Abstract: An apparatus to align the deposition of scintillator material on a radiation detector array includes a cover mask assembly configured to be positively positioned on a detector array and underlying pallet assembly to provide proper alignment of the mask with the array so that the active portion of the detector array may be coated with scintillator material without having the scintillator material on the adhesive and electrical contact portion of the detector array. An adhesive rim is disposed around the periphery of the active portion of the array and sized to provide the desired precise alignment of the mask over the detector array and form a seal with the array substrate and the pallet assembly to prevent migration of the scintillator material beyond the active area to be coated.