目的 提供一种实现柔性聚合物表面金属电路的激光高性能直写及无损聚合物的电路精修方法。方法 以聚酰亚胺（PI）表面铜电路为例,利用由乙酸铜、正辛胺、2-氨基-2-甲基-1-丙醇（AMP）、甲酸及甲醇,配备了低分解温度的铜前驱体油墨,并通过功率仅1 W量级、波长532 nm的连续激光,将油墨以激光光热还原沉积的原理在PI表面直写形成铜线条;使用绿皮秒激光（12 ps、532 nm）及红外飞秒激光（小于1 ps且1 030 nm）,对前述PI表面铜线条和磁控溅射法在PI表面镀覆的1 μm铜膜进行局域化去除;使用TG-DSC测试铜前驱体油墨分解温度。结果 所配备前驱体油墨热分解温度为180 ℃,这有利于在直写过程不伤PI;铜电路直写效率和效能分别为2.0×106 μm3/s（即0.12 mm3/min）、0.067 mm3/min/W,且所写铜材电阻率为11.8×10-8 Ω·m;展示了可使用绿皮秒激光高选择性擦除PI表面铜膜且不伤PI的效果,而与之形成鲜明对比的是使用红外飞秒激光易出现的PI损伤问题：对于不同波长和脉宽组合形成的加工效果反差,结合铜反射谱,从铜和PI各自的去除阈值对激光波长和脉宽的依赖关系进行了机理分析。结论 采用连续激光辐照所配置的低成本铜前驱体油墨,可实现PI表面铜的高效且较高导电性的直写效果;超快激光脉宽和波长的协同调控,可促进聚合物与金属加工阈值的异化,从而易实现无伤聚合物的电路精修,其中以绿皮秒激光为代表的光源可适用于多种金属电路的高选择性刻除。
Abstract
A method was proposed for the high-performance laser direct writing of metal circuits on flexible polymer films and its selective removal of metal circuits, under the premise of non-destructive to polymers. Laser direct writing and selective removal of copper films on polyimide (PI) was considered as the example. For the aspect of laser direct writing, precursor ink with low decomposition temperature was prepared using copper acetate, n-octylamine, 2-amino-2-methyl-1-propanol (AMP), formic acid, and methanol. A linearly polarized, continuous-waved (CW) laser, with a power of only 1 W level and a central wavelength of 532 nm, was used to irradiate the precursor ink to form a copper film on the PI substrate via laser-thermal induced reduction and deposition. For the aspect of laser selective removal of the metal film from polymer dielectrics, two types of ultrafast lasers, namely green picosecond laser (12 ps and 532 nm) and near-infrared femtosecond laser (less than 1ps and 1 030 nm), were considered. Meanwhile, a Cu-PI composite film, made from the either magnetron sputtering technique by depositing a 1 μ m-thick copper film on the PI film, or the above-mentioned laser direct writing technique for generating a copper film on the PI substrate, was considered. For the aspect of laser direct writing, it was shown that a material deposition rate of 2.0 × 106 μm3/s (or 0.12 mm3/min) onto the PI film, as well as a deposition efficiency of 0.067 mm3/min/W, could be achieved for the copper film, with the electrical resistivity 11.8 ×10-8 Ω·m for the laser written copper. For the aspect of laser selective removal of metal circuits from polymer dielectrics, the underlying physical mechanism for using ultrafast laser with a suitable combination of wavelength and pulse was analyzed, aiming at a thorough removal of the metal film on the polymer film surface without damaging the PI film during laser ablating of the metal film. The key was to highly control the ablation threshold for polymers and metals, respectively, by considering the evolution law of linear light-absorption characteristics of metals and the nonlinear light-absorption characteristics of polymers at the wavelength. At the same time, the effect of using green picosecond laser to selectively erase the copper film on the PI surface was demonstrated, while near-infrared femtosecond laser was prone to damage the PI. Based on the light absorption characteristics corresponding to the reflection spectrum of copper, it was analyzed that green femtosecond laser could significantly promote the ablation threshold difference between the PI and copper, thus creating a wide range of processing parameter selection for pulse energy fluence, and facilitating an effect of a thorough removal of the metal film from the PI film without damaging the polymer during laser ablating of the metal film. In contrast, near-infrared femtosecond laser acted oppositely to the green picosecond laser mentioned above, namely damage the PI substrate once the laser etching reached the Cu-PI interface. A blackening of the PI substrate after finishing the selective removal of Cu was demonstrated. In conclusion, The CW green laser direct writing technique, together with the precursor ink proposed in this study, balances the manufacturing needs of low cost, high conductivity, and high manufacturing efficiency. By controlling both the pulse width and wavelength of ultrafast laser, ablation threshold difference between polymer and metal can be greatly promoted, thereby robustly removal of metal circuit materials on flexible polymer. Light sources such as green picosecond lasers can be applied to highly selective removal of various metal circuits.
关键词
激光直写 /
聚合物 /
表面电路 /
选择性刻除 /
前驱体油墨 /
超快激光 /
加工阈值
Key words
laser direct writing /
polymer /
surface circuit /
selective removal /
precursor ink /
ultrafast laser /
ablation threshold
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基金
国家重点研发计划项目(2022YFB4601302); 2024年中国航天科技集团有限公司自主研发项目; 国防基础科研计划（JCKY2023405C003）
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