Numerical study of the gas flow velocity space in convection reflow oven

In this paper, numerical study of the gas flow velocity space is presented in a convection type reflow oven. Convection reflow ovens usually apply the nozzle-matrix heater system which generates numerous gas streams perpendicularly to surface of the soldered assembly. The ovens are divided into zones; every zone contains an upper and a lower nozzle-matrix. The temperature can be independently controlled in each zone; however the velocity of the influent streams is usually fixed. The gas flow velocity space is one of the most important parameter of the local heat transfer coefficient in the oven. The gas flow space cannot be examined by classical experimental methods due to the extreme circumstances in the reflow oven. Therefore the effect of the soldered assembly, the different component sizes, the position of the conveyor belt and the vent hood between the zones on the gas flow velocity space was studied by CFD simulations. These results can be useful during the overview of the actual assembly design and manufacturing rules

Numerical Simulation of Condensate Layer Formation During Vapour Phase Soldering

This paper presents a modeling approach of the condensate layer formation on the surface of printed circuit boards during Vapour Phase Soldering (VPS) process. The condensate layer formation model is an extension to a previously developed board level condensation model, which calculates the mass of the condensed material on the surface of the soldered printed circuit board. The condensate layer formation model applies combined transport mechanisms including convective mass transport due to the hydrostatic pressure difference in the layer and the gravity force; conductive and convective energy transport. The model can describe the dynamic formation and change of the condensate layer after the immersion of the soldered assembly into the saturated vapour space and can calculate the mass and energy transport in the formed condensate layer. This way the effect of the condensate layer changes on the heating of the soldered assembly can be investigated. It was shown that the numerical modeling of the VPS process becomes more accurate with application of dynamic condensate layer instead of a static description

3D mapping of forced convection efficiency in reflow ovens

In this paper, the investigation of the heating efficiency in forced convection reflow ovens which apply nozzle-matrix blower system is discussed. In these ovens the forced convection heat transfer coefficient (AA) determines manly the efficiency of heating. Therefore we present here a method where the 3D distribution of AA is determined from temperature distribution measurements in each heater zone of the reflow oven. The method has two steps: first, the temperature distribution in the oven is measured as a function of distance from the circuit board under chosen reference nozzle-line; in the second step, the heating efficiency of the neighbouring nozzle-lines is compared - at a dedicated measuring height - to the reference nozzle-line. From these data the distribution of AA is calculated by the heat equation of the measurement system and extrapolated to the whole oven. The result is a 3D distribution map of AA which is very important to the effective thermal modelling of the reflow soldering process and to the calibration of the reflow oven

Electrochemical Migration of Micro-alloyed Low Ag Solders in NaCl Solution

The reliability investigation of the lead-free solders is still a current issue. In this paper, Electrochemical Migration (ECM) behavior of novel lead-free micro-alloyed low Ag content solders were investigated by water drop test in NaCl solution. The results were compared to commonly used lead-free and lead bearing solder alloys. It was found that some micro-alloyed solders can have similar low ECM susceptibility than lead bearing ones. X-ray photoelectron spectroscopy was also carried out to find the root cause of different ECM behaviour of micro-alloyed solders. The results of water drop test and x-ray photoelectron spectroscopy were in good agreement relating electrochemical migration susceptibility. Since SAC0807 solder alloy has shown higher corrosion rate than SAC0307 and has also higher ability for ECM as well. It is concluded, that some lead-free micro-alloyed low Ag content solder alloy (e.g.: SAC0807) could have a high reliability risk in the electronic devices during operation

Modeling Method of Heat Transfer During Vapour Phase Soldering Based on Filmwise Condensation Theory

The paper presents a practical method for calculating the heat transfer during Vapour Phase Soldering (VPS) process. VPS is a reflow soldering method based on condensation heating and used in the electronics manufacturing. The presented explicit model describes solutions for filmwise condensation heat transfer based on the Nusselt theory. Different approaches on describing the filmwise condensation were investigated, compared and modified in order to determine a proper heat transfer coefficient for the VPS process - where the heated assembly can be considered as a horizontal plate. For the verification, measurements were done in an experimental soldering oven. The results of the calculations show a proper approximation with the measured temperature data. Finally the results were compared with a solution obtained from complex multi-physics simulation. The results point out, that the application of filmwise condensation model for VPS can be more practical than a complex multi-physics model, from the aspect of calculation error and computation time