A package that resists creation of particles in a package cavity. A package according to one embodiment of the present invention contains a mechanical device attached to the floor of the package substrate. Epoxy typically is used to attach the device. Electrical connections are provided by bond wires connecting bond pads on the substrate with bond pads on the device. A window is attached to the substrate to form a cavity around the device. A thin masking layer on portions of the package cavity surface prevents the surface from generating particles. The thin masking layer may be any material that resists particle generation. The masking layer on the cavity walls optionally extends out of the cavity and onto the upper surface of the package.