Failure Analysis of Film Capacitors
Film capacitors use stacked metallized polymer films to form the capacitor structure. The metal plates are usually evaporated aluminum. The polymers can be Polyethylene-terephthalate (PET), polycarbonate (PC), polypropylene (PP) and others. The internal structure of these capacitors is illustrated here.
Film capacitors can fail due to the following:
- Corrosion damage to the metallized film
- Electrical overstress
- Solder stresses
- Mechanical damage
The metallization on the film is made thicker to support termination to the metal contact layer (see next image). The relative peak heights for aluminum (Al-Ka1) and carbon (C-Ka1) are a measure of the aluminum thickness..