Since the development in mobile display requires high data transmission speed, there is a growing need in the development of flexible copper clad laminate (FCCL) for flexible printed circuit board (FPCB) that has a high signal propagation at high frequency range. The circuit for signal transmission uses FCCL which is composed of copper foil and polyimide film. The surface roughness of copper foil has to be low to reduce the pathway of signal because the current flows near the surface at high frequency range. However, such low roughness of the copper foil results in poor adhesion to polyimide, which is a problem that should be addressed. In this study, the poly(amic acid)s (PAAs) having various structures were synthesized and the silane functional group was introduced as end group to investigate the enhancement in the adhesion with the copper metal. Various polyimide structures were synthesized with the combinations of pyromellitic dianhydride (PMDA), 4,4'-(hexafluoroisopropylidene) diphthalic anhydride (6FDA), 3-aminopropyltriethoxysilane (TEOS), 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA), m-tolidine (mTB) and 2,2'-bis(trifluoromethyl) biphenyl-4,4'-diamine (TFDB). The synthesized PAAs were casted on the copper foil and were imidized for the fabrication of polyimide for FCCL. The adhesion strength between the polyimide and the copper foil was investigated by peel strength test and interfacial characteristics was investigated with AFM, SEM, FTIR and contact angle measurement.

차세대(5G) 디스플레이의 발전으로 인하여 데이터 전송량이 점차 증가하므로, 신호전송이 빠른 대역대인 고주파 대역을 사용한다. 신호전송을 위한 회로는 동박과 폴리이미드 필름으로 이뤄진 유연동박적층판(FCCL)이 사용되는데, 고주파는 표면으로 신호가 흐르므로 두 소재 사이의 계면 조도를 낮춰 경로를 최소화하여야 한다. 그러나 저조도 동박을 사용하면 동박과 폴리이미드 수지와의 접착 강도가 떨어지게 되므로 이러한 문제점을 보완해야 한다. 본 연구에서는 동박과 접착력 향상을 위해 다양한 폴리이미드 구조를 설계하고, 아민계 실란 기능기를 도입한 폴리아믹산을 합성하였다. 다양한 구조의 폴리아믹산은 pyromellitic dianhydride(PMDA), 3,3'4,4'biphenyltetracarboxylicdianhydride(BPDA), 4,4'-(hexafluoroisopropylidene) diphthalic anhydride(6FDA)와 m-tolidine(mTB), 2,2'-bis(trifluoromethyl)-[1,1'-biphenyl]-4,4'-diamine(TFMB) 등의 조합으로 합성하여, 이를 동박에 코팅하고 이미드화하여 FCCL을 제조하였다. 접착력에 대한 특성은 다양한 폴리이미드 구조에 따른 박리 강도 시험과 분리된 계면에 대한 AFM, SEM, 접촉각 측정으로 상관관계를 비교 해석하여 확인하였다.

Keywords: FPCB; 2-layer FCCL; polyimide; peel strength; adhesion property; end-capping