For the various next generation flexible devices such as wearable devices, implantable devices, etc., adhesion strength between different surfaces is very important for the reliable operation of the devices. In this study, to improve the adhesion strength between metal (Cu) and polymer substrate (prepreg), a plasma press process, where two surfaces are hot pressed together while generating a plasma between them, were used and the effect of plasma press method on the adhesion strength between prepreg and Cu were investigated and the results were compared with a conventional hot press method. When the prepreg surface was treated with a plasma using He/N 2 /O 2 or He/O 2 before hot press, the adhesion strength was decreased compared to the hot press without previous plasma treatment due to the hardening of the prepreg surface before the hot press. In contrast, when the Cu surface was treated with a plasma using He/N 2 /O 2 or He/O 2 before hot press, the adhesion strength was increased about 20% compared to the hot press only due to the formation hydroxyl group and Cu 2+ on the Cu surface before the hot press. However, when the prepreg and Cu were plasma pressed together, the use of He/O 2 and He/N 2 /O 2 improved the adhesion strength significantly about 35% and 75%, respectively, compared to the hot press only due to the activation of the prepreg surface and Cu surface during the hot press by forming dangling bonds on the surfaces in addition to the formation of hydroxyl group and oxygen bonding on the surfaces.