There are many types of manufacturing technology for ceramic products in circuit board factory. It is said that there are more than 30 manufacturing methods, such as dry pressing, grouting, extrusion, injection, casting and isostatic pressure. Because the electronic ceramic substrate is of “flat plate” type (block or round sheet) and its shape is not complex, the manufacturing process of dry forming and processing is simple and low cost, so it is large Dry pressing is used in many ways. The manufacturing process of dry pressing plate type electronic ceramics mainly includes three parts: blank forming, blank sintering and finishing and forming circuit on the substrate.
1. manufacturing (forming) of raw blanks
High purity alumina (Al2O3 with content ≥ 95%) is used (different particle sizes are required depending on the application and manufacturing method). For example, from several illiterate to tens of microns, and additives (mainly adhesive, dispersant, etc.) form “slurry” or processing material.
(1) Dry pressing method is used to make the blank (or “green”).
Dry pressing blank is to control the high purity alumina (the alumina content used for electronic ceramics is more than 92%, and most of them are 99%) (the particle size used for dry pressing shall not exceed 60 μ m, while the size of powder particles used for extrusion, casting, injection, etc. shall be controlled at 1 Add appropriate plasticizer and adhesive within μ m, mix evenly and dry press the blank. At present, the offspring of the square or disc can reach 0.50mm, or even ≤ 0.3 mm (related to the size of the plate).
The blank after dry pressing can be processed before sintering, such as the external dimension and drilling, but the compensation of size shrinkage caused by sintering (enlarge shrinkage size) should be paid attention.
(2) Casting method is used to make blank.
The process of flow glue solution (mixed uniformly + sieved) with flow glue solution (alumina powder + solvent + dispersant + binder + plasticizer) manufacturing + Flow Drawing (evenly spreading the glue solution on the metal or heat-resistant polyester belt on the calender) + drying + finishing (also processing holes etc.) + degreasing + sintering, etc. It can be produced automatically and in scale.
2. sintering and finishing of raw blank. The raw parts of ceramic substrate often need to be “sintered” and then finished.
(1) Sintering of raw blank.
Sintering of ceramic billets refers to the process of evaporation, combustion and extrusion of cavities, air, impurities and organic matter in the raw billet (volume) of dry pressing, etc. through the sintering process, and the alumina particles reach close contact or bond synthesis. Therefore, after sintering, the ceramic billets will lose weight, shrink size and shape change The shape, compressive strength and porosity decrease. The sintering methods of ceramic raw materials include: ① sintering under normal pressure, sintering without pressure will bring great deformation; ② pressing (hot pressing) sintering method and sintering under pressure can get good planar products, which is the most commonly used method at present; ③ hot isostatic pressing sintering method, sintering method with high pressure and high heat gas, and the product with its characteristics The whole product is completed at the same temperature and pressure. All kinds of performance are balanced and the cost is high. This sintering method is often used in the added value products, or aerospace and defense military products, such as mirrors, nuclear fuel, barrel and other products in the military field.
The sintering temperature of the dry pressed alumina billet is mostly between 1200 ℃ and 1600 ℃ (related to composition and flux).
(2) Finish machining of sintered (cooked) blank.
Most sintered ceramic blanks need to be refined. The purpose is to obtain a flat surface. During the high temperature sintering process, the defects can be solved by surface finishing; ② high-level surface can be obtained; 2) high surface can be obtained; 2 The surface of finish, reflecting like a mirror, or improving lubrication (wear resistance).
Surface polishing is to use polishing materials (such as SiC, B4C) or diamond paste, and grind the surface from coarse to fine abrasive step by step. Generally speaking, most of them are made by using alo powder or diamond paste with a value of ≤ 1 μ m, or by laser or ultrasonic treatment.
(3) Strong (steel) treatment.
After surface polishing, in order to improve mechanical strength (such as bending strength, etc.), a layer of silicon compound film can be coated by vacuum plating, sputtering vacuum coating, chemical vapor evaporation plating, etc. and the mechanical strength of ceramic blank can be obviously improved by heat treatment at 1200 ℃ ~ 1600 ℃!
3. the conductive figure (line) is formed on the substrate
To form a conductive pattern (circuit) on the ceramic substrate, first, we must manufacture the copper clad ceramic substrate, and then we can make the ceramic printed board according to the PCB technology.
(1) The ceramic substrate with copper foil is formed. There are two methods to form copper clad ceramic substrate.
① Laminating method. The copper foil with one side oxidation and alumina ceramic substrate are formed by hot pressing. That is, the ceramic surface is treated (such as laser, plasma, etc.) to obtain the activated or coarsened surface, and then the ceramic laminate with double-sided copper foil is formed by laminating the “copper foil + heat-resistant adhesive layer + ceramic + heat-resistant adhesive layer + copper foil” and sintering at 1020 ℃ ~ 1060 ℃.
② Plating method. After plasma treatment, the ceramic substrate was treated with “sputter titanium film + sputter nickel film + sputter copper film”. Then, the conventional copper plating was carried out to the required copper thickness, which means that the double-sided copper clad ceramic substrate was formed.
(2) Manufacture of single and double-sided ceramic PCB board. The single and double-sided copper clad ceramic substrate is used according to the conventional PCB manufacturing technology.
(3) Manufacture of ceramic multi-layer plate.
① The multilayer board is formed by repeatedly coating the insulating layer (alumina), sintering, wiring and sintering on the single and double-sided board, or by the casting manufacturing technology.
② The ceramic multilayer plate is manufactured by casting method. The ceramic multilayer plate can be formed by forming the blank belt on the calender, then drilling, plugging (conductive adhesive, etc.), printing (conducting circuit, etc.), cutting, laminating and isostatic pressing sintering. Figure 1 shows the completed multilayer ceramic sheet capacitor.
Note: flow forming method – flow glue (alumina powder + solvent + dispersant + binder + plasticizer, etc.) manufacturing + Flow Drawing (evenly coating the glue solution on the metal or heat-resistant polyester belt on the calender) + drying + finishing + degreasing + sintering, etc.
In a word, ceramic printed boards belong to PCB category, and also the result of derivation and extension of PCB Factory Development and progress. In the future, it may form one of the important types of PCB field. Because of the advantages of the best thermal insulation medium, high melting point and thermal dimension stability, ceramic PCB will have a broad development prospect in the field of high temperature and high heat conduction!