Rubber Keypad Application Guide
When look, feel and performance count, Epec is your global source for rubber keypads.
The Application Guide is an aid in the design and development of silicone keypads and specialty products. Silicone combines excellent feel, reliability and long life in the most rugged environment. Silicone keypads are used in a wide range of applications including medical, industrial, instrumentation and communications equipment.
The Application Guide includes:
- Material and Processes
- Mechanical Tolerances
- Graphics Criteria
- Design Recommendations
- Drawing Information
Silicone material is supplied to the keypad industry in two forms, liquid and gumstock. Liquid silicone is a two part system mixed as it is used; gumstock is a one part system that has a shelf life. Both are heat cured. Liquid silicone has the consistency of vaseline while gumstock is more like putty or clay. Silicone is measured for hardness in a shore A scale. The lower the number, the more silicone there is in the product and the softer it feels. The higher the numbers the less silicone and the more filler there is in the product and the harder it feels. Fillers and tensile strength.
Molding silicone rubber varies by process. The tools themselves are very similar and are usually made from P20 steel or 6061 aluminum. Wear on the tooling is usually negligible over the life of a project unless fillers that cause abrasion are added.
The types of molding processes are liquid, compression, transfer and extruding. Liquid molding is a closed loop system and molded under pressure using computer controlled repeatable equipment. Compression molding is open-air system similar to a waffle iron, material is hand cut and weighed. Transfer molding is a combination of compression molding and gumstock material pushed into a mold under low pressure. Extruding molding uses gumstock molding processes for continuous product such as tubing.
Epec design options include:
- Custom Shapes and Surface Finishes
- Various Key Travel and Actuation Forces
- Wrap Around Designs
- Back Lighting, Light Pipes and Clear Windows
- Sealing Features
- Insert Molding
- Distance of a key's diaphragm to the edge of the keypad's matte and any through hole is 0.040"
- Minimum key pitch dimension is 0.080"
- Distance between two diaphragms is 0.040" (measured at base of diaphragm)
- The smallest blend radius of key's side wall to top of key is 0.010"
- Typical key taper is ± 1° depending on key height
- Typical chamfer dimension on tactile keypad is 0.020"
- Typical chamfer angle on tactile keypad is 45
- Clearance between a bezel to a key is 0.012"
- Typical base (matte) thickness is 0.040"
- Standard air channel geometry is 0.080" to 0.125" wide by 0.010" to 0.013" deep
- Conductive contact area is 0.030" based on keypad application and size
- Sealing bead(s) top and/or bottom for environmental design requirements
- Assembly aids via rattails and/or perimeter lip to hold rubber keypad to feature
- Through hole diameter is 0.025"
- Corner radius on matte and key's 0.015"
- Corner radius on matte and key's 0.015"
Display/ LED lightpipe/ Window opening:
- Maximum depth of undercut for feature window opening is 0.250"
- Underside lip for window opening is the depth of undercut(#14) x 0.660"
- Minimum size for molded in silicone window/lightpipe is 0.060"
- Minimum thickness for molded in silicone window is 0.030"
- Minimum height for molded in silicone lightpipe is 0.030"
- Minimum distance from window/lightpipe to and edge is 0.030"
- Min / Max. wrap around underside is 0.060" to 0.500". Deeper wraps may be considered depending on design
- Sealing rib diameter is 0.030"
Keypad Wrap - Around Design:
- The wrap-around design offers unique capabilities in silicone rubber. Using liquid injection process, one can create hand held units similar to complete plastic cases. With the wrap-around feature, an appealing product can be designed with all the protection requirements for harsh environments.
Typical Part Tolerances
|0.401 - 0.800||0.006|
|0.801 - 1.200||0.008|
|1.201 - 1.600||0.010|
|1.601 - 2.000||0.012|
Digital Mechanical Designs
Epec has the capability to accept 2D and 3D solid modeling designs created with software like Autocad, ProE, Solidworks and using several file type formats including:
|Accepted File Types|
All positive and reverse graphics are surface printed using proprietary silicone inks that are cross-link bonded to the keypad during the curing process. Screening can be done on both sides of keypad when using clear silicone. Each graphic color represents an additional step in the manufacturing process. Also, Pantone numbers are used for specifying colors, but color chips can be matched.
Special attention must be given to keytop design when screening graphics on curved surfaces. Generally, the larger the curvature radius is the better. Also, single curvature geometry is easier to print on than compound curves.
Digital Graphic Designs
Epec has the capability to accept graphic designs created with software like Adobe Illustrator, Corel Draw, Micrograph, Autocad and using several file type formats including:
|Accepted File Types|
Recommended Graphic Parameters
- Solid colors can be screened up to the edge of flat keytop
- On curved keytops, solid colors can be screened up to 0.015" to the tangent point of the outer radius
- Distance from edge of the keypad to legend is 0.015"
- Distance of matte legends to key is dependent on key height
- Minimum line weight for legends is 0.007"
- Minimum text height is 0.050"
- Color consistency is within 1 Delta for production run
- Typical screening tolerances is 0.015"
Keytops Considerations for Graphic Screening
- Minimum radius allowable for printing over the edge is 0.375"
- On legend overrun onto matte surface, a minimum transition radius of 0.010" is required
- Maximum curvature depth for concave keytops with a minimum radius of 0.375" is 0.060"
- Maximum curvature height for convex keytops with a minimum radius of 0.375" is 0.060"
Typical Drawing Information
- Overall Keypad Size
- Keypad Mat Thickness
- Keytop Dimensions
- Mounting Hole Details
- Mounting Boss Details
- Radii Dimensions (keypad and buttons)
- Key Spacing
- Actuation Force (grams)
- Material Specifications (durometer)
- Legends & Color(s) (PMS numbers, etc.)
- Keypad Color
|F = Return Force|
|A = Actuation force||A = 350 grams|
|C = Contact force||C = 230 grams|
|Snap Ratio = (A-C)/A)||(350-230)/350=0.343)|