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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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#77128

PCB Design Question - Hard gold or ENIG for keypad button contacts | 21 February, 2017

Looking for advice on soldering lead free paste to a board with very heavy gold plating, In my opinion, Gold contact surfaces are often used on circuit boards with membrane switches which is a choice of technology for industrial, commercial and consumer products. A Nickel underlayer is electo-plated onto the PCB with a minimum thickness of 50 microinch. Nickel not only provides mechanical support it also provides a diffusion barrier as well as an inhibitor to pore and creep corrosion. ENIG (Electroless Nickel Immersion Gold) is a two layer metallic coating of 2-8 μin Au over 120-240 μin Ni. The gold protects the nickel during storage and also provides the low contact resistance required for the thin gold deposits. ENIG is now arguably the most used finish in the PCB industry due the growth and implementation of the RoHs regulation. More info at http://www.solder.net/

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#77130

PCB Design Question - Hard gold or ENIG for keypad button contacts | 21 February, 2017

We're a custom PCB manufacturing services provider based in China and we have made many high quality circuit boards for high end products. Based on your project requirements and our years' experience, we are positive that ENIG is totally sufficient.

In case you need more information about ENIG surface finish, check here http://www.pcbcart.com/article/content/ENIG-and-ENEPIG-comparision.html

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