Steel foil for capacitors

Film / foil capacitors continue their advantage in many places, and are very much in use today for several applications. It is of interest to understand the pros and cons of the two types of construction. Capacitor element is made by winding alternate layers of plastic film and metal foil (mostly aluminium. Plastic film could be PP, PET, PPS etc.).

Some large power factor capacitors may also use extended foil construction for the same benefits. Foil has naturally much lower resistance (ESR) than a thin metal layer (as for metallized film), which give much lower loss factor. High stability of capacitance throughout lifetime.

Conventionally, capacitors are made with two layers of dielectric film (PP, PET, PC etc.) and metal foils. During 1980s, metallized film capacitors were introduced, which later became popular because of several advantages they offer.

Terminations of film / foil capacitors may be made brought out as extended foil construction, or may be brought through the winding by insertion of tabs for external connection. Extended foil gives much smaller loss factor and high pulse capacity, while tab insertion if preferred for large capacitors for large DC or AC capacitors.

Aluminum foil for capacitors is treated electrochemically to increase the surface area, which improves capacitance. However, the greater surface area tends to decrease bending strength. UACJ and UACJ Foil collaborate to solve this dilemma.

The metal electrode foil on conventional capacitors is replaced by an extremely thin layer of metal deposited directly on plastic film trough a vacuum deposition process. This eliminates the thickness and volume occupied by metal electrode. The film metallization has following characteristics.