NEW ELECTROMIGRATION FAILURE MODE IN FLIP CHIP SOLDER JOINTS

摘要

A new electromigration failure mechanism in flip chiprnsolder joints is reported. The solder joints failed through arnvery rapid, localized dissolution of the Cu on the cathodernside. The regions of the dissolved Cu include not only thernCu under bump metallurgy but also the internal Curnconducting trace on the chip. From the location andrngeometry of the dissolved Cu, it can be concluded thatrncurrent crowding played an important role for the rapidrndissolution. The dissolved Cu atoms were then driven byrnelectrons to the anode side, and a large amount of Cu6Sn5rnwas formed there. To avoid this type of failure, anotherrnmetal more resistant to dissolution should be used in placernof or over Cu. Moreover, the geometry of the under bumprnmetallurgy and conducting trace might have to berncarefully designed to achieve a more uniform currentrndistribution to reduce the effect of current crowding.