Poor thermal management in electronic systems can lead to higher junction temperatures, accelerating failure mechanisms and reducing component lifespan. Integrating efficient thermal management techniques, such as heat sinks, is essential for ensuring durability and efficiency of electronic equipment. Heat sinks have limited capacity, but integrating phase change materials (PCMs) enhances cooling performance by harnessing latent heat storage. However, leakage and low thermal conductivity limit PCM's effectiveness. The current study developed highly conductive leakage-proof PCMs based composites using an ultrasonic and vacuum impregnation method with lauric acid as base, hexagonal boron nitride and expanded graphite as additives. The results demonstrate persistence of chemical integrity, as proven by FTIR analysis, and complete encapsulation of PCMs inside the expanded graphite structures. The form-stable composite PCMs exhibit a 450% increase in thermal conductivity and 77% photo-transmittance decrease compared to base PCMs. Despite a trade-off of a 11.5% reduction in latent heat, the composite demonstrates thermal stability up to 220 °C. Further, excellent chemical and thermal reliability is maintained even after 500 cycles. Furthermore, in thermal management for heat sink, the form stable composite efficiently dispersed heat, resulting in a 16 °C decrease in peak temperature compared to the heat sink without the composite.