Thermal management and characterization of flip chip BGA packages

Abstract

This paper presents the various types of thermally enhanced flip chip packages and its thermal characterization with thermal management options at package level. The conventional one-piece lid high performance flip chip BGA package (HP-fcBGA) has its strength in good thermal dissipation capability, however its board level solder joint reliability could be comprised due to the direct contact of the one-piece metal lid with the substrate. By encapsulating the flip chip with molding compound leaving the die top exposed, a planner top surface can be formed. And a flat lid can then be mounted on the planer mold/die top surface. In this way the direct interaction of metal lid with the substrate can be removed. The new extra performance flip chip BGA package (XP-fcBGA) is thus less rigid under thermal loading and solder joint reliability enhancement is expected. A third option of flip chip package XPs-fcBGA (with a dummy die between flip chip and metal lid as spacer) has been explored by UTAC for the solution of taller-than-flip-chip decoupling capacitors. This paper examines the thermal performance of XP-fcBGA and XPs-fcBGA packages versus the HP-fcBGA design. A series of experimental and computational studies were conducted to obtain the thermal resistance under JEDEC still and forced air (1m/s, 2m/s and 3m/s) environmental conditions. Experimental data of HP-fcBGA and XP-fcBGA recorded a thermal resistance thetasja 8.89deg.C/W and 8.86deg.C/W at zero airflow respectively, achieving good correlation with simulation results. Correlation within 10% range was also obtained for forced convection conditions of 1m/s, 2m/s and 3m/s airflow. Slight degradation in thermal performance of XPs-fcBGA was observed. Proper selection on the dummy die size is deemed necessary