Vapour Phase Soldering

© ASTRON

Currently, the R&D department is assembling some prototype PCB's (Printed Circuit Boards) for the NCLE project. Some of the components however, are hard to solder by hand because all solder pads are located on the bottom side of the component. Usually these components are soldered in an automated reflow process, but for a prototype, outsourcing gives a lot of overhead and time loss. Soldering them by hand with a hot air pencil is an option, but both component and board are easily overheated and thus damaged, because the PCB contains 4 layers with a lot of copper that conducts heat away from the solder location. So a lot of heat has to be applied to the solder location.

However, since a few months we have access to a so called Vapour Phase soldering unit. This has a lot of advantages over the previously mentioned soldering techniques. To solder components with this machine, we first have to apply solder paste to the solder pads on the PCB. This is done by hand using a dispenser, or by using a solder paste stencil with holes. Next, we place all components on the solder paste, and finally we put the PCB on the rack inside the Vapour Phase unit's tank. On the bottom of the tank is a small amount of a special inert Fluorcarbon fluid, Galden 230 or 210. When this fluid is heated by the machine it evaporates, the vapour rises to the level of the PCB. The vapour starts condensating on the "cold" PCB and components, heating them to the desired temperature (230 degrees for lead/free and 210 degrees for lead solder). As soon as the PCB reaches this temperature the solder paste reflows and the components are soldered. Then the vapour rises even further and reaches a sensor that automatically switches off the machine and starts the cooling process. The complete cycle takes about 15 minutes.

In this way it is feasible to reliably solder PCB's with "difficult" parts, even for space applications, something which is much harder to accomplish when soldering manually.