Design, Fabrication, Electrical Characterization and Reliability of Nanomaterials Based Embedded Passives

This paper discusses thin film technology based on barium titanate (BaTiO3)-epoxy polymer nanocomposites. In particular, we highlight recent developments on high capacitance, large area, thin film passives and their integration in System in a Package (SiP). A variety of nanocomposite thin films ranging from 2 microns to 25 microns thick were processed on PWB substrates by liquid coating or printing processes. SEM micrographs showed uniform particle distribution in the coatings. The electrical performance of composites was characterized by dielectric constant (Dk), capacitance and dissipation factor (loss) measurements. We have designed and fabricated several printed wiring board (PWB) and flip-chip package test vehicles focusing on resistors and capacitors. Two basic capacitor cores were used for this study. One is a layer capacitor. The second capacitor in this case study was discrete capacitor. Resin Coated Copper Capacitive (RC3) nanocomposites were used to fabricate 35 mm substrates with a two by two array of 15mm square isolated epoxy based regions; each having two to six RC3 based embedded capacitance layers. Cores are showing high capacitance density ranging from 15 nF to 30nF depending on Cu area, composition and thickness of the capacitors. In another design, we have used eight layer high density internal core and subsequent fine geometry n (1 to 3) buildup layers to form a n-8-n structure. The eight layer internal core has two resistance layers in the middle and 2 to 6 capacitance layer sequentially applied on the surface. The study also evaluates the resistor materials for embedded passives. Resistors are carbon based pastes and metal based alloys NiCrAlSi. Embedded resistor technology can use either thin film materials, that are applied on the copper foil, or screened carbon based resistor pastes that can achieve any resistor value at any level. For example, combination of 25 ohm per square material and 250 ohm per square material enables resistor ranges from 15 ohms through 30,000 ohms with efficient sizes for the embedded resistors. Similarly, printable resistors can be designed to cover the resistance in the range of 5 ohms to 1 Mohm. The embedded resistors can be laser trimmed to a tolerance of <5% for applications that require tighter tolerance. Reliability of the test vehicles was ascertained by IR-reflow, thermal cycling, PCT (Pressure Cooker Test ) and solder shock. Embedded discrete capacitors were stable after PCT and solder shock. Capacitance change was less than 5% after IR reflow (assembly) preconditioning (3X, 245 °C) and 1400 cycles DTC (Deep Thermal Cycle).