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TACTILE POLYESTER DOME

Description:

A tactile polyester dome is produced by thermoforming a pre-printed polyester sheet into an array of domes with a specific shape and set of operating characteristics. In collapsing the dome with an actuator, a crisp tactile response is achieved, which indicates continuity has been established.

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Applications:

• Cell phone: Used in conjunction with a silicone rubber keypad to provide switch shorting. Can mate to a flexible multi-layer circuit or a PCB.
• Appliance panel: Used in conjunction with graphic overlay mated to a multi-layer flexible circuit.
• Replacement for elastomeric pad with carbon shorting pads. Domes may be actuated directly by a plastic actuator that is integral with a molded keycap.

Presentation Options:

• Individualized; attached to a flex circuit or as a domesheet with release liner.
• Reel or fanfold; Dome layer only may be supplied in continuous web with or without tractor feed for use in automated assembly line.

DESIGN CONSIDERATIONS

• Clearance for dome
• Actuator size
• Desired Peak Force (Fmax) and Tactile Feel (Tactile Ratio)

Tactile ratio is the snap or tactility of the dome when depressed and is computed using the following formula: (F_max - F_min)/F_max

Peak Force (F_max) is the maximum gram force measured at the point of dome snap. F_min is the point past dome snap at which the printed contact area on the inside of the apex of the dome contacts the shorting pad on the circuit. Figure 1 depicts graphically the relationship between force and travel and the F_max and F_min points.

DOME FEATURES AND SPECIFICATIONS

Environmental
Storage Temperature:	-40°C to 100°C, 120 hours
Humidity Range:	10% to 85%
Temperature Shock:	-40°C to 85°C, 32 cycle @ 30 minute interval dwells
Accelerated Aging:	85°C/85% relative humidity for 120 hours
Dome Construction	See Figure 2 for typical dome detail
Actuator:	Typically specified by customer based on keypad size Hard plastic or silicone rubber Size: typically ½ dome diameter
Dome Layer:	.004" or .005" polyester (PET) Clear PET preferred, white PET available for reflectance Thickness of PET will affect peak force and dome height
Spacer Layer:	.002" acrylic adhesive on either side of a .001"-.004" PET support liner. Thickness of spacer will affect tactile feel and dome height
Bottom Circuit: (if required):	.004" or .005" PET circuit with inter-digitated fingers
Dome venting:	Domes may be vented internally if more than 4 domes in series or externally via a hole in dome layer or channel to perimeter through spacer layer

Figure 2: Dome Construction Detail

Dome characteristics
Peak Force:	150 to 300 grams, +/-25%, Application dependent
Tactile Ratio:	.30 to .65, Application dependent
Displacement:	.023 to .034 Smaller dome, less displacement Lower peak force or tactile ratio, less displacement
Dome diameter:	.187 to .375 inches, application dependent
Number of actuations at 25°C	1,000,000

 

Other White Papers

Flip Chip
Polymer Thick Film Material Performance and Reliability

 

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