A base plate for a power module includes: a metal plate, a ceramic base plate joined to the metal plate, and a release agent provided in a joint surface between the metal plate and the ceramic base plate. A remaining amount of the release agent is less than 5 as an amount of boron measured by fluorescence X-ray analysis, and a crystal grain straining region in the joint surface is equal to or less than 40%, or an amount of crystal grain straining in the joint surface is equal to or less than 0.03%.
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