Polymer ceramic composites form a suitable material system .for low temperature fabrication of embedded capacitors appropriate for the MCM-L technology. Improved electrical properties such as permittivity can be achieved by efFcient filling of polymers with high dielechic constant ceramic powders such as Lead Magnesium Niobate-Lead Titanate (PMVPT) and Barium Titanate (BT). Photodefinable epoxies as the matrix polymer allow fine feature definition of the capacitor elements by conventional lithography techniques. The optimum weight percent of dispersant is tuned by monitoring the viscosity of the suspension. The dispersion mechanism (steric and electrostatic conhibution) in a slightly polar solvent such as PGMEA is investigated @om electrophoretic measurements. A high positive zeta potential is observed in the suspension, which suggests a strong conhibution of electrostatic stabilization. By optimizing the particle packing using a bimodal distribution and mod$ed processing methodology, dielectric constant greater than 135 was achieved (PMN-PT + epoxy). Suspensions are made with the lowest PGMEA content to ensure the e c i e n q of the dispersion and efficient particle packing in the driedfilm. Improved colloidal processing of nanoparticle-filled e p o v is a promising method to obtain ultra-thin capacitor films (< 2 microns) with high capacitance density and improved yield. Capacitance of 35 nFicm2 was achieved with the thinnestfdms (2.5-3.0 microns).
The National Electronics Manufacturing Technology roadmap indicates that a capacitance density of 50 nF/cm2 will be required in 2001 for successful implementation of integral passive technology. Polymer-ceramic composites are a favorable choice for thin-film capacitors in low-temperature MCM-L technology. Improvement in dielectric properties of the material, achievement of thin and defect-free films and integration on to large area substrates form the cornerstones for this technology. The Packaging Research Center at Georgia Tech. has been actively involved in achieving improved dielectric properties by developing high solids loading and well-dispersed suspensions based on colloidal techniques. The integration of thin-film composites into the subsequent fabrication process becomes increasingly challenging with higher filler content.For example, delamination of the composite from the bottom copper layer has been consistently observed during the modification of composite surface for increasing the adhesion between the electroless copper deposit (top electrode) and composite surface. The surface modification typically involves an etchtreatment with a powerful oxidizing agent such as permanganate. This delamination was not observed in fully cured neat epoxies. The role of fillers in preventing the curing of the epoxy, the reactions between permanganate and uncured epoxy and the lack of adhesion between ceramic and bottom electrode are some of the key issues involved in this delamination problem. This is further complicated by the classic copper-epoxy de-adhesion problem originating from the copper oxide film at the copper-epoxy interface. This work presents our investigation of the origin of this delamination problem by delineating these issues and identifying the key effects. In particular, the role of epoxy curing and filler content based on the interface and epoxy characterization is addressed here. A failure mechanism is proposed from the correlation between epoxy cure and the delamination during etch treatment
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