As electronics miniaturization has continued, the use of flexible pcb circuit in electronics systems has flourished. Rigid substrates, common in the first multichip module technologies, have been replaced with flexible pcb circuit and either integrated or chip-on-flex.
Likewise, the use of flexible pcb circuit as a substrate for electronic systems utilizing chip-sized and chip-scale packages has increased dramatically. However, during the period that flexible pcb circuit has supplanted PCB as a substrate and increased its share as an interconnect technology, direct chip attach has been developed to circumvent the lack of high-density interconnect. For example, the earliest displays utilized in electronic systems included display electronics mounted on PCBs. These PCBs were attached to the display by means of a standard connector. Over time, PCBs with standard connectors were replaced by flexible cables, constructed using one to a few metal and dielectric layers, with standard and novel connectors. As the size of displays shrank to meet the demands of portable electronics, chip-on-glass technology was perfected.
Directly attaching the electronics to the display I/O reduced the system I/O demands to a quantity compatible with flexible pcb circuit capability. This is a key point to consider in the application of flexible pcb circuit.