The Plating Forum: The Significance of IPC ENIG Specification 4552 Revision B

The ENIG Specification 4552 was issued in 2002. Since then, it has undergone a series of amendments and revisions to meet ever-changing industry requirements. Although it started as a thickness specification that did not reference lead-free soldering or nickel corrosion, its latest iteration, 4552B, addresses all aspects of nickel corrosion.

The IPC Specification 4552B was issued in April 2021 as a performance specification. It is already having a profound effect on how the industry (suppliers, manufacturers, and end users) views the ENIG surface finish. The document is a revision of its predecessor, 4552A, issued in 2017. Revision 4552A addressed nickel corrosion for the first time. It described the corrosion defects as viewed in a cross-section at 1000X magnification by coining the terms “spike,” “spreader spike,” and “black band.” It also addressed the level of corrosion and defined three levels. The levels were based on depth of defect and frequency of occurrence in the field of view at 1000X magnification.

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Table 1: Revision 4552A addresses corrosion effects.

ENIG Specification 4552A went a long way in defining the defect and its evaluation. The way the specification read was that if a single Level 3 defect was encountered, the product was deemed “rejectable.” Rejecting a production lot due to a single occurrence of a Level 3 defect in the 1000X field of view did not make any sense. There had to be a method to determine the frequency of occurrence or prevalence of corrosion in the board. This was addressed in the revised ENIG specification 4552B.

In revision 4552B, the term “product rating” was introduced. Product rating is a way to assess the frequency of occurrence or prevalence of the corrosion defect. Product rating is determined by assessing the defect levels of multiple cross-section locations (seven for a through-hole and five for a single pad).

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Table 2: Revision 4552B assesses the frequency of occurrence or prevalence of the corrosion defect.

To arrive at a product rating, a cross-section of the board is examined at lower magnification (200X) where multiple holes are within the field of view. The specification then states that holes or pads with the most prevalent defects are to be evaluated at 1000X (Table 2). The results are tabulated, and a product rating value is extrapolated depending on the frequency of each of the levels.

This is a significant development in corrosion evaluation. Now there is a standardized method for corrosion evaluation that produces a product rating number. Specification 4552B also addressed the disposition of the extent of corrosion.

4552B contains details on how to calibrate and qualify XRF thickness measuring equipment. It also describes how to generate “guard bands” for instruments that do not meet statistically acceptable repeatability.

4552B added a method to measure the phosphorous content of the EN deposit. The method uses energy dispersive X-ray florescence (EDXRF). Here, a number is generated for % phosphorous in the EN deposit. This number is a good indicator of the EN bath performance over its life as measured by MTOs (metal turnovers). The number can also be used to establish a correlation between the occurrence of corrosion and the % phosphorous content of the EN deposit.

With this methodology, manufacturers can gain a good understanding of the defect. They can track it, attempt to define a root cause, and eventually eliminate the defect. Products can be shipped with confidence, knowing that the product will not be rejected for ENIG corrosion.

Buyers can request that the manufacturer perform corrosion testing per 4552B and supply support documentation that the product is corrosion-free, or with an acceptable level of corrosion that will not cause solderability issues.

Suppliers now have a way to evaluate the performance of products in the field. They can increase the robustness of their products and service to ensure that customers can produce acceptable ENIG finishes in different manufacturing environments. Manufacturing sites vary dramatically in level of engineering support, lab support, plater experience, equipment, QC capability, etc.

Specific examples of increasing product robustness include:

  • A modified catalyst that will produce a uniform catalyzed surface
  • A more corrosion-resistant electroless nickel
  • A non-aggressive immersion gold
  • A reduction-assisted immersion gold

For technical service, the supplier must have a team of service engineers that are well versed on nickel corrosion and are supported by an analytical lab with capable personnel that can produce product rating numbers and % phosphorous as specified in 4552B.

The revised ENIG Specification 4552B gave the industry a tool by which manufacturers, buyers, CMs, and suppliers can measure the extent of ENIG corrosion. With this measurement tool, the problem of ENIG corrosion is well on its way to be eliminated.

“You can’t fix a problem that you can’t measure.”

This column originally appeared in the November 2021 issue of PCB007 Magazine.

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2021

The Plating Forum: The Significance of IPC ENIG Specification 4552 Revision B

11-24-2021

The ENIG specification 4552 was issued in 2002. Since then, it has gone through a series of amendments and revisions in an attempt to meet the everchanging industry requirements. It started as a thickness specification that did not mention lead-free soldering or “nickel corrosion” and ended in the latest performance specification 4552B where all aspects of nickel corrosion were addressed. Suppliers now have a way to evaluate the performance of products in the field. They can increase the robustness of their products and service to ensure that customers can produce acceptable ENIG finishes in different manufacturing environments.

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The Plating Forum: The IPC Surface Finish Specifications

10-06-2021

Specifications are reference documents to be called out by OEM board designers in specifying the attributes of a surface finish. Designers may take exception with one or more items in the specification to ensure that the product meets the requirements of its intended use. The term “AAUBUS” (As Agreed Upon Between User and Supplier) is part of any specification.

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The Plating Forum: An Overview of Surface Finishes

09-06-2021

Surface finishes’ research and development departments on the supplier side have been very busy coming up with new finishes to meet the everchanging demands of the electronics industry. Today, designers have wide variety of finishes to choose from. George Milad breaks it down.

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The Plating Forum: DIG—The Next Generation

06-16-2021

DIG stands for “Direct Immersion Gold.” The acronym is used to specify direct deposition of gold on copper as a surface finish. It is a metallic solderable finish. At assembly, DIG forms a Cu/Sn intermetallic with the gold layer dissipating into the bulk solder.

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The Plating Forum: RAIG (Reduction Assisted Immersion Gold) for Gold Surface Finishes

04-05-2021

RAIG was introduced a few years ago to meet the requirements of newer designs. Since its inception, more gold finishes are finding RAIG gold to be a viable alternative to standard immersion gold. RAIG gold is a mixed reaction bath that functions as an immersion gold and with the added reducing agent it also functions as an electroless (autocatalytic) bath.

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2020

The Plating Forum: Training for Plating Processes in the Electronics Industry

12-24-2020

Plating is a very old industry and has been studied for many generations. Its basic principles are well understood and documented. However, when it comes to the intricate details of plating a circuit board, there is so much to learn and apply. George Milad explains.

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The Plating Forum: Via Plating for PWBs

11-19-2020

Vias are an integral part of PWB design and manufacturing. They are the means by which different layers of a board are connected. George Milad addresses the electroplating of vias, including the three main types of vias: through-hole vias, buried vias, and blind vias.

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The Plating Forum: The Critical Role of Pretreatment for Plating

10-22-2020

Pretreatment is usually customized to the incoming substrate and the plated metal. George Milad explains how it is a critical step and must be completed before plating to achieve the desired adhesion and to enhance the quality of the deposited metal.

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The Plating Forum: Immersion Plating Reaction in Electronics Manufacturing

09-16-2020

Plating or metal deposition is a key component in the manufacturing of electronic packages (circuit boards and integrated circuits). Plating occurs when a metal ion in solution (electrolyte) is reduced to the metal. The reduction takes place when electrons are supplied to the ion. George Milad dedicates this column to the immersion reaction.

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The Plating Forum: Minimizing Signal Transmission Loss in High-Frequency Circuits

07-06-2020

All PCB materials have both conduction and dielectric RF signal losses. In this column, George Milad highlights resistive conduction losses by the copper layer used in the board.

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The Plating Forum: Can ‘Nickel Corrosion’ Occur in ENEPIG?

05-25-2020

Nickel palladium gold (ENEPIG) surface finish is being referred to as the “universal finish.” ENEPIG was also the answer to the nickel corrosion “black pad” encountered occasionally with electroless nickel/immersion gold (ENIG) deposits. In this column, George Milad answers the question, "Can 'nickel corrosion' occur in ENEPIG?"

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The Plating Forum: Eliminating Waste From Electrolytic Acid Copper Plating

03-15-2020

Acid copper plating in most shops is done in vertical plating tanks. Acid copper solutions are not dumped but are continuously used with occasional carbon treatment to remove organic build-up from the additives and from dry film leaching. George Milad explains.

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The Plating Forum: EPIG—A Nickel-free Surface Finish for Next-generation Products

01-11-2020

In recent years, electronic devices, such as smartphones and tablet PCs, have been miniaturized. Chip-size package (CSP) used inside the electronic devices have been miniaturized as well, and the spacing between the lines continues to diminish every year. Some of the latest packages have spacing as little as 15 µm or less. If electroless nickel electroless palladium immersion gold (ENEPIG) is used with an EN thickness of 5–6 µm, only 5 µm of spacing would be left, increasing the risk of shorts between the traces. George Milad explains.

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2019

The Plating Forum: New Developments in ENIG

12-08-2019

ENIG has been around the printed circuit industry for more than 25 years. George Milad provides an update and explains how although the occurrence of corrosion was recognized, a better understanding of the defect has led to a series of improvements over time.

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The Plating Forum: Update on IPC-4552 ENIG Specification Revisions

10-20-2019

George Milad's columns will cover PCB plating, IPC specifications, and more. In this debut installment, he gives us an update on the IPC-4552 ENIG specification, including Revision A and B.

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2014

The Plating Forum: Wire Bonding to ENIG

03-05-2014

The IPC-4552 ENIG specification was written in 2002, but the committee is currently updating and revising the document. The thickness of the immersion gold layer is being revised with the intent of reducing the minimum thickness from 2.0 µin to 1.6 µin. A series of studies were conducted to find out if this reduction is possible.

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The Plating Forum: ENIG and the Plating Process

01-07-2014

ENIG continues to gain market share due to its versatility in a wide range of component assembly methods including solder fusing, wave soldering, and wire bonding. The plating of ENIG is a complex multi-step process. Each process step is carefully designed and must be well understood and controlled to produce the desired end product. George Milad reports.

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2013

Acid Copper Plating for High Aspect Ratio and Via Fill

07-16-2013

To meet new specification requirements, board shops are forced to seek new and advanced processes in every department. Acid copper plating comes under heavy scrutiny, as it is the process that forms the traces and the through-hole connectivity that conveys the signal from end-to-end of the final device. George Milad, a new columnist for The PCB Magazine, explains.

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