Seiya Kido, Tsuyoshi Amatani
MEC Company LTD.
Development of information and telecommunications network is outstanding in recent years, and it is required for the related equipments such as communication base stations, servers and routers, to process huge amount of data in no time. As an electrical signal becomes faster and faster, how to prevent signal delay by transmission loss is a big issue for Printed Circuit Boards (PCB) loaded on such equipments. There are two main factors as the cause of transmission loss; dielectric loss and conductor loss. To decrease the dielectric loss, materials having low dielectric constant and low loss tangent have been developed.
On the other hand, reducing the surface roughness of the copper foil itself to be used or minimizing the surface roughness by modifying surface treatment process of the conductor patterns before lamination is considered to be effective in order to decrease the conductor loss. However, there is a possibility that reduction in the surface roughness of the conductor patterns will lead to the decrease in adhesion of conductor patterns to dielectric resin and result in the deterioration of reliability of PCB itself.
In this paper, we will show the evaluation results of adhesion performance and electrical properties using certain type of dielectric material for high frequency PCB, several types of copper foil and several surface treatment processes of the conductor patterns. Moreover, we will indicate a technique from the aspect of surface treatment process in order to ensure reliability and, at the same time, to prevent signal delay at the signal frequency over 20 GHz.
We developed new surface treatment process (FlatBOND GT process) on copper conductor for high-speed and high-frequency PCBs. As mentioned above, the FlatBOND GT process achieved superior performance for transmission loss over 20GHz frequency, and its adhesion performance for low dielectric resins was confirmed as superior than that of our surface roughening treatment. FlatBOND GT process improved the transmission loss of signal especially at high frequency region, on which roughening treatments have problems for transmission loss.
Furthermore it can deliver the high adhesion performance for low dielectric resins with smooth and profile free surface. In the future, technologies of electric device related to base station, servers and routers will grow more and more for the development of information and telecommunications network such as IoT. Accordingly, the requirement for the high-speed and high-frequency applications should increase more and more. We firmly believe that our FlatBOND GT process solves the issues of signal transmission loss and improve the reliability of advanced PCBs.
Initially Published in the IPC Proceedings