Reliability Research On Electronic Packaging

The thesis is composed of two parts, including simulation on the environment of car and reliability research on electronic packaging.In the first part, the temperature and the relative humidity were recorded by several sensors in a car. Based on the experimental data, three physical models and corresponding analytical expressions were developed including the exponential temperature model, the closed-box model for calculation of relative humidity and the passenger model for revising the closed-box model. The finite element simulation with computational fluid dynamics (CFD) method was used to calculate the heat dissipation by airflow and the temperature distribution in passenger compartment of a car. The reasonability of three models as above mentioned was validated. The values of some physical constants were determined from the CFD simulation. The condensation of moisture due to sun radiation was analyzed. The result indicated that the condensation was dependent on the initial humidity in a car. After translating the action records into the state table that can be called by computer, the simulation with Visual Basic and MATLAB/Simulink were carried out, respectively. The software developed could be adopted as a tool for the reliability design of automotive electronic packaging.In the second part, the reliability research on electronic packaging was concentrated with finite element method (FEM) on moisture diffusion in plastic materials, die cracking of flip-chip with no-flow underfill and thermal performance of high power electronic components. In the last chapter, the design tool for advanced electronic package was studied. The main conclusions in the second part are as follows.1. The moisture diffusion in plastic electronic packaging was investigated from both experiment and finite element simulation. The diffusion coefficient and thesaturate concentration were determined on the Pick's law. The results showed that the water molecules inside the plastic material were chemically bonded with polymers by hydrogen bonds in the micro-holes formed by the polymer molecule chain. On the saturate concentration, the moisture density in the micro-holes was 100 times larger than the vapor density in the standard state, but only 8% of liquid water. The water inside the plastic material was in a special liquid state. The delamination and the delamination recovery were observed by C-SAM. Delamination occurred when the liquid and gas phases of water coexist in micro-holes at chip/underfill interface. The adhesive strength between underfill and chip would be reduced due to the absorbed water molecules, resulting in extension and linkage of these micro-holes to form the delamination. The simulation results showed that the delamination might be observed when the moisture concentration was in the range of 50% and 95% of saturate concentration for non-coating, topside coating and both sides coating samples. The delamination at the interface would initiate due to the reduced adhesive strength and the high vapor pressure at high temperature would cause the popcorn during reflow. The moisture concentration of the interface was simulated to predict popcorning during the subsequent reflow.2. The die cracking with no-flow underfill was analyzed during cooling process from the curing temperature of underfill to the room temperature or to the lowest temperature (-55) in thermal cycle test. The stress intensity factor (SIF) and the strain energy release rate were simulated with different pre-crack length for the cases with no-flow underfill and with capillary-flow underfill. The cracking with these two types of underfill might become unstable and lead to catastrophic failure at the end. The critical length was about 12m for the assembly with no-flow underfill and 20m for the package with capillary-flow underfill at 20癈. The height and angle of no-flow underfill fillet little effects on the die cracking. However, the die cracking was dependent on the Young's modulus and CTE of underfill materials. Due to the higher CTE...