Metallographic analysis of solder joints

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Dr. Gordon Péter Róbert
Department of Electronics Technology


I analysed the effect of laser heat transfer on soldered joints formation. My object was to find relationship between the microstructure of the formed solder joint and the process parameters. The great advantage of laser heat transfer is that it is capable of producing reproducible joints with small heat impact zone and concentrated energy couple.

I used my earlier results to develop a measurement setup and I performed systematic experiments. After evaluating these results, I measured the average thickness of intermetallic layer as well as the quantity and distribution of intermetallic compounds dissolved into the solder bulk. I have created image processing macros in order to aid the evaluation.

Parallel with the experimental work I performed research in journals on metallography and formation of soldered joints. Concluding this research, it can be said that in the studied technical literature, there was no allusion about how the intermetallic compounds get into the solder bulk. There are only models about the formation and evolution of the intermetallic layer.

As a conclusion it can be said that the formation and growing rate of the intermetallic layer is determined, beyond the material qualities (e.g. solder coatings), by the time and method of heat transfer. The thickness of intermetallic layer is not equal along the solder-substrate interface. The presence of voids in the solder has significant effect on the formed metallographic structure and it influences the quality of the cross sections, what makes the evaluation inaccurate.


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