Solid electrolytic capacitor for use in a humid atmosphere

A solid electrolytic capacitor comprising:

• a sintered porous anode body that includes tantalum;
• a dielectric that overlies the anode body, wherein the dielectric includes an oxide of tantalum;
• a solid electrolyte that overlies the dielectric, wherein the solid electrolyte includes a plurality of conductive polymer particles, wherein the conductive polymer particles include a thiophene polymer;
• and
• a cathode coating that contains a metal particle layer that overlies the solid electrolyte, wherein the metal particle layer includes a plurality of silver particles dispersed within a resinous polymer matrix, where the particles constitute from about 50 wt. % to about 99 wt. % of the layer and the resinous polymer matrix constitutes from about 1 wt. % to about 50 wt. % of the layer, wherein the cathode coating exhibits a moisture content of about 10 wt. % or less when exposed to an atmosphere having an 85% relative humidity in accordance with ASTM D6869-03 (2011).

A method for forming a capacitor, the method comprising:

• anodically oxidizing a sintered porous anode body to form a dielectric that includes an oxide of a valve metal compound;
• applying a dispersion that contains conductive polymer particles to form a solid electrolyte layer;
• and
• applying a metal paste over the solid electrolyte layer, wherein the paste contains a plurality of conductive metal particles, a vinyl acetal polymer, and an organic solvent;
• and
• drying the metal paste.