PCB Technical - About the surface roughness of copper conductors in PCB

Since the birth of the printed circuit board (PCB), due to the low bonding force between the copper conductor and the insulating (dielectric) layer and the large difference in thermal expansion coefficient, it is extremely prone to failures such as delamination. In order to overcome this problem, the most traditional method for a long time is to increase the surface roughness of copper conductors. This solution, in essence, is to increase the contact area between the copper and the insulating dielectric layer to improve the bonding strength. Obviously, this is a physical method to increase the contact area.

With the advancement of science and technology and the development of information technology, PCBs are rapidly moving towards high density and high frequency (or high speed), especially the development and progress of high frequency (high speed) signal transmission. The skin of copper conductors in PCBs Effect and high-density development brought about the miniaturization of copper wire size (the roughness of the wire is increasing), so high-frequency or high-speed signal transmission will be more and more carried out on the roughness surface layer.

The result is It causes signal transmission in the roughness layer to produce "standing waves", "reflections", etc., resulting in transmission signal loss or "distortion" (signal attenuation), and in severe cases, it will cause transmission signal failure. Therefore, the use of roughening on the surface of the copper wires in the PCB to improve the bonding strength is out of date and encounters serious challenges!

In PCB board, the bonding strength (force) requirement is to increase the surface roughness of copper conductors, and the requirement from high-frequency signal transmission is to reduce the surface roughness of copper conductors. The main aspect of this contradiction is the surface roughness of copper. In the PCB, it is necessary to meet the development requirements of high density and signal high-frequency (high-speed) speed, so it solves the problem of bonding between the roughness-free copper surface and the insulating dielectric layer and achieves the bonding strength (force) that meets the (regulated) requirements. The best solution is to use chemical methods to replace the traditional physical methods of increasing the surface roughness, such as adding a very thin "shared" bonding layer between the copper and the insulating (dielectric) layer, one side of which can be connected to the copper surface Reaction, and the other side can "polymerize" or "fusion" (or compatibility) with the insulating (dielectric) layer. Such a "shared" bonding layer can firmly bond the copper conductor and the insulating (dielectric) layer together, Improve or meet the requirements of the bonding strength between the two, and also provide a roughness-free copper surface to facilitate the development of high-frequency (high-speed) signal transmission.

Generally speaking, the traditional copper surface roughening (contour) process technology is challenged, and the result of the challenge will inevitably lead to the birth, growth and development of new process technology, which is the law of development of things. Therefore, the use of chemical methods to replace the traditional physical combination method in the combination between the micro, roughness-free copper wires and the insulating dielectric layer in the PCB will enter a new stage, and it is also the direction of future PCB development and efforts!