Abstract
Solder joint fatigue is a common failure in wafer-level packages (WLP) under thermal cycling loads, caused by the expansion and contraction of materials with different thermal expansion coefficients. This leads to crack formation and electrical failures. In WLP design, the dimensions of upper and lower copper pads influence the shape, height, and angle of solder balls, affecting their contact area, mechanical support, and stress distribution. These factors determine the stability and reliability of solder joints during long-term thermal cycling, impacting the overall reliability of the package. In this study, we will use different sizes of upper and lower copper pads in multiple test vehicles to observe their impact on performance and reliability. Due to the time-intensive nature of evaluating multiple vehicles, full adoption of three-dimensional (3D) modeling methods is impractical. Instead, we will employ 3D models to validate the accuracy of two-dimensional (2D) models and establish optimal design criteria based on insights from 2D simulations. This study identifies the expected optimal design criteria through successfully validated 2D models, aiming to use the finite element method (FEM) to simulate reliability tests, reducing testing time and revealing potential failure mechanisms for design improvement. In WLP design, different sizes of upper and lower copper pads affect the solder balls' shape, height, and angle, thereby influencing their mechanical support and thermal stress distribution. By observing the impact of these variations on performance and reliability in different test vehicles, we ultimately establish cost-effective and reliable optimal packaging design standards.