March 20, 2019

    Multi-layer ceramic capacitors (MLCCs) are the workhorses of the electronics industry. They’re used in many different types of products, including cars, smartphones, computers, Wi-Fi equipment, and Internet of Things devices. Demand for MLCCs is increasing rapidly, due largely to growing use by the smartphone and automotive industries. This is creating global shortages of MLCCs, making it more difficult for Wi-Fi equipment manufacturers to obtain adequate supplies and resulting in longer lead times and higher pricing. Though MLCC suppliers are adding more production capacity, analysts predict that shortages will continue through 2020 and beyond. Wi-Fi equipment makers are therefore unlikely to see much relief in the near future. During this MLCC shortage, engineers would benefit from exploring new design strategies to mitigate possible supply constraints and production issues. One strategy emerging in the Wi-Fi equipment industry is the move toward integration in the RF front-end (RFFE).

    Factors Driving MLCC Shortages

    Several factors are contributing to the shortages in MLCCs. One is simply that demand has outstripped the available manufacturing capacity. But in addition, manufacturers are experiencing difficulties in maintaining high yields, so the number of MLCCs produced is constantly in flux and typically lower than required. Furthermore, only companies with deep knowledge in ceramic- and metal- stacking processes can make MLCCs profitably, due to the manufacturing complexity and expertise required (Figure 1). It is difficult or impossible for manufacturers of other capacitor technologies to switch to making MLCCs profitably. Thus, barriers to entry in MLCC manufacturing are very high and the number of suppliers is limited. Finally, due to the parts shortage, MLCC manufacturers are focusing on more-profitable businesses at the expense of lower-margin products, especially those that use precious metals during the manufacturing process; this makes it more challenging to obtain those less-profitable products.

    Figure 1. Multi-layer ceramic capacitor (MLCC)

    Multi-Layer Ceramic Capacitor (MLCC)

    Design Strategies to Help You Survive MLCC Shortages

    When designing Wi-Fi equipment, two main approaches can be used in combination within the RFFE to mitigate the problems caused by MLCC shortages. One approach is to use integrated modules instead of discrete components; the other is to substitute easier-to-find components such as alternative dielectrics or higher-tolerance MLCCs.

    Several levels of integration are possible, as shown in Figure 2. The greater the level of integration, the fewer MLCCs are needed. The optimal approach is therefore to use highly integrated front-end modules (iFEMs) as these enable the greatest reduction in the number of MLCCs. iFEMS also provide other advantages: they can offer higher performance than discrete components, use less current, and require less PCB space, and they simplify the overall bill of materials.

    Figure 2. Differing integration levels in Wi-Fi front-end design

    Differing integration levels in Wi-Fi front-end design

    It may also be possible to use higher-tolerance MLCCs in some cases (e.g. products with a 10% tolerance as opposed to 1%). Higher-tolerance MLCCs are often more readily available than lower-tolerance components.

    The other strategy is to balance board designs by substituting some alternative dielectric components such as polymer tantalum, polymer aluminum and SMD film chip capacitors. Though it’s clear that an engineer’s first choice is always an MLCC capacitor due to its technical advantages, it may be necessary to use alternative capacitors to meet product release timescales. Whichever option is chosen, it’s important to consider whether there may be supply-chain constraints when your design moves into production mode.

    Below are some of the key parameters to consider when deciding which type of capacitor to use.

    • Capacitance. MLCCs are greatly affected by the DC bias effect: increases in the applied voltage cause fluctuations in capacitance. Most alternative capacitor solutions, such as polymers or SMDs, are less affected by DC bias swings. These alternatives may therefore be a good option as long as their other parameters are not an issue.
    • Voltage. Knowing the maximum operating voltage of your application is critical. All capacitor technologies have voltage limits. You need to understand how a specific capacitor will resist the maximum applied voltage and any possible transient overvoltage within your application.
    • Equivalent Series Resistance (ESR). ESR is an important consideration when selecting capacitors. It is dependent on frequency and temperature, and it changes as the component ages. MLCCs have very low ESR, and they therefore degrade at a much slower pace than other capacitors. Thus, it is important to consider factors such as operating temperature and the length of time that the product will remain in service. ESR is also important in applications with low duty-cycles and high-frequency current pulses, which makes it a critical parameter in Wi-Fi applications.
    • Frequency. MLCCs are used in RFFE design to control frequency response; functions include impedance tuning and DC blocking. MLCCs have very good frequency response characteristics due to their stacked construction.
    • Case size and height. MLCCs are very small, while alternatives are somewhat larger. If your design is under height or size constraints an MLCC is a good choice. Alternatives such as polymer tantalum, polymer aluminum or SMD film chips may suffice if the size or height don’t present problems.

    Summary

    Engineers have several capacitor technologies to choose from when designing Wi-Fi front ends. MLCC capacitors are by far the most widely used due to their low ESR, small size, durability and cost. However, today these MLCC capacitors can be difficult to obtain — and the supply shortages are likely to continue well into the future. Depending on the application’s design parameters, it may be possible to reduce the impact of MLCC shortages by using integrated RFFE modules and by substituting MLCC alternatives such as polymer tantalum, polymer aluminum and SMD film chip capacitors. Careful analysis of their characteristics and limitations, as well as potential supply-chain constraints, is key to success.


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