Epec offers keyboard design and assembly technologies that support the selection of the best keyboard style for every application in any industry. Each core technology has features and advantages that we will compare in order to aid you in the best selection for your specific application. Epec brings solid engineering solutions based on proven designs and experience with a reputation for technical support, customer service and quality second to none in the industry. Our AS9100 facility enables us to manufacture ruggedized military and aerospace keyboards and keypads with expertise including integration of all kinds of switches and input devices, displays, indicators, meters, interface electronics, cable assemblies and case housings, whether they are metal or plastic.

1.  DELIVERING QUALITY SINCE 1952.
High Reliability Keypad
Design and Assembly
09.26.13

2. 2
Topics Covered
 Target Markets
 Terms and Definitions
 Basic Core Switch Technology
 Factors That Can Help or Harm Long-term Performance
 Extending Electrical and Mechanical Operating Life

3. 3
Target Markets
 Target markets are end applications requiring critical-mission
performance, long service life, or capital equipment applications where
the cost of the keypad assembly is a tiny portion of the equipment cost
and expected service life.
 Markets that are not considered target markets are applications where
the cost of the keypad is a large portion of the application cost or the
application service life is very short such as “throw-away” electronics
or applications with rapid obsolescence.

4. 4
Target Markets
 Target Markets
– Military Electronics
– Satellite Communications Ground Support Equipment
– Mobile Communications
– Medical Electronics
– Electronic Test Equipment
– Larger Process Control Equipment

5. 5
Terms and Definitions
 Single Pole Switch
– A simple on-off switch with two terminals or contacts which are either
connected together (closed switch) or disconnected from each other (open
switch). Each single switch is also called a “pole”, so the symbol shown is
a single pole switch.
 Normally Open Switch
– Switch terminals or contacts that are not connected when the switch is not
pressed or actuated. Tactile metal dome switches are all normally open
switches.

6. 6
Terms and Definitions
 Contact Bounce
– Unwanted circuit noise caused by the switch mechanism. When the
contacts strike together, their momentum and elasticity act together to
cause the switch contacts to bounce apart one or more times before
making steady contact. The result is a rapidly pulsed electric current
instead of a clean transition from zero to full current. The effect is usually
unimportant in power circuits, but causes problems in some logic circuits
that respond fast enough to misinterpret the on off pulses as a data‑
stream.

7. 7
Terms and Definitions
 Switch Array
– A group of switches connected together in a scheme to minimize the
number of switch terminal connections for interfacing with electronics.
Common switch arrays are “common pole” and “Row-Column matrix” or X-
Y matrix”.
– Common-connected switch arrays have one
switch terminal from each switch connected
to a common circuit and the other switch
terminals are connected individually.

8. 8
Terms and Definitions
 Row-Column
– Or X-Y matrix arrays have switches connected where switches share
interface circuits but no two switches share the same two interface circuits.
X-Y matrix arrays decrease the number of required interface circuits for a
larger number of switches.

9. 9
Terms and Definitions
 Logic-Level Circuit Switches
– Resistive only switching with open circuit voltage less than 30 volts and
closed circuit current less than 20 milliamps. Tactile metal dome switches
are not suitable for high voltage, high current or capacitive or inductive
loads. Logic level switches can control power circuits but require suitable
buffering.

10. 10
Terms and Definitions
 High Reliability Low-Profile Keypads
– A keypad assembly using tactile metal dome switches providing
momentary, normally open switches in an environmentally sealed switch
array with suitable interface connectors and finished with graphic overlay
or silicone molded rubber boots. Keypads can include shielding, displays,
discrete LEDs, backlighting, other electronics and mechanical hardware
such as studs.

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Basic Core Switch Technology
 Core Switch Technology revolves around tactile metal dome switches
with supporting structure and esthetic touches designed for long
service life while looking like the keypad assembly belongs in the
application.
 Switch domes were developed in the early 1970s for consumer
electronics requiring a low-profile, long life keypad including hand-held
electronic calculators and television onset and remote controls.

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Basic Core Switch Technology
 Virtually all switch domes in use today are stamped from high tensile
strength stainless steel for predictable mechanical life.
 Properly designed keypad applications using tactile metal switch
domes have very low closed switch resistance, very high open switch
resistance, and very low closing and opening switch contact bounce.

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Basic Core Switch Technology
 Dome switches provide tactile snap because the stainless steel has
high tensile strength and the stamped dome shape defines the applied
force versus tactile snap (force-deflection curve).

14. 14
Performance Factors
 Factors That Can Harm Long Term Performance
– Non-conductive oxides forming on the tactile metal dome switches
– Non-conductive oxides forming on the printed circuit board pads directly
under the tactile metal dome switches
– Outside contaminants entering into the switch dome cavity
– Exceeding switch dome voltage
or current limits
– Dome switches controlling circuits
other than resistive loads
(no capacitive or inductive loads)

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Performance Factors
 Non-conductive Oxides Forming on the Tactile Metal
Dome Switches
– Virtually all tactile metal dome switches available today are stamped from
stainless steel alloys.
– All stainless steel alloys contain a small amount of chromium in the alloy.
Chromium reacts with oxygen in the air and forms a thin layer of chromium
oxide on the surface of stainless steel.
– The chromium oxide is transparent so you cannot see it. This oxide layer
seals the iron particles in the stainless steel from the oxygen in the air so
that there's no formation of iron oxide (iron rust). This action is what
makes stainless steel "stainless.” However, chromium oxide is also
nonconductive – big problem for any switch. Chromium oxide can be
temporally worn off by dome switch use but quickly forms again.

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Performance Factors
 Non-conductive Oxides Forming on Printed Circuit
Board Pads Under Tactile Metal Dome Switches
– Printed circuit board plating or finishes over copper other than gold will
form oxides or will not be flat as required for proper dome switch
operation.
 Outside Contaminants Entering the Switch
Dome Cavity
– Any airborne contaminants such as dirt, dust, lint or dissolved
contaminates in liquid form must not enter the switch dome cavity as
virtually all contaminates are non-conductive.

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Performance Factors
 Exceeding Dome Switch Voltage or Current Limits
– Exceeding dome switch open circuit voltage of 30 volts or closed circuit
current of 20 milliamps quickly deteriorates the switch contact surfaces
and causes pitting.
– Contact pitting increases contact resistance, intermittent operation and
over-heating.

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Performance Factors
 Dome Switches Controlling Circuits Other Than
Resistive Loads (No Capacitive or Inductive Loads)
– Non-resistive switch dome loads causes switch contact surface pitting
faster than exceeding voltage and current limits.

19. 19
Performance Factors
 Solutions to Factors That Can Harm Long Term
Performance
– Prevention of Non-conductive Oxides Forming on Tactile Metal Dome
Switches
• The best solution is gold plated metal dome switches for prevention of
chromium oxide.
• The problem with standard gold plating process is the hydrogen-based plating
chemistry causes hydrogen embrittlement in the stainless steel that
dramatically reduces the mechanical life of the dome switches.
• Our proprietary gold plating process does not use hydrogen-based plating
chemistry, prevents chromium oxide on surfaces of stainless steel metal dome
switches and does not affect mechanical life.
– Prevention of Non-conductive Oxides Forming on Printed Circuit
Board Dome Switch Pads
• Gold plated printed circuit boards are necessary for the longest performance.

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Performance Factors
 Solutions to Factors That Can Harm Long Term
Performance
– Stopping Outside Contaminants Entering the Dome Switch Cavity
• Printed circuit boards used with metal dome switches must be designed to
prevent printed circuit board vias under or near dome switches from acting as
outside air vents. Many commercial industry custom keypad manufacturers
purposely place printed circuit board vias under the dome switches to make
construction easier and maximizing the dome switch tactile feel.
• Design and construction techniques allow Suncoast Digital Technology to
internally vent the switch cavities without venting to the outside atmosphere.
• Dome switch cavities need to be environmentally sealed for best long term
performance.

21. 21
Performance Factors
 Solutions to Factors That Can Harm Long Term
Performance
– Stay Within Dome Switch Voltage and Current Limits and Using Only
Resistive Loads
• Logic-level tactile metal dome switches should only interface with CMOS or
high impedance circuits at logic-levels to prevent contact surface pitting.
• Dome switches should never directly control reactive loads such as discharging
capacitors or switching inductive loads..

22. 22
Performance Factors
 Other Design and Manufacturing Characteristics of
High Reliability Keypads
– Most high reliability custom keypad assemblies require shielding from
internally or externally generated RF energy, or electrostatic discharge.
– Shields can be incorporated into keyboard designs and must be positioned
between the user’s finger that pushes against the switches and all circuitry
below including the dome switches.
– Electrostatic discharges follow the path of least resistance from a charge
contained on a user's finger to earth or chassis ground. It is imperative
that this discharge path be intercepted prior to entering any of the keypad
and electronic circuitry including the tactile metal dome switch.
– Shield selection and termination methods must consider RF frequency and
level of interference attenuation required. At the same time, the shield
material must be flexible to allow the dome switch to operate properly
while preserving tactile feel.

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Performance Factors
 Other Design and Manufacturing Characteristics of
High Reliability Keypads
– Best tactile feel for unambiguous switch operation for the end-user
requires that the tactile feel of the raw dome switch is not diminished by
the keypad’s construction methods and materials.
– Materials between the dome switch circuitry and the user's finger and
sealing the dome switch cavities can reduce the tactile feel.
– Overall keypad design and construction must be coordinated with the
customer’s engineering staff for
successful user interface products.
– All of these factors must be dealt
with as a combination instead of
individual parts to preserve the
best tactile feel.

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Our Products
Battery Packs Flex & Rigid-Flex PCB’s User Interfaces
Fans & Motors Cable Assemblies Printed Circuit Boards

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Design Centers &
Technical Support
 Battery Pack & Power Management – Denver, CO
 User Interfaces – Largo, FL
 Fans & Motors – Wales, UK
 PCB’s – New Bedford, MA & Shenzhen, China
 Flex & Rigid Flex – Toronto, Canada
 Cable Assemblies – New Bedford, MA
 Our Engineering and Design teams are ready to help
our customers create world class and cost effective
product solutions.

26. 26
Q&A
 Questions?
– Enter any questions you may have
in the Control Panel.
– If we don’t have time to get to it, we
will reply via email.

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Thank You
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