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Method for four-probe conductivity for finding the optimum partial pressure of oxygen during controlled-atmosphere sintering of metal oxides

IP.com Disclosure Number: IPCOM000010249D
Publication Date: 2002-Nov-13
Document File: 3 page(s) / 46K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a method for four-probe conductivity for finding the optimum partial pressure of oxygen during controlled-atmosphere sintering of metal oxides. Benefits include improved functionality and improved reliability.

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Method for four-probe conductivity for finding the optimum partial pressure of oxygen during controlled-atmosphere sintering of metal oxides

Disclosed is a method for four-probe conductivity for finding the optimum partial pressure of oxygen during controlled-atmosphere sintering of metal oxides. Benefits include improved functionality and improved reliability.

Background

        � � � � � Before the technology enabling nickel electrodes to be used in multilayer ceramic capacitors (MLCCs) was developed, expensive platinum or silver/palladium electrodes were used. The high cost of noble metal electrodes prevented the MLCCs from widespread usage. Because of the introduction of cheap nickel electrodes (MLCCs with nickel electrodes), the market has been expanding to meet the demand for decoupling capacitors. As a result, manufacturing a large volume of MLCCs with a high yield rate is becoming more important. One of the key manufacturing steps of MLCCs is the cosintering operation. Ceramic powder and nickel powder are heat-treated at temperatures in excess of 1000°C in a furnace that contains a reducing atmosphere (a mixture of CO and CO2 gases or a mixture of H2 and H2O gases). This step requires that the partial oxygen pressure be kept within a narrow range to assure that the nickel electrodes do not react to form insulating nickel oxide. The ceramic dielectric (such as doped barium titanate) must not convert to a leaky conducting state (n-type) by losing oxygen.

        � � � � � The actual values of partial pressure of oxygen and furnace temperature fluctuate during the sintering process. The effect on the nickel electrodes and the barium titanate dielectric is not known until the sintering is complete and the MLCC is ready to be tested. Electrical testing of finished MLCCs at room temperature only helps to screen out the leaky capacitors. The harmful effects of any random fluctuation of furnace temperature and oxygen partial pressure cannot be corrected by room temperature electrical measurements of finished capacitors. A system is required for detecting and correcting the problem in the furnace.

General description

        � � � � � The disclosed method is a monitor for the in-place four-probe DC conductivity in test capacitors as they are being sintered in a reaction chamber. The information provides feedback to the computer that monitors the sintering process so it can adjust the temperature and partial pressure of oxygen in the furnace. This method directly increases the yield of the MLCC manufacturing line by reducing or eliminating leaky capacitors.

Advantages

        � � � � � The disclosed method provides adv...