Flex Circuit Termination Methods

There are a variety of terminations for flex circuits, and we can provide all these as a standard manufacturing process. Adding connectors and other minor component assembly is a common practice when producing a flex circuit. Traditional thru-hole and SMT connectors, ZIF (zero insertion force), high density circular connectors, D-Subminiature connectors, pogo pin/spring loaded, straddle mount, encapsulated, pin and socket connectors, point-to-point or multibranch connectorized jumpers, leaded and RoHs compliant, are all options to consider with flexible materials. In many of the connector options, stiffeners (FR4, polyimide, aluminum) are required to help support the connection as the connectors are heavier than the flex materials, which will cause stress on the interface between the PCB and the connector.

One of the major functions of connectors on flexible and rigid-flex PCBs is the protection of signal continuity from the I/O interface to the board, including high-speed, matched impedance signal management, EMI/RFI shielding, and others. Your choice of connector and termination method on the flex or rigid-flex PCB will determine how much loss there is during that transition.

When choosing connectors, you should work with your fabricator early in the design process on your flex and rigid-flex PCB requirements so they can ensure that the design is robust enough to handle all your application needs. Listed below are some of the common termination methods used in flex circuit technologies.

ZIF Connectors

A ZIF is a type of connector that requires very little force for insertion. They allow for top and bottom contact options, vertical and right-angle orientations, surface mount, and thru-hole terminations. The ZIF contact can be simply a flexible flat cable, a complex flexible PCB, or a flex tail from a rigid-flex PCB.

Contact spacing options are allowed down to 0.2mm pitch. Using a ZIF connector eliminates the need for a mating connector. The flex circuit end "mates” into the connector usually located on the rigid board. The ZIF contacts also allow for repeated cycling with minimal wear.

Tight geometrical tolerances must be maintained on the flex or rigid-flex PCB so that the ZIF contact fits optimally in the ZIF connector. In many instances these enhanced tolerances can only be realized through the investment in laser direct imaging and laser cutting.

Thru-Hole Connectors or Surface Mount Connectors

Thru-hole or surface mount are the traditional technology that is used in today's printed circuit boards. Right angle, Co-Planar, Parallel, Circular, D-Sub, Micro-D, I/O (including MIL-DTL-38999, Series 80 Mighty Mouse, MIL-DTL-24308, MIL-DTL-83513), and many other options are available.

With today's technology, the biggest challenge is being able to hold tolerances on flex and rigid-flex PCBs to accommodate the smaller centerline or pitch spacing, lower profile heights, and lighter SMT and thru-hole connector options. Many of the newer technologies in connectors use an actuator to secure the cable termination, are field terminatable (require no tooling), and are available in centerline spacing of 0.25mm, 0.3mm, 0.5mm, 1.0mm, and 1.25mm, and incorporate a low-profile height and light weight.

Grounding can be achieved by directly grounding the connector shell to flex circuitry.

Crimped Contacts & Displacement Connectors

  • Contacts are crimped through the dielectric material into the copper conductor.
  • Contacts are available for 0.100" (2.54mm) or 0.050" (1.27mm).
  • Pin headers and sockets (standard, walled, with locking, snap-in).
  • Crimp connectors, contacts, and built-in self-stripping connectors (2.54mm).
  • Pins (w/ capillary action, positioner, flat pins, U pins) and cable terminations (2.54mm).
  • Centerline housings can also be added to encapsulate the contact.
  • High insertion force for high retention and high vibration situations.

End of Line Test Requirements

Most flex and rigid-flex PCB customers specify a certain level of validation testing as a required part of the documentation package after the connectors are added to the PCB. Tests may include DWV/IR, continuity, impedance, microsections, ionic contamination, thermal testing, resistance, and others.

Most Common Suppliers of Connectors

  • Samtec
  • 3M
  • TE Connectivity/AMP
  • Glennair
  • Molex
  • JST
  • Amphenol
  • Hirose
  • JAE Electronics
  • Harwin
  • JCT
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