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DuPont Microcircuit Materials

Green Tape™ Technology Shrinks Size of Impedance Matching Arrays for Digital Interconnects

Portable consumer products now incorporate digital circuits operating at increasingly faster clock speeds. New circuit designs must also offer reduced size, power consumption, and cost. One solution is integrated passive components.

In a recent example, AVX Corporation of Myrtle Beach, S.C., has developed a fully integrated resistor/capacitor (R/C) multilayer array designed for AC bus termination of data transmission lines in high-speed digital interconnects. These terminations are used to maintain signal integrity (by controlling signal reflections), adjust propagation delays, and minimize power consumption.

|Z| ChipTM is AVX Corporation's trade name for its impedance matching devices. These fully integrated R/C chips can be made very small because of high volume efficiency, and thus can save space and assembly costs.

Challenge: Multiple Functions with High Power Handling in a Small Footprint

In the AVX design, the arrays are made with a stack of closely spaced resistor elements arranged as electrodes in a multilayer capacitor structure. The device resistance comes from the parallel resistance of the individual layers, and the device capacitance arises from capacitive coupling of planar resistor elements that are terminated in the multilayer structure. In this novel structure, the resistor layers themselves are the electrodes of a parallel plate capacitor. Although the cross-section of the co-fired device is simple, the device is electrically complex, because the capacitance and resistance are physically distributed throughout the entire device.

Internal electrodes, which are ruthenium chemistry-glass composites, are matched to the thermal expansion of the Low Temperature Co-fired Ceramic (LTCC) body. They have high reliability when exposed to combined thermal shock (wave solder with no preheat), thermal cycle (-55°C/+125°C), and high humidity/high temperature (85°C/85% RH) testing at twice rated voltage. The integrated R/C arrays also have high power handling, because power dissipation takes place throughout the entire body rather than just a single layer, as is typical with discrete components.

Solution: Green TapeTM and Custom Resistor Compositions Facilitate Integration of Components

The AVX design utilizes DuPont LTCC Green Tape™ technology and custom thick film resistor compositions. To meet the requirements for performance and ease of manufacture, DuPont scientists developed a resistor chemistry which matures in one firing, has controlled interaction with the glass in the LTCC ceramic, and has a sintering rate matching that of the tape dielectric. Resistor compositions yield a +/-10 percent resistor tolerance after co-firing.

These series R/C chips are the first in a line of integrated passive components based on Green Tape technology emerging from AVX Corporation's research laboratories. R/C chip products are now available with capacitance in the range of 33-150 pF, and resistance between 22 and 100 ohms. Integrated R/C chips with a 0603 (0.060 x 0.030 inch) footprint, in which each chip replaces two discrete passive components, are currently in production. Integrated arrays with four resistors and four capacitors in the footprint of a 1206 chip component (.120 x .060 inch), in which each array replaces eight discretes, are also in development.

For more information, call DuPont at 1-800-284-3382, press 3.