Layout of Silicone Keypads For Hazardous or Tough Conditions

Keypads are utilized in sites where the environmental situations can have an effect on the keypad integrity. I have shown in this article some of the principal design elements that can be utilized to safeguard the keypad and the instrument it operates.

Flame resistance

Wherever necessary, the American UL-94 specifications are utilized. Most silicone rubbers will satisfy the grade UL-94-HB. In quick, this specifies that the rubber, if ignited in a horizontal place, will self-extinguish rapidly. Most silicone rubbers are inherently complicated to melt away. A far more stringent specification is UL-94-V1. At this degree, the specification demands that the rubber when held in a vertical place will not have on burning when ignited, nor will the embers have on glowing for any time. This is a rough précis of the UL specification which goes into significant element on the take a look at regime. If the UL-94-V1 degree is essential, it have to be realised that this has implications for other bodily qualities, as the polymer has to be loaded with hearth retardants.

Weather conditions resistance

This typically resolves into resistance in opposition to possibly h2o ingress or extremely violet light-weight resistance. Water resistance is achieved by simply getting a mechanical compression seal all-around the perimeter of keypad to end h2o obtaining on to the call place of the laptop board. To make a compression seal, a perimeter bead of .5mm radius all-around perimeter will compress and seal. Alternatively a elevated bead could be extra to the underside of the facia. If there is no facia to seal in opposition to, then sealing is almost certainly best achieved by bonding the keypad to the laptop board with double sided adhesive.

The outcomes of extremely violet light-weight can cause discolouration of the pigments utilized in the silicone rubber and in the legend inks. The foundation polymer silicone has exceptional resistance to UV light-weight. If the keypad is heading to be utilized outdoors in particular in sunnier climates like California, then this need to be clearly pointed out on the drawing.

Electrical troubles

If there is a possibility of destruction to electrical factors by static, then an anti-static grade of silicone need to be specified as this will avert a build up of demand. Earning a keypad conductive is functional, as the additional loading of conductive additive will degrade the bodily qualities.

Solvent or oil contamination

Typically speaking, silicone rubber does not resist continual call with oils and solvents, and degradation can be predicted, though there is no dilemma with typical alcohols. If solvent presence is unavoidable then distinctive polymers need to be regarded other than silicone. Effective in opposition to a great deal of solvents is fluorosilicone rubber. This has a disadvantage as a keypad in that it can not be printed on. It is also pretty costly. Some degree of solvent resistance is achieved by spray coating the keypad with polyurethane or parylene coating. The parylene coating is an costly process which can double the value of a silicone keypad.


I have heard that the worst situation for a silicone keypad is a command panel up coming to a initially class seat on a very long haul flight, where the passenger has lots of time to fiddle! Keys can be prised out with fingernails or a biro. Answer to this dilemma is to protect the keys with a plastic or steel cap. Caps can be provided as an assembly with the keypad and can be designed captive under the facia. If influence vandalism is to be guarded in opposition to, then the keys which are capped need to have journey restricted by design. The laptop board need to be pretty sturdy or supported beneath by a steel plate. Strange hazard I hope.

One situation we experienced to design for formerly was for a keyboard utilized on a battlefield when a nuclear bomb explosion was to be predicted. The dilemma (only dilemma!) was that the thermal flash would cause warmth absorption by particular legend pigments and melt away. The solution was to use colours and pigments that did not take up warmth so conveniently. I just hope the operator was just as well warmth resistant.

These notes are meant only as help memoir to clearly show some of the troubles and achievable solutions. I am positive there are many far more troubles and predicaments, with far more ways to satisfy them nonetheless to be devised.

Post time: 09-21-2016