Influence of Materials and Packaging Solutions on Thermal Behaviour of Power Modules

Nowadays, designing ever more efficient power modules requires complex materials and more innovative methodologies. To significantly reduce the lead time of the devices and decrease the costs, especially during the prototyping and the testing phases, a Finite Element Analysis (FEA) can be the simplest way to deal with a matrix of parameters to be studied on a single setup. In this work, a thermal characterization is addressed to a stationary simulation using the COMSOL Multiphysics® software, coupling the Heat Transfer Module and the CFD Module. The study is applied to two types of power modules with different technologies, one with Direct Bonded Copper (DBC) substrate and the other one with Insulated Metal Substrate (IMS). An experimental phase follows in order to test the most performing module. A DBC module is composed by (bottom-up) a substrate (copper base, an alumina insulating layer, copper top layer with a specific electrical layout), soldering layers, the dice, the metallic pins, a covering insulating gel and an external protective box. The IMS modules are equal, except for the substrate made up by (bottom-up) a metal base (copper or aluminium), a polymer with ceramic fillers as insulating layer and a copper top layer with the same electrical layout of DBC. The experimental setup used to test real devices is composed by an aluminium water heatsink with a macroscopical copper plate on the top, separated by a thermal grease layer. The device is then mounted on the copper plate with a defined thermal grease layer in between. The geometry considered in the simulation reproduces accurately this experimental setup. The Heat Transfer Module is set to dissipate about 110 W per die. Air natural convection is neglected since it contributes only marginally to the exchange process. This has been assessed with a specific simulation that allows to fix the total insulating condition on the external boundaries, so that only conductive phenomena are considered at this point. The CFD Module is responsible of the water flux entering the heatsink, while the Multiphysics captures the non-isothermal behaviour of the fluid as it flows inside the heatsink. The mesh incorporates different element sizes, depending on the layers thickness. As a result, the FEA solution, provided by COMSOL Multiphysics®, is mostly in accordance with the experimental data. For DBC module, also the packaging is investigated. Different solutions, such as Vacuum Potting Gel (VPG), are applied to the standard module, analysing thermal resistance and heat dissipation. As an example, the VPG solution consists in filling a protective plastic case with a silicone dielectric gel. The layers disposition is precisely the one described in the DBC section above. The modules are imported in the software and placed upon the testing setup already in use for the previous part. The simulations return interesting insight in the thermal behaviour of the modules

Clathrate Hydrate Equilibrium Data for the Gas Mixture of Carbon Dioxide and Nitrogen in the Presence of an Emulsion of Cyclopentane in Water

Carbon dioxide and nitrogen gas separation is achieved through clathrate hydrate formation in the presence of cyclopentane. A phase diagram is presented in which the mole fraction of CO₂ in the gas phase is plotted against the mole fraction of CO₂ in the carbon dioxide + nitrogen + cyclopentane mixed hydrate phase, both defined with respect to total amount of CO₂ and N₂ in the respective phase. The curve is plotted for temperatures ranging from 283.5 K to 287.5 K and pressures from 0.76 MPa to 2.23 MPa. The results show that the carbon dioxide selectivity is moderately enhanced when cyclopentane is present in the mixed hydrate phase. Carbon dioxide could be enriched in the hydrate phase by attaining a mole fraction of up to 0.937 when the corresponding mole fraction in the gas mixture amounts to 0.507. When compared to the three phase hydrate–aqueous liquid–vapor equilibrium in the ternary system {water + carbon dioxide + nitrogen}, the equilibrium pressure of the mixed hydrate is reduced by 0.95 up to 0.97. The gas storage capacity approaches 40 m³ gas·m^–3 of hydrate. This value turns out to be roughly constant and independent of the gas composition and the operating conditions