In hard disk drive assembly process, a number of small screws around the perimeter of the top cover are used to attach the top cover to the base. When one of the screws is fastened, screw loosening at the other screw heads can frequently be observed. . This research employs a three-dimensional finite element analysis to compare the effects of three different screw tightening sequences to top cover loosening in a 3.5-inch hard disk drive assembly. The top cover deformation and the contact forces at the screw heads of the three sequences are presented and discussed. Among the three sequences, the across pattern has shown to be the most appropriate sequence in which a minimum screw loosening occurs.