Did you know that ceramic chips can be made with two different material technologies? Not everyone has heard about the difference between PME and BME.
Ceramic capacitors made with Precious Metal Electrodes, or PME, use a silver-palladium (AgPg) alloy for their electrode plate. Typically this alloy has less than 25% silver, to reduce silver migration effects.
When fired, high temperatures could cause the silver to migrate, reducing insulation resistance, leading to a failure. The barium titanate dielectric material is doped with small amounts of lead (Pb) to reduce the temperature required to bake the barium titanate.
PME-based ceramic capacitors are not RoHS-compliant.
KEMET’s commercial or automotive grade ceramics are not PME based. Instead, we use a different technology or electrode system.
Today, all of KEMET’s commercial and automotive grade ceramics use a Base Metal Electrode (BME) system. The dielectric is either barium titanate (X5R/X7R) or calcium zirconate (C0G).
BME electrode plates use either copper or nickel, with nickel being the most common–by far. Copper-based electrodes allow our CBR-series of RF capacitors to achieve High-Q (Ultralow ESR) in a BME ceramic.
Reliability between PME and BME
Being a newer technology (as in, two decades old), sometimes there are questions about the reliability of BME parts. When first developed, BME systems produced flaws in the dielectric layers due to a phenomenon known as “Oxygen Vacancies.”
Since 2000, KEMET has developed and uses a process for baking BME parts that use a reduced oxygen atmosphere and a re-oxidation process. These combined steps reduce oxygen vacancies in BME parts.
Additional testing by KEMET has shown that BME C0G may be more reliable than PME parts, as demonstrated in this CARTS paper.
How to tell difference between BME and PME
It may not be possible to identify BME versus PME, by looking at a capacitor with the naked eye.
However, Nickel is a ferromagnetic material, so you could use a magnetic to see if parts stick to it!
Look at the Datasheet!
The best place to look is the data sheet. KEMET’s data sheets will typically call out the electrode system in the Feature section. If not, they include construction diagrams that call out the materials used.