Low Loss BT resin for substrates in 5G communication module

Roles of low-loss PCB materials are becoming more important along with the expansion of IoT (Internet of Things). Particularly, high speed and wide band data transmissions in 5G and the following generations are core technologies to progress IoT [1], and many PCB materials have been proposed and the evaluations are ongoing. However, the low loss transmission still has to be improved furthermore so that the advanced communications can be utilized without any limitation. BT (Bis-maleimide & Triazine) resin, a kind of thermosetting resin materials has excellent mechanical and electrical properties derived from unique polymer net-working [2]. In this study, new BT resin designed for 5G and the following generations was developed [3]. Generally, PCB materials aiming for low loss transmission need to have low Dk (Dielectric Constant) and low Df (Dissipation Factor). Then the new BT resin was designed to have lower Dk and Df than the conventional BT resins ever had.In this study, compatibility of BT resin varnish was investigated firstly. Because, typically, some components bringing low Dk and low Df to BT resin show poor compatibilities with the main components due to the difference of polarity. Secondly, adhesion to copper foils was studied. To reduce the transmission loss, copper foils laminated on BT composite (BT resin fillers glass clothes) are desired to have low surface profiles. So, it was necessary to keep adhesion even if anchoring effect became smaller. Finally, BT laminates and package substrates were fabricated to assess mechanical behaviors, the electrical reliability and the transition of Df under high temperature or/and high humidity conditions. Especially, the stability of the dielectric properties under harsh conditions is very important to ensure the advanced electrical modules under actual environments.As the conclusion of this study, the novel BT resin has been developed and the excellent performances were successfully demonstrated. The next challenge following this study is ongoing.