Failure of high performance electronic and computing device due to inefficient generated heat dissipation is a major problem and challenge for electronic cooling industry. Liquid cooling is the most prominent techniques used in micro-channel heat sink (MCHS) devices for electronic cooling industry. Optimal design of cooling system with suitable working fluid to maximise the performance and heat dissipation is the active area of research. In the present work, MCHS is designed and three-dimensional numerical simulation of conjugate heat transfer and fluid flow behavior is done. The investigation is also performed with different working fluids (deionized water, water propylene glycol and Dynalene HC-30) to propose the techniques for maximum system performance. This study covers Reynolds number values in the range of 300-500 and heat fluxes up to 189 kW/m² are considered. Different channel aspect ratios and fin width are considered to achieve the desired heat removal rate. Numerical studies of the heat sink for laminar flow are carried out to predict the maximum junction temperature and pressure drop involved. The MCHS is optimized in terms of channel width and fin width. The maximum junction temperature is found to be less than the allowable temperature (80-85°C) corresponding to the maximum thermal design power of 600W. Numerical results are compared with theoretical analysis and they are in good agreement with each other.