Dan's Biz Bookshelf: 'Move Your Bus'
Driving Innovation: Direct Imaging vs. Conventional Exposure
It’s Only Common Sense: Selling to Today's Generation of Buyers
ENEPIG: The Plating Process
June 1, 2015 | George Milad, Uyemura International CorporationEstimated reading time: 1 minute
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.
Editor's Note: This article originally appeared in the May 2015 issue of The PCB Magazine.
Share on:
Suggested Items
The Evolution of Picosecond Laser Drilling
06/19/2025 | Marcy LaRont, PCB007 MagazineIs it hard to imagine a single laser pulse reduced not only from nanoseconds to picoseconds in its pulse duration, but even to femtoseconds? Well, buckle up because it seems we are there. In this interview, Dr. Stefan Rung, technical director of laser machines at Schmoll Maschinen GmbH, traces the technology trajectory of the laser drill from the CO2 laser to cutting-edge picosecond and hybrid laser drilling systems, highlighting the benefits and limitations of each method, and demonstrating how laser innovations are shaping the future of PCB fabrication.
Day 2: More Cutting-edge Insights at the EIPC Summer Conference
06/18/2025 | Pete Starkey, I-Connect007The European Institute for the PCB Community (EIPC) summer conference took place this year in Edinburgh, Scotland, June 3-4. This is the third of three articles on the conference. The other two cover Day 1’s sessions and the opening keynote speech. Below is a recap of the second day’s sessions.
Day 1: Cutting Edge Insights at the EIPC Summer Conference
06/17/2025 | Pete Starkey, I-Connect007The European Institute for the PCB Community (EIPC) Summer Conference took place this year in Edinburgh, Scotland, June 3-4. This is the second of three articles on the conference. The other two cover the keynote speeches and Day 2 of the technical conference. Below is a recap of the first day’s sessions.
Preventing Surface Prep Defects and Ensuring Reliability
06/10/2025 | Marcy LaRont, PCB007 MagazineIn printed circuit board (PCB) fabrication, surface preparation is a critical process that ensures strong adhesion, reliable plating, and long-term product performance. Without proper surface treatment, manufacturers may encounter defects such as delamination, poor solder mask adhesion, and plating failures. This article examines key surface preparation techniques, common defects resulting from improper processes, and real-world case studies that illustrate best practices.
RF PCB Design Tips and Tricks
05/08/2025 | Cherie Litson, EPTAC MIT CID/CID+There are many great books, videos, and information online about designing PCBs for RF circuits. A few of my favorite RF sources are Hans Rosenberg, Stephen Chavez, and Rick Hartley, but there are many more. These PCB design engineers have a very good perspective on what it takes to take an RF design from schematic concept to PCB layout.