Bench Talk

Optimizing Capacitor Selection to Address Power Challenges in AI and Cloud Reliability

(Source: Roman Krochuk/stock.adobe.com)

Modern enterprise computing platforms are pushing the boundaries of electronic power system design. The latest artificial intelligence (AI) accelerators, memory, and storage systems present much higher-density circuits with higher current requirements, lower voltage thresholds, and faster switching speeds.

Though passive components like capacitors are often underrated in their role in circuit performance outcomes because of their perceived simplicity, poor capacitor selection can result in substantial reliability and performance issues. For instance, minimal equivalent series inductance (ESL) capacitors are instrumental in providing clean power to double data rate (DDR), peripheral component interconnect express (PCIe), or non-volatile memory express (NVMe) controllers, while capacitors with minimal drift help to avoid timing and voltage errors during heavy power system loads. With little margin for error, it is essential to avoid common pitfalls that can prove critical in capacitor selection.

To help understand these pitfalls and how capacitor selection impacts power integrity, let's explore key challenges that can disrupt performance: capacitance drift, space constraints, and limitations in ESL and ripple current handling.

Capacitance Drift and Voltage Dependency

With Class II ceramic capacitors, which are sensitive to temperature fluctuations compared to Class I ceramic capacitors, the overall capacitance exhibited by the component can vary significantly with DC bias and temperature. These sensitivities can result in unpredictable behavior for circuits that depend on the absolute value of the capacitance presented, such as filter performance and voltage regulation. For instance, capacitors with high drift can negatively impact converter response and lead to degraded ripple suppression under load. This inconsistency with performance often leads designers to overcompensate for the complexity and resilience of their designs based on Class II ceramic capacitors, for example, with parallel capacitor configurations to average out the variations. Such an approach often increases the bill-of-materials (BOM) and layout complexity while only partly compensating for the potential 40–60 percent reduction in capacitance under load that these capacitors experience. 

Space Constraints

The ever-increasing density of server circuit boards and blade systems means increasingly stricter space allocation for parts, especially on the external layers. This directly conflicts with the need to spread capacitor arrays across the external layers to provide the necessary capacitance performance. Capacitor arrays are not an ideal approach in regard to routing complexity and parasitic inductance. This design challenge often compromises thermal performance, capacitance, or space by using capacitors of mixed dielectric types. As capacitors with different dielectrics exhibit widely different thermal and aging responses, this approach can lead to inconsistent long-term capacitance behavior, increased validation times, and lower confidence in edge-case reliability.

ESL and Ripple Current Limitations

A critical role for capacitors in enterprise power stages is to absorb high ripple currents, which often reach hundreds of kilohertz frequencies. Traditional multilayer ceramic capacitors (MLCCs) tend to have limitations in ripple current handling and exhibit excessive ESL. Poor capacitance performance in these key metrics often results in degraded power integrity, especially during transient loads, such as AI inference spikes and high-speed memory access. Competitive capacitor technology for MLCCs, such as polymer or aluminum electrolytic capacitors, can deliver the necessary absolute capacitance; however, they generally perform worse than MLCCs in size, thermal range, or reliability.

KONNEKT U2J Capacitors: A Multi-Chip Solution

These challenges are not impossible to overcome. As shown in Figure 1,  YAGEO Group's KONNEKT™ U2J Capacitors provide an effective solution through their multi-chip bonding technique. This design enables efficient connection of multiple MLCCs without metal frames or external structures, resulting in significantly lower equivalent series resistance (ESR), reduced ESL, and improved thermal management. KONNEKT capacitors can be bonded using transient liquid phase sintering (TLPS) material, which is technology that enables a low-temperature reaction between a low-melting-point metal and a high-melting-point metal. This process creates a strong, stable metal matrix that efficiently bonds multiple MLCCs together. The result is the ability to efficiently connect multiple MLCCs to form a single surface mount component, representing a leadless multi-chip solution with extremely high density and enhanced power handling capability.

Figure 1: YAGEO Group's KONNEKT U2J capacitor construction, illustrating the multi-layered structure of these capacitors, highlighted by the TLPS bonding method that connects multiple MLCCs into a compact, high-density form. This design reduces ESR and ESL while optimizing power density and thermal management. (Source: YAGEO Group)

Moreover, these capacitors are fabricated with YAGEO Group’s U2J dielectric, a Class I dielectric material (CaZrO3) known for the its extremely stable behavior that enables low-loss (ESR down to 0.35mΩ) and low-inductance (ESL down to 0.4nH) capacitor fabrication capable of handling high ripple currents at frequencies of several hundred kilohertz. YAGEO Group's U2J capacitors benefit from U2J's negligible shift in capacitance with respect to voltage, minimal aging effect (<0.1 percent capacitance loss per decade hour), and predictable linear change in capacitance referenced to ambient temperature. These features lead to U2J capacitors retaining over 99 percent of the nominal capacitance at full rated voltage with a maximum capacitance change of -750 +/- 120 ppm/°C from -55°C to +125°C.

U2J capacitors are packaged in a standard 1812 case size, even with the TLPS-bonded multi-chip constructions that deliver greater power handling in the same footprint. This line of capacitors does not require any special parameters in the reflow soldering process and is commercial grade, as well as being RoHS and Pb-free. These factors—alongside KONNEKT U2J capacitors being tested to industry-standard methods for thermal shock, moisture resistance, high-temperature life, mechanical shock, and vibration—lead to a very straightforward qualification.

YAGEO Group's KONNEKT U2J capacitors address each of the key challenges presented above. The low voltage dependency and minimal capacitance drift ensure consistent performance, even under high-frequency and thermal stress, directly tackling the issue of capacitance variability. The multi-chip configuration reduces board space by consolidating multiple MLCCs into a single package, addressing space constraints while maintaining high density. Additionally, with ESR as low as 0.35mΩ and ESL down to 0.4nH, these capacitors enhance ripple current handling and power stability, making them ideal for demanding applications like AI inference and high-speed data processing.

Conclusion

The sheer density and complexity of modern cloud hardware, including AI accelerators, results in passive component requirements that far exceed typical passives. Significantly better performing, more stable, and more reliable MLCCs are needed to minimize the downtime and failure rates of the latest enterprise hardware. MLCCs with low loss, low drift, and high mechanical durability that do not sacrifice high ripple current capacity are necessary. This opportunity has paved the way for YAGEO Group's KONNEKT U2J capacitors, which deliver on these requirements with YAGEO Group's innovative TLPS technology for leadless multichip construction.

Author

Principal of Information Exchange Services: Jean-Jacques DeLisle
Jean-Jacques (JJ) DeLisle attended the Rochester Institute of Technology, where he graduated with a BS and MS degree in Electrical Engineering. While studying, JJ pursued RF/microwave research, wrote for the university magazine, and was a member of the first improvisational comedy troupe @ RIT. Before completing his degree, JJ contracted as an IC layout and automated test design engineer for Synaptics Inc. After 6 years of original research—developing and characterizing intra-coaxial antennas and wireless sensor technology—JJ left RIT with several submitted technical papers and a US patent.

Further pursuing his career, JJ moved with his wife, Aalyia, to New York City. Here, he took on work as the Technical Engineering Editor for Microwaves & RF magazine. At the magazine, JJ learned how to merge his skills and passion for RF engineering and technical writing.

In the next phase of JJ’s career, he moved on to start his company, RFEMX, seeing a significant need in the industry for technically competent writers and objective industry experts. Progressing with that aim, JJ expanded his company's scope and vision and started Information Exchange Services (IXS).