A Brief Discussion on the Manufacturing Process of PCBA Boards

The layout of the PCBA board is very important, and the processes of gold plating and tin plating are also very crucial. Let's talk about various processes.

The advantages and disadvantages of various coatings: First, we need to understand why we need to nickel plate, silver plate, tin plate, zinc plate, gold plate. Generally, we use tin plate and gold plate most frequently. The common point is that all the coatings have a common benefit, which is to prevent corrosion (improve the anti-oxidation ability) and have a decorative effect.

Here are the differences:

1. Zinc plating: The main purpose is to prevent corrosion. Its characteristics are low cost, convenient processing, good effect, but it is not suitable for friction parts, which will affect the welding performance. Generally, it is used by fewer people.

2. Nickel plating: It makes the work in the atmosphere and alkaline solution chemically stable, does not change color easily, oxidizes above 600 degrees Celsius, has high hardness, is easy to polish, but has porosity.

3. Tin plating: It has high chemical stability. It hardly dissolves in dilute solutions of sulfuric acid, nitric acid, and hydrochloric acid. The welding performance is good.

4. Chromium plating: It is divided into decorative chromium and hard chromium. Decorative chromium mainly serves for aesthetics and anti-corrosion, but it is not wear-resistant. Hard chromium mainly improves the hardness, corrosion resistance and hardness of the workpiece.

5. Gold and silver plating: They mainly serve for decoration and anti-corrosion. The disadvantage is that the price is high. Why use gold plated boards?

A. As the integration degree of ICs increases, the IC pins also become more and more numerous and dense. The vertical spray tin process is difficult to flatten the fine pads, which brings difficulties to the SMT assembly;

B. In addition, the service life of tin-plated boards (shelf life) is very short, while gold-plated boards exactly solve these problems: For surface mount technology, especially for 0603 and 0402 ultra-small surface mount, because the flatness of the pads directly affects the quality of solder paste printing process, it has a decisive influence on the reflow welding quality. Therefore, whole board gold plating is often seen in high-density and ultra-small surface mount technology.

C. During the trial production stage, due to factors such as component procurement, the board is not immediately welded but often needs to wait for several weeks or even months before being used. The shelf life (shelf life) of gold-plated boards is many times longer than that of lead-tin alloy, and the cost of gold-plated PCB in the sample stage is almost the same as that of lead-tin alloy board.

3. Why use electroless gold plating:

Gold plating processes are divided into two types (here, the gold is generally not pure gold but nickel gold), one is electroplated gold and the other is electroless gold (chemical method). For gold plating processes, the effect of plating with tin is greatly reduced, while the plating effect of electroless gold is better; unless the manufacturer requires bonding, most manufacturers will choose the electroless gold process!

1. Because the crystal structure formed by electroless gold and gold plating is different, electroless gold is golden yellow and more yellow than gold plating, and customers are more satisfied.

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

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

4. Because electroless gold has a more compact crystal structure than gold plating, it is less prone to oxidation.

5. Because the electroless gold board only has nickel gold on the pads, there will be no gold wire causing micro-short circuits.

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

7. Engineering compensation will not affect the spacing.

8. Because the crystal structure formed by electroless gold and gold plating is different, the stress of the electroless gold board is easier to control, which is more conducive to the processing of bonding for products with bonding requirements. At the same time, because electroless gold is softer than gold plating, the electroless gold board is not wear-resistant for gold fingers.

9. The flatness and shelf life of the electroless gold board are as good as those of the gold-plated board.