When the humidity in the air is too high, the water film will condense on the surface of the capacitor shell, which will reduce the surface insulation resistance of the capacitor. Moisture can also penetrate into the capacitor medium, reducing the insulation resistance of the capacitor medium.
The impact of high temperature and high humidity environment on the deterioration of capacitor parameters is extremely significant. If vacuum packaging is not used, tantalum capacitors exposed to the air for a long time need to be dried and dehumidified before use, but the consequences of electrolysis of water molecules cannot be eradicated.
This is why vacuum packaging for tantalum capacitors is requeested.

The impact of high temperature and high humidity environment on the deterioration of capacitor parameters is extremely significant. The electrical performance of the capacitor can be improved after drying and dehumidification, but the consequences of electrolysis of water molecules cannot be eradicated. For example, when a capacitor works under high temperature conditions, water molecules are electrolyzed into hydrogen ions (H+) and hydroxide ions (OH-) under the action of an electric field, and electrochemical corrosion occurs at the root of the lead wire. It is impossible to restore the lead wire even if it is dried to remove moisture.

Ion migration can seriously damage the silver layer on the surface of the positive electrode. Between the lead solder joint and the silver layer on the electrode surface, silver oxide with semiconductor properties is separated, which increases the equivalent series resistance of the non-dielectric capacitor and increases the loss of the metal part. The loss tangent value increased significantly.

Since the effective area of the positive electrode is reduced, the capacitance of the capacitor will decrease accordingly. The surface insulation resistance is reduced due to the presence of silver oxide semiconductor on the surface of the dielectric between the two electrodes of the inorganic dielectric capacitor. When the migration of silver ions is serious, a dendritic silver bridge is built between the two electrodes, which greatly reduces the insulation resistance of the capacitor.

In summary, the migration of silver ions will not only deteriorate the electrical properties of non-hermetic inorganic dielectric capacitors, but may also lead to internal short circuits, high leakage currents, loss of capacitance, rise in ESR values, and open circuits. And it may cause the dielectric breakdown field strength to drop, and finally lead to the breakdown of the capacitor.