1. Green body manufacturing (forming)
Uses high-purity alumina (Al2O3 content ≥95%) powder (different particle sizes are required depending on the application and manufacturing method. For example, from a few illiterates to tens of microns) and additives (mainly binders, dispersants, etc. ) Form "slurry" or processed material.(1) Manufacture of green parts (or "green") by dry pressing.
Dry-pressed blanks are powders of high-purity alumina (alumina content for electronic ceramics greater than 92%, most of which are 99%) (the particle size for dry pressing must not exceed 60 μm, and is used for extrusion) (The particle size of the powder, casting, injection, etc. should be controlled within 1 μm) Add the appropriate amount of plasticizer and binder, and mix evenly to dry the compact. At present, the descendants of its squares or discs can reach 0.50mm, even ≤ 0.3 mm (relative to board size).
The blanks after dry pressing can be processed before sintering, such as the dimensions and drilling, but attention should be paid to the compensation of dimensional shrinkage caused by sintering (enlargement of shrinkage size).
(2) Casting to produce green parts.
Glue solution (alumina powder + solvent + dispersant + binder + plasticizer, etc. + uniformly sieved) manufacturing + casting (the glue solution is evenly coated on metal or heat-resistant polyester on the casting machine) Bring) + drying + trimming (also can process holes) + degreasing + sintering and other processes. Production can be automated and scaled.
2. Sintering of green parts and finishing after sintering. Green substrates of ceramic substrates often need to be "sintered" and finished after sintering.
(1) Sintering of the green body.The "sintering" of ceramic green bodies refers to the removal of voids, air, impurities, and organic matter in the green body (volume) such as dry pressing by volatilization, combustion, and extrusion through the "sintering" process, and the removal of alumina particles. The process of achieving close contact or the formation of knots (bonds) between them results in changes in weight loss, dimensional shrinkage, shape deformation, increased compressive strength, and reduced porosity of the ceramic green body after sintering (cooked body). The sintering methods of ceramic green body are: ① Atmospheric pressure sintering method, sintering without pressure, which will bring large deformation, etc .; ② Pressing (hot pressing) sintering method, sintering under pressure, can get good This is the most commonly used method at present; ③ hot isostatic sintering method, using high pressure and high heat gas for sintering method, the characteristics of the product as a whole is the product at the same temperature and pressure to complete, various Various properties are balanced and the cost is high. This sintering method is mostly used on value-added products, or in aerospace, defense and military products, such as military mirrors, nuclear fuel, gun barrels and other products.
The sintering temperature of dry-pressed alumina green parts is mostly between 1200 ℃ ~ 1600 ℃ (related to composition and flux).
(2) Finishing of sintered (cooked) blanks.
Most of the sintered ceramic blanks need to be machined. The purpose is: ① to obtain a flat surface. During the high temperature sintering of the green part, due to the uneven distribution of particles, voids, impurities, organic matter, etc. in the green part, so It can cause deformation, unevenness (concave and convexity) or excessive roughness and difference. These defects can be solved by surface finishing; ② to obtain a high-quality surface, reflecting like a mirror surface, or to improve lubrication (wear resistance).
The surface polishing process uses polishing materials (such as SiC, B4C) or diamond paste to grind the surface gradually from coarse to fine abrasives. Generally, AlO powder or diamond paste ≤1 μm or laser or ultrasonic wave is used to achieve it.
(3) Strong (steel) treatment.
After the surface is polished, in order to improve the mechanical strength (such as bending strength), a silicon compound film can be plated by electron beam vacuum coating, sputtering vacuum coating, chemical vapor deposition, etc., and subjected to 1200 ° C ~ Heat treatment at 1600 ℃ can obviously improve the mechanical strength of ceramic blanks!
3. Formation of conductive patterns (circuits) on the substrate
To form a conductive pattern (circuit) on a ceramic substrate, first, a copper-clad ceramic substrate is manufactured, and then a ceramic printed board is manufactured according to the printed circuit board technology.(1) A copper-clad ceramic substrate is formed. There are currently two methods for forming a copper-clad ceramic substrate.
① Lamination method. A one-sided oxidized copper foil and alumina ceramic substrate are formed by hot pressing. That is, the ceramic surface is treated (such as laser, plasma, etc.) to obtain an activated or roughened surface, and then laminated and combined according to "copper foil + heat-resistant adhesive layer + ceramic + heat-resistant adhesive layer + copper foil", Sintered at 1020 ℃ ~ 1060 ℃ to form double-sided copper-clad ceramic laminate.
②Plating method. After the ceramic substrate is treated with plasma or the like, "sputtered titanium film + sputtered nickel film + sputtered copper film is performed, and then conventional copper plating is performed to the required copper thickness to form a double-sided copper-clad ceramic substrate.
(2) Manufacturing of single and double-sided ceramic PCB boards. Single and double-sided copper-clad ceramic substrates are used in accordance with conventional PCB manufacturing process technology.
(3) Manufacturing of ceramic multilayer boards.
① Repeatedly apply insulating layer (alumina), sintering, wiring, and sintering on single and double-sided boards to form multilayer boards, or use casting manufacturing technology to complete.
② Cast ceramic multilayer board. Forming a green tape on a casting machine, and then drilling, plugging (conductive glue, etc.), printing (conductive wires, etc.), cutting, laminating, and isostatic sintering, ceramic multilayer boards can be formed.
Note: Casting method—flow glue (alumina powder + solvent + dispersant + binder + plasticizer, etc. mixed + sieved) manufacturing + casting (the glue is uniformly distributed on the casting machine) Coating on metal or heat-resistant polyester tape) + drying + trimming + degreasing + sintering and other processes.
In short, the ceramic substrate belongs to the PCB category, and it is also the result of the development and progress of PCB factories. It may form one of the important types in the PCB field in the future. Since the ceramic printed board has the advantages of the best thermally conductive insulating medium, high melting point and thermal dimensional stability, ceramic PCBs will have broad development prospects in the application of high temperature and high thermal conductivity!
