Shielding Solutions to Protect Your FFC CablesPatrick Walsh
Ever increasing signal speeds and high noise environments make EMI/RFI shielding an essential requirement for FFC’s (Flat Flexible Cables). PICA can offer various shielding options.
The least expensive option is a foil laminated to the outside of the cable. This can be applied to one or both sides. The foil shield is a 0.35 mils (9 µm) aluminum base with 0.5 mils (12µm) heat sealable coating to cable side and 2 mils (50 µm) polyester dielectric outer coating. This is an excellent solution for floating shields where there is no connection to internal traces. Connection to internal traces can be achieved by crimping IDC type pins through the foil layers and into the traces of the cable. This system of connecting the shield is generally limited to cable pitches of either 1.27mm or 2.54mm with accompanying crimp pin technology. Drain wires can also be connected to the foil for grounding.
Another option is the application of a silver loaded epoxy shield. The silver epoxy is applied on either one or both sides of the cable and then covered with either a PET film or Conformal Coat as dielectric. The conformal coating is flexible and easy to fold while the PET provides superior dielectric strength and abrasion resistance. Typical coating thickness of silver epoxy is from 0.5 mils (12 µm) to 1 mil (25 µm). This yields 360 degree shielding with resistance from one side of the circuit to the other of less than 1 ohm.
The method to apply the silver shielding is by racking and masking uncoated sections, then using HVLP (High Volume Low Pressure) spray guns to coat the cables. This method is generally used for smaller cables or anything requiring selective coating. Appearance and accuracy of shield lines are easy to control, however, shield thickness is harder to control and overspray results in some waste.
Attachment of silver shield to internal traces is facilitated through openings in the base cable insulation. Any number of traces may be attached in this manner and resistance between shield and trace is typically less than 2 ohms. This shielding system is applicable to all flat flexible cable pitch sizes.
Furthermore, openings in the outer dielectric can be used to ground either silver or foil shielding to a chasse if necessary. All of the shielded FFC’s offered by PICA can be REACH and RoHS compliant.
Please contact PICA Engineering for more information regarding your shielded FFC circuit application.