Figure 3 shows an SEM cross-section of a TE leg. Here it is demonstrated that the thermal bump is structurally identical to a CPB with an extra layer, the TE layer, incorporated into the stack-up. The addition of the TE layer transforms a standard copper pillar bump into a thermal bump. This element, when properly configured electrically and thermally, provides active thermoelectric heat transfer from one side of the bump to the other side. The direction of heat transfer is dictated by the doping type of the thermoelectric material (either a P-type or N-type semiconductor) and the direction of electric current passing through the material. This type of thermoelectric heat transfer is known as the Peltier effect. Conversely, if heat is allowed to pass from one side of the thermoelectric material to the other, a current will be generated in the material in a phenomenon known as the Seebeck effect. The Seebeck effect is essentially the reverse of the Peltier effect. In this mode, electrical power is generated from the flow of heat in the TE element. The structure shown in Figure 3 is capable of operating in both the Peltier and Seebeck modes, though not simultaneously.