Process for making a capacitor foil with enhanced surface area

DETAILED DESCRIPTION The instant invention is directed to the benefits obtained by deep etching of the anode foil for aluminum electrolytic capacitors.
Anode foil is not normally etched to this degree because such an etch leaves the foil so brittle that it cannot be wound into capacitors without breaking or cracking the foil and anode foils of flat stacked capacitors are difficult to join together.
By deeply etching the anode foil to this degree one can produce 30% to 50% more capacitance than with foil that is not deep etched.
The invention provides a way to deep etch the anode foil for the advantages of high capacitance while leaving strategic regions of high flexibility.
The first capacitor type to benefit from the process of the invention is a stacked capacitor where anode plates are stamped from high gain capacitor foil and are then stacked into a capacitor element without bending the brittle plates.
Each anode plate must have an electrical connection to the anode terminal.
Joining of the anode plates at a weld tab on each plate is made possible by masking the area where this tab is to be attached during the etch process to provide a region of high strength so that the plates may be electrically joined and also connected to the anode terminal by welding.
Flexibility in the tab region also allows the tabs of, for example, the upper and lower anode foils in a stack to be bent together for welding.
Such a construction also may benefit from masking the periphery of the plate so that strong edges are maintained when the plate is stamped or die cut and thereby reducing the possibility of cracking that would normally occur during the stamping and assembly operations.
The second capacitor type to benefit from the process of the invention is a flat or oval capacitor that is made by rolling or winding the capacitor element on a large arbor, and then flattening the element by compressing it in a press.
When flattening a capacitor element of this shape, having a cross section similar to a doughnut, the material will flatten with a bend at each side and will have flat areas in between