Composite Embedded Capacitor Films Research Articles

Effects of Curing Agent and Curing Temperature on Material Properties of Epoxy/BaTiO<sub>3</sub> Composite Embedded Capacitor Films

Epoxy/BaTiO3 composite embedded capacitor films (ECFs) were fabricated using dicyandiamide (DICY) as a curing agent and 3-(4-chlorophenyl)−1,1-dimethylurea as a curing accelerator to investigate the curing behavior and material properties of the ECFs with different curing systems and curing temperatures. The curing behaviors of the ECFs with three different curing systems were identified using differential scanning calorimeter analysis. The chemical structure changes of the ECFs were analyzed using Fourier transform infrared (FT-IR) spectroscopy. The intensity changes of a carbonyl peak in the FT-IR with different curing temperatures indicated that cyclization and hydrolysis reactions increased as curing temperature increased. In addition, the effect of this chemical structure change according to curing temperature was investigated in terms of glass transition temperature ( $T_{g})$ , peel adhesion strength, and coefficients of thermal expansion. In the case of the ECF with low DICY content, the degree of cure increased as curing temperature increased and the improvement in the material properties of the ECF with low DICY content resulted mainly from the increase in the degree of cure. The material properties of the ECF with curing accelerator improved after the degree of cure reached 100% due to the low DICY amount and the addition of curing accelerator. However, the material properties of the ECF with high DICY content did not show improvement as curing temperature increased, because the dominance of the two primary amines of the DICY to cure promoted the cyclization and hydrolysis.

A Study on Dielectric Constants of ${\rm Epoxy/SrTiO}_{3}$ Composite for Embedded Capacitor Films (ECFs)

Epoxy/BaTiO3 composites have been of great interest as embedded capacitor materials, mainly due to high dielectric constant of ceramic powders, and good process compatibility of epoxy with printed circuit boards (PCBs). However, one of the potential problems of epoxy/BaTiO3 composite is the dielectric relaxation at gigahertz range. In this paper, epoxy/SrTiO3 composite embedded capacitor films (ECFs) were fabricated for high-frequency applications. Dielectric constants of epoxy/SrTiO3 composite embedded capacitor films with various SrTiO3 particles loading for three different commercial SrTiO3 powders were measured, and experimental data were fitted to the Lichtenecker equation for the prediction of the effective dielectric constant of SrTiO3 powders in epoxy/ SrTiO3 composite ECFs. Using a rectangular cavity resonator method, dielectric constants of epoxy/SrTiO3 composite ECFs were measured at gigahertz range (1-10 GHz). At gigahertz frequencies, dielectric constants of epoxy/SrTiO3 composite ECFs were nearly constant. In contrast, epoxy/BaTiO3 composite ECFs showed decrease of dielectric constants above 5 GHz. Therefore, it is concluded that epoxy/SrTiO3 composite ECFs can be more effectively to be applied for high-frequency 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.

A study on the temperature dependence of epoxy/BaTiO3 composite embedded capacitor films

In this study, the temperature dependence of capacitance, one of the most important properties of embedded capacitor films (ECFs), was investigated. The temperature dependence of the capacitance of ECFs was determined by the temperature dependence of the dielectric constant and thickness, and among these, the main factor was the dielectric constant of ECFs. The dielectric constant of ECFs was determined by that of epoxy and BaTiO3 powders. Below 130°C, the dielectric constant of ECFs increased as temperature increased, and was mainly affected by an epoxy matrix. However, above 130°C (the Curie temperature of BaTiO3), the increased rate of the dielectric constant of ECFs started decreasing. This was due to the fact that BaTiO3 powder undergoes a phase transition from a tetragonal to a cubic structure, and its dielectric constant decreases at 130°C. The dielectric constant of BaTiO3 powder was obtained from measured dielectric constants of ECF and application of the Lichtenecker logarithmic rule.

Comparison of theoretical predictions and experimental values of the dielectric constant of epoxy/BaTiO3 composite embedded capacitor films

Polymer/ceramic composites are the most promising embedded capacitor material for organic substrates application. Predicting the effective dielectric constant of polymer/ceramic composites is very important for design of composite materials. In this paper, we measured the dielectric constant of epoxy/BaTiO3 composite embedded capacitor films with various BaTiO3 particles loading for 5 different sizes BaTiO3 powders. Experimental data were fitted to several theoretical equations to find the equation useful for the prediction of the effective dielectric constant of polymer/ceramic composites and also to estimate the dielectric constant of BaTiO3 powders. The Lichtenecker equation and the Jayasundere-Smith equation were useful for the prediction of the effective dielectric constant of epoxy/BaTiO3 composites. And calculated dielectric constants of the BaTiO3 powders were in the range of 100 to 600, which were lower than the dielectric constant of BaTiO3 bulk ceramics probably due to the presence of voids or pores.

Comparison of theoretical predictions and experimental values of the dielectric constant of epoxy/BaTiO3 composite embedded capacitor films

Polymer/ceramic composites are the most promising embedded capacitor material for organic substrates application. Predicting the effective dielectric constant of polymer/ceramic composites is very important for design of composite materials. In this paper, we measured the dielectric constant of epoxy/BaTiO3 composite embedded capacitor films with various BaTiO3 particles loading for 5 different sizes BaTiO3 powders. Experimental data were fitted to several theoretical equations to find the equation useful for the prediction of the effective dielectric constant of polymer/ceramic composites and also to estimate the dielectric constant of BaTiO3 powders. The Lichtenecker equation and the Jayasundere-Smith equation were useful for the prediction of the effective dielectric constant of epoxy/BaTiO3 composites. And calculated dielectric constants of the BaTiO3 powders were in the range of 100 to 600, which were lower than the dielectric constant of BaTiO3 bulk ceramics probably due to the presence of voids or pores.

Study on epoxy/BaTiO 3 composite embedded capacitor films (ECFs) for organic substrate applications

Embedded capacitor films (ECFs) were newly designed for high dielectric constant and low capacitance tolerance (less than ±5%) embedded capacitor fabrication for organic substrates. ECFs are transferable and B-stage films which can be coated on a releasing film. In terms of materials formulation, ECFs are composed of high dielectric constant BaTiO 3 (BT) powder, specially formulated epoxy resin, and latent curing agent. And in terms of coating process, a roll coating method is used for obtaining film thickness uniformity in a large area. Differential scanning calorimeter (DSC) thermal analysis was conducted to determine the optimum amount of curing agent, curing temperature, and curing time. Changes in the dielectric constant of epoxy/BaTiO 3 composite ECFs with BT particle sizes and contents were investigated. Dielectric constant of 90 was obtained using two different size BaTiO 3 powders mixture. Typically, capacitors of 12 μm thick film with 8 nF/cm 2 with less than ±5% capacitance tolerance and low leakage current (less than 10 −7 A/cm 2 at 10 V) were successfully demonstrated on PCBs using epoxy/BaTiO 3 composite embedded capacitor films.