Failure analysis of Cu electroplating process with Polyimide substrate fabricated for flexible packaging

Failures like short circuit are always encountered in PCBs (printed circuit boards) due to defects in the flexible interconnection. In this paper, systematic analysis such as macro and micro observation was carried out on shorting trace in Polyimides (PI) films used for flexible substrates interconnection (FSI) packaging applications. The thin flexible PI films have desirable properties for use in the electrical and electronics industry because they are a group of good thermal stability, high flexibility, low dielectric constants, excellent mechanical strength, low loss tangent and electrical insulating properties. Since, they offer so many excellent characteristics, this enables a wide range of applications, particularly for flexible packaging. The fine traces with 50 μm pitch (25 μm line/space) built on a flexible 12.5 μm thick polyimide film using wet fabrication process are reported in this paper. The thick copper (Cu) film was obtained from the Cu plating process using evaporated thin film of Cu as the adhesion layer. The fabricated fine-pitch test vehicles are the failure analysis using scanning electron microscope (SEM), energy-dispersive spectrometry (EDS) and X-ray spectrometry technologies.