Analysis of package cracking during reflow soldering process

Package cracking that occurs in surface-mount devices that have absorbed moisture has been studied by means of a moisture-diffusion analysis of the plastic, deformation and stress analysis of the package, and measurement of some high-temperature properties of the plastic. The validity of the analysis has been confirmed by a measurement of the deformation of packages heated by infrared radiation. Several packages with different level of moisture saturation and hysteresis of moisture absorption have been heated by soldering and the occurrence of package cracking investigated. The vapor pressure and distribution of moisture content of these packages have been calculated by the present analysis. It was found that generated vapor pressure is lower than saturated vapor pressure and depends on the moisture content at the part of the plastic facing the space in which vapor pressure is generated. This example shows that it is possible to evaluate package cracking by the present analysis method quantitatively