Comparing solder joints formed by forced convection and vapour phase soldering

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Supervisor:
Dr. Krammer Olivér
Department of Electronics Technology

Based on the literature survey – I have done – the main reason of the vapour phase soldering method’s re-entering is the elimination of problems caused by the increased soldering temperatures. The heat transfer of the vapour phase is more homogeneous, which reduces the failure taking shape because of the temperature difference.

To compare the vapour phase and the forced convectional soldering I set heat profiles with approximately equal heating factors, and I measured the temperature difference between the outer and inner bumps by plastic BGA components. As it is revealed by the results the temperature difference by the forced convection is twice as much, like the vapours phase soldering method. The difference measured on the peak temperature is not significant in one of the cases.

As it is revealed by the results of the X-ray microscope analyses the solder joints formed by vapour phase soldering contain less macro voids. The main reason of this is that the vapour phase soldering process is longer, so the steam of the flux can leave from the solder much more easily.

During the cross section analyses of the solder joints a big difference was observed by the position of micro voids in the centre plane of the bumps. In the solder joints formed by forced convection soldering the micro voids are located the same rate in the component side and PCB side of the solder joints. As opposed to this, the 90 % of the micro voids in the solder joints formed by vapour phase soldering was found in the PCB side of the soldered joints. My conclusion based in this result is that the solder joint formed by vapour phase soldering are weaker in the PCB side.

To compare the reliability of the solder joints I performed accelerated aging tests. The samples were subjected to 1000 cycle thermal shock ageing, after every 250 cycles cross section and dye penetration analyses were done.

The cross section analyses of the solder joints proved, that the solder joint formed by vapour phase soldering are weaker in the PCB side. As it is revealed by the results, the reliability of solder joints formed by vapour phase soldering are better on both side.

During the dye penetration analyses of the samples, pad cratering has been found in the PCB, in an equal percentage by both soldering methods.

The vapour phase soldering assures a good alternative of forced convectional soldering both from quality, reliability and economically viewpoint.

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