under extreme temperature condition by TiO2 nanoparticles doping: Experiments and first principles calculations

Electronic components of the spacecraft during their service may endure intricate and extreme temperature environments. In this study, the interfacial microstructure evolution and reliability of Cu/Sn-3.0Ag-0.5Cu (SAC305)/Ni and Cu/Sn-3.0Ag-0.5Cu-0.05TiO2 (SAC305–0.05TiO2)/Ni interconnections under thermal shock from −196 °C to 150 °C are investigated. Short-column-type (Cu,Ni)6Sn5 intermetallic compounds (IMCs) are developed at the solder/Ni interface for both interconnections after the reflow process, and their morphology changes to long-rod type after 200 cycles. Extremely thin and discontinuous (Ni,Cu)3Sn4 phases are generated between (Cu,Ni)6Sn5 and Ni only in SAC305 interconnections after 200 cycles. The rate of interfacial IMCs growth in SAC305–0.05TiO2 interconnections is slower than that in the SAC305 interconnections. Cracks are formed in the IMC layer of the SAC305 interconnection after 200 cycles, which propagate through the whole IMC layer after 250 cycles. While for the SAC305–0.05TiO2 interconnection, no crack is observed until after 250 cycles. TiO2 nanoparticles doping could suppress the interfacial IMC growth, leading to an enhancement in the interconnection reliability under thermal shock. First-principles calculations are performed to further understand the mechanism for phase transformation of Ni-Cu-Sn IMCs and the reliability improvement of interconnections.

Insight into the improvement of service performance of Sn/Cu solder joint by Pt doping in Cu6Sn5 interfacial intermetallic compound

The effects of Pt doping on the mechanical properties of (Cu,Pt)6Sn5 interfacial intermetallic compound (IMC), bonding properties of the (Cu,Pt)6Sn5/Cu interface, and growth behavior of (Cu,Pt)6Sn5 IMC during the aging stage were investigated using first-principles calculations. The results indicate that Pt doping improves both the deformation resistance and ductility of the (Cu,Pt)6Sn5 phase, and that Cu2Pt4Sn5 demonstrates the highest ductility, as indicated by the maximum B/G value (3.14) and Poisson’s ratio (0.356). This phenomenon can be attributed to the smallest standard deviation of the charge density of 0.097 e/Å3. Comparisons of the interfacial work of adhesion and tensile strength of the Cu2Pt4Sn5/Cu and Cu6Sn5/Cu interfaces show that Pt doping enhances interfacial atomic interaction. Based on semi-classical Boltzmann theory, the electrical conductivity of the Cu2Pt4Sn5/Cu interface is smaller than that of the Cu6Sn5/Cu interface, with an amplitude of 9.26%, owing to the enhanced electron localization after Pt doping and resulting in a slight increase in the service temperature. Nevertheless, Pt doping still significantly suppresses the diffusion of Cu atoms, as evidenced by the millions of times reduction in the diffusion coefficient of Cu atoms across the Cu2Pt4Sn5/Cu interface compared to that across the Cu6Sn5/Cu interface because of the latter interface’s larger diffusion activation energy (3.52 eV > 2.08 eV), which was investigated by climbing image nudged elastic band methods. Therefore, Pt doping not only strengthens the mechanical properties of the (Cu,Pt)6Sn5 phase and improves the bonding strength of the (Cu,Pt)6Sn5/Cu interface, but also suppresses the growth of IMC during the aging stage, playing a positive role in obtaining a highly reliable Sn/Cu solder joint.

Improvement of weldability and fracture behavior of mild steel and A7075 aluminum alloy dissimilar friction stir welded joints by increasing welding speed

In this study, dissimilar friction stir welding of mild steel and A7075 aluminum alloy was conducted at a constant tool rotational speed (900 rpm) and different welding speeds of 100–400 mm/min with an interval of 100 mm/min. A thermocouple was employed to record the thermal cycle and the maximum reached temperatures of the A7075/steel interface during the joining process. The higher the welding speed, the lower the maximum temperature recorded during the joining process. Conducting the joining process at a high welding speed also enhanced the cooling rate and, thus, effectively contributed towards eliminating the thermal residual stresses and suppressing the interfacial intermetallic compounds growth. As a result, 100% joint efficiency with a steel base metal fracture was obtained for the joints fabricated at the welding speeds of 300 and 400 mm/min.

Comprehensive analysis of Sn58Bi/Cu solder joints reinforced with Mg particles: Wettability, thermal, mechanics, and microstructural characterization

In this study, the Sn58Bi-xMg (x = 0, 0.2, 0.4, 0.6, 0.8, 1.0) composite solders were synthesized to explore the impact of Mg particles. The study examined the wettability, thermal properties, mechanical properties, microstructure, and growth of interfacial IMC (intermetallic compound) of composite solder. Experimental results showed that adding Mg particles had no significant impact on the melting point of Sn58Bi solder. However, increasing the Mg content increased the undercooling of the solder. Moreover, the incorporation of Mg particles resulted in a consistent rise in the coefficient of thermal expansion (CTE) of the composite solder, ranging from 11.4 × 10−6/°C to 15.6 × 10−6/°C. It was worth noting that including Mg particles enhanced the wetting ability of Sn58Bi alloy on Cu substrates. With a 0.4 % addition of Mg particles, the wetting area could be increased by 60.14 %, and the lowest wetting angle was approximately 10.43°. Adding Mg particles resulted in an amelioration in the brittleness of the Bi-rich phase within the solder matrix, coupled with a decrease in both the thickness of IMC and the grain size at the joint interface. Compared to the joints without mixed Mg particles, the shear strength of Sn58Bi-0.4Mg solder joints and the microhardness of the alloy increased by 30 % and decreased by 10 %, respectively. Also, the presence of dimples within the fracture indicated a rise in the ductility of the solder joints. Overall, adding 0.4 wt% Mg particles in this experiment resulted in a more effective modification of the Sn58Bi solder comprehensive properties.

Effect of the addition of Cu6Sn5 nanoparticles on the growth of intermetallic compounds at the interfaces of Sn3.0Ag0.5Cu solder joints

To solve the issue of overgrowth of intermetallic compounds (IMCs) at the interfaces of solder joints in electronic devices, this study has focused on the modification of Sn3.0Ag0.5Cu (SAC305) solder by adding Cu6Sn5 nanoparticles (NPs). It was found that Cu6Sn5 NPs would adsorb on the surfaces of the interfacial IMCs due to the high surface energy in solid–liquid reactions and resulted in a peculiarly ordered growth pattern of the new grains. In addition to this, a combined growth mechanism involving encapsulated and engulfed crystal growth of the interfacial IMCs was identified. The addition of Cu6Sn5 NPs was also calculated to increase the activation energy associated with interfacial IMCs growth during high-temperature service, thereby effectively inhibiting the overgrowth of interfacial IMCs. When the mass fraction of Cu6Sn5 NPs was 0.6 wt%, the activation energy for interfacial IMCs growth was the highest (31.9 kJ/mol).

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.

Microstructure Evolution and Growth of Interfacial Intermetallic Compounds in NiCr/Ti Alloy Laminated Composite after Explosive Welding and Heat Treatment

The paper considers the issues of interaction of the molten metal at the interface of explosively welded NiCr/titanium alloy laminated composites with the reaction zone formed during heat treatment, as well as the features of its destruction after welding. It was established that the molten metal is a heterogeneous mixture based on Ni(Cr,Ti) and Ti(Ni,Al) solid solutions and NiTi and Ni3Ti intermetallic compounds. The estimated existence time of molten metal areas in the liquid state was ~10−8–10−11 s. The obtained values are comparable with the time of the unloading wave arrival at the contact surface, which is the reason for the presence of fracture areas in the form of detachments on the fracture surface. Continuous nanometer-size interlayers with an amorphous structure, due to the ultra-high cooling rate of the liquid melt, induce viscous destruction of the interface. Heat treatment at temperatures of 700 and 850 °C led to the formation of a layered reaction zone at the NiCr/Ti boundary, consisting of interlayers of solid solutions based on Ti2Ni, TiNi, and TiNi3 intermetallic compounds, as well as inclusions of a Cr(Ti) solid solution. The diffusion flow gradient was predominantly directed into the titanium alloy.

Effect of multi-walled carbon nanotubes on the microstructure and properties of Sn-58Bi solder alloys

The influence of multi-walled carbon nanotube (MWCNT) content on the melting properties, wettability, microstructure, and intermetallic compounds (IMCs) of Sn-58Bi-xMWCNT (x = 0, 0.01, 0.02, 0.03, 0.05, and 0.10 wt.%) and the effects of MWCNT on the tensile strength of Cu/Sn-58Bi-xMWCNT/Cu solder joint were analyzed. The results show that MWCNT addition at a small trace amount into Sn-58Bi solder could increase the spreading area of Sn-58Bi solder, refine the solder matrix microstructure, inhibit the growth of interfacial IMCs, and significantly improve the tensile strength of Sn-58Bi solder joints. However, the melting point and melting range remained the same or slightly changed. The wettability of Sn-58Bi alloys increased first and then decreased with the addition of MWCNT. The spreading area and the tensile strength of solder joint were the maximum when the MWCNT content was 0.01 wt.%, and they were 42.23 mm2 and 50.07 MPa, respectively. The reason may be related to the improved microstructure of solder alloys and the morphology of IMCs due to MWCNT addition at trace level.

Effects of Bi and Cu addition on mechanical properties of Sn9Zn alloy and interfacial intermetallic growth with Ni substrate

Sn9ZnxBixCu (x = 0, 1.0, 2.0, 3.0 and 4.0 wt%) solder alloys were prepared by adding different contents of Bi and Cu elements, and the effects of Bi and Cu addition on the mechanical properties, wettability, and interfacial intermetallic compound (IMC) layer were researched. The addition of Bi and Cu can significantly improve the mechanical properties and creep resistance of the alloy. When the addition of Bi and Cu reaches 2 wt%, small Bi phases are dispersed in the matrix, and moderate Cu5Zn8 phases appear, which strengthens the solder matrix. The ultimate tensile strength (UTS) of the Sn9Zn2Bi2Cu alloy reaches 51.01 MPa, which is 149.32% higher than that of the Sn9Zn alloy, and the elongation reaches 26.56%. Nanoindentation results show that the holding displacement of the Sn9Zn4Bi4Cu alloy decreased by 28.48% compared with that of the Sn9Zn alloy at a loading rate of 0.1 mN/s. In addition, proper addition of Bi and Cu can improve the wettability of the solder alloy and inhibit the growth of interfacial intermetallic compounds (IMCs) between the solder and Ni substrate. When the reflow time reaches 40 min (min), the interfacial IMC thickness of the Sn9Zn2Bi2Cu/Ni solder joint is 1.93 µm, which is 46.09% smaller than that of the Sn9Zn alloy. Moreover, the shear strength of the Sn9Zn2Bi2Cu/Ni solder joint increases by 33.3%, reaching the maximum value (38.76 MPa). When the Bi and Cu addition reaches 2 wt%, the wetting area reaches a larger value (13.525 mm2), which is 28.35% higher than that of Sn9Zn alloy.

Characterization of Sn-xIn Solders and Thermomigration-Induced Interfacial IMC Growth of Cu/Sn-xIn/Cu Micro Solder Joints

The melting behavior and microstructure of bulk Sn-xIn (x = 6, 12 and 24, wt.%) solders and the thermomigration, elemental distribution and intermetallic compound (IMC) growth in Cu/Sn-xIn/Cu micro solder joints during soldering and aging under temperature gradient (TG) were investigated. The results indicate that In addition effectively decreased the melting temperature of the bulk solders. Only the InSn4 phase was detected when In addition was increased to 24 wt.%. During soldering under TG, the growth rate of the interfacial IMC layer at the cold end interfaces gradually decreased as the In content increased. The mechanism of microstructure evolution and elemental distribution in the micro solder joints was revealed based on the TG-induced atomic thermomigration (TM). The chemical potential gradient of atoms was enhanced by TM, and the rapid diffusion of atoms in the liquids resulted in a uniform distribution of In element in both solders and the IMC phase during soldering. While during aging under TG, there was a smaller chemical potential gradient due to the slow atomic diffusion rate. At this time, TG dominated the atomic migration, which resulted in a nonuniform distribution of the In element in the whole joints. This study provides further insight into the application of In-containing solders in electronic packaging.

Study on Microstructure and Mechanical Properties at Constant Electromigration Temperature of Sn2.5Ag0.7Cu0.1RE0.05Ni-GNSs/Cu Solder Joints

To solve the electromigration problem of micro-electronic connection solder joints, an ideal electromigration tester was designed, and the thickness of the intermetallic compounds (IMCs), average void diameter, grain orientation, failure, shear strength, and fracture path of Sn2.5Ag0.7Cu0.1RE0.05Ni-GNSs/Cu solder joints under constant-temperature electromigration were studied. The results indicate that the solder joints show evidence of typical electromigration polarity in the asymmetric growth of interfacial IMCs on the anode and cathode sides under the conditions of a current density ≥7 × 103 A/cm2 and an included angle between the c-axis of the β-Sn grains and the current direction θ ≤ 53.2°. The anode-side interfacial IMC is dominated by a Cu6Sn5 phase with a gradually increasing thickness, forming a Cu3Sn phase and showing evidence of microcracks. The Cu6Sn5 phase of the cathode-side interfacial IMC is gradually completely dissolved, and the growth of the Cu3Sn phase is accompanied by the formation of Kirkendall voids. The anisotropic diffusion of Cu atoms in the β-Sn of the micro-solder joints causes increased solder joint resistance and reduced shear strength. The shear fracture path of the solder joints moves from the cathode side near the IMC solder seam to the Cu3Sn interface. The shear fracture mechanism changes from ductile transgranular fracture dominated by β-Sn dimples to brittle fracture dominated by interfacial IMC cleavage and slip steps.

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.

Phase field study on the effect of roughness on interfacial intermetallic compounds of micro-solder joints under multifield coupling

In order to investigate the influence of roughness on the evolution of interfacial intermetallic compounds (IMCs) and stress states at the micro-solder joints under the strongly coupled thermo-mechanical-electric diffusion, the two-dimensional model of the rough interface for the Cu/Sn/Cu sandwich micro-solder joints was established using phase field method. Parameter A as the evaluation parameter of the interface roughness was used to represent the contour arithmetic mean deviation Ra. The evolutions of the average thickness of the interfacial IMCs and stress distribution at the Cu/Sn/Cu micro-solder joints were investigated with the variation of A. The thickness of interfacial IMCs in anode reached its maximum when A was 0, while obtained the minimum when A was 9. In cathode, the average thickness of the interfacial IMCs at A = 0 was thicker than that at A = 1, 3, 5, but thinner than that at A = 7 and 9. In other words, the growth of the interfacial IMCs was inhibited by the interface roughness in anode. While in cathode, the interfacial roughness inhibited the growth of the interfacial IMCs when 0 ≤ A ≤ 5, but promoted the growth of the interfacial IMCs when 7 ≤ A ≤ 9.

Alloying regulation mechanism toward microstructure evolution of Sn-bi-based solder joint under current stress

Sn–Bi-based solder alloys have triggered substantial concern in development of low-temperature interconnecting materials of multi-level packaging electronic devices. However, with the high-density current treatment, dramatic atom migration occurs in Sn–Bi-based solder joint, which accelerates the evolution of solder joint microstructure, including the aggregation of Bi phase and the excessive growth of interfacial intermetallic compound (IMC). In this work, Sb element shows a unique influence mechanism on the electromigration (EM) resistance of Sn-Bi-based solder joint. Doped Sb in Sn58Bi-1Sb (SB-Sb) solder massive precipitate as Sn-Sb and Bi-Sb nano precipitations under current stress. These nano precipitates show the ability to capture the migrating atoms, inhibit the migration of Bi atoms and Sn atoms, and enhance the EM resistance of solder joint. Importantly, Bi twin crystal structure is observed in Sn-Bi-Sb solder for the first time. The variation of twins' phase orientations in different positions of solder joint is associated with atomic migration paths induced by the current stress and would eliminate the overgrowth of the Bi rich phase and IMCs. The presented study provides the valuable insights into the regulates mechanism of alloy elements on atom migration in Sn-Bi-based solder joint.