Tactile Metal Domesfor Keypads
Phil Heft – PEMS Specialist
4 Legged Domes4 Legged Domes
RANGE of DOMES
Pros:Readily AvailableLarge offeringTape and Reel & ArraysTubesDimpled and Non-DimpledNickel and Tin PlateSingle Side Circuit CapableHighest Trip ForceHighest Life Cycle
Cons:Comparative large sizeMust match shape to Circuitry
Circular DomesCircular Domes
RANGE of DOMES
Pros:Readily AvailableLarge offeringArraysLower profileDimpled and Non-DimpledNickel and Tin PlateSmaller Sizes than 4 legged available
Cons:Must be used in multiple layer circuitsLess trip force than 4 leggedLess life expectancy than 4 legged
Triangular DomesTriangular Domes
RANGE of DOMES
Pros:Readily AvailableNarrow or limited space capableMay have mounting feetDimpled and Non-DimpledNickel and Tin PlateHigh trip force available
Cons:Orientation a mustMore expensive
Oblong DomesOblong Domes
RANGE of DOMES
Pros:Readily AvailableNarrow or limited space capableOne or two activation locationsDimpled and Non-DimpledNickel and Tin PlateLarge keys or overpopulated boards
Cons:Orientation a mustMore expensive
Custom Designs of Metal DomesCustom Designs of Metal Domes
RANGE of DOMES
Pros:Creative designsLED friendlyDouble action
Cons:Limited inventory and offeringMore expensive
Why Plated Domes?
AVOID:
Resistance and Corrosion
Problems
Dimpled or Nondimpled Domes?
Dimpled Domes prevent overtravel
and make contact in dusty or less clean
environment
Nondimpled domes specifications are
better and life expectancy more
The contact force (Fc) is the force required to obtain the electrical contact between the dome and the PCB.
The trip force (Ft) is the force required during the cycle of the dome actuation. The rebound force (Fr) is the amount of force required to snap the dome during release
What the heck is this and why should we care?
Tease Effect
Click Ratio= Ft-Fr/Ft
See next slide for explanation
This is a force curve. It defines the force over time addressing the full travel of a dome to full depression and the return or rebound. When you look at a dome defined by this chart it allows you
to compare lot to lot or competitor to competitor.
The top line shows the trip force while depressing the dome and of course the bottom line on the rebound. The marked points
FT – is the trip force – the grams or newtons or ounces the dome is rated at.FC – is the making contact full depression of the dome
FR – is the release pointTC is the travel
The tease effect is based on the thought that a dome can trip and not complete the circuit, there is that extra activation needed.
From a curve we can derive activation force and click ratio/ which can be defined 2 ways – we define it as
FT-FR/FT, there are some that use the FT-FC/FT. This click ratio is important in defining a dome and especially dome quality. It is expressed as a percentage (range) and helps define a good feeling
switch (the higher the percentage).
Force Curve Explained