Choosing the right coating is critical to the success of your connector system. Electroplating can affect the performance, life cycle, quality and cost of connectors.
The main costs of the connector are the plastic body, the pins, the plating on the pins, the labor to assemble it, and the packaging. For most connectors, the larger items are pins and plating.
For example, on micro-pitch, high-density interconnect products, pins and plating can account for about 25%-30% of the total cost of the connector. But on the basic 2.54mm centerline terminal strip (” pin holder “), it can account for 60%-70% of the total cost of the connector.
This is because the relative size of the plastic body on a miniature, mould-to-position miniature connector is almost always larger than the body basically cut into place on a strip-line connector. And, of course, if you use gold plating, the pins will cost more.
As I mentioned in my previous blog, I can’t speak for all connector companies when it comes to cost. Most of the examples I’ve used here have to do with Samtec interconnect, but I bet these principles apply to other connector companies as well.
What do we recommend?
Designers often ask us which plating finish we recommend. There are many considerations to consider (as evidenced by the variety of plating options on most basic connectors), but the best plating surface finish meets your system requirements at the lowest cost. In other words, make sure it works and meets your quality design specifications, but don’t over-engineer it on plating.
gild
Gold is usually specified for high reliability, low voltage or low current applications. Gold is used in high cycle applications because it is rugged and has excellent wear resistance (this is an example of a high cycle connector). Our gold is alloyed with cobalt, which increases the hardness. We also recommend using gold in harsh environments, as it will remain free of oxides that can cause an increase in contact resistance.
Gold is a precious metal, which means it doesn’t react much to the environment.
tinning
Tin is a lower cost alternative to gold and has excellent weldability. Unlike gold, tin is not a precious metal. The tin plating begins to oxidize the moment it is exposed to air. Therefore, the tinning contact system requires a larger normal force and a longer contact wiping area to break through this oxide film
On top of that, tin is better suited for applications with fewer cycles because of the extra force exerted on the contacts, and simply because it is a softer metal.
Normal force
The difference between gold and tin comes down to the normal force. Compared to tin, gold requires a much lower normal force. Fine-pitch connectors do not have room for relatively large, thick contact beams with high deflection; This is necessary to produce the normal force tin required for tin-plated contacts.
Therefore, due to the physical size limitations of miniature connectors, gold is usually the only option. In other words, we use tin if we can. Tin is used in connector contact areas where appropriate normal forces can be generated and in benign environments. Tin oxidizes, so higher normal forces and contact wiping are required to break through the inherent oxide layer. Again, check out the video above.
Optional gold + tin plating options
Selective gold-plated tin is Samtec’s most popular plating option because it offers designers the best of both worlds. The contact area is the key area for contact and terminal pin interface and transmission signal, with gold reliability. The tail welded to the circuit board has the low cost and weldability of tin.
Tin lead, sparkly gold palladium nickel
Of course, other plating options are also available for specific applications. Two common examples include tinned lead and glitter palladium nickel. Tin lead is used in military applications and its advantages include low eutectic temperature, and the presence of lead inhibits tin whisker formation. Palladium nickel for extremely high cycle applications. However, for most typical applications, gold, tin, or selective plating will work fine.
Quick summary
Gold for high reliability, high cycle, low voltage applications.
Tin is used for applications that have fewer cycles, are cheaper, and can accommodate solder.
Selective plating, using gold in the contact fitting area and tinning at the tail, is usually the best choice.
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