Plasma decapsulation of plastic IC packages with copper wire bonds for failure analysis

Decapsulation of plastic integrated circuit (IC) packages with copper wire bonding is achieved by using an atmospheric pressure microwave induced plasma. A thermal model is built to estimate the bulk IC package temperature under different plasma etching conditions. Temperature measurements of the plasma effluent and IC package are made to validate the model. Due to the low heat transfer rate from gas to solid, the plasma effluent of 700°C raises the bulk temperature of an IC package to 150°C only. This brings a great advantage in processing because a high temperature on a focused area where the plasma etching takes place results in a high etching rate, while a low IC package bulk temperature ensures minimum thermally induced damage to the internal components. Recipes for three etching steps are developed. An IC package with 38 um copper wire bonds and a 2 mm * 3.5 mm die is decapsulated in 20 minutes. Copper bond wires, aluminum bond pads, and structures on the die are undamaged after decapsulation.