Showing papers in "Journal of Electronic Packaging in 1989"

Advances in Thermal Modeling of Electronic Components and Systems, Vol. 1

Abstract: This volume opens with a sweeping overview of the physical design of electronic systems-methodology, technology, and future challenges-thermally induced failures in electronic systems. Subsequent chapters examine the causes for thermally induced failures of electronic components and the techniques used to analyze and prevent such failures. It gives a comprehensive bibliograhy of project managers and lead engineers, packaging engineers and mechanical analysts, consultants, and academic, industrial, and government laboratory researchers.

Observations on the Mechanisms of Fatigue in Eutectic Pb-Sn Solder Joints

Abstract: Near-eutectic Pb-Sn solders are widely used for joints in electrical devices. These are liable to failure by thermal fatigue during operation of the device. Since the thermal fatigue load is often in shear, the mechanisms of thermal fatigue in shear fare of particular interest. Recent research has shown that the thermal fatigue of eutectic solders in shear is preceded by the formation of bands of coarsened material in the eutectic microstructure, which concentrate the deformation and cause the nucleation of fatigue cracks. Such coarsened bands are also observed in isothermal fatigue and unidirectional creep in shear. Since creep experiments are relatively simple to conduct and analyze, these have been used to study the formation and growth of coarsened bands. The mechanism includes three steps: the formation of inhomogeneous shear bands, the onset of recrystallization in the shear band to create a planar region of coarsened material, and the propagation of the coarsened band by progressive recrystallization at its tip. The results are applied to thermal fatigue and some of their implications are discussed. 12 refs., 12 figs.

The Effect of Variations in Stream-Wise Spacing and Length on Convection From Surface Mounted Rectangular Components

Abstract: The effect of variations in stream-wise spacing and component length on convection from rectangular, surface mounted components in a channel flow are reported. Component dimensions are the same order of magnitude as the channel wall-to-wall spacing. The channel Reynolds number, with air as the coolant, ranged from 670 to 3000. Flow visualization showed that under the above conditions the channel flow is transitional. The effect of variations in component stream-wise spacing on the level of turbulence in the channel and on the interaction between the core of the channel flow and the recirculating flow in cavities between components is discussed. Pressure drop measurements show that the dominant loss mechanism is due to form drag caused by the components. Local heat transfer measurements are made using an interferometer. Analysis of the results shows that the overall heat transfer is properly correlated in terms of a flow Reynolds number based on the component length. At small component Reynolds number, the overall conductance tends towards the laminar smooth wall value. An overall correlation is proposed which includes the effect of component Reynolds number, channel wall-to-wall spacing, and component stream-wise spacing.

Thermal Stress Analysis of SMT PQFP Packages and Interconnections

Abstract: An elasto-plastic analysis of the thermal stresses and strains in a surface mounted plastic-quad-flat-pack (PQFP) assembly by using a 3-D finite element method is presented in this paper. Detailed stress and strain distributions and whole-field displacements of the assembly are also provided for a better understanding of its mechanical behavior during thermal cycling. It was found that the stresses and strains in the PQFP solder joint are smaller than those in the plastic-leaded-chip-carrier (PLCC) solder joint. The results presented herein should be useful in the design for reliability of this class of surface mount assemblies.

Thermal Stress Analysis of a Bimaterial Strip Subject to an Axial Temperature Gradient

Abstract: Formulas are derived for the stresses and displacements in a bimaterial strip which is subjected to a temperature gradient that varies linearly in the longitudinal direction. The solution is obtained by superposing certain fundamental linear elastic stress states which are compatible with bar and beam theory. The analytical results are approximate in the sense that stress-free boundary conditions are not satisfied exactly, since only zero resultant force and moment conditions are enforced. Finite element calculations have been performed to verify the results and to ascertain the level of stress concentration near the ends of the strip.

An Overview of Integrated Circuit Device Encapsulants

Abstract: The rapid development of integrated circuit technology from small-scale integration (SSI) to very large scale integration (VLSI) has had great technological and economical impact on the electronics industry. The exponential growth of the number of components per IC chip, the exponential decrease of device dimensions, and the steady increase in IC chip size have imposed stringent requirements, not only on the IC physical design and fabrication, but also on IC encapsulants. This report addresses the purpose of encapsulation, encapsulation techniques, and a general overview of the application of inorganic and organic polymer materials as electronic device encapsulants.

Ceramic Materials for Electronic Packaging

Abstract: The paper reviews ceramic materials that are used or can be used in electronic packaging. Main attention is given in relatively new packaging materials such as highly thermal conductive AlN and SiC (BeO-doped) or low-firing cordierite and spodumene glass-ceramics. Application of sol-gel processes in preparation of ceramic powders is discussed.

Finite Element Modeling for Optimizing Hermetic Package Reliability

Abstract: The thermal stresses in microwave packages are studied by the finite element method. Emphasis is placed on the effects of material construction and design on the reliability of very small hermetic packages. Three different microwave packages have been designed and six finite element models (two for each design) have been analyzed. To verify the validity of the finite element results, some leak tests have been performed and the results agree with the analytical conclusions. The results presented herein should provide a better understanding of the thermal behavior of hermetic packages and should be useful for their optimal design.