Optics and Lasers in Engineering 139 (2021) 106509 Contents lists available at ScienceDirect Optics and Lasers in Engineering journal homepage: www.elsevier.com/locate/optlaseng Direct bonding of copper foil and liquid crystal polymer by laser etching and welding Le Jia a , Haifeng Yang a,b,∗ , Yisai Wang a , Baocai Zhang a , Hao Liu a , Jingbin Hao a a School of Mechatronic Engineering, China University of Mining and Technology, XuZhou, 221116, China b Jiangsu Key Laboratory of Mine Mechanical and Electrical Equipment, China University of Mining & Technology, XuZhou, 221116, China a r t i c l e i n f o Key words: laser conduction welding laser etching copper foil LCP micro-tensile test peeling test a b s t r a c t The reported laser welding of dissimilar materials (metal and plastic) mostly focuses on the optimization of pa- rameters and process, the process is complex and the cost is high. Liquid crystal polymer (LCP) has attracted much attention due to its excellent electrical properties. With the rapid development of information technol- ogy, 5G high-frequency communication is gradually emerging. At the same time, there are many problems to be solved, such as the serious skin effect caused by the large copper foil surface roughness and large energy consumption. Therefore, it is urgent to solve this problem for the development of communication technology. Nowadays, the manufacturing process of a two-layer flexible copper clad laminate is not only complex, but also high production cost. In order to try a new manufacturing method and balance the copper foil surface roughness and the bonding strength between the copper foil and LCP, this study proposes a laser integrated manufacturing method for two-layer flexible copper clad laminates, including LCP laser etching, copper foil laser etching and laser welding. We fabricated regular microstructures on the copper foil surface by laser etching, used ultraviolet laser to irradiate the LCP surface, the copper foil and LCP were welded together by laser conduction welding. The surface roughness of the sample was measured by atomic force microscope, the surface morphology was observed by optical microscope, and the bonding strength and peel strength between the etched copper foil and LCP were tested by micro-tensile test. The welding sample bonding strength obtained by this way can reach the ultimate tensile strength of the copper foil, and the peel strength can reach 682.78 N/m, which is close to the reported peel strength obtained by other methods. High-resolution field emission scanning electron microscope and X-ray photoelectron spectrometer were used to reveal the bonding mechanism of the samples. The integrated method is easier to realize automation for the actual production process. Therefore, we have verified that the two-layer flexible copper clad laminate with high bonding strength and peel strength can be prepared by laser processing. 1. Introduction Copper foil is widely used in the current electronic field research due to its excellent performance [1,2], such as good conductivity, ductility [3,4]. The application of copper foil in printed circuit board is partic- ularly prominent, especially in flexible printed circuit board [5,6]. As an advanced polymer material, LCP is widely used in the research of flexible printed circuit board substrate [7,8], especially the two-layer adhesive-free flexible copper clad laminate [9,10], compared with other polymer materials such as polyethylene terephthalate (PET) and poly- imide (PI) [11]. With the rapid development of electronic technology, the function of electronic products is becoming more and more pow- erful, the three-layer flexible copper clad laminate (3L-FCCL) is gradu- ally withdrawing from the stage of powerful electronic products by the existence of adhesive. A two-layer flexible copper clad laminate (2L- ∗ Corresponding author. E-mail address: 4841@cumt.edu.cn (H. Yang). FCCL) combines copper foil with insulating substrate directly by some technologies such as laminating, coating and sputtering electroplating, which has excellent heat resistance and flexibility. However, the above- mentioned technology has the defects of high production cost and com- plex process [12-14]. As a kind of clean energy, laser is widely used in the research of special processing. In addition, it has the advantages of friendly envi- ronment, simple operation, no direct contact with workpiece, and high efficiency processing. The related researchers have made good achieve- ments in the large application fields of laser processing. Yang et al. conducted the temperature-assisted laser shock imprinting experiment, which proved that the laser shock imprinting technology can greatly improve the forming depth, forming accuracy and forming stability of the formed parts, and pointed out that this is caused by the influence of temperature on the physical properties of materials [15]. They also con- https://doi.org/10.1016/j.optlaseng.2020.106509 Received 13 October 2020; Received in revised form 26 November 2020; Accepted 1 December 2020 0143-8166/© 2020 Elsevier Ltd. All rights reserved.