From the LM2832 Data Sheet (attached) with regard to WSON - 6 package power pad:
The PCB size, weight of copper used to route traces and ground plane, and number of layers within the PCB can greatly effect Rthermal.The type and number of thermal vias can also make a large difference in the thermal impedance. Thermal vias are necessary in most applications. They conduct heat from the surface of the PCB to the ground plane. Four to six thermal vias should be placed under the exposed pad to the ground plane if the WSON package is used.
More info about this is in the Data Sheet as well.