Shur-Fen Liu

Embedded capacitors technology in 2.4 GHz power amplifier with multi-layer printed wiring board (PWB) process

In addition to the technology of system on a chip (SOC), the board level, system in a package (SIP) technology, will be another trend concordant with SOC technology to meet the requirements of future high frequency products. Therefore, the Embedded Passives technology becomes an important subject for both SOC and SIP technology to implement and extend their application field. For SIP technology, the integral substrate technology is a solution to realize embedded passives. The integral substrate technology is a noble design and manufacturing methodology which uses special materials to achieve specific circuit functions, and combines fine processes such as high density interconnection (HDI) technology. In this paper, a newly achieved high dielectric constant (Hi-DK) material, which is suitable for the Multi-Layer Printed Wiring Board (PWB) lamination process, is used to implement embedded capacitors. The electrical parameters such as dielectric constant and loss tangent versus frequency of the Hi-DK material were extracted from circuit characteristics. Many different types and sizes of embedded capacitors were designed and had been fitted by some circuit equivalent models; then we constructed a library of these elements. Furthermore, we verified these embedded capacitors by a 2.4 GHz power amplifier on a 6-layer, built-up process PWB, for wireless LAN application. The performance of the power amplifier designed by embedded capacitors was as good as the one designed by surface mount capacitors.

Reliability and failure analysis of capacitive substrate

In this study, the high dielectric constant of the polymer/ceramic composites is used to fabricate capacitive substrates. The reliability and failure analysis of the capacitive substrate under temperature and voltage stress have been studied. The mean time to failure (MTTF) of the capacitive substrate shows a voltage exponent value dependence on applied voltage with a constant of ≃3.3 as the measurement temperature at 175 °C. The lifetime also indicates a temperature dependence of the MTTF with an activation energy of 1.2 eV in the temperature range of 125°C to 175°C under dc bias of 300 VDC. The failed samples exhibited a rapid increase leakage current indicating avalanche breakdown. Moreover, it is also shown that the failed samples have a decrease in the insulation resistance and capacitance value and an increase in dissipation factor, equivalent series resistance, reactance and impedance value.

Electrical and aging characterization of organic capacitive substrate

In this study, the high dielectric constant material of the polymer/ceramic composited material was used to fabricate capacitive substrate. The I-V curve of capacitive substrate has been measured under different temperature. It was found that the leakage current was increased for these samples when temperature and applied voltage were increased. In AC electric field measurement, It was found that dielectric properties almost did not change when AC electric field was less than (threshold field) 2.5V/μm at testing frequency of 1 K, 10 K, 100 K and 1 MHz, respectively. Moreover, aging properties of the capacitive substrate were measured under the testing condition of DC 50V/85 °C /85%RH for 500 hrs. It was exhibited that the capacitance, dissipation factor, equivalent series resistance and leakage current of the capacitive substrates were increased, but the impedance and reactance were decreased. Furthermore, the experiment results indicate that the aging in dissipation factor was attributed to an increase in the equivalent series resistance value and a decrease in reactance value of the capacitive substrate.

Temperature effects on electrical characterization of high dielectric constant substrates

In this study, the polymer/ceramic composites with high dielectric constant (HK=20 substrate) were prepared to investigate the temperature effects on electrical properties. The material properties of HK substrate were compared with those of FR4 substrate and MLCC-NPO capacitor device. Curie temperature of the HK substrate could be obtained from the curves of current densities varied with temperatures. The dielectric strength of the HK substrate was higher than 200kV/cm in the temperature range between 25°C and 125°C. The dielectric constants (DK) were slightly decreased but the dielectric losses were increased as the temperature higher than 100°C. Moreover, an effective value near 0.74 eV of the trap depth and barrier height was predicted by Frenkel-poole and Schottky-controlled process. Furthermore, Electrical properties of HK substrate after thermal treatments were also measured in this study. It was found that the variations of capacitance (ΔC/C) and dielectric loss (ΔDF/DF) of HK substrate were about <±3% and <±20% respectively, after thermal cycle of 85°C for 1000 hrs. The temperature coefficient of capacitance (TCC) of HK substrate near −300ppm/°C was also obtained as measuring temperatures range from 25 to 125°C. These results indicated that the HK substrates have excellent electrical properties to meet the applications of embedded capacitors via PCB process.