Thermal grease can be applied using either a roller or stencil mask. An inappropriate thermal grease thickness will negatively affect heat radiation to the heat sink. We strongly recommend using a stencil mask that enables a uniform thickness to be applied over the back surface of the module. For details on application methods, refer to Application Manual Chapter 6-3.3 or Mounting Instruction. An optimum outline drawing for each module is also available. Please contact Fuji Electric Corp. of America or your local sales representative or distributor to answer your question.