The ability to produce large-area, fine-pitch flexible interconnect is driven by a number of elements. Those elements are comprised of materials, processes, facilities, equipment, design, and engineering support. The demand for thin, fine-pitch flexible interconnect requires unique considerations that are not possible with traditional printed circuit board (PCB) technologies. Fine feature requirements, over large areas, must have clean process facilities and tooling. Most PCB facilities have limited clean-room capabilities and are often restricted to Class 10,000 in the pattern transfer area. Fine-pitch interconnect processing of structures with less than 100um pitch requires clean process areas—i.e., Class 100-1,000–to be able to produce interconnect with acceptable yield. The clean-room facilities must also be augmented with tooling, processes, and operator controls for low-defect densities.
Defects found on flexible interconnect can include trapped fibers, hole in trace, and conductor-to-conductor shorts. These defects are the result of particles generated from process materials or the process environment, including tooling, operators, and the process facility. Many PCB manufacturers have designed clean process tools that contain the work and protect it from an unclean facility.
Flexible printed circuits, with respect to features and process environments, are at the intersection of their semiconductor and printed circuit board equivalents. Fine-pitch flexible interconnect resides at the intersection; tooling, facilities, and expertise from the semiconductor industry are more closely coupled to fine pitch.