ITO is a sputter coated, metalized polyester used in window areas where shielding is required over the display window to protect the display technology from errant electrical charges. It is optically transparent and can be used in conjunction with other shielding technologies sandwiched within the layers of the membrane switch.

ITO is also the one of the key materials in the construction of electroluminescent lamps and touch screens. It is available on PET, PES, PC and PEN materials, as well as well as hard coated clear and antiglare finishes.

Attributes

• Available in several different resistance coatings for flat panel displays, touch screens, EMI and ESD shielding, and EL displays.
  
• Can be sceen printed with conventional conductive inks to provide additional shielding strength and termination options

Printed shields offer shielding against ESD, RFI, and EMI depending on where in the membrane switch stack up they are located. Printed shields can drain errant electrical charges at different rates based on:

• The type of ink used; silver, graphite, carbon, or a blend of inks
• The screen-printed pattern grid, static ring or solid block
• The termination point, through the common switch tail, through a separate ground tail, through and eyelet or through chassis tab

Attributes

• Lowest cost shielding option on membrane switches since no additional layers are added to the stack up. The shielding is printed on the non-switch contact side of the PET polyester layer
• Charges can be drained at different rates depending on the ink type used and screen-printed pattern
• The shield pattern can be screen-printed on an ITO layer for additional shielding protection

Foil shielding is a thin layer of aluminum material with a acrylic adhesive backer that is die cut and placed over the top of membrane layers to protect against EMI and RFI interference.

Attributes

• Can be terminated through common switch tail and terminated via standard connector
• Can be terminated through a foil chassis tab
• Can be terminated via an eyelet

Ground planes can be utilized on PCB backed membrane switches and flex circuits as a means to protect the input device from errant electrical charges. By minimum etching a PCB or flex circuit — and only removing copper in critical areas to create the circuit layout and leaving the copper in areas that are typically removed by the etching process — the remaining copper creates a shield plane to protect the copper traces it surrounds.

Attributes

• There is no additional cost to the piece price of the part since ground planes are an element of the design
• Can be terminated via a stud, standoff, through the header, via a discrete wire or an eyelet

ESD – Electro Static Discharge is the process of a charged non-conductive entity becoming neutral through electron recombination with a conductor. Should an electro static discharge take place, the role of an ESD shield is to offer a path to ground for the charge to dissipate, thereby protecting sensitive circuitry.

RFI – Radio Frequency Interference is a subset of EMI and involves the mid-range radio signals often given off by communication electronics. RFI shielding blocks these signals from interfering with a devices operation.

EMI – Electro Magnetic Interference is a term covering all electrical signals up either received or emitted by an electrical system (it can be low frequency – mains hum, mid-range radio signals – RFI, or microwave signals in the gigahertz range). It is caused when conductors are not adequately shielded and is measured in the dB (dB is a logarithmic measure of the degree of shielding).