A numerical method on thermal-humidity behavior of electronic packaging

Reliability issues associated with thermal-humidity and vapor pressure have become increasingly significant for electronic devices. With the more density of the electronic packaging and the trend of lead-free material application, the film between IC and substrate will experience more harsh stress condition in the packaging process. The interface delamination is caused by these factors. Therefore, it is important to develop numerical implementation for the study of delamination mechanism. This paper presents a combined numerical methodology for predicting the thermal-humidity behavior of the process of electronic packaging. Firstly, the sequentially coupled thermal-mechanics finite element model has been applied to simulate the process of Chip on Glass (COG) packaging. Secondly, the moisture absorption and desorption have been investigated by numerical approaches. The direct concentration approach (DCA) which is able to settle the issue on the discontinuity of moisture concentration at interfaces between two materials which have distinct saturated moisture concentrations is applied in a bio-material system. Currently, commercial finite element method software such as ABAQUS is of the modulus of mass diffusion which is competent to achieve the DCA. According to the simulation, the numerical results have very good agreement with experimental data on the distribution of moisture concentrations. Further in this paper, the vapor pressure has been predicted in terms of the whole-field vapor pressure model which is put forward by Fan and the simplified Fan´s vapor pressure model respectively. Compared with the results of these two models, the former one is more precise but less efficient than the latter one. At last, hygroscopic stress and thermal stress are calculated in terms of former numerical analysis and compared with the vapor pressure during the reflow process. It is reasonable to consider the vapor pressure as a major factor of failure during the reflow process b- - y comparison.