PTH vs. Blackhole vs. Shadow PCB Hole Metallization Process

More than 80 years have passed since 1936 when Paul Eisner officially invented the PCB manufacturing technique. PCB has become an essential basis for the electronics industry with PCB's rapid development. Although PCB generally only accounts for 5~10 % of the cost of the finished circuit board, the reliability of PCB is far more important than a single component. Because if the component is broken, the circuit board can be repaired, but if the PCB is broken, the circuit board can only be scrapped!

PCB Hole Metallization

Speaking of reliability, this has to bring up the problem of PCB hole metallization. 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 key point that the 2-layer PCB and the multi-layer board can play a role. Therefore, many giants in the electronics industry, such as Apple and Samsung attach great importance to it.

But in fact, hole metallization technology is not complicated and can be divided into two simple parts: preparation before copper plating, and copper plating. The quality of copper plating depends on the preparation of copper plating to a large extent.

As a result, practitioners in the industry tend to focus on PCB reliability in the preparation of copper plating. At present, there are three main preparation processes for copper electroplating in the industry: PTH, Blackhole, and Shadow.

PTH

Plated Through Hole is a hole metallization process in circuit board manufacturing, also commonly called PTH, and is an autocatalytic redox reaction. It is mainly based on the displacement reaction in chemistry to deposit a layer of copper on the pore wall as a conductive lead for subsequent copper plating. If it is conventional copper, its thickness is generally about 0.5 μm. As the most traditional copper plating preparation process, it has the following advantages and disadvantages:

Advantages of PTH:

• Copper has excellent electrical conductivity (wire inside, the conventional use of copper wire as conductive).
• The thickness can be adjusted in a wide range, and wide adaptability (the lowest in the industry is about 0.3 μm, and the highest is up to 30 μm presently, directly replacing the subsequent copper plating process).
• The process is mature and stable, which can be applied to all types of circuit board products (PCB/FPCB/RFPCB/metal substrate/ceramic substrate, etc.).

Disadvantages of PTH:

• Containing formaldehyde, adverse to the health of workers.
• Large equipment investment, high production costs, and serious environmental pollution.
• The aging control is short, and the effective time is generally 3-6 hours.

Blackhole

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

Advantages of Blackhole:

• No formaldehyde, small impact on the health of workers, and small pollution to the environment.
• The equipment investment is small, the waste treatment is simpler, and the process cost is lower than that of PTH.
• The potion and process are relatively simple, the timeliness can reach 48 hours, and it is easier to maintain and manage.

Disadvantages of Blackhole:

• In terms of conductivity, the conductive toner is weaker than the PTH.
• Its applicability is not as wide as that of PTH. Therefore, although it has been used on a large scale, it is mainly used for 2-layer PCB in the industry at present. High-end products such as HDI PCB are almost not used.

Shadow

Strictly speaking, Shadow is a further development of the Blackhole process. Their principle, advantages, and disadvantages are similar, but Shadow is better than the black hole. The main difference is that the conductive layer of the Blackhole is carbon powder, while the conductive layer of the Shadow is graphite.

In addition, Blackhole is generally not used for high-end products, or with complex processes. but the black shadow can do that. The PTH process has been partially replaced by Shadow, widely used in high-end circuit boards, such as HDI boards, and IC substrates.

Conclusion

As mentioned above, you may think that the PTH process will be better than Blackhole, Shadow process. The industry generally thinks so, but when it comes to the actual application level, it is not. Because every PCB process will have its advantages and disadvantages, and then establish its status in practical application. If indeed has been comprehensively backward, that will naturally be eliminated by the industry.

So, it is considered that the effect of PCB Hole Metallization: PTH > Shadow > Blackhole, can be used as a reference answer, but it can not be used as a final standard answer. Because it also involves the actual situation of each process using the factory, as well as the equipment used in the process, potion, parameters, and so on.

Therefore, in reality, the process is just a means to make products. As long as the products produced can meet the requirements of shipping, and the manufacturer can obtain satisfactory profits, then the process can be adopted.

After factory verification, as a PCB manufacturer focusing on the high-end direction, in order to meet customer demand and achieve highly reliable production, NextPCB decided to adopt the most stable and mature process to ensure better delivery quality.