Wireless communication and broadband technology such as 5G has progressed dramatically and the market of high performance portable devices like 5G mobile phones is expanding. To meet the ever-increasing requirements of transmission data, high-frequency substrates and their raw materials with low dielectric properties and good adhesivity for low transmission loss are required. We developed solvent-soluble polyimides with good heat resistance and low dielectric constant（ Dk） / dissipation factor （Df） characteristics by optimizing the composition ratio of the aliphatic, cycloaliphatic, and aromatic groups present in the polyimide back bone. We found that the adhesives prepared using our polyimides showed low Dk / Df and good adhesion to polyimide films and low profile copper foils. Furthermore, we developed a three-layer flexible copper clad laminate （3LFCCL） with our polyimde （PI） adhesives, low-pofile copper foils, and normal PI films. This 3LFCCL showed a transmission loss similar to that of liquid crystal polymer （LCP） FCCLs at frequencies less than 20GHz. This result indicates that by using our PI adhesives, lower cost FCCLs can be prepared, which can then be used as high-frequency substrates.

Temporary bonding tapes for Fan-Out Panel Level Packaging are required to possess high heat resistance. Hence, silicone adhesive tapes are coonly used in the industry. However, silicone adhesives transfer low-molecular siloxane to the adherend, which causes connection failures of the circuit joints. This paper reports that a newly designed pressure-sensitive adhesive（ P.S.A.） performed high heat resistance and low adhesive transfer to an adherend surface. The P.S.A. consists of 2-ethylhexyl acrylate as the main monomer, polyisocyanate including an isocyanurate ring as the crosslinker, and a reactive elastomer （RE） with polybutadiene as the additive agent. Furthermore, the P.S.A exhibited excellent peeling performance with extremely low adhesive transfer to silicon wafers with patterned steps. We found that RE effectively enhanced the performance of the P.S.A. by increasing the true breaking strain and breaking stress.

The present studies focused how large effects of the ratio of joints diameter, edge’s corner radius and adhesive thickness on the tensile strength of adhesive joints was studied. Finite element analysis and the corresponding experiments of butt joints with adhesive surface edge with round corner were conducted to study the above-mentioned effects. The calculated results showed a constant value of strength of adhesive joints with round corner edge on condition that the ratio of round bar diameter to adhesive thickness and the round bar corner to adhesive thickness were constant. While the experimental results of the tensile strength decreased with the increase of adhesive thickness, the experimental results showed the good agreements with the estimated strength calculated by FEM in the case of applying an appropriate adhesive thickness. It should be noted that it is important to control the adhesive thickness of butt joint for the strength of the adhesive.