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Keywords
Thermal analysis, Deformation, Measurement, Surface mount technology
Abstract
Integrity of surface mount technology (SMT) components depends on their response to temperature changes caused by operating conditions. Temperature induced differential thermal expansions lead to strains in the interconnection structures of active devices. To evaluate these strains, temperature profiles of the interconnected components must be known. In this paper, a methodology for developing thermal models of SMT components is presented using thermal analysis system (TAS) and its application is demonstrated by simulating thermal fields of a representative package. Then, thermomechanical deformations of the package are measured quantitatively using state-of-the-art laser-based optoelectronic holography (OEH) methodology.
1. Introduction
Driven by demand for delivery of more efficient devices, surface mount technology (SMT) has become the mainstream packaging technology of electronic equipment manufacturers. The significant driving force for the use of SMT is the reduced package size and cost, as well as improved board utilization as the package-to-board interconnection spacing is minimized, when compared to pinned-through-hole packages. However, placing more functions in a smaller package has resulted in higher heat densities, which require that thermal management be given a high priority in design so as to maintain system performance and reliability.
SMT components comprise of different materials, each with a different coefficient of thermal expansion (CTE). As active components dissipate heat to their surroundings, or as the ambient system temperature changes, differential thermal expansions, due to different CTEs, cause stresses in the interconnection structures. These stresses produce elastic and plastic strains, as well as time-dependent deformations of the joints between the relatively rigid package body and circuit board. This becomes important as the devices are thermally cycled during operation, given the differences in CTEs for...