Facile chemical method of etching polyimide films for failure analysis (FA) applications and its etching mechanism studies

A new strategy has been developed for discovering a novel/facile way of etching polyimide film for FA application. The aromatic polyimide synthesized from pyromellitic dianhydride and 2,2′-dimethyl-4,4′-diaminobiphenyl in the presence of an acid catalyst. This polyimide film was used to study its physical attributes and the chemical etching rate which can be evaluated in microelectronic package application as dielectric film. Chemical etching rates of polyimide film by an alkaline etching solution with the presence of different kinds of etchants were studied by film-thickness measurement and UV absorption spectroscopy of dispersible etching residue. The etching rate of polyimide film in alkaline ethylenediamine solution is highest among the etching solution studied in the present experiment. If an external bias voltage was applied during etching, the etching rate was increased. The effect of temperature, solubility of the etchant was also discussed. The presence of a radical in the process of etching reveals that the etching reaction is a type of radical chain reaction. It was found that the deprocessing technique (drenched alkaline aqueous solution of ethylenediamine and then instantaneously combined with mix acid (2:1 Nitric 90% fuming to Sulfuric mix at 40 °C)) could be extended to remove polyimide in different package geometry and different thickness of film.