Thermally conductive insulating sheet, power module, and manufacturing method for same

In order to retain superior thermal conductivity and electrical insulation when using a transfer mold method to manufacture a power module equipped with a thermally conductive insulating sheet in which an inorganic filler is dispersed in a thermosetting resin, the inorganic filler containing secondary aggregated particles formed from aggregates of primary particles of flaky boron nitride, in the present invention the curing of the thermally conductive insulating sheet is carried out so that the percentage of change, indicated in formula (1), of the curing degree of the uncured or semi-cured thermally conductive insulating sheet reaches at least 30%. (1) Percentage (%) of change of curing degree of thermally conductive insulating sheet = [(B-C)/B]×100 (In the formula, B represents the calorific value (cal/g), as measured by a differential scanning calorimeter, from the pre-transfer molding uncured or semi-cured thermally conductive insulating sheet until curing is complete, and C represents the calorific value (cal/g), as measured by a differential scanning calorimeter, from the pre-transfer molding uncured or semi-cured thermally conductive insulating sheet after being heat treated at 180°C for 90 seconds until curing is complete)