Trying to understand why three keys stop working

[Isaac]

Trying to understand why three keys stop working when the laptop gets hot.

Example of what happens: My built-in netbook keyboard gets hot with the laptop. When the laptop says it's about 56c degrees the "H", "G" and "Backspace" keys start to have trouble registering key strokes. As the netbook gets hotter, I have to rapidly, but lightly, tap these keys a to get them to register. Once the laptop is around 60c degrees, I have to either plug in a usb keyboard or let my system cool for a few minutes. Currently my system is 46c as a type this.

My main question is, what is happening inside the built-in keyboard when it gets hot? Isn't a keyboard key just a rubber thing touching a circuit? Why would that be effected by a slight temperature change?

My theory is, the "G" and "H" key are located where the ribbon is, so I can imagine heat being transferred to that point, through the ribbon. The backspace key is over the hottest area on the netbook, where the CPU and GPU are.

[fliptw]

I wouldn't be surprised if the heat is physically affecting the switches of the keys in question, deforming the frame just enough to hamper registering the key press.

[Isaac]

Like, they expand just enough so that they don't conduct, I guess. I don't get circuitry.

[Duper]

HERE is an example of what a button (KB or otherwise) looks like on the circuit board level. You press down on the button and conductive material on the the back side bridges those lines completing the circuit (or shorting it)

Expansion from heat is probably warping something or is could be liquifying the solder ...in which case you really need to have that laptop looked at as those temperatures are over 500 degrees F. (I doubt it's getting that hot!)


I'm probably way off on all of this. ^_^

[Krom]

It is probably a common membrane/dome switch. The switches are actually a sort of rubber or silicone dome with a pad in the middle that is coated with something conductive (typically graphite). Probably what is happening is as the temperature rises, the resistance of the graphite coating in the switch rises to a point where it no longer passes sufficient current for the keyboard to recognize the circuit.

[Isaac]

So the graphite won't conduct at high temperatures because heat makes the electrons bounce against each other more, causing them to be lost. I have a theory.

My system is old and the area around the fan has never been opened and cleaned. I think the processor is getting so hot it's able to cause this problem with the keyboard, meaning it might not actually be a keyboard problem, but a heat sync problem.