Intermetallic Compounds In Joints Research Articles

Role of Cr addition in Ni-based interlayer on strengthening titanium and steel dissimilar bimetallic structures enabled by directed energy deposition with laser beam

For searching alternative strategies to improve reliability of titanium and steel dissimilar bimetallic joints manufactured by directed energy deposition with laser beam (DED-LB), pure titanium was considered as cladding deposited on carbon steel substrate with Ni-based alloy interlayers in this work. Effect of different interlayer modification methods on the microstructure evolution and mechanical properties of joints was analyzed systematically. The distribution of intermetallic compounds (IMCs) such as β-Ti, Ti2Ni, TiNiFe0.2, Ti2Ni3Si and TiB2 in joints was revealed. The results showed that original deposition cracks caused by residual stress during processing could be alleviated by substrate preheating treatment while suppressed by the modified interlayer with Cr completely. Notably, additional Cr could reduce reaction activity between Ti and Ni atoms by raising laser molten pool liquidus, leading to fewer IMCs in joints. As a result, both bonding strength and toughness of joints were remarkably improved. The findings emphasize more significance of optimizing Ni-based interlayer composition with Cr than preheating method to improve the mechanical performance of DED-LB joints.

Applications of Ni and Ag metallizations at the solder/Cu interfaces in advanced high-power automobile interconnects: An electromigration study

An advanced Pb-free solder interconnect, Cu line/Cu pillar/Ni/Sn1.8Ag/Ag/Cu lead frame/Sn3Ag0.5Cu/Au/Ni(P)/Cu trace, using the flip-chip quad flat no‑lead (FCQFN) packaging technology was designed for high-power automobile applications. An electromigration study revealing the Ni and Ag metallization effects on the interfacial reaction was investigated. Current stressing was conducted at a 2 A direct current at 160 °C until the defined 200 %-electrical-resistance-rise failure occurrence. Electromigration induced a two-stage electrical resistance increase mode in the advanced automobile test vehicle with a mechanism transition time of 585 h, as evidenced by the in situ resistance monitoring. Phase transformation from the constituent phases into the predominant (Cu,Ni)6Sn5 and Cu3Sn intermetallic compounds (IMCs) at the interfaces was proposed to explain the rapid resistance rise in the early-stage electromigration. Void formation and coalescence due to the Kirkendall effect and volume shrinkage during the phase transformation were proposed to explain the following steady resistance increase after the critical current stressing time. Furthermore, the phase transformation and growth of the IMCs behaved divergently at different interfaces and electron flow directions. The rapid phase transformation occurred in the downstream Sn1.8Ag solder interconnect due to the accelerated Ni metallization dissolution and formed a complete IMC joint. The anisotropic diffusion driven by the competitive or synergetic effect between the electron wind force and chemical potential gradient was proposed to explain the asymmetric microstructures after the electromigration experiment. The application of Ag metallization benefited the flip-chip soldering process, and the layer-type Ag3Sn IMC served as a diffusion barrier against Sn/Cu interdiffusion at the solder/Cu lead frame interface during the solid-state electromigration. In contrast, the Ni metallization was designed as a diffusion barrier to hinder interdiffusion and the undesirable Cu3Sn growth at the solder/Cu interface. The findings presented in this study could benefit the solder interconnect design with an appropriate metallization combination against undesirable electromigration failure.

Optimizing temperature gradient for rapid fabrication of Cu/Sn/Cu full intermetallic compounds joints via vacuum thermal compression bonding

Optimizing temperature gradient for rapid fabrication of Cu/Sn/Cu full intermetallic compounds joints via vacuum thermal compression bonding

Microstructural and mechanical characteristics of Cu-Sn intermetallic compound interconnects formed by TLPB with Cu-Sn nanocomposite

Transient liquid phase bonding (TLPB) is a promising technology for three-dimensional integration of circuits (3D IC), but it can be slow and less productive. A novel Cu-Sn nanocomposite interlayer (Cu-Sn NI) composed of Sn matrix with an embedded Cu nanowire array prepared by electrodeposition can significantly accelerate the bonding process, approximately by 20 times. Bonding time with a Cu-Sn NI can be as short as ~2 min to achieve a full Cu-Sn intermetallic compound (IMC) joints, whereas it can take ~60 min with a pure Sn interlayer of the same thickness under the same bonding conditions (250 °C). Unlike the columnar Cu 6 Sn 5 grains commonly formed with Sn interlayer, refined equiaxed Cu 6 Sn 5 grains with an average size of ~1.6 µm are found to be formed with Cu-Sn NI. Such grain refinement has significantly contributed to the improvement of shear strength of IMC joints formed with Cu-Sn NI (23.1 ± 3.3 MPa), higher than those bonded with pure Sn interlayer (17.9 ± 2.1 MPa). The underlying mechanisms of the new TLPB process and the formation of finer microstructure when bonding with Cu-Sn NIs are also illuminated and validated based on the experimental observation. • A unique Cu-Sn nanocomposite interlayer with Cu nanowire array embedded in Sn. • TLPB with this layer is >20 times faster than conventional Cu-Sn TLPB. • IMC joint bonded with this layer possesses refined equiaxed Cu 6 Sn 5 grains. • Strength of IMC joint bonded with this layer is higher than pure Sn layer. • Clarified the growth mechanisms of IMC in the joints bonded with this layer.

Defect formation and mitigation in Cu/Cu joints formed through transient liquid phase bonding with Cu-Sn nanocomposite interlayer

Joining based on transient liquid phase bonding (TLPB) has a great prospect in microelectronic packaging. However, this process is plagued with its low throughput. In this work, we designed and utilised a preformed Cu-Sn nanocomposite interlayer (Cu-Sn NI) to speed up the TLPB process. Comparing with the uses of a Sn interlayer only, the preformed Cu-Sn NI enabled the bonding process to be accelerated by >20 times. Furthermore, instead of columnar Cu6Sn5 grains, Cu-Sn intermetallic compounds joints formed with Cu-Sn NIs were mostly filled by refined equiaxed Cu6Sn5 grains with an average size of ~1.6 μm. As a result, the shear strength of IMC joints achieved with Cu-Sn NI was found to be higher than those bonded with Sn interlayer. However, various kinds of defects, one of the main drawbacks in TLPB, were still found from this unique bonding process, which is likely to deteriorate the performances and long-term reliability of resultant TLPB joints. This study aims to observe and analyse various defects formed during TLPB with Cu-Sn NI, hence propose possible mitigation solutions to prevent their occurrence and consequently improve the reliability of the joints obtained by TLPB with Cu-Sn NIs.

Study on the evolution of interfacial (Cu,Ni)6Sn5 and shear property of (111)Cu/Sn/Ni micro joints under isothermal and TG-bonding

Single-crystal Cu can be potentially applied as pad or micro bump in bonding technology for advanced packaging. A novel bonding method with an extra temperature gradient (TG, TG-bonding) was carried out to bonding single-crystal (111)Cu and poly-crystal Ni substrates with Sn as interlayer. The morphology and orientation evolution, elemental distribution and growth kinetics of interfacial (Cu,Ni)6Sn5 intermetallic compound (IMC) in (111)Cu/Sn/Ni micro joints during isothermal and TG-bonding were investigated. Regular roof-type (Cu,Ni)6Sn5 grains along three intersectant directions with an angle of 60° formed at the initial Sn/(111)Cu interface and maintained the roof-type morphology with (112‾0) preferred orientation throughout the isothermal bonding. For TG-bonding, TG-induced atomic thermomigration (TM) and Cu–Ni cross-interaction co-played a critical role in the morphology, grain feature and growth kinetics of the interfacial IMCs. Moreover, rapid growth of (Cu,Ni)6Sn5 phase was achieved by TG-bonding with (111)Cu as hot end to fabricate full IMC joints which had higher shear strength than the cases of isothermal and TG-bonding with (111)Cu as cold end. The proposed method would provide a further insight for developing bonding technology for advanced packaging.

Controlling the distribution of porosity during transient liquid phase bonding of Sn-based solder joint

The rapid growth of (Cu,Ni)6Sn5 intermetallic compounds (IMCs) when Sn reacts with Cu containing 6 wt%Ni (Cu-6Ni) offers huge potential for resolving the lengthy transient liquid phase (TLP) processing time. However, the uncontrolled formation of voids at the centre of the joint remains a serious issue. Therefore, we have studied the influence of different Ni concentrations (0, 2 and 6 wt%) in the Cu substrate and the relative location of the porosity when reacting with Sn-0.7Cu solder in the sandwich structure of the joint. Through in-situ X-ray microradiography, the changes in the void positions and the reaction time required to form the IMC joints was interpreted with reference to growth kinetics equations. The results indicate that the different growth rates of (Cu,Ni)6Sn5 and Cu6Sn5 IMCs due to the different Ni concentrations of the Cu-Ni substrates can control the location of the porosity and influence the shear strength of the TLP lap joint. This discovery is a potential gateway to developing reliable electronic interconnects for the power device industry.

Microstructure evolution and mechanical properties changes during the formation of full Cu41Sn11 joint in high-temperature electronic packaging

In this study, Cu/Sn/Cu structure under a pressure of 1.5 N was soldered at 390–450 °C. Then, microstructure evolution and changes in mechanical properties of solder joint during the formation of full Cu41Sn11 joint were systematically analyzed. Experimental results showed that Cu6Sn5 and Cu3Sn were observed in the interfacial region at 420 °C in the early stage of soldering. The Cu/Sn/Cu structure completely transformed into Cu/Cu3Sn/Cu at 1 h. With the further progress of the interfacial reaction, Cu41Sn11 appeared and grew at the expense of Cu3Sn. Eventually, the full Cu41Sn11 joint was formed at 10 h. The growth of Cu41Sn11 was controlled by volume-diffusion. Moreover, diffusion activation energy of Cu41Sn11 was about 108.19 kJ/mol. The shear strength of full Cu3Sn joints was 45 MPa, while that of the solder joints with 25, 50, 75 and 100% Cu41Sn11 was 50, 52.2, 59 and 64.5 MPa, respectively. For full Cu3Sn and full Cu41Sn11 joints, respectively, the fracture occurred partly within intermetallic compounds (IMCs) layers and partly along the Cu/IMC interface. However, for the joints composed of Cu3Sn and Cu41Sn11, all fractures occurred in the IMCs layer. Besides, all IMCs joints were brittle fracture, and the fracture of Cu3Sn was mainly intergranular, while the fracture that occurred in Cu41Sn11 was mainly transgranular.

In-depth evaluation of laser-welded similar and dissimilar material tab-to-busbar electrical interconnects for electric vehicle battery pack

A recent increase in the use of electric vehicles demands an efficient and faster joining process for making electrical interconnects within the battery pack. The choice of tab and busbar materials to produce those electrical interconnects is mainly based on weldability, weight, electrical/ thermal conductivity and cost. To meet the high joining demand and low cycle time, laser welding is emerging as the main joining technology due to its ability to weld a variety of materials at a high speed. This paper investigates laser overlap welding for producing similar and dissimilar material tab-to-busbar interconnects for Li-ion battery assembly. In this research, 0.3 mm Al, Cu, Cu[Ni] and Ni tabs were welded with 1.5 mm Al and Cu busbars using a 150 W pulsed fibre laser system integrated with a wobble head. The weldability and joint suitability analyses were conducted by evaluating joint strength, joint intermetallic compound (IMC) formation, joint resistance and temperature rise with the aim of developing a better and safer battery system. It was observed that a maximum joint strength of 930 N was obtained from the Ni tab to Al busbar joints which was approximately 109%, 44% and 66% more than the strength obtained for Al, Cu[Ni] and Cu tab to Al busbar joints respectively. In the case of Cu busbar based tab connections, the maximum joint strength (1320N) was obtained from the Ni tab, which is 152%, 71% and 76% more than Al, Cu[Ni], and Cu tab to Cu busbar joint strength respectively. The strength obtained for the Cu tab to Al busbar (about 560 N) was slightly more than the Al tab to Cu busbar (about 520 N) due to the formation of CuAl 2 IMCs at the weld interface of Al tab to Cu busbar joints. Weld microstructure studies provided insightful information on under-weld, good-weld and over-weld characterisation with respect to IMC formation and correlated with the joint strength. In addition, electrical resistance and temperature rise at the joint are equally important for electric vehicle battery applications. The change in contact resistance and joint temperature rise was measured simultaneously for 180 s at different amplitudes of current (i.e., 100 A, 150 A and 200 A) passed through the joints. • Joining and selection of suitable tab and busbar materials for producing electrical interconnects for EV batteries • In-depth analysis on laser-welded Al, Cu, Cu[Ni] and Ni tab to Al and Cu busbar joints were performed • Joint suitability analyses were conducted by evaluating joint strength, intermetallic, resistance and temperature rise • The results on critical-to-quality criteria should guide the battery manufacturers to design an efficient battery system

Vacuum Brazing of C/C Composite and TiAl Intermetallic Alloy Using BNi-2 Brazing Filler Metal.

C/C composite was brazed to TiAl intermetallic compound using a commercial BNi-2 brazing filler metal under vacuum brazing condition. The brazing temperature was 1030~1150 °C and the holding time was 20 min. The joint interfacial microstructures and mechanical properties were studied, and the fracture behavior and joining mechanism were also investigated. The effect of brazing temperature on the joint shear strength was explored. The results showed that a perfect interface joint can be obtained by using BNi-2 to braze C/C and TiAl. During brazing, Ti, Cr, and other carbide forming elements diffused to C/C composite side, forming Cr3C2, Cr7C3, TiC, and other carbides, and realizing metallurgical joining between the brazing filler metal and C/C composite. The microstructure of the interface of C/C composite and TiAl intermetallic compound joint is as follows: TiAl alloy → TiAl + AlNi3 → AlNi2Ti → Ni(s, s) + Ti3Al + Ni3Si → Ni(s, s) + Ni3(Si, B) + CrB → Ni(s, s) + Ni3Si + TiCr2 → (Ti, Cr)C → C/C composite. When the holding time is fixed, with the increase of brazing temperature, the shear strength of the joint increases first and then decreases. The maximum average room temperature shear strength of the brazed joint was 11.62 MPa, while the brazing temperature was 1060 °C and the holding time was 20 min.

Effect of Isothermal Aging and Copper Substrate Roughness on the SAC305 Solder Joint Intermetallic Layer Growth of High Temperature Storage (HTS)

This study aims to evaluate the effect of copper (Cu) substrate surface roughness on the intermetallic compound (IMC) growth and interfacial reaction of SAC305 lead-free solder joint after undergone an aging process. Aging process was conducted using high temperature storage (HTS) at temperature of 150 °C and aging times of 200, 400, 600, 800, and 1000 h. IMC morphology and growth were examined using infinite focus microscope (IFM). Then, the SAC305 solder joint IMC growth kinetic was measured based on power law relationship and diffusion coefficient formula. It was noted that the morphology of IMC for the rougher Cu substrate has scallop-shaped and uniform layer as compared to that of smoother Cu substrate for the initial exposure to the HTS. In addition, Cu substrate with Ra of 579 nm is the turning point for the creation of Cu6Sn5 towards more Cu3Sn of IMC. In addition, Cu substrate with Ra of 579 nm also acts as the turning point for the IMC growth of SAC305 solder joint on Cu substrate for the solid-state diffusion to be happened during 150 °C of aging from grain boundary dominant toward volume diffusion dominant.

Preparation and sintering properties of Cu10Sn3 IMCs nanopaste as die attach material for high temperature power electronics

Cu10Sn3 intermetallic compound (IMC) nanoparticles (NPs) were synthesized by one-step thermal decomposition method with low cost. The in-situ formed metal amide in the presence of LiN(iPr)2 can be reduced and thermally decomposed into metal NPs, and then the Cu10Sn3 NPs were obtained, which have an average diameter of 65 nm and good oxidation resistance. The microstructures and mechanical properties of Cu/Cu10Sn3/Cu joints at different sintering temperatures were investigated. The full-Cu10Sn3 IMC joints show high shear strength of 26.8 MPa after sintering at 300 °C for 20 min, demonstrating its broad potential as an interconnect material for high-temperature power electronics.

Precipitation of intermetallic compounds in brazing of titanium and steel using brass filler

Abstract The effect of carbon content on the precipitation and distribution of intermetallic compounds in titanium to decarbonized carbon steel brazed joint was studied. In this work, decarbonization treatment was employed to change the carbon content in the low carbon steel surface and thus influence the diffusion behavior of Ti and Fe elements in the joint. The microstructure, fracture surface and bonding strength of joints were detected by SEM/EDS, XRD and shear strength test. As a result, rich-carbon state in the steel surface profited the bonding of dissimilar joint to some extent during brazing process. TiC generated near carbon steel side can improve the bonding strength of joints by hindering the precipitation of FeTi and Fe2Ti. Precipitation and distribution of TiC, FeTi and Fe2Ti intermetallic compounds in joints were investigated.

GTA Weld Brazing a Joint of Aluminum to Stainless Steel

The relationship between heat input, microstructures, and mechanical properties was studied in the gas tungsten arc (GTA) weld brazing process of aluminum alloy and stain-less steel dissimilar metals with a pure aluminum core wire (ER1100). The mechanisms involved were further revealed by hot-dip aluminizing experiments. The intermetallic compounds (IMCs) of the brazing interface consisted of a thin layer of -Fe2Al5 next to the steel, and a thick layer of -Fe4Al13 adjacent to the Al joint, surrounded by eutectic identified to be Al-FeAl6 and Al-Fe2Al9 distributed uniformly in the weld metal. With increasing heat input, the total thickness of the IMCs decreased first, reaching a minimum value of 3.5 m, and then increased. The decrease in IMC thickness with heat input was observed for the first time and had never been reported before in welding or brazing processes. The joint strength increased to a maximum value of 238 MPa and then declined, suggesting an inverse relationship between IMC thickness and joint strength. The results of the hot-dip aluminizing, regarding the relationship between IMC thickness and temperature, were consistent with the change of IMC thickness in the welds. A possible mechanism in action is that interfacial kinetics and thermodynamics play a role in the dissolution and decomposition of the thick layer of -Fe4Al13 into the FeAl6 and Fe2Al9 phase. Promoting the IMC dissolution or decomposition by adjusting welding procedures is a promising new way to control the IMC growth and improve the joint strength.

The thermal cycling reliability of copper pillar solder bump in flip chip via thermal compression bonding

In this paper, the thermal-mechanical reliability of flip chip on board (FCOB) with copper pillar solder joint is investigated. By increasing the temperature and time of the thermal compression bonding (TCB) process, the copper pillar solder joint with intermetallic compound (IMC) as the main body is obtained. Then the Cu pillar/Sn-Ag/Cu pad and Cu pillar/IMC/Cu pad joint structures are carried out the thermal cycling test separately. It is observed that the crack of the Sn-Ag solder joint caused by ductile fracture, which is leaded by fatigue and then extension through microvoids caused by creep. And the crack of IMC joint is mainly caused by the brittle fracture along the Cu6Sn5 and Cu3Sn phase interface. At the same time, two constitutive of viscoplasticity and elastic-plastic-creep and life prediction models are compared. The effect of underfill on the thermal-mechanical reliability of copper pillar solder joint is evaluated by comparing the underfills filled with different weight ratio filler particles.

Nickel–tin transient liquid phase sintering with high bonding strength for high-temperature power applications

We performed 30Ni–70Sn (wt%) transient liquid phase sintering (TLPS) bonding with micro-sized Ni and Sn powders for high-temperature power applications. A Ni–Sn paste was fabricated and TLPS bonding was performed. We investigated the interfacial reactions, transformations into Ni3Sn4 intermetallic compound (IMC) phases, and joint strength in this study. The Ni–Sn TLPS bonding was an easy and simple process under a relatively low bonding temperature and short bonding time. After TLPS bonding, low melting point Sn element was completely consumed, and the bonded joint was composed of Ni3Sn4 IMCs and the remaining Ni particles. The Ni3Sn4 IMC joint formed with remaining Ni particles was very stable. All the Ni–Sn TLPS samples had high shear strengths of over 70 MPa, and the shear strength was approximately 32% higher than that of the conventional Sn–3.0Ag–0.5Cu solder joint. The Ni–Sn TLPS bonded joints in the present study were not brittle and exhibited superior adhesion strength. This suggests high applicability of the Ni–Sn TLPS bonding for high-temperature power electronic applications in future EV/HEV systems.

Microstructure evolution and growth behavior of Cu/SAC105/Cu joints soldered by thermo-compression bonding

Purpose This paper used a novel technique, which is thermo-compression bonding, and Sn-1.0Ag-0.5Cu solder to form a full intermetallic compound (IMC) Cu3Sn joints (Cu/Cu3Sn/Cu joints). The purpose of the study is to form high-melting-point IMC joints for high-temperature power electronics applications. The study also investigated the effect of temperature gradient on the microstructure evolution and the growth behavior of IMCs. Design/methodology/approach In this paper, the thermo-compression bonding technique was used to form full Cu3Sn joints. Findings Experimental results indicated that full Cu/Cu3Sn/Cu solder joints with the thickness of about 5-6 µm are formed in a short time of 9.9 s and under a low pressure of 0.016 MPa at 450°C by thermo-compression bonding technique. During the bonding process, Cu6Sn5 grew with common scallop-like shape at Cu/SAC105 interfaces, which was followed by the growth of Cu3Sn with planar-like shape between Cu/Cu6Sn5 interfaces. Meanwhile, the morphology of Cu3Sn transformed from a planar-like shape to wave-like shape until full IMCs solder joints were eventually formed during thermo-compression bonding process. Asymmetrical growth behavior of the interfacial IMCs was also clearly observed at both ends of the Cu/SAC105 (Sn-1.0Ag-0.5Cu)/Cu solder joints. Detailed reasons for the asymmetrical growth behavior of the interfacial IMCs during thermo-compression bonding process are given. The compound of Ag element causes a reduction in Cu dissolution rate from the IMC into the solder solution at the hot end, inhibiting the growth of IMCs at the cold end. Originality/value This study used the thermo-compression bonding technique and Sn-1.0Ag-0.5Cu to form full Cu3Sn joints.

Stress analysis and structural optimization of 3-D IC package based on the Taguchi method

PurposeThe transistor circuit based on Moore's Law is approaching the performance limit. The three-dimensional integrated circuit (3-D IC) is an important way to implement More than Moore. The main problems in the development of 3-D IC are Joule heating and stress. The stresses and strains generated in 3-D ICs will affect the performance of electronic products, leading to various reliability issues. The intermetallic compound (IMC) joint materials and structures are the main factors affecting 3-D IC stress. The purpose of this paper is to optimize the design of the 3-D IC.Design/methodology/approachTo optimize the design of 3-D IC, the numerical model of 3-D IC was established. The Taguchi experiment was designed to simulate the influence of IMC joint material, solder joint array and package size on 3-D IC stress.FindingsThe simulation results show that the solder joint array and IMC joint materials have great influence on the equivalent stress. Compared with the original design, the von Mises stress of the optimal design was reduced by 69.96 per cent, the signal-to-noise ratio (S/N) was increased by 10.46 dB and the fatigue life of the Sn-3.9Ag-0.6Cu solder joint was increased from 415 to 533 cycles, indicating that the reliability of the 3-D IC has been significantly improved.Originality/valueIt is necessary to study the material properties of the bonded structure since 3-D IC is a new packaging structure. Currently, there is no relevant research on the optimization design of solder joint array in 3-D IC. Therefore, the IMC joint material, the solder joint array, the chip thickness and the substrate thickness are selected as the control factors to analyze the influence of various factors on the 3-D IC stress and design. The orthogonal experiment is used to optimize the structure of the 3-D IC.

Effect of electric current on grain orientation and mechanical properties of Cu-Sn intermetallic compounds joints

Electric current-assisted bonding experiments have been performed on Cu/Sn/Cu joints using an electric current density of 2.0 × 102 A/cm2 at 260 °C. The effect of electric current on the grain orientation of Cu–Sn intermetallic compounds (IMCs) and mechanical properties of Cu/Sn/Cu joints were evaluated. The scanning electron microscopy (SEM) observation indicated that the electric current had obvious polarity effect on Cu6Sn5 growth. The Electron backscatter diffraction (EBSD) analysis revealed that Cu6Sn5 showed a preferred orientation of [0001] direction being parallel to the electric current. On the contrary, the morphology and grain orientation of Cu3Sn were barely influenced under the electric current density of 2.0 × 102 A/cm2. The calculation results indicated that the Cu6Sn5 (0001) plane showed the lowest projection atomic density of 27.9 atoms/nm2. Therefore, the Cu6Sn5 grains with their [0001] directions oriented along electric current could grow faster because of smaller electron wind force and greater Cu atom flux. The results of nanoindentation experiment and shear test also proved that the full-Cu6Sn5 joints formed under electric current had lower Young's modulus mismatch between Cu6Sn5 and Cu3Sn, and had a joint shear strength of 44.87 MPa. The present work offers a method to adjust the texture of Cu–Sn IMCs in the joints for achieving better electrical and mechanical properties.

Morphology transformation on Cu3Sn grains during the formation of full Cu3Sn solder joints in electronic packaging

PurposeThis paper aims to analyze the morphology transformation on the Cu3Sn grains during the formation of full Cu3Sn solder joints in electronic packaging.Design/methodology/approachBecause of the infeasibility of analyzing the morphology transformation intuitively, a novel equivalent method is used. The morphology transformation on the Cu3Sn grains, during the formation of full Cu3Sn solder joints, is regarded as equivalent to the morphology transformation on the Cu3Sn grains derived from the Cu/Sn structures with different Sn thickness.FindingsDuring soldering, the Cu3Sn grains first grew in the fine equiaxial shape in a ripening process until the critical size. Under the critical size, the Cu3Sn grains were changed from the equiaxial shape to the columnar shape. Moreover, the columnar Cu3Sn grains could be divided into different clusters with different growth directions. With the proceeding of soldering, the columnar Cu3Sn grains continued to grow in a feather of the width growing at a greater extent than the length. With the growth of the columnar Cu3Sn grains, adjacent Cu3Sn grains, within each cluster, merged with each other. Next, the merged columnar Cu3Sn grains, within each cluster, continued to merge with each other. Finally, the columnar Cu3Sn grains, within each cluster, merged into one coarse columnar Cu3Sn grain with the formation of full Cu3Sn solder joints. The detailed mechanism, for the very interesting morphology transformation, has been proposed.Originality/valueFew researchers focused on the morphology transformation of interfacial phases during the formation of full intermetallic compounds joints. To bridge the research gap, the morphology transformation on the Cu3Sn grains during the formation of full Cu3Sn solder joints has been studied for the first time.