Detailed explanation of the production process of surface mount capacitors (MLCC)
Surface mount capacitors (MLCC) are essential basic components in modern electronic devices, and their production is a highly precise, automated and complex process, which mainly includes the following core steps:
Material preparation:
Ceramic powder synthesis: This is the core starting point. The ceramic powder with high purity, specific particle size distribution and dielectric properties is prepared from a specific proportion of oxide raw materials (such as barium titanate or other high dielectric materials) by solid state reaction or chemical synthesis (such as sol-gel method, hydrothermal method).
Slurry preparation: Ceramic powder is mixed with organic binders, solvents, plasticizers, dispersants, etc. according to precise formulas, and thoroughly ground and dispersed in a ball mill to form a uniform and stable ceramic slurry (used for casting) and internal electrode slurry (usually nickel or copper slurry, used for printing electrodes) with suitable rheological properties.
Green body forming:
Casting molding: The ceramic slurry is uniformly coated onto a moving carrier substrate (such as polyester film) through the Doctor Blade of a precision casting machine. The thickness of the slurry is precisely controlled (usually ranging from a few micrometers to tens of micrometers), and then the solvent is evaporated in the drying zone to form a thin and flexible, dry ceramic green film.
Internal electrode printing: Using high-precision screen printing or gravure printing technology, the internal electrode paste (nickel paste or copper paste) is printed on a dry ceramic green film according to the designed pattern. The pattern is usually a rectangular array, corresponding to the internal electrodes of future capacitors.
Stacking and laminating: Accurately align and stack multiple green films with printed inner electrodes. When stacking, the positions of the inner electrodes of adjacent film layers are staggered (i.e. one layer of electrodes extends to the left and the next layer extends to the right), forming a staggered structure. After stacking to the required number of layers in the design (ranging from tens to thousands of layers), the layers are laminated under heating and pressure to tightly bond the green films of each layer, forming a whole multi-layer green block.
Cutting:
Cut the laminated multi-layer green blocks into independent micro rectangular units containing internal electrodes and ceramic media according to the design dimensions (such as standard dimensions or customized dimensions such as 0402, 0603, 0805, etc.) using a precision cutting machine or laser cutting machine. These units are green chips of individual capacitors.
Glue dispensing:
Put the cut green monomer into the glue discharge furnace. Under a strictly controlled oxygen atmosphere and a slow heating curve (usually within the range of 200 ° C-500 ° C), organic binders, plasticizers, etc. in the green body are gradually heated, decomposed, oxidized, and evaporated. This step is crucial to completely remove organic matter and prevent the formation of bubbles, deformation, or carbon residue during subsequent high-temperature sintering, which can lead to product defects.
Sintering:
The green monomer after rubber extrusion enters the high-temperature sintering furnace (usually using a tunnel kiln). Under reducing or neutral atmosphere (such as nitrogen hydrogen mixture) and precisely controlled temperature curve (peak temperature usually above 1100 ° C-1300 ° C, depending on the material), ceramic particles undergo densification sintering, grain growth, and form a hard and dense ceramic medium. At the same time, the internal electrode metal (nickel/copper) particles are also sintered and melted, forming a continuous conductive network. The sintering process determines the final mechanical strength, dielectric properties, and reliability of capacitors.
End electrode formation:
Coating end paste: Apply end electrode paste mainly composed of silver or copper powder, glass powder, and organic carrier on both ends of the sintered ceramic chip. The terminal electrode needs to cover the chip end face and partially extend to the side, ensuring good contact with all intersecting inner electrode layers.
End electrode firing: The chip coated with end paste is sent back to a low-temperature sintering furnace (usually at 700 ° C-900 ° C) to sinter the metal particles in the end electrode paste and form a strong ohmic contact with the ceramic body and inner electrode. The glass phase plays a role in sealing and enhancing adhesion.
Electroplating:
Nickel plating: Electroplating a layer of nickel on the surface of the fired end electrode (silver or copper). The nickel layer mainly serves as a barrier layer, preventing tin in the solder from diffusing into the end electrode during welding, while providing a good weldability foundation.
Tin plating (or tin alloy): Electroplating a layer of tin or tin lead/tin copper alloy on the surface of a nickel layer. This layer of tin plating provides excellent solderability, oxidation resistance, and appearance protection, ensuring that capacitors can be reliably soldered to circuit boards through reflow soldering or wave soldering processes.
Testing and Sorting:
Electrical performance testing: Use automated testing equipment to conduct 100% testing on each capacitor. The key parameters include capacitance value (C), loss tangent value (Df/DF), insulation resistance (IR), and withstand voltage (Rated Voltage/Withstand Voltage).
Appearance inspection: Check for appearance defects such as cracks, broken edges, and poor end electrodes through machine vision or manual sampling.
Sorting/Strip: Based on the test results (such as the accuracy level of the capacitance value) and size specifications, qualified capacitors are automatically sorted into different bins (grades). Then, according to the customer's requirements, the capacitor is loaded into the tape and reel for automatic retrieval by the SMT surface mount machine. Defective products are removed.
Packaging and Shipping:
Put the pre woven reel into a moisture-proof and anti-static packaging bag, and put in a desiccant. After sealing, label (including model, specifications, quantity, production batch number, environmental protection label, etc.), and then pack and ship to the customer.
Summary of Key Features
Materials science is at the core: the formulation of ceramic powders and slurries is the decisive basis for performance (dielectric constant, temperature characteristics, losses, etc.).
Precision manufacturing process: from controlling the thickness of the casting, printing accuracy, layer alignment to cutting size, all require extremely high precision (micrometer level).
The key to high-temperature technology is the temperature curve control of rubber extrusion and sintering, which is crucial for product yield and final performance.
Highly automated: From printing, lamination, cutting, testing to tape production, most processes rely on high-precision automation equipment to ensure efficiency and consistency.
Multilayer trend: In order to achieve larger capacity in a smaller volume, there is a constant pursuit of thinner dielectric layers, more layers of stacking, and finer electrodes.
This process reflects the precision and complexity of modern electronic component manufacturing, and strict control of each link is the foundation for ensuring high performance and reliability of surface mount capacitors.