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The most complete and meticulous process flow of MLCC
- Categories:News
- Time of issue:2022-09-30 11:41
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(Summary description)
The most complete and meticulous process flow of MLCC
- Categories:News
- Time of issue:2022-09-30 11:41
- Views:
MLCC, namely multilayer ceramic capacitor, also known as chip capacitor, laminated capacitor, laminated capacitor, etc., is the most widely used capacitor. MLCC is formed by overlapping ceramic dielectric films with printed electrodes (internal electrodes) in a staggered way, sintering at high temperature to form ceramic blocks, and sealing metal layers (external electrodes) on both ends of the ceramic blocks.
The structure of MLCC mainly includes three parts: ceramic dielectric, metal inner electrode and metal outer electrode.
Ceramic dielectric: mainly oxide materials with excellent insulating properties, such as barium titanate and strontium titanate, which are the basis of electrical characteristics of capacitors.
Internal electrode: The internal electrode exists between each layer of ceramic medium and plays the role of conducting current.
The outer electrode is divided into outer electrode, barrier layer and welding layer. The external electrode is mainly a copper metal electrode or a silver metal electrode, which is connected with the internal electrode for external power input. The main component of the barrier layer is Ni coating, which acts as a thermal barrier. The welding layer is mainly Sn coating, which provides weldability.
MLCC has the advantages of small size, large capacitance, low loss rate when used at high frequency, low price and high stability, etc. It is suitable for the light, thin, short and small requirements of information functional products, so it is widely used and is an indispensable component of modern electronic products. So how was MLCC made?
- Ingredients
Ceramic powder, binder, solvent and various additives are ball-milled or sanded in a certain proportion for a certain time to form uniform and stable porcelain paste. Porcelain paste is a complex system, which generally consists of porcelain powder, solvent, dispersant, adhesive, plasticizer, defoamer, etc. Ceramic powder, as the most important material, determines the basic characteristics of MLCC. The adhesive is a polymer resin, and its function is to keep a certain distance between ceramic powders and provide strength. The solvent toluene and ethanol are mixed in a certain proportion. Dispersant is a kind of surfactant, which is used to avoid adhesion and agglomeration of ceramic powder due to electrostatic action on the surface and ensure that ceramic slurry can form a stable dispersion suspension. Additives are used to adjust the electrical characteristics of ceramic powder itself, meet some requirements of product reliability, and ensure that sintering can be carried out well.
Ceramic powder, binder, solvent and various additives are ball-milled or sanded in a certain proportion for a certain time to form uniform and stable porcelain paste. Porcelain paste is a complex system, which generally consists of porcelain powder, solvent, dispersant, adhesive, plasticizer, defoamer, etc. Ceramic powder, as the most important material, determines the basic characteristics of MLCC. The adhesive is a polymer resin, and its function is to keep a certain distance between ceramic powders and provide strength. The solvent is a mixture of toluene and ethanol in a certain proportion, which is used to avoid adhesion and agglomeration of ceramic powder due to electrostatic action on the surface and ensure that ceramic slurry can form a stable dispersion suspension. Additives are used to adjust the electrical characteristics of ceramic powder itself, meet some requirements of product reliability, and ensure that sintering can be carried out well.
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Tape casting
Porcelain paste is coated on the bypass silicone film through the pouring port of the casting machine, thus forming a uniform thin layer of porcelain paste. Then, through the hot air zone, a uniform film with a certain thickness and density is formed by heating and drying.
There are two kinds of casting extrusion methods in the molding process. On-roll mode is generally applicable to thick film, and it is the extrusion mode of slit die, so that the center of the rear roller faces the nozzle of the upper die; Off roll method is generally used for thin films, in which the nozzle of the mold is above the center line of the rear roller, and the base material is coated with slurry at the place where it is not in contact with the rear roller. This method is also called air cushion method or net stretching method.
Drying needs to adjust the linear speed, temperature and pump flow rate, which will volatilize most of the solvent in the porcelain paste, and make the film shrink and densify, thus having a certain thickness and film density.
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Printing
The internal electrode paste was printed on the ceramic membrane by screen printing, and a clear and complete dielectric membrane was obtained after drying.
There are four types of printing: 1. Letterpress printing, which is pressure printing after the protruding part is dipped in the inner electrode paste. 2. Gravure printing: after the whole board is dipped with the internal electrode paste, only the internal electrode paste is left in the concave part for printing. Flat printing, using the repulsion of water and oil, the layout is dipped in internal electrode paste for printing. 4. Screen printing: printing after discharging the internal electrode paste through the screen hole.
Compared with roll printing/gravure printer, screen printing has low equipment and tooling costs, high utilization rate of inner paste and less waste, less edge leakage of electrode pattern, and flexible screen design. Therefore, most manufacturers use a printing method similar to SMT solder paste or red glue process to print the inner electrode slurry onto the ceramic membrane through screen printing plate, and some manufacturers use a printing machine to let the ceramic membrane pass through the slurry pool, Let the metal paste adhere to the ceramic film.
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Lamination
Lamination is the fourth step in the MLCC manufacturing process. It is used to stack printed media diaphragms orderly one by one in a certain dislocation to form bars with consistent thickness. After printing, the membrane is cut and stripped during lamination, and ceramic membrane protective sheets are also required at the bottom and top during lamination to increase mechanical strength and improve insulation performance. What this process needs to control is the temperature, pressure and time of the lamination, as well as the alignment control of the dislocation position and the cleanliness of the environment, so it also needs to be completed in the clean room.
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laminate
The process of making each laminated film in the printed and laminated ceramic block closely combine with each other by hydrostatic pressure equalization at uniform temperature, so as to improve the compactness of the sintered ceramic body and make it more closely combined. The process pressure, pressure holding time and temperature are the key quality factors (CTQs), which need to be controlled. Besides, the uniformity of the pressure is very important, so the best way is to press it in water. Generally, it is necessary to confirm the uniformity and binding degree of the pressing by sampling the slices to ensure the quality.
The main process of lamination: packing the block into the sealing bag → feeding the laminator → pressurizing and heating lamination → cooling → bag removal
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Cutting
According to the design requirements of the product, the laminated bar is cut horizontally and longitudinally according to the design size with a thin-chip blade, so that it becomes a completely separated independent chip (capacitor green body). Cutting principle: When the blade cuts the bar block, the knife seat pushes the blade downward, the blade touches the face of the bar block, and the knife seat continues to push the sharp blade down to press down, when the knife edge reaches the cutting glue under the action of the knife seat and inertia When the surface of the PET substrate is touched, the knife seat is lifted up quickly to complete a cut.
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Degumming
Debinding refers to the heat treatment of the ceramic green body after cutting to remove organic substances such as binders. The air degumming temperature of nickel electrode MLCC is about 250℃. The specific temperature is related to the size specification and formula. The temperature of nitrogen degumming can be higher, about 400℃-500℃. The main process of degumming: loading the bowl and rowing → into the degumming furnace to degumming → out of the degumming furnace
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Sintering
Sintering can make the chip after debinding into a ceramic body with intact internal electrodes, good compactness, qualified size, high mechanical strength and excellent electrical properties, which can be divided into two stages: densification stage and reoxidation stage. The sintering process is carried out in an atmosphere furnace, and the general sintering temperature is between 1100°C and 1350°C. Due to the high temperature sintering, in order to prevent oxidation, etc., the sintering furnace needs to be filled with nitrogen/hydrogen. The key to sintering is that the temperature in the furnace is uniform and consistent, and that it should be carried out in a thermal dynamic equilibrium, and the air should flow sufficiently to make the crystal phase of the porcelain grow evenly and densely. The main process of sintering: placing → sintering → sintering → unloading
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Chamfer
Chamfering, also called grinding. The capacitor body after sintering into porcelain has sharp edges and corners, which is not conducive to the connection with the external electrode, so it needs to be ground and chamfered. The chamfering process is to install the capacitor, water and grinding medium in a chamfering tank, and move through ball milling, planetary grinding, etc., to remove the surface burrs of the ceramic chip, so that the chip surface is smooth and clean, and at the same time, the electrodes in the end face are fully exposed. The key points of control are speed, time, and temperature, and the focus of inspection is parameters such as appearance size, radian, and exposure rate. The main process of chamfering: canning → chamfering → cleaning → canning → drying
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End capping
Through the end capping machine, the end paste is coated on both ends of the exposed internal electrodes of the chip after the chamfering treatment, and the internal electrodes on the same side are connected to form the external electrodes. The main process of end capping: chip implantation → paste paste → drying → export
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Burning end
At a high temperature of about 750°C, nitrogen, air, and sometimes under humidification conditions, the organic binder in the terminal electrode slurry is fully burned, the glass body is melted and the copper powder is infiltrated, so that the terminal is solidified and formed well with the porcelain body and the inner electrode. Connection.
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Electroplating
It refers to the end treatment of the end-burning product, which is essentially an electroplating process, that is, in an electrolyte solution containing nickel and tin metal ions, the end electrode of the MLCC is used as a cathode, and a certain low-voltage direct current is passed through the cathode. Deposited as a layer of nickel and tin. The role of nickel: improve the thermal shock resistance of the capacitor, protect the external electrode and prevent the external electrode and Sn from forming an alloy state. The role of tin: improve the solderability of the capacitor, so that the MLCC chip can be better soldered on the PCB in the surface package.
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Test
According to the performance of capacitance, loss, insulation and withstand voltage of capacitor products, 100% testing and sorting are carried out on the products, the defective products are eliminated, and at the same time, they are sorted according to different capacity ranges. Main test items: capacity, loss, withstand voltage and insulation.
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Visual inspection
Check the appearance of capacitor products, and reject products with poor shape. Main identification items: appearance defects, abnormal size products
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Taping
Taping engineering is to tape the tested MLCC chips into a carrier tape, and roll them into a plastic disc according to a fixed number. Taping is to facilitate a large number of high-speed automatic placement production in the SMT process, and can also prevent problems such as MLCC collision and rupture caused by transportation and other processes. At the same time, in order to prevent mixing, generally on the tape machine, each piece of MLCC will be tested for capacity again.
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Packaging
Packaging is the process of attaching identification labels and packaging before transportation. The product labels taped by MLCC manufacturers generally only carry the manufacturer's own information. During the packaging process, labels and barcodes of customer information will be added to facilitate customer identification.
The main process of packaging: tray labeling - product loading into boxes and box labeling - box loading into boxes and box labeling. In the subsequent packaging process, automatic management and inspection are generally adopted. After scanning the barcode, it is automatically adjusted to avoid mixing wrong materials.
Founded in 2017, Micro Rong Technology actively develops and rapidly mass-produces key high-end MLCC series such as ultra-miniature, high-capacity, vehicle gauge, and high-frequency.
source: ab-sm.com
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