## 1 Introduction  
Phase change materials (PCMs) are potential temperature regulators in electronic devices. They absorb the heat generated by the device as latent heat during duty period and release it to the ambient during off-duty period. The heat exchange occurs reversibly at isothermal conditions [1; 2], which can restrict the device temperature within the desired range [3]. The time duration for the PCM heat storage varies depending on the PCM's thermo-physical properties [4] thus making the choice of an optimum PCM crucial. The cooling effect produced by integrating PCMs into electronic packaging has been widely studied numerically and experimentally [5; 6; 7; 8; 9]. The integration of PCM into aluminum foam with conductive fins has yielded better cooling performance than natural ventilation cooling and aluminum foam only cooling [7; 8]. The design optimization of a latent heat thermal management system (LHTMS) concluded a relationship between the number of fins, fin spacing, HS volume and heat generation rates [9]. The most commonly used PCMs for thermal management of electronics are salt hydrates [10] and paraffin waves [11; 12] because they are abundantly available at low cost [13]. The most attractive characteristics of salt hydrates are their higher latent heat of fusion [14], higher thermal conductivity of 0.6 \(W\)/(m\(\cdot\)K) [15; 16], negligible volume change during phase transition [16],favorable transition temperatures [17], and lower cost [18]. The salt hydrates are abundantly available [19] in large quantities as by-products of industrial processes [14; 20] and as waste co-products in many chemical processes including production of soda ash [21]. The main problems with salt hydrates as temperature regulators are their lower thermal stability [22; 23], chemical instability [14], corrosion to metals [23; 24], incongruent melting [22] and sub-cooling below the solidification temperature [24]. The incongruence can be solved by mechanical stirring, using excess water to prevent forming a supersaturated solution from melted crystals and modification of their chemical composition. Mechanical stability can be improved by PCM encapsulation to reduce separation. Sub-cooling is suppressed by addition of thickening agents and nucleating agent such as borax [13]. However, high-density borax may settle down when added into PCM [25], which may require further investigation to solve this problem. Paraffin waves have suitable thermo-physical properties such as higher heat of fusion [26], lower corrosion rates to metals [27] and negligible sub-cooling with no phase segregation [28]. Such characteristics allow paraffin to withstand multiple thermal cycles with no substantial change in their thermo-physical properties. Paraffin waxes as PCMs do possess the disadvantage of a lower thermal conductivity of 0.20 W/(m\(\cdot\)K), higher volume expansion during melting-freezing up to 15%, convective currents, fumes discharge at high temperature [29] and a lower density of 800 kg/m\({}^{3}\)[30] which occupies more volume and requires larger containment size for PCM housing which will add additional weight to the system and will reduce energy storage density. The thermal conductivity can be improved by addition of metallic and carbon nano-tube/fiber fillers to render them effective temperature regulators [31; 32]. Milk fat is introduced as a PCM being human-friendly [33], with favorable thermo-physical properties of thermal conductivity being 0.29 W/(m\(\cdot\)K) [34] and density being 911 kg/m\({}^{3}\). Milk fat is a water-in-oil emulsion resulting from an inversion of the cream [33] containing different fatty acid, esters and glycerol with a wide melting from \(-\)40 \({}^{\circ}\)C to 40 \({}^{\circ}\)C [34; 35]. The molecular formula of butter is CH\({}_{3}\)(CH\({}_{2}\))\({}_{16}\)COOH and CH\({}_{3}\)(CH\({}_{2}\))\({}_{7}\)CH=CH(CH\({}_{2}\))\({}_{7}\)COOH [36] for stearic acid and oleic acid, respectively. Since milk fat has never been used as PCM, its key data of heat of fusion are not widely reported.