Abstract
Electroanalytical tests were carried out to investigate the corrosion behavior of various lead-free solder alloys in 3.5 wt% NaCl bulk solution under room temperature. Scanning electron microscope (SEM) method was applied to investigate the corroded surface structure and corrosion depth using cross-sectional samples. Furthermore, energy dispersive spectroscopy (EDS) method was also applied to identify the chemical elemental composition of the corrosion products of the solders. The results showed that the bismuth and silver bearing solders have lower corrosion resistance compared to other lead-free solders and to the widely used SAC305 as well. The different corrosion resistance was explained by the different silver and bismuth content and volume of the corrosion products, which can lead back to the differences of the original alloying components. This study is highlighted that the bismuth and silver content may pose a relative high corrosion risk related to lead-free solder alloys used in electronics.
Highlights
One of the key reliability issues of the electronics technology is carry about the solder joints testing
The results showed that the bismuth and silver bearing solders have lower corrosion resistance compared to other lead-free solders and to the widely used SAC305 as well
The reason could be that the corrosion potential (Ecorr) is shifted towards less noble values with the addition of bismuth and silver (See Table 2 and [18])
Summary
One of the key reliability issues of the electronics technology is carry about the solder joints testing. The different failures can lead back to the not adequate physical properties (e.g. wetting behaviour, mechanical strength, etc.) of the solder alloy and/or the not adequate applied technological processes (e.g. reflow temperature profile), which have to be improved. This challenge was updated in 2006, with the introduction of lead-free solder alloys governed by the RoHS directive of EU [1]. When the sample reaches the passivation potential, if possible a passivation film begins to form on the surface and the current density at this point is called the critical current density (Icrit) After this point the corrosion current density begins to drop to a much lower value.
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