Rheology of Silver- Filled Glass Die Attach Adhesive for High-Speed Automatic Processing

Conductive adhesives for use on high-speed automatic application equipment require well-controlled viscoelastic properties. The theological properties of a new silver/glass die attach adhesive for cerdip packages under a wide range of flow conditions are described. The theology required to achieve dispersion stability and excellent performance under high-speed automatic die bonding conditions is discussed. The adhesive paste is a concentrated dispersion of silver and glass particles in an organic solvent medium. Interparticle interactions promote formation of a three-dimensional solidlike structure at a low shear rate to provide long-term dispersion stability. Under moderate to high shear the dispersion becomes a fluid which shear thins and dispenses readily for application. After dispensing, the paste structure recovers rapidly, retaining the shape of the adhesive pattern. The viscoelastic response of the adhesive was measured under both steady and oscillatory shear to define flow behavior during the different shear/time conditions of the application process: storage, filling, dispensing, pulloff, pattern retention, and die attachment.