To provide a board unit for a high-frequency module and its manufacturing method by which peeling or side etch can be prevented when a seed metal layer is removed during formation of lead wiring.

The method is used to manufacture a board unit 1 for a high-frequency module that is provided with a base board 3, an electrode layer 4 and a wiring layer 7. First, a seed metal layer is formed, a photo resist is applied onto the upper layer of the seed metal layer, and an opening is formed by lithography technology in an area corresponding to an area where lead wiring is formed in the photo resist and a peripheral area of the electrode layer. Then the seed metal layer exposed over the opening is grown. Next, the photo resist and the unnecessary seed metal are removed.