Field of the Invention
The present invention relates to a power-module substrate and power module used for a semiconductor device controlling a large electric current and a large voltage.
Priority is claimed on Japanese Patent Application No. 2012-191607, filed Aug. 31, 2012, the content of which is incorporated herein by reference.
Description of the Related Art
Conventionally, a power module in which: a metal plate forming a conductor-pattern layer is laminated on one surface of a ceramic substrate; an electronic component such as a semiconductor chip is soldered on the conductor-pattern layer; a metal plate being a heat-radiation layer is formed on another surface of the ceramic substrate; and a heat sink is bonded to the heat-radiation layer is known.
In a power-module substrate for the power module, the metal plates are bonded on the surfaces of the ceramic substrate by brazing. For example, in Patent Document 1, a power-module substrate in which a metal plate and a ceramic substrate are brazed is manufactured by: temporarily tacking a brazing-material foil on a surface of the ceramic substrate by surface tension of volatile organic-medium; heating a conductor-pattern layer which is stamped out from a base material in a state of temporary tacking on a surface of the brazing-material foil so as to volatilize the volatile organic-medium; and pressing it in a thickness direction.
Meanwhile, the power-module substrate of this type is required to have a function of a circuit board along with high integration in recent years other than a function of an insulated board and a function of a heat-radiation board, so multi-layering is examined.
For example, in a metal-ceramic bonded substrate (i.e., a power-module substrate) disclosed in Patent Document 2, a plurality of ceramic substrates in which through holes for via holes are formed and metal plates intermediate between the ceramic substrates are provided in a multi-layered structure. In this case, the metal plates are formed by casting molten metal into a mold in which the ceramic substrates are stacked and solidifying the molten metal. Accordingly, the molten metal is poured into the through holes formed in the ceramic substrates and then solidified. As a result, the metal plates on the both side of the ceramic substrates are electrically connected to each other via the metal in the through holes.
In Patent Document 3, it is disclosed that a metal post is provided in a through hole formed in a ceramic substrate and also metal plates on both sides of the ceramic substrate are electrically connected by the metal post.