What does hermeticity mean, how is it defined and tested, and what is the difference between hermetic and quasi-hermetic packaging?
New capacitor types are entering the market on a regular basis, to the point that there are now supercapacitors, electric double-layer capacitors (EDLC) and ultracapacitors. To cover their demand for electricity, electric vehicles, high power applications, renewable energy and aerospace applications will all draw on this electric storage technology.
Aluminum electrolyte capacitors are efficient yet have a weakness, as over the lifetime of their applications they are prone to electrolyte dry-out, which is often experienced as a result of imperfect terminal seals. Small amounts of moisture can penetrate an imperfect seal, which can cause gases to build up inside the capacitor over time. This causes continuous deterioration in performance levels. The slow and continuous evaporation of electrolytes can lead to a capacity loss of up to 20 %, which is significant in terms of efficiency.
Polymer seals are often used to seal capacitor terminals, which as a result have become one of the main perpetrators where loss of electrolytes through evaporation is concerned. Polymers, as with all organic materials, are prone to become brittle over time and will therefore lose their gas tightness, and it is this aging process that it the enemy of aluminum electrolyte capacitors. The solution lies in the capacitor lids. “By replacing seals made from organic compounds with a specialty glass seal, capacitor terminals can be hermetically sealed into the aluminum lids,” explains Dr. Frank Kroll, development engineer for the product division Automotive at SCHOTT. “This protects the capacitor from moisture intrusion via the pin sealing and eliminates the issue of electrolyte dry-out.”
Leak-tight, glass-sealed lids can be customized to suit a wide range of applications. Glass-to-aluminum sealing is a new technology specifically developed for capacitors and batteries with high energy density. Moving to glass-to-aluminum seals has wide-ranging peripheral benefits. They can provide high temperature resistance ranging from – 40 °C to +150 °C. The leak-tight nature of the seals also means that smaller or the same size units with higher capacitance can be designed. It not only allows for the extension of shelf life of a product, but also increases the life of the product itself. Dr. Kroll concludes: “Every day, we see the continuing growth of next-generation power applications that rely on capacitors. Technology comes at a perfect time to support even more reliable, long-lasting electrical storage performance in sectors shaping the future of our day-to-day lives.”