Evolution Of Intermetallic Compounds Research Articles

Intermetallic Compounds in Solder Alloys: Common Misconceptions

Intermetallic compounds (IMC) or intermediate phases are formed between two or more metallic elements in many metal alloy systems. During soldering, an IMC is formed at the soldered interface as the molten solder reacts with an element in the substrate. IMCs also can form within the bulk solder as the joint solidifies. IMCs have critical roles in the solder joint quality and reliability. Unlike most metal alloys, an intermetallic compound typically has a fixed stoichiometry and is in variance with the conventional phases or constituents in the metal system (e.g., alpha and beta). IMCs have a different crystal structure than any of its constituents and some but never all the characteristics and properties of its constituents. Ductility is an important solder joint property, and the low intrinsic ductility of IMCs is associated with brittle behavior and reliability risk in service. However, a review of published solder field failures shows little evidence that IMC properties or IMC evolution under service conditions reduce solder joint reliability. Most IMC-induced solder joint failures are found to result from incorrect material specification or uncontrolled soldering processes. This paper describes the IMCs that occur typically in eutectic, Sn63Pb37 solder and near-eutectic SAC305 or other tin-based Pb-free solder alloys, including how they impact solder joint reliability. The paper also describes the potential impact of IMCs on the solder joint reliability for the newest generation of Pb-free high-performance solder alloys.

The role of Sn grain orientation in Cu depletion of Sn-based solders

The miniaturization of solder bumps in flip-chip packages results in large variability in their microstructure making the prediction of joint lifetime challenging. This is of particular importance in Sn-rich solders due to the anisotropic diffusion behavior of Sn and the presence of fast diffusion pathways, such as grain boundaries and twins that vary from joint to joint. We developed a multi-physics phase-field model to predict the electromigration-enhanced evolution of intermetallic compounds in Cu/Sn system with different grain structures. We present simulations of solder joints with polycrystalline Sn with grains with different orientations to observe the effect of Sn anisotropy and grain boundaries on electromigration failure. The simulations predict Cu depletion in the cathode and the formation and accumulation of intermetallic compounds along Sn grain boundaries dependent on the Sn grain orientation. Additionally, Cu6Sn5 clusters are formed in the Sn matrix when high diffusion rates at the interfaces are considered.

Microstructure evolution and multi-reinforcement mechanisms in Al-Cu-Ag alloys

As one of the most commonly used binary alloys, the effect of intermetallic compounds (IMCs) of Al-Cu alloys in powder metallurgy on their structure and properties is instructive for tailoring Al-Cu alloys for different applications. In this investigation, a series of Al-Cu-Ag alloys with varying Cu compositions were fabricated via hot pressing. TEM analysis identified CuAl2 as the primary intermetallic compounds, with Ag existing in forms including Ag2Al, elemental Ag, and an Ag-(Cu) solid solution. The modulation of Cu content influenced the state of Ag and the mechanical behaviors of the Al-Cu-Ag alloy. Particularly, the high Al/Cu alloy, benefiting from a synergistic effect comprising stacking faults, nanoscale precipitates, and solid solutions, exhibited outstanding mechanical properties. Conversely, the Al-50Cu-3Ag alloys displayed significant brittleness, attributed to the adverse impact of large-scale intermetallic compounds and increased grain size due to the formation of CuAl2. The incorporation of nanoparticles effectively mitigated the grain size in high Al/Cu alloys. This study elucidates the correlation between the evolution of intermetallic compounds and composition in Al-Cu alloys, offering novel insights into the reinforcement of both Al-based and Cu-based alloys.

Phase field simulation of interface evolution behavior of copper–tin micro-solder joints under thermal–mechanical–electrical coupling

The thermal–mechanical–electrical-diffusion strongly coupled equations are established, and the phase field method is employed to investigate the dynamic simulation of intermetallic compound (IMC) evolution at the Cu/Sn/Cu micro-solder joint interface. By comparing with experimental results on IMC evolution in micro-solder joints, this study explores the evolution law of IMCs under the influence of current, temperature, and applied load coupling. Both simulation and experimental findings indicate that higher current density promotes IMC formation, with the largest average thickness observed at a current density of 5000 A/m2. When the analog current density is 5000 A/m2, the anode IMC has a rapid growth period at 62 h, and the corresponding cathode has a rapid consumption period; when the analog current density is 4000 A/m2, the anode has the same phenomenon in 95 h; when the analog current density is 3000 A/m2, this phenomenon is not evident. The observed phenomena are consistent with the evolutionary trend of IMC from the fourth to the fifth day of the experiment, considering it may be affected by ‘electronic wind stress’ which makes the cathode IMC migrate to the anode. The average thickness of IMCs with an analog ambient temperature of 323–353 K is the largest, which is most suitable for the growth of IMCs. The experimental results also indicate that IMC growth is the fastest at 353 K. The anode IMC was inhibited by tensile stress and shear stress, but the effect on cathode was not obvious.

Mechanical Alloying Synthesis and Spark Plasma Sintering Consolidation of Al-Ti-Si-W Alloys

Al-Ti-Si-W quaternary powders were mechanically synthesized by planetary ball milling; and further consolidated by spark plasma sintering. The nominal compositions of the quaternary alloys were designed to be Al60Ti30Si5W5 and Al45Ti40Si10W5 (wt.%). The microstructural evolution of intermetallic compounds in Al-Ti-Si-W alloys included titanium aluminide, titanium silicide, and ternary alloys (AlxTiy, TixSiy, and TixAly,Siz), whereas W was embedded in the Al-Ti matrix as a single phase. The phase composition and grain size distribution were investigated using electron backscatter diffraction analysis, in which refined and uniform microstructures (less than 0.3 μm) were attributed to severe plastic deformation and rapid densification of the pre-alloyed powders. The mechanical properties were correlated with the Al content in the quaternary alloys; a high hardness of 1014.6 ±73.5 kg/mm2 was observed.

Solder joint shape optimization and thermal-mechanical reliability improvement for microwave RF coaxial connectors

Coaxial connectors are widely used in microwave RF components in wireless communication, aerospace, and other fields. However, the poor interconnection reliability between their inner conductors and circuit boards has been a key factor restricting their development. Thermal cycling and high temperature are the most common working loads for high-frequency devices and the failure generally takes place at the solder joint interface. Therefore this study investigated the solder joints thermal-mechanical reliability of coaxial connectors through a combination of numerical simulation and reliability experiments. Three innovative initial models were used to solve the shape simulation problem of solder joint in planar-curved composite structures. The optimal solder joint shape and structural parameters were obtained through finite element simulation, and the impact mechanism of different parameters on solder joint reliability was explained. After optimization, the maximum stress of the solder joint decreased by 44 % with thermal cycling, while the average stress decreased by 55 %. The reliability tests effectively verified the accuracy of the simulation. In addition, the 150 °C aging tests clarified the kinetics of the growth and evolution of intermetallic compounds in this solder joint structure. The results contribute to the advancement of coaxial connectors solder joints reliability and support the development of more robust and durable interconnects for microwave devices and digital communication systems.

Intermetallic compound evolution and mechanical properties of Sn-0.7Cu-0.1Ni-xZn lead-free solder alloys prepared by directional solidification

The addition of Ni and Zn is known to improve the properties of Sn-0.7Cu solder. However, previous research has only focused on the improvement of Sn-0.7Cu solder performance through microalloying methods, and the impact of preparation processes and microalloying on the properties of Sn-0.7Cu solder remains unclear. In this study, Sn-0.7Cu-0.1Ni-xZn solders were prepared using the directional solidification (DS) method. DS eliminates transverse grain boundaries, making it an advantageous method to study the effect of Zn content on the mechanical properties of Sn-0.7Cu-0.1Ni solder. The results showed that some CuZn intermetallic compounds (IMCs) and Cu6Sn5 IMCs transformed into Cu5Zn8 IMCs of better mechanical properties and (Cu,Ni)6(Sn,Zn)5 IMCs of more thermodynamic stability with the increase of Zn content. The tensile results indicated that the ultimate tensile strength (UTS) and yield strength (YS) of the solders followed the same pattern as the Zn content increased. Additionally, the fracture elongation (EL) of the solders initially increased and then decreased with the increase of Zn content. The peak EL was observed at 21.9% when the Zn content was 0.5 wt%. Finally, the fracture surface analysis of the tensile specimens revealed that the solder deformation was primarily plastic, with a small degree of necking observed.

A Review of Silver Wire Bonding Techniques.

The replacement of gold bonding wire with silver bonding wire can significantly reduce the cost of wire bonding. This paper provides a comprehensive overview of silver wire bonding technology. Firstly, it introduces various types of silver-based bonding wire currently being studied by researchers, including pure silver wire, alloy silver wire, and coated silver wire, and describes their respective characteristics and development statuses. Secondly, the development of silver-based bonding wire in manufacturing and bonding processes is analyzed, including common silver wire manufacturing processes and their impact on silver wire performance, as well as the impact of bonding parameters on silver wire bonding quality and reliability. Subsequently, the reliability of silver wire bonding is discussed, with a focus on analyzing the effects of corrosion, electromigration, and intermetallic compounds on bonding reliability, including the causes and forms of chlorination and sulfurization, the mechanism and path of electromigration, the formation and evolution of intermetallic compounds, and evaluating their impact on bonding strength and reliability. Finally, the development status of silver wire bonding technology is summarized and future research directions for silver wire are proposed.

Formation and Evolution Mechanism of Intermetallic Compounds of Friction Stir Lap Welded Steel/Aluminum Joints.

Interfacial layers with brittle intermetallic compounds (IMC) greatly influence the performance of steel-aluminum friction stir lap welding (FSLW) joints. Thus, the formation and evolution of IMC between 7075-T6 aluminum alloy and galvanized DP590 steel in steel-aluminum FSLW joints were investigated. An FSLW numerical model was developed using the computational fluid dynamics method to analyze the interface temperature between the aluminum alloy and steel. Scanning electron microscopy (SEM) was conducted to observe the microstructure characterization and measure the IMC thickness. Phases among different joint zones were analyzed by X-ray diffraction (XRD) and energy dispersive spectroscopy (EDS). IMC layer formation was predicted by the effective Gibbs free energy model presented in this paper according to thermodynamic principles. The Monte Carlo method was utilized to predict the thickness of IMC layers. It was found that the IMC layer at the interface of the welded joint is composed of Fe2Al5, FeAl3, and Al-Zn eutectic. The IMC thickness decreased from 4.3 μm to 0.8 μm with the increasing welding speed, which was consistent with the Monte Carlo simulation results.

Kinetics of intermetallic compound layers between AISI 321 stainless steel and molten aluminum

The interfacial reaction between liquid aluminum and solid steel is critical to understanding the evolution of intermetallic compounds (IMCs) in the brazing and weld brazing processes of aluminum-to-steel dissimilar alloys. In this study, hot dip aluminizing of AISI 321 stainless steel at different temperatures was conducted to reveal the influence of reaction temperature and time on interfacial IMCs. Electron microscopy analyses were employed to investigate the interfacial microstructures. A single layer of θ-Fe4Al13 was observed at 700°C. In contrast, the IMCs of interfaces dipped at 800–1000°C consisted of a thin inner layer of η-Fe2Al5 + ζ-FeAl2 next to the steel and a thick layer of θ-Fe4Al13 close to the aluminum. For the inner layer, the thickness increased with increasing dipping temperature and time. Its growth was described by a parabolic rate law, which suggested a diffusion-controlled mechanism at the interface. An activation energy of 66.5 kJ mol−1 was obtained. For the Fe4Al13 layer, the thickness evolution at different temperatures was different from that of the inner layer, with a thick IMC layer at 700°C, a thinner IMC layer at intermediate temperatures (from 800 to 900°C), and a slightly thicker IMC layer from 950 to 1000°C. The growth kinetics of Fe4Al13 at 700°C were controlled by diffusion, interfacial reactions, and dissolution mechanisms. The evolution of Fe4Al13 between 800 and 1000°C was governed by diffusion and dissolution mechanisms. The appearance of the inner layer and the evolution kinetics of Fe4Al13 accounted for the decrease in thickness with increasing temperature between 700 and 900°C.

Evolution of intermetallics between solid Fe-Cr/Fe-Ni alloys and molten aluminium

Investigations of the evolution of intermetallic compounds (IMCs) at the interface between iron-based alloys and molten aluminium have important technical and scientific significance in many key areas. Most previous studies of IMCs formed at molten aluminium/solid steel interfaces have been focused on relatively long reaction times, but less research has been performed on the evolution of IMCs at the aluminizing interfaces of Fe-Cr and Fe-Ni alloys within a few seconds. In this study, hot-dip aluminizing experiments under natural convection conditions were employed to study the evolution of two interfacial IMCs (Fe-15Cr alloy and Fe-35Ni alloy with molten aluminium) at 700–900°C within 30 s. The IMCs for Fe-15Cr consisted of an Fe4Al13 layer next to the aluminium and an Fe2Al5 layer adjacent to the steel. In contrast, only one layer of Fe4Al13 was detected at the interface between the Fe-35Ni alloy and molten aluminium. The growth of Fe2Al5 was described by a parabolic rate law. An activation energy of 7.53 kJ/mol was determined for the temperature range of 700–900°C. The evolution of Fe4Al13 for the two alloys was similar: their thicknesses decreased anomalously with increasing dipping temperature, and their kinetics were controlled by both diffusion and dissolution. In this study, based on reaction-diffusion theory, growth and dissolution equations of the IMCs were established, and the diffusion coefficients of Al atoms in Fe2Al5 and Fe4Al13 were obtained for the first time. The similarities and differences in the IMCs for the two alloys were explained mainly by the different diffusion coefficients.

Effect of reflow temperature and solder size on Cu-Ni cross-interaction in the Cu/Sn/Ni micro solder joints

PurposeSolder bumps for chip interconnections are downsizing from current approximately 100 µm to the expected 1 µm in future. As a result, the Cu-Ni cross-interaction in Cu/Solder/Ni solder joints will be more complicated and then strongly influence the growth of the intermetallic compounds (IMCs). Thus, it is critical to understand the fundamental aspects of interfacial reaction in micro solder joints. This paper aims to reveal the effect mechanism of reflow temperature and solder size on the interfacial reaction in Cu/Solder/Ni solder joints.Design/methodology/approachThe Cu-Ni cross-interaction in the Cu/Sn/Ni micro solder joints with 50 and 100 µm solder sizes at 250°C and 300°C were observed, respectively. The line-type interconnects were soaked in silicone oil, and the temperature of the line-type interconnects was 250 ± 3°C and 300 ± 3°C, which were monitored by a fine K-type thermocouple, and followed by an isothermal aging process at various times. After aging, the specimens were removed from the silicone oil and cooled in the air to room temperature.FindingsThe major interfacial reaction product on both interfaces was (Cu,Ni)6Sn5, and the asymmetric growth of (Cu,Ni)6Sn5, evidenced by the thickness of (Cu,Ni)6Sn5 IMCs at the Sn/Ni interface was always larger than that at the Sn/Cu interface, resulted from the directional migration of Cu atoms toward the Sn/Ni interface under Cu concentration gradient. The morphology of (Cu,Ni)6Sn5 IMC at Sn/Cu interface was columnlike at 250°C, and which changed from columnlike to scallop with large aspect ratio at 300°C, while that at Sn/Ni interface gradually evolved from needlelike to the mixture of needlelike and layered at 250°C, and which evolved from needlelike to scallop with large aspect ratio at 300°C. The evolution of morphology of (Cu,Ni)6Sn5 is attributed to the content of Ni. Furthermore, the results indicate that the Cu-Ni cross-interaction was stronger with small solder size and relatively low temperature in the Cu/Sn/Ni micro solder joints.Originality/valueThe asymmetric growth of (Cu,Ni)6Sn5 in the Cu/Sn/Ni micro solder joints, evidenced by the thickness of (Cu,Ni)6Sn5 IMCs at the Sn/Ni interface, was always larger than that at the Sn/Cu interface. The morphology evolution of (Cu,Ni)6Sn5 IMC at both interfaces was attributed to the content of Ni. The Cu-Ni cross-interaction was stronger with small solder size and relatively low temperature in the Cu/Sn/Ni micro solder joints.

Intermetallic compound evolution and mechanical properties of Cu/Sn58Bi/Cu 3D structures blended with B4C nanoparticles during isothermal aging

The Cu/Sn58Bi/Cu and Cu/Sn58Bi-0.6B4C/Cu joints were prepared by transient liquid phase (TLP) bonding technology to verify the reliability of low-temperature connection joints. Intermetallic compound (IMC) evolution at the interface under different isothermal aging times was analyzed, and the mechanical properties of the joints were tested. The results show that two kinds of IMC, lamellar Cu3Sn and fan-shaped Cu6Sn5, are formed on both sides of the joint. With increasing soldering time, the thickness for both kinds of IMC become thicker, and it is significantly thicker for the IMC near the cold end. Furthermore, the IMC growth rate of the Cu/Sn58Bi-0.6B4C/Cu solder joint is significantly lower. When the isothermal aging time reaches 36 h, the Cu/Sn58Bi/Cu joint has been almost composed of IMC, while it needs a longer time for the Cu/Sn58Bi-0.6B4C/Cu joint. The growth of Cu3Sn IMC is in line with parabolic law, being mainly controlled by volume diffusion near the hot end, while the grain boundary diffusion significantly affects it at the cold end. The joints shear strength decreases gradually with extending bonding time, but it is always higher for the Cu/Sn58Bi-0.6B4C/Cu joint. When the heating time is not long, the fracture mainly appears at the Bi-rich phase in the solder matrix. With increasing bonding time, the location of fracture gradually transformed from the Cu6Sn5 grains to the junction of the two IMC and Cu3Sn grains, along with the intercrystalline fracture and transcrystalline fracture. In summary, B4C nanoparticles can significantly improve the joint reliability and enhance its mechanical properties.

Phase Field Simulation of Intermetallic Compound Evolution at the Interface of Copper–Tin Coating Under Thermal–Mechanical–Electrical Diffusion Coupling

Phase Field Simulation of Intermetallic Compound Evolution at the Interface of Copper–Tin Coating Under Thermal–Mechanical–Electrical Diffusion Coupling

Effect of Annealing on the Interface and Properties of Pd/Al Composite Wires

This paper investigates the changes in the interface organization and properties of 0.10 mm Pd/Al composite wires annealed at different temperatures. The optimum comprehensive performance of the material was obtained after annealing at 300 °C for 120 s. Its tensile strength, conductivity and elongation are 140.61 MPa, 46.82%IACS and 14.89%, respectively. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to observe the intermetallic compounds on the interface. The annealing temperature and the formation heat of intermetallic compounds determine the categories and evolution of intermetallic compounds. When the thickness of the intermetallic layer is more than 1 μm, it has a serious effect on the electrical conductivity and elongation of the materials.

Effect of diffusion bonding time on microstructure and mechanical properties of dissimilar Ti6Al4V titanium alloy and AISI 304 austenitic stainless steel joints

Abstract The main objective of this investigation is to study the effect of diffusion bonding time on microstructure and mechanical properties of dissimilar Ti6Al4V titanium alloy and AISI 304 austenitic stainless steel joints. The dissimilar joints of Ti6Al4V titanium alloy and AISI 304 steel were developed using the different levels of bonding time (30, 45, 60, 75 and 90 min) in a vacuum chamber at a bonding temperature of 900 °C and compressive pressure of 14 MPa. The microstructure of joints was analyzed using optical microscopy (OM) and scanning electron microscopy (SEM). The elemental analysis of joint interface was studied using the SEM energy dispersive spectroscopy (EDS). The evolution of intermetallic compounds at the joint interface was analyzed using X-ray diffraction (XRD). The ram tensile tests and lap shear tests were performed to assess the bonding strength and lap shear strength of dissimilar joints. Results showed that the dissimilar joints of Ti6Al4V alloy–AISI 304 steel developed using the diffusion bonding time of 75 min showed higher lap shear strength of 151 MPa and bonding strength of 244 MPa due to the better coalescence of the joining surfaces and evolution of optimum width of diffusion region having minimum embrittlement effects.

Modeling of temperature- and strain-driven intermetallic compound evolution in an Al–Mg system via a multiphase-field approach with application to refill friction stir spot welding

The prospect of joining dissimilar materials via solid-state processes presents an opportunity to obtain multi-material structures having a synergy of desirable properties of the joined materials. However, the issue of the formation of intermetallic compounds at the weld interface of dissimilar materials arises with that, depending upon the temperature and pressure conditions as per phase diagram. As the thickness of the intermetallic compounds may determine the mechanical properties of the joint, understanding the driving mechanisms and evolution of these intermetallic compounds in solid-state joining processes, such as refill friction stir spot welding (refill FSSW), is crucial. In this contribution, we account for the effect of different driving forces in a multiphase-field approach and investigate the evolution of the intermetallic compounds driven by chemical and mechanical forces. A finite-element simulation of the refill FSSW is pursued to obtain the peak temperature and strain at different locations of the weld interface. The microstructure simulations obtained via the multiphase-field model give insight into the morphology and kinetics evolution of the intermetallic compounds for both, the absence of strain (purely chemically-driven model) as well as presence of strain (chemo-mechanically-driven model). The consideration of strain proves to result in thicker intermetallic compound layer. Furthermore, the impact of interface energy and initial grain configuration is found to be significant on the overall intermetallic compounds evolution.

Investigation of phase equilibria of the Au–Ni–Sn ternary system and interfacial reactions in the Au/Sn/Ni/Cu multilayer couple

Au and Ni are widely used in the under-bump metallization, whereas Sn and Cu serve as common bonding materials and substrates, respectively. Solder joints consisting of an Au/Sn/Ni/Cu multilayer structure are widely found in the electronic packaging. Both phase equilibria of the Au–Ni–Sn ternary alloys and interfacial reactions of the Au/Sn/Ni/Cu multilayer structure were applied to the solid/solid-state reaction couple technique. The results showed that the Ni3Sn2 and AuSn4 phases respectively had a great solubility of the third element and the ternary AuNi2Sn4 phase existing in the Au–Ni–Sn ternary alloys was formed at 180 and 240 °C. The Sn/Ni/Cu multilayer structure was prepared by electroplating Sn/Ni layers on the Cu substrate. Afterward, the Sn/Ni/Cu multilayer and Au foil were screwed together to obtain the Au/Sn/Ni/Cu multilayer structure, followed by reactions at 150, 180 and 200 °C for different durations. The thickness of the intermetallic compounds (IMCs) increased with the increase in the reaction time and temperature. The IMC evolution in the couple remained unchanged at different temperatures. An increase in the reaction time converted the AuSn4 and AuSn2 phases to the AuSn phase. The voids formed in the couple were attributed to the volume shrinkage effect, which decreased with an increase in the reaction temperature. The (Ni, Au)3Sn2 phase was formed at the Ni side; the Ni layer functioned as an effective diffusion barrier to prevent the formation of the Cu–Sn IMCs.

Interfacial structures and mechanical properties of Cu/Sn/Cu containing SiC nanowires under transient liquid phase bonding

In order to achieve low-temperature bonding and high-temperature service, Cu/Sn/Cu and Cu/Sn-0.6SiC/Cu structure were fabricated by transient liquid phase (TLP) bonding, and the microstructure evolution of intermetallic compound (IMC) and mechanical performance of TLP bonding solder joints were investigated. The results demonstrated that the scalloped Cu6Sn5 IMC and lamellar Cu3Sn IMC formed at Sn/Cu interface gradually grew up in both solder joints as the bonding time increased. The asymmetrical growth of IMC was formed on both sides at TLP solder joints interface, whereas the interfacial IMC growth rate of Cu/Sn-0.6SiC/Cu was smaller than that of Cu/Sn/Cu solder. After TLP bonding for 120 min, Cu/Sn/Cu structure was composed of total Cu6Sn5 and Cu3Sn IMC and Cu/Sn-0.6SiC/Cu structure still contained remaining Sn phase. SiC nanowires (SiC NWs) dispersed in the solder matrix could impede the growth path between Sn and Cu, so SiC NWs doped to Sn solder could slow down the IMC growth. Moreover, introducing SiC NWs could promote the shear strength of composite solder compared with Sn solder joints during TLP bonding.

Microstructural evolution of intermetallic compounds between crystalline/amorphous Cobalt-Phosphorous coatings and lead-free solders

In the advanced microelectronic packaging, Cu/Sn joints require high-quality diffusion barriers to inhibit Cu–Sn intermetallic compounds (IMCs) growth and improve the interface brittleness. Cobalt-Phosphorous (Co–P) alloy coatings are ideal candidates due to their good wettability, promising diffusion resistance and low interfacial brittleness. In this work, the microstructural evolution of IMCs between crystalline/amorphous Co–P coatings and lead-free solders during the solid-state diffusion were systemically investigated. The microstructure, phase distribution, and grain characteristics of coatings and IMCs were carefully characterized by SEM, EPMA, EBSD, and TEM. It was found that the consumption rate of crystalline Co–P, 21.2 nm/h, was significantly slower than that of amorphous Co–P, 96.4 nm/h, and exhibited an excellent diffusion resistance, which was attributed to the nanocrystalline structure and the P-rich layer which performed the diffusion barriers for Sn and Cu atoms. Compared with Ni, amorphous Co–P coatings could better improve the interfacial brittleness with soft and ductile Co–Sn compounds (hardness of 3.0 GPa) growing with the rapid diffusion of Co, and the toughened Co–Sn–P attributing to the diffusion of Sn. Kinetic analysis showed that the growth rate-controlling process of Co–Sn IMCs was jointly controlled by interfacial reaction and volume diffusion, and the effect of the interfacial reaction is more pronounced in the amorphous system, which leads to coarse Co–Sn grains that are beneficial to the softness and ductility of IMCs. Crystalline and amorphous Co–P coatings can be applied to the surface treatment for die pads and print-circuit-board pads according to their own characteristics, respectively.