Wafer thinning process before dicing, die attach, wire bonding, and in resin molding package operations requires the protection of the silicon wafer surface by means of a sticking grinding tape. The adhesive layer between this tape and wafer front side can leave glue residuals both in terms of ''macroscopic'' particles and organic ultra-thin layer. The organic contamination (OC) in these features is potentially detrimental for a good final passivation to plastic molding compound adhesion, leading to local package de-lamination, especially at the silicon die corners, where stress effects are known to be maximized. As a consequence, reliability issues are enhanced right from the interface original weakness. Different empirical and analytical techniques are available in order to characterize the starting conditions of final passivation surface and an oxygen plasma cleaning process has been chosen as most reliable and applicable eventually in a manufacturing environment to overcome such a kind of constraints. As a matter of fact, oxygen burns out the organic nature particles and ''mono-layer'', eventually left on the wafer front side after back grinding tape peeling off operation. This paper, deals with the direct adhesion study of the package resin to silicon nitride and PSG final passivation films correlated to water droplet contact angle, ToF-SIMS measurements, and packaging resin shear tests, revealing the effectiveness of a downstream oxygen plasma cleaning treatment in increasing plastic package to die mechanical coupling.