NEWSLETTER - August 2019
LiloTree is an advanced materials technology company, providing next-generation technology solutions through chemistry and materials innovations. Based in Seattle, Washington, we're an NSF-funded company, manufacturer & distributor of ENIG-PremiumTM, an eco-friendly patent pending solution offering enhanced reliability at lower cost.
This month's focus:
The ENIG-Premium™ solution to black pads

ENIG-Premium is a patent pending surface finish solution which resolves ENIG's "black pad" problem.
ENIG-Premium includes the following advantages over traditional corrosion-prone ENIG surface finish solutions:
  • 10x resistance to black pads!
  • No brittle failures at solder joints
Let's learn a little about black pads, and see how ENIG-Premium measures up against traditional ENIG plating:
What are black pads?


Blacks pads occur due to the way immersion gold plates onto the nickel-phosphorous plating.

The immersion gold process is a type of galvanic corrosion process where a gold atom displaces a nickel atom, and puts itself in that spot. However, if that process goes out of control, the phosphorous that is left over from the nickel-phosphorous plating becomes increasingly concentrated. This can occur repeatedly, carving into the nickel-phosphorous plated layer, creating a deep crevice. The leftover phosphorous looks black, and so these areas were named "black pads".


These areas of high phosphorous concentration are brittle and much mechanically weaker than areas with higher concentrations of nickel. Additionally, solder doesn't wet onto black pads, so they are both weak and a non-wetting zone (shown above1). Therefore, black pads are absolutely unacceptable in high-reliability electronics applications which often use ENIG.
Identifying black pads

Black pads look black from the surface, but there's more going on beneath the surface. Let's look at some cross-sections:

Below is an image of a cross-sectioned pad using an optical microscope.2 The red boxes show where there are black pad crevices in the nickel-phosphorous plating.


On a smaller scale, we can see how black pads form between the nickel grains from these images taken in a scanning electron microscope (SEM):3,4

Eliminate black pads with ENIG-Premium

When you plate with liloTree's ENIG-Premium, you don't have to worry about black pads!

Our Premium nano-engineered formula alleviates any issues with black pads. The Barrier Layer chemistry passivates and protects the nickel-phosphorous layer, increasing corrosion resistance by 10x. Then, when our proprietary immersion gold deposits onto the barrier layer-treated nickel, there's no black pad formation, even with 3+ MTO Nickel solution.

Below, you can see the comparison between traditional ENIG plating with black pads,5 and the unblemished nickel-gold interface of our ENIG-Premium plating without black pads.

Traditional ENIG:
Black Pads
ENIG-Premium:
No Black Pads

The immersion gold process is corrosive; always expecting it to go perfectly is asking for a miracle! Instead, you can rely on the rigorously-tested nanoengineering of liloTree's ENIG-Premium to make your boards and assemblies highly reliable, free from corrosion and black pads.
LiloTree Office:
2904 266th AVE NE,
Building B, 
Redmond WA 98052-2936 
Phone:
425-780-2732

Email:
contact.us@lilotree.com

[1] Lee, Bab Hui, Multek. Dec 11 2003. Implementing a Simple Corrosion Test Method for Early Detection of "Black Pad" Phenomenon in ENIG Plating. HKPCA-IPC Conference Proceedings.
[2] Bunce, Martin; MACDERMID ENTHONE. Sept 2017. Achieving a Successful ENIG Finished PCB Under Revision A of IPC 4552, Proceedings of SMTA International, Rosemont, IL. Page 891. Image has been cropped from the original and red boxes were added.
[3] Zeng, K. June 2006. The Root Cause of Black Pad Failure of Solder Joints with Failure of Solder Joints with Electroless Ni/Immersion Gold Plating. JOM. Page 75-79.
[4] Schmidt, R., Dipl.-Ing, Fraunhofer Institute for Reliability and Microintegration IZM. Substrate Finish and Reliability (English). Image has been cropped from original.
[5] Lee, Kong Hui, Jabil Circuit Inc. Jan 17, 2013. Identification and Prevention of "Black Pad". smtnet.com. Annotation added.

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