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Flex and Rigid + Flex PCB Construction

The following are examples of some of the more commonly used constructions for Flex and Rigid+Flex PCBS found in common applications.

Flex Construction

Flex circuit layer counts typically vary from 1-6 layers. Constructions can accommodate plated through holes (PTH) and surface mount technology (SMT) components. Polyimide or FR4 stiffeners are commonly added to meet application mechanical requirements.

1 Layer Dual Access Flex:

  • Common Applications: Zero Insertion Force (ZIF) to ZIF interconnect systems.
  • Allows access to one layer of copper from both sides of the design.

1 Layer Flex:

  • Common Applications: Connector to connector requirements.
  • Flex core can be Adhesive based or not, depending upon finished thickness required to meet bend requirements.

2 Layer Flex:

  • Common applications: Surface micro-strip controlled impedance, ZIF to ZIF interconnect, PTH or SMT Connector interconnects,
  • Flex core can be Adhesive based, or not depending upon finished thickness required to meet bend requirements.

3 Layer Multilayer Flex:

  • Common applications: Controlled impedance, radio frequency (RF)/electromagnetic interference (EMI) shielding.
  • Flex cores are typically with-out adhesive to minimize flex thickness and allow for bend requirements.
  • Higher layer counts available. Review of bend requirements recommended.

Rigid + Flex Construction:

A combination of rigid PCB technology and flex circuit technology allows for a very wide variety of rigid and flex layer counts and combinations. Rigid areas can utilize blind and buried vias, with some limitations, and via in pad technology. Rigid area layer counts range from 2–20+ and flex area layer counts from 1–6+.

2 Layer Rigid with 1 Flex Layer:

  • Common application(s): Simple designs with limited space and performance requirements.

3 Layer Rigid with 1 Flex Layer:


4 Layer Rigid with 2 Flex Layers:


The above illustrates a small sample of available flex and rigid-flex PCB constructions. When designing your flex circuit, refer to IPC specifications for specific flexible materials, circuit design, performance, and assembly of flexible circuits.

(Source: epectec.com)