- Posted by doEEEt Media Group
- On June 25, 2019
SOLID ALUMINUM ELECTROLYTICS (SAL) with MANGANESE DIOXIDE (obsolete capacitor technology)
The SAL is aluminum electrolytic capacitors with anodic oxidized aluminum oxide as dielectric and with the semiconducting solid manganese dioxide as an electrolyte. They are made of etched and formed aluminum anodes, which are folded for the dipped pearl types or wound into a roll for the axial style. The solid manganese dioxide electrolyte is formed onto this roll in a pyrolytic process, similar to that for solid tantalum capacitors.
SAL-capacitors were developed and introduced in the market in the 1960s by Philips. Up until December 30, 2015, it was a single source product manufactured by Vishay.
As of December 31, 2015, the SAL is end-of-life and have ceased production. Nevertheless, we still list the technology features here for comparison and overview.
The electrolyte is a solid one. Thus, life is independent of drying effects and leakage currents and theoretically unlimited. Storage has no impairing effect on the dielectric. The stability is much better than that of wet types. The capacitance tolerance is ±20%. The price is high.… Compared to solid tantalums the price for solid aluminum (Al) electrolytics of the same CV product is between two and three times higher. The solid electrolyte doesn’t penetrate the pores of the highly etched aluminum foil equally well as a wet one. Its conductivity, however, is between one and two orders of magnitude larger than that of the wet electrolyte and its temperature dependence smaller.
Thus, the solid Al electrolytic is relatively insensitive to the pore effect that in wet Al electrolytics creates a deep network of series and parallel resistances as was shown in Figure C3-13. The capacitor can’t stand any breakdowns. This requires large margins between the forming and rated voltages. The forming rate usually is 2 to 3 times and the rated voltage maximum of 40 V DC. Unlike solid tantalums, the capacitor is relatively insensitive to pulse loads which, among other things, depends on its higher ESR that reduces the need for an additional circuit impedance.
Principle cross section of a SAL capacitor with solid manganese oxide electrolyte, graphite/silver cathode connection, 1: Anode, 2: Al2O3, 8: MnO2, 9: graphite, 10: silver; source: Vishay
Nevertheless, just as in solid tantalums, very high pulse currents can initiate a fire. There were two construction styles on the market, the epoxy encapsulated radial types for maximum 175 °C and the axial aluminum can type designed for maximum 200 °C. The radial lead design has a stacked aluminum plate construction which renders a very low ESL (equivalent series inductance). It ranged from 9 to 20 nH. The cylindrical can has a winding of anode and cathode foils plus glass fiber spacers. The reliability of the cylindrical can types is high. Of these, there are designs with epoxy fillings intended for extreme acceleration and shock stress.
Capacitance versus temperature
Both the radial and axial lead types are represented in Figure 1.
ESR versus temperature
In comparison with wet aluminum electrolytics, ESR of the solid ones has a less pronounced temperature dependence as shown in Figure 2.
ESR versus frequency Typical normalized diagrams are shown in Figure 3 and 39. The former concerns the radial lead designs with their lower ESL and higher operating frequency range.
Note the lower frequency range of the following axial lead design. The steeper slope of the diagrams in the lower part of the frequency range depends on the oxide losses (Figure 4).
The ESR characteristics are poorer than those of solid tantalums, especially at cooler temperatures. In other words, the impedance curve levels off and touches the ESR bottom at lower frequencies in solid Al electrolytics of comparable sizes.
Leakage current versus temperature
The permissible reverse voltage is stated to be:
- @ ≤ 85°C max 0.3 x VR .
- @ 85 → 125°C from max 0.3xVR → max 0.15xVR .
Epoxy-dipped types with radial leads are sensitive to mechanical forces applied on the leads at mounting. Inappropriate handling results in an increase in the leakage current.
EPCI licensed content by:
 EPCI European Passive Components Institute experts original articles
 CLR Passive Components Handbook by P-O.Fagerholt*
*used under EPCI copyright from CTI Corporation, USA
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