Softbank Corp. plans to sell ¥400 billion in bonds targeting individual investors to fund its $20.1 billion purchase of Sprint Nextel Corp.

The mobile phone company will price the five-year notes to yield from 1.25 percent to 2.25 percent on June 3, according to a filing with the Finance Ministry on Tuesday. The securities will be offered from June 4 to 19, according to the filing. The offering will be the largest by Softbank, which has raised the equivalent of $6.9 billion in bonds since the transaction was announced in October, data compiled by Bloomberg show.

The acquisition is being challenged by Dish Network Corp.'s $25.5 billion offer. President Masayoshi Son, Japan's second-richest person, reiterated this month he won't increase the bid, even as firms from Daiwa Securities Group Inc. to BNP Paribas SA say the company has scope to raise the amount by $5 billion. Softbank plans to complete the deal under the terms announced on July 1.