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Solid state drive (SSD) is widely used for modern computing systems. As design of systems becomes more complex, concern for thermal fatigue lifetime has enlarged by increasing thermo-mechanical stress. Thermal cycling test (TCT) is the most common and important reliability item to determine solder joint reliability. The differences between the TCT conditions at component manufacturer's sites and the user environment, however, can cause a change in fatigue lifetime and failure location because of the difference in mechanical load condition such as housing, connector, screw and so on. For that reason, a proper test method is required reflecting various environmental and field conditions. This paper proposes a novel TCT method that is designed in considering the mounted condition of M.2 next generation form factor (NGFF) SSD. The reliability assessment was conducted in two temperature range and loading conditions, and the test results were analyzed on a SSD level test equipment and a test program. Test result show acceleration relationship is verified by temperature acceleration. Test jig reflecting real use environment was manufactured to verify the differences between the loading conditions. In the case of mounting SSD to test jig, Weibull characteristic parameters were degraded. Test results show shape parameter is decreased from 6.25 to 2.02, and 10 percent life is also decreased 60.7 percent with SSD mounting condition. Failure location was changed from solder on NAND side to solder between DRAM and controller side according to the loading condition. This implies that it is completely different reliability assessment depending on whether the jig is applied or not. Failure analysis was conducted by cross section analysis method. Finite element analysis (FEA) was conducted to understand the failure location and stress level changes caused by test conditions. These results are verified by strain measurement of each location. The strain rate of the point of DRAM and controller side was increased by approximately 20 percent due to applying test jig, and the increase in strain rate leads to an initial lifetime deterioration. This work provides the results of the impact of loading conditions under TCT of M.2 SSD. In conclusion, the cause of reliability characteristics degradation and failure location change derived from the difference in loading conditions of M.2 SSD is investigated, and more accurate modeling and evaluation methodology for predicting product level reliability characteristics are introduced. Thus, SSD level reliability test design reflecting a condition mounted on end-products is needed to verify more accurate reliability prediction. |
