Growth Behavior Of Intermetallic Compounds Research Articles

Effects of the grain size and orientation of Cu on the formation and growth behavior of intermetallic compounds in Sn-Ag-Cu solder joints

The rapid development of semiconductor packaging technology has accelerated the applications of flip-chip bonding technology using fine-pitch micro bumps and Cu pillar bumps. These micro-bump systems are composed of metallic Cu and Sn. The properties of the Cu- and Sn-based bonding materials applied in these technologies have a significant effect on the mechanical properties and long-term reliability of micro-joints. This study focuses on the effects of the grain size and orientation of the Cu substrate on the formation and growth of intermetallic compounds (IMCs) at the Sn/Cu interface. The Cu substrate was annealed from 200 to 1000 °C to alter its grain size, which was measured via electron backscatter diffraction analysis. Sn-3.0Ag-0.5Cu (SAC) solder paste was printed onto the Cu substrate, and the Sn/Cu interfacial microstructure was observed by scanning electron microscopy and energy-dispersive X-ray spectroscopy after the reflow soldering process. A thin IMC formed on substrates with small grain sizes, whereas larger grain sizes resulted in the formation of thick and elongated IMCs. In addition, the IMC growth exhibited a specific directional preference in the (21̅1̅0) direction on substrates annealed at 1000 ℃. The effects of the Cu grain size and orientation on the interfacial reactions and growth of IMCs were compared and analyzed by observing IMCs formed at the SAC/Cu interface. Microstructural analysis revealed that controlling the Cu grain size and orientation significantly impacts the reliability of the solder joints. This study shows that the effect of grain size and orientation can be utilized to micro-solder joints, which can significantly enhance their mechanical strength and reliability.

Influence of Al2O3 Nanoparticles on the Morphology and Growth Kinetics of Cu-Sn Intermetallic Compounds in Sn-Ag-Zn/Cu Solder Joints

Intermetallic compounds (IMCs) growth can simultaneously bring about low-resistance electrical pathways and drastically reduce joint lifetime. Recently, incorporated trace nanoparticles into the free-Pb solder were found to promote the performance of the solder joints. Sn3Ag0.9Zn (SAZ) nano-composite solders were developed by doping 0.5 wt.% Al2O3 nanoparticles into the SAZ solder. The IMCs formation and growth behavior at the interfacial reactions between the SAZ-0.5Al2O3 nano-composite solder and the Cu substrate during soldering at temperatures ranging from 250 to 325 °C for 30 min were investigated. The results showed that after the addition of Al2O3 nanoparticles into the SAZ solder, the elongated-type IMCs layer changed into a prism-type IMCs layer, and Ag3Sn nanoparticles were absorbed on the grain surface of the interfacial Cu6Sn5 phase, effectively suppressing the growth of the IMCs layers. The activation energies (Q) for the IMCs layers (Cu6Sn5 + Cu3Sn) were determined to be 36.4 and 39.1 kJ/mol for the SAZ/Cu and SAZ-Al2O3/Cu solders, respectively.

Interfacial IMC growth behavior of Sn-3Ag-3Sb-xIn solder on Cu substrate

PurposeThe reliability of solder joints is closely related to the growth of an intermetallic compound (IMC) layer between the lead-free solder and substrate interface. This paper aims to investigate the growth behavior of the interfacial IMC layer during isothermal aging at 125°C for Sn-3Ag-3Sb-xIn/Cu (x = 0, 1, 2, 3, 4, 5 Wt.%) solder joints with different In contents and commercial Sn-3Ag-0.5Cu/Cu solder joints.Design/methodology/approachIn this paper, Sn-3Ag-3Sb-xIn/Cu (x = 0, 1, 2, 3, 4, 5 Wt.%) and commercial Sn-3Ag-0.5Cu/Cu solder were prepared for bonding Cu substrate. Then these samples were subjected to isothermal aging for 0, 2, 8, 14, 25 and 45 days. Scanning electron microscopy and transmission electron microscopy were used to analyze the soldering interface reaction and the difference in IMC growth behavior during the isothermal aging process.FindingsWhen the concentration of In in the Sn-3Ag-3Sb-xIn/Cu solder joints exceeded 2 Wt.%, a substantial amount of InSb particles were produced. These particles acted as a diffusion barrier, impeding the growth of the IMC layer at the interface. The growth of the Cu3Sn layer during the aging process was strongly correlated with the presence of In. The growth rate of the Cu3Sn layer was significantly reduced when the In concentration exceeded 3 Wt.%.Originality/valueThe addition of In promotes the formation of InSb particles in Sn-3Ag-3Sb-xIn/Cu solder joints. These particles limit the growth of the total IMC layer, while a higher In content also slows the growth of the Cu3Sn layer. This study is significant for designing alloy compositions for new high-reliability solders.

Reactive diffusion at the interface between Cu and Sn–Ag alloys

This study investigates the microstructural evolution and growth behavior of intermetallic compound (IMC) layers in the Cu/(Sn-yAg, y = 0.29–2.00 wt%) system during isothermal aging within the temperature range of 433–473 K. Through systematic variations in Ag content, aging temperature, and time, the fundamental mechanisms governing IMC formation and growth in Cu/(Sn–Ag) solder joints are elucidated. The results demonstrate that IMC growth kinetics follow a power-law relationship, with IMC layer thickness increasing systematically with annealing time. The addition of Ag significantly influences IMC nucleation and growth, with higher Ag content correlating with faster growth rates. Furthermore, the temperature dependence of IMC growth rates is investigated, revealing higher temperatures leading to increased growth rates, indicative of boundary diffusion-controlled growth. By calculating activation enthalpies, values of 36.4 kJ/mol for Sn-2.00Ag and 30.2 kJ/mol for Sn-0.50Ag were obtained, providing quantitative insights into the faster growth rate of intermetallic compound thickness in the Cu/(Sn-2.00Ag) diffusion couple within the experimental temperature range. These findings offer valuable insights into factors affecting the reliability and performance of solder joints in electronic packaging applications.

Intermetallic compound growth behavior and mechanical performance in Sn58Bi/Cu solder joint bearing Mg particles incorporation during thermal aging

The microstructure and intermetallic compound (IMC) growth in Sn58Bi/Cu and Sn58Bi-0.4 Mg/Cu solder joints were examined in this study under varied thermal aging time (6, 12, 18, 24, and 30 h) at 120 °C. The Shear test was conducted to assess the solder joint mechanical performance. The results indicated that the precipitation of the Bi phase in Sn58Bi/Cu and Sn58Bi-0.4 Mg/Cu solder joints was not significantly inhibited by adding Mg as aging time increased. The IMC layer thickness of both solder joints increased as the aging time increased, but the Cu3Sn IMC thickness in Sn58Bi-0.4 Mg/Cu solder joint was consistently thinner than that in Sn58Bi/Cu joint. The temporal evolution of the Cu3Sn IMC layer was investigated, and it was found that the inclusion of Mg particles reduced the diffusion coefficient of Cu3Sn IMC. Furthermore, the shear test revealed that throughout the initial phases of thermal aging, fractures occurred within the solder matrix for both joints. As thermal aging time increased, fractures extended into the IMC layer, accompanied by transgranular and intergranular fractures. Simultaneously, adding Mg particles delayed brittle fracture in the solder joints, enhancing their mechanical properties.

Solid-state interfacial reaction of Sn-Ag solders with polycrystalline Cu and (0 0 1) Cu substrate

• For sn-Ag solder, the growth of Cu 3 Sn on (0 0 1)Cu is faster than on polycrystalline Cu in aging. • Ag increases the difference in Cu 3 Sn thickness on (0 0 1)Cu and polycrystalline Cu in aging. • Ag is beneficial to maintain the preferred orientation of Cu 6 Sn 5 in aging. The growth of Cu 3 Sn is associated with the formation of Kirkendall voids and is important to the reliability of solder joints. In this paper, the effect of Ag on the growth behavior of Cu 3 Sn on (0 0 1) Cu and polycrystalline Cu during aging was compared. Besides, the orientation evolution of Cu 6 Sn 5 on (0 0 1) Cu during aging was also investigated. Results suggested the growth rate of Cu 3 Sn on (0 0 1) Cu is higher than that of polycrystalline Cu during solid-state aging and the difference in the Cu 3 Sn layer thickness increases with the increases of Ag content in the solder. Moreover, the addition of Ag is beneficial to maintaining the preferred orientation of Cu 6 Sn 5 on (0 0 1) Cu during solid-state aging. The results have great help to deepen the understanding of the difference in growth behavior of intermetallic compounds on (0 0 1) Cu and polycrystalline Cu during aging.

Intermetallic Compound Growth Induced by Electromigration in Sn-2.5Ag Solder Joints with ENEPIG Surface Finish

The equation for predicting the growth behavior of intermetallic compounds (IMC) by electromigration (EM) of the Cu/ENEPIG/Sn-2.5Ag/Cu solder joint was modeled, and the actual behavior observed through experiments and the predicted behavior were compared. After reflow, (Cu, Ni)<sub>6</sub>Sn<sub>5</sub> was formed near the ENEPIG/solder interface, and Cu<sub>6</sub>Sn<sub>5</sub> was produced near the solder/Cu interface. Furthermore, Cu<sub>6</sub>Sn<sub>5</sub> islands and Ag<sub>3</sub>Sn were formed with the β-Sn matrix in the solder. The mobility of Cu, Ni, and Sn atoms at the ENEPIG/IMC/solder interface was calculated to derive a thickness variation equation of the IMC with respect to the current application time. The modeling predicted that if the current density was maintained for 250 h at 10 kA/cm<sup>2</sup>, the IMC thickness increased by 4.2 ㎛. As a result of the EM experiment, the IMC at the ENEPIG/solder interface grew by 4.2 ㎛; this exactly matched the prediction. A comparison of the thickness of the IMC layer indicated that the OSP/solder interface produced approximately 9 ㎛, and the ENEPIG/solder interface grew by approximately 4.2 ㎛. Therefore, the Ni plating layer of the ENEPIG surface treatment prevented the diffusion of Cu and suppressed the growth of IMC by approximately 50 %.

Texture and intermetallic compounds of the Cu/Al dissimilar joints by high power ultrasonic welding

The welded joints of copper (Cu) to aluminum (Al) were increasingly being used for electric vehicle battery applications. To better understanding the interface connection mechanism of the Cu/Al joints produced by high power ultrasonic welding (HUSW), the texture and intermetallic compounds of Cu/Al HUSW joints were systematically investigated. The grain morphology and size of pure copper along welding interface had little change with the increasing welding time, whereas the microstructure of aluminum alloy changed from elongated grains to equiaxed grains and the grain size increased rapidly at the welding time from 0.3 s to 0.5 s. The texture intensity of both copper and aluminum alloy decreased at first owing to ultrasonic softening and then increased due to the shear work hardening. The texture type of the copper had little change, whereas the gaussian texture {110}〈110〉 and the cubic rotation texture{001}〈110〉 were formed in aluminum alloy owing to the occurrence of recrystallization driven by the severe shear deformation. The formation mechanism and accelerated growth behavior of intermetallic compounds at the welding interface during HUSW were discussed based on the atom rapid diffusion and the effective thermal formation model.

Interfacial Microstructure and Mechanical Reliability of Sn-58Bi/ENEPIG Solder Joints

The 42 wt.% Sn–58 wt.% Bi (Sn-58Bi) Ball Grid Array (BGA) solder balls were mounted to electroless nickel-electroless palladium-immersion gold (ENEPIG) pads by employing the reflow process profile. The effects of reflow cycles and aging time on the interfacial microstructure and growth behavior of intermetallic compounds, as well as the mechanical properties, were investigated. Pd-Au-Sn intermetallic compound (IMC) was formed at the Sn-58Bi/ENEPIG interface. With the increase in reflow cycles and aging time, the IMC grew gradually. After five reflow cycles, the shear strength of the Sn-58Bi/ENEPIG solder joints first decreased and then increased. After 500 h of aging duration under −40 °C, the shear strength of the Sn-58Bi/ENEPIG solder joints decreased by about 12.3%. The fracture mode transferred from ductile fracture to ductile and brittle mixed fracture owing to the fact that the fracture location transferred from the solder matrix to the IMC interface with the increase in reflow cycles and aging time.

Study of the Growth Behavior of Intermetallic Compounds at the Liquid-Solid Interface of Bal88si/Cu

Study of the Growth Behavior of Intermetallic Compounds at the Liquid-Solid Interface of Bal88si/Cu

The growth behavior of Al2Cu phase in confined spaces constituted by γ–Al2O3 particle clusters

The growth behavior of intermetallic compounds in confined spaces is an interesting research topic as it may differ from conventional growth models. In this work, an Al–15Al2O3 master alloy rod was inserted into an Al–33.2Cu melt. After holding at the selected temperature 640 °C, the rod keeps still in the melt, while Cu atoms diffuse inwards the rod. During the cooling process, wormlike coarse Al2Cu particles were achieved inside the rod. It is regarded that due to the restriction effect of γ–Al2O3 particle clusters the as–constituted confined spaces act as barriers for the growth of Al2Cu.

Quasi-in-situ observation on diffusion anisotropy dominated asymmetrical growth of Cu-Sn IMCs under temperature gradient

Quasi-in-situ method was carried out to observe the growth behavior of intermetallic compounds (IMCs) in Cu/Sn-3.0Ag-0.5Cu/Cu micro solder joints with single β-Sn grain during aging with and without temperature gradient (TG). The bilayer IMCs of Cu6Sn5 + Cu3Sn showed symmetrical growth at both interfaces without TG, proving that β-Sn grain orientation had no effect on interfacial IMC growth during isothermal aging. Many Kirkendall voids were detected due to the dominated growth of Cu3Sn. However, during aging under TG, the IMCs in the joints with different β-Sn grain orientations showed quite different growth behavior and Cu6Sn5 was always the dominant IMC phase with little Cu3Sn and no Kirkendall voids formation. In the joints with small or medium θ angle β-Sn grains, remarkably asymmetrical IMC growth with thick Cu6Sn5 at the cold end and thin discontinuous Cu6Sn5 at the hot end was clarified. Meanwhile, the cold end Cu6Sn5 in medium θ angle joints also presented step-like morphology. The diffusion anisotropy of Cu atoms in β-Sn was responsible for the asymmetrical growth and step-like morphology. In the joints with large θ angle β-Sn grains, the Cu6Sn5 presented similar symmetrical growth to the isothermal aging cases. The different mechanisms of inhibiting Cu3Sn and Kirkendall voids formation at the cold and hot ends were revealed based on TG-induced Cu flux. Finally, a method was proposed to predict the IMC morphology and thickness considering β-Sn grain orientation, which could be helpful for reliability assessment and may also be suitable for IMC growth analyzes under current stressing.

Influences of silicon carbide nanowires’ addition on IMC growth behavior of pure Sn solder during solid–liquid diffusion

In this paper, various mass fractions (0, 0.2, 0.4, 0.6, 0.8, 1.0 wt%) of silicon carbide nanowires (SiC NWs) were incorporated into pure Sn solder to enhance the performances of Sn solder joint. The wetting behavior, shear strength, and intermetallic compound (IMC) growth mechanism of Sn–xSiC/Cu solder during solid–liquid diffusion at 250 °C were investigated systematically. The experimental results demonstrated that the wettability of Sn–xSiC/Cu solder had a significant improvement when the addition of SiC NWs was up to 0.6 wt%, and excessive additives would degrade the wettability of the composite solder. The formation of the Cu6Sn5 IMC layer was observed at the Sn–xSiC solder/Cu interface. Meanwhile, SiC NWs as additives were conducive to restraining the growth of interfacial IMC during soldering process and the IMC thickness overtly fell down after doping 0.8 wt% SiC NWs into Sn solder. Moreover, SiC NW addition would contribute to enhancing the mechanical performance of Sn solder joint. The fracture mechanism of solder joint changed from a mix of brittle and ductile fracture to a characteristic of typical ductile fracture.

Growth Behavior of Intermetallic Compounds in Various Solder Joints Induced by Electromigration

With the development of the fine pitch technology, the size of the solder bumps contacting the chip and the substrate has decreased, thereby significantly increasing the current density. As a result, intermetallic compounds (IMCs) are formed in solder bumps, and the formation/growth of Kirkendall voids is the main reason for failure, which is accelerated by electromigration. Therefore, various studies have been conducted to restrain the growth of IMCs and Kirkendall voids. This study summarizes the issues that should be considered when investigating the effects of electromigration on solder joints. The prediction and observation of the growth behavior of the IMCs is summarized for various solder bump joints. In addition, we provide an effective method for assisting the fine pitch technology. Key words: Electromigration, Solder bump joints, Intermetallic compounds, Kirkendall voids, Modeling

Significant effect of orientation on Cu6Sn5 coarsening behavior in isothermal aging process

Intermetallic compound (IMC) formed on (001) and (111) Cu single crystal has strong orientation and texture characteristics. The special interface morphology and uniform orientation provide a direction for the regulation of IMC growth behavior. In this study, the significant effect of orientation on Cu6Sn5 growth behavior in isothermal aging process was investigated. Synchrotron radiation technology and high pressure air blowing methods were employed to obtain the growth kinetics and the morphology of Cu6Sn5 during the heat preservation stage. The results indicate that scallop-like Cu6Sn5 grains were formed in heat preservation stage. These grains exhibited an abnormal coarsening behavior that their average diameter at a high temperature of 300 °C was smaller than that at a low temperature of 250 °C after aging for 30 min. Besides, the growth orientation and kinetic controlling factor of these interfacial Cu6Sn5 also changed with the increase of reaction time, which was closely related to the appearance of the abnormal coarsening phenomenon. These results are significant and meaningful to the electronic packaging industry.

Effect of Graphene Nanosheet Addition on the Wettability and Mechanical Properties of Sn-20Bi-xGNS/Cu Solder Joints.

Graphene nanosheets (GNSs) have an extensive application in materials modification. In this study, the effects of graphene nanosheets on the wettability of Sn-20Bi lead-free solder on copper (Cu) substrate and the growth behavior of intermetallic compound (IMC) layers at Sn-20Bi-xGNS/Cu solder joints were investigated. The experimental results indicate that the wettability of Sn-20Bi solder firstly diminished and then increased by the addition of GNSs. Meanwhile, a prism-shaped and scallop-shaped Cu6Sn5 IMC layer was clearly observed at the interface of the solder/substrate system. Moreover, it was found that a small amount of GNS addition can significantly inhibit the growth of the IMC layer at the interface as well as refine the microstructure. Additionally, by nano-indentation apparatus, it can be concluded that the hardness and elastic module of IMCs show the same variation trend, which firstly decreased and then increased. Besides, to intuitively demonstrate the reliability of IMCs, the relationship between the hardness and elastic module was established, and the ratio of hardness/elastic module (H/E) was adopted to characterize the reliability of IMCs. The results show that when the addition of GNSs was 0.02 wt%, the value of H/E is the minimum and the solder joint has the highest reliability.

Influence of External Interface Normal Stress on the Growth of Cu–Sn IMC During Aging

A U-shape clamp was designed to apply stress perpendicular to the interface of Cu/Sn/Cu solder joints, and its influence on the growth behavior of Cu–Sn intermetallic compound (IMC) during thermal aging at 150 °C was investigated. The results show that compared with the sample at general stress-free state, the growth rate of IMC under compression is faster, while that under tension is slower. Moreover, the interface between IMC and Sn is smoother under compressive stress, and the corresponding IMC grains are smaller and more uniform than that under tensile stress. According to the growth kinetic analysis, the growth of IMC under general, compressive and tensile states is all controlled by the combination of grain boundary diffusion and volume diffusion with a similar growth exponent (n ≈ 0.4). However, external stress can affect the Ostwald ripening process of grain growth, causing a change of grain size and grain boundary density in the IMC layer. As a result, the IMC growth behavior at the interface of the solder joint will be affected by the applied external normal stress.

Evolution of interface and tensile properties in 5052 aluminum alloy/304 stainless steel rotary friction welded joint after post-weld heat treatment

The inhomogeneous properties of 5052 aluminum alloy/304 stainless steel rotary friction welded joint and the growth behavior of intermetallic compound (IMC) layer were investigated. The ultimate tensile strength (UTS) of as-welded joint in 0R location with discontinuous IMC layer reached the maximum value of 203 MPa, and that in R/2 and 3R/4 locations decreased with the increase of IMC layer thickness, but that in R/4 location was the lowest due to the initiation of crack. After post-weld heat treatment at 250 °C/20 min, the thickness of IMC layer remained invariant, but the UTS of entire joint increased from 153 MPa to 161.4 MPa. In addition, the difference of UTS along the radius direction decreased, which benefited the engineering application. During post-weld heat treatment at 450 °C, the growth of IMC layer in R/4, R/2 and 3R/4 location were faster than that in 0R location. However, the growth of IMC layer deviated from parabolic law, which was attributed to (i) a large number of dislocations, grain boundaries and storage energy in the interface, (ii) the linear growth of Fe4Al13 phase, and (iii) the effect of Cr element.

Fracture behavior and mechanical strength of sandwich structure solder joints with Cu–Ni(P) coating during thermal aging

Coating at the interface of solder joint has a great impact on the growth behavior of intermetallic compounds (IMCs) and the mechanical properties. In this study, the sandwich structure samples of Cu/Sn3.0Ag0.5Cu/Cu solder joints with coatings of Ni(P) monolayer and dual Cu–Ni(P) layers on Cu substrate were designed to conduct the shear test. The mechanical strength, fracture modes, and fractographic morphologies of Sn3.0Ag0.5Cu/Cu, Sn3.0Ag0.5Cu/Ni(P)–Cu, and Sn3.0Ag0.5Cu/Cu–Ni(P)–Cu solder joints reflowed at 280 °C for 10 min and then aged at 150 °C for up to 360 h were investigated. Experimental results show that the mechanical strength of Sn3.0Ag0.5Cu/Cu solder joints firstly increased because of the pinning effect of IMC, and then decreased due to the brittleness of excessive growth of IMC during solid-state aging processes. The Sn3.0Ag0.5Cu/Cu solder joints presented ductile fracture, mixed fracture, and brittle fracture modes during shear testing processes. The shear strength of Sn3.0Ag0.5Cu/Ni(P)–Cu solder joints decreased to about 17 MPa after 120 h thermal aging. At the same time, the shear failure mode of Sn3.0Ag0.5Cu/Ni(P)–Cu solder joints changed from the ductile dominant fracture to the brittle dominant fracture. The shear strength of Sn3.0Ag0.5Cu/Cu–Ni(P)–Cu solder joints remained approximate 21 MPa and the fractured position always occurred inside the IMC layer regardless of aging time.

Effect of Sn surface diffusion on growth behaviors of intermetallic compounds in cu/Ni/SnAg microbumps

The growth behaviors of intermetallic compounds (IMCs) in Cu pillar solder bumps during high temperature aging were studied by microstructural observations and mathematical calculations. Different from larger solder joints, in microbumps, surface diffusion becomes much more significant when considering IMCs growth. With transmission electron microscope (TEM), lateral Ni3Sn4 (near the interface between Ni3Sn4/Ni), sidewall Ni3Sn2 (on the surface of Ni barrier) and sidewall Cu3Sn (around the surface of copper pillar) are observed for Sn atoms diffusion. In our model, we assume that the growth area of lateral Ni3Sn4 equals that of Ni3Sn4 layer, and the growth constant for lateral Ni3Sn4, which can be calculated, is about 0.0257 μm/h1/2. Based on experimental results and diffusion theory, formation mechanisms of IMCs in microbumps are proposed. The extra growth of IMCs caused by surface diffusion can be a potential failure hazard in high-density electronic packaging.