A board level study of an array of ball grid components part I: aerodynamic measurements

摘要

Electronic package manufacturers publish thermal characteristics of components, which are measured using standard tests. Generally this characterisation is in the form of a thermal resistance value measured for a single component on a standard test printed circuit board (PCB). This limits the applicability of the characterisation, as it does not show what aerodynamic or thermal interaction each package will have in a real system. There are many elements of an electronic system that will affect the junction temperature of an electronic package: two examples of which are an upstream fluid flow distarbance and the thermal conductivity of the PCB. This paper, Part I, presents a new board-level electronics system test vehicle for assessing some of these elements consisting of an array of ball grid components (304-SuperBGA with thermal test chips) on three multi-layer PCBs of different effective thermal conductivity. Extensive two-dimensional measurements of the airflow over the components, taken using a Particle Image Velocimetry (PIV) system, are presented. The purpose of these experiments was to understand the airflow so that the convective heat transfer and hence junction temperature can be better predicted. It appears that PCBs populated with low profile electronic packages behave like flat plates, leading to the proposition that component temperatures can be calculated using flat plate predictions. Part II [1] presents thermal measurements from the test vehicle.