A comprehensive analysis which was based on macro-structure inspection,chemical composition analysis,matellurgical structure,mechanical performance analysis and fracture morphology observation was made on fracture failure of 20CrlMolVTiB bolt of steam turbine.The results show that the improper heat treatment process used in manufacture,causes coarse crystal and incompetent impact toughness,leades bolt to brittle fracture.

The ternary Sn–Cu–Co system eutectic composition was obtained by means of CALPHAD (CALculation of PHAse Diagram) methodology and it was found to be 0.4% Co and 0.7% Cu (wt%) with a melting point of 224°C. The tensile behavior of this alloy was investigated at different strain rates (10−5, 10−4 and 10−3s−1) and compared to both Sn–37Pb and Sn–4.0Ag–0.5Cu. The Sn–4.0Ag–0.5Cu alloy depicts the highest ultimate tensile strength (UTS) followed by the Sn–37P and finally the Sn–0.7Cu–0.4Co system. The elastic modulus was also higher for the Sn–4.0Ag–0.5Cu followed by the Sn–0.7Cu–0.4Co and last the Sn–37Pb. The microstructure of the Sn–0.7Cu–0.4Co alloy is composed of two types of intermetallic phases, (Cu,Co)6Sn5 and (Co,Cu)Sn2 dispersed in a Sn-rich matrix. The microstructure of this alloy proved to be very stable, after aging at 150°C for 24h. The eutectic Sn–0.7Cu–0.4Co solder alloy can therefore be a very good alternative for the SAC alloys for surface mount technology applications.

PurposeThe purpose of this paper is to compare the growth kinetics of interfacial intermetallic compound (IMC) layer and its effect on the tensile strength of two solder (Sn3.0Ag0.5Cu and Sn0.4Co0.7Cu) joints.Design/methodology/approachThe samples annealed, respectively, at 85, 120 and 150°C up to 1,000 h were tensile tested and their cross‐sections were observed by scanning electron micrography.FindingsThe results showed that, for both solder joints, an approximately linear reduction in tensile joint strength with an increase in the IMC layers' thickness occurred. The tensile strength of Cu/Sn3.0Ag0.5Cu solder joints is slightly better than that of Cu/Sn‐0.7Co‐0.4Cu solder joints under analogous aging conditions. In addition, the growth kinetics of the overall interfacial IMC layer in Sn0.4Co0.7Cu solder joints can be simply described by the classical growth kinetic theory for solid‐state diffusion with an activation energy of 2,996.85 J/mol and interdiffusion constant of 4.15×0−17 m2/s which are relatively lower, compared with Sn3.0Ag0.5Cu solder on copper with 14,167.8 J/mol and 65.33×10−17 m2/s, respectively.Originality/valueThe paper is of value in evaluating the growth kinetics of Sn3.0Ag0.5Cu and Sn0.4Co0.7Cu solder joints, and in discussing and contrasting the influence of IMC growth on their tensile strength.

Microstructural features and tensile properties of Sn-3.0Ag-0.5Cu solder joints on copper with various aging time at 150degC were examined. The solder inner and solder/Cu interface were analyzed by SEM to identify the fracture location, morphology and compositions. The study has showed, the tensile fracture strength of the solder joints decreases with the increased aging time, and the crack initiates mostly at the interfaces between the solder and IMC layer or/and IMC and IMC layer. The morphology of fracture surface changes from dimple-like to cleavage-like surfaces. The needle-like or block-like interfacial IMCs form at the interface of Cu/solder and grow into the solder matrix. Otherwise, the Kirkendall voids can be observed in the multilayer structure close to the copper substrate. These voids have probably a detrimental effect on the tensile fracture behavior.

The mechanical bending test results, as well as the modeling and calculation data were presented in this study to characterize the solder joint reliability. Bending test was completed simply by loading a series of displacements on the FR-4 printed circuit board (PCB) with devices and solder joints in single direction. A special bending tester that can control displacement exactly by a cam system was designed and used for reliability study. The three group samples need to endure bend distortion with different deflections respectively, namely 3 mm, 4 mm, and 5 mm. The electrical resistance was probed every 3600 cycles by multimeter. When the resistance of solder joint got 10% increase, the failure can be defined. The experimental results indicate that the fatigue life decreased obviously with the displacement increased. By using optical microscope and SEM photographs, two kinds of failure model were found in solder joints. The majority failure model, which took place at the bottom corner of solder joint under the termination of resistor initially, and propagated into the solder matrix. The delamination appeared at the interface between the termination of resistor and its ceramic body. The finite element analysis was presented to support this experiment. The shear strain ranges under the different deflections were obtained from simulation. A Coffin-Mason equation of Sn-4.0Ag-0.5Cu from literature was used to compare with this experimental result and prove the feasibility of two points bending test in fatigue life prediction.

Two key technologies used by the electronics industry are chip technology and packaging technology. Solder plays a crucial role in both of them. During the last decade, there has been a strong worldwide environmental movement towards lead-free electronic products. The Sn-Zn solder system has been presented as a promising lead-free candidate, recommended mainly for its low melting temperature, around 200°C, which is close to the melting temperature of the traditional binary Sn-Pb alloy, 183°C. The alloy composition chosen to be studied in this work was the ternary Sn-8Zn-3Bi. The low cycle fatigue behavior of this alloy was investigated using single lap shear samples. Finite element modeling was performed and the Coffin-Manson equation was given based on results from experiment and simulation both: Nf = 0.0294 (Δγ)-2.833 Another important issue relating to the reliability of solder joints also investigated in this work, is the intermetallic compounds (IMCs). During soldering and the build-up of solder joints, IMCs are formed at the interface between the solder and the pad metallization. The reliability of the whole package is typically affected by the integrity of the solder joints, and the integrity of the solder joints is greatly affected by the IMCs mainly due to their inherent brittle nature and tendency to generate structural defects. The interfacial reactions between the eutectic Sn-0.4Co-0.7Cu alloy and electroless nickel, immersion gold (ENIG) metallization was investigated after reflow soldering. Common Sn-4.0Ag-0.5Cu and eutectic Sn-0.7Cu solders were used as reference. Two types of IMCs were found in the solder matrix of the Sn-0.4Co-0.7Cu alloy, namely coarser CoSn2 and finer Cu6Sn5 particles, while only one ternary (Cu,Ni)6Sn5 interfacial compound was detected between the solder alloy and the ENIG coated substrate. It was noted that the thickness of the interfacial IMC layers in the Sn-Co-Cu solder joint were thinner than both Sn-Ag-Cu and Sn-Cu IMC layers. The interfacial reaction of Sn-3.5Ag and Sn-4.0Ag-0.5Cu solders on ENIG metallization after high temperature storage (HTS) testing was investigated from a metallurgical point of view. It was noticed that only Ni3Sn4 IMCs were found in the Sn-Ag system, while two kinds of interfacial products, (Ni,Cu)3Sn4 and (Cu,Ni)6Sn5 existed in the Sn-Ag-Cu system. The interfacial layer between the Sn-Ag-Cu solder and electroless Ni(P) coating showed better thermal stability than eutectic Sn-Ag solder since no spalling was observed. Furthermore, the coupling effect in both Sn-3.5Ag-3.0Bi and Sn-8.0Zn-3.0Bi solder joints in sandwiched structure was studied as a function of reflow time. The coupling effect between the ENIG metallization and the Cu substrate was confirmed since the type of IMCs on Ni(P) layer changed from being a Ni-Sn phase to a Cu-Sn phase, apparently as a result of the diffusion of Cu atoms from the opposite Cu substrate. Furthermore, the ternary (Cu,Ni)6Sn5 compounds were formed at the interface between Sn-Ag-Bi solder and Ni(P) substrate. One complex alloy Sn-Ni-Cu-Zn was formed at the Sn-Zn-Bi/Ni(P) interface; however the growth of this complex alloy on the ENIG coated substrate was suppressed.

Interfacial reactions between Sn-0.4Co-0.7Cu eutectic alloy and immersion Ni/Cu substrate have been investigated after reflow and high temperature storage. The reflow peak temperature at 265degC and a total duration time of 6 minutes were used. The duration time at the peak temperature of the reflow process was approximately 2 min. The aging temperature was 150degC and the duration time was 100 h, 200 h, 550 h and 1000 h, respectively. In the solder matrix of the Sn-0.4Co-0.7Cu alloy, the intermetallic compounds (IMC) CoSn2 were found. At the interface between the solder alloy and the electroless nickel substrate, a ternary (Cu, Ni)6Sn5 intermetallic compound was detected. The intermetallic compound layer became thicker as a function of thermal aging time. The IMCs were continuous and their morphology was faceted at the interface. No voids and gaps were observed at the interface between the nickel layer and the Sn-0.4Co-0.7Cu eutectic alloy after thermal aging.

The present work was mainly focused on the evolution of interfacial intermetallic compounds (IMCs) between solder and Au/Ni/Cu metallization in PBGA Sn-Ag-Cu solder balls during thermal cycling test. The PBGA package was assembled on the FR-4 board using a typical surface mounting assembly process, and the thermal cycling was carried out in a systematic manner for two different temperature cycling profiles in a single chamber Heraeus climate cabinet. The first temperature profile ranged between 0degC and 100degC and the second between -55degC and 100degC. It was found that the type of IMCs existing in the solder matrix and on the PCB metallization was not affected by the thermal cycling. The growth rate of the interfacial IMC (Cu,Ni)6Sn5 was very low, and the thickness of the Sn-Ni-Cu ternary IMCs layer on the PCB metallization did not show a significant change during thermal cycling testing. For the temperature profile ranging between 0degC and 100degC and up to 6000 cycles, no fatigue cracks were found in the PBGA solder balls, while fatigue cracks could be observed after 3000 cycles, both at the solder/package side and solder/PCB side for the temperature profile ranging between -55degC and 100degC. The common failure mode of the solder joints analyzed in this work were cracks originating at the solder joint corners, firstly at the component solder mask defined (SMD) pad side and propagating within the solder along the PBGA metallization interface; no fatigue cracks were found to propagate through the interfacial intermetallic layer for all the cases (both on the package and PCB side). The cracks were found to propagate near and almost parallel to the interface of the bulk solder and the intermetallic layer. The ternary (Cu,Ni)6Sn5 IMCs layer attached very well to the substrate and no spalling could be observed

The Sn–3.5Ag and Sn–4.0Ag–0.5Cu solders on Au/electroless Ni(P) metallization exhibited different interfacial morphologies after high temperature storage (HTS) at 150°C. Ni3Sn4 intermetallic compounds (IMCs) were found in the Sn–Ag system, while for the Sn–Ag–Cu system the IMCs consisted of two kinds of interfacial reactions. For the Sn–3.5Ag solder, the Ni3Sn4 IMC particles lost adhesion/contact to the electroless Ni(P) layer and clear gap was observed in the samples after high temperature storage (HTS) aging for 1000h. In the Sn–4.0Ag–0.5Cu solder joint, both (Cu,Ni)6Sn5 and (Ni,Cu)3Sn4 compounds were observed after HTS aging. Since the difference in nucleation site and growth rate for kinds of IMCs, (Cu,Ni)6Sn5 was observed at top and (Ni,Cu)3Sn4 at bottom when the interfacial compound layer became thicker as a function of thermal aging. Some voids were found between the electroless Ni(P) interface and the Sn–Ag solder after 168 and 500h of thermal aging, while the clear gap between the solder and the Ni layer existed after 1000h aging. The formation mechanism for this gap could be the interconnection and growth of the voids. In the Sn–Ag–Cu system, voids were found inside the Sn–Ni–Cu ternary interfacial compounds after 500 and 1000h. The formation mechanism for these voids was thought to be Kirkendall effect or etching process. The interfacial layer of Sn–Ag–Cu solder on electroless Ni(P) coating showed the better thermal stable than eutectic Sn–Ag solder.

Solder joints of Sn-37Pb, Sn-3.5Ag, Sn-4.0Ag-0.5Cu and Sn-8Zn-3Bi (all compositions in wt%) were tested by means of isothermal low cycle mechanical fatigue at room temperature over a wide range of strain ranges (1%-10%). The eutectic Sn-37wt%Pb was used as a reference. Single lap shear samples with solder joints 0.45mm in height and 1.6mm in diameter were used. The testing was executed in a displacement-controlled mode, at three different amplitudes namely, 30, 40 and 50mum. The frequency used was 0.2Hz. The displacement waveform was triangular, due to its constant strain rate. The Coffin-Manson law was compared to the Morrow's energy model and both the energy density value and the plastic strain range values were calculated in different ways to analyse the uncertainty in the calculation methodology of fatigue life. According to the results, the solder alloy with the best isothermal fatigue properties is the ternary Sn-4.0Ag-0.5Ag. The Sn-3.5Ag-3Bi exhibited quite poor fatigue properties, worse than all the other alloys tested. Regarding the model used for fatigue life prediction, both methods gave consistent results

This paper studied the coupling effect in Sn-3.5Ag-3.0Bi solder joint with sandwich structure by long time reflow soldering. It was found that the interfacial compound at the Cu substrate was binary Cu-Sn compound on Cu substrate and the ternary (Cu,Ni)(6)Sn-5 compound formed at the Sn-Ag-Bi/Ni(P)-Cu metallization interface. It was observed that Cu atoms could diffuse from the Cu substrate through the solder matrix to the Ni(P)-Cu metallization within 1min reflow soldering time for both solder systems, indicating that just 30 second was long enough for Cu to go through 250 mu m diffusion length in the Sn-Ag-Bi solder joint at 250 degrees C. The coupling effect between Ni(P)/Cu metallization and Cu substrate was confirmed as the type of IMCs at Ni(P) layer had been changed from Ni-Sn system to Cu-Sn system apparently by the diffusion effect of Cu atoms. The (Cu,Ni)(6)Sn-5 layer at the Ni(P)/Cu metallization grew significantly and its thickness was even greater than that of the Cu-Sn compound on the opposite Cu substrate.

In this paper, the coupling effect in Sn–3.5Ag–3.0Bi and Sn–8.0Zn–3.0Bi solder joint with sandwich structure by long time reflow soldering was studied. It was found that the interfacial compound at the Cu substrate was binary Cu–Sn compound in Sn–Ag–Bi solder joint and Cu5Zn8 phase in Sn–Zn–Bi solder joint. The thickness of the Cu–Zn compound layer formed at the Cu substrate was greater than or equal to that of Cu–Sn compound layer, although the reflow soldering temperature of Sn–Zn–Bi (240°C) was lower than that of Sn–Ag–Bi (250°C). The stable Cu–Zn compound was the absolute preferential phase in the interfacial layer between Sn–Zn–Bi and the Cu substrate. The ternary (Cu, Ni)6Sn5 compound was formed at the Sn–Ag–Bi/Ni(P)–Cu metallization interface, and a complex alloy Sn–Ni–Cu–Zn was formed at the Sn–Zn–Bi/Ni(P)–Cu metallization interface. It was noted that Cu atoms could diffuse from the Cu substrate through the solder matrix to the Ni(P)–Cu metallization within 1min reflow soldering time for both solder systems, indicating that just 30s was long enough for Cu to go through 250μm diffusion length in the Sn–Ag–Bi solder joint at 250°C. The coupling effect between Ni(P)/Cu metallization and Cu substrate was confirmed as the type of IMCs at Ni(P) layer had been changed from Ni–Sn system to Cu–Sn system apparently by the diffusion effect of Cu atoms. The (Cu, Ni)6Sn5 layer at the Ni(P)/Cu metallization grew significantly and its thickness was even greater than that of the Cu–Sn compound on the opposite side, however the growth of the complex alloy including Sn, Ni, Cu and Zn on the Ni(P)/Cu metallization was suppressed.

The dynamic tensile test of 0.11C-0. 62Si-1.65Mn TRIP steel was carried out at different strain rates and test temperatures. The results show that both temperature and strain rate affect the retained austenite transformation. At high strain rates, the uniform elongation decreases, whereas the total elongation and energy absorption increase. The tensile strength is less strain rate sensitive. With raising test temperature, the tensile strength is reduced and the mechanical properties generally deteriorate, especially at 110 °C. However, excellent mechanical properties were obtained at 50 °C and 75 °C.

The interfacial reactions between Sn–0.4Co–0.7Cu eutectic alloy and immersion Au/electroless Ni(P)/Cu substrate were investigated after reflow soldering at 260°C for 2min. Common Sn–4.0Ag–0.5Cu and eutectic Sn–0.7Cu solders were used as reference. Two types of intermetallic compounds (IMC) were found in the solder matrix of the Sn–0.4Co–0.7Cu alloy, namely coarser CoSn2 and finer Cu6Sn5 particles, while only one ternary (Cu, Ni)6Sn5 interfacial compound was detected between the solder alloy and the electroless nickel and immersion gold (ENIG) coated substrate. The same trend was also observed for the Sn–Ag–Cu and Sn–Cu solder joints. Compared with the CoSn2 particles found in the Sn–Co–Cu solder and the Ag3Sn particles found in the Sn–Ag–Cu solder, the Cu6Sn5 particles found in both solder systems exhibited finer structure and more uniform distribution. It was noted that the thickness of the interfacial IMCs for the Sn–Co–Cu, Sn–Ag–Cu and Sn–Cu alloys was 3.5μm, 4.3μm and 4.1μm, respectively, as a result of longer reflow time above the alloy's melting temperature since the Sn–Ag–Cu solder alloy has the lowest melting point.

Purpose To determine the Coffin‐Manson (CM) equation constants for fatigue life estimation of Sn‐8Zn‐3Bi solder joints, since Sn‐8Zn‐3Bi solder has a melting temperature of around 199°C which is close to that of the conventional Sn‐Pb solder which has previously been used in the electronics assembly industry. Design/methodology/approach Three dimensional finite element (FE) simulation analysis was used for comparison with the experimentally measured data and to determine the CM constants. Low cycle fatigue tests and FE simulations were carried out for these lead‐free solder joints, and eutectic Sn‐37Pb solder was used as a reference. Findings The CM equation for Sn‐8Zn‐3Bi solder joints was fitted to the lifetimes measured and the shear strains simulated. The constants were determined to be 0.0294 for C , the proportional constant, and for the fatigue exponent, β , −2.833. Originality/value The CM equation can now be used to predict the reliability of Sn‐8Zn‐3Bi solder joints in electronics assembly and the knowledge base for the properties of the Sn‐Zn solder system has been increased.

Flip chip packaging with anisotropically conductive adhesive (ACA) joint is increasingly used in the electronic industry because of its environmental benefits, fine pitch capability and simpler process. The mechanical deformation has a great impact on electricity ability of the particles in flip chip assembly. The stress analysis of ACA joining in flip chip assembly is one of key steps towards a better understanding of the performance of ACA joints under various process and service conditions. A new finite element simulation for large deformation and residual stress in ACA joining has been made in this work, and there has been no known prior reported on it. A new method was suggested to simulate the force equilibrium and residual stress in conductive ball and resin matrix in flip chip joining using anisotropic conductive adhesive. The link elements with varied Young's module were introduced in present FE simulation. The results from this simulation in ACA bonding process indicated that after the pressure removed, the deformation ratio RD decreased from 80% to 75.7%, and the deformation recovery ratio DeltaRD = 4.3% only. A force equilibrium between resin and ball was built, and the ball can not revert its original state after the external load on the chip had been completely removed. The residual equivalent stress Seqv,ball in ball center was remained at a high value, 318 MPa, and the average residual stress Seqv,resin in resin matrix was only 25 MPa. Comparing with the residual stress in ball, the residual stress in resin matrix would be not important, due to the simulation result Seqv,resin << Seqv,ball The assumption Seqv,resin = 0 usually used, i.e. the residual stress in resin matrix can be omitted, may be a useful approximation in reliability analysis of ACA joining. The relaxation of residual stress in conductive ball may play a more important role for reliability of ACA joi- - ning. It is necessary to investigate the viscoelastic and plastic behavior of ball material, and to build its constitutional equation more reasonably in the future research. The simulation method suggested in this work can serve as a basis for stress analysis and for lifetime analysis of flip chip packaging with ACA joint in the future work

The 3D FE simulation performed in this work was used to deal with the experimental measured data, and to get the Coffin-Manson equation for lifetime prediction. Low cycle fatigue tests and FE simulations were performed on Sn-8Zn-3Bi lead free solder joints, and the Sn-37Pb eutectic solder was used as reference. The Coffin-Manson equation for the Sn-8Zn-3Bi lead free solder was fitted from the experimental measured lifetime and the shear strain calculated according to the equation Nf = 0.0294(Deltagamma)-2.833 , where the Nf is the number of cycles to failure and Deltagamma is the plastic shear strain