gold versus nikel plated connector pins for small signals

[Simon]

I've tried in vain to find some realistic and simple information about connector plating in relation to small signals. As far as i know all contacts that switch/carry small signals need to be gold as otherwise they build up oxide that large currents would overcome / burn away but small currents won't. We usually use deutsch connectors and they usually come with nikel plated pins that we have used for years with no problem even on thermistors. But as we look at having ever more signals I feel it is time to look at the situation properly and make a company policy for the future before we have problems.

Any suggestions ?

[coppice]

I've tried in vain to find some realistic and simple information about connector plating in relation to small signals. As far as i know all contacts that switch/carry small signals need to be gold as otherwise they build up oxide that large currents would overcome / burn away but small currents won't. We usually use deutsch connectors and they usually come with nikel plated pins that we have used for years with no problem even on thermistors. But as we look at having ever more signals I feel it is time to look at the situation properly and make a company policy for the future before we have problems.

Any suggestions ?

What constitutes a good contact material varies a lot with how big a signal you consider small, your bandwidth, and your environment. For example, in a lot of environments you might use silver plated connectors for RF, because of its excellent skin resistance. However, if you are in a high humidity location those connectors might blacken in days, and give horrible results. Gold is a pretty good general purpose contact material for fairly small signal connections. However, it does film over with atmospheric gunge quite easily. Your contacts need to wipe well enough as they mate to have a good chance of clearing that. If you have really small signals, or a really nasty environment, you might want to download some material from the people making connectors with exotic alloys, and see why people would pay the high prices associated with them.

[Simon]

Well deutsch connectors are IP67 rated so while yes the working environment is specified as potentially humid they should be mated in a decent environment and never touched unless they need servicing. We use them on temperature thermistors in air conditioning units that get soaked inside and have never had a problem.

Signals I'm thinking of using would usually be 5V and vary from uA (Uc inputs) to mA (optoisolators as a load), frequency wise never more than 1 KHz

[T3sl4co1l]

If the connector housings are doing their job, the pin plating shouldn't have any restrictions, certainly not if it's gold anyway.

Nickel is the worst contact plating because the oxide is a good semiconductor.  Tin is preferred for low cost, general purpose and power contacts because it is soft enough to wipe mechanically.  Gold is preferred for small signals because it doesn't oxidize at all.

Also, do not mix platings.  Gold on tin is undesirable due to contact / high pressure formation of intermetallic compounds.  Tin on tin is better than tin on gold, but not as good as gold on gold.

Tim

[Simon]

Well the beauty of deutsch connectors is that you insert the pins so can choose each individual cavities pin and match accordingly unless it's a PCB connector which already have the pins fixed in.