The demand for thin, lightweight, high-density interconnect continues unabated. Similarly, application strategies for satisfying the ever-changing and ever-growing demand for high-density interconnect continue to change. Since their inception, flexible PCB have evolved into a cornerstone technology of high-density interconnect. Flexible PCB has become a fundamental interconnect technology, from its first application in tape automated bonding (TAB) and corresponding simple, point-to-point configurations to the fine-pitch, multilayer designs that are commonplace in today’s mobile electronic products. However, the approaches in using flexible PCB to satisfy the demands of high-performance, highly reliable systems with high volumetric density I/O are still evolving.

Following a familiar path of technology development, the use of flexible PCB has changed from first-level to second-level interconnect applications; More recently, the role of flexible PCB has been expanded to include system-level interconnect. At each point in its changing role in applications, flexible PCB technology has been modified to meet the application demands. For example, to meet the demands of die-to-die interconnect, the single-layer, via-less, point-to-point circuits found in 1970s TAB packaging sprouted additional layers. The transformation to multilayer interconnect required the development of new features such as vias for interconnecting layers; new materials such as adhesives to bond dielectric and conductor layers; and new processes and equipment for manufacturing the resulting incarnation of flexible PCB. As device I/O increased beyond the capabilities of existing multilayer technology, the trace and space features of flexible PCB were reduced. Over the past twenty years, feature sizes in flexible PCB such as conductor geometry, via diameter, dielectric thickness, etc., have been improved significantly. These improvements positioned flexible PCB for its now-dominant position in portable consumer, display, and medical electronics interconnect applications.

As witnessed over the past ten years, the reduction in interconnect feature size has slowed. At the same time, device I/O counts have increased as semiconductor features have decreased, according to Moore’s Law. This disparity in interconnect and semiconductor feature size has created an interconnect “brick wall” that demonstrates the need for advancing the capabilities of interconnect systems. Semiconductor device minimum feature size (and rate of decrease in feature size) far exceeds the equivalent in flexible PCB and PCB Clone technologies. The corresponding gap in interconnect capability has and will limit advances in semiconductor applications until advances in volumetric I/O density, form factor, weight, flexibility, etc., are implemented in flexible PCB. In the meantime, flexible PCB must be utilized as an integral part of the interconnect system.

Although the complexity of electronic systems has increased over the past ten years, the challenges in interconnect systems have been minimized due to the functional partitioning of electronic systems into key subsystems:  encoding/decoding ic, processing, display, and power.

Typically, flexible PCB is utilized for interconnection within a subsystem as well as for system interconnect.

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