Sung-Dong Cho

Frequency and Temperature Dependence of Dielectric Constant of Epoxy/BaTiO3 Composite Embedded Capacitor Films (ECFs) for Organic Substrate

In this study, temperature dependence of capacitance, one of the most important properties of ECFs, was investigated. Temperature dependence of ECFs capacitance was determined by temperature dependence of dielectric constant and thickness, and among these, main factor was dielectric constant of ECFs. Dielectric constant of ECFs is determined by that of epoxy and BaTiO3 powders. Below 130degC, dielectric constant of ECFs increased as temperature increased, and was mainly affected by an epoxy matrix. However, above 130degCs the Curie temperature of BaTiO3, the increase rate of ECFs dielectric constant started decreasing, because BaTiO3 powder undergoes a phase transition from a tetragonal to a cubic structure and its dielectric constant decreases at 130degC. Dielectric constant of BaTiO 3 powder was obtained from measured dielectric constants of ECF and applying the Lichtenecker logarithmic rule. Dielectric constants of ECFs at high frequency range (0.1~10GHz) were measured using a cavity resonance method. For both powders, dielectric constants in high frequency range were about 3/4 of the dielectric constants at 1 MHz. This difference is mainly due to the decrease of dielectric constant of epoxy matrix. For BaTiO3 ECFs, there was a dielectric relaxation at 5~9GHz presumably due to the polarization mode change of BaTiO3 powder

Study on the amorphous Ta2O5 thin film capacitors deposited by dc magnetron reactive sputtering for multichip module applications

Tantalum oxide (Ta2O5) thin film capacitors for multichip module (MCM) applications were investigated. Through the capacitor characterization and RBS compositional analysis, it was found that when the sputtering power and Ar flow rate is 200 W and 60 sccm, respectively, the stoichiometric Ta2O5 film can be obtained at the O2 gas flow rate of 50 sccm. The low temperature annealing (150°C) is useful to increase the capacitor yield, but the annelaing in oxygen atmosphere causes the leakage current to increase. When the Ta-oxide capacitors were fabricated on the polymer-laminated substrate, leakage current increased and breakdown field strength decreased. These are due to the surface roughness effects of the polymer films and also the Al bottom electrode layer. It was demonstrated that the Ta2O5 capacitors fabricated on the Upilex-S polymer film can meet the requirements of integrated capacitors for MCM applications.

Epoxy/BaTiO/sub 3/ composite films and pastes for high dielectric constant and low-tolerance embedded capacitors fabrication in organic substrates

Epoxy/BaTiO/sub 3/ composite embedded capacitor films (ECFs) were newly designed for high dielectric constant and low-tolerance (less than /spl plusmn/5%) embedded capacitor fabrication for organic substrates. In terms of material formulation, ECFs are composed of a specially formulated epoxy resin and latent curing agent, and in terms of a coating process, a comma roll coating method is used for uniform film thickness in large area. The dielectric constant of ECF in high frequency range (0.5/spl sim/3 GHz) is measured using the cavity resonance method. In order to estimate dielectric constant, the reflection coefficient is measured with a network analyzer. The dielectric constant is calculated by observing the frequencies of the resonant cavity modes. Calculated dielectric constants in this frequency range are about 3/4 of the dielectric constants at 1 MHz. This difference is due to the decrease of the dielectric constant of the epoxy matrix. The dielectric relaxation of barium titanate (BaTiO/sub 3/: BT) powder is not observed within measured frequency. An alternative material for embedded capacitor fabrication is epoxy/BaTiO/sub 3/ composite embedded capacitor paste (ECP). It uses similar materials formulation like ECF and a screen printing method for film coating. The screen printing method has the advantage of forming a capacitor partially in the desired part. However, the screen printing makes surface irregularities during mask peel-off. Surface flatness is significantly improved by adding some additives and by applying pressure during curing. As a result, a dielectric layer with improved thickness uniformity is successfully demonstrated. Using epoxy/BaTiO/sub 3/ composite ECP, a dielectric constant of 63 and specific capacitance of 5.1 nF/cm/sup 2/ were achieved.

Relationships between suspension formulations and the properties of BaTiO/sub 3//epoxy composite films for integral capacitors

Although integral capacitors fabricated using polymer/ceramic composite film have been intensively investigated, there was no systematic study of relationships between suspension formulation and properties of capacitors made from the suspension. In this paper the effects of the suspension formulation such as powder size, amount of dispersant, and amount of solvent, on the capacitor properties such as dielectric constant, dielectric loss, leakage current were investigated using BaTiO/sub 3/ as a ceramic filler and epoxy resin as a polymer. It was found that high packing density could not only provide high dielectric constant and high capacitance but also high leakage current.

Novel epoxy/BaTiO/sub 3/ composite embedded capacitor films embedded in organic substrates

Embedded passive technology is an essential technology for further miniaturization and higher performance of electronic package systems. Polymer/ceramic composites have been of great interest as embedded capacitor materials, because they did combine not only the processability of polymers with high dielectric constant of ceramics but also good compatibility with printed circuit boards (PCBs). Novel embedded capacitor films (ECFs) were newly designed for low tolerance embedded capacitor fabrication for organic substrates. In terms of material formulation, ECFs are composed of specially formulated epoxy resin and latent curing agent. And in terms of coating process, a comma roll coating method is used for uniform film thickness in large area. In this paper, it is demonstrated that low tolerance (less than 5%) capacitor can be fabricated using ECFs, and properties of epoxy/BaTiO/sub 3/ composite ECFs are reported. Fabrication process and various properties of ECFs such as dielectric constant, leakage current, adhesion strength, thereto-mechanical characteristics, reliability, and high frequency behavior up to 3 GHz will be presented.

Study on the epoxy/BaTiO/sub 3/ embedded capacitor films newly developed for PWB applications

Embedded passives technology is a promising method for miniaturization and higher electrical performance of electronic package systems. High dielectric constant epoxy/ceramic composites have been considered as embedded capacitor materials for organic substrates, because they have processability and compatibility with printed wiring boards (PWB), in addition to high dielectric constant. In this work, we have developed embedded capacitor films with flexibility, processability, and uniform characteristics, and demonstrated an epoxy/BaTiO/sub 3/ composite capacitor with small capacitance tolerance could be fabricated using the film. Curing temperature and amount of curing agent were optimized using differential scanning calorimeter (DSC) analysis. Dielectric constant of embedded capacitor films with BaTiO/sub 3/ powder volume loading was observed and this behavior is explained using SEM images and density measurement of the films. As a result, using a bimodal mixture of two different size BaTiO/sub 3/ powders, a dielectric constant of 100 was achieved. A 7 /spl mu/m thick capacitor film showed 10 nF/cm/sup 2/ with less than /spl plusmn/5% tolerances, and low leakage current less than 10/sup -8/ A/cm/sup 2/ at 10 V was demonstrated.

Low tolerance epoxy/BaTiO/sub 3/ composite embedded capacitor films (ECFs)

Embedded capacitor technology is one of effective packaging technologies for further miniaturization and higher performance of electronic package systems. High dielectric constant epoxy/ceramic composites have been of great interest as embedded capacitor material, because they have good process compatibility with multilayer organic substrates applications such as printed circuit boards (PCBs). In this work, less than 7% tolerance embedded epoxy/BaTiO/sub 3/ composite capacitors made of newly developed embedded capacitor films (ECFs) composed of low temperature rapid curing epoxy resin, latent curing agent, and barium titanate powder were successfully fabricated on PCBs and Si wafers. Then capacitor properties were characterized. Compared to epoxy/BaTiO/sub 3/ composite capacitor solutions (or pastes) deposited by a spin coating method, ECFs have excellent advantages such as lower capacitance tolerance over large area, no waste of materials, good film formation capability and processability, long shelf life, and good thermo-mechanical stability after final epoxy cure. Over 100 dielectric constant numbers were obtained using two different size BaTiO/sub 3/ powders mixtures. Another important capacitor property of the capacitor films, leakage current, was also less than 10/sup -7/ A/cm/sup 2/ which is excellent enough for decoupling capacitor applications. Epoxy resin formulation, curing agent, dispersant, and several additives were optimized to produce good film formation capability, fast curing characteristics at 180/spl deg/C of less than 20 seconds, good BaTiO/sub 3/ powder dispersion control, and excellent shelf life for handling. Typically, capacitors of /spl plusmn/7 /spl mu/m film thickness with 10 nF/cm/sup 2/ with less than 7% tolerances and low leakage current (less than 10/sup -7/ A/cm/sup 2/ at 10 V) were successfully demonstrated on PCBs and Si wafers using newly developed epoxy/BaTiO/sub 3/ composite capacitor films. These capacitor films can be embedded on selective areas of PCBs during build-up processes or other substrates such as Si and ceramic substrates.

Effects of particle size on dielectric constant and leakage current of epoxy/barium titanate (BaTiO/sub 3/) composite films for embedded capacitors

Polymer/ceramic composite film is of great interest as dielectric material for embedded capacitor applications. In this paper, effects of powder size on dielectric constant and leakage current of epoxy/BaTiO/sub 3/ composite film fabricated by spin-coating were investigated using bisphenol-A type epoxy and 6 kinds of barium titanate powders with diameter ranges of 0.1-0.9 /spl mu/m. Dielectric constant of the composite films increased as particle size increased. This was due to tetragonality increase, which was observed by XRD analysis, with particle size increase. In addition to tetragonality, better dispersibility also contributed to high dielectric constant of bigger powder. Leakage current of composite films increased dramatically as particle size increased. It is presumably due to the decrease of the number of particles per unit length, resulting in decrease of the number of contacts. As the number of contacts acting as a potential barrier reduces, potential barrier lowering effects become larger. When we use larger powder, we can obtain higher dielectric constant with larger leakage current. As a result, there is tradeoff between high dielectric constant and low leakage current, and 0.5/spl sim/0.7 /spl mu/m size powder would be optimum for embedded capacitor applications.

Epoxy/BaTiO/sub 3/ (SrTiO/sub 3/) composite films for high dielectric constant and low tolerance embedded capacitors fabrication in organic substrates

Epoxy/BaTiO/sub 3/ composite embedded capacitor films (ECFs) were newly designed for high dielectric constant and low tolerance (less than /spl plusmn/5%) embedded capacitor fabrication in organic substrates. In terms of material formulation, ECFs were composed of specially formulated epoxy resin and latent curing agent. And in terms of coating process, a comma roll coating method was used for a uniform film thickness over large area. Dielectric constants of BaTiO/sub 3/ & SrTiO/sub 3/ composite ECFs were measured with MIM (metal-insulator-metal) capacitors at 100 kHz using LCR meter. Dielectric constants of BaTiO/sub 3/ ECFs were larger than these of SrTiO/sub 3/ ECFs, due to the difference of permittivity of BaTiO/sub 3/ and SrTiO/sub 3/ particles. Dielectric constants of BaTiO-, & SrTiO/sub 3/ ECFs at high frequency range (0.5/spl sim/10GHz) were measured using a cavity resonance method. For both powders, dielectric constants in high frequency range were about 3/4 of the dielectric constants at 1 MHz. This difference is mainly due to the decrease of dielectric constant of epoxy matrix. For BaTiO/sub 3/ ECFs, there was a dielectric relaxation at 5/spl sim/9GHz presumably due to the polarization mode change of BaTiO/sub 3/ powder. However in case of SrTiO/sub 3/ ECFs, there was no relaxation up to 10GHz.

Epoxy/BaTiO3 Composite Embedded Capacitor Films (ECFs) for Organic Substrate Applications

Embedded capacitor technology is one of the effective packaging technologies for further miniaturization and higher performance of electronic package systems. High dielectric constant epoxy/ceramic composites have been of great interest as embedded capacitor materials, because they have good process compatibility with multilayer organic substrates applications such as printed circuit boards (PCBs). In this work, it was demonstrated that low (less than ±5%) tolerance epoxy/BaTiO3 composite capacitors were successfully fabricated on PCBs using newly developed embedded capacitor films (ECFs), which were composed of specially formulated epoxy resin, latent curing agent, and BaTiO3 powders. And some properties of the capacitors were characterized. Compared with the dielectric layer formation method by spin coating using epoxy/BaTiO3 suspension, ECFs have excellent advantages such as lower (<5%) capacitance tolerance over large area, no waste of materials, good film formation capability, and processability, long shelf life, and good thermo-mechanical stability after final epoxy cure. Dielectric constant about 93 was obtained using two different size BaTiO3 powders mixture. Epoxy resin formulation, curing agent, solvents, and dispersant were optimized to produce good film formation capability, fast curing characteristics at 180°C within 5 minutes, good BaTiO3 powder dispersion control, and excellent shelf life for handling. And the effects of BaTiO3 particle size and BaTiO3 powder content on dielectric constant and adhesion strength were investigated. These capacitor films can be embedded on selective areas of PCBs during build-up processes or other substrates such as Si wafers and ceramic substrates.© 2003 ASME