Silicon nitride has very obvious reliability as a substrate material. The AMB ceramic liner made of silicon nitride ceramic substrates is closer to the thermal expansion coefficient of the third-generation semiconductor substrate SiC crystal material, and the match is more stable. Silicon nitride ceramic substrates with high thermal conductivity and high mechanical properties are gradually becoming the preferred substrate material for wide bandgap semiconductor devices.
The overall production process of silicon nitride ceramic substrates includes mixing, ball milling, degassing, tape casting, stamping, powder coating (powder spraying), debinding, sintering, powder removal and cleaning, edge grinding, sweeping, grinding, ultrasonic cleaning, drying, laser cutting, quality inspection, and other processes. Let’s take a look at the road to forming a silicon nitride substrate.
1. Mixing, ball milling, degassing
Mix silicon nitride powder, yttrium oxide powder, and other powders with organic additives, and the materials after mixing are transported to the ball milling process.
The ball milling process includes primary ball milling and secondary ball milling:
The purpose of primary ball milling is to mix solid raw materials with liquid materials. The particle size of the ball milling product is large but can forma slurry.
The slurry after primary ball milling is transported to the secondary ball mill through a closed belt conveyor. At the same time, PVB resin (binder, to ensure the bonding of ceramic particles after the slurry is dried), polyethylene glycol, and diethyl phthalate (plasticizer, to make the substrate flexible and convenient for subsequent cutting) are added to the secondary ball mill in proportion. The secondary ball mill further mixes and grinds the slurry.
The ball-milled slurry is transported to the degassing machine through a closed belt conveyor to remove bubbles in it by physical methods, so as to obtain a tape-casting slurry with a certain colloidal viscosity suitable for tape-casting.
Required equipment: mixing grinder, ball mill, degassing machine
2. Tape-casting
The tape-casting process includes tape-casting and drying processes. Connect the degassing tank to the feed pipe of the tape casting machine, pressurize the slurry into the tape casting machine through nitrogen, spread it into a uniform film on the film belt, and transport it to the drying tunnel through the conveyor belt. The hot air generated by electric heating dries the slurry. The heating temperature is about 150~180℃. During the drying process, some organic matter with low boiling points evaporates and is removed from the slurry to obtain a dry substrate.
Required equipment: tape casting machine
3. Punching and cutting
Punch and cut the tape-cast blank to form a silicon nitride green sheet.
Required equipment: punching machine
4. Powder coating/powder spraying
A layer of boron nitride powder is applied to the surface of the blank by a powder sprayer. Boron nitride powder acts as an isolation tile to ensure that the tiles will not stick to each other during the sintering process.
Required equipment: powder sprayer
5. Debinding
The powder-coated green body is sent to the debinding furnace, which is used to debond the green body at 500~700℃ so that the organic additives are volatilized and decomposed during the debonding process and removed from the green body.
Required equipment: degreasing furnace/debinding furnace
6. Sintering
Sintering is a process of obtaining a block product with a certain strength by heating the powder material at a high temperature to produce physical and chemical processes such as particle bonding and recrystallization. The ceramic green body after debonding is placed in an atmosphere-pressure sintering furnace, and nitrogen is used for protection during the sintering process.
Required equipment: sintering furnace
7. Powder removal and cleaning
The boron nitride layer on the surface of the sintered substrate is removed by polishing and ultrasonic cleaning (cleaning with pure water). Or the sintered ceramic substrate is brushed and then dried. There will be a small amount of powder on the surface of the ceramic substrate after brushing and drying, and a sandblasting machine is required for secondary cleaning.
Required equipment: grinder, dryer, sandblasting machine, ultrasonic cleaning machine,
8. Edge grinding, polishing, grinding
Through edge grinding, polishing, grinding, and other processes, the side and surface of the substrate are smoother and the product precision is improved.
The curved surface polishing machine first rinses the polishing liquid on the surface of the substrate. After the polishing liquid moistens the surface of the substrate, the surface of the substrate is polished with a brush disk. Curved surface polishing can improve the parallelism of the upper and lower surfaces of the substrate. When the substrate is further processed later, the inductance and capacitance of the substrate can be more strictly controlled to improve the parallelism of the circuit.
Required equipment: curved surface polishing machine, edge grinding machine, polishing machine
9. Cleaning and drying
Use ultrasonic cleaning to remove the grinding liquid on the surface of the ceramic tile, and the cleaned ceramic substrate is dried by a spin dryer.
Required equipment: ultrasonic cleaning, spin dryer
10. Laser cutting
The finished ceramic substrate is cut into corresponding sizes by a laser cutting machine.
Required equipment: laser cutting machine
11. Quality inspection and warehousing
Inspect the appearance and internal structure integrity of the product through visual inspection and equipment inspection, and sort the ceramic tiles that meet the quality requirements in the warehouse.
Required equipment: testing equipment
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