Silicon rubber keypad at low temperatures

I have a product that uses a silicon rubber keypad which works well, but I now need to start a new project where the keypad needs to operate down to -40C.

Initial feedback from my engineering guys is that a silicon rubber keypad will freeze and the keys will stick at that temperature.

They have suggested we move to a membrane keypad which I really don’t want. Any ideas how you can have a rubber keypad operate at -40C without external housings or heater kits?

-40 is your operating temperature?

Are you looking at a silicone keypad with carbon pucks, or with snap domes? I would think that if you had snap domes they would not stick even if the rubber was very brittle.

Looking at all of our freezer use products, the specs the lowest storage temperature is -40C but the operating temperature is -20C. The products all use silicone somewhere in the keypad and I have not heard of any issues.

Thanks for the quick reply.

I’m not sure if the existing keypad uses carbon pucks or snap domes but I’ll find out. The operating temperature is -40C as the keypad is used outdoors in northern Scandinavia. It’s unlikely to get that low, but possible.

I think the issue is linked to water ingress to the keypad which then freezes causing the keys to stick.

Well thats really a sealing issue then. Seal the perimeter of the keypad and include some space for a dessicant packet to soak up any internal humidity that may develop. Done and done. :smiley:

Thanks for the ideas. The rubber key mat currently sits behind a plastic molding with the keys protruding through, so maybe a redesign is needed as the water sits between the molding and the keys.

This should not be an issue. If you have ice between the frame/bezel of the keypad it will not prevent the key from moving down. Even if it froze tightly to both of them, chances are it would instantly pop right off with enough force on the key.

It may prevent it from properly returning, but I don’t see this as being an issue in any real world environment. Even if you’re out in a blizzard and snow is seeping into the product, as long as everything electronic is sealed off that moisture should not impact the travel of the keys.

You can also design drainage features in if necessary that route any water away from areas that may cause an issue.

Hi Steve,
What keypad technology did you finally go for to resolve the key sticking issues?. I am also working on a similar project where we are facing keysticking issues when the condensed water between the keypad bezel and keys freezes into ice.

@ Cyberdom,
You are absolutely right on the point that “ice between the frame/bezel of the keypad it will not prevent the key from moving down”. But what we are oberving is that , after actucation any of the keys in this state ,it is not retracting backwards . I can sent you the test images by email if you would like to have a look on it

We have finalized two concepts, both with internal bezels rather that external bezel to take care of this icing issue.

I would be interested to know whether any simple modification on the existing keypad can resolve the issue.

Anybody out there has a solution to this mind boggling issue?

With addition of plasticizers the glass transition temperature (Tg) of polymers can be altered. So they do not become hard and brittle if that is also a part of the problem. So if you are using custom made silicon keypad, the manufacturer can alter the somposition of the silicone to produce a low-temperature one.

The elastomer is not becoming brittle at this cold temperature. The issue is the ice formation between the bezel and the keypad . Please go through the image attached. This will give u a better understanding.