Sealing Methods for Rubber Keypads

Sealing Methods for Rubber Keypads

When designing a product, one of the most critical considerations is sealing requirements. A properly sealed product prevents unwanted substance intrusion into the device. While internal components (most importantly electronics) are typically protected by the main enclosure, it is equally important that the keypad or interface area is also properly designed and sealed. Any weak-points related to the HMI or HMI area, can potentially allow for ingress of dust, liquids, and other substances that can cause permanent damage to the product. 

The good news is that there are a few methods that can be designed into the HMI to completely prevent particulate ingress. Below are some of the most common types of sealing methods used in our keypad designs:

Perimeter or Frame Seal: One of the most common methods of sealing, this method involves designing a frame of adhesive that goes around the perimeter of the keypad preventing any liquid or chemical ingress. Because it requires a specific amount and type of adhesive for an effective seal, the available space on the bezel and under the overlay is an important consideration. It is also important that there are no components on the edge of the keypad in order to accommodate this frame of adhesive.

Compression Seal: When using a rubber keypad design, the elastomer can act as an excellent seal as it has great compression and gasket-like characteristics. The silicone rubber is molded to be compression sealed to the front of the part or compressed from the sides into a well where the keypad sits. The compressed rubber offers a high level of protection from liquids and chemicals.

Wrap Around Seal: When using a rubber keypad design, the silicone rubber can be designed so the rubber actually wraps around the edge of the part, sealing off the front and edges of a device. The rubber wraps around the keypad’s internal layers, keeping the circuitry safe from any particulate ingress.

Front Surface Seal: If there are any openings in the front of the product’s bezel or case (typically around the perimeter of the part), front surface sealing can be an effective option. A sealant compound is dispensed into any openings or gaps in order to prevent particulates or liquids from entering. This is typically a “last resort” type of option, as the sealing process can be labor intensive and the final outcome not as aesthetically pleasing with a potting compound around the perimeter of the keypad. 

Rear Surface Seal: Rear sealing involves sealing any openings behind the keypad, typically around tails or cables that come through the rear housing of the device.

Perimeter Seal
Compression Seal
Wrap Around Seal

Designing a Sealed & Backlit Rubber Keypad​

Designing a Sealed & Backlit Rubber Keypad​

Designing a rubber keypad that is both backlit and completely sealed may seem like a daunting task, but that’s what the experts at CSI are here for!  There are essentially two main components of the keypad assembly that must be properly designed: the rubber and the circuit. To better speak to the process, we will use the sample keypad on the right side of this post.

 

Rubber Decorating Process:

  1. The rubber starts off as a clear/milky translucent color (the color of the base material). The black portions of the keypad are rubber light blocks that are molded into the rubber to prevent light from bleeding into other portions of the keypad.
  2. The rubber is then sprayed translucent white.
  3. The rubber is then sprayed opaque black and then laser etched down to the translucent white material (for the power button) and hte clear base material (for the LED indicators) in the areas that are backlit.
  4. The rubber is carefully designed so that the actuators on the back of the keys press into the metal dome switches efficiently. 
  5. The rubber is also designed so that it provides a seal. Silicone is typically used for gasketing in many products, so why not utilize it’s properties for the same reasons in your keypad?!
  6. The rubber is then sprayed with a UV resistant coating that protects the keypad from ultraviolet exposure, while also providing chemical resistance. 

 

Additional Sealing Features:

Copper Flex Circuitry, also known as polyimide Kapton circuitry, are used in the majority of CSI Keyboards’ keypad designs due to its excellent dielectric strength, thermal stability, chemical resistance and flexibility. Copper Flex membrane switch panels are produced using polyimide (Kapton) as the base material. Copper flex switches are manufactured by laminating a thin sheet of copper to a flexible film substrate. The copper is then chemically etched away, leaving the copper traces. An additional layer of polyimide is laminated to the circuit leaving the gold contacts exposed. Copper flex has become the superior choice over printed silver especially for outdoor applications. Copper flex circuitry construction designs offer a significant advantage over printed silver and a printed silver circuit can be replaced with a copper and polyimide construction with minimal additional cost.

Seal Frame is a perimeter frame of adhesive that protects your circuitry from any moisture ingress. It have proven to be as robust as other sealing methods such as perimeter temperature sealing and can be included in your design at minimal additional cost.

PU (polyurethane) Coating was applied, which protects the printed and molded colors on the rubber keypad, and also increases the longevity of the printing and graphics. This coating ensures a longer keypad life regardless of the environment. We also utilize a proprietary coating specially formulated for marine and outdoor applications which provides added protection against UV exposure.

Rear 3M 300LSE Adhesive was utilized, which is the top of the line adhesive specially formulated to provide high bond strength to surfaces. Our adhesives are resistant to humidity, UV, water, temperature, and chemicals.

EMI/RFI and ESD Protection is obtained using a metalized Mylar shield layer. A separate tail for the shielding layer was designed to connect to the housing or another mechanical piece already grounded. Another option could have been grounding to a trace on the interface panel and then routed to a grounded plane on the motherboard to carry the static charge away from any nearby conductive components.

CSI Develops Heavy Duty Military Keypad

CSI Develops Heavy Duty Sealed Military Keypad

Product: Heavy Duty Military Keypad

Case: Customer approached CSI requiring an environmentally sealed keypad solution that would not only be able to withstand constant outdoor usage, but more importantly withstand exposure to mustard & sarin gas. 

CSI Final Solution:

  • Liquid-Injection Molded Santoprene (mustard and sarin gas resistant) with debossed graphics and LED indicators
  • 100% environmentally sealed keypad that passes all of the customer’s requirements including mustard and sarin gas resistance.
  • Metal dome switches with LED indicators with additional customer electronics/components integrated into the circuit
  • Copper flex circuit for additional environmental durability
  • Stainless steel backer for rigidity

What are UV Resistant Coated Membrane Keypads?

What are UV Resistant Coated Membrane Keypads​

Many of the user interface products designed and manufactured by CSI will eventually live in extremely harsh environments. Some being exposed to UV exposure from the sun for days, months or even years at a time. Luckily, there are methods to protect the keypad from the effects of the sun. One of these methods is using a UV Resistant Coating. 

A UV resistant coating is typically applied to the keys. The coating is glossy in appearance and looks very similar to epoxy coatings that were once used on membrane switches. The major difference between the UV resistant coating and the epoxy coating however, is that the epoxy was not durable. Over time, the epoxy not only became embrittled but it tended to discolor and yellow. 

The UV resistant coating is designed with special barrier resins and compounds that are activated with ultraviolet light. Once activated, they prevent any damage from occurring to the coating or the base material of the keypad.

The UV resistant material’s  “glossy-like” look also enhances the appearance of keypads. The glossy and clean look of the material really makes the product snap and stand out. Between the UV resistant benefits and the enhanced aesthetics, using the UV coating is really a no-brainer when designing a keypad that is going to be used outdoors. 

CSI Develops Heavy Duty Sealed Keypad

CSI Develops Heavy Duty Sealed Keypad

Product: Mounted on the outside of an auxiliary vehicle exposed to: water, dust, dirt, ice, rock bombardment, etc.

Case: Customer approached CSI with a keypad that was failing out in the field.

Product Issues:

  • Keypad failing out in the field due to moisture ingress
  • Domes collapsing
  • Graphic overlay fading from UV exposure
  • Lack of tactile response when pressing keys
  • Keypad peeling off of surface
 

CSI Final Solution:

  • 100% Environmentally Sealed Keypad (as a standalone part)
  • Durable and Ruggedized Rubber Keypad Design
  • UV Resistant Keys
  • Improved the Design & Tactility of Keys
  • Upgrade Rear Adhesive for Stronger Adhesion to Surface

Designing a Waterproof (IP67) Membrane Switch

Designing a Waterproof (IP67) Membrane Switch

Many customers reach out to CSI Keyboards with a waterproof IP67 requirement for their membrane switch or user interface. CSI utilizes a few different design techniques in order to waterproof a membrane switch which include utilizing a frame seal gasket, the use of copper flex circuitry, and the use of high performance adhesives. There are other methods and ways of waterproofing that can also be integrated into the design, but the frame seal, the type of circuitry and the adhesive used are the foundation to ensuring that your keypad is environmentally sealed. 

Frame Seal Gasket:
 

The Achilles heel for membrane switch sealing is most always the flex tail breakout area. The tail typically breaks out of the rear of the switch and because the tail is made of the same material as the circuit, a filler piece replaces the ribbon cable shape in the materials of the membrane switch. The gaps on either side of this tail filler is typically where moisture can enter the membrane switch.

A gasket or perimeter seal frame design can solve this problem. A membrane switch with a gasket or perimeter seal does not have a tail filler therefore there is no direct pathway for liquid ingress. CSI Keyboards’ perimeter seal frame switches have proven to be as robust as other sealing methods such as perimeter temperature sealing and can be included in your design at minimal additional cost.

 

  • Construction Concept: Setting the membrane switch circuit within a frame seal gasket, protecting it from the environment.
 
  • Width & Thickness: The thickness of the membrane switch whereby the switch layer printing thickness also taken into consideration, should flush with the gasket making them even as a whole. One whose height is greater than the gasket will budge & cause delamination over time between the product & the interfacing panel, eventually water leakage. The width of the frame seal gasket is also a critical factor dictating the strength of water immerse pressure protection.
 
  • Gasket Adhesive Tape Selection: Not neglecting the gasket, industrial closed cell foam carrier tapes are among the options providing superb adhesion strength.
 
  • Enhancement: For an even more stringent environmental requirement, the conductive printed PET can be substituted with a double-sided through-hole, single conductive print design where the insulator between the two conductive print is the substrate itself, posing an advantage over the insulating dielectric print depreciation between conductive prints of a single sided design when functioning in a high humidity environment.

Copper Flex Circuitry:

CSI Keyboards uses copper flex circuitry in the majority of our custom keypad designs due to its excellent dielectric strength, thermal stability, chemical resistance and flexibility. Copper flex, also known as Kapton circuits, have become the superior choice over printed silver especially for outdoor applications. 

A printed silver circuit can be replaced with a copper and polyimide construction with minimal additional cost. Copper flex circuitry construction designs offer a significant advantage over printed silver. Additional information on the benefits of copper flex circuity can be found here: Benefits of Using Copper Flex Circuitry vs. Printed Silver.

Copper Flex membrane switch panels are produced using polyimide (Kapton) as the base material. Copper flex keypad switches are manufactured by laminating a thin sheet of copper to a flexible film substrate. The copper is then chemically etched away, leaving the copper traces. An additional layer of polyimide is laminated to the circuit leaving the gold contacts exposed.

How to Protect a Membrane Switch from UV Exposure

How to Protect a Membrane Switch from UV Exposure

Membrane switches intended for outdoor use are most susceptible to fading from sun exposure. Being constantly exposed to the sun’s ultraviolet (UV) rays will eventually cause the outer graphic overlay layer to fade over time. In many cases, the keys will eventually become transparent or otherwise difficult to see preventing users from being able to distinguish between the different keys.

An outdoor weatherable hardcoat material is essential when designing a membrane keypad that is used outdoors. The UV weatherable material utilizes a coating technology that resists yellowing and hazing, no matter how bright the sun is. Along with good UV resistance, this material also has chemical and abrasion resistance. This material is the perfect choice for outdoor keypad applications.

Additional Key Benefits of the UV Weatherable Material:

  • Extreme durability
  • Printable
  • Abrasion resistance
  • Chemical resistance to strong household cleaners and industrial chemicals

What is a Gasket Design or Perimeter Seal in a Membrane Switch?

What is a Gasket Design or Seal Frame in a Membrane Switch?

The Achilles heel for membrane switch sealing is most always the flex tail breakout area. The tail typically breaks out of the rear of the switch and because the tail is made of the same material as the circuit, a filler piece replaces the ribbon cable shape in the materials of the membrane switch. The gaps on either side of this tail filler is typically where moisture can enter the membrane switch.

A gasket or perimeter seal frame design can solve this problem. A membrane switch with a gasket or perimeter seal does not have a tail filler therefore there is no direct pathway for liquid ingress. CSI Keyboards’ perimeter seal frame switches have proven to be as robust as other sealing methods such as perimeter temperature sealing and can be included in your design at minimal additional cost.

Epoxy Key Top Coating for Rubber Keypads

Epoxy Key Tops for Rubber Keypads

Epoxy key top coating is a protective clear epoxy resin coating applied to only the silicone rubber key tops. This thick coating gives keys a hard plastic feel and glossy appearance. Epoxy coating can extend the longevity of key top artwork as it has abrasion resistance and protects the tops of the keys from chemicals, dirt and oils. 

The epoxy key tops can really make your product stand out from the competition as it is more visually appealing than standard rubber key tops. The keys have a plastic appearance but producing the epoxy coated rubber keypads is considerably less cost than manufacturing plastic keys. We recommend epoxy key top coating for keys that receive a high number of actuations or applications that are exposed to abrasion. Additionally, the epoxy coated keys can also be backlit similar to a standard rubber keypad. The rubber is laser etched prior to the epoxy being applied to the key tops.  

Polyurethane Coating for Rubber Keypads

Polyurethane (PU) Coating for Rubber Keypads

Polyurethane (or PU) is a protective overcoat applied to rubber keypads. This clear coating provides wear resistance for very high use applications or products that are used in harsh environments. Adding the polyurethane coating to rubber keypads ruggedizes the keypad, increases abrasion resistance, adds UV resistance and prolongs the longevity of the rubber. It provides superior resistance to corrosion andchemical exposure. This particular coating is also a cost effective solution. 

PU coatings protect rubber keypads from oils, dirt, and contamination. The polyurethane may be applied in a glossy or matte finish, to meet the aesthetic requirements of the rubber keypad. The polyurethane coating is deposited on the top surface of the keypad over the printing. Polyurethane coatings are used across all industries to improve the appearance and lifespan of the materials.