PCB Tech - The process of PCBA board gold plating and tin plating

PCBA plate making is very important, and the process of gold plating and tin plating is also very important. Let's talk about various processes below.

The advantages and disadvantages of various PCB coatings: First, we have to understand why nickel plating, silver plating, tin plating, chrome plating, zinc plating, and gold plating are necessary. Generally we usually use tin plating and gold plating.

Common point: The plating layer has a common advantage, it can be anti-corrosion (improve the anti-oxidation ability) and play a decorative role.

Here are the differences:

1. Galvanizing: The main purpose is to prevent corrosion. It is characterized by low cost, convenient processing, and good effect. The disadvantage is that it is not suitable for friction parts, which will affect the welding performance of PCB, and it is generally used by fewer people.

2. Nickel plating: After plating, it has good chemical stability in the atmosphere and in lye, and it is not easy to change color. It can be oxidized at 600 degrees Celsius. It has high hardness and is easy to polish. The disadvantage is porosity.

3. Tin plating: It has high chemical stability, is almost insoluble in dilute solutions of sulfuric acid, nitric acid, and hydrochloric acid, and has good solderability.

4. Chrome plating: divided into decorative chrome and hard chrome. Decorative chromium is mainly for aesthetics and anti-corrosion, and its shortcomings are not wear-resistant. Hard chromium mainly improves the hardness, corrosion resistance and hardness of the workpiece.

5. Gold-plated and silver-plated: mainly for decoration and anti-corrosion. The disadvantage is that it is expensive.

Why use gold-plated PCB?

A. With the increasing integration of ICs, the more IC pins become denser. The vertical PCB tin spraying process is difficult to flatten the thin pads, which brings difficulty to the placement of SMT;

B. In addition, the shelf life of the spray tin plate is very short. The gold-plated board just solves these problems: For the surface PCB mounting 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 is important for the quality of the subsequent reflow soldering. To decisive influence, therefore, the whole board gold plating is common in high-density and ultra-small surface mount processes.

C. 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 better than that of lead. The tin alloy is many times longer, and the cost of the gold-plated PCB in the sample stage is almost the same as that of the lead-tin alloy board.

3. Why use heavy gold?

The gold plating process is divided into two types (the gold here is generally not pure gold, but nickel gold), one is electroplating gold, and the other is immersion gold (chemical method). For the gold plating process, the effect of tin is greatly reduced., And the tinning effect of Immersion Gold is better; unless the manufacturer requires bonding, most manufacturers will now choose Immersion Gold technology!

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 weld than gold plating, and will not cause poor welding 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 the crystal structure of immersion gold is denser than that of 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 PCB pads, the solder mask on the circuit and the copper layer are more firmly bonded.

7. The project will not affect the distance during compensation.

8. Because the crystal structure formed by PCB immersion gold and PCB gold plating is different, the stress of the immersion gold plate is easier to control, and for PCB 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 PCB immersion gold board are as good as the gold-plated board.