Process considerations and long term thermal performance of power packages with heat slug soldered to PCB

Power packages are developed to meet the demand of high power dissipation. The common feature of these power packages is the exposed Cu heat slug. The slug is soldered to the printed circuit board (PCB) during surface mount (SMT) assembly. The primary thermal path is die => die attach (DA) glue => slug => thermal solder joints => PCB => ambient. This configuration gives superior thermal performance. Furthermore, the power package thermal performance relies on the integrity of this thermal path. It is important to ensure the thermal performance of the power packages for the entire product service life. This requires the understanding of their thermal path reliability. To proceed, C²BGA, Power SO 20 and Power TQFP with thermal dice are subjected to -45/125°C temperature cycles. Junction to ambient thermal resistance (θ_ja) before and after temperature cycles are compared. It is found that there is no visible thermal resistance degradation due to temperature cycle stressing. The power package thermal path is reliable. Further study shows that even with up to 60% DA delamination and 40% thermal solder joint cracking, there is no significant θ_ja rise at zero hour and after temperature cycles.