Phase change materials shows promising ability of absorbing and significant heat through the latent heat of phase change, once the temperature reaches the melting range. Therefore, they have huge potential in electronic packaging and automotive battery cooling systems. However, due to the low thermal conductivity of phase change materials, in the phase change material cooling system, high thermal conductivity materials (metals) or fluids are often utilized to achieve efficient heat transfer between the heat source and the phase change material. Thus, it is necessary to obtain the optimal layout of phase change materials and high thermal conductivity materials in the PCM heat sink through topology optimization. This study assumes that the thermal conductivity of high thermal conductivity material is much higher than that of phase change materials, that is, the natural convection effect of phase change can be neglected. In terms of PCM-based problem for minimizing temperature oscillation, the gray-scale regions are prone to be generated and enforcing higher penalty may lead to decline in the thermal performance of the heat sink. Regarding to that contradict, low melting point alloy (LMPA), which shares similar phase change characteristics and higher thermal conductivity with PCM is introduced. It turns out that the LMPA takes the place of gray-scale regions and furtherly suppress the temperature oscillation. The topology optimization framework for transient heat transfer system is built upon FEniTOP (FEniCSx-based topology optimization), which combines Method of Moving Asymptotes (MMA), Helmholtz PDE filter, nonlinear PDE solver and its corresponding adjoint solver via petsc4py. This work offers the topological optimization design of dual-PCM heat sink considering the minimization of temperature oscillation through several 2D and 3D numerical cases and lays the foundation for the subsequent phase change material problems considering the natural convection effect.