Examination of lead-free selective soldering process

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Hajdu István
Department of Electronics Technology

The development of the electrical technology and application construction, the increasing usage of the surface mounted technology resulted in the development of the soldering processes. The mixed mounting technologies – surface and through hole – and the special soldering problems need discrete solutions. Therefore the selective soldering is a dynamically advancing field. The lead-free applications create new challenges for the selective soldering.

In my work I detail the two- and three-component solders and the development of the soldering processes. I summarize the most significant selective soldering technologies. The higher contact temperature, the increased contact time and high tin concentration of the lead-free solder materials increase the dissolution of copper from the contact pads. The high copper dissolution could increase the cost of the manufacturing.

The aim of my examinations is to determine the effect of the contact time and contact temperature on the copper dissolution and on the quality of the solder joints. I conducted examinations to determine the optimal parameters for mini-wave soldering. I made cross-sections from samples manufactured with different contact time and contact temperature to examine the copper dissolution and I verified the results with XRF (X-ray Fluorescence Spectroscopy) measurements on samples from the solder bath. From my examinations the optimal parameters are: contact time=2.6 s, contact temperature=295°C.

The meniscus of the solder joint’s top side could be increased by increasing the contact time, however this result in increasing significantly the copper dissolution. The effect of the temperature isn’t that grand.

Subsequent upon the results of my measurements another selective soldering machine was modified. The XRF measurement showed that the copper concentration decreased in the solder bath, this confirm the previous measurements.


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