Damage on the top metal layer caused by backend packaging processes often results in unlocalizable electrical failures like column select fails in DRAM products. Consequently, crosssections through an exact address are unhelpful. Decapping from the front side of the die by removing the package (Top- Down preparation), only uncovers the damaged die area. The root cause is removed with the package. A preparation method that preserves the package at the failure (Bottom-Up preparation) is necessary. This paper presents a preparation method for investigations and assessment of backend related problems by removal of the Si-die from the back side, leaving the package and connections layers free for a quick and reliable review. Typical applications described here are the localization of imprint-originated fails or monitoring of the bonding processes.

The electrical interface, in terms of a reliable, low ohmic and defined connection with the device or die is the most relevant aspect in the characterization of products. Bad or undefined contacts inhibit an exact assessment of the functionality. This paper describes different contact related failures analyzed in our lab and gives the solutions we used to solve the problems. Especially an electroless (nickel)-gold plating method has been optimized and is described in details. Low ohmic and reliable contacts can be produced; the paper shows several applications to improve the contact quality in different domains of the failure analysis business