Measurement of Nonlinearity of Lead-free Vapour Phase Reflowed Solder Joints

The goal of the study is to compare quality of vapour phase reflowed solder joints soldered on different printed circuit board (PCB) surface finishes. Vapour phase reflow soldering guarantees the highest reliability, quality of processing and process safety. The big advantage of heat transfer in vapour phase soldering (VPS) is the extremely efficient transfer of latent heat through the condensing vapour of a chemically inert liquid. The heat transfer process is about ten times faster than hot air and about eight times faster than infra red heat. The condensation mediums used are perfluorocarbon, perflouropolyeter, flouriertes phenandren or perflouramin liquids, which are clear and colourless, have no odour, no taste, are non-flammable, non-corrosive and non-ozone depleting. For lead free soldering a boiling point of 230 °C of these liquids is recommended. The temperature of any saturated vapour cannot exceed the temperature of the boiling liquid, therefore the temperature of the PCBs and components can never be higher than that of the vapour in the machine. As the liquid boils, a layer of saturated vapour forms above the fluid creating a 100 % inert atmosphere – it allows use of less aggressive flux than in other forms of reflow. The reflow in inert gas atmosphere defines an own unique standard. As there is no danger of overheating, there is no need to set temperature profiles. Vapour phase provides probably the best possible solder reflow conditions with only minimal temperature differences across the PCB. Vapour phase is independent of size, shape or geometry with the maximum surface area exposed and every component part seeing precisely the same temperature. Comparison of quality of the solder joints is based on measurement of the solder joints nonlinearity of the currentvoltage (C-V) characteristics.