The mechanisms of forming a molding compound on a semiconductor device substrate to enable fan-out structures in wafer-level packaging (WLP) are provided. The mechanisms involve covering portions of surfaces of an insulating layer surrounding a contact pad. The mechanisms improve reliability of the package and process control of the packaging process. The mechanisms also reduce the risk of interfacial delamination, and excessive outgassing of the insulating layer during subsequent processing. The mechanisms further improve planarization end-point. By utilizing a protective layer between the contact pad and the insulating layer, copper out-diffusion can be reduced and the adhesion between the contact pad and the insulating layer may also be improved.