Thermal Cycling Environments Research Articles

Thermal Cycling Effects on Dynamic Mechanical Properties and Crystallographic Structures of Silicon Nitride-Based Structural Ceramics

Thermal cycling effects on dynamic mechanical properties of hot pressed silicon nitride (HPSN) based structural ceramics were investigated in a simulated thermal cycling environment from room temperature up to 1100°C. Two monolithic silicon nitrides and two silicon nitride composites reinforced with silicon carbide whiskers were studied in such an environment. Experiments show that the dynamic mechanical properties of the tested materials are influenced by thermal cycle. The materials stiffened slightly while damping capacity decreased slightly during each thermal cycle. X-ray diffraction (XRD) was subsequently used to examine the corresponding crystallographic alterations. The XRD patterns show that the amorphous glass phases in the silicon nitride matrix were partially crystallized during thermal cycling.

Dynamic Mechanical Properties of Ceramics and Ceramic Composites at Elevated Temperatures

This paper presents the preliminary results of our research on dynamic mechanical properties of silicon nitride based ceramics and ceramic composites at elevated temperatures. The temperature-dependent dynamic elastic modulus and internal damping of the cantilever beam samples were measured from room temperature up to 1100°C. The dynamic mechanical behavior is found to be rather stable up to 700°C, but damping peaks are found to occur at around 900°C, accompanied by a corresponding relaxation in elastic modulus for the tested samples. By simulating the thermal cycling environment of engines, the resulting changes in the dynamic mechanical properties of the samples are observed. The possible mechanisms affecting the dynamic mechanical properties of these ceramics and ceramic composites, with special emphasis on high-temperature behavior, are discussed.

Thermal fatigue behavior of J-lead solder joints

Thermal cycling environments were applied to test specimens with J-lead eutectic Sn-Pb solder joints to assess the effect of lead and package material selection. Metallographic examination and finite element analysis were used to evaluate the effect of thermal cycling environments on solder joints. Matching the coefficient of thermal expansion (CTE) of the lead and solder was found to be crucial to reducing thermal cycling damage for the J-lead solder joints examined. Matching the CTE of the package and the board was substantially less important. The number of thermal cycles 1.9 nucleate cracks in the J-lead solder joints correlated reasonably well with the number of cycles to produce a 50% drop in the load range in isothermal strain controlled mechanical fatigue tests on Sn/Pb solder.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Crack Propagation in Solder Joints During Thermal-Mechanical Cycling

Differential expansion induced creep-fatigue resulting from temperature cycling is an important cause of solder joint failure. The deterioration of solder joint integrity typically involves a sequential development of local stressing, microcracks, crack initiation and crack propagation, ultimately resulting in electrical open-circuiting by total joint separation from the PWB footprint. To better understand the failure process, a series of combined analytical and experimental investigations have been performed on flat-pack parts with gull-wing leads ranging in height from 9 to 56 mils. JPL’s special purpose nonlinear finite element computer program has been modified to dynamically simulate the crack propagation process. Solder creep properties, including the effect of grain growth, are also incorporated into the model. Depending upon the system geometry and materials properties, the combination of crack development and grain growth may have either a positive or negative effect on the rate of cracking of the solder elements. Consequently, the crack propagation process may accelerate or decelerate as cycles progress. Sensitivity studies are used to highlight the individual effects of crack propagation and grain growth and compare the failure prediction results with those obtained using conventional finite element techniques. The analytical results are corroborated using visual observations obtained using SEM photography of test samples exposed to the thermal-cycle environment used in the analysis.

Durable glass–epoxy composites cured at low temperatures—Effects of thermal cycling, UV irradiation and wet environment

AbstractGlass‐fibre‐epoxy composites cured with oligomeric polyaminophenolic agents have shown good dimensional stability during thermal cycling at temperatures over 100°C, even if their curing is carried out at room temperature. It was therefore believed important to evaluate their behaviour in different environmental conditions. Their good mechanical characteristics are maintained after saturation with water, UV irradiation, and thermal cycling between 0 and 110°C. From the following tests the environmental resistance is clearly higher than that of composites cured with other aminic agents.

The application of scanning laser extensometry to explore thermal cycling creep of metal matrix composites

In-cycle creep data for metal matrix composites undergoing thermal cycling while under load are essential to the understanding of composite stress relaxation mechanisms. Such information may enable life predictions to be made for structural components in thermal cycling environments. Non-contacting laser scanning extensometry is here shown to be a relatively straightforward technique for making in-cycle strain measurements. Accuracy of ±2 μm is maintained. Preliminary results utilizing this novel technique are shown for the Al-10vol.%C fibre composite system. The composite is observed to creep in the reverse sense to the applied load during the cooling part of the cycle. This is unsurprising in view of calculations from the Eshelby model, indicating that internal stresses from differential thermal expansion can be highly significant compared with those from an external load.

A Systems Approach to Solder Joint Fatigue in Spacecraft Electronic Packaging

Differential expansion induced fatigue resulting from temperature cycling is a leading cause of solder joint failures in spacecraft. Achieving high reliability flight hardware requires that each element of the fatigue issue be addressed carefully. This includes defining the complete thermal-cycle environment to be experienced by the hardware, developing electronic packaging concepts that are consistent with the defined environments, and validating the completed designs with a thorough qualification and acceptance test program. This paper describes a useful systems approach to solder fatigue based principally on the fundamental log-strain versus log-cycles-to-failure behavior of fatigue. This fundamental behavior has been useful to integrate diverse ground test and flight operational thermal-cycle environments into a unified electronics design approach. Each element of the approach reflects both the mechanism physics that control solder fatigue, as well as the practical realities of the hardware build, test, delivery, and application cycle.

Creep-Fatigue Behavior of Microelectronic Solder Joints

ABSTRACTEven at room temperature, solder joints exhibit both creep and fatigue behavior that is strongly dependent on solder joint configuration, the thermal environment, and the solder alloy properties. The microstructures of solder joints with up to 25 years of aging have been studied using SEM/EDS and metallographic techniques. Data are presented on grain growth and metallurgical composition versus aging time. A special non-linear finite element creep-fatigue simulation model has been developed, based on measured strain-rate hardness relationships, and used to analytically predict the effects of observed metallurgical changes and the effects of lead stiffness in solder joint creepfatigue interaction. To corroborate the analytical results, a special bi-metallic test fixture has been developed to accelerate the thermo-mechanical loading of solder joints in thermal cycling environments. Measured time-to-failure data for various electronicpackage lead configurations/stiffnesses, including gullwing and J-lead, are presented and shown to be in reasonable agreement with the analytical results.

Creep-Fatigue Behavior of Microelectronic Solder Joints

AbstractEven at room temperature, solder joints exhibit both creep and fatigue behavior that is strongly dependent on solder joint configuration, the thermal environment, and the solder alloy properties. The microstructures of solder joints with up to 25 years of aging have been studied using SEM/EDS and metallographic techniques. Data are presented on grain growth and metallurgical composition versus aging time. A special non-linear finite element creep-fatigue simulation model has been developed, based on measured strain-rate hardness relationships, and used to analytically predict the effects of observed metallurgical changes and the effects of lead stiffness in solder joint creepfatigue interaction. To corroborate the analytical results, a special bi-metallic test fixture has been developed to accelerate the thermo-mechanical loading of solder joints in thermal cycling environments. Measured time-to-failure data for various electronicpackage lead configurations/stiffnesses, including gullwing and J-lead, are presented and shown to be in reasonable agreement with the analytical results.

Survivability of thermal barrier coatings

Thermal barrier ceramic oxide coatings are gaining wide acceptance for applications in heat engines. Such ceramic thermal shields are used in conjunction with MCrAlY-type intermediate bond coatings, applied over superalloy substrates. The thermal barrier coatings must endure extreme thermal cycling and hostile chemical environments. A discussion is presented on the various important features which need to be addressed in the design of viable thermal barrier coating systems.

The Reliability of Surface Mounted Solder Joints Under PWB Cyclic Mechanical Stresses

The advent of Surface Mounting Technology (SMT) has led to concern about the long term reliability of solder joints during environmental thermal cycling, power cycling and PWB mechanical flexure. This paper describes the results of testing PWB assemblies of both through hole and SM components in a mechanical flexure jig in which the amplitude and frequency of cycling were varied. The apparent degradation of through hole solder joints (particularly to DIL devices) was often found to be worse than the SMT joints. Lower flexure cycle frequencies were much more damaging to all solder joints than higher frequencies. The results indicate that most SMT solder joints survive realistic flexure cycling very well but that poorly formed joints, which may appear visually to be acceptable, can fail prematurely. Solder joints to leadless ceramic chip carriers are the most susceptible to flexure stresses and special precautions should be taken in their application to substrates which are not entirely rigid, such as PWBs.

Stress testing and reliability

Two empirical equations giving the test strength of constant temperature and thermal cycling environments are compared for effectiveness in precipitating defects in electronic components. Analysis of the equations shows that they can be put into a form which has a theoretical basis although the structure still remains empirical.

Comparison of screen-printed with vacuum-deposited film resistors under thermal cycling environment

Comparison of screen-printed with vacuum-deposited film resistors under thermal cycling environment