Film capacitors are widely used because of their superior characteristics. This capacitor type is not polarized, which makes them suitable for AC signal and power use. Film capacitors can be made with very high precision capacitance values, and they retain that value longer than other capacitor types. This means that the aging process is generally slower than in other capacitor types, such as the electrolytic capacitor. Film capacitors have a long shelf and service life, and are very reliable, with a very low average failure rate. They have low ESR (Equivalent Series Resistance), low self-inductance (ESL), and as a result very low dissipation factors. They can be made to withstand voltages in the kilovolt range and can provide very high surge current pulses. A special class of film capacitors, which is called power film capacitors is available, and this class of film capacitors can withstand reactive power in excess of 200 volt-amperes. These capacitors may have special screw-type terminals which can withstand high currents. Screw-type terminals replace soldered joints because power film capacitors sometimes need to be changed in the field. Unfortunately, their superior electrical properties and stability come at a price. Film capacitors are bulkier than their electrolytic equivalents, which means that limited SMT (Surface Mount Technology) packages are available. They can also burst into flames if overloaded, but this characteristic is somewhat common among different capacitor types. Read more
Failure analysis of film capacitors is important to find the root cause, however, just as important and even more so is construction analysis. Gideon Analytical Labs made a comparison between two decoupling 63V film capacitors which evaluate the materials, the termination, the potting encapsulation, the terminal, the seal integrity, the PET film, the metallization coverage, and the electrical performance of Vishay and Wima vendors. We have inserted some pictures from that analysis to demonstrate the difference.
Gideon Analytical Labs can compare most any equivalent parts. This comes in especially handy in determining counterfeit parts.