The paper aims at the transient numerical modelling under mixed convection for the cooling of seven protruding asymmetric IC chips mounted on an SMPS board using the phase change material (n-eicosane). The phase change material (PCM) is kept inside the mini-channels fabricated on the board. The objective is to bring down the temperature (minimize the maximum temperature) of the configuration (SMPS board with 7 IC chips) using the n-eicosane inside the mini-channels. It is seen that n-eicosane absorbs the heat dissipated by the IC chips and thus the maximum temperature of the configuration reduces by 5.5%. The effect of channel hydraulic diameter (2.5 mm ≤ Dh ≤ 3.5 mm) on the temperature of the IC chips is also studied. The results suggest that the mini-channel with lower hydraulic diameter gives a better rate of heat transfer from the IC chips and thus cools these effectively. The study is extended using four different phase change materials out of which, n-eicosane has resulted in maximum temperature drop from the IC chips among different PCMs due to its lower melting point value. A correlation is proposed for the non-dimensional temperature (θ) of the IC chips in terms of Fourier number (Fo) to predict the IC chip temperatures during the melting of PCM. © 2019 Elsevier Ltd