Film Capacitor Failure Analysis
Film capacitors can fail due to a number of causes including:
- Corrosion damage to the metallized film
- Electrical overstress
- Soldering stresses
- Mechanical damage
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 below.
The metallization on the film is made thicker to support termination to the metal contact layer (see below). The relative peak heights for aluminum (Al-Ka1) and carbon (C-Ka1) are a measure of the aluminum thickness.
The image below shows a capacitor roll prior to application of the metal contact layer. The distortion in the roll can lead to unpredictable results with the application of the metal contact layer and contribute to thermal-mechanical instability.