A board level study of an array of ball grid components - Aerodynamic and thermal measurements

Electronic package manufacturers publish thermal characteristics of components, which are measured using standard tests, measuring a thermal resistance value for a single component on a standard test printed circuit board (PCB). This limits the applicability of the characterization, as it does not show what aerodynamic or thermal interaction each package will have in a real system. This paper presents a new board-level electronics system test vehicle consisting of an array of ball grid components on three different effective thermal conductivity multi-layer PCB's. Aerodynamic and thermal measurements are presented. It appears that PCB's populated with low profile electronic packages behave like flat plates, leading to the proposition that component temperatures can be calculated using flat plate predictions. It is shown how both the airflow and the board conductivity can have a critical effect on the junction temperature, and a simple design rule is suggested, in terms of influence factors, to take account of these effects. These will lead to better estimates of electronic system reliability in the early part of the design cycle.