Detailed Embossing
EmbossingSometimes embossing is used over a snap-dome switch, or to create rails on membrane switches. An important benefit is that the rails serve as finger guides to guide the user's finger onto the keypad. This helps prevent accidental actuation of two keys simultaneously.
Embossing is recommended only on .005 through .008 polyester and on polycarbonate up through .010 inches. Some configurations can be embossed through .030 on polycarbonate.
Note: All measurements are in inches.
Tolerances to Remember
Minimum embossing width – .040 through .010 substrates. Thicker substrates may require adjusting.
Maximum height of emboss – 2.5 times the material thickness.
Height tolerance – plus/minus .005
Registration – plus/minus .015 (registration to graphic image.)
Minimum distance between embossed areas – .050
Material Stress Considerations
Embossing will make the sidewalls of the emboss thinner. For example, .010 polycarbonate embossed to .025 will have sidewalls which are .004 at their thinnest spot. PPS cannot accept liability for stress cracks, fracturing or failure of the overlay due to embossing.
Additional variables in embossing may include:
• Configuration of the emboss
• Draft of the sidewalls
• Material
• Emboss height
• Adhesive configuration
• Physical size of part
We recommend that you consult with your PPS representative while in the design phase to make sure your finished part will meet your needs.
Specification and Technical Information for Embossing
Many keyboard overlay applications require embossing of the overlay in order to aid in tactile response, and for the operator to easily locate the keypad. In addition, embossing can be used for a styling effect on overlays and front panels.
The key considerations to keep in mind when specifying embossing are material, embossing dimensions and registration:
Material – Either polyester or polycarbonate overlays can be embossed:
• Polycarbonate will emboss better and retain the emboss better through heat-cycle testing. Polycarbonate can be readily embossed in thickness up to .010 inch, with embossing on heavier materials (up to .020 inch) attainable with certain configurations. The most common thickness for polycarbonate keyboard overlays is .007 inch.
• Polyester tends to lose some embossing height and definition when heated to temperatures of 150° F to 180° F. Polyester overlays are normally either .005 inch or .007 inch, due to the cloudiness that occurs in this material in heavier stock. While both .005 inch and .007 inch are commonly used, .005 inch is somewhat preferable from a fabrication standpoint, and we recommend specifying it if there are no other determining factors.
Note: If overlays are to be subjected to heat-cycle testing, please note this on the blueprint so appropriate materials and processing can be used.
Embossing Dimensions
Embossing Width – We recommend a minimum emboss width of .040 inch on .005 inch and .007 inch material, and .050 inch minimum width if the material is .010 inch. While somewhat thinner emboss widths can be achieved, this tends to distort the surrounding material, excessively stressing the stock in the emboss areas and possibly resulting in eventual fracturing.
Note: If adhesive liner is not zoned away from the emboss area, its thickness must be added to material thickness when determining minimum width.
Emboss Height – We recommend that the emboss height not exceed 2.5 times the thickness of the material (excluding adhesive liner), with the material thickness included in the measurement.
Again, please note that emboss heights that exceed this recommendation can be achieved, but the risk of material failure is increased.
Emboss Spacing – We recommend a spacing between emboss areas of not less than .050 inch. Emboss spacing below these minimums may lead to material failure and/or distortion of the overlay.
Note: All embossing techniques result in thinning of the material in the sidewall areas. This area can be expected to fail first in life cycle testing. If extended cycling is a consideration, polyester is indicated as the preferred base material.
Registration – A tolerance of + or - .010 inch is standard for registration of emboss to printing and emboss to finish cut (perimeter and cutouts). A tolerance of + or - .005 inch can be achieved, but this will result in a higher cost due to increased spoilage and slower running speeds. Emboss to emboss (spacing) tolerance is + or - .005 inch.
Tooling and Artwork for Embossing
Tooling – In general, a matched male/female tool set is needed for embossing overlays. The most common types of tooling are made of brass, plastic, magnesium or combinations of these. Often these plates are heated during the emboss operation.
The variables involved in emboss tooling and in the emboss process include:
• Male/female die clearance
• Angle of draft on tooling
• Die temperatures
• Well time and pressure
The exact specifications are determined by PPS for each application. Because of competitive considerations, these specifications are considered proprietary. PPS has consistently led the industry in developing and implementing embossing techniques.
Artwork – Artwork needed for producing the emboss tool is developed from the base art for the overlay graphics. PPS completes this emboss tooling artwork at the time of the order and remains PPS property.
Additional Considerations
Adhesive Backing –
• If adhesive backing is required on the embossed overlay, the adhesive should either be held back from the embossed areas ( "zoned").
• If adhesive is needed in the keypad area, an adhesive with a polyethylene liner should be specified.
• If standard paper liners are used in the emboss areas, they will tend to separate along the emboss lines making it difficult to remove the liner for application.
Backlighting of Embossed Areas – If embossed areas are to be backlit, it must be specified on the blueprint, since many inks will tend to fracture slightly during embossing. (This fracturing is not visible in non-backlit applications.) If the part is backlit, appropriate processing will be used during production to minimize this problem.
Tolerances – A tolerance of + or - .005 inch is standard on embossing height and width. As previously noted, a tolerance of + or - .010 inch is standard on registration of embossing, and + or - .005 inch on spacing.
Specific Embossing Examples
Please refer to accompanying embossing sample for examples of various embossing techniques.
1. Combination of RIDGE EMBOSS on keys 1, 2 and 3 and PILLOW EMBOSS on other keys aids in locating proper key in a crowded keyfield.
2. "Bright" key uses a RIDGE EMBOSS, "Off" key uses a DOME EMBOSS and PILLOW EMBOSS is used on the "Dim" key to aid in locating proper key in dimly lighted conditions.
3. EMBOSSED LED WINDOWS improves visibility from a wide range of viewing angles – The embossment in effect becomes a lens.
4. RIDGE and PILLOW EMBOSS combined on same key gives both positive tactile response and assistance with location.
5. LED indicators are included in keyfields for visual feedback.
6. Standard PILLOW EMBOSS stresses base material the least and allows room for tactile feedback hardware.
7. Keyfields are connected by a common RIDGE EMBOSS for styling effect. This is often referred to as WINDOW - FRAME or LADDER EMBOSSING, and is often used when spacing on keys approaches minimum to avoid overstressing of material.
8. PILLOW EMBOSS is used with contrasting keyfield colors for styling effect.
9. RIDGE EMBOSS is used on only three sides of key for styling effect.
10. Combination DOME EMBOSS and RIDGE EMBOSS is used, plus LED indicator window.
Also note how embossing has been used purely for styling effect at both top ("EMBOSSING") and bottom ("QUALITY PARTS, etc.").
Important Do's and Don'ts
1. DO stay within recommended minimums/maximums whenever possible to reduce cost and improve reliability.
2. DO specify on your drawing any special considerations such as heat cycle testing, backlit areas and extended life-cycle testing.
3. DON'T forget that embossing can be used for styling effects as well as for more functional purposes. If you already have embossing on the part, the additional cost of doing this is negligible.
4. DO feel free to contact us with any specific questions about embossing. Each overlay is unique, and we are pleased to consult with you at the design phase.
5. DO consider PPS first when it comes to embossed overlays, as well as all your overlays and front panels. We know what we're doing, and can ensure you get the results you want!
