Which is better PCB ENIG or PCB gold plating?

 Table of Contents

1. The difference between names of PCB ENIG and PCB gold plating
2. The difference in the craftsmanship of PCB ENIG and PCB gold plating
3. The impact on the PCB assembly
4. The impact on electrical function
5. How to identify the PCB ENIG and PCB gold plating
6. Advantages and disadvantages

 

1. The difference between names of PCB ENIG and PCB gold plating

A. Immersion gold is mostly used to call this ENIG (Electroless Nickle Immersion Gold) surface treatment method. The advantage is that nickel and gold can be attached to the copper skin without the use of an electroplating process, and its surface is flatter than electroplated gold. This is especially important for increasingly shrinking electronic parts and components that require flatness. Because PCB ENIG uses a chemical replacement method to produce the effect of the surface gold layer, the maximum thickness of the gold layer cannot reach the same thickness as electroplated gold, and the more the bottom layer is, the less gold content will be.

B.Electroplating gold itself can be divided into hard gold and soft gold. Because electroplated hard gold is actually an electroplated alloy (that is, plated with Au and other metals), the hardness will be relatively hard, and it is suitable for use in places where friction is required. In the electronics industry, it is generally used as the side contact of the circuit board. Point (commonly known as “golden finger,” as shown in the front picture); soft gold is generally used for aluminum wire on COB (Chip On Board) or the contact surface of mobile phone keys. Recently, it has been widely used in BGA, The front and back of the carrier board.

 

 

2. The difference in the craftsmanship of PCB ENIG and PCB gold plating

A. Immersion gold board uses a chemical deposition method, which generates a layer of plating through a chemical oxidation-reduction reaction method, which is generally thicker. It is a kind of chemical nickel-gold layer deposition method, which can reach a thicker gold layer. The immersion gold process deposits a nickel-gold coating with stable color, good brightness, flat coating, and good solderability on the surface of the printed circuit. Basically, it can be divided into four stages: pre-treatment (degreasing, micro-etching, activation, post-dipping), immersion of nickel, immersion of gold, and post-treatment (washing waste gold with water, washing with DI water, and drying). The thickness of the immersion gold board is between 0.025-0.1um. Through a chemical reaction, the gold particles crystallize and adhere to the PCB pads. Because of the weak adhesion, it is also called soft gold. After the solder mask is done, the same chemical method as the tin sink, the gold is attached where there is a copper leak.

B. PCB Gold plating uses the principle of electrolysis, also called electroplating. Through electroplating, the gold particles are attached to the PCB board, all called electro-gold, because of the strong adhesion, also called hard gold, the gold finger of the memory stick is hard gold, wear-resistant, and the bound PCB is generally plated with gold. Do this process before doing a solder mask because gold plating requires two electrodes. One is a PCB board, and the other is a tank. If the PCB board is finished with a solder mask, it will not conduct electricity, and it cannot be plated with gold.

 

3. The impact on the PCB assembly

A. Immersion gold plate, good weldability; gold-plated plate, general weldability, occasionally poor welding;

B.The immersion gold board only has nickel and gold on the pads, so the solder mask on the circuit and the copper layer are more firmly combined. The project will not affect the spacing during compensation.

C. For high-demand boards, the flatness requirements are better and generally use immersion gold, and immersion gold generally does not appear black pad phenomenon after assembly. Immersion gold plate has better flatness and service life than gold plate.

D. For the gilding process, the effect of tinning is greatly reduced, and the tinning effect of immersion gold is better; unless the manufacturer requires binding, most manufacturers will now choose the immersion gold process.

E.Gold-plating is done before the solder mask. After it is done, the green oil may not be cleaned, and it is not easy to tin. Immersion gold: After doing a solder mask, the patch is easy to tin.

 

4. The impact on electrical function

A. The immersion gold board only has nickel and gold on the pads. In the skin effect, the signal transmission is on the copper layer and will not affect the signal; the gold-plated board, the skin effect is not conducive to the transmission of high-frequency signals;

B. Gold plating. Before PCB gold plating, it is necessary to plate a layer of nickel and then a layer of gold. The metal layer is copper-nickel-gold. Because nickel is magnetic, it has an effect on electromagnetic shielding. Immersion gold is to sink gold directly on the copper skin. The metal layer is copper-gold, without nickel, and no magnetic shielding.

 

 

5. How to identify the PCB ENIG and PCB gold plating

A. Immersion gold is different from the crystal structure formed by gold plating. Immersion gold is much thicker than gold-plated gold.

B. Immersion gold board has a denser crystal structure than gold plating, and it is not easy to produce oxidation; gold-plated board, the gold surface is easy to oxidize, and the solder mask bonding force is not strong;

C. As circuit board processing accuracy requirements are getting higher and higher, the line width and spacing have been below 0.1mm. The immersion gold board only has nickel gold on the pad, so it is not easy to produce a gold wire short circuit; gold plating is easy to produce a gold wire short circuit.

D. Gold-plating process Because PCB contains nickel, it is magnetic. When distinguishing whether it is gold-plated or immersed gold, a magnet can be used to attract the PCB board. Attractive is gold-plated, and non-attractive is immersed gold.

E. There are also differences in color. Immersion gold is golden yellow, while gold plating is generally thin due to the large area of ​​gold plating, which tends to be white. Of course, there is also thick plating, which is also golden yellow. At this time, it is not easy to distinguish from the pads. Then use a knife to scrape the solder mask and leak the metal layer. Because the gold plating process is to plate the entire PCB, the metal layer under the green oil is a stack of gold, nickel, and copper, so it looks golden yellow. If the plating layer is not thick, the yellow inside Transparent white, but the stacking method of the immersion gold process is different. The solder mask is copper underneath, which is red.

 

6. Advantages and disadvantages

A. In actual product applications, 90% of the PCB gold plate is an immersion gold plate because the poor weldability of the gold plate is his fatal shortcoming, and it is also the direct reason why many companies abandon the gold plating process!

B. The most fundamental difference between gold-plated board and immersion gold board is that gold-plated is hard gold (wear-resistant), while immersion gold is soft gold (not wear-resistant).

C. Immersion gold and PCB gold plating have different crystal structures. Immersion gold is easier to weld than gold plating and will not cause poor welding.

D. The stress of the immersion gold board is easier to control, and for COB (chip on board) products, it is more conducive to the processing of wire bonding. At the same time, it is precise because the immersion gold is softer than the gold plating, so the immersion gold plate is not wear-resistant as the gold finger (the disadvantage of the immersion gold plate).

E. In terms of gold plating, it can make the PCB storage time longer, and the temperature and humidity changes of the outside environment are small (compared to other surface treatments), generally can be stored for about one year;

F. Nowadays, the price of gold on the market is expensive. In order to save costs, many manufacturers are no longer willing to produce gold-plated plates and only make immersion gold plates with nickel-gold on the pads. The price is indeed much cheaper.