Thermal-mechanical analysis of a QFN stacked-die leadframe under reflow process

The copper-based leadframe is practically proven effective in the thermal and reliability of a Quad Flat No Lead (QFN) three dimension (3D) stacked-die semiconductor package. Reducing the copper thickness is understood to present various thermal and reliability failure mode and mechanisms, such as die cracking and delamination. However, no in-depth study has been pursued to determine the capability of achieving the product requirements in terms of thermal and reliability in a 3D stacked-die package. The drive towards a Die-Free Package Cost (DFPC) reduction has led the authors to study the used of a thin leadframe in a QFN 3D stacked-die. Hence, the work presents basis for the qualification of a thin leadframe design, and also to demonstrate the thermal and reliability performance. Finally, an extensive virtual thermal-mechanical prototyping has to be achieved in order to understand the physics of materials during the assembly and reliability testing of a 3D stacked-die package with a thin leadframe. This design rule was found to be developed in order to prevent a die crack occurrence between die and leadframe in the semiconductor package.