Analytical and experimental study for designing molding compounds for surface mounting devices

In order to qualitatively understand the popcorn (package cracking) phenomenon, Nitto corporation engineers have studied two approaches. One is a detailed investigation of the physical properties of molding compounds, such as moisture absorption, thermal conductivity, and adhesion to lead frames. The other is the establishment of an analytical system to estimate the induced stress in packages under soldering conditions using FEM (finite-element method) analysis, mathematical analysis, and other techniques. These two results are combined to generate an experimental equation including four parameters (moisture solubility coefficient, moisture diffusion coefficient, Young´s modulus at soldering temperature, and mechanical strength at soldering temperature) for designing molding compounds for use in surface-mounting applications