Development of low elastic modulus die attach material and clean cure process

Thermal stress in a large silicon die bonded to a copper lead frame was investigated using the finite-element method and a die-bonding experiment. It was found that even curing at a temperature as low as 100°C is not sufficient to reduce the thermal stress and that decreasing the Young´s modulus of the die-bond adhesive to less than 100 MPa is more effective than lowering the cure temperature. Based upon the calculation results, silicon elastomer with a hydrosilylation reaction curing mechanism was selected as a die-bond adhesive, considering both reliability and productivity. Volatile organic species such as cyclic siloxane were intensively removed from the adhesive to minimize contamination on the die surface. Furthermore, a clean curing process was developed to increase the process margin. The newly developed die-bond adhesive, together with the novel curing system, has enabled the bonding of a large die to a copper lead frame with good reliability and productivity. This technology has been applied to the assembly of memory device packages