The breakthrough in base metal electrode (BME) technology has made nickel powder the mainstream material for internal electrodes, replacing precious metals such as palladium or silver-palladium alloys. BME-MLCCs now account for more than 90% of global MLCC output. Today, with the further spread of 5G communications, new energy vehicles, and AI computing equipment, MLCCs are accelerating toward miniaturization and higher capacitance. As a key foundational material, the technical requirements for nickel powder used in internal electrodes are also undergoing profound changes.
Key Requirements for Nano Nickel Powder for Miniature High-Capacitance MLCCs
The essence of MLCC miniaturization and higher capacitance is ultra-thin dielectrics, refined electrodes, and scaled-up layer stacking. To eliminate dielectric breakdown and electrode short circuits caused by coarse particles, while ensuring the uniformity of electrode printed coatings, the thickness of the nickel internal electrode layer must precisely match that of the ultra-thin dielectric. Therefore, the most critical requirement for nickel powder application is the trend toward ultra-fine particle size. According to industry information, for every 10 nm reduction in nano nickel powder particle size, the MLCC dielectric layer thickness can be reduced by 5–8 nm accordingly.
Traditional mid- to low-end MLCCs generally have dielectric layer thicknesses above 1 μm and layer counts within 200. Process redundancy for electrode thickness is high, and tolerance for nickel powder performance is relatively high. Conventional nickel powder with a particle size of 200–300 nm is sufficient to meet mass production requirements. However, with the iterative upgrading of high-end MLCCs, 100 nm nickel powder has become the mainstream choice for high-capacitance MLCCs and can stably adapt to large-scale mass production processes for 0.5 μm-thick electrode layers. Some high-end applications even require nickel powder particle size to be reduced to 80 nm to meet the process requirements of dielectric layers 0.35–0.5 μm thick. At the same time, the particle size distribution must be extremely narrow, with D90 controlled within 2 times D50.
On the basis of extremely fine particle size and narrow distribution, the stringent co-firing and reliability conditions of miniaturized MLCCs are also driving a comprehensive upgrade in the overall quality of nickel powder:
(1) Higher sphericity: To adapt to dense forming of thin electrode layers and high-temperature co-firing, nickel powder needs excellent sphericity. Regular spherical particles can ensure slurry flowability and uniform packing, avoiding voids and thickness deviations in the electrode layer.
(2) Good monodispersity: To ensure uniform coating of the electrode slurry and uniform dispersion of nickel powder in the slurry. However, the finer the nickel powder, the higher its surface energy and the more prominent the agglomeration problem, which often needs to be solved through surface modification technologies.
(3) Higher crystallinity: The powder structure can stably regulate the sintering shrinkage rate and thermal expansion characteristics, achieving perfect matching with the ceramic dielectric and avoiding structural defects such as interlayer cracking and delamination.
(4) Higher purity: High-purity nickel powder with low oxygen and low impurities can effectively inhibit oxidation/precipitation and resistance drift under high-temperature conditions, greatly improving the long-term service stability and weather resistance reliability of high-end miniature MLCCs.
Which Preparation Methods Can Produce Nano Nickel Powder for MLCCs?
Based on the above stringent requirements, traditional liquid-phase and solid-phase methods such as chemical reduction and spray pyrolysis can no longer fully meet the production requirements for nano-scale, ultra-fine, highly uniform nickel powder for high-end miniature MLCCs. Therefore, gas-phase preparation technologies represented by CVD and PVD, with the advantage of precisely controllable particle formation, have become core technical routes for preparing nano nickel powder for high-end MLCCs.
01 Carbonyl Nickel Decomposition Method
The essence of carbonyl nickel powder is the use of the selectivity of a gas-solid reversible reaction. At relatively low temperature and a certain pressure, metallic nickel in the solid phase reacts with CO to form volatile nickel tetracarbonyl (Ni(CO)₄), while impurities remain in the solid phase. The nickel tetracarbonyl is then thermally decomposed at higher temperature and lower pressure to regenerate solid pure nickel particles and carbon monoxide gas, finally yielding ultra-fine spherical nickel powder.
The greatest advantages of this process are extremely high purity, excellent sphericity, and high sintering activity. The particle size can be precisely controlled within 1–20 μm, with a narrow and uniform particle size distribution, making it perfectly suitable for the mass production requirements of high-layer-count, high-capacitance MLCCs with ultra-thin dielectrics below 1 μm. However, its core shortcomings are the difficulty of process safety and environmental control. Nickel tetracarbonyl is a highly toxic and hazardous medium, placing extremely high requirements on production containment, explosion-proof equipment, tail gas treatment, and safety operation and maintenance systems, and it has gradually been phased out.
02 CVD Chemical Vapor Deposition Method
CVD chemical vapor deposition is a high-end nickel powder preparation technology monopolized by Japanese companies. Its core principle is that precursor gases such as nickel chloride are reduced to elemental nickel atoms in a high-temperature gas-phase environment and then uniformly nucleate, grow, and condense into ultra-fine nano nickel powder.
The core advantages of this process are a uniform reaction environment, controllable nucleation, high purity, no agglomeration, and excellent co-firing compatibility. It is currently the core supporting powder for internationally high-end ultra-thin dielectric, ultra-high-layer-count MLCCs. However, its core equipment and process technology are monopolized overseas, with extremely high equipment investment costs, high mass-production process thresholds, and high production costs.
03 PVD Physical Vapor Condensation Method
PVD nickel powder is a key breakthrough direction for domestic substitution. This process abandons chemical reactions. Instead, in a vacuum or under an inert gas (such as argon) protective environment, solid metallic nickel is vaporized by high-temperature heating (such as resistance heating, plasma heating, arc discharge, laser heating, etc.) to form nickel atom vapor. The gas atoms then collide with one another and lose energy, achieving rapid nucleation, and finally rapidly condense in a low-temperature region into nano- to submicron-sized nickel powder particles.
Principle of Preparing Nano Nickel Powder by PVD
The nano nickel powder produced by this method has high purity, good crystallinity, a smooth surface, and strong oxidation resistance. It can fully meet the requirements for nickel powder used in MLCC internal electrodes, and the production process is environmentally friendly. However, due to complex production equipment and low efficiency, controlling stability in large-scale mass production and optimizing costs remain urgent problems to be solved.