PURPOSE: To prevent the exfoliation of a side face part and to obtain a punched piece without warp by pressing and heat-processing the punched part after punching a clad material in the direction of a lamination with a drop-through blanking method.

CONSTITUTION: Because a drop-through blanking method is applied in a punching process, a punched piece 13 is dropped downward by being received a friction of only one direction between the space with an internal wall surface of a die 12. Therefore, the exfoliation between each metal of the side face is prevented. Further, because the warp of the punched piece 13 generated during the punching time is corrected on the next press process, so the trouble is nothing. More, because the residual stress inside the punched piece 13 generating during the punching time is relaxed on the next heating process, so the trouble is nothing. Therefore, the punched piece 13 without the side face exfoliation and the warp, and with little residual stress can be manufactured with the well yield. As a result, when it is used as a heat sink material, the radiating property of a ceramics package can be kept and the quality can be improved.