Solder Interface Research Articles

Core-Sheath Heterogenous Interlocked Stretchable Conductive Fiber Induced by Adhesive MXene Modulated Interfacial Soldering.

Whereas high electrical conductivity and mechanical stretchability are both essentially required for flexible electronics, simultaneously achieving them remains a great challenge due to the "trade-off" effect. Herein, an ultrastretchable conductor with core-sheath heterogeneous interlocked structure was developed, induced by interfacial soldering silver nanowires (AgNWs) which gradually evolved into elastic conductive fiber. Adhesive polydopamine-functionalized MXene (PDM) was proposed as an interfacial solder to assemble AgNWs along fibers while induced strong cold-welding effect soldered them into superelastic interconnected network. In situ coaxial heterogeneous interlocking between core AgNWs and sheath PDM network gradually formed during the interfacial soldering process, which enables elastic conductor simultaneously owning large mechanical stretchability and high electrical conductivity. Stretchable conductive fiber with core-sheath heterogeneous interlocking structure not only exhibits excellent electrical conductivity (1.13 × 105 S/m) but also could maintain stability (ΔR/R0 < 0.19) even under large mechanical deformations (300%). Ultrastretchable fibrous conductor with core-sheath heterogeneous interlocked microstructure induced by adhesive PDM interfacial soldering holds great promise in soft electronics.

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.

Effects of Ni addition on wettability and interfacial microstructure of Sn-0.7Cu-xNi solder alloy

Purpose This paper aims to study the effect of different Ni content on the microstructure and properties of Sn-0.7Cu alloy. Then, the spreading area, wetting angle, interface layer thickness and microstructure of the soldering interface was observed and analyzed at different soldering temperatures and times. Design/methodology/approach Sn-0.7Cu-xNi solder alloy was prepared by a high-frequency induction melting furnace. Then Sn-0.7Cu-xNi alloy was soldered on a Cu substrate at different soldering temperatures and times. Findings It was found that Ni made the intermetallic compounds in the Sn-0.7Cu solder alloy gradually aggregate and coarsen, and the microstructure was refined. The phase compositions of the solder alloy are mainly composed of the ß-Sn phase and a few intermetallic compounds, Cu6Sn5 + (Cu, Ni)6Sn5. The maximum value of 12.1 HV is reached when the Ni content is 0.1 Wt.%. When the Ni content is 0.5 Wt.%, the wettability of the solder alloy increases by about 15%, the interface thickness increases by about 8.9% and the scallop-like structure is the most refined. When the soldering time is 10 min and the soldering temperature is 280 °C, the wettability of Sn-0.7Cu-0.2Ni is the best. Originality/value It is groundbreaking to combine the change in soldering interface with the soldering industry. The effects of different soldering temperatures and times on the Sn-0.7Cu-xNi alloy were studied. Under the same conditions, Sn-0.7Cu-0.2Ni exhibits better wettability and more stable solder joint stability.

High performance Cu/SAC305 solder low temperature bonding using Ti3C2 MXene interlayer

Ti3C2 MXene (MX) was introduced as the interlayer between the Cu film and Sn-3.0Ag-0.5Cu (SAC) solder to inhibit the overgrowth of intermetallic compounds (IMCs) at the bonding interface of Cu and SAC solder. The Cu-MX-SAC bonding was fabricated at 160 °C for 6 mins under a load of 10 MPa. Compared with Cu-SAC bonding, after 72 h aging, the average thickness of the IMCs layer in the Cu-MX-SAC structure is about 47 % thinner. As aging time increases, the diffusion rate of Cu atoms is limited due to the introduction of MXene interlayer, and the growth of IMCs in the Cu-MX-SAC structure is controlled by volume diffusion. For the Cu-MX-SAC solder bonding, after prolonged aging, the shear strength increases, and contact resistance at the bonding interface is almost no change compared with Cu-SAC solder bonding.

Solid-phase transient soldering method based on Au/Ni–W multilayer thin-film-modified copper-based structures

The copper crystal cone-shaped micro-nanostructure is used as the substrate, and the Ni–W alloy layer and Au nanolayer are plated sequentially. Instantaneous soldering with lead-free solder is realized under ultrasonic assistance at room temperature. This solves the residual stress and thermal damage caused by high melting point lead-free solder on thin chips and thermal components, and ensures the safety and reliability of electronic components. Copper-based microstructures are deposited by electrochemical methods. An amorphous Ni–W alloy layer with a thickness of 180 nm is deposited on the Cu-based microstructures by adjusting the atomic ratio of the plating solution. The Ni–W layer is further coated with a 50 nm Au layer to prevent oxidation. Solid-phase transient soldering is realized by combining the Au/Ni–W multilayer thin-film-modified Cu substructures with commercial solder (SAC305) for a holding time of 3 s at a soldering pressure of 10,000 gf (20 MPa) while ultrasonically assisted. The soldered samples are aged at 180 °C for 10 min, 30 min, and 60 min, respectively. Copper substructures with different surface modifications are subjected to destructive shear experiments with solder balls. Scanning electron microscope and X-ray fluorescence thickness gauge are used to study the microstructure, intermetallic compound (IMC) composition thickness and properties of the soldered interface and section. The cone height of the Cu-based structure is 2–4 μm, and the diameter of the bottom is 800 nm–1200 nm, which has a sharp tip and an excellent L/D ratio. The interface between the Au/Ni–W modified Cu substructure and the solder ball is almost free of holes. The average shear strength at the soldering interface is about 43.06 MPa. The fracture surface after the shear experiment basically occurs inside the solder ball matrix, which belongs to the pure toughness fracture. The interface between the Au/Ni–W-modified Cu-based structure and the solder ball is subjected to long aging treatment at 180 °C. The soldering interface showed a “bright layer”. New phases are generated on the solder side above the “bright layer”, while no new phases appear on the Cu substructure side below the “bright layer”. The copper-based microstructure is inserted into the inside of the solder ball to form an inlay and produce mechanical interlocking. Au/Ni–W alloy modification layer can effectively improve the surface hardness of copper-based structures. This creates a large hardness difference with soft solder and enables the formation of fewer holes in the insertion solder. Amorphous Ni–W alloys are prone to form dense oxide films during ultrasonication. The Au film modification prevents oxide generation and increases the average shear strength of the soldering interface. The Ni–W alloy layer retards the interdiffusion between Cu–Sn, blocks the excessive growth of Cu–Sn IMCs, and reduces the reliability problems caused by interface failure.

Hydrogen evolution and thermal treatments for removal of plating induced impurities from Ni to extend life of solder joints

As operating temperatures and times continue to increase for solder joints with Ni pads, large voids inevitably form at the intermetallic compound (IMC) – solder interface when the IMC thickness nears 5 μm. This leads to a significant reduction of strength, thermal conductivity, and fatigue resistance, and in small joints, also to electromigration life degradation. We have identified the voiding root cause as the breakdown and subsequent outgassing of deposition-related Ni-oxo-hydroxide impurities, impractical to avoid during Ni commercial electroplating. This work takes as the starting point a successful post-deposition voiding-mitigation treatment with 24-hour annealing at 450 °C. It then explores the possibility of rendering this routine more practical by lowering the annealing temperature down to 250 °C. While that approach shows relatively limited success, an alternative strategy, involving treatment with hydrogen evolution reaction for one hour at room temperature, alone or in combination with thermal, leads to a substantial reduction in the voiding propensity.

Active element Ti improves the Sn-based alloy filler/graphite soldering interface: A combined first-principles and experimental study

Active element Ti plays a crucial role in the graphite soldering process. However, the atomic interaction mechanism between the active element Ti and graphite remains unclear. In this study, the enhancement effect of the active element Ti on the Sn-based alloy filler/graphite soldering interface was investigated by employing first-principles calculations combined with experimental methods. Based on the first-principles calculations, the adhesion work of the Sn/graphite interface models doped with two and four Ti atoms is 0.884 J/m2 and 1.896 J/m2, respectively, while that of the clean model is negative. Moreover, the segregation heat of the Sn/graphite interface model doped with more Ti atoms is more negative. All of these results indicate that Ti atoms doped at the Sn/graphite interface play a significant role in enhancing the interface. The electronic structures of the interface models with different numbers of titanium atoms were analyzed. The results revealed that the enhancement of the Sn/graphite interface was attributed to the transfer of electrons from the Ti-3d orbitals to the C-2p orbitals, leading to a strong interaction between the Ti and C atoms. The segregation of Ti was clearly observed at the Sn3·5Ag4Ti (Ce,Ga)/graphite soldering interface in the experiments, which was consistent with the results from the first-principles calculations. The shear strength of the Sn3·5Ag4Ti (Ce,Ga)/graphite soldered joint was tested, and an enriched region of titanium was found in the fracture surface on the graphite side. In addition, a tensile simulation was performed on the clean and Ti-doped Sn/graphite interfaces, and the results indicated that the Sn/graphite interface model enriched with Ti atoms had greater tensile simulation strength than that of the clean Sn/graphite interface model. These results further showed that Ti played a reinforcing role at the Sn/graphite interface. The results from our study provide a theoretical basis for exploring low-temperature active bonding methods in the packaging process of graphite connected to the heat dissipation surface of electronic devices.

Low temperature soldering technology based on superhydrophobic copper microlayer

Cu–Cu soldering is realized under certain pressure and low temperature conditions by using a surface silver film to modify the copper microlayer structure, thus solving the problems of high thermal stress and signal delay aggravation caused by high temperature in the traditional reflow soldering process. The copper microlayer modified with silver film is obtained by electrodeposition. The surface substructure of the Cu microlayer is a nano cone-shaped protrusion. The diameter of the bottom of the cone is 500 nm∼1 μm, and the height of the cone is 1∼2 μm. The thickness of the silver film is about 320 nm, and the modification of the copper layer with silver film can effectively prevent the oxidation of the copper layer. Two silver-modified copper microlayers are placed in face-to-face contact as a soldering couple. A certain pressure and low temperature are applied to the contact area to realize the soldering and interconnection.The morphology of the soldered interface and the average shear strength of the soldered joints are analyzed by scanning electron microscopy, transmission electron microscopy and solder joint tester. It is found that under the optimal soldering parameters of soldering temperature 220 °C, soldering pressure 20 MPa and soldering time 20 min, the nano-conical projections of the Cu micrometer layer are inserted into each other to produce a physical blocking effect. The highly surface-meltable silver film effectively connects the surrounding copper layer as an intermediate buffer layer. The average shear strength of soldering joints is significantly increased. Heat treatment experiments have shown that the average shear strength can be effectively increased by heat treatment for an appropriate period of time. Prolonged exposure to heat has little effect on the average shear strength. With the special morphology of the copper microlayer structure and the nano-size effect of the silver layer, soldering can be done at low temperatures. The quality of the soldering interface is good and small soldering dimensions can be obtained.

Significant inhibition of interfacial Cu6Sn5 IMC and improvement of solder joint strength and reliability by applying (111) nanotwinned Cu substrate and vacuum soldering

In this research, (111) oriented nanotwinned Cu (nt-Cu) substrates, combined with vacuum soldering, were utilized to enhance the strength and reliability of the solder joints. The wettability of the composite solder Sn1.0Ag0.5Cu-Si3N4 (SAC105-Si3N4) was improved on the (111) nt-Cu substrates and the oxidization of the molten solder was avoided by the vacuum environment, ensuring the formation of regular and uniform solder joints. The (111) nt-Cu substrates, characterized by their low surface energy, are demonstrated to be highly efficient in restricting the growth of interfacial IMCs, and this effects becomes particularly pronounced in three-dimensional (3D) solder joints following extended high-temperature aging. In addition, with vacuum soldering, a continuous and uniform interfacial structure was obtained, which is essential for upgrading the reliability of 3D solder joints. Furthermore, the electron back scatter diffraction (EBSD) testing of the solder matrix and interface formed on the nt-Cu substrates revealed that the c-axis of the β-Sn grains was parallel to the (111) nt-Cu substrates, and that the c-axis of the Cu6Sn5 grains was approximated to be perpendicular to the (111) nt-Cu substrates in an air environment. Finally, the shear strength and fracture morphology of the solder joints were evaluated. The macroscopic voids inside the solder joints were suppressed under vacuum, and the solder joints formed on the (111) nt-Cu substrates provided the highest shear strength.

Microstructural transformation and mechanical properties of Cu-sputtered alumina ceramic/Zn5Al/AA2024 ultrasonic soldering joints

Cu films were deposited on the surfaces of alumina (Al2O3) ceramics via magnetron sputtering, and the ceramics were then joined to AA2024 by using a Zn5Al solder assisted by ultrasonic soldering. Increasing the duration of Cu sputtering led to the continued diffusion of Al from the Al alloy substrate into the solder. This led to the growth of the ZnAl eutectic phase within the solder joint, with the precipitation of CuZn5 diffusing into the ZnAl eutectic and η–Zn phases. The increased formation of the ZnAl eutectic phase enhanced the mechanical strength and stability of the solder. The CuZn5 phase formation suppressed solder shrinkage during cooling, improving the coefficient of thermal expansion to match those of the metallised ceramic and AA2024 alloy. This reduced the residual stress at the joint interfaces in the metallised Al2O3 ceramic/Zn5Al/AA2024 joint. A maximum average shear strength of 65.835 MPa was achieved with 2 h of Cu sputtering, representing a 224.95% increase compared to the joints without Cu. Fractures occurred at the ceramic–solder interface, combining adhesive, cohesive, and mixed failures.

Interfacial Properties of Sn-Cu-xCr Alloy using Laser-Assisted Bonding

Conventional hot air reflow soldering is one of major bonding technology when bonding is proceeded on automotive electronics applications. However, here we focus on modifying the bonding process and composition of solder to enhance mechanical and thermal properties. This study experimentally investigated the mechanism of how laser-assisted bonding (LAB) form a small size of initial intermetallic compounds (IMC), and 0.2 wt% Cr element was added to Sn-0.7Cu eutectic solder to suppress the IMC growth. As a result, Sn-0.7Cu and Sn-0.7Cu-0.2Cr initial grain refinement was achieved by LAB. Isothermal aging was conducted to observe the mechanical and thermal properties depending on the IMC growth under 100, 125, 150 ℃ respectively. Sn-0.7Cu-0.2Cr tended to inhibit the growth of IMC at solder matrix and interface compared to Sn-0.7Cu throughout all aging temperature and time. The shear test was proceeded and Sn-0.7Cu-0.2Cr shear force was achieved 18% higher than Sn-0.7Cu. Even after isothermal aging, Sn-0.7Cu-0.2Cr showed lower reduction rate of shear force compared to Sn-0.7Cu.

In Situ Study the Grooving Effect Induced by Ag Particles on Rapid Growth of Cu6Sn5 Grain at Sn-xAg/Cu Soldering Interface during the Heat Preservation Stage

Synchrotron radiation X-ray imaging technique was applied for in situ observation of Cu6Sn5 intermetallic compounds (IMC) growth in Sn/Cu and Sn-3.5Ag/Cu joints under isothermal temperature conditions of 250/300/350 °C and time duration of 1.5 h. The IMC in Sn-Ag solder was characterized by the formation of grooves during the interfacial reaction, and this can be attributed to the Ag content. Kinetically, the growth rate constants for the height of Cu6Sn5 were observed to increase with temperatures and the presence of Ag in solder. As compared to pure Sn solders, the Sn-3.5Ag solders were observed with interfacial IMC of greater height, smaller base width, and lowered aspect ratio.

Effect of leveler on performance and reliability of copper pillar bumps in wafer electroplating under large current density

This work investigated the effects of levelers on the electroplating performance and reliability of copper pillar bumps (CPBs) on wafer. Under large current density, the usage of Janus green B (JGB) or a commercial leveler (L1) could obtain a satisfied performance in flatness, co-planarity and growth rate. It was found that this qualified leveler possessed a remarkable electrochemical characteristic, i.e., strong convection dependent adsorption (CDA). The void growth at the plated CPBs/Sn-Ag soldering interface during thermal aging was greatly accelerated when the leveler was applied during electroplating. The mass spectrum analysis showed that the level of impurities in the plated CPBs using JGB was much higher than that plated without JGB. The usage of leveler could produce a high level of impurities in the plated CPBs, which accounted for the boosting of voids at the soldering interface during thermal aging.

Effect of thermal contact resistance on the CHF and HTC for pool boiling heat transfer

In recent years, there has been increasing interest in the demand for heat dissipation of electronic devices. Constructing micro/nanostructures and using nanofluid for the pool boiling heat transfer have proved to be a notoriously effective method to increase the critical heat flux (CHF) as well as the heat transfer coefficient (HTC). When the tested samples with micro/nanostructures are soldered to the upper of the heated copper block, the CHF boiling curves of the tested samples always shift right, which may be caused by the thermal contact resistance (TCR) from the soldering interface. However, it is rarely for the research to be reported the effect of the thermal contact resistance on the pool boiling heat transfer performance. This paper highlights the effect of the TCR on the CHF and HTC for pool boiling heat transfer by comparing the boiling curve of the non-soldering, the soldering, and the Rohsenow curve. The relationship between the difference in temperature with increased heat flux is established by measuring the TCR of the soldering interface, and the relationship at the different soldering interface morphology has been explored. The results show that the CHF boiling curve with soldering shift right 106–144 % than that of the non-soldering, and the HTC decreases by 45.6–63.5 %. The shifted boiling curve could be corrected by the relationship between the TCR with increased heat flux. However, the boiling curve cannot be corrected by the relationship when the soldering interface has voids. This work demonstrates that the deviation between the boiling curve of soldering with the boiling curve of non-soldering is universal for engineering applications by comparing similar studies. Regardless of whether soldering is used in pool boiling heat transfer experiments, the Rohsenow curve is still an important reference, but the effect of TCR must be considered in the pool boiling curve of soldering.

Atomistic simulation of mechanical behavior of Cu/Cu3Sn solder interface with Kirkendall void under shear and tensile deformation

Atomistic simulation of mechanical behavior of Cu/Cu3Sn solder interface with Kirkendall void under shear and tensile deformation

Properties of Cu/Zn+15%SAC0307+15%Cu/Al joints by different ultrasonic-assisted degrees

PurposeThis paper aims to investigate the effects of different ultrasonic-assisted loading degrees on the microstructure, mechanical properties and the fracture morphology of Cu/Zn+15%SAC0307+15%Cu/Al solder joints.Design/methodology/approachA new method in which 45 μm Zn particles were mixed with 15% 500 nm Cu particles and 15% 500 nm SAC0307 particles as solders (SACZ) and five different ultrasonic loading degrees were applied for realizing the soldering between Cu and Al at 240 °C and 8 MPa. Then, SEM was used to observe and analyze the soldering seam, interface microstructure and fracture morphology; the structural composition was determined by EDS; the phase of the soldering seam was characterized by XRD; and a PTR-1102 bonding tester was adopted to test the average shear strength.FindingsThe results manifest that Al–Zn solid solution is formed on the Al side of the Cu/SACZ/Al joints, while the interface IMC (Cu5Zn8) is formed on the Cu side of the Cu/SACZ/Al joints. When single ultrasonic was used in soldering, the interface IMC (Cu5Zn8) gradually thickens with the increase of ultrasonic degree. It is observed that the proportion of Zn or ZnO areas in solders decreases, and the proportion of Cu–Zn compound areas increases with the variation of ultrasonic degree. The maximum shear strength of joint reaches 46.01 MPa when the dual ultrasonic degree is 60°. The fracture position of the joint gradually shifts from the Al side interface to the solders and then to the Cu side interface.Originality/valueThe mechanism of ultrasonic action on micro-nanoparticles is further studied. By using different ultrasonic loading degrees to realize Cu/Al soldering, it is believed that the understandings gained in this study may offer some new insights for the development of low-temperature soldering methodology for heterogeneous materials.

Microstructure and morphology of the soldering interface of Sn–2.0Ag–1.5Zn low Ag content lead-free solder ball and different substrates

Eutectic Sn–Ag–Cu lead-free solder has limited applications due to cost and reliability issues. Sn–Ag–Zn solder has the advantages of low melting point, good mechanical properties and reliable welding interface. However, the research system of low silver content Sn–Ag–Zn solder is incomplete. In this paper, Sn–2.0Ag–1.5Zn low silver content alloy solder is soldered to different substrates. The interfacial reaction after soldering and the microstructure and reliability under different aging treatment conditions are studied. Sn–2.0Ag–1.5Zn solder is made into solder balls by direct melting method. The solder balls are placed in a solder strength tester to be heated and welded to the substrate, and then the solder joints are placed in a heating furnace for aging treatment. The results show that the solder is soldered to the bare Cu substrate, and a dense double-layer Intermetallic Compound (IMC) structure of Cu5Zn8 and Ag3Sn is formed at the interface after aging treatment. The double-layer structure blocks each other, limiting the development of copper-tin IMCs. The solder is soldered with the Cu substrate electroplated with Ni barrier layer, and the soldering interface forms a thin layer of Ni3Sn4 metal compound. After aging for 1000 h, the thickness of Ni3Sn4 is about 1 μm, the thickness of Ni barrier layer is kept at 2–3 μm, and the barrier effect of Ni barrier layer is stable. Sn–2.0Ag–1.5Zn solder has excellent loss performance in long aging treatment. It has good heat-resistance aging treatment, good quality of solder connection, high interface reliability and less environmental pollution. The low silver content in Sn–2.0Ag–1.5Zn solder results in a significant cost reduction. Coarse IMC Ag3Sn is not easily formed. The optimized ratio of Ag and Zn in Sn–2.0Ag–1.5Zn solder improves the strength and toughness of the solder joint. The performance has been improved, and it is a very promising alloy solder.

Microstructure Evolution and Interfacial Reaction of Cu/SAC305/Cu and Co-P/SAC305/Cu Solder Joints under High Current Density

The size of solder joints in electronic packaging is gradually decreasing, which directly leads to a sharp increase in the current density experienced by the solder joints. Therefore, it is of great significance to study the effect of electromigration on the interface of the lead-free solder. In this paper, the effect of electromigration on the microstructure of Cu UBM and Co-P UBM solder joints was compared. By comparing the morphological changes of CoSn3 and Cu6Sn5 at the interface, combined with the calculation of the thickness of the intermetallic compound, it was found that the consumption rate of Co-P UBM in the solder joint was much lower than that of the Cu substrate. Moreover, when the Co-P UBM is completely consumed, the consumption rate of the Cu substrate is also significantly reduced.

Study on interfacial reaction behavior of Sn[sbnd]Ag based lead-free solder with (111) single crystal copper substrate

The morphology and crystal orientation of intermetallic compounds formed by the reaction between SAC305 solder/(111) and SABI333 solder/(111) single crystal copper substrate were investigated. The morphology of Cu6Sn5 at the interface of SAC305 solder/(111) single crystal copper substrate changes from scallop to prismatic with the increase of reflow time. The Cu6Sn5 grains grow parallel to the horizontal direction of the Cu substrate and grow along the vertical direction, and there is an Angle of 60° between different Cu6Sn5 crystals. The calculated b ~ t0.23 relation satisfies the growth kinetics of prismatic Cu6Sn5. In addition, the morphology of Cu6(Sn, In)5 at the interface of SABI333 solder/(111) single crystal copper substrate is between scallop-type and prismatic-type. Cu6(Sn, In)5 grains grow at a certain angle with a single crystal copper substrate due to the addition of In element. Furthermore, it is considered that the deflection mechanism of Cu6(Sn, In)5 grains is controlled by the length and strength of inter-atomic bonds within the grains after the In atom substitution reaction.

The Effect of Micro-Alloying and Surface Finishes on the Thermal Cycling Reliability of Doped SAC Solder Alloys.

The surface finish (SF) becomes a part of the solder joint during assembly and improves the component’s reliability. Furthermore, the SF influences the solder joint’s reliability by affecting the thickness of the intermetallic compound (IMC) layer at the solder interface and copper pads. In this experiment, five different alloys are used and compared with the SAC305 alloy, two of which, Innolot and SAC-Bi, are bi-based solder alloys. This study includes three common SFs: electroless nickel immersion gold (ENIG), immersion silver (ImAg), and organic solderability preserve (OSP). The performance of three surface finishes is examined in terms of component characteristic life. All of the boards were isothermally aged for twelve months at 125 °C. The boards were then exposed to 5000 cycles of thermal cycling at temperatures ranging from −40–+125 °C. Most of the current research considers only one or two factors affecting the reliability of the electronic package. This study combines the effect of multiple factors, including solder paste content, SF, isothermal aging, and thermal cycling, to ensure that the test conditions represent real-world applications. In addition, the electronics packages are assembled using commercialized alloys. The current study focuses on a high-performance alloy already present in the electronic market. The failure data were analyzed statistically using the Weibull distribution and design of experiments (DOE) analysis of variance (ANOVA) techniques. The findings reveal that the micro and uniformly distributed precipitates in solder microstructures are critical for high-reliability solder joints. Re-crystallization of the thermally cycled solder joints promotes the local formation of numerous new grains in stress-concentrated zones. As the fracture spreads along these grain boundaries and eventually fails, these new grains participate in crack propagation. Aging significantly worsens this situation. Finally, although the ENIG surface finish with its Ni layer outperforms other SFs, this does not imply that ENIG is more reliable in all solder paste/sphere/finish combinations.