The effect of plasma etching process on rigid flex substrate for electronic packaging application

The demand for high-speed signal transmission circuits triggers the use of polymer substrates having the superiorly mechanical and electrical reliability properties. Foremost among them, rigid-flex polymer substrates are being used in the printed circuit board (PCB) of electronic packaging technologies by utilizing their property compatible with device miniaturization and packaging integration. Modifying the polymer interfacial property further before subsequent processing, plasma treatment is employed to adjust the physical and chemical changes of the surface and subsurface. One special issue of plasma-induced change is the surface roughness (hydrophobic or hydrophilic) depending on every detail of process cycle conditions. Thus, it is difficult to be precisely controlled so as to deliver the desirable outcome. This study employs Taguchi experimental method to find the parameter critical to plasma etching particularly on rigid flex substrate. In contrast to the traditional use of atomic force microscopy (AFM) and/or scanning electron microscopy (SEM) to characterize the surface roughness morphology and thus deduce the optimal process conditions. It adopts a set of standard orthogonal arrays to determine parameters configuration and analysis results. These kinds of arrays use a small number of experimental runs but obtain maximum information and have high reproducibility and reliability. Taguchi method provides the experimenter with a systematic and efficient approach for conducting experiments to determine near optimum parameter settings for performance and cost.