Oscillating heat pipe addition to the heat sink was considered for the cooling performance improvement of heat sink. Hydrofluoroolefins (HFO) was chosen as the refrigerant to be encapsulated into the heat pipe, as it is nonflammable and has low global warming potential (GWP) index. HFO is proven to have the equal performance as the existing refrigerant of flammable butane. The optimum liquid volume ratio of the refrigerant encapsulated into the heat pipe is about 40%. By insulating the heat between the heat source and the chassis, the oscillating heat pipe could improve the cooling performance by 26.4%.