ENEPIG: The Plating Process


Reading time ( words)

Electroless nickel/electroless palladium/immersion gold (ENEPIG) is sometimes referred to as the universal finish, because of the versatility of its applications. It is a multifunctional surface finish, applicable to soldering and wire bonding (gold, aluminum, copper and palladium clad copper). In addition, it is also suitable as the mating surface for soft membrane and steel dome contacts, low insertion force (LIF) and zero insertion force (ZIF) edge connectors, and for press-fit applications. ENEPIG is formed by the sequential deposition of electroless Ni (120–240 µin) followed by 2–12 µin of electroless Pd with an immersion gold flash (1–2 µin) on top.

Chemical Definitions

Electroless Process: This chemical process promotes sustained deposition of a metal or metal alloy onto the PWB surface through an oxidation-reduction chemical reaction, without the application of an external electrical potential. Reducing agents, such as sodium hypophosphite or sodium formate, react at catalytic surfaces to release electrons, which immediately reduce the positively charged metal ions (e.g., nickel ions in ENIG and ENEPIG and palladium ions in ENEPIG), promoting their deposition onto the PWB.

This type of reaction is described as autocatalytic, as the deposition process will continue even after the substrate is completely covered by a continuous layer of the plated deposit. The deposit thickness will therefore continue to rise in the presence of source metal ions and a reducing agent, until the board is removed from the plating bath. The thickness of plated deposits will vary depending on the bath temperature, chemical parameters (such as solution pH) and the amount of time spent in the plating bath.

Immersion Process: This chemical process uses a chemical displacement reaction to deposit a layer of a second metal onto a base metal surface. In this reaction, the base metal dissolves, releasing the electrons that reduce the positively charged ions of the second metal present in solution. Driven by the electrochemical potential difference, the metal ions in solution (e.g., gold ions in ENIG or ENEPIG process) are deposited onto the surface of the board, simultaneously displacing ions of the surface metal into solution.

Read The Full Article Here

Editor's Note: This article originally appeared in the May 2015 issue of The PCB Magazine.

Share

Print


Suggested Items

New Solder Joint Technology From Schmartboard

08/17/2020 | I-Connect007 Editorial Team
Schmartboard has a surprisingly simple patented process to improve solder joint reliability; in this interview, they discuss the process in detail, along with their search for a go-to-market partner.

IPC Education Foundation: STEM and Online Learning Resources

04/09/2020 | Nolan Johnson, I-Connect007
Nolan Johnson recently caught up with Charlene Gunter du Plessis, senior director of the IPC Education Foundation, about how the COVID-19 outbreak is affecting the IPCEF, including how they are continuing to connect with IPC Student Chapter members and seek industry support. Charlene also discussed the increased usage of IPCEF’s online educational modules and shares STEM resources.

Institute of Circuit Technology Spring Seminar 2020

03/11/2020 | Pete Starkey, I-Connect007
Back to Meriden, the nominal centre of England where the daffodils were blooming. A good crowd made it to the spring seminar that followed the Annual General Meeting of the Institute of Circuit Technology (ICT), with five specialist presentations and excellent opportunities to network with their peers in the industry. Pete Starkey shares his overview of the event.



Copyright © 2020 I-Connect007. All rights reserved.