The present invention relates to the manufacture of multilayer ceramic capacitors (MLC's) and particularly to silver and palladium silver powders which are used to form the internal electrodes within the MLC's. MLC's are typically made by laminating together a number of layers of a dielectric tape onto which internal electrodes have been screen printed. The laminated block is cut or diced apart to form the individual MLC's which are then fired at high temperatures. The dielectric tape is made by making a slurry of a ceramic dielectric powder such as BaTiO.sub.3 or lead magnesium tungsten niobates and an acrylic or polyvinyl butyrol resin in a fast evaporating liquid or solvent. The slurry is cast onto glass plates, plastic sheets or metal belts and then dried to form a thin tape or film about 1.0 to 2.0 ml. thick. Internal electrode inks are made by dispersing the fine metal powders typically 1.0 to 5.0 microns average particle size, into a vehicle system of resins and solvents. This ink is screen printed onto the dielectric tape in a pattern which is determined by the final size of the capacitor that is desired. A monolithic block is then formed by stacking layers of the tape on each other according to a predetermined number based on the desired capacitance and then the stack is laminated under heat and pressure. The stack or block is then cut up into individual MLC's. The MLC's are then slowly heated over a period of generally 12 to 48 hours to a temperature of about 300.degree. to 350.degree. C. This heating cycle is referred to as a binder burnout cycle and is used to remove most of the organic components from the MLC's by slowly burning them out prior to firing. After the organics have been removed, the MLC's are fired in a kiln to a temperature which is determined by the dielectric composition and usually ranges from 1150.degree. to 1350.degree. C.
During the firing cycle, the MLC's are very weak because the organic binders have been removed and are therefore susceptible to damage by stresses such as mechanical shock, differentials in sintering rates and thermal shock, due to rapid heating. As the temperature is raised during the firing cycle, the internal electrode powders sinter and shrink about 20 percent in the 500.degree. to 850.degree. C. range. During this period, the dielectric undergoes very little change. As the temperature continues to rise, the dielectric then sinters and shrinks about 20 percent in the 850.degree. to 1100.degree. C. range. Because the two materials sinter at different temperatures or times, stress is developed in the MLC's which causes the different layers of materials to separate and result in defects which are referred to as delaminations or "delams". The delams are quite often the site for subsequent failure in the MLC. This delamination problem is minimized as much as possible by careful selection of internal electrode powders, binder systems and process controls. Unfortunately, these become very restrictive to the manufacturer because of excessive times for certain operations such as binder burn-out or very narrow processing windows for different operations involving temperatures and times.
USPTO Backgrounds
USPTO Backgrounds