Solid Tantalum Capacitors: MnO2 vs. Polymer Cathodes for Optimal Performance in High-Reliability Military and Space Applications

Solid Tantalum Capacitors: MnO2 vs. Polymer Cathodes for Optimal Performance in High-Reliability Military and Space Applications
Written By: Ron Demcko

Abstract:
Solid tantalum capacitors have a long history of proven performance in high-reliability military and space applications. But not all capacitors are created equal — even within the same class. As is the case with virtually all component technologies, materials matter. This paper will discuss the differences in performance and reliability between solid tantalum capacitors with manganese dioxide (MnO2) cathodes and those with conductive polymer cathodes.

Bell Laboratories introduced the first solid tantalum capacitors to market in the early 1950s. The first military specification for surface-mount tantalum capacitors (MIL-PRF-55365) was released in 1989 and introduced CWR09-style components. Since then, the product offerings governed by this specification have expanded to include CWR19-style capacitors with an extended range of CV values and CWR29-style capacitors, which offer low ESR limits for all of the ratings in the CWR09 and CWR19 product categories.

In the late 1990s, AVX began offering COTS-Plus families of tantalum capacitor products with extended CV (Capacitance x Voltage) values and low equivalent series resistance (ESR). These commercial- or professional-grade components could then be up-screened (i.e., tested and reliability graded per military test methods and requirements) for use in high-reliability military and aerospace applications, often with lower costs and shorter lead-times than true milspec components. Then, in the early 2000s, AVX launched its first space-level tantalum product line, the SRC9000 Series, which includes both military QPL and COTS-Plus products and offers several advantageous features, such as 100% X-ray screening, statistical screening, DPA sampling, and functional/life testing on each batch. By 2008, the SRC9000 Series had become the basis for the introduction of the T-level space solutions introduced into the MIL-PRF-55365 specification, which — just like all of the other specifications that regulate the use of tantalum capacitors in high-reliability military and aerospace applications (e.g., MIL-PRF-39003, MILPRF-39006, MIL-PRF-49137) — is based on tantalum capacitors with MnO2 cathode technology.1

Tantalum capacitors with current-conducting polymer cathodes, rather than MnO2 cathodes, have been around since the 1990s and offer a number of performance advantages over MnO2 variants. However, although polymer cathode tantalum capacitors are included in some DSCC drawings, there are no military specifications for these products, as the advantages they offer come with serious trade-offs in terms of reduced long-term reliability, the introduction of wearout mechanisms, and variability in parametric performance under environmental stress.

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