Thermal performance comparison of chip-on-board, flip chip-on-board and standard TQFP package

The focus of this paper is on the thermal performance of wire-bonded chip on board (WB-COB) and flip chip on board (FCOB) packages, which were evaluated and compared to that of a standard thin quad flat pack (TQFP). The effect of five different enhancements of WB-COB and FCOB assemblies on their thermal performance was also investigated. Furthermore, the thermal limits (maximum allowable power dissipation under still-air conditions, based on a maximum junction temperature of 125°C) of each assembly were defined. According to the results, the standard 32-TQFP package shows the lowest thermal resistance (θ_ja), compared to the θ_ja of WB-COB and FCOB assemblies. The thermally-enhanced WB-COB assembly, in which the die is directly attached to the Al or Cu stiffener, shows the most significant thermal improvement. Maximum power dissipation (based on a 125°C maximum junction temperature) of the same assembly is raised by a factor of 2.6. The impact of solder bump voids on the thermal performance of FCOB assembly is shown to be insignificant. The underfill `total´ air gap increases θ_ja of a thermally-enhanced FCOB assembly by 16.5%