Thin Ni-B films, 1 μm thick, were electrolessly deposited on Cu bus electrode fabricated by electro deposition. The purpose of these films is to encapsulate Cu electrodes for preventing Cu oxidation and to serve as a diffusion barrier against copper contamination of dielectric layer in AC-plasma display panel. The layers were heat treated at 580 ? C (baking temperature of dielectric layer) with and without pre-annealing at 300 ? C ( Ni 3 B formation temperature) for 30 minutes. In the layer with pre-annealing, amount of Cu diffusion was lower about 5 times than that in the layer without pre-annealing. The difference of Cu concentration could be attributed to Cu diffusion before Ni 3 B formation at grain boundaries. However, the diffusion behavior of the layer with pre-annealing was similar to that of the layer without pre-annealing after Ni 3 B formation. With increasing annealing time, Cu concentration of both layers increased due to grain growth.