Miniaturised circuitry produces more heat that must be controlled to avoid temperature and improve the system's functional reliability. Phase Change Material (PCM) based Heat Sink (HS) design development is a flexible thermal management solution for electronic packages. This work uses the Neopentyl Glycol (NPG)-CuO composite as the Solid-Solid Phase Change Material (SSPCM) composite for the PCM-based heat sink. A twodimensional transient thermal analysis of the SSPCM in an HS with different plate fin configurations was conducted to analyse the effect of fin parameters over the thermal response and performance under different heat dissipation rates of 2 W, 4 W and 8 W. The influence of the number of fins, fin thickness, fin spacing, and power levels were investigated over the safe operational time (SOT) corresponding the temperature limit of 80 °C. The effect of the number of fins over the operational period was evident at 2 W and 4 W. SOT improvement ranging from 10.71% to 333.33% was achieved through different plate fin configurations when compared with SSPCMbased HS without fin configuration. From 2 to 4 W power levels, a significant improvement was observed in increasing the SOT. The influence of percentage thermal conductivity enhancer, fin thickness, and fin spacing was evident from the numerical investigation of SSPCM-based HS.