Dielectric Breakdown Property

The term electrical breakdown ean apply to the failure of an electric circuit. Alternatively, it may refer to a rapid reduction in the resistance of an electrical insulator that can lead to a spark jumping around or through the insulator. 

If the dielectric material is fluid or gas, the electrical field in it can fully recover its insulating properties through the plasma channel interactions. Ceramic processed insulator is mixed with polymer or synthetic polymer to vary its dielectric property. 

The theoretical dielectric strength is an intrinsic property of the bulk material and depends on the material composition and also on the configuration of the electrodes with which the field is applied. For a given configm-ation of dielectric material and electrodes, the minimum electric field that produces breakdown is the breakdown voltage in this particular set up the maximum electric stress to the material is just before breakdown. 

Material Thermal conductivity Coefficient of thermal expansion (ppm/°C) 

The electrical breakdown of an insulator due to excessive voltage can occur in 

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Equipment is now available to produce the thin tapes (less than 3 pm). There is also equipment available to screen-print and laminate these very thin tapes. Multilayered capacitors with 5-pm layers that are 300 layers thick are currently being manufactured. Maher states that there is a practical limitation where the dielectric constant of the material itself reaches its peak value as a function of the sintered grain size. If the grain size is in the range of 0.8 to 1.1 pm then there is a limitation on the minimum tape thickness at about 4 to 5 pm in order to maintain the dielectric breakdown properties of the chip capacitor. Maher also contends that a minimum of about 5 grains in series is desirable for reliability. It is generally believed that the 3-pm limitation on tape thickness will be the norm in the future. 

Electrical. Glasses are used in the electrical and electronic industries as insulators, lamp envelopes, cathode ray tubes, and encapsulators and protectors for microcircuit components, etc. Besides their abiUty to seal to metals and other glasses and to hold a vacuum and resist chemical attack, their electrical properties can be tailored to meet a wide range of needs. Generally, a glass has a high electrical resistivity, a high resistance to dielectric breakdown, and a low power factor and dielectric loss. 

These lead-based materials (PZT, PLZT, PMN) form a class of ceramics with either important dielectric, relaxor, pie2oelectric, or electrooptic properties, and are thus used for appHcations ia actuator and sensor devices. Resistive properties of these materials ia film form mirror the conduction processes ia the bulk material. Common problems associated with their use are low dielectric breakdown, iacreased aging, and electrode iajection, decreasiag the resistivity and degrading the properties. 

Some important dielectric behavior properties are dielectric loss, loss factor, dielectric constant, direct current (DC) conductivity, alternating current (AC) conductivity, and electric breakdown strength. The term dielectric behavior usually refers to the variation of these properties as a function of frequency, composition, voltage, pressure, and temperature. 

Polymeric materials usually have low dielectric breakdown voltages. Fortunately, the electrical insulation property of PDMS is sufficient (R > 1015 O/cm) [159]. Moreover, the use of a lower electric field ( 1100 V/cm) helps alleviate this... 

Banford et al. studied the radiation effects on electrical properties of low-density polyethylene (LDPE) at 5 K with the use of a 60Co gamma source and a thermal nuclear reactor [86]. They reported that both the electrical conductivity and the dielectric breakdown strength of LDPE at 5 K were not significantly affected by radiation absorbed doses up to 10s Gy, but an erratic pulse activity under high applied fields was observed in the sample irradiated at 106 Gy. 

The second group consists of properties that are important at very high electric field strengths, such as electric discharge, dielectric breakdown and arc resistance. They may be regarded as the ultimate electrical properties. Properties of the first group are directly related to the chemical structure of the polymer those of the second are greatly complicated by additional influences in the methods of determination. 

Fig. 2.70. (a) The field between the plates is notmal and the water dielectric is chemically stable. Its property as an insulator depends on the concentration of ions but it is highly resistive, (b) When the field applied is sufficiently high, dielectric breakdown occurs the liquid no longer supports the field and the charges flow away, forming streamers. ... 

When plasma polymers of hydrophilic monomers were deposited or the surface of LDPE grafted with hydrophilic poly(acrylic acid), the dielectric breakdown occurred in a very short time. These observations indicate that hydrophilic sites act as the gate for salt intrusion. Since the bulk properties of LDPE are believed to be unchanged with these surface modifications, the quick failure can be interpreted as the consequence of an interfacial phenomenon. The population of the potential salt intrusion sites is a very important factor that ultimately determines the breakdown of the insulation occurring in the presence of salt and electrical stress. 

Recently, Sen and Kar-Gupta (1994) and Kar-Gupta and Sen (1995) proposed a new percolation model to mimic the properties of nonlinear composites. However, it can also be interpreted as a special model for the dielectric breakdown problem. 

The electrical properties of interest for ceramics include conductivity, resistivity, dielectric breakdown strength, dielectric constant, loss factor, and electromechanical coupling. Most ceramics do not have high electrical conductivity, and thus ceramics have found application as electrical insulators for many years. The electrical insulating capability of some ceramics is also retained under high electric field this is referred to as high dielectric breakdown strength... 

The third problem associated with water based varnishes is poor electrical insulation properties of the laminate after moisture conditioning. This problem is probably the most critical problem because insulation failures of the laminate can lead to electrical failure of the finished printed circuit board. This property is measured by conditioning the finished laminate in a high moisture environment and then testing the dielectric breakdown strength. ED24574 has excellent insulation resistance. This was achieved by a proprietary resin composition. 

Figure IV gives the general properties of the new water based resin ED24574. The key properties to note are the electric properties. Specifically, the dielectric breakdown voltage is a safe margin above the minimum requirements. The remainder of the electrical properties are also well above the requirements.

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