Thermo-mechanical reliability analysis of a RF SiP module based on LTCC substrate

Abstract

The RF SiP module based on LTCC substrate has attracted considerable attention in wireless communications for the last two decades. However, the thermo-mechanical reliability of this 3D LTCC architecture has not been well-studied as common as its traditional ceramic package structure. A practical RF SiP module based on LTCC substrate was presented and its thermo-mechanical reliability was analyzed in this paper, with emphasis on the reliability of heat reflow process, the operating state and fatigue of second-level solder joints. The configuration and assembly process of the SiP module were briefly introduced at first, and qualitative analysis was made according to the reliability problem that may occur in the manufacturing process and the operating state. Through FEM simulation, this paper studied the warpage and stress variation of the RF SiP module, as well as parametric studies of some key package dimensions. Solder joint reliability under temperature cycling condition was also analyzed in particular in this paper. The results show that for the heat reflow process and operating state, the maximum warpage is both on the top LTCC substrate, but the maximum stresses are on the outermost solder ball and the kovar column at the corner, respectively. There is a large residual stress on the critical solder ball at the end of the reflow process and the key package dimensions has little effect on it. The thickness of top LTCC substrate has a significant impact on the thermal deformation and thermal stress, followed by the height of kovar columns. The reason for the considerable thermal stress on the kovar column is the non-uniform of temperature distribution. The key to reducing thermal deformation and stress in the operating state is the employment of effective cooling measures. It is found by comparison that the reliability of critical solder joints can be greatly improved by adding suitable underfill.