Hermetically sealed polymer capacitors with high stability at elevated temperatures
View Patent ↗A process for providing an improved hermetically sealed capacitor which includes the steps of applying a solder and a flux to an interior surface of a case; flowing the solder onto the interior surface; remove flux thereby forming a flux depleted solder; inserting the capacitive element into the casing; reflowing the flux depleted solder thereby forming a solder joint between the case and the solderable layer; and sealing the case.
1. A process for forming a capacitor comprising:
providing a case;
a solder including a flux to an interior surface of said case;
reflowing said solder onto said interior surface to form an electrically conductive bond between said solder and said case;
washing to remove said flux thereby forming a flux depleted solder;
providing a capacitive element comprising:
an anode of a valve metal;
an anode lead in electrical contact with said anode;
a dielectric on said anode; and
a cathode layer on said dielectric wherein said cathode layer comprises a doped conductive polymeric cathode and a solderable layer;
inserting said capacitive element into said case;
reflowing said flux depleted solder thereby forming a solder joint between said case and said solderable layer; and
sealing said case.
2. The process for forming a capacitor of claim 1 wherein said solder comprises lead and tin.
3. The process for forming a capacitor of claim 2 wherein said solder comprises 30-50 wt % lead, 45-69 wt % Sn and 1-5 wt % Ag.
4. The process for forming a capacitor of claim 1 wherein said solder comprises of Pb/Sn/Ag in 36/62/2 wt. % ratio.
5. The process for forming a capacitor of claim 1 wherein said solder and said flux are provided in a flux cored solder.
6. The process for forming a capacitor of claim 1 wherein said flux is an organic acid based flux.
7. The process for forming a capacitor of claim 6 wherein said flux is a rosin mildly activated (RMA) flux.
8. The process for forming a capacitor of claim 1 wherein said washing is with a solvent and further comprising reclaiming and analyzing said solvent after said washing.
9. The process for forming a capacitor of claim 8 wherein said analyzing is by chromatography.
10. The process for forming a capacitor of claim 8 comprising repeating said washing until said reclaimed solvent comprises less than 1 wt % flux.
11. The process for forming a capacitor of claim 10 comprising repeating said washing until said reclaimed solvent comprises less than 0.1 wt % flux.
12. The process for forming a capacitor of claim 1 wherein said doped conductive polymeric cathode comprises a conductive polymer selected from the group consisting of polypyrrole, polyaniline, polythiophene and their derivatives.
13. The process for forming a capacitor of claim 12 wherein said doped conductive polymeric cathode comprises polythiophene.
14. The process for forming a capacitor of claim 13 wherein said doped conductive polymeric cathode comprises poly 3,4-ethylenedioxypolythiophene.
15. The process for forming a capacitor of claim 1 wherein said doped conductive polymeric cathode comprises a dopant selected from the group consisting of polystyrene sulfonate.
16. The process for forming a capacitor of claim 1 further comprising attaching an external anode lead to said anode lead.
17. The process for forming a capacitor of claim 1 further comprising electrically attaching an external cathode lead to said cathode.
18. The process for forming a capacitor of claim 1 wherein said washing is with a solvent is selected from the group consisting of alcohol, glycol, ketone, ether, ester, dimethyl-formamide, dimethyl sulfoxide, methylene chloride and N-methyl-2-pyrrolidinone.
19. The process for forming a capacitor of claim 18 wherein said solvent is selected from the group consisting of isopropyl alcohol and acetone.