PCB Technical - The special place of PCB immersion gold process

There is a very common process used in the surface treatment of circuit boards, which is called the immersion gold process. During the production, the cost of the immersion gold board is relatively high, and the immersion gold process is not generally used. Then how do we distinguish which PCB board needs to be gold-immersed? What kind of circuit board does not require immersion gold? It can be analyzed and judged according to the following situations.

Analysis of Main Uses of Immersion Gold Circuit Board

1. The board has gold fingers that need to be gold-plated, but the layout other than the gold fingers can be tin-sprayed or immersed gold according to the situation, that is, the usual "immersion gold + gold-plated fingers" process and "spray tin + gold-plated fingers" process, occasionally A small number of designers choose the full-page immersion gold method to achieve their goals in order to save costs or time is urgent, but the immersion gold does not reach the thickness of the gold plating, and if the gold fingers are frequently inserted and peeled, the connection will be poor.

2. The board's line width and pad spacing are insufficient. In this case, it is often difficult to produce with the tin spraying process. Therefore, for the performance of the board, the process such as immersion gold is usually used, which basically does not happen.

3. Immersion gold or gold plating. Because there is a layer of gold on the surface of the pad, the solderability is good and the board performance is also stable. The disadvantage is that immersion gold is more expensive than conventional tin spraying, and it is usually more expensive if the thickness of the gold exceeds the PCB factory convention. Gold plating is more expensive, but it works well.

After understanding the above three situations, you will know under what circumstances it is necessary to make an immersion gold circuit board.

Immersion gold process is to deposit a nickel-gold plating layer with stable color, good brightness, smooth plating and good solderability on the surface of the printed circuit. What is the difference between the immersion gold process and other processes?

The difference between PCB immersion gold process and other processes

1. Comparison of heat dissipation

The thermal conductivity of gold is good, and the pad made of it has the best heat dissipation due to its good thermal conductivity. Good heat dissipation. The lower the temperature of the PCB board, the more stable the chip work. Immersion gold board has good heat dissipation. Comprehensive heat dissipation holes can be used on the CPU bearing area of the notebook board and the BGA component soldering base, while the OSP and silver board heat dissipation The sex is average.

2. Comparison of PCB welding strength

After three times of high temperature, the solder joints of the immersed gold board are full, and the solder joints of the bright OSP board are gray and dark after three times of high temperature, similar to oxidation. After three times of high temperature soldering, it can be seen that the solder joints of the immersed gold board are full and the bright soldering The activity of solder paste and flux will not be affected, while the solder joints of the OSP process board are dull and luster, which affects the activity of solder paste and flux, which is easy to cause empty soldering and increased rework.

3. Comparison of electrical measurability

Immersion gold boards can be directly measured before and after production and shipment. The operation technology is simple and is not affected by other conditions; OSP boards are organic solderable film on the surface, and the organic solderable film is non-conductive, so it cannot be directly measured at all. It must be measured before OSP, but after OSP, excessive micro-etching is prone to cause poor soldering; the surface of the silver plate has a general film stability, which requires harsh external environments.

4. Process difficulty and cost comparison

Immersion gold craft boards are difficult to process, require high equipment, and have strict environmental protection requirements. Because of the large amount of use of gold, the cost is the highest among lead-free craft boards; the process of silver fusion boards is slightly less difficult, and has equivalent water quality and environmental requirements. Strict, the cost is slightly lower than that of the immersion gold board; the OSP board has the simplest process and the lowest cost.