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