Isothermal Aging Tests Research Articles

Interfacial structure and stability in Ni/SKD/Ti/Ni skutterudite thermoelements

Abstract Ni/Ti/SKD/Ni (SKD: skutterudite) thermoelements were fabricated by spark plasma sintering and electroplating procedures. The interfacial stability was evaluated by long-term isothermal aging and multi-round thermal shock tests. The interfacial diffusion at Ni/SKD and Ni/Ti in the thermoelements during high temperature aging up to 15 days was systematically studied by scanning electron microscopy with elemental distribution. The growth kinetics of the intermetallic compounds was analyzed, and the coefficients of the intermetallic compound growth rate were calculated. For the Ni/SKD interface, there was no inter-diffusion at temperatures below 200 °C. However, three intermetallic compound layers for the Ti/Ni interface were confirmed to be TiNi3, TiNi and Ti2Ni sequentially from the Ni side to the Ti side at temperatures above 500 °C, leading to an interfacial structure of Ti/Ti2Ni/TiNi/TiNi3/Ni. All interfaces maintained good bonding strength after long-term isothermal aging and multi-round thermal shock tests. The experimental data demonstrated that Ni is an ideal candidate as the electrode of skutterudite thermoelements at both the hot and cold sides.

Prediction of the phase composition of the refractory 45Cr26Ni33Si2Nb2 alloy in the process of stabilization

This paper is devoted to material aging in the operational temperature range of pyrolysis equipment. The EBSD analysis of the alloy phase composition after isothermal aging or stress-rupture tests at 800–1100°C for 1000–5000 h shows that the role of niobium and the two stable forms of its existence, namely, the G-phase Nb6Ni16Si7 at a temperature below 900°C and carbide NbC above 1000°C, is crucial in the process of stabilization (thermodynamic equilibrium approach). The approximate dependences of the saturation concentration of carbon and the current concentration of carbides are in satisfactory agreement with numerical modeling and, at the same time, reveal the effect of temperature and doping either in a direct way (through the equilibrium constant, the specified concentrations of carbon, chromium, niobium) or via the activity coefficients of elements and their components.

M5C2 carbide precipitates in a high-Cr martensitic steel

The precipitate phases in an advanced 11% Cr martensitic steel, expected to be used at 650 °C, have been investigated to understand the effect of precipitates on the creep-rupture strength of the steel. M23C6 and MX precipitates were dominant phases in this steel. Needle-like precipitates with a typical length of 180 nm and width of 20 nm; and metallic-element compositions of 53–74Fe, 16–26Cr, 3–18Ta, 2–8W, and 2–4Co (at%); were observed mainly within the martensite laths of the normalized-and-tempered steel. The needle-like precipitates have been identified as monoclinic carbide M5C2, which is not known to have been reported previously in high chromium steels, or in heat-resistant steels those have been normalized-and-tempered. This indicates that the formation of M5C2 carbides can occur in heat-resistant steels produced under appropriate tempering conditions, and that this does not require long-term isothermal aging or creep testing, in all cases.

Wetting and the reaction of multiwalled carbon nanotube-reinforced composite solder with a copper substrate

Abstract In this work, contact angle, spreading area, and isothermal aging tests were conducted to study the difference between Sn-3Ag-0.5Cu lead-free solder and its composite solder at different multiwalled carbon nanotube reinforcement volume fractions. The material interaction between the solder and the substrate at different aging temperatures and times was investigated using scanning electron microscopy elemental analysis. The experimental results indicated that the composite solder had a lower contact angle as well as good spreading area. An intermetallic compound layer was found between the solder and the copper substrate, and the thickness of this reaction layer increased with increasing aging temperature and time. Meanwhile, the intermetallic compound layer of multiwalled carbon nanotube reinforcement composite solder was thicker than that of the Sn-3Ag-0.5Cu lead-free solder. The composite solder with 0.1 vol% multiwalled carbon nanotube reinforcement addition exhibited better comprehensive properties than composite solders with other reinforcement volume fractions.

Intermetallic growth study on SnAgCu/Cu solder joint interface during thermal aging

The intermetallic compound (IMC) growth behavior at SnAgCu/Cu solder joint interface under different thermal aging conditions was investigated, in order to develop a framework for correlating IMC layer growth behavior between isothermal and thermomechanical cycling (TMC) effects. Based upon an analysis of displacements for actual flip-chip solder joint during temperature cycling, a special bimetallic loading frame with single joint-shear sample as well as TMC tests were designed and used to research the interfacial IMC growth behavior in SnAgCu/Cu solder joint, with a focus on the influence of stress–strain cycling on the growth kinetics. An equivalent model for IMC growth was derived to describe the interfacial Cu-Sn IMC growth behavior subjected to TMC aging as well as isothermal aging based on the proposed “equivalent aging time” and “effective aging time”. Isothermal aging, thermal cycling (TC) and TMC tests were conducted for parameter determination of the IMC growth model as well as the growth kinetic analysis. The SnAgCu/Cu solder joints were isothermally aged at 125, 150 and 175 °C, while the TC and TMC tests were performed within the temperature range from −40 to 125 °C. The statistical results of IMC layer thickness showed that the IMC growth for TMC was accelerated compared to that of isothermal aging based on the same “effective aging time”. The IMC growth model proposed here is fit for predicting the IMC layer thickness for SnAgCu/Cu solder joint after any isothermal aging time or thermomechanical cycles. In addition, the results of microstructure evolution observation of SnAgCu/Cu solder joint subjected to TMC revealed that the interfacial zone was the weak link of the solder joint, and the interfacial IMC growth had important influence on the thermomechanical fatigue fracture of the solder joint.

Laboratory Investigation on the Feasibility of Light-Oil Autoignition for Application of the High-Pressure Air Injection (HPAI) Process

Whether thermal effects have a contribution on oil recovery mechanisms in the high-pressure air injection (HPAI) process in a light-oil reservoir has confused many people over several decades. The argument is due to the lack of convictive evidence from both direct laboratory and simulation studies. This paper is the prelusion for the subsequent study for a better understanding of the influence of thermal effects on oil production. In a previous study, thermogravimetry/differential thermogravimetry (TG/DTG) and differential thermal analysis (DTA) tests were employed to investigate the kinetic parameters and exothermic behavior of Keke Ya light crude oil (Tarim Basin, China) and oil + cuttings, showing that Keke Ya light crude oil as well as oil + cuttings exhibited very low activation energy and favorable exothermic behavior. In this study, we develop a thermal effect monitoring device, which is similar to the isothermal oxidation tube, and we have detected the obvious exothermic phenomenon of Keke Ya light crude oil in porous media in the isothermal aging test at reservoir conditions (80 °C and 16.7 MPa). The witness of the combustion (or high-temperature) process is exhibited, which is expressed in specific characteristics made up of the self-heating behavior, low hydrogen/carbon (H/C) ratio of 1.50 from gas composition analysis, and generated precipitation coverings (halite crystalloid) in the core section surface through scanning electron microscopy (SEM) analysis. This study provides new insight that thermal effects should exist during the light-oil isothermal aging process in porous media and proposes a laboratory analysis method to understand the feasibility of light-oil autoignition at the oil-bearing reservoir during application of HPAI.

Reliability and failure analysis of fine copper wire bonds encapsulated with commercial epoxy molding compound

The small outline transistor (SOT) devices which were interconnected with 20 μm copper bonding wire and encapsulated with commercial epoxy molding compound (EMC) have been used in a series of reliability tests which including the thermal shock test, the electrical service life test, and the isothermal aging test. Isolated IMC spots were found at the bonding interface during the thermal shock test. No void or crack was observed even after 1500 cycles thermal shock test. No electrical failure was happened. The isolated IMC spots also occurred at the Cu/Al bonds interface after 500 h electrical operation. After 1000 h electrical operation, the sizes of the IMC spots were about 0.5 μm. No layered IMC was observed. The IMCs were formed at the bonding interface when the aging temperature was between 150 °C and 250 °C. Micro cracks and Kirkendall voids were observed with the aging time of 9 days at 200 °C and the aging time of 9 h at 250 °C. The minor element in the EMC, Sb, has reacted with Cu wire and Cu bond surface at 250 °C when the aging time was more than 16 h. Cu 3Sb was the main product of the diffusion reaction. With the aging time of more than 49 h, the Cu wire was crashed into pieces and the Cu bond periphery has been severely corroded.

IMC Growth Mechanisms of SAC305 Lead-Free Solder on Different Surface Finishes and Their Effects on Solder Joint Reliability of FCBGA Packages

Intermetallic compound (IMC) growth behavior of lead-free solder plays an important role in ball grid array (BGA) solder joint reliability for flip chip BGA (FCBGA) packaging applications. The growth mechanism of IMC is reported based on a diffusion model. Thermal treatment such as accelerated thermal cycling (ATC) and isothermal aging exposure also contribute to the growth rate and morphology of lead-free solder IMC. Among the lead-free solder alloys, Sn-3.0wt.%Ag-0.5wt.%Cu (SAC305) solder is a promising substitute for Sn-Pb because of its good mechanical properties and wettability with current surface finishes. After thermal exposure, BGA solder joint reliability is degraded due to IMC formation and growth. In this study, two different thermal treatments, ATC and isothermal aging, and two different pad surface finishes, solder on pad (SOP) and electroless Ni immersion gold (ENIG), are considered in terms of IMC growth rate and mechanical solder joint reliability. An SOP finished interface forms a thin ε-phase Cu3Sn layer and a scallop-like η-phase Cu6Sn5 layer. In contrast, the ENIG finished interface forms a thick (Cu,Ni)6Sn5 IMC layer and prevents overall IMC growth. Different surface finished test vehicles are evaluated in an ATC test in a 0°C to 100°C temperature range and the Ni diffusion layer shows a longer solder joint fatigue lifetime than the nondiffusion barrier interface based on the micro cross-section and dye penetration analysis results. In an isothermal aging test at 100°C and 150°C, the aging temperature and time are valid factors to decide mechanical shock reliability. Interfacial fractures are found in the 100°C aged test vehicle due to easier crack propagation at the interface between the thin Cu3Sn layer and the scallop-like Cu6Sn5 layer based on SEM microstructure analysis results. Finally, this investigation proposes how to improve solder joint reliability and prevent interfacial fracture for SAC305 lead-free application.

Microstructure Evolution of SnAgCuEr Lead-free Solders Under High Temperature Aging

In this work, we have systematically investigated the evolution of microstructure and of intermetallic compounds (IMCs), in particular, for lead-free SnAgCuEr solders during isothermal aging tests. The effect of trace amounts of the rare earth element Er on this process has also been studied. The results indicate that diffusion and reassembly occur in the solder matrix during the aging process, and the major influence of the rare earth element Er is concentrated on the nucleation sites. ErSn3 IMCs formed from the molten solder provide heterogeneous nucleation sites for the IMCs in the soldering and aging process. Subsequently, the Cu-Sn IMCs produced during soldering and Ag-Sn IMCs precipitated during the aging process have uniform size and evenly distribute in the solder matrix, and the refinement effect has been achieved in Er-containing solder joints. In addition, some cracks can be seen in Er-free solder joints, and the cracks may nucleate and propagate in the structure along the compound/solder boundaries after long aging times.

Influences of microstructure on service properties of 5Cr21Mn9Ni4N heat resistant alloy

The plates of four diesel engine exhaust valves used in a truck failed when servicing for 2000 h, which are made of 5Cr21Mn9Ni4N (21-4N) heat resistant alloy. Scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction were performed on the plate material of the failed valves and a new valve. The results show that the plate material before service is composed of first carbides (Cr23C6) and γ austenite matrix. However, appearance of the lamellar structure and plate-like precipitates within the grain is the general metallurgical features of the plate material of the failed valves, which indicates that the austenite matrix decomposed in service. XRD and electron diffraction results demonstrate that the lamellar structure is mainly composed of Cr23C6 and γ austenite, coexisting CrN phase, which formed by the discontinuous precipitation mechanism. Electron diffraction shows that the convex lens-like CrN phases precipitate within the grain, which formed by the continuous precipitation mechanism. Fractographic studies indicate that the fatigue is the dominant failure mechanism of the three valves and burning-through occurred on the plate of another failed valve. Formation of the lamellar structure and plate-like precipitations within the grain is mainly responsible for the failure of the valves. Isothermal aging tests were conducted on the plate material from the new valve to study the material stability at high temperatures. The microstructure development during aging was observed by SEM and optical microscopy. The influence of the microstructure on the service properties was discussed and possible failure causes of the valves were assessed.

Forward and Backward Compatibility of Solder Alloys With Component and Board Finishes

The primary objective of the research presented in this paper is to qualify the reliability of mixed assemblies by comparing them to the conventional Sn-Pb assembly and completely Pb-free assembly. The research investigates both forward and backward compatibility in electronic assemblies using a design of experiments (DOE) approach. The investigation utilized a test vehicle containing an area array component (BGA169) and chip components (0603 resistors). Hot air solder leveling (HASL) and organic solderability preservative (OSP) surface finishes were used on the test vehicles to represent Sn-Pb and Pb-free alternatives, respectively. The assembled test vehicles were cut into two panels - one containing a resistor section for isothermal aging and the other containing a BGA and another resistor section for thermal shock. The assemblies were subjected to isothermal aging and thermal shock tests as per Interconnecting and Packaging Electronic Circuits/Joint Electronic Device Engineering Council (IPC/JEDEC) standards. The resistors were sheared in the as-soldered condition, and at various isothermal aging intervals and thermal shock cycles. In order to simulate an intermetallic failure in isothermal aging, a reduced shear height (20 mum) was used for the shear test. The performance of the resistor solder joints were quantified in terms of the shear force. The performance of the ball grid array (BGA) solder joint during thermal shock testing was quantified in terms of the number of cycles to failure. Experimental results from shear analysis of resistor solder joints show that Pb-free alloy assemblies' performance is superior to those assembled using Sn-Pb alloy. Also, the ductile nature of the Sn-Ag-Cu (SAC) alloy provides the joints a better fatigue life. With the area array components, Pb-free assembly joints outlived the traditional Sn-Pb joints when subjected to thermal shock loading. Among the mixed assemblies, backward-compatible assemblies (Pb-free bumps and Sn-Pb solder alloy) showed superior performance. The microstructural analysis of the solder joints indicate a uniform distribution of lead in the solder joint matrix.

Material Degradation during Isothermal Aging and Thermal Cycling of Hybrid Mica Seal with Ag Interlayer under SOFC Exposure Conditions

Hybrid phlogopite mica seals with silver interlayers were evaluated in terms of material degradation in a combined isothermal aging and thermal cycling test. The hybrid mica was composed of a phlogopite mica paper sandwiched between two foils. The hybrid micas were first aged at for in a low hydrogen fuel , followed by short-term thermal cycling between and . The combined test was repeated three times for a total of aging at and 119 thermal cycles. The results of high-temperature leak rates showed very good thermal stability and thermal cycle stability with leak rates of . The hybrid mica was also tested in a high-water-content fuel and demonstrated similar leakage during the isothermal aging and the subsequent thermal cycles. Postmortem analyses showed no extensive reaction of Ag with phlogopite mica as well as the mica degradations. The issues of volatility of Ag and mica in the solid oxide fuel cell (SOFC) environments were discussed. Simple models were simulated to estimate the effect of leakage on the open-circuit voltage and the total fuel loss at various SOFC stack sizes. The results showed very minute fuel loss for the current hybrid micas and demonstrated it to be a good candidate for SOFC sealing.

Effects of bismuth on growth of intermetallic compounds in Sn-Ag-Cu Pb-free solder joints

The effects of Bi addition on the growth of intermetallic compound (IMC) formation in Sn-3.8Ag-0.7Cu solder joints were investigated. The test samples were prepared by conventional surface mounting technology. To investigate the element diffusion and the growth kinetics of intermetallics formation in solder joint, isothermal aging test was performed at temperatures of 100, 150, and 190 °C, respectively. The optical microscope (OM) and scanning electron microscope (SEM) were used to observe microstructure evolution of solder joint and to estimate the thickness and the grain size of the intermetallic layers. The IMC phases were identified by energy dispersive X-ray (EDX) and X-ray diffractometer (XRD). The results clearly show that adding about 1.0% Bi in Sn-Ag-Cu solder alloy system can refine the grain size of the IMC and inhibit the excessive IMC growth in solder joints, and therefore improve the reliability of the Pb-free solder joints. Through observation of the microstructural evolution of the solder joints, the mechanism of inhibition of IMC growth due to Bi addition was proposed.

An investigation of effects of Sb on the intermetallic formation in Sn-3.5Ag-0.7Cu solder joints

This study investigates the microstructural evolution and kinetics of intermetallic (IMC) formation in Sn-3.5Ag-0.7Cu lead-free solder joints with different percentages of Sb element, namely, Sn-3.5Ag-0.7Cu-xSb (x=0, 0.2, 0.5, 0.8, 1.0, 1.5, and 2.0). To investigate the elemental interdiffusion and growth kinetics of IMC formation, isothermal aging test is performed at temperatures of 100/spl deg/C, 150/spl deg/C, and 190/spl deg/C, respectively. Scanning electron microscope (SEM) is used to measure the thickness of intermetallic layer and observe the microstructural evolution of solder joint. The IMC phases are identified by EDX and XRD. Results show that some of the antimony powders are dissolved in the /spl beta/-Sn matrix (Sn-rich phase), some of them participate in the formation of Ag/sub 3/(Sn,Sb) and the rest dissolves in the Cu/sub 6/Sn/sub 5/ IMC layer. There is a significant drop in IMC thickness when Sb is added to 0.8 wt%. Over this amount the thickness of the IMC increases slightly again. The activation energy and growth rate of the IMC formation are determined. Results reveal that adding antimony in Sn-3.5Ag-0.7Cu solder system can increase the activation energy, and thus reduce the atomic diffusion rate, so as to inhibit the excessive growth of the IMC. The solder joint containing 0.8 wt% antimony has the highest activation energy. SEM images reveal that the number of small particles precipitating in the solder matrix increases with the increase in Sb composition. Based on the observation of the microstructural evolution of the solder joints, a grain boundary pinning mechanism for inhibition of the IMC growth due to Sb addition is proposed.

Reliability studies of Sn–9Zn/Cu solder joints with aging treatment

Sn–9Zn (in wt.%) solder ball was bonded to Cu pad, and the effect of aging on shear reliability was investigated. After reflow, the intermetallic compound (IMC) phase formed at the interface was Cu 5Zn 8, and the as-reflowed Sn–9Zn/Cu joint had sufficient shear strength. In the isothermal aging test, only Cu 5Zn 8 IMC was observed in the samples aged at temperatures between 70 and 120 °C. On the other hand, after aging at 150 °C for 250 h, Cu 6Sn 5 phase was observed at the interface between the interfacial Cu 5Zn 8 IMC layer and the Cu substrate. And, the layer-type Cu 5Zn 8 IMC layer was disrupted locally at the interface. In the ball shear test conducted after aging treatment, the shear strength significantly decreased after aging at all temperatures for initial 100 h, and then remained constant by further prolonged aging. The fracture mainly occurred at the interface between the solder and Cu 5Zn 8 IMC layer. The aged Sn–9Zn/Cu solder joint had an inferior joint reliability.

Aging treatment characteristics of solder bump joint for high reliability optical module

The joint strength and fracture surfaces of Sn–37 mass% Pb and Au stud bumps for photo diode packages after isothermal aging testing were studied experimentally. Al/Au stud bumps and Cu/Sn–37 mass% Pb solders were adopted, and aged for up to 900 h to analyze the effect of intermetallic compound (IMC). The joint strength decreased with aging time. The diffraction patterns of Cu 6Sn 5, scallop-shaped IMCs, and planar-shaped Cu 3Sn were characterized using transmission electron microscopy (TEM). The formation of Kirkendall voids and the growth of IMCs at the solder were found to be a possible mechanism for joint strength reduction.

솔더범프와 TiW/Cu/electroplating Cu UBM 층과의 금속간 화합물 형성과 범프 전단력에 관한 연구

The joint strength and fracture surface of Sn-Pb solder bump in photo diode packages after isothermal aging testing were studied experimentally. Cu/Sn-Pb solders were adopted, and aged for up to 900 hours at 12<TEX>$0^{\circ}C$</TEX> and 17<TEX>$0^{\circ}C$</TEX> to analyze the effect of intermetallic compound(IMC). In 900-hour aging experiments, the maximum shea strength of Sn-Pb solder decreased by 20％ and 9％. The diffraction patterns of Cu<TEX>$_{6}$</TEX>Sn<TEX>$_{5}$</TEX>, scallop-shape IMC, and planar-shape Cu<TEX>$_3$</TEX>Sn were observed by Transmission Electron Microscopy (TEM).EM).

Shear Strength in Solder Bump Joints for High Reliability Photodiode Packages

The shear strength and fracture surfaces of Sn-Pb bump and Au stud bump for photodiode packages after isothermal aging testing were studied experimentally. Al/Au stud bumps and Cu/Sn-37 mass%Pb solders were adopted, and aged at 373 K and 423 K for up to 900 hours to analyze the effect of intermetallic compound (IMC). The shear strength decreased with aging time. The diffraction patterns of Cu6Sn5, scallopshaped IMCs, and planar-shape Cu3Sn were observed by transmission electron microscopy (TEM). The formation of Kirkendall voids with the growth of IMCs at the solder was found to be a possible mechanism for shear strength reduction. IMCs between Au stud bumps and Al pads were identified as AlAu2.

Study of epoxy and epoxy-cyanate networks thermal degradation to predict materials lifetime in use conditions

Composite materials are used more and more for aeronautical applications and they have to be as thermally stable as possible. The thermostability of carbon-fiber/epoxy–cyanate composites elaborated with an autoadhesive and autoextinguish prepreg were tested. Dynamical and isothermal aging tests were carried out to evaluate the composite thermal stability. Thermal degradation products were identified by chromatography/mass spectrometry analysis and the results obtained were compared with data known on the material network structure. The physicochemical network structure evolutions and the thermal aging data are correlated with the interlaminar shear strength (ILSS) mechanical results. For epoxy–cyanate composites, cracking appears after a longer time of aging than for epoxy composites. This new epoxy–cyanate material isothermal stability seems to be good and particularly good if it was postcured after processing. The comparison of chemical, mechanical, and crack formation results obtained by accelerated aging tests allowed us to determine models to predict long-term behavior. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 3142–3153, 2000

Isothermal aging test results (up to 100 000 h) of NiCrMoV steels for low-pressure steam turbine

Isothermal aging test of NiCrMoV rotor steel was carried out up to 100 000 h and change in the Charpy transition behavior was investigated. The test result revealed considerable embrittlement of the steels tested. Even at 343°C, the embrittlement of around 100°C was observed and higher temperature enhanced the embrittlement significantly. This embrittlement behavior strongly depends on the impurity contents of the materials and temper embrittlement parameter J factor or X well characterize the temper embrittlement susceptibility. Based on these test results, the amount of the temper embrittlement can be estimated from the information of chemistry. A correlation between the step cooling embrittlement and 100 000 h embrittlement was also found.