Abstract: Several reports of cracked die in flip chip assemblies on underfilled organic substrates, motivated this work to study the effects of backside (non-active surface) scratches on die strength. These failures resulted in a thorough investigation of the evolution of backside scratches through the flip chip bumping process, assembly and test. In this study the effect of fine scratches (between 1 and 2microns in depth) was investigated. The possible causes and sources of these scratches as well as other backside defects were systematically investigated, and samples were subjected to air to air testing (-55C to 150C) to evaluate the effect of these scratches on the reliability performance of the defective die. Scratches of varying degrees and types were measured and archived as visual aids. Evaluations showed that the fine scratches do not affect reliability of flip chip assembled dies when subjected to 1000 cycles of -50C to 150C air to air temperature cycling.