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ENIG vs. Plated Gold PCB: Key Differences | Gold Phoenix PCB

Time: 2021-06-29 20:06:58

ENIG and Plated Gold

This Gold Phoenix PCB Knowledge Center article explains the differences between ENIG and plated gold PCB surface finishes, including their applications and key characteristics.

1. Why Apply Gold on PCB

A gold finger is made up of a number of gold conductive contacts, which are arranged like fingers. Gold fingers are created by coating gold onto a copper-clad board using a special process, because gold is highly resistant to oxidation and also highly conductive. However, because the price of gold is high, alternative surface finishes such as tin plating have become widely used in many applications since the 1990s. Gold plating may still be preferred in certain high-reliability applications where frequent insertion and removal or long-term contact stability is required.

2. Why Use Gold-Plated PCB

As the integration degree of ICs becomes higher and higher, IC pins become more and more dense. The vertical hot air solder leveling (HASL) process has difficulty achieving smooth fine pads, which makes SMT mounting difficult. In addition, the shelf life of tin-sprayed boards is very short. Gold-plated boards are a good solution to these problems.

1. For the SMT process, especially for small components such as 0603 and 0402, the flatness of solder pads is directly related to the quality of the solder paste printing process. Whole-board gold plating is often used in high-density and ultra-small SMT processes.

2. In the trial production stage, influenced by factors such as component procurement, boards are often not soldered immediately but may need to wait for several weeks or even a month before use. The shelf life of gold-plated boards is many times longer than that of lead-tin alloy boards. Moreover, gold-plated boards may offer comparable lead times to lead-tin alloy boards during the sample stage.

However, as wiring becomes more and more dense, with trace width and spacing reaching 3–4 mil, the problem of short circuits appears. As signal frequency increases, the skin effect causes signals to be transmitted across multiple coatings, which affects signal quality more noticeably.

Skin Effect: At high frequencies, the current tends to concentrate on the surface of the wire. Based on calculation, the skin depth is related to frequency.

3. Why Use ENIG PCB

In order to solve the problems of gold-plated PCBs, ENIG (Electroless Nickel Immersion Gold) has the following characteristics:

1. Since the crystal structure of plated gold and ENIG is not the same, the color of ENIG is more yellow, which is generally more widely accepted.

2. Because the crystal structure of plated gold and ENIG is different, immersion gold is generally easier to solder than plated gold and may offer more consistent soldering results.

3. Since there is only nickel-gold on the solder pad of the ENIG board, signal transmission in the skin effect occurs in the copper layer, which will not affect the signal.

4. Because the crystal structure of ENIG is denser than that of plated gold, it is less prone to oxidation.

5. Because there is only nickel-gold on the solder pad of the ENIG board, gold wires will not be produced, preventing short circuits.

6. Since there is only nickel-gold on the solder pad of the ENIG board, the solder mask on the trace bonds to the copper layer more firmly.

7. It will not affect the spacing when engineering makes compensation adjustments.

8. Because the crystal structure of plated gold and ENIG is different, the stress of the ENIG board is easier to control, and it is more conducive to the processing of bonded products. At the same time, because immersion gold is softer than plated gold, the ENIG board’s gold finger is not as wear-resistant.

9. The flatness and service life of the ENIG board is as good as that of the plated gold board.

ENIG Board vs. Plated Gold Board

For plated gold technology, the effectiveness of tin application is greatly reduced. The effectiveness of tin application on ENIG boards is better. ENIG is commonly selected for applications that require a relatively flat surface and good solderability.

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