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Silicone Dynamics, Inc.

Custom Silicone Rubber Keypad Manufacturer

Custom Design & Manufacturing of Silicone Rubber Keypads

basic silicone keypad design

Figure 1. Basic Silicone Rubber Keypad Design.

With the advent of technology, silicone keypads have become an integral part of the electronics industry. As it is a low cost and versatile material, silicone rubber has been the ideal material for keypads. Silicone rubber compounds boast of their organic and inorganic properties that makes it a superior material for some electronic parts that must have special features. Compared to organic rubber, silicone rubber is significantly better in heat/cold resistance, weatherability, electrical insulation and conductivity, flex fatigue resistance and tear strength.

Cost-Effective

In various manufacturing and high-end processing applications that call for high quality and cost-effective production, silicone rubber comes in as the safest bet. This is due to the fact that this elastomer could be utilized in a range of formulations for molding, curing and manufacturing. This flexibility will empower businesses to streamline processing of their products as they will be assured of consistent quality production.

Property/Material

Nitrile

EPDM

HNBR

Hypalon

Natural
Rubber

Neoprene

PVC/NBR

Pure
Silicone

Silicone

Blend

Urethane

XNBR

Tensile Strength

F

F

E

G

G-E

G-E

G

P

F

E

E

Hardness Range

20-100

25-90

45-98

45-85

30-100

10-95

20-80

35-95

40-90

10-100

45-95

Relative Cost

E

E

P

G

E

G

E

F

G

F

G

Max. Service Temp (°F)

250

350

350

300

212

250

250

500+

400

212

275

Ozone Resistance

P

E

E

E

P

F-G

G

E

E

E

P

Cut Resistance

F

F

E

F-G

G

G

F

P

F

E

E

Abrasion Resistance

F-G

F

E

G

G-E

G-E

G-E

P

F

E

E

Tear Strength

F

F

E

G

G

G

G

P

F

E

E

Resistance To: 

Compression Set

F-G

G

G

F

F

G

P

E

G

F-G

F

Heat Build Up

P

F-G

G

P-F

E

E

P

G-E

F

E

P

ASTM #1 Oil

E

P

E

F-G

P

F-G

E

G

P

E

E

ASTM #3 Oil

E

P

E

F

P

F

E

F

P

E

E

Reference Fuel B

G-E

P

G

P

P

F

G-E

P

P

E

G

Ketones: MEK

P

E

F

F

E

F

P

F

E

P

P

Aromatics: Toluene

G-E

P

E

P

P

P-F

G

P

F

E

G

Aliphatics: Hexane

E

P

G

G

P

G

E

P

P

E

E

Ethyl Acetate

P-F

E

P

F

E

G

P

G

G

P-F

P

Cellosolve

F

E

F

G

E

E

P

E

G

P-F

F

Methylene Chloride

P

P

G-E

P

E

P

P

F

F

P

P

Trichloroethylene

P

P

G-E

P

P

P

P

P

F

P

P

Diethylene Glycol

E

E

G-E

E

E

E

E

E

E

G

G

Isopropyl Alcohol

G-E

E

E

E

E

G-E

E

G

E

G

G-E

Water (75 °F)

G

E

F

E

E

G

G-E

G

G-E

G

G

Caustics: 10% NaOH

G-E

G-E

G-E

E

E

G-E

G

E

G-E

P

G

Acids: H2SO4

 F

E

G

E

G

 G

 G

F

 G

P

G

*Legend:  

E =

Excellent

G =

Good

F =

Fair

P =

Poor

  Table 1. Chart Comparing Different Elastomer Properties

Versatility

With silicone rubber, there is virtually a limitless range of design possibilities. The compound itself is highly praised for its extraordinarily versatile and useful properties that can be maximized by engineers and product developers. As it easily flows and could be injected into durable and pliable parts, silicone rubber tend to be extruded, molded or pressed with the implementation of lower energy leading to the simplification of the production process.

design options for silicone keypads

Figure 2. Versatility in Design of Silicone Rubber Keypads.

Compared to organic rubber which is less heat and chemical resistant, silicone rubber even possesses fast curing properties that can make production efficient in terms of industrial packaging and assembly. Manufacturers even have the choice whether to benefit from a ready-to-process compound to generate their products or they can enhance silicone rubber by combining it with another compound for a special product that can withstand stringent technical specifications. With its versatile qualities, silicone rubbers has become indispensable base material in applications that require sophisticated and complicated capabilities. Rising new markets in technology can take full advantage of silicone rubber for its qualities as it can be suitable for innovative solutions in different industries, like in medical, manufacturing, automotive and communications.

Safety

Silicone rubber does not promote microbial growth. Studies have proven that silicone is safe to use even for children’s toys as it can be tear resistant, water resistant, pleasing to touch, easy to color and these toys can be sterilized at high temperatures without compromising its appearance. This material is also odor-free, hypoallergenic and does not contain animal-derived ingredients that makes it safe for medical devices too.

Extreme Properties

Properties

Non-Conductive Silicone Rubber

Temperature for use

-67 °F – 482 °F (-55 °C – 250 °C)

Specific Gravity

1.15

Tensile Strength

90 kg/cm2

Tear Strength

13 kgf/cm2

Compression Set

10% (180 °C x 22 hours)

Elongation at Break

350%

Volume Resistivity

8 x 1014 ohm-cm

Contact Resistance

Insulation Breakdown

24 kV/mm

Color

Unlimited color possibilities

Dielectric Constant

4.2 (50 Hz)

Dielectric Tangent

50% (50 Hz)

*Depending on the size of contacts and keyboard layout

Table 2. Silicone Rubber Mechanical and Electrical Properties

Almost nothing compares to the unique performance of silicone rubber as a compound. Unlike other polymers, silicone rubber has excellent weatherability, chemical resistance and electrical properties that makes it the best material for keypads used in extreme conditions. You can use it to control machinery that produce high heat. Or in an instrument that you can use outdoors that can withstand UV radiation, rain, cold or humid weather. In fact, it can even withstand extreme pressure that it is used as the gasket for pressure cookers. Most of all, it has an excellent bending fatigue where it can outlast several squishing, bending and other stress tests allowing it to be the superb choice for keypads that need these capabilities.

Aside from its somewhat invulnerability to wear and tear, silicone rubber can adapt to any color you wish. Unlike organic rubber which tends to be black or yellow, silicone rubber can be translucent to any shade of color. This is why LED lights can be used to widen the capabilities of user interface as it can be employed in devices that can be used in the dark.

Inside the Silicone Keypad

Acting as the most functional part of a switch, the silicone keypad provides the electrical contact from the user to any device. As it combines the smooth feel and the durability of silicone rubber to withstand several hundred thousand actuations without failure, the keypad relies on a great diversity of contact systems beginning from gold pills actuating tactile metal domes to carbon pills — which are the most common type of contact. There can be two common methods of mounting silicone rubber in a membrane switch assembly. The first one is placed in a mounting rubber actuator where double-sided pressure-sensitive silicone rubber adhesive is employed on a holder on one side and the applicable mounting adhesive is applied to the other. The second mounting method incorporates a simple pull-through molded into the rubber itself. The pull-through is then “pulled” through a printed circuit board substrate, where an interference fit protects the rubber component into the assembly.

Force-Stroke Curve Graph

Stroke

S1 – Peak Stroke

S2 – Contact Stroke

 

Force

FP – Peak Force

FU – Maximum Return Force

FC – Contact Force

FR – Minimum Return Force

FM – Maximum Return Force

FD – Drop Force (FD = FP – FC)

FG – Drop Force (FG = FP – FM)

Location

O – Original Point

P – Peak Point

R – Return Point

C – Contact Point

M – Maximum Return Point

Travel

O – P – Peak Force (FMAX)

C – S – Minimum Return Force

S-R-M-O – Gap Force (FG = FP – FM)

Figure 3. The Force – Stroke Curve of Silicone Rubber Keypads.

 

Structure

rubber keypad 1

rubber keypad 2

silicone rubber keypad 3

silicone keypad 4

silicone rubber keypad 5

silicone rubber keypad 5

Force-Stroke Curve

force stroke curve 1

force stroke curve 2

force stroke 3

force stroke curve 4

stroke force curve 5

force stroke 6

Force Range (grams)

30 to 350

30 to 250

30 to 150

30 to 80

30 to 200

20 to 80

Stroke Range (mm)

0.5 to 3.0

0.7 to 2.5

0.5 to 3.0

2.0 to 4.0

1.0 to 2.5

0.2 to 1.0

Life Cycle (x 103)

500 to 2,000

500 to 2,000

1,000 to 3,000

5,000 to 20,000

500 to 3,000

500 to 10,000

Common Usage

Automotive, calculators, radio, toys, telephone, remote control, etc.

Calculators, game pads, toys, telephone, remote control, etc.

Measuring instruments, office machines, toys, telephone, remote control, etc.

Computer keypads, typing machines, etc.

Typing pads, testing instruments, telephones, etc.

Computers, remote controls, calculator, typing pads, etc.

Table 3. Common Constructs of Silicone Rubber Keypads and Their Characteristics.

Silicone rubber keypads can be customized for various uses. The standard silicone keypads should deliver a tactile and mechanical feedback when gently pressed. Typical silicone keypads are supposed to have medium actuation force (150g to 250g), a standard snap (25% to 35%) and a standard stroke (1mm). These keypads are the most useful bargain between good tactile feedback and durability. Most keypads could performing at 100,000 presses before they are unusable. Some permutations of high force and high snap could reduce the life span of a silicone keypad. The ideal shape of a keypad for optimal performance is square or round as it distributes the forces inside the radius. Shapes with unequal length and width can be prone to rocking, which can ultimately affect electrical contact and the command will not be transmitted into the device. In this case, pins or pills are used in order to maintain the effectiveness of the keypad.

Silicone Dynamics has the capability to assist your silicone keypad needs with free engineering advice to your designs. Even if you have difficulty in coming up with effective keypad designs, you can delegate this task to an engineer from Silicone Dynamics who will design your keypads for an affordable rate.

For a detailed look at our silicone keypads, we encourage you to download our Free Design Guide. If you already have a project ready for production, we can guide you on a route that is most beneficial to you. We can do production tooling as well as prototype tooling. All you have to do is Request a Quote and we can begin working with you on your project.