Gold is using for surface finish of PCB, such as key board and gold finger and so on, as the gold has a great conduction, strong oxidation resistance, long life. However, it is essential difference between plating gold and plating gold that plating gold is hard gold as well to resistance, but immersion gold is flexible gold which is on the contrary.
For the gilding process, the effect of tin on it is greatly reduced, while the effect of tin on heavy gold is better. Unless what the manufacturer asks is to bind, otherwise now most manufacturer will choose sink gold craft! Generally, the surface treatment of PCB is as follows: gold plating (electroplating, gold sinking), silver plating, OSP, tin spraying (lead and lead-free). These are mainly used for fr-4 or cem-3, paper substrate and rosin coating. Bad tinning (bad tin eating) if the tin paste manufacturers such as tin paste excluded from the production and material technology.
There are some differences between immersion gold and gold plating as follows:
1. Gold thickness in immersion gold board is more than that in a gold plating board. Immersion gold board is more yellow than a gold-plating board, that’ because gold-plating board has the color of nickel.
2. Their crystal structures are different. Comparatively speaking, immersion gold is easier to be soldered with less poor solder issues. Immersion gold board is easier to control the stress, which is benefit for the bonding products. At the same time, immersion gold has a poor anti – abrasion when doing gold finger as immersion gold is more flexible than plating gold.
3. Nickel is only used on immersion gold board’s pad, thus the signal transmission in the skin effect does not affect the signal at the copper layer.
4. The crystal structure of immersion gold is much denser than that in gold plating board, thus it is not easy to produce oxidation.
5. With the strict requirements for higher precision in PCB fabrication process, line width and spacing have below 0.1mm. Gold-plating board is easier to produce short circuit than immersion gold board.
6. Nickel is only used on immersion gold board’s pad, therefore solder resist on the circuit is solidly combined with the copper layer.
7. The flatness and service life of immersion gold board is better than the gold plating board.
What are the advantages of immersion gold and gold plating?
Why use gold plating?
As IC become more and more integrated and IC pins are also denser. This brings difficulty to SMT placement. In addition, the shelf life of the HASL board is very short, so gold plateing board solves these problems:
However, as the circuit lines become denser and it brought short circuits. And as the frequency of the signal become higher, the effect of the skin that affect signal quality become more obvious.
Skin effect: High-frequency alternating current, the current will tend to concentrate on the surface of the wire.
Why use immersion gold?
In order to solve the above problems of the gold plating board, so adopt immersion gold technology:
1. Due to the difference of crystal structure between Immersion Gold and Gold Plating, Immersion Gold is easier to weld than Gold Plating and will not cause bad welding. The stress is more easily to control.
2. Since only pad has nickel-gold, the signal transmission in the copper layer in skin effect and will not affect the signal.
3. Not easy to oxidation.