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Low Temperature Co-fired Ceramic (LTCC) with low dielectric loss is suitable for use on microwave and millimeter wave circuits. Thick film gold or silver conductors are used as metallization on LTCC substrates. Gold prices are increasing at a rapid rate, so efforts were made to lower the dependency on gold by substituting silver with Ni/Au surface finishes as the top conductor. The external thick film silver conductors were plated using a standard Electroless Nickel Immersion Gold (ENIG) process. The Ni/Au surface finishes provides substantial improvement to fretting corrosion, environmental protection, contact resistance, wire bond strengths, solder ability and solder joint reliability. The reliability testing of DuPont™ GreenTape™ 9K7 LTCC with Ni/Au surface finishes is being conducted. The reliability test methods & conditions were chosen from well-established industry standard test protocols. This paper reports the reliability and high frequency testing results on the ENIG plated GreenTape™ 9K7 LTCC system.

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Low Temperature Co-fired Ceramic (LTCC) material systems offer a highly versatile microwave and millimeter wave packaging platform. Extremely low microwave loss, excellent control of dielectric constant, uniform dielectric thickness, non-existent water absorption leading to very high hermeticity, ability to support multilayer structure leading to 3-dimensional packaging, ability to embed passive functions within the tape layers, availability of a wide range of metallizations, etc. are some of the key advantages of LTCC for microwave packaging. One of the important parameters which needs to be determined at the very early stages of circuit designs are the dielectric properties - dielectric constant and loss tangent, both of which are functions of frequency. These properties need to be known accurately over the entire frequency range of operation for the circuit. For LTCC based designs, the use of dielectric constant of bulk material can lead to deviations between the performance expected at the design stage and for the fabricated circuit. Such deviations are a significant concern for broadband circuits as well as for circuits with sharp resonant behavior such as filters. One of the significant sources of deviation between bulk LTCC and “in-circuit” dielectric constant is the nature of the thick film metallizations used in LTCC technology. Work described here is a comprehensive characterization of three DuPont™ GreenTape™ LTCC systems 951, 943, and 9K7 - in the frequency range 10 to 70 GHz. Both bulk and “in-circuit” dielectric properties with silver and gold metallizations are studied to quantify the deviations in dielectric properties. A Fabry-Perot open resonator technique is used for the bulk characterization while printed ring resonators are used for the in-circuit characterization. This comprehensive characterization will provide key design data for LTCC designers in the 10 – 70 GHz frequency range.

Novel LCP films have been developed by iQLP, LLC in a Joint Development effort with Dupont, for commercialization in the Printed Circuit Board (PCB) industry, for high frequency applications. The films will be commercialized as Copper Clad Laminate (CCL), and thermoplastic bond ply. Prototype PCB's have been built to evaluate integrity during processing, and tested for mechanical reliability. The films/laminates were well suited for PCB manufacture, and the resulting board's surpassed reliability testing requirements. Of particular note, is the low Z axis coefficient of expansion of the LCP which allows for multilayer reliability and the large difference in melting temperature between the bond and circuit layer which allows for ease of manufacture. In addition RF test vehicles were established that demonstrated that the material supports very low loss signal transmission in Millimeter wave frequencies in the range 40 to 110 GHz, making this material system one of the best circuit laminates available for Millimeter wave applications today.