New method for decapsulation of copper wire devices using LASER and sub-ambient temperature chemical etch

IC packages have been greatly improved over the past several years. With the adoption of Cu wires and new green EMC (Epoxy Molding Compound), the suppression of lead, the use of Cu pillars and the increased number of dies, the verification of the quality of the assembly and failure analysis becomes critical. Starting twelve years ago, LASER ablation was introduced as a means to facilitate the pre-decapsulation of packages aiming at a completion by wet chemistry (acids) or dry chemistry (plasma). The decapsulation process with acid at medium temperature (75°C) does not permit to keep the Cu wires intact. Our studies and work in the past several years has consisted in lowering the temperature of acid use in order to minimize the effect of acid attack on the Al pads and Cu wires. Currently the thinnest wires used are 0.6 mil in diameter (approximately 15µm). In this article we will demonstrate that decapsulations at sub-ambient temperatures are now possible and give expected results. Moreover, openings at near ambient temperature reduce the component deformation and also the deformation of its constituents compared to decapsulations at medium or high temperature.