Integrated vapor pressure, hygroswelling, and thermo-mechanical stress modeling of QFN package during reflow with interfacial fracture mechanics analysis

Materials and Thermal Management

“…Although recent improvements in the mechanical properties of molding compounds, plastic package designs, and manufacturing technologies have resulted in substantial increase in the reliability of plastic packages, there still exists one major industry-wide concern associated with these packages -their moisture-induced failures ("popcorn" cracking) [55][56][57] . Such failures typically occur during surface mounting the packages onto PCBs using high temperature (220˚C-280˚C) reflow soldering.…”

Interface delamination analysis of TQFP package during solder reflow

“…Fick's second law can be applied to describe the moisture diffusion process in polymer materials [1][2][3][4][5][6][7][8][9][10][11][12][13]. According to Fick's second law, moisture diffusion in a material is defined by Fickian diffusion law in three dimensions as follows [23]:…”

“…The moisture diffusion coefficient D and moisture saturation concentration C sat of epoxy molding compound and die attach materials are listed in Table 1. In this study, material parameters of the die attach from [11] are used since the same die attach material is used in both studies.…”

“…However, stress fields around bonded corners show singular behaviors and the calculated maximum stress depends sensitively on the finite element mesh size [7,8]. The fracture mechanics approach has been used in many recent works on the popcorn cracking phenomenon [7][8][9][10][11][12][13]. The relative contribution of temperature, moisture diffusion and vapor pressure to the delamination driving force during the solder reflow process for eutectic tin-lead solder and lead-free solder has recently been investigated [12,13].…”

“…Finally, the transient development of the stress intensity factors due to thermal stress only K t , hygrostress only K h , vapor pressure only K p and combined energy release rate G tot are computed and studied by using MVCCM. The results show that the material properties of epoxy molding compound have important effects on the stress intensity factors and strain energy release rates which are extensively used to predict the interface delamination in IC packaging [7][8][9][10][11][12][13]. Based on this study, an effective epoxy molding compound selection scheme is developed based on overall consideration of the material properties such as the adhesion ability, Young's modulus, coefficient of thermal expansion (CTE), moisture diffusion parameters and CME.…”