The power density of modern power electronics is rising steadily, particularly in the areas of electromobility and decentralized energy supply. At the same time, higher demands are being placed on reliability, vibration resistance, thermal management and integration into ever more compact assemblies. The choice of suitable passive components, especially aluminum electrolytic capacitors, is crucial here.
Cylindrical standard designs are increasingly reaching their limits in terms of high requirements for packing density and thermal management, as they do not make optimal use of the available installation space, offer limited mechanical integration and can only be cooled efficiently to a certain extent. Rectangular aluminum electrolytic capacitors with liquid electrolyte provide an alternative solution. Following the installation recommendations significantly enhances thermal performance, packing density and mechanical robustness.
Modular stackable, vibration resistant and now also SMD compatible
This is where the rectangular AAR capacitors in low-profile aluminum packages with liquid electrolyte come into play. Their geometry allows for particularly efficient use of space. Compared to conventional cylindrical snap-in capacitors, the footprint of a capacitor bank system can be reduced by up to 35 percent. Their compact design makes them particularly attractive for applications with limited installation space, such as on-board chargers, inverters or wall charging stations (Fig. 1).
AAR capacitors can be combined into stackable modules, arranged either horizontally or vertically. They feature a mechanically robust design. The AAR70 series can withstand sinusoidal vibrations of up to 40 g and the AAR80 series up to 20 g – in both cases, this is based on what is known as SIN vibration. This is a standardized test with a sinusoidal vibration profile across a defined frequency range, as specified, for example, in the AEC-Q200 qualification for automotive components. Achieving this vibration resistance requires rigid mounting of the component on the printed circuit board or package, ideally using a thermally conductive adhesive. This is the only way to reliably obtain high mechanical resilience in the application. Without sufficient reinforcement of the connection, wire connections are prone to fatigue fractures.
The AAR8S series (Fig. 2) is the first ever available SMD-compatible version of these capacitors. It was developed for fully automatic assembly and is particularly suited to high-volume applications, such as those typically found in the automotive industry and electromobility. The AAR8S series offers high capacity, strong ripple current capability and a compact, low-profile form factor. The latter is particularly advantageous for applications with limited installation height. The series is rated for operating temperatures up to 105°C. Its package geometry facilitates thermal coupling to a heat sink, enhancing heat management and thus significantly boosting the component’s lifespan and reliability. The AAR series is AEC-Q200 qualified and therefore also suitable for use in automotive environments.
Table 1: Differences and strengths of AAR capacitors.
| Characteristic | AAR8S | AAR70 | AAR7V | AAR80 |
| Type of mounting | SMD | THT | THT | THT |
| Manufacturing | Can be fully automated | Can be partially automated | Can be partially automated | Can be partially automated |
| Installation height | Very low | Standard | Standard | Standard |
| Heat sink connection | Easily possible | Possible | Possible | Possible |
| AEC-Q200 qualification | Yes | Yes | Yes | Yes |
| Vibration resistance | Up to 20 g (SIN) | Up to 40 g (SIN) | Up to 40 g (SIN) | Up to 20 g (SIN) |
| Temperature range | -40 to 105 °C | -40 to 85 °C | -40 to 85 °C | -40 to 105 °C |
| Voltages | 450 V | 400 to 450 V | 500 V | 450 V |
| Special characteristics | SMD compatible, low profile, optimized for higher temperatures | Highest vibration resistance, modular stackable | High voltage up to 500VDC, modular stackable | Optimized for higher temperatures, modular stackable |
Mechanically secure and thermally optimized mounting
AAR capacitors can be mounted flexibly – horizontally or vertically, with or without heat sinks. Thermal coupling of the package to a metal chassis significantly increases the ripple current carrying capacity. Thermally conductive adhesive or paste also contributes to better heat dissipation (see Fig. 3 and Fig. 4).
Rigid mounting is crucial for vibration resistance: An insufficiently secured printed circuit board can vibrate like a membrane and generate resonance peaks that amplify accelerations by up to tenfold. Relative movement of the capacitor on the printed circuit board can lead to fatigue fractures at the wire connections. Therefore, the mounting points on the printed circuit board should be placed close together, and the capacitor should be rigidly connected to the printed circuit board or chassis.
Mounting instructions:
- Fix the capacitor rigidly to the printed circuit board or chassis
- Use thermal adhesive or paste for efficient cooling
- Do not cover the safety valve and rubber seal on the positive terminal with adhesive
- Do not point the safety valve downward (except for vertical PCBs)
- Do not use halogenated hydrocarbons (e.g., chlorinated solvents) for cleaning to avoid damage to the capacitors
- Custom solutions: Insulation and other mounting options are available upon request.
Summary
The AAR series offers an advanced solution for high-performance and compact capacitor applications. Its special form enables modular designs with high vibration resistance, improved heat dissipation and optimized space utilization. The introduction of the SMD-compatible AAR8S series allows for fully automated production, marking a significant advance toward modern power electronics.