The small spot sizes and short residence times involved in microwelding demands the use of extremely high power density heat sources, which is beyond the feasible range in welding. The present work explores the use of volumetric heating as a key to employ such high heat intensities for microwelding. Electron beam is represented as a volumetric heat source and a numerical model is developed using commercial finite element softwares to predict the temperature distribution in the solid as a result of beam scanning. The effect of weld speed and beam interaction volume are evaluated to propose the optimum conditions of microwelding. Optimality is based on limited heat flow into the material, high controllability, and tolerable maximum temperature of the process. For the choice of AISI 304 material as an example, the optimum welding conditions required to produce a 2.5 mu m weld depth are determined in the non-dimensional form of Peclet number 100 and relative beam penetration in the range of 0.8-1.2. (C) 2011 Elsevier Ltd. All rights reserved.