| The polymer material which is commonly used in microelectronics packaging is easy to absorb moisture when exposed to humid ambient conditions. The presence of moisture in the packages induces hygroscopic stress through swelling and vapor pressure in reflow that is the cause for the eventual popcorn cracking. Therefore, moisture plays an important role in the integrity and reliability of electronic packaging. More and more researches are focused on the study of moisture absorption, diffusion and moisture induced failure.First, the basic theories of moisture diffusion, hygro-swelling, vapor pressure and equivalent thermal stress are introduced. The method of how to simulation the moisture diffusion process is developed by using thermal part of commercial finite element analysis (FEA) software. The FEA can also simulate the hygroscopic stress which is induced by the coefficient of moisture expansion mismatch among various materials. The vapor pressure can be calculated based on the local moisture concentration after preconditioning. It is found that the vapor pressure introduces the additional strain which is with the same order as the thermal strain and hygro-mechanical strain to the package.Secondly, the general scheme of the development of moisture analysis automation system based on ANSYS Workbench and Excel is developed. At the same time, the development tools such as Visual Basic, Access and so on are introduced for further interface study. The third, the moisture analysis automation system has been applied to moisture diffusion, hygro-swelling, vapor pressure and equivalent thermal stress analysis for a component level MLP model. The results are compared with those from classical ANSYS.At last, 16 patterns of different parameter design are simulated by the automatic moisture analysis system to optimize the MLP6×6 package model. It can be found that the best solution in which the Von Mises stress of EMC part and the first principle stress of Die are the minimum. |
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