Evaluation of area bonding conductive adhesives for flip chip attach of area bonded die

The new technologies of flip chip, DCA, and CSP require conversion from perimeter bond pads to total area bonded dies. To fill this need, new low-cost area bonding conductive (ABC) adhesives have been developed under an ARPA TRP grant. An ABC adhesive is a two region thermoset adhesive with electrically conductive epoxy adhesive pads surrounded by a continuous oxide filled dielectric adhesive to form a total area bond. Both regions are solvent free, B-staged, non tacky epoxies supplied on a Mylar carrier release film, which cure, with no volatiles or outgassing to yield high Tg, high strength adhesive bonds. In contrast to previous random particle Z-axis adhesives, the ABC adhesives have conductive areas only at the bond pad locations. Area bond test die, designed and fabricated by the Auburn University Microelectronics Center have been successfully bonded to FR4, flex, and thin film ceramic substrates. Test die features include four point Kelvin contact strings and interdigitated daisy chains on 10 mil and 20 mil pitch. Various surface metallizations have been explored and evaluated. Cure times and temperatures are being optimized. This paper will discuss design and fabrication of the test die, including surface metallization and the problems encountered therein. It will describe the process and its optimization.