3D organic packages with three-die stack were evaluated by finite element analyses and thermal cycle tests. The thermal cycle tests with different silicon thickness configurations were performed. The die-stack test vehicles with thin top die (150μm) did not show any failures during the 2000 cycles of thermal cycle tests. However, failures were detected for the test vehicles with thick top dies (400μm) and thick interposers (200μm). The finite element analysis showed that the minimum in interchip joint stress occurs at the range of silicon interposer thickness, 100-200μm. The analysis for underfill failures showed that the underfill strains at the filet edge and at the die-corner are greater for the packages with a thick top die (400μm) than for those with a thin top die (150μm). The analysis also showed a greater die-warpage for the packages with top die thickness of 150μm than those with the top die thickness of 400μm. The use of a low CTE laminate in a 3D package as a potential solution for achieving stress reduction and warpage was shown to be effective in reducing die-warpage and in reducing strains in underfill materials at the filet edge. The result of the thermal cycle test was consistent with the finite element analysis result which showed a greater underfill strains at the filet edge for the failed 3D die stack packages. © 2013 IEEE.