Abstract
In the present study, the thermal characteristics of the flip-chip BGA package on board are numerically investigated under both natural and forced convection conditions. Heat generated at the junction could be considered to be dissipated by two paths. Heat could transfer to the upward and downward directions of the package and then dissipates to the ambient by both convection and radiation. Simulated results show that over 90 % of heat is dissipated downward for the flip-chip BGA package under natural convection. Here, we introduced a tiny heat sink to improve the thermal performance. The tiny heat sink could force the heat flow upward and thus effectively enhance thermal performance without dramatically enlarging the occupied space of the overall package. An interesting phenomenon is observed that the thermal resistance is the function of cross flow velocity only regardless of the power dissipation rate, when other heat transfer conditions keep unchanged. The alternative part of present study is that a workable correlation is proposed. The correlation, which incorporates the effect of the junction-to-ambient thermal resistance, Reynolds number, Prandlt number and conductivity of the coolant, yields the form as follows: The correlation form above could be applied to various package types, only if the package is extremely thin. The values of the parameter C, m, n and g depend on the packaging type, the packaging structure, the coolant, the flow patterns and the cross flow velocity, etc., and should be experimentally or numerically determined.