Failure Analysis of Film Capacitors

Metallized Layers

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.

FAILURE ANALYSIS OF CAPACITORS

electronic component f/a

 

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..

Film capacitors can fail due to the following:

  • Corrosion damage to the metallized film
  • Electrical overstress
  • Solder stresses
  • Mechanical damage

 

 

BSE SEM image on left, and EDS spectra on right.
BSE SEM image on left, and EDS spectra on right.
Secondary Electron SEM image of the end of a film capacitor roll.
Secondary Electron SEM image of the end of a film capacitor roll.