TABLE OF CONTENTS The imaging process comprises several sequential steps that together allow for the metal interconnect pattern to be formed on a bare substrate. The steps themselves are interactive and it is a balance between them that allows for the reproduction of a master pattern into a metal pattern with high fidelity. The success of the steps in the sequence is dependent on the materials or chemicals used, but also to a large extent on the equipment utilized. Thus, again there is a balance of various factors needed in order to obtain a stable, reproducible, and high-yield/low-cost process. The details of the chemistry and the equipment used to perform it will be outlined, and as often as possible the tradeoffs of various choices will be highlighted so that both the inexperienced process engineers and the designers and procurers of PCBs who need an overview of the process considerations will be able to proceed in their work to obtain a manufacturable product.
The process sequence for imaging is given in Fig. 2.14, where the resulting pattern is used for either subtractive or additive metal pattern transfer. The details of these processes are given in the subsequent chapters. In a generic sense the process involves the coating of a polymeric material onto the substrate of interest, patterning the material either by depositing the initial layer in a patterned fashion (screen printing) or by the use of a master of the pattern desired and a photographic sequence of...
