Product Information: Electrolytic Capacitor

Aluminum Electrolytic Capacitor Technical Notes

2. Manufacturing Process

Etching To obtain higher capacitance, surface area of aluminum foil for electrolytic capacitor increases through the etching process.
During the etching process, a DC or AC current is applied to the aluminum foil. This is done in a chloride solution to assist to dissolve the surface. Surface area is increased by 60-150 times for low voltage foils and 10-30 times for high voltage foils.
Anodization Aluminum foil for electrolytic capacitor are further formed with anodic oxide film (Al2O3) on the surface as dielectric layer.
Etched aluminum foil is immersed into a solution including ammonium salt of boric or phosphoric acid and applied with DC voltage so that the foil becomes positive and the solution becomes negative. Then the aluminum oxide film is formed on the surface in proportion to the applied voltage. The anodic oxide film, having the thickness of 13-15 angstrom/V (1.3-1.5 nm/V), is extremely thin, compact and highly insulating.
Slitting The master formed roll is then slit into individual rolls with specified width as per the specification.
Stitching Winding Slit anode and cathode foils are then stitched with aluminum tabs and wound into cylindrical element together with separator paper. The Separator paper has the function of containing the liquid electrolyte that functions as the real cathode and restores the damaged dielectric layer. It also maintains a safe distance between anode and cathode foils to prevent a short circuit.
Fig. 6
                                            Fig. 6
Impregnation The wound element is immersed into an electrolyte bath under either a low or normal air pressure condition to impregnate the paper. Electrolyte contains one or more polyhydric alcohols such as ethylene glycol as the major solvent and one or more ammonium salts as solutes to restore the damaged dielectric layer and significantly improve the performance and life of the capacitor.
Assembling Attach rubber bung / rubber-lined terminal plate / molded terminal plate to impregnated element and seal it with the aluminum case.
Fig. 7
                                            Fig. 7
Attaching Sleeve The sealed capacitor is then covered with sleeve made of a heat shrinkable resin. The purpose of sleeve is to indicate key information of the capacitor. When electric insulation of the inner element or aluminum case are required, consult our team for proper materials selection vs standard sleeving.
Not all of our products employ a sleeving procedure. Our surface mount is an example. We employ a laminated can with printing on the case.
Photo 4
                                            Photo 4
Aging A dielectric layer is formed during the anodization (forming) process, but aluminum substrate is exposed during the slit and stitching process. The dielectric layer can also expose imperfection areas during the winding procedure. Restoring the dielectric layer is necessary for the capacitor to function properly per our specification. During the aging process, the capacitors are applied with a high DC voltage and temperature. This repairs the damaged dielectric layer. The aging process also assists to stabilize the leakage current of capacitor and helps to debug initial failures.
SMD type: Terminal processing and a seat plate are attached.
Lead terminal type: taping applied, lead wire cutting, forming and bending processing according to customer request.
In-line inspection Capacitors are packaged after electrical screening and appearance inspection are performed.
Outgoing inspection Outgoing inspection is conducted based on our own sampling plan and criteria.
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