Characterization of time and temperature dependent mechanical behavior of underfill materials in electronic packaging application

The thermo-mechanical testing of HYSOL FP4549 polymer-filled underfill material was conducted under different strain rate and temperature environment. A new specimen preparation procedure and further test methodology are developed to characterize the underfill time-temperature mechanical behaviors. The stress-strain behavior of materials is simulated with constitutive framework, and the dependence of Young's modulus on temperature and strain rate was evaluated. In addition, the specimens were tested with micro-tensile system to evaluate the underfill materials creep curve as a function of temperature and stress level. In view of the uncertainty of the Young's modules determination, the specimens were tested with unloading-reloading technique to verify the test results and investigate its cyclic mechanical behaviors. On the other hand, the adhesion strength are tested between different adhesion surface by different deformation rate after some isothermal and hygro-thermal environments attack, which is to simulate the environment that the electronic components may be encountered. The results reveal that the rise of the temperature and moisture cause the apparent reduction of the surface adhesion strength, due to the material microstructure transition and the diffusion and concentration of moisture. For all conditions of the experiment after environmental preconditioning, the specimen fracture surfaces occur between solder mask and FR4 substrates, which means the measured strength is the adhesion strength between solder mask and FR4. Comparing different adhesion surface, the adhesion strength of underfill/FR4 is higher than solder mask/FR4. In addition, it has found that the fracture strain and the slope of the load-deformation diagram increases with the decreasing deformation rate. The interface of solder mask/FR4 is more sensitive to the temperature and moisture.