The invention describes a process and a device for wave and/or reflow soldering in the form of vapour-phase soldering for electronic units. In prior art processes and devices, either wave soldering or vapour-phase soldering alone can be performed in a single chamber. For electronic units which contain both components which are to be wave soldered and those to be reflow soldered, at least two soldering devices and two process steps are necessary. There is the further drawback that temperature-sensitive components impose either a limitation on the soldering temperature and hence the solders which can be used or laborious post-fitting. The invention performs wave soldering and vapour-phase soldering as a form of reflow soldering in a single chamber, in which an electronic unit can be placed and/or the portion of the volume of the chamber filled with the saturated vapour of a primary fluid can be controlled in such a way that, at the worst, temperature-sensitive components of the unit lie only partly in the saturated vapour and the connections of the electronic components of the unit are in the saturated vapour during soldering. The invention permits the soldering of surface-fitted, penetrating and temperature-sensitive components, e.g. large electrolytic capacitors, in a single chamber and in a single process stage and is therefore eminently suitable for economical mass production with high soldering quality.