Investigations on the Processing Zone of a Vapour Phase Soldering Station with Sensors

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Dr. Géczy Attila
Department of Electronics Technology

As Vapour Phase Soldering (VPS) has again become a significant alternative method for reflow soldering, several investigations are in progress to determine the possibilities of the re-introduced technology. Yet, qualitative and quantitative measurements are still not common for the VPS process itself. Therefore, critical parameters of the processing zone of a locally developed experimental VPS system were measured with novel methods. This thesis sums up the technology and heat transfer attributes of VPS; describes the methods and devices for pressure and temperature measurements based on literature research.

A test board with nine type K thermocouples in the grid points of a 3x3 matrix was developed for temperature measurements and small extension boards were constructed for pressure sensor interfacing, after choosing the appropriate sensors (Sensirion SDP and Sensortechnics LBA series differential pressure sensors and a Fluke 922 manometer). Preliminary calibration measurements using a water column pointed out that the Sensirion and Sensortechnics sensors would indicate the relative change of the pressure, while Fluke characteristic would show the exact, actual values inside the tank.

In-situ analysis of the processing zone was performed at various heights inside the processing zone. Using the results of the 3D thermal mapping, a database of isothermal shells at custom time points and custom temperatures can be created. After comparing further temperature measurement results with the corresponding pressure values, it was found that from the aspect of soldering, the saturated vapour indication is more precise and immediate than measurements with thermocouples. The heating up process consisted of three different stages and without pressure measurement inside the process zone the optimal circumstances for soldering could be recognized in the wrong stage, where non-saturated vapour would not be optimal from the aspect of soldering.

The conclusions could serve as a calibration procedure for specific VPS processes.


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