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The core function of hole metallization is to realize the conduction between PCB layers by plating copper on the hole wall. It is the core and key point for double-sided boards and multilayer boards to play a role. The hole metallization technology is not complicated, and can be simply divided into two parts: preparation before copper plating and copper plating. The quality of copper electroplating depends on the preparation before copper electroplating to a large extent.
At present, there are three main preparation processes for copper electroplating in the industry: copper precipitation, black hole and black shadow.

1. PTH

The main principle of copper deposition, also known as chemical copper deposition, is to deposit a layer of copper on the hole wall by using the chemical replacement reaction as the conductive lead for subsequent copper plating. If it is conventional sunk thin copper, its thickness is generally 0.5μM or so. As the most traditional preparation process before copper electroplating, it has the following advantages and disadvantages:

Advantages:

(1) Metal copper has excellent conductivity (in the wire, copper wire is usually used as conductivity);
(2) The thickness can be adjusted in a wide range with wide adaptability (the lowest in the industry is 0.3μM, up to 30μm. Directly replace the subsequent copper electroplating process);
(3) The process is mature and stable, and can be applied to all PCB products (pcb/fpc/rfpcb/ carrier board / metal substrate / ceramic substrate, etc.).

Disadvantages:

(1) It contains formaldehyde, which is harmful to the health of operators;
(2) Large equipment investment, high production cost and great environmental pollution;
(3) The time limit control is short, and the general effective time is 3~6 hours.

2.Black hole

Black hole is one of the direct electroplating technologies. Its main principle is to use the physical principle to make the carbon powder adsorb on the hole wall surface to form a conductive layer, which can be used as the conductive lead for subsequent copper electroplating. Generally, its thickness is 0.5~1μm。As one of the mainstream preparation processes before copper electroplating, it has the following advantages and disadvantages:

Advantages:

(1) It does not contain formaldehyde, which has little impact on the health of operators and little pollution to the environment;
(2) The equipment investment is small, the waste treatment is simpler, and the process cost is lower than that of copper precipitation;
(3) The potion and process are relatively reduced, and the timeliness can reach 48h, which is more convenient for maintenance and management.

Disadvantages:

(1) In terms of conductivity, the conductive carbon powder is weaker than the deposited copper layer;
(2) Its applicability is not as wide as that of sunk copper. Therefore, although it has been used on a large scale, it is mainly used for double-sided boards in the industry, and high-end products such as HDI are rarely used

3.Shadow

Black shadow, in a strict sense, is the further development of black hole process. Its principle, advantages and disadvantages are similar, and better than black hole. The main difference is that the conductive layer of the black hole is carbon powder, while the conductive layer of the black shadow is graphite.

In addition, black holes are generally not used in high-end products or with complex processes, but black shadow can. The black shadow process has partially replaced copper deposition and is widely used in high-end circuit boards, such as HDI boards and IC carrier boards. Sometimes, the black shadow process is better than copper deposition process, such as selective pattern plating.

As mentioned above, you may think that the copper sinking process is better than the black hole and black shadow process. Generally speaking, the industry generally thinks so. However, if it involves the actual application level, it is not true. Each PCB process will have its advantages and disadvantages, so as to establish its position in the practical application. If it has been completely backward, That will naturally be eliminated by the industry.

Therefore, it is considered that the effect of copper deposition > black shadow > black hole can be used as a reference answer, but it can not be used as a final answer, because it also involves the actual situation of each process plant, as well as the equipment, liquid medicine, parameters, etc. used in the process.

Therefore, from a real point of view, the process is only a means of making products. As long as the products produced can meet the requirements of shipping, and the manufacturer can also obtain satisfactory profits, this process can be adopted.