Showing papers by "Avram Bar-Cohen published in 1997"

Coffin-Manson fatigue model of underfilled flip-chips

Abstract: The fatigue life of an underfilled flip-chip package has been evaluated using the Coffin-Manson relation and finite element modeling (FEM)-computed solder shear strain for typical flip-chip structures. In the course of this effort, numerical simulations were performed for underfill materials of varying thermo-structural properties, two chip sizes, and two solder bump heights. The results were used to examine the parametric sensitivity of the thermal strain in the solder joints and the axial, as well as shear stress in the underfill material. The predicted improvement in the number of cycles-to-failure of the underfilled flip-chip was found to agree with empirical observation. However, the maximum improvement achievable by underfilling was found to be limited by the adhesion strength of the underfill material.

Thermal characterization of chip packages-evolutionary development of compact models

Abstract: The expanded R/sub jc/ methodology, first proposed in 1989, makes it possible to extend the use of this common figure-of-merit to chip packages with nonisothermal cases. This proposal spurred considerable debate and contributed to renewed efforts to provide "compact" thermal models of single chip packages, for preliminary design, as well as for detailed numerical simulation of populated printed circuit boards. This presentation offers a review of the development of this modified R/sub jc/ methodology and its efficacy in replicating the chip, or junction, temperature predicted by detailed numerical simulation.

Combined Pressure and Subcooling Effects on Pool Boiling From a PPGA Chip Package

Abstract: This study presents a detailed experimental investigation of the combined effects of pressure and subcooling on nucleate pool boiling and critical heat flux (CHF) for degassed fluorocarbon FC-72 boiling on a plastic pin-grid-array (PPGA) chip package. In these experiments pressure was varied between 101.3 and 303.9 kPa and the subcooling ranged from 0 to 65°C. As expected, lower wall superheats resulted from increases in pressure, while subcooling had a minimal effect on fully developed pool boiling. However, the superheat reductions and CHF enhancements were found to be smaller than those predicted by existing models. The CHF for saturated liquid conditions increased by nearly 17 percent for an increase in pressure from 101.3 to 202.7 kPa. In experiments with both FC-72 and FC-87 further increases in pressure did not produce any significant increase in CHF. At a pressure of 101.3 kPa a subcooling of 30°C increased CHF on horizontal upward-facing chips by approximately 50 percent, as compared to 70 percent on vertically oriented packages. The enhancement in CHF due to subcooling decreased rapidly with increasing pressure, and the data showed that the influence of pressure and subcooling on CHF is not additive. A correlation to predict pool boiling CHF under the combined effects of pressure and subcooling is proposed.

Distance learning paradigms in electronics packaging: a national course on thermal design of electronic products

Abstract: Electronics packaging education requires a multidisciplinary approach, integrating concepts in electrical engineering, materials, structural analysis, heat transfer, reliability and computational methods. The availability of advanced instructional technologies is allowing an unprecedented opportunity to incorporate several desirable attributes to courseware development in such areas. This paper describes an ongoing multi-university effort undertaken to develop a national course on thermal design of electronic products. The participating institutions provide a combination of faculty with expertise in various aspects of thermal design. Examples of course materials developed so far include: (i) videotaped lecture segments on specialized topics, (ii) case studies, and (iii) multi-media computational design simulations. At each institution, the modules are integrated with traditional classroom lectures. These materials will form a central online resource base, accessible through the world wide web (WWW). In addition to their possible use in courses dealing specifically with electronics cooling, it is anticipated that instructors of more comprehensive packaging courses, as well as more general heat transfer and thermal design courses, will find it possible to incorporate these modules in their syllabi and thus dramatically expand the number of engineering students exposed to these critical issues.