PCB Tech - PCB process PK: spray tin VS gold plating VS immersion gold

Today I will talk to you about the difference between gold-plated and gold-plated PCB circuit boards. Immersion gold boards and gold-plated boards are processes often used in PCB circuit boards. Many customers cannot distinguish the difference between the two correctly. Some customers even think that the two do not exist. Difference, this is a very wrong point of view and must be corrected in time. So what impact will these two kinds of "golden boards" have on circuit boards? Below I will explain it specifically for you, and help you to clarify the concept thoroughly.

So everyone chooses gold plating, what is gold plating, what we call the whole plate gold plating, generally refers to "electroplating gold", "electroplating nickel gold plate", "electrolytic gold", "electric gold", "electric nickel gold plate", there are soft gold The difference between hard gold and hard gold (generally hard gold is used for gold fingers), the principle is to dissolve nickel and gold (commonly known as gold salt) in chemical water, immerse the circuit board in the electroplating tank and connect the current to the circuit board A nickel-gold plating layer is formed on the surface of the copper foil. Electro-nickel-gold is widely used in electronic products because of its high hardness, wear resistance, and resistance to oxidation.

So what is heavy gold? Immersion gold is a method of chemical oxidation-reduction reaction to generate a layer of plating, generally thicker, is a kind of chemical nickel-gold layer deposition method, can reach a thicker gold layer.

The difference between circuit board immersion gold board and gold-plated board:

1. Generally, the thickness of immersion gold is much thicker than that of gold plating. Immersion gold will be golden yellow and yellower than gilding. Customers are more satisfied with immersion gold depending on the surface. The crystal structure formed by the two is different.

2. Since the crystal structure formed by immersion gold and gold plating is different, immersion gold is easier to weld than gold plating, and will not cause poor welding and cause customer complaints. At the same time, it is precisely because the immersion gold is softer than the gold plating, so the gold finger plate generally chooses gold plating, hard gold is wear-resistant.

3. The immersion gold board only has nickel and gold on the pad, and the signal transmission in the skin effect is on the copper layer without affecting the signal.

4. Immersion gold has a denser crystal structure than gold plating, and it is not easy to produce oxidation.

5. As the wiring becomes denser, the line width and spacing have reached 3-4MIL. Gold plating is prone to short circuit of gold wire. The immersion gold board only has nickel gold on the pad, so it will not produce gold wire short circuit.

6. 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.

7. Generally used for boards with relatively high requirements. The flatness is better. Immersion gold is generally used. Immersion gold generally does not appear as a black pad after assembly. The flatness and stand-by life of the immersion gold board are as good as the gold-plated board.

The above is the difference between gold-plated boards and gold-plated boards. 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 boards. A lot cheaper. I hope this introduction can provide you with reference and help.

1. Immersion gold board and chemical gold board are the same process product, electric gold board and flash gold board are also the same process product, in fact, it is just a different name for different people in the PCB industry. Immersion gold board and electric gold board are more common in The title of the mainland counterparts, while the Huajin board and the flash gold board are more commonly referred to by the Taiwan counterparts.

2. Immersion gold plate/chemical gold plate is generally called chemical nickel gold plate or chemical nickel immersion gold plate. The growth of nickel/gold layer is plated by chemical deposition; gold electrogold plate/flash gold The plate is generally called electroplated nickel-gold plate or flash-plated gold plate. The growth of the nickel/gold layer is plated by DC electroplating.

3. Refer to the table below for the difference in mechanism between electroless nickel gold plate (immersion gold) and electroplated nickel gold plate (gold plating):

The difference between the characteristics of the immersion gold board and the gold-plated board

Why do not "spray tin" in general?

As the integration level of IC becomes higher and higher, IC pins become more denser. The vertical spray tin process is difficult to flatten the thin pads, which brings difficulty to the placement of SMT; in addition, the shelf life of the spray tin plate is very short. The gold-plated board just solves these problems:

1. For the PCB surface mount process, especially for 0603 and 0402 ultra-small surface mounts, because the flatness of the pad is directly related to the quality of the solder paste printing process, it has a decisive impact on the quality of the subsequent reflow soldering, so the whole Plate gold plating is common in high-density and ultra-small surface mount processes. 2 In the trial production stage, due to factors such as component procurement, it is often not that the board is soldered immediately, but it is often used for several weeks or even months. The shelf life of the gold-plated board is more than that of lead-tin combine

However, as PCB wiring becomes denser, the line width and spacing have reached 3-4MIL. This brings about the problem of short circuit of gold wire:

As the frequency of the signal gets higher and higher, the signal transmission in the multi-plated layer caused by the skin effect has more obvious influence on the signal quality:

The skin effect refers to: high frequency alternating current, the current will tend to concentrate on the surface of the wire to flow.

Why choose immersion gold board instead of gold-plated board?

In order to solve the above problems of gold-plated boards, PCBs using gold-plated boards mainly have the following characteristics:

1. Because the crystal structure formed by immersion gold and gold plating is different, immersion gold will be golden yellower than gold plating, and customers will be more satisfied.

2. Because the crystal structure formed by immersion gold and gold plating is different, immersion gold is easier to solder than gold plating, and will not cause poor PCB soldering and cause customer complaints.

3. Because the immersion gold board only has nickel and gold on the pad, the signal transmission in the skin effect will not affect the signal on the copper layer.

4. Because immersion gold has a denser crystal structure than gold plating, it is not easy to produce oxidation.

5. Because the immersion gold board only has nickel and gold on the pads, it will not produce gold wires and cause slight shortness.

6. Because the immersion gold board only has nickel and gold on the pads, the solder mask on the circuit and the copper layer are more firmly bonded.

7. The project will not affect the distance when making compensation.

8. Because the crystal structure formed by immersion gold and gold plating is different, the stress of the immersion gold plate is easier to control, and for products with bonding, it is more conducive to bonding processing. At the same time, it is precisely because the immersion gold is softer than the gilding, so the immersion gold plate is not wear-resistant as the gold finger.

9. The flatness and stand-by life of the immersion gold board are as good as the gold-plated board.