Modeling and design of 2.5D package with mitigated warpage and enhanced thermo-mechanical reliability

The objective of this research is to investigate the design factors that contribute to the thermal deformation and stress development of lidless 2.5D package, and to provide design guidelines for building thermo- mechanically reliable lidless 2.5D packages. A three-dimensional finite element model of a lidless 2.5D package was analyzed under different design parameters. Finite element analyses were performed to compare the package warpage and die stress among different material selections with the consideration of substrate core CTE and modulus, stiffener CTE, C4 bump underfill modulus and CTE, microbump underfill modulus and CTE as well as adhesive modulus. Geometric effects such as interposer thickness, stiffener thickness, stiffener foot width, adhesive thickness and adhesive coverage were also explored. Moreover, the solder joint reliability were analyzed on the board level model considering important design factors obtained from package level analysis. Optimal design factors were achieved through both package level analysis and board level analysis. It was found that several design factors show totally different trends in affecting package level and board level reliability. Simulation results show that, lower substrate core CTE, higher substrate core modulus, higher stiffener CTE, lower adhesive modulus, a thicker and wider stiffener, and a thinner adhesive with higher coverage will help to minimize the package warpage. Using a substrate core with higher CTE and lower modulus, a stiffener with lower CTE, and adhesive with lower modulus and higher thickness, will help to improve the board level solder joint reliability for the lidless 2.5D package PCB assembly.