Since Paul Eisner officially invented PCB manufacturing technology in 1936, more than 80 years have passed, PCB has developed rapidly and has become an indispensable foundation for the electronics industry. Although the PCB generally only accounts for 5-10% of the cost of the finished circuit board, the reliability of the PCB is far more important than a single component – the component is broken, the circuit board can still be repaired, and the PCB is broken, the circuit board is damaged Can only be scrapped!
When it comes to reliability, we have to mention the metallization of PCB holes.
Hole metallization, its core function is to achieve conduction between PCB layers by plating copper on the hole wall. It is the core key point for double-sided and multi-layer boards to play a role. Therefore, many electronic industries Giants, such as Apple and Huawei, all attach great importance to this.
But in fact, the hole metallization technology is not complicated, and can be simply divided into two parts: preparation before electroplating copper, and electroplating copper. The quality of electroplating copper depends to a large extent on the preparation before electroplating copper.
Therefore, people in the industry tend to focus on the reliability of PCBs on the preparations before electroplating copper.
At present, there are three main preparation processes before copper electroplating in the industry: sinking copper, black hole, and black shadow. (There are also colloidal palladium, metal grouting, etc., but they are not the current mainstream and will not be discussed here)
1. Immersion Copper
Immersion copper, also known as electroless copper immersion, its main principle is to use the substitution reaction in chemistry to deposit a layer of copper on the hole wall as a conductive lead for subsequent electroplating copper. If it is conventional sinking thin copper, its thickness is generally about 0.5μm. As the most traditional preparation process before electroplating copper, it has the following advantages and disadvantages:
(1) Metal copper has excellent electrical conductivity (inside wires, copper wires are conventionally used as electrical conductors)
(2) The thickness can be adjusted in a large range and has wide adaptability (currently the lowest in the industry is about 0.3μm, and the highest can reach 30μm, directly replacing the subsequent electroplating copper process)
(3) The process is mature and stable, and can be applied to all circuit board products (PCB/FPC/RFPCB/carrier board/metal substrate/ceramic substrate, etc.)
(1) Contains formaldehyde, which is harmful to the health of operators
(2) Large equipment investment, high production cost, and serious environmental pollution
(3) Time-limited control is short, and the general effective time is 3 to 6 hours
Two, black hole
Black hole is a kind of direct electroplating technology. Its main principle is to use physical principles to make carbon powder adsorb on the surface of the hole wall to form a conductive layer to serve as a conductive lead for subsequent copper plating. Usually, its thickness is 0.5~1μm. As one of the current mainstream copper electroplating preparation processes, it has the following advantages and disadvantages:
(1) Does not contain formaldehyde, has little impact on the health of workers, and has 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 sinking copper
(3) The potions and processes are relatively reduced, and the timeliness can reach 48H, which is easier to maintain and manage
(1) In terms of conductivity, conductive carbon powder will be weaker than deposited copper layer
(2) Its applicability is not as wide as that of sinking copper. Therefore, although it has been used on a large scale, it is currently mainly used for double-sided panels in the industry, and high-end products such as HDI are hardly used.
Strictly speaking, black shadow is a further development of black hole technology. Its principle, advantages and disadvantages are similar, and it is 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 shadows can be used. Black shadow technology has partially replaced sinking copper and is widely used in high-end circuit boards, such as HDI boards, IC carrier boards, etc. Even, sometimes the black shadow process is better than the sinking copper process, such as selective pattern plating.
As mentioned above, you may think that the sinking copper process is better than the black hole and black shadow process. If you look at it generally, the industry generally thinks so, but if it comes to the actual application level, it is not always the case. Every kind of PCB technology will have its advantages and disadvantages, and then establish its position in practical applications. If it is indeed completely behind, it will naturally be eliminated by the industry.