Thermal substrates

A thermal substrate comprising:

• a multilayer film comprising:
• a first outer layer comprising a first thermoplastic polyimide;
• a core layer comprising a polyimide;
• and
• a second outer layer comprising a second thermoplastic polyimide, wherein:
• the thicknesses of the first and second outer layers are each in a range of from 3 to 6 μm;
• wherein a glass transition temperature (Tg) of the core layer is higher than both a Tg of the first outer layer and a Tg of the second outer layer;
• the multilayer film has a total thickness in a range of from 15 to 100 μm;
• and
• the first outer layer, the core layer and the second outer layer each comprise a thermally conductive filler;
• wherein the thermally conductive filler of each of the first outer layer, the core layer and the second outer layer are individually selected from the group consisting of BN, Al2O3, AlN, SiC, BeO, diamond, Si3N4 and mixtures thereof;
• a first conductive layer adhered to the first outer layer of the multilayer film;
• and
• a second conductive layer adhered to the second outer layer of the multilayer film, wherein the first conductive layer and the second conductive layer each comprise a metal sheet and have a thickness in a range of from 250 to 3000 μm.