Difficult process of PCB board prototype ceramic substrate
There are many types of manufacturing techniques for ceramic products in circuit board manufacturing plants. It is said that there are more than 30 manufacturing methods, such as dry pressing, grouting, extrusion, injection, casting and isostatic pressing, etc., due to electronics. The ceramic substrate is of the "flat" type (square or wafer type), the shape is not complicated, and the manufacturing process using dry molding and processing is simple and the cost is low. Therefore, the dry pressing method is mostly used. There are three main contents in the manufacturing process of dry-pressed flat-panel PCB electronic ceramics, namely blank forming, blank sintering and finishing, and forming circuits on the substrate.
1. Ceramic substrate green parts manufacturing (forming)
Use high-purity alumina (content of ≥95% Al2O3) powder (requires different particle sizes depending on the application and manufacturing method, such as from illiterate to tens of micrometers) and additives (mainly adhesives, dispersants, etc.) Forming a "slurry" or processing material.
(1) A green substrate is dry pressed to produce a green piece (or "green body").
Dry-pressed blanks are high-purity alumina (used for electronic ceramics with an alumina content greater than 92%, mostly 99%) powder (for dry pressing, the particle size must not exceed 60 μm, and for extrusion) The powder particle size of casting, casting, injection, etc. should be controlled within 1 μm.) Add appropriate amount of plasticizer and binder, mix and evenly dry the blank, and the current generation of the square or wafer can reach 0.50mm, or even ≤ 0.3 mm (depending on the size of the board).
The dry pressed blank can be processed before sintering, such as the outer dimensions and drilling, but attention should be paid to the compensation of dimensional shrinkage caused by sintering (magnification shrinkage size).
(2) Ceramic substrate casting method for manufacturing green parts.
Flow glue (alumina powder + solvent + dispersant + binder + plasticizer, etc.) + cast (uniformly spread the glue on metal or heat-resistant polyester on the casting machine) With) + dry + trim (can also be processed by holes) + degreasing + sintering and other processes. It can be automated and scaled for production.
2. Sintering of green parts and finishing after sintering. The green parts of the ceramic substrate often need to be "sintered" and sintered for finishing.
(1) Sintering of ceramic substrate green parts.
"Sintering" of a ceramic green body means that voids, air, impurities, and organic substances in a green body (volume) such as dry pressure are removed by volatilization, combustion, extrusion, etc. by a "sintering" process, and alumina particles are removed. The process of achieving close contact or knot (bonding) is long, so that after the ceramic green body is sintered (boiled blank), weight loss, dimensional shrinkage, shape deformation, compressive strength improvement, and porosity reduction are caused. The sintering method of the ceramic green body is as follows:
1 atmospheric pressure sintering method, sintering without pressure, will bring greater deformation, etc.;
2 pressurization (hot pressing) sintering method, sintering under pressure, can obtain a good planar product, which is the most widely used method;
3 hot isostatic pressing sintering method, using high pressure and high heat gas for sintering method, the product of which is characterized by the same temperature and pressure to complete the product, various properties are balanced, high cost, added value This type of sintering method is used in products, or in aerospace and defense military products, such as mirrors, nuclear fuels, and barrels in military fields.
The sintering temperature of dry pressed alumina green parts is mostly between 1200 ° C and 1600 ° C (related to composition and flux).
(2) Finishing of the (cooked) blank after sintering of the ceramic substrate.
Most sintered ceramic blanks require finishing, and their purposes are:
1 obtain a flat surface, in the high-temperature sintering process, due to the imbalance of particle distribution, voids, impurities, organic matter, etc. in the green body, it will cause deformation and high (low) unevenness or excessive roughness and difference Etc., these defects can be solved by surface finishing;
2 Get a high finish surface, reflect like a mirror, or improve lubrication (wear resistance).
The surface polishing treatment uses a polishing material (such as SiC, B4C) or a diamond paste to grind the surface from coarse to fine abrasive. In general, it is mostly achieved by using AlO powder or diamond paste of ≤1 μm or by laser or ultrasonic treatment.
(3) Strong (steel) treatment.
The surface after surface polishing treatment can be coated with a silicon compound film by electron beam vacuum coating, sputtering vacuum coating, chemical vapor deposition, etc., in order to improve mechanical strength (such as bending strength), and after 1200 ° C ~ Heat treatment at 1600 °C can significantly improve the mechanical strength of ceramic blanks!
3. Conductive patterns (lines) are formed on the substrate
To form a conductive pattern (line) on a ceramic substrate, a copper-clad ceramic substrate is first fabricated, and then a ceramic printed board is fabricated according to the printed circuit board process technology.
(1) Forming a copper clad ceramic substrate. There are currently two methods for forming a copper clad ceramic substrate.
1 lamination method. A copper foil having an oxidation side and an alumina ceramic substrate are formed by hot pressing. That is, the surface of the ceramic is treated (such as laser, plasma, etc.) to obtain an activated or roughened surface, and then laminated together according to "copper foil + heat resistant adhesive layer + ceramic + heat resistant adhesive layer + copper foil". The double-sided copper-clad ceramic laminate is formed by sintering at 1020 ° C to 1060 ° C.
2 plating method. After the ceramic substrate is subjected to plasma treatment or the like, a "sputtered titanium film + sputtered nickel film + sputtered copper film is performed, and then conventional copper plating is performed to a desired copper thickness, that is, a double-sided copper clad ceramic substrate is formed.
(2) Manufacture of single and double-sided ceramic PCB boards. Single and double-sided copper-clad ceramic substrates are used in accordance with conventional PCB manufacturing techniques.
(3) Manufacture of ceramic multilayer boards.
1 Repeatedly coating an insulating layer (alumina) on a single or double-sided board, sintering, wiring, and sintering to form a PCB multilayer board, or by using a tape casting technique.
2 casting method to manufacture ceramic multilayer boards. A green ply is formed by forming a green tape on a casting machine, followed by drilling, plugging (conductive paste, etc.), printing (conductive wiring, etc.), cutting, lamination, and isostatic pressing. Figure 1 shows a completed multilayer ceramic chip capacitor.
Note: Casting method - flow glue (alumina powder + solvent + dispersant + binder + plasticizer, etc.) + cast (uniform the glue on the casting machine) Apply to metal or heat-resistant polyester tape) + dry + trimming + degreasing + sintering.
In short, ceramic printed boards belong to the category of PCBs and are the result of the derivation and extension of the development and progress of PCB factories. In the future, one of the important types of PCBs may be formed. Since ceramic printed boards have the best thermal insulating dielectric, high melting point and thermal dimensional stability, ceramic PCBs will have broad prospects in high temperature and high thermal conductivity applications!