Measurements of surface deformations and strains using an AFM moiré method

An AFM (atomic force microscope) moiré method has been developed to measure surface deformations and strains. The scanning lines in the AFM monitor are used as the reference grating. The reference grating interferes with the specimen grating and forms a moiré pattern on the monitor. The condition of forming scanning moiré with an AFM is described. The deformation measurement principle using AFM moiré is discussed in detail. The AFM moiré method was used to measure the thermal deformations in QFP (quad flat pack) and BGA (ball grid array) packages. The experiment results verify the feasibility of the AFM moiré method and show its ability to measure the in-plane deformations and strains.