Barium Titanate based MLCC is very important device in electronic components. To enable high capacitance in small devices, dielectrics/insulator is constructed in multi-layer formation with each layer of 1 μm thickness.
For the materials of this dielectric layer, barium titanate or its relative compound, suited to characteristics required in capacitor, are used. These materials are not naturally available therefore they are synthesized from various raw materials.
Fine grinding of raw materials of dielectric
To synthesize the dielectric for the MLCC, barium titanate, barium carbonate and various materials for doping are mixed and reacted under solid state at very high temperature (calcinations). To accelerate this reaction, these materials should be closely contacted each other and should be fine enough to avoid non-reacted part in the internal port.
Production process of fine BTO in dry process by use of our grinding machines has been established for a few decades. Depending on the raw material size, the type of grinding machines should be selected, such as the Mikro Pulverizer, the ACM Pulverizer, the Super Micron Mill and the Innomizer.
Super fine grinding after synthesizing of the dielectrics material
Grinding of secondary particles
Capacitance of the dielectric layer can be increased with the thinner layer. Recently the layer thickness has come to the range of sub-microns. In order to realize sub-micron layer, it is required to make the dielectric particles size smaller. The primary size of the dielectric particles obtained through the calcination is 100nm. However, during the calcination, particles are sintered and agglomerated to the secondary particle size becomes larger than 1μm. Because of this, it is required to disintegrate the dielectric particles down to the primary particle size. Here, wet ball mills are used in general. Since micro beads cannot disintegrate micron disagglomerates, it is necessary grind it to the size suitable for feeding to the wet ball mills.
The Innomizer or the ACM pulverizer, which have many references in disintegration of various calcined ceramics, conducts preliminary grinding. The particles of barium titanate are highly abrasive and there is high risk of metal contamination in the MLCC products. Therefore, it is required to design the grinding machines to avoid any metal contamination as low as possible. The Innomizer with internals of tungsten carbide or the ACM-HC with ceramics parts for internal powder contact part can be applied for this purpose.
Drying after synthesizing of the dielectrics
The Nano-submicron sized dielectric particles obtained through the wet milling have to be dried before molding to MLCC. In this process wet raw material with a few dozen percent W.B. moisture should be dried low to less 1%W.B. The conventional drying process has problems of high-energy consumption and agglomeration. A flash dryer, the Drymeister suited for drying of wet cake material at very high heat exchange efficiency, and a media-agitating dryer the Xerbis are applicable for solving these problems. The Xerbis has the same construction as the media agitating mill Pulvis which has advantages of very low adhesion on the internal part. For any dryers, it is required to avoid metal contamination. Especially the Xerbis has such references with the ceramic construction part on powder contact part.