Temperature Cycling Conditions Research Articles

BGA Board Level Reliability Analysis & Optimization

The solder joint reliability of semiconductor package interconnects to printed circuit boards is critical for product durability. A dominant failure mode is solder fatigue due to the CTE mismatch between the BGA component and PCB at thermal cycling. However, it is well known that other factors can impact fatigue behavior and time to failure such as solder joint geometry, die geometry, solder system, etc. Finite element modeling (FEM) and simulation can play an integral role in providing deeper insight into the impact of these package parameters on the overall assembly. However, a major challenge of accurately modeling these systems includes simulation of multiple length scales from the package, substrate, and solder joints. The FEM approach addressing these can lead to reduced cycle time, accurate simulation, and improved package performance. In this work, the finite element modeling and simulation procedure is demonstrated for a BGA package at accelerated temperature cycling conditions. At the component level, key details regarding the properties and constituents of the BGA package mold compound and substrate are established by coupling measured experimental warpage data and finite element modeling. Comparison of simulated & Thermoire measurements shows excellent agreement at the package level, with warpage correlation achieved over the entire temperature range. At the assembly level, the truncated sphere model is used to arrive at precise solder joint profiles for accurate representation to tie the package to the board. The combined validated package-level results and solder joint profiles are employed towards a subsequent thermo-mechanical analysis of the full BGA assembly. The entire simulation procedure is demonstrated for a BGA design, where inelastic creep and reliability test data are compared. High strain regions in the solder joint array are shown to compare closely with regions of failure from experimental reliability test data. The validated FEM model allows for extrapolating to similar package conditions allowing faster design cycle time and less time consuming experimental work.

Simulation of ionomer membrane fatigue under mechanical and hygrothermal loading conditions

Understanding the fatigue lifetime of common perfluorosulfonic acid (PFSA) ionomer membranes under fluctuating hygrothermal conditions is essential for the development of durable fuel cell technologies. For this purpose, a finite element based fatigue lifetime prediction model is developed based on an elastic–plastic constitutive model combined with a Smith-Watson-Topper (SWT) fatigue formulation. The model is validated against previously reported experimental results for a membrane under cyclic mechanical loadings. The validated model is then utilized to investigate the membrane fatigue lifetime in ex-situ applications under cyclic humidity and temperature conditions. The simulations suggest that the membrane fatigue lifetime is shorter under fluctuating humidity loadings than for temperature loadings. Additionally, the membrane fatigue lifetime is found to be more sensitive to the amplitude of the strain oscillations than to the mean strain under hygrothermal cycling. Most notably, the model predicts that simultaneous humidity and temperature cycling can exacerbate the fatigue process and reduce the fatigue lifetime by several orders of magnitude compared to isolated humidity or temperature cycling. The combination of measured mechanical fatigue data and the present numerical model provides a useful toolkit for analysis of membrane fatigue due to hygrothermal variations, which can be costly and time-consuming when addressed experimentally.

Improved Reliability of Power Modules: A Review of Online Junction Temperature Measurement Methods

Power electronic systems play an increasingly important role in providing high-efficiency power conversion for adjustable-speed drives, power-quality correction, renewable-energy systems, energy-storage systems, and electric vehicles. However, they are often presented with demanding operating environments that challenge the reliability aspects of power electronic techniques. For example, increasingly thermally stressful environments are seen in applications such as electric vehicles, where ambient temperatures under the hood exceed 150 °C, while some wind turbine applications can place large temperature cycling conditions on the system. On the other hand, safety requirements in the aerospace and automotive industries place rigorous demands on reliability.

Superionic conductivity of Sr0.68Pr0.32F2.32 (type CaF2) and Pr0.85Sr0.15F2.85 (type LaF3) crystals, as-grown and after high-temperature annealing

The influence of high-temperature annealing (900°C, 14 days) in a fluorinating atmosphere on the superionic conductivity σ of as-grown Sr0.68Pr0.32F2.32 single crystals with fluorite structure (CaF2) and Pr0.85Sr0.15F2.85 single crystals with tysonite structure (LaF3), obtained by the directional solidification of melts in the SrF2-PrF3 system using the Bridgman method, is studied. The annealing that brings the defect structure of crystals to equilibrium at 900°C (which is retained by quenching) does not affect σ values. At 500 K, σ is 4 × 10−4 and 2 × 10−2 S/cm for Sr0.68Pr0.32F2.32 and Pr0.85Sr0.15F2.85, respectively. As-grown superionic conductor single crystals, which are formed in some MF2-RF3 systems (M = Ca, Sr, Ba; R are rare earth elements), where the mutual solubility of components in nonstoichiometric phases depends weakly on temperature, can be used in solid-state electrochemical devices operating at high temperatures and under temperature cycling conditions without the deterioration of their electrical characteristics.

Effect of Temperature Cycling on Stress Relaxation Behavior of Electrical Connector Contacts

This paper mainly studies the effect of temperature cycling on stress relaxation behavior of contacts for electrical connectors. Based on the analysis of the test specifications of electrical connectors, this paper provides a kind of test method on stress relaxation behavior of electrical connector contacts under temperature cycling conditions. The detecting circuit is designed; the test is carried out and finally, according to the test data, it can be concluded that 1) for the same temperature change, the absolute change of strain within the temperatures above zero is bigger than that within the subzero temperatures; 2) the deformation of contacts gradually increases as the number of cycles increases. The length of the degradation process for electrical connectors might be related with the high temperature value, temperature variation or temperature variation rate.

Fatigue behaviour of coke drum materials under thermal-mechanical cyclic loading

Coke drums are vertical pressure vessels used in the delayed coking process in petroleum refineries. Significant temperature variation during the delayed coking process causes damage in coke drums in the form of bulging and cracking. There were some studies on the fatigue life estimation for the coke drums, but most of them were based on strain-fatigue life curves at constant temperatures, which do not consider simultaneous cyclic temperature and mechanical loading conditions. In this study, a fatigue testing system is successfully developed to allow performing thermal-mechanical fatigue (TMF) test similar to the coke drum loading condition. Two commonly used base and one clad materials of coke drums are then experimentally investigated. In addition, a comparative study between isothermal and TMF lives of these materials is conducted. The experimental findings lead to better understanding of the damage mechanisms occurring in coke drums and more accurate prediction of fatigue life of coke drum materials.

Development of Medium-Temperature Solid Oxide Fuel Cell Materials and Single Cells in Estonia

Estonian solid oxide fuel cell program started in 2001. Solid oxide fuel cell single cells based on Ni-Ce0.9Gd0.1O2-δ or Ni-Zr0.92Y0.08O2-δ supporting anodes, bi-layered Zr0.92Y0.08O2-δ | Ce0.9Gd0.1O2-δ or Zr0.9Sc0.1O2-δ | Ce0.9Gd0.1O2-δ electrolytes and micro-meso-porous La0.6Sr0.4CoO3-δ, Gd0.6Sr0.4CoO3-δ or Pr0.6Sr0.4CoO3-δ cathodes prepared from nano/microporous powders at different sintering temperatures and pore former additions in the raw cathode and anode pastes have been studied. Different physical (XRD, high-temperature XRD under electrochemical working conditions, FIB-SEM, AFM, and BET) and electrochemical (cyclic voltammetry, chronoamperometry and electrochemical impedance) methods have been applied. Influence of the anode and cathode porosity, depending on the electrode preparation methods, and also of the bi-layered electrolyte properties (chemical composition, thickness, etc.) on the power density of the single cells has been shown and discussed. During last two years the synchrotron radiation based X-ray absorption spectroscopy under electrochemical polarization, gas feeding and temperature cycling conditions has been applied for analysis of anode surface composition.

Prediction of thermo-mechanical fatigue for solder joints in power electronics modules under passive temperature cycling

A thermodynamically consistent cohesive zone model accounting for mixed-mode loadings suitable for analysis of thermo-mechanical fatigue is presented in this work. Fatigue effect on cracking is included using a damage evolution law which is dependent not only on the displacement jump, but also on the damage accumulation. The damage state is irreversible and evolves during loading, but not unloading. The stiffness of the cohesive zone is degraded with the increase of damage level. Temperature dependence of both stiffness and fracture energy is incorporated in the fatigue model due to the high operating temperature experienced by the solder material. Simulations are carried out in order to predict the number of cycles to failure of the solder joint in power electronics modules under passive temperature cycling conditions.

Surface finish effect on reliability of SAC 305 soldered chip resistors

PurposeThe purpose of this paper is to assess the long‐term reliability of lead‐free Sn96.5Ag3.0Cu0.5 (SAC305) under accelerated temperature cycling (ATC) conditions. Test vehicles consisted of commercial 2512 ceramic chip resistors soldered to printed circuit boards (PCBs) using three different Pb‐free surface finishes: organic solderability preservative (OSP), immersion silver (IAg) and electroless nickel immersion gold (ENIG).Design/methodology/approachTwo populations of solder joints were monitored continuously during a thermal cycle of 0°C to 100°C with a ramp rate of 10°C/min and a 30 min dwell at the temperature extremes. One population was cycled to 2,500 cycles, the other population was cycled to 8,250 cycles. Failures were defined in accordance with the IPC‐9701A industry test guidelines and failure data are reported as characteristic life, η. Microstructural evolution was characterised using metallographic techniques and back‐scattered scanning electron microscopy (SEM). Fractography was performed on post‐cycled resistors to determine failure mechanisms.FindingsThe results showed that the lifetime of the chip resistors could be ranked as follows: OSP>ENIG>IAg after 8,250 thermal cycles, when>73 per cent of the population had failed. It was found that the relative performance of OSP finishes improved with longer periods of cycling. This was attributed to diffusion of copper into the bulk solder and which subsequently, over time, acted as a dispersion strengthening mechanism. The relatively poor performance of IAg finishes was attributed to void formation.Originality/valueThe paper provides new and valuable information to end‐users about the long‐term reliability of lead‐free solder on three commonly used lead‐free surface finishes. The performance of each surface finish is explained in terms of microstructural evolution and void formation.

Oxide scale exfoliation and regrowth in TP347H superheater tubes

AbstractThis paper provides an introduction to a comprehensive model being developed to predict and control oxide scale exfoliation from the steam‐side of superheater and reheater tubes in steam boilers. The model deals with the main phenomena involved in scale growth and failure in steam, and incorporates major variables related to boiler design and operation. The considerations used to calculate oxide growth under the specific constrains of small diameter tubes carrying high‐pressure steam and operating with large temperature gradients under temperature and pressure cycling conditions, as well as the evolution of stresses and strains in the scales, are indicated but only a cursory description is given of the details of the analytical treatments. An example is presented of calculations made with the model to predict the extent of blockage expected in a single superheater loop as a function of time and outlet steam temperature under several realistic service conditions. The results suggest that problems due to scale exfoliation would be expected early in the operating life of superheater tubes made from austenitic steel TP347H.

Field failure mechanism study of solder interconnection for crystalline silicon photovoltaic module

This study investigates a solder interconnection failure of a 25-year-old crystalline silicon photovoltaic (c-Si PV) module and draws conclusions on the failure mechanism of the solder interconnection. The efficiency degradation of the 25-year-old c-Si PV module is –23%. Physical analysis of the solder interconnection failure finds solder to solder cracking and solder to Ag paste cracking. The main failure mechanism of the solder interconnection crack is caused by coefficient of thermal expansion (CTE) mismatch between the module material and the ribbon wire solder as shown by FMEA. To demonstrate the failure mechanism, a thermal cycle test is designed and conducted on a small c-Si PV module. The temperature cycle condition is −45°C to 85°C and the dwell time is 20min. Measurements are carried out every 100cycles monitoring the series resistance (Rs) through dark I–V. The result shows that Rs increases. After 1,000cycles, the characteristics of dark I–V and light I–V are compared and analyzed. Failure mechanism analysis is conducted for the modules for which Pmax decreased with 20%. Water-jet techniques for cross-section and SEM are used to analyze the factor of resistance change and efficiency degradation. The failure mechanism of solder interconnection for c-Si PV Module is proved.

Development and tests of thermally stable potting and impregnating compounds

The results of investigation of domestic impregnating and potting compounds that can function at temperatures up to 180–200°C developed at JSC Kompozit are presented. It is shown that these materials function at temperatures up to 200°C, as well as under conditions of elevated humidity and temperature cycling.

A numerical procedure for simulating delamination growth on interfaces of interconnect structures

A fracture mechanics based numerical approach is developed for modeling delamination growth on materials interfaces in integrated circuit (IC) interconnects. In this approach, the heterogeneous interconnect structures neighboring the cracked interface are approximated by homogenized layers with transversely isotropic elastic properties. Evolution of the interface crack under fatigue condition is modeled by using an incremental approach, in which the fracture mechanics parameters including the strain energy release rate, the normalized stress intensity factors and phase angles are first estimated by post-processing finite element solutions. The fracture mechanics parameters along the curvilinear front of the interface crack are then substituted into a steady-state fatigue crack growth model for obtaining the crack growth increments. The process is repeated to simulate subsequent crack growth for predicting interconnect structural reliability under fatigue condition. The evolution of an interface corner crack in a back-end-of-line (BEOL) Cu/low-k interconnect structure under temperature cycling condition is considered as an application example of the procedure.

Early-age tensile properties of structural epoxy adhesives subjected to low-temperature curing

The early-age mechanical property development of structural adhesives during low temperature curing is critical for the outdoor construction of engineering structures, such as bridges or buildings. Construction of these structures is also carried out during winter time at low curing temperatures. Experimental investigations showed that the development of the tensile properties of a commercial structural epoxy adhesive strongly depended on the curing temperature. Lower curing temperatures significantly decelerate the process and consequently the rate of development of mechanical properties. At 0°C, curing was inhibited or did not initiate at all. Tensile strength and stiffness developed at the same rate, although the former was slightly delayed compared to the latter. Significant development of the mechanical properties began only after the onset of material vitrification. This was in contrast to the development of the glass transition temperature, which increased particularly before vitrification. A proposed analytical model predicted the development of mechanical properties well, particularly under low isothermal and cyclic temperature conditions.

BGA Solder Life Prediction under Combined Power and Temperature Cycling Condition

Solder interconnect failure is a known life limiting failure mechanism that is induced by cyclic temperature excursions. Thermal fatigue reliability of solder interconnects is conventionally assessed by simple temperature cycling test, which applies a constant temperature range, fixed dwell times and ramp rates during the test. However, due to the user controlled power cycles, non-constant workloads, and changes in the surrounding environment, electronics in the field often experience a complex combination of temperature and power cycling. In this study, the effect of power cycling superposed on a simple temperature cycling is experimentally examined. Furthermore, a scheme for modeling the solder interconnect fatigue life of Plastic Ball Grid Array (PBGA) parts under the concurrent power and temperature cycling. Damage, defined as the number of applied cycles over the number of survivable cycles, from the simple temperature cycle and the power cycle are linearly added using Miner's rule, and compared with the concurrent temperature and power cycling test. Cycles to failure of each condition is derived by life testing conducted on Plastic Ball Grid Array (PBGA) assembled with eutectic and SAC305 solder.

J061035 はんだ接合部のき裂進展特性に及ぼす温度サイクル条件の影響 : 損傷パスシミュレーションによる検討

J061035 はんだ接合部のき裂進展特性に及ぼす温度サイクル条件の影響 : 損傷パスシミュレーションによる検討

Thermal Cycling Analysis of BGA Solder Joint Reliability

The solder joint reliability of semiconductor package interconnects is critical to product durability. A dominant failure mode is solder fatigue due to the CTE mismatch between BGA component and PCB at thermal cycling. It is well known that besides thermal expansion mismatch of component and board, the solder joint geometry has a great impact on fatigue behavior and time to failure. In this study, a combination of Surface Evolver and finite element analysis are use to predict the solder joint shapes for the assembly of medium pin count BGA's and to estimate the reliability at accelerated temperature cycling conditions. Results of Surface Evolver are compared with the assumption of a truncated sphere. The solder shape predictions are applied for a subsequent thermo-mechanical analysis of the BGA assembly. Inelastic creep deformation is evaluated for critical solder balls, and the Coffin-Manson relation is used to estimate the solder joint lifetime. The entire simulation procedure will be demonstrated for a product design study for high reliability automotive BGA's. A fractional factorial design is defined that considers solder sphere diameter and solder pad sizes on BGA substrate and on PCB side. Resulting creep values and lifetime estimates will be compared.

Effects of package geometry on thermal fatigue life and microstructure of Sn–Ag–Cu solder joint

Soldering experiments of chip scale package devices were carried out by means of diode laser soldering system with Sn–Ag–Cu solders. In addition, pull tests and a scanning electron microscope were used to analyse the effect of processing parameters on mechanical strength of solder joints. Viscoplastic finite element simulation was utilised to predict solder joint reliability for different package geometry under accelerated temperature cycling conditions. The results indicate that under the conditions of laser continuous scanning mode as well as the fixed soldering time, an optimal power and package geometry exists, while the optimal mechanical properties of microjoints are gained.

Development of a Life Test Platform for Bearings Lubricated by Solid Lubricant under the Vacuum and Temperature Cycling Environment

In order to investigate the life of bearings lubricated by solid lubricant (BLSL), which are installed in the rotational parts of spacecraft, a test platform has been developed. The platform can test the life of BLSL working under the vacuum environment with high-low temperature cycle conditions. The test platform consists of three systems of loading, measurement, and power and speed control. A corresponding computer program was also developed to measure, monitor and record test data. The working life of deep groove ball bearings lubricated by MoS2 solid lubricant was tested in 5×10-4Pa vacuum. The surface observation and analysis for the damage condition of the failed bearings were also conducted.

Assessment of Solder-Dipping as a Tin Whisker Mitigation Strategy

Tin whiskers have been brought back into the spotlight due to the transition of the electronics industry to lead-free solders. Many different tin whisker failure mitigation strategies are being evaluated by researchers. This paper investigates the technique of solder-dipping as a tin whisker mitigation strategy for tin-based lead-free finished surfaces used in electronic products. Tin finished Alloy 42 lead-frame parts are subjected to the solder-dip process. For this paper, the solders included eutectic tin-lead and tin-silver-copper. In addition, tin-bismuth (Sn-Bi) finished alloy 42 lead-frame parts are also examined to assess the effectiveness of the Sn-Bi finish in mitigating tin whisker growth. Parts under study are subjected to temperature cycling conditions to promote whisker formation. It is observed that whiskers are formed on all treatment surfaces, with the longest whiskers occurring on the pure tin-finished parts. The solder-dipped parts showed better mitigation of tin whiskers than the pure tin-finished parts.