Parlex shielding options for flexible printed circuits and flexible flat cable
As signal speeds within circuits and cables extend into the gigahertz range, it is imperative to protect critical parts of an assembly with appropriate electrical shielding to maintain signal fidelity, circuit timing and impedance control. Protecting equipment from data breach and malfunction due to EMI / RFI signal interference in security applications may also be a major motivation for specifying additional shielding for a flexible circuit assembly or cable.
Parlex offers many different shielding options for all of its product offerings including flat flexible cables (FFC), polymer thick film circuits (PTF) and flexible printed circuits (FPC). Consult with your local Parlex Applications Engineer during the design phase of your project for help in choosing the right shielding system for your specific project requirements.
Parlex can apply shielding to your flexible circuit using three basic techniques- silk screening, lamination or spray coating. The properties and advantages of all three techniques are outlined in this guide.
Parlex shielding can be applied to PTF or FPC circuits with a variety of techniques and substrates including silver ink (A) or copper ink (B) silkscreening using Parlex’s exclusive HSI+ shielding. Aluminum (C) or copper (D) film laminations can also be applied to FFC, PTF or FPC. Silver conductive inks can also be silkscreened onto PTF and FPC (E) or sprayed onto FFC (F) using Parlex PEMACS 101 shielding. For extreme EMI situations, ferrite beads may be added to FFC assemblies.
Shielding Selection Guide
The exclusive Parlex HSI+ shielding process applies various types of conductive materials to flexible printed circuits such as silver epoxy or copper epoxy through automated silk-screening techniques. The material is applied in a specific weave pattern to achieve effective shielding and impedance control while minimizing thickness in order to maintain maximum flexibility. For additional information, see our HSI+Technical Description.
Advantages
· Controlled weave pattern requires less silver or copper in the coating, saving on material costs.
· High flexibility- Impedance-controlled conductors can be achieved with less dielectric separation vs. techniques using solid patterns
Disadvantages
· HSI+ Coating is not applicable for pieces longer than ~30” in length.
· Less protection on the sides of a circuit for maximal Z-axis protection (Note: we recommend using guard rail ground conductors on the edges of each circuit to create 360° shielding)
Lamination of foil shields
Aluminum or copper foils may be laminated to either side of a flexible circuit to provide additional shielding as needed. Foils may be laminated with nonconductive outer coatings to prevent shorting of other components.
Advantages
· Compatible with all circuit types including FFC, FPC and PTF.
· Multiple laminations may be used within a multilayer circuit to shield internal layers of the same circuit from interference.
· Copper lamination on one side of a circuit may be used for both shielding and as a ground return to save on material cost.
· Materials may be perforated at the periphery for improved edge shielding protection.
· High abrasion resistance.
· Foils may be wrapped 360° around a circuit for ultimate protection on all sides.
Disadvantages
· Aluminum shielding not as effective as a signal return in this application.
PEMACS 101 Shielding
Parlex's PEMACS 101 shielding provides a thin, highly flexible shield that can be applied to a laminated cable, flexible circuit, or almost any other surface that requires flexible shielding and can be grounded directly to any conductor or combination of conductors. The PEMACS 101 shielding process utilizes silver conductive ink that is a highly effective shield and meets the EMI / RFI requirements of today's complex designs. Silver shielding may also be applied to FPC and PTF with silkscreening.
Advantages
· Silver shield is coated with nonconductive conformal coatings to improve durability and prevent shorting of adjacent components.
· Spray shielding can be applied after parts are manufactured.
· Masking can be applied to areas where exposed shield is desired for attaching ground straps
· Can be applied to FFC, FPC or PTF.
Disadvantages
· Most expensive option due to increased material use and silver costs.
For help in choosing the right shielding system, contact your local Parlex Applications Engineer today!
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