摘要
在激光诱导前向转移(LIFT)技术中,通常使用金属薄膜作为供体材料,并通过转移金属液滴的逐点堆叠来实现金属微结构的打印成形。然而,采用该方法制备的铜微结构存在内部孔隙率高和电阻率高的问题,难以满足实际应用的需求。为此,提出了一种LIFT复合化学沉积的新工艺。该工艺首先利用LIFT技术制备铜骨架结构,然后通过化学沉积技术对骨架进行填充,从而形成致密的实体结构。实验结果表明,采用该新工艺制备的铜微结构的内部孔隙率仅为3.2%,且电阻率低至块体铜的2.7倍。该方法为高质量金属铜微结构的增材制造提供了一种新的可能方案。
Objective Twodimensional(2D)and threedimensional(3D)microscale metal structures are widely used in applications such as microelectromechanical systems(MEMS),printed circuits,and sensor devices.Various additive manufacturing technologies have been proposed to prepare microscale 2D and 3D metal structures.Among them,laserinduced forward transfer(LIFT)is a noncontact printing technique that utilizes the localized pressure generated by laser ablation as a driving force to drive the transfer of a donor material.Compared with other technologies,LIFT does not require fine electrodes or nozzles and can be realized directly under atmospheric conditions,thus providing higher application flexibility and relatively low application costs.However,the metal structures prepared via LIFT have many microdefects,such as holes,amorphous layers,and nanocrystals,which result in poor electrical properties.To address the above challenges,this work proposes a novel method that combines LIFT and electroless plating to prepare lowresistance microscale copper structures.The technique utilizes electroless plating to grow a highquality metal layer on the metal skeleton prepared via LIFT and achieves dense filling of the skeleton.The micro defects of the structures prepared using the proposed method are considerably lower than those prepared using LITF.The proposed method provides a new technique for the highquality additive manufacture of microscale Cu structures.Methods A laser beam with a wavelength of 532 nm and a pulse width of 2 ns was passed through a beam expander and quarterwave plate before entering a galvanometer scanner equipped with a scan lens.Cu films were coated on quartz plates to act as donor films.The focused laser beam was used to shoot the donor film and then form Cu particles on receivers.For comparison,Cu structures were prepared using two methods in this work.First,Cu structures were directly prepared using LIFT via pointbypoint stacking of the Cu particles.Second,periodic Cu pillars with different pillar spacings were first prepared using LITT via pointbypoint stacking of the Cu particles.Subsequently,the structures with the periodic Cu pillars were immersed into a solution for electroless plating.Copper was deposited on the pillars according to the following reaction:Cu2++2HCHO+4OH-→Cu+2HCOO-+H2+2H2O.Results and Discussions A Cu structure measuring 800μm×350μm and with a thickness of 28μm was directly prepared using LIFT.The porosity of the structure reaches 11.2%,and the electrical resistance is(36.96±3.68)μΩ·cm,which is 22 times that of bulk copper(Fig.2).For comparison,periodic Cu pillars with the pillar spacing(d)varying from 5.0μm to 12.5μm were first prepared by LIFT,and then the gaps between the pillars were filled by electroless plating(Fig.3).The surface roughness increases with the pillar spacing,but the porosity and resistance reach their lowest values when d=10.0μm(Fig.4).The optimized d was set to 7.5μm to balance the surface roughness and electrical performance of the prepared structures.Figure 5 further compares the elemental composition and micro sections of the structures prepared using the two methods.Conclusions Herein,an additive manufacturing method that combines LIFT and electroless plating is proposed to prepare lowresistance microscale Cu structures.When preparing Cu structures directly using LIFT,the formation of the bulk structure depends on the pointbypoint stacking of the metal particles formed by the transfer.The transferred particles cool rapidly after contacting the receiver owing to their high velocity and small size.It is difficult to form a dense bond between these particles,making it prone to various micro defects.The porosity of the structure prepared by LIFT is as high as 11.2%,and the atomic number fraction of silica and oxygen impurities is as high as 3.0%.These microstructural defects drastically increase the bulk resistivity,making it as high as 22.0 times that of bulk copper resistance.By contrast,in our proposed method,LIFT is used only for the preparation of periodic Cu pillar arrays,while the gaps between the copper pillars are effectively filled by electroless plating.The Cu structures prepared using electroless plating show high density and purity.A smooth surface can be obtained with appropriate pillar spacing;additionally,the internal porosity and impurity atomic number fraction are drastically reduced to 3.2%and 0.8%,respectively,and the resistivity is reduced to 2.7 times that of bulk resistance.
作者
杨鹏飞
罗炳军
伍志恒
苏新虹
李亮
金立奎
龙江游
Yang Pengfei;Luo Bingjun;Wu Zhiheng;Su Xinhong;Li Liang;Jin Likui;Long Jiangyou(School of Electromechanical Engineering,Guangdong University of Technology,Guangzhou 510006,Guangdong,China;Guangdong Engineering Technology Research Center of Intelligent Inspection and Laser Precision Repair,Guangdong Greatsense Intelligent Equipment Co.Ltd.,Guangzhou 510700,Guangdong,China;Universal Circuit Board Equipment Co.Ltd.,Dongguan 523000,Guangdong,China;Zhuhai Founder Technology High Density Electronic Co.Ltd.,Zhuhai 519000,Guangdong,China)
出处
《中国激光》
北大核心
2025年第12期305-313,共9页
Chinese Journal of Lasers
基金
国家自然科学基金(52475437)
广东省基础与应用基础研究基金(2023A1515030202)。
关键词
激光诱导前向转移
金属微结构
增材制造
3D打印
化学沉积
laserinduced forward transfer
microscale metal structures
additive manufacturing
3D printing
electroless plating
