The Properties Of Copper Thin Films Prepared By Roll To Roll Processing And DC Magnetron Sputtering Methods

In recent years, flexible printed circuit boards based on two layer flexible copper clad laminate has been widely applied in folding mobile phone, digital camera and notebook computer etc. Flexible printed circuit boards have many advantages, such as light, thin and lexible structure. There have many methods to make two layer flexible copper clad laminate, such as coating, laminating and sputtering/plating methods. Copper thin films made by sputtering/plating methods have advantages of good smoothing, bending, compact structure and easy to make double panel. But at present, two layer flexible copper clad laminate has weaknesses of poor conductivity and low peeling strength, thereby improving it's conductivity and peeling strength has become a urgent problem.Copper thin films were deposited on polyimide flexible substrate by roll to roll DC magnetron sputtering. The influence of the sputtering power, argon ion bombardment and transition layer on the contact angle, preferred orientation, average grain size, resistively and peeling strength were characterized by contact angle measurement, x-ray diffraction, four point probe measurement and other instruments. The results show that: (1) As sputtering power increasing, <111> crystal plane exhibits obvious preferred orientation, average grain size increases, resistively decreases, peeling strength of copper thin films increase. But as sputtering power overrun 7500W, peeling strength become decreasing. (2) Contact angle decreases with argon ion bombardment time passing; At 3 minute, the lowest contact angle 45.0°was obtained; After 3 minutes, contact angle increases as time prolong. When argon ion bombardment time prolong, average grain size increases, resistively decreases, peeling strength increases, but as argon ion bombardment overrun 3 min, peeling strength of copper thin films become decreasing. (3) Transition layer can reduce interface mutation, mitigate stress, decrease internal stress produced by lattice mismatch, difference of thermal expansion coefficient. Compared to copper thin films without plating transition layer , the peeling strength of copper thin films plating CuO transition layer increases 1.46 times, the peeling strength of copper thin films plating TiO₂ transition layer increases 5.22 times.