Development of an ultra low moisture polymer adhesive for die attach applications

Abstract

A new type of die attach material based on a modified olefin thermoset polymer has been developed. Due to its hydrophobic molecular structure, moisture absorption is inherently very low. For example, it absorbs less than 0.05% moisture at 85/spl deg/C/85% RH/168 hrs. Even in HAST test (150/spl deg/C/85% RH/168 hrs.), moisture content is only 0.1%. The olefinic polymer is formulated as a low stress, electrical and thermally conducting paste adhesive. Its other principal features include good processability, less resin bleed and low temperature cure. The new die attach candidates were evaluated using 208 LD PQFP packages with standard epoxy molding compounds. This type of package passed moisture reliability tests at level 3. At JEDEC level 1, there were still package cracks and delaminations at the mold compound interfaces. However, no die attach delamination was observed. These studies clearly demonstrated the need for replacing conventional epoxies with low moisture absorbing polymers for die attachment and encapsulation in order to produce moisture insensitive packages. In summary, the new olefinic thermoset adhesives have shown promise for many die attach applications. These materials will provide important process and reliability improvement for advanced device packaging.