ENIG and Plated Glod

1. Why apply gold on PCB.

The Gold finger is made up of a number of golden conductive contacts, which are arranged like fingers. Gold finger is actually coated with gold on copper-clad board in a special process, because gold is highly resistant to oxidation and also highly conductive. But because the price of gold is high, currently tin plating is used to replace for more memory. Tin material began to spread from the last century 90s, currently the gold finger in the motherboard, memory, and video devices is almost made with tin material, only some Accessory contact points for high performance servers/ accessory contact points for workstations continue the practice of using gold plated, which is expensive.

2. Why use gold plated PCB

As the integration degree of IC becomes higher and higher, IC pins become more and more dense. Vertical tin spraying process is difficult to smooth the fine pads, which makes it difficult to mount SMT. Besides, the shelf life of the tin sprayed board is very short. And gold-plated board is a good solution to these problems

1) For SMT process, especially for small SMT like 0603 and 0402, since the flatness of solder pads is directly related to the quality of solder paste printing process, plaing gold for whole board is often taken in high density and ultra-small SMT process.

2) In the trial production stage, influenced by factors such as the purchase of components, the boards are often not welded immediately when they come, but have to wait for several weeks or even a month before they are used. The shelf life of gold-plated boards is many times longer than that of lead tin alloy, so everyone is willing to adopt them. Moreover, the cost of gold-plated PCB in the sample stage is almost the same as that of lead-tin alloy board.

But as the wiring becomes more and more dense, the track width and space have reached 3-4mil

Hence the problem of short circuit of the wire appears: As the signal frequency is higher and higher, the skin effect causes signals to be transmitted across multiple coating, which effects signal quality more and more obviously.

Skin Effect: At high frequencies, the current will tend to concentrate on the surface of the wire. Base on calculation, the skin depth is in relation to frequency.

3. Why use ENIG PCB

In order to solve above problems of gold-plated PCB, ENIG PCB mainly has the following characteristics:

1) Since the crystal structure of plated gold and ENIG is not the same, the color of ENIG will be more yellow, normally it’s more popular among customers.

2) Because the crystal structure of plated gold and ENIG is different, immersion gold is easier to weld than plated gold, will not cause poor welding, causing customer complaints

3) Since there’s only nickel gold on the solder pad of the ENIG board, the signal transmission in the skin effect is 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 not easy to produce oxidation.

5) Because there is only nickel gold on the solder pad of the ENIG board, it will not be produced into gold wire resulting in short

6) Since there is only nickel gold on the solder pad of the ENIG board, the solder mask on the track binds to the copper layer more firmly

7) It won’t affect the space when engineering make compensation.

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

To plating gold technology, the effect of the tin is greatly reduced. The effect of tin on ENIG board is better. Unless there’s specific requirement, most manufacturers will choose the gold sinking process.