generated while soldering. With the higher heat of fusion, melting the solder and subsequent solidification will take longer. This increases the time the sensitive electronics are exposed to high temperatures, making potential damage to them more likely. As can be seen in Table 3 , the measured melting temperature deviates from the theoretical melting temper- ature by 4 ± 1 o C. As the deviation is fairly consistent, it is most likely a calibration issue. The heat of fusion, however, deviates from the theoretical values less consistently.A reason for this could be a mismatch of thermal 3
conductivity of the purge gases between the reference and sample pans. This mismatch is caused by a change of the thermal conductivity of the gas surrounding the sample during the melting process  . For future research, lead-free alternatives with a lower heat of fusion should be considered, as they will decrease the potential for damage to the electronics. Additionally, further lead-free alternatives with lower melting temperatures should be found. For achieving this lower melting temperature other alloying elements need to be considered. Some elements that lower the melting temperature and are already used in some low- temperature soldering applications, to consider are Antimony, Bismuth and Indium. However, they all have different drawbacks, such as pricing or widening of the melting range  . Table 3: Differences between the theoretical and measured melting temperatures and heats of fusion Composition (%) Tm theoretical - Tm experimental ( o C) Δ Hf theoretical - Δ Hf experimental (J/g) Pb 100 4 0.6  Sn 100 3 -0.2  Sn Pb eutectic 4 -2.5  Sn 95.5 Ag 3.8 Cu 0.7 3 3.8  Sn 97 Cu 3 5 4.1  Sn 99.3 Cu 0.7 5 2.5  5 Conclusions The experimental data establish that the solders with the highest melting points are the pure ones: Pb100% and Sn100%. The addition of other alloying elements decreases the melting temperature of the solders.
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- Spring '18
- Dr. maarten bakker