Validation of Heat-Level Vapor Phase Soldering Process and Workspace Leakage Detection with Applied Pressure Sensors  
[PERSON]  
1 Department of Electronics Technology, Faculty of Electrical Engineering and Informatics, Budapest University of Technology and Economics, I111 Budapest, Hungary; [EMAIL_ADDRESS] (M.A.A. ), [EMAIL_ADDRESS] (B.I. )1  
[PERSON]  
1 Department of Electronics Technology, Faculty of Electrical Engineering and Informatics, Budapest University of Technology and Economics, I111 Budapest, Hungary; [EMAIL_ADDRESS] (M.A.A. ), [EMAIL_ADDRESS] (B.I. )1  
[PERSON]  
soldering failures [2]. The second and most widely used reflow method in mass manufacturing is the forced-convection heating, where heat is transferred via controlled gas flow in separated work zones. [3]. The third method is the Vapour Phase Soldering (VPS). It is based on filmwise-condensation based heat transfer. After the 1980s, this technology fell out of focus. It was due to a toxic component in the heat transfer medium that was used in the process [4]. Nowadays, inert and chemically stable PFPE-based Galden fluids [5] enable clean and harmless reflow procedures [6]. This material reintroduced the vapour phase soldering method again to the manufacturers, starting a new age in the application of VPS. During VPS process, the vaporized medium is distributed and saturated inside the oven [7], and the colder printed circuit board (PCB) assembly (PCBA) is immersed into a vapour \"blanket\" or \"column\" in other words. Heat transfer occurs when condensation starts on the cold PCBA surfaces. During the reemergence of VPS, different new oven constructions and control paradigms appeared on the market. One of these was the \"heat-level\" based VPS approach (HL-VPS) [7]. This method is based on the standard process, but it is refined in many aspects. At first, the PCBA is positioned onto a sample holder at the top of a reservoir (or tank) at the loading height. Then, a lid closes on this tank, and the PCBA is lowered into the workspace of the oven. During standard VPS processes, saturated vapours are already present in the tank at this point. In HL-VPS, the vapour is generated onto the surfaces of the assembly from the bottom of the tank after the board reaches the lower position specified for soldering. The workspace control is based on thermocouple sensor measurements from different height points of the reservoir. They provide feedback on heating and eventual boiling of the heat transfer medium. The measurement points are usually located at the level of the boiling fluid in contact with it, at the vertical level of the PCBA where the PCBA is positioned in the tank, and at a specific height above the soldering level. When increased temperatures are measured above the PCBA level, the given sensor sends a signal that the vapour developed over this vertical position, while the heated assembly does not draw away any more significant amounts of vapour with condensation. The overreaching vapour heats the upper thermocouple, and after a programmed delay (the so-called heating delay, which keeps the maximum temperature for a specific time), the oven halts (or as the jargon says: breaks) the soldering process. Finally, the PCB is elevated to the loading height. The power of the heater can be controlled with percentage-based settings, and heating time delays (in the second range) could be programmed to extend the soldering process at peak temperatures. One soldering job (which can be batched processing) takes between 10-15 min altogether. The heating power can cause variations in the transients of the process; also, it can affect the vapour column height, thus consequently controlling the temperature profile of the soldering, including the heating gradient. This approach was a significant improvement upon standard, saturated-vapour based soldering principles, and in this paper, we focus on HL-VPS. It is important to highlight that this approach has its practical limits.