Structural reliability of electronic packages has become an increasing concern for a variety of reasons including the advent of higher integrated circuit densities, power density levels, and operating temperatures. Especially, solder joints are a continuing reliability concern in 1st and 2nd level packaging. Thermal deformations are the major cause of fatigue failures of the interconnections of many electronic assemblies, or packages. As the electronic technology advances, electronic components are becoming smaller and smaller. Stress/strain concentrations are localized in very tiny zones with high magnitudes. Measurements of thermal deformations and predictions of failure become more and more difficult. For the reliability assurance of electronic packaging, suitable schemes for the accelerated testing and reliability assessment are essential.
For this purpose, a micro-mechanical testing system was developed for reliability evaluation of the interconnections in electronic packaging and solder bump specimen is designed to measure the creep behaviors and isothermal fatigue life of solder interconnections. Shear strength tests and creep tests at 25℃ and 100℃ and room temperature low cycle fatigue tests were performed for 63Sn/37Pb solder joint specimens. Steady-state creep behavior obtained from the creep tests has good agreements with the results of other researcher's creep tests. From the test results, it is shown that the testing scheme using the micro-mechanical testing system and the solder bump specimen is sufficient to evaluate the mechanical behaviors and isothermal fatigue life of solder interconnections.
The thermal deformations of wafer-level CSP assemblies during various thermal-loading conditions were investigated by real-time moire interferometry and nonlinear finite element analysis. For real-time moire measurement of the thermal deformation, a small-sized thermal chamber having optical window was developed. To investigate the thermal deformations of the wafer-level CSP assembly during temperature cycling, real-time measurement technique was used to measure the deformations of solder joints and the relaxation of warpage during a thermal cycles of (25℃)-(100℃)-(0℃)-(25℃) and (25℃)-(125℃)-(0℃)-(25℃). And, to investigate the thermal deformations of the CSP assemblies during power cycling, the moire test was performed for the thermal load induced by electrical heating of 0.6 watts. In addition, the test results obtained from the moire interferometry technique were compared with the predicted values obtained from the finite element analysis. It is shown that the deformation values predicted from the finite element analysis have a good agreement with those obtained from the test. From the test results, it is shown that the real-time moire interferometry scheme is effective and powerful tool in experimental studies of electronic packaging.
In addition to thermally induced stresses, electronic systems often are subject to vibration environments. These vibrations occur during shipping, handling, and operation. To assure high product reliability, it is necessary to provide estimating tools of vibration fatigue life. For this purpose, an automated fatigue-testing system was developed as an experimental study on the integrity of the electronic packaging subjected to mechanical vibration. With the fatigue testing system, the mechanical integrity of the solder joints in surface mounted components has been studied by a mechanical flexural fatigue test. The high cycle fatigue tests of solder joints are performed under constant amplitude loading.
