Failure Analysis of Film Capacitors

Metallized Layers

 

Failure Analysis of film capacitors usually involves corrosion to the metallized film, electrical overstress, solder stresses or 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 here.

 

Film capacitors can fail due to the following:

 

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

F/A 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..

 

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.