Capacitors: one of three main passive component families

Capacitors are essential building blocks of electronic circuits and, together with resistors and inductors, form the three main passive component families. Electronic components are divided into active and passive devices. Active devices, also called semiconductor devices, contain a power source during operation. Passive devices contain no power source of any kind and do not consume electrical energy themselves, or convert it into another form of energy, and can operate with an input signal alone. A capacitor is a passive device that stores charge and electrical energy.

A capacitor consists of two conductive plates separated by a dielectric insulator. It stores and releases energy as static electricity. When charge moves under an electric field, the dielectric hinders further movement, so positive and negative charge accumulate on the two plates. Capacitors pass alternating current and block direct current, which makes them widely used in high and low frequency circuits and in power supplies for charge storage, voltage smoothing, coupling, decoupling, filtering, bypass and frequency division.

Classification of capacitors

Capacitors can be classified in several ways, and manufacturers generally organise production and operations by dielectric. By structure they are fixed, variable or trimmer capacitors. By polarity they are polarised or non-polarised. By application field they are military, industrial or consumer grade. By function they are bypass, tuning, coupling or filter capacitors. By dielectric they fall into four main families: ceramic, aluminium electrolytic, tantalum and film. Manufacturers typically classify by dielectric material.

What is a ceramic capacitor?

Ceramic capacitors are divided into multilayer ceramic capacitors (MLCC) and single layer ceramic capacitors (SLCC), with MLCC holding more than 90 percent of the share. An SLCC is made by printing silver layers on both faces of a ceramic substrate and firing them at low temperature to form silver film electrodes, usually in a disc shape.

MLCC uses a multilayer stacking process in which pairs of metal electrodes are embedded in a ceramic dielectric and co-fired at high temperature. MLCC is further divided into leaded and chip types. Because an SLCC has only a single layer, its electrode area and capacitance are small, but it offers good high frequency performance and high voltage withstand, making it suitable for high frequency and high voltage circuits. Mass produced MLCC typically ranges from 1 pF to 10 µF, and offers good frequency characteristics, a wide operating voltage and temperature range, small size and no polarity, giving it an advantage in both cost and performance. MLCC accounts for more than 90 percent of the ceramic capacitor market and close to 50 percent of the total capacitor market.

Classification, performance and application areas of ceramic capacitors

The ceramic capacitor supply chain

Upstream raw materials are mainly ceramic powder, electrode materials and capacitor chips. Ceramic powder and electrode materials strongly influence product performance. Ceramic powder is the main cost element of MLCC, accounting for 20 to 25 percent in low capacitance MLCC and as much as 35 to 45 percent in high capacitance MLCC.

Mainstream domestic manufacturers mostly purchase ceramic powder from suppliers in the United States and Japan. Internal and external electrodes have traditionally used silver-palladium, which is expensive and volatile in price, and the growing number of MLCC layers has greatly increased palladium consumption. Manufacturers have therefore begun replacing palladium with base metals such as nickel and copper to reduce cost. Some domestic manufacturers also use capacitor chips as a raw material. A capacitor chip is a chip type MLCC used as an input for leaded MLCC and multi-chip ceramic capacitors. According to the prospectuses of Torch Electron and Hongyuan Electronics, capacitor chips are the main direct material of their own production business, accounting for 65 to 90 percent of direct materials.

There are three main MLCC manufacturing processes: dry tape casting, wet printing and ceramic slurry film transfer.

Dry tape casting. Ceramic powder is milled with binder, plasticiser, solvent and dispersant into a highly suspended slurry. After vacuum de-airing, the slurry is cast under a blade onto a carrier tape as a continuous layer of uniform thickness. Surface tension gives the layer a smooth natural surface, and after drying it forms a leather-like flexible film. Electrodes are then printed, and the stack is laminated, punched, binder burned out and sintered to form capacitor chips.

Wet printing. Ceramic dielectric slurry is screen printed into ceramic thin films that serve as the dielectric. Metal electrodes and the upper and lower protective layers are also screen printed, in the order lower protective layer, electrode, dielectric, electrode, dielectric, upper protective layer, until the designed layer count is reached. The stack is then dried and cut to the chip dimensions required.

Ceramic slurry film transfer. A roll of adhesive film acts as carrier, and a special extrusion device spreads ceramic slurry evenly onto it, producing a continuous roll of dielectric layer with accurate thickness down to below 2 µm and enabling ultra-thin dielectrics. Capacitors are made by printing metal electrodes onto the dielectric roll and then overprinting a ceramic slurry layer.

Domestic manufacturers mostly use dry tape casting, which requires low investment and offers high efficiency for volume production, but has performance and quality limitations that make entry into high-end markets difficult. As market requirements rise and demand for high-end MLCC grows, wet printing and ceramic slurry film transfer are attracting attention for their advanced processes and are gradually becoming the development trend for MLCC manufacturing.

Ceramic capacitors are used downstream in military, industrial and consumer applications, and appear in almost every circuit. MLCC applications include aerospace and weapon systems, industrial control equipment, medical electronics, automotive electronics, precision instruments and consumer electronics. According to Qianzhan Industry Research Institute, consumer applications hold the majority of the market, with high-end and general consumer segments together accounting for 73 percent of MLCC market share.

Market size of ceramic capacitors

The global MLCC market has passed the 100 billion yuan mark and continues to grow steadily. According to statistics and forecasts from the China Electronic Components Association, the global MLCC market grew from 91.5 billion yuan in 2019 to 120.4 billion yuan in 2022, and is expected to reach 154.7 billion yuan by 2026, a compound annual growth rate of about 6.47 percent from 2022 to 2026.

Figure 4. Global MLCC market size and forecast, 2019 to 2026

China's MLCC market has expanded steadily and is now the largest in the world. According to the China Electronic Components Association, the domestic market grew from 31 billion yuan in 2017 to 53.7 billion yuan in 2022, a compound annual growth rate of 7.03 percent, accounting for about 40 percent of the global total. With the rapid growth of new energy vehicles and 5G, the domestic market was expected to reach 57.5 billion yuan in 2023.

Figure 5. China MLCC market size and forecast, 2018 to 2023

Electrification and intelligence in vehicles will also drive MLCC demand. MLCC is used mainly in powertrains, safety systems, infotainment and ADAS. According to Murata, an L0 conventional combustion vehicle uses about 3,000 MLCC per vehicle, an L2 hybrid more than 6,000, and an L3 battery electric vehicle more than 10,000. Murata expects overall automotive MLCC usage in 2024 to reach about 1.6 times the 2019 level, a compound annual growth rate of about 9.8 percent.

Automotive qualification of ceramic capacitors

AEC-Q certification is the recognised general test standard for automotive-grade components. Ceramic capacitor manufacturers that want to enter the automotive electronics field and its component supply chain must obtain AEC-Q200 among other certifications.

1. AEC-Q certification is the entry threshold for automotive electronics. AEC stands for Automotive Electronics Council. It was founded in 1994 by Chrysler, Ford and General Motors, and its membership now spans major vehicle makers, automotive electronics companies and semiconductor manufacturers worldwide. Components that comply with AEC specifications can be adopted by all three manufacturers at the same time, which encouraged part makers to exchange product characteristic data, drove standardisation of automotive parts and laid the foundation for the rapid growth of the automotive parts market. AEC-Q is the automotive reliability test standard issued by the AEC and an important passport for part makers entering automotive electronics and tier one supply chains.

2. AEC-Q200 is the entry threshold for automotive-grade passive components. AEC-Q200 is the quality and reliability validation standard issued by the AEC for passive components used in vehicles. It verifies whether passive components can withstand extreme temperature, humidity, vibration and ageing in automotive applications. The standard is intended to prevent performance drift or latent failure in passive components, ensure their quality and reliability, and keep function and performance stable and consistent over continuous use.

3. Products covered by AEC-Q200. Tantalum and niobium capacitors, supercapacitors, ceramic capacitors, aluminium electrolytic capacitors, film capacitors, electromagnetic devices such as inductors and transformers, networks (R-C, C/R), resistors, thermistors, variable capacitors and resistors, varistors, ferrite EMI suppressors and filters, quartz crystals, ceramic resonators and polymeric self-resetting fuses.

4. AEC-Q200 test flow. Revision E defines the test flow explicitly, as shown below.

For lead-free SMD components, special quality requirements apply, and AEC-Q005 defines the reliability issues that arise with lead-free processes, together with the lead-free test requirements. Materials used in lead-free processing include termination plating and board connection solder. These materials usually require higher board connection temperatures to produce acceptable solder joint quality and reliability. The revised AEC-Q200 also states that, to ensure automotive lead-free passive components do not fail after lead-free reflow, certain reliability tests must be completed after reflow before the next step can proceed. Different component sizes also require different numbers of test cycles.

5. NTEK testing capability and AEC-Q200 requirements for ceramic capacitors. AEC-Q200 qualification for ceramic capacitors comprises 17 tests. Sample quantities are defined by product size, with the new standard specifying three categories: below 10 cm³, from 10 cm³ to 330 cm³, and above 330 cm³. Larger components require fewer samples.

About NTEK

NTEK Group was founded in 2009 and is headquartered in Shenzhen. The group provides quality research and technical services covering R&D verification, inspection and testing, failure analysis, simulation and market access for intelligent connected vehicles, electronic communications and new energy.

NTEK has extensive experience in automotive-grade electronic certification and has helped more than 100 companies pass AEC-Q series certification. Driven by the need of vehicle makers to localise automotive-grade components and supported by the domestic semiconductor industry, NTEK provides comprehensive testing and certification services, applying AEC-Q automotive standards to control the safety and quality of automotive components, supporting the growth of domestic automotive-grade components and adding new momentum to the intelligent vehicle safety system.