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PCB Design Question - Hard gold or ENIG for keypad button contacts

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#77118

PCB Design Question - Hard gold or ENIG for keypad button contacts | 17 February, 2017

I'm a PCB designer working on a board that has a rubber keypad with control buttons mounted to it. The PCB contains the corresponding contact patterns for the buttons - a typical interlocking finger pattern.

In the past when I've encountered this scenario I've specified hard gold over nickel plating for the button contacts. However, the engineers I'm working with are considering using the standard ENIG finish to save some cost.

The application in question is an industrial control that will see what I would consider moderate usage of the buttons over a 10-20 year projected lifespan. I'm thinking that max button presses would be in the 10,000 to 20,000 range over the product's lifespan with the average probably being much lower than that. These devices are typically mounted indoors and not subject to extremely harsh environmental conditions but could possibly experience temperature fluctuations between 0F and 100F over their lifespan.

Does anyone have any opinions on this? Is ENIG sufficient for this type of application?

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#77119

PCB Design Question - Hard gold or ENIG for keypad button contacts | 17 February, 2017

An interesting paper on the topic is "The evolution of surface finishes in mobile phone applications" by Claus Würtz Nielsen at Nokia Mobile Phones R&D [http://www.cicmt.org/adv_micro/papers/Nordic2004paper.pdf]

The paper reported corrosion problems with ENIG pad and argued for moving away from ENIG on wear surfaces in the mobile phone industry.

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