Hexagonal boron nitride thin films (h-BN) were deposited by RF magnetron sputtering on 160-keV N+-implanted polycarbonate (PC) substrates at fluences ranging between 1 and 8 x 10(15) N+ cm(-2). Before coating deposition, he PC substrates were treated by plasma ion etching in the deposition chamber. Plasma treatment of the polycarbonate ensured good adhesion of the h-BN coating on virgin and ion-implanted PC substrates. For implantation fluences up to 2 x 10(15) N+ cm(-2), the h-BN layers deposited exhibited lower levels of intrinsic stresses and better resistance to delamination under scratch tc:;ting compared to the coating deposited on the virgin PC substrate. This result can be related to the formation, by ion implantation, of a PC surface layer with improved thermal and mechanical properties. The thermal expansion coefficient of this surface layer matches well with that of the h-BN thin films, thus limiting the level of the thermal intrinsic stresses in the coating. Moreover, surface hardening of the PC, induced by the ion beam, produced less substrate deformation than in the virgin PC substrate under a scratch test load, thus reducing the level of mechanical stresses in the h-BN coating. For implantation fluences greater than 2 x 10(15) N+ cm(-2) the h-BN layers deposited delaminate at low scratch test loads, indicating embrittlement of the PC surface layer.