Effect of water on the dielectric behavior of solder

The electrical conduction behavior of solder is well-known, but the dielectric behavior has been reported only recently. Water in the environment commonly affects electronics performance. This work provides the first study of the effect of water on the dielectric behavior of solder (along the solder bar axis). It also provides the first report of a mixed dielectric, which is a new concept referring to the combination of an electronic dielectric and a molecular dielectric. The mixed dielectric here is a combination of Sn-4Ag solder (an electronic dielectric with relative permittivity 3.24 × 10⁶) and water (a molecular dielectric with relative permittivity 80). In this mixed dielectric, the electric field from the high-permittivity solder promotes the electric field in the low-permittivity water, so the relative permittivity of the solder-water combination exceeds that of the corresponding solder-air combination. The relative permittivity of the combination decreases with decreasing solid (solder) volume fraction. For the highest water/air volume fraction in the combination, corresponding to the lowest solid volume fraction of 0.937, the replacement of air with water increases the relative permittivity at 100 kHz by 1.3%, from 3.09 × 10⁶ to 3.13 × 10⁶. The measured relative permittivity is higher than the corresponding calculated value based on the Rule of Mixtures, due to the fringing electric field associated with the water or air, which is not as able as the solder in trapping the electric field in the capacitance measurement using coplanar electrodes.