Thermo-mechanical simulation of a SiP (System-in-a-Package) LGA (Land Grid Array): Impact of the internal IC (Integrated Circuits) on the 2nd level solder joint reliability

System-in-a-Package (SiP) aims to integrate a functional sub-system with one or more semiconductor chips along with passive components onto a substrate. SiP is transferred molded to the OEM for second level assembly using industry standards and high volume equipment. In most recent applications (high I/O density, improved electrical performance), LGA (Land Grid Array) is a very practical solution for the 2^nd solder joint level. LGA packages reduce integrated circuit mounted height by eliminating the solder balls that are used for mounting BGA (Ball Grid Array) packages to system circuit boards. Instead, LGA packages are reflow-mounted using solder that has been applied to the board. This paper addresses the thermomechanical lifetime reliability of a 104 lead SiP LGA with lead-free solder joints submitted to thermal cycles in environmental chamber. The goal is to determine the impact of the internal IC (Integrated Circuits) on the 2^nd level solder joint reliability. It firstly explains how to conduct preliminary technological analyses (RX views, chemical attacks, layout re-design) and material property characterization (CTE in the 3 axis on very small samples) before the construction of an accurate 3D model. Then it focuses on simulation tools (boundary conditions and post-processing cartography methods) necessary for unsymmetrical geometries. Simulation results (life-time prediction and damage localization) lead to quite satisfactory data when compared with first experimental data. Even at the 2^nd solder joint level, the first failures (not located in the periphery of the LGA device) are highly linked with the internal components and with the layout of the SiP. The more realistic are the geometry and the material properties, the better are the numerical results. Such 3D simulation models can then be used to predict the life-time as well as to define microsection axis in complex failure analyses. The paper also shows that dummy compon- - ents (daisy-chained) are not convenient for the process assessment of SiP LGA.