Methodology development of packaging substrate warpage analysis

Abstract

A new warpage analysis method was developed for predicting the warpage behavior of packaging sub-strates at room temperature and during thermal process by comparing curvatures of experimental specimens, analytic solution and FEM simulation. We adopted the specimen’s curvature instead of maximum deflection to quantify warpage phenomena. Curvature contains the information of entire shape of specimen such as curva-ture mode and orientation. The warpage analysis is performed in the order of scanning 3D surface, calculating curvature and built-in stress of film and verifying the result using FEM simulation. Through the in-situ measurement of curvature, we find main factors of affecting the warpage behavior of packaging substrate. Warpage at room temperature is observed without thermal history that cause the thermal strain due to CTE misfit. Built-in stress in film layers such as Cu, solder resist and prepreg is the one main factor. Another is the thermal stress occurred from misfit of coefficient of thermal expansion between layers. Warpage is changed its mode and orientation under heating and cooling condition. Shortly after the thermal process, warpage slowly recover its initial value which is before thermal process. The other is moisture absorption due to porous core substrate. Built-in stress could be calculated from the specimen’s curvature using curvature-stress relation. Computed built-in stress is verified to be reasonable through the FEM simulation and predicted curva-ture shows good agreement with the experiment measurement. Our research suggest effective method for solv-ing warpage problems.