The document discusses different types of tactile metal domes that can be used for keypads, including their pros and cons. It describes 4-legged, circular, triangular, and oblong domes. It also mentions custom dome designs and the benefits of plated domes. The document explains terms like trip force, contact force, and rebound force. It provides a diagram labeling these forces on a force curve graph to illustrate dome actuation measurements.

1. Tactile Metal Domes
for Keypads
Phil Heft – PEMS Specialist

2. 4 Legged Domes4 Legged Domes
RANGE of DOMES
Pros:
Readily Available
Large offering
Tape and Reel & Arrays
Tubes
Dimpled and Non-Dimpled
Nickel and Tin Plate
Single Side Circuit Capable
Highest Trip Force
Highest Life Cycle
Cons:
Comparative large size
Must match shape to Circuitry

3. Circular DomesCircular Domes
RANGE of DOMES
Pros:
Readily Available
Large offering
Arrays
Lower profile
Dimpled and Non-Dimpled
Nickel and Tin Plate
Smaller Sizes than 4 legged available
Cons:
Must be used in multiple layer circuits
Less trip force than 4 legged
Less life expectancy than 4 legged

4. Triangular DomesTriangular Domes
RANGE of DOMES
Pros:
Readily Available
Narrow or limited space capable
May have mounting feet
Dimpled and Non-Dimpled
Nickel and Tin Plate
High trip force available
Cons:
Orientation a must
More expensive

5. Oblong DomesOblong Domes
RANGE of DOMES
Pros:
Readily Available
Narrow or limited space capable
One or two activation locations
Dimpled and Non-Dimpled
Nickel and Tin Plate
Large keys or overpopulated boards
Cons:
Orientation a must
More expensive

6. Custom Designs of Metal DomesCustom Designs of Metal Domes
RANGE of DOMES
Pros:
Creative designs
LED friendly
Double action
Cons:
Limited inventory and offering
More expensive

7. Why Plated Domes?
AVOID:
Resistance and Corrosion
Problems

8. 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

9.
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

10. 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 point
TC 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