This paper is concerned with pressure welding, which has been known as a main bonding mechanism during the cold and warm formings such as clad extrusion or bundle extrusion/drawing. Bonding characteristics between the Cu and Al plates by pressure welding are investigated focusing on the weak bonding. Experiments are performed at the cold and warm temperatures ranging from the room temperature to 200 degrees C. The important factors examined in this work are the welding pressure, pressure holding time, surface roughness, and temperature. A bonding map, which can identify the bonding criterion with a weak bonding strength of 1 MPa, is proposed in terms of welding pressure and surface roughness for the cold and warm temperature ranges.