Tact Switch Low Temp High Humidity Failures

[jpop]

Hello all,

I am a newbie, so I apologies if anything I say doesn't make sense or if I am not providing the right information. I am basically asking for advice or where to look for more information. Or if you know what the issue is and how to help that would be greatly appreciated.

Basic background:
We use tact switches to operate a product(open switch and closed switch) that is on a vehicle.The switches are encased in a plastic housing, but the housing has direct contact to the outside elements. Both switches are on the same board. It is an open circuit using 10v regulated by an ECU. When pressed the circuit is closed and the product operates. 

Issue:
We have had issues in which the product begins to operate by itself or doesn't work. At first we suspected the ECU, but then we checked the resistance at the connection points of the tact switch where it connects to another loom. We found that there was resistance present. We then checked a new working product and found no resistance. So we concluded that if there is resistance the product won't work.We suspect that moisture could be getting into the tact switch causing a false contact. We have spoken to the supplier and they fully enclose the switch and use potting to close all gaps on the circuit board and in and around the tact switch.

We suspect, that given the temperature conditions, low temperature (-4-10 degrees celsius) and high humidity (80-95%) that there could be a dew point being reached and initiating moisture on the tact switch contact. But we don't really know.   

Assistance:
Has any one had issue with tact switches, if they have what type of failures and what was done to fix the issue. What test can you do to verify if it is moisture or condensation is present? Any pieces of advice would be great.

Cheers,

J

[wraper]

There are silver dendrites growing between contacts in switches. Lower resistance pull-up will increase reliability as it prevents failure when switches start to conduct. However it would be the best to use switches with gold plated contacts to really fix the issue.

[tom66]

One 'trick' I picked up from our switch supplier (we do a lot of Hi-Rel stuff) is to put a small capacitor on the output of the switch and a resistor in the ground path of the switch, assuming it is switching on the low side with a pull up.  The capacitor will pass a wetting current through the switch on every activation cycle, which may help keep the switch contacts clean.   The resistor in the ground path limits this current so it does not cause pitting or arcing of the contacts.