Technical Library
Two things get specified loosely on connector drawings and cause most of the field failures: the contact finish, and a current rating read as if it were an absolute.
| Finish | Typical thickness | Mating cycles | Strengths | Watch for |
|---|---|---|---|---|
| Gold over nickel | 0.05-0.8 µm Au | High, hundreds | Lowest and most stable contact resistance. Does not oxidise. Essential for low-level signal and for anything mated repeatedly. | Cost. Thin "flash" gold is porous and behaves much more like the nickel underneath than like gold. |
| Tin | 1-3 µm | Low, roughly 10-25 | Cheap and entirely adequate for power and for connections that are mated once and left alone. | Fretting corrosion under vibration or thermal cycling. Tin oxide is hard and insulating, and micro-motion grinds it into the contact interface. |
| Silver | 2-10 µm | Moderate | Highest conductivity of the three. Used where current density is the binding constraint. | Tarnishes in sulphur-bearing atmospheres. Usually needs sealing or a controlled environment. |
| Nickel underplate | 1.3-2.5 µm | n/a | Diffusion barrier stopping copper migrating into the surface finish, and a hard support layer. | Not a contact finish in its own right. Specify it under gold, and check it is there. |
Never mate tin against gold. The tin side transfers to the gold, the gold loses its low-resistance surface, and the joint degrades faster than either finish would alone. Keep both halves of a mated pair on the same finish system.
A connector's current rating is not a fuse value. It is the current that produces a specified temperature rise - commonly 30°C above ambient - under defined test conditions. Two numbers matter as much as the rating itself:
If a current rating appears on a datasheet without the temperature rise, the ambient and the number of energised contacts stated alongside it, it is not yet a specification.
A contact callout that will not be ambiguous at the plant:
The plant will quote to whatever is on the drawing. Anything left off becomes their choice, not yours.
How to use these tables. The values here are standard reference figures published to help you specify and compare parts. They are guidance, not a substitute for your own engineering standard, and several of them (torque above all) depend on assumptions about friction, lubrication and joint material that will differ in your application. Where a number matters, confirm it against the governing specification and against the part drawing. We will supply the plant's actual test data with any quotation.