【作者】 朱中正；

【导师】 孟惠民；

【作者基本信息】 北京科技大学 ， 材料科学与工程， 2023， 博士

【摘要】 中国是全球最大的制造业中心,也是世界第二大电子设备消费市场,全球大部分电子产品在中国生产,微型计算机和智能手机产量分别占全球50%、80%以上。电子产品均是由多个部件或电子系统通过电子连接器连接复合或集成而成,为达到高可靠和长寿命以及适合电子产品制造工艺流程的需要,对电子连接器的接触端子要施加上导电、耐磨、耐蚀的电镀镀层。目前普遍使用表面镀“硬金”(添加1%以下Co的AuCo合金,ASTM B488 Type Ⅱ)层的AuCo/Ni复合镀层体系,但一直存在成本高、性能不足和使用氰化物镀液体系而不环保等问题。为此,本文综述分析了电接触镀层国内外的生产和研究现状,从贵金属的用量决定着贵金属复合电接触镀层的成本出发,依据合金化可降低合金元素用量并可能提高合金性能的材料学原理,确定将AuCu合金、PdNi合金、Pt以及Ni基高熵合金镀层和它们复合构成的复合镀层作为研究体系,进行各体系的电镀制备工艺和成分-结构-性能关系的系统研究,探讨了各体系的影响因素、影响规律和机理,期望获得少用贵金属的更低成本、更高性能的新电接触镀层体系并提供理论支撑。以超过传统的Au/Ni复合镀层体系并达到工业应用要求为目标,采用电子连接器镀层实际要求的目标性能进行考核评估,包括成本、耐磨性和耐蚀性,耐蚀性上不仅要考核一般的化学、电化学腐蚀,还考察了对材料很苛刻、也是Au/Ni镀层比较差的耐通电电解腐蚀的能力。研发出了具有低成本、高性能的AuCu46合金镀层,满足电子连接器镀层工业标准导电、耐磨、耐蚀各方面的要求,可取代硬金AuCo镀层使金消耗量降低33 wt%,贵金属使用成本降低达到1/3。合金化Cu元素可使Au镀层晶粒细化至10nm以下,AuCu合金镀层晶粒尺寸的反平方根与硬度呈Hall-Petch直线关系,产生细晶强化和固溶强化共同作用,使其硬度比硬金AuCo高3倍以上、比Au高6倍以上,耐磨性明显高于硬金AuCo镀层、远高于纯Au镀层,由于其保持了纯Au镀层的晶体结构因此具有了优异的耐腐蚀性能。开发了低成本、高性能的PdNi15合金镀层和电镀技术,由于PdNi合金镀层密度较低,电镀相同厚度的镀层时,用PdNi15取代硬金镀层的可使贵金属使用低35%。PdNi合金电沉积可操作电流密度范围广、镀速快,PdNi15合金细化为9.5 nm纳米晶结构的平整镀层,保持着Pd金属面心立方结构的单相固溶体,晶格常数和镀层中镍原子比例遵循Vegard定律呈线性关系;明确了 PdNi合金镀层成分、结构与镀层耐磨性、耐蚀性之间的关系:由于细晶强化、固溶强化以及单相面心立方结构的共同作用,PdNi合金镀层的硬度、耐磨性高,具有和纯Pd镀层类似的耐蚀性,在亚硫酸蒸汽试验中未出现腐蚀。开发了高质量Pt镀层和其脉冲电镀技术。Pt价格比Au低,并在耐腐蚀性能上极具优势。通过系统研究,确定了最佳脉冲电镀工艺参数,脉冲电镀铂镀层的晶粒尺寸从直流电镀镀层的21 nm降低到16 nm,具有更高的平整度和硬度,硬度和晶粒尺寸呈现Hall-Petch关系。脉冲电镀层表面结构和结晶取向的变化提升了耐磨性能。但与硬金相比,脉冲电镀Pt作为表层仍然存在耐磨失效的风险,主要表现为耐磨测试后镀层出现裂纹,底层贱金属Cu迁移至表层。研发了高性能的CoNiWReP高熵合金镀层和水溶液脉冲电镀环保制备技术。首次从水溶液体系成功制备了 CoNiWReP高熵合金镀层,确定了优化电镀液配方和工艺条件,脉冲电镀获得的CoNiWReP合金各元素含量在5%～35%范围内符合高熵合金定义,可对铜基体起到牺牲阳极型阴极保护作用,保护效率高达73.8%;制备复合镀层进行测试表明,用含有高于0.1 μm高熵合金镀层的“AuCo/CoNiWReP/Ni”三层结构镀层即可显著改善表面低金厚度条件下传统硬金AuCo/Ni体系的耐硝酸腐蚀的性能。利用以上四种镀层的特性,设计并构建成功了两类新型低成本、高性能连接器电接触镀层系统和成套电镀技术:一是适用于正极接触端子的低成本耐电解腐蚀复合镀层,为AuCu/Pt/Ni复合镀层,贵金属使用成本比硬金AuCo/Ni复合镀层降低30%,而性能远高于传统的硬金AuCo/Ni复合镀层,尤其耐电解腐蚀性能比传统硬金AuCo/Ni复合镀层高30倍以上;二是适用于非正极接触端子的低成本耐电化学腐蚀复合镀层,为PdNi/HEA/Ni复合镀层,贵金属使用成本比硬金AuCo/Ni复合镀层低35%,性能远高于传统的硬金AuCo/Ni复合镀层,并且工艺中不含氰化物,是环保制造技术。揭示了贵金属复合镀层的电解腐蚀失效机理是贵金属的通电使其阳极腐蚀和孔隙腐蚀使镀层剥离,而AuCu/Pt/Ni复合镀层具有高耐电解腐蚀性能的原因在于:1)Pt镀层材料本身在阳极电解条件下腐蚀较慢,2)AuCu电沉积更易于填充Pt镀层中的孔隙。更多还原

【Abstract】 China is the world’s largest manufacturing center and the world ’s second largest consumer market for electronic equipment.Most of the world’s electronic products are produced in China,and microcomputers and smartphones account for more than 50%and 80%of global production respectively.Electronic products are made up of multiple components or electronic systems connected by electronic connectors combination or integration,in order to achieve high reliability and long life and suitable for the needs of electronic products manufacturing process,the contact terminal of the electronic connector to apply conductive,wear and corrosion resistant electroplating coating.At present,AuCo/Ni composite coating system with surface plating’hard gold’(AuCo alloy with less than 1%Co,ASTM B488 Type Ⅱ)layer is widely used,but there are always problems such as high cost,insufficient performance and the use of cyanide plating liquid system without environmental protection.In this paper,the production and research status of electrical contact coatings at home and abroad are reviewed and analyzed.Starting from the fact that the amount of precious metals determines the cost of precious metal composite electrical contact coatings,based on the material principle that alloying can reduce the amount of alloying elements and may improve the performance of alloys,AuCu alloy,PdNi alloy,Pt and Ni-based high-entropy alloy coatings and their composite coatings are determined as research systems.The electroplating preparation process and composition-structure-performance relationship of each system are systematically studied,and the influencing factors,influencing rules and mechanisms of each system are discussed.It is expected to obtain a lower cost and higher performance new electrical contact coating system with less precious metals and provide theoretical support.In order to exceed the traditional Au/Ni composite coating system and meet the requirements of industrial application,the target performance of the actual requirements of the electronic connector coating was used for assessment and evaluation,including cost,wear resistance and corrosion resistance.In terms of corrosion resistance,not only the general chemical and electrochemical corrosion should be assessed,but also the ability to resist electrolytic corrosion,which is very harsh to the material and relatively poor for Au/Ni coating.A low-cost and high-performance AuCu46 alloy coating was developed to meet the requirements of industrial standard conductivity,wear resistance and corrosion resistance of electronic connector coatings.It can replace the hard gold AuCo coating to reduce the gold consumption by 33 wt%and the precious metal cost by 1/3.Alloying Cu element can refine the grain size of Au coating to less than 10 nm.The inverse square root of grain size of AuCu alloy coating has a Hall-Petch linear relationship with hardness,which produces the combined effect of fine grain strengthening and solid solution strengthening.The hardness of AuCu alloy coating is more than 3 times higher than that of hard gold AuCo coating and 6 times higher than that of Au coating.The wear resistance of AuCu alloy coating is significantly higher than that of hard gold AuCo coating and much higher than that of pure Au coating.Because it maintains the crystal structure of pure Au coating,it also has excellent corrosion resistance.At the same time,PdNi 15 alloy coating and electroplating technology with low cost and high performance were developed.Due to the low density of PdNi alloy coating,the cost of replacing hard gold coating with PdNi15 can be reduced by 35%when electroplating the same thickness of coating.The electrodeposition of PdNi alloy has a wide range of operating current density and fast plating speed.The PdNi 15 alloy is refined into a flat coating with a 9.5 nm nanocrystalline structure,maintaining a single-phase solid solution of the Pd metal face-centered cubic structure.The lattice constant and the proportion of nickel atoms in the coating follow the Vegard law.The relationship between the composition and structure of PdNi alloy coating and the wear resistance and corrosion resistance of the coating was clarified:due to the combined action of fine grain strengthening,solid solution strengthening and single-phase face-centered cubic structure,the hardness and wear resistance of PdNi alloy coating are high,and the corrosion resistance of PdNi alloy coating is similar to that of pure Pd coating.A high-quality Pt coating and its pulse electroplating technology were developed.Pt is cheaper than Au and has great advantages in corrosion resistance.Through systematic research,the optimum pulse plating process parameters were determined.The grain size of pulse plating platinum coating was reduced from 21 nm of DC plating to 16 nm,with higher flatness and hardness.The hardness and grain size showed Hall-Petch relationship.The change of surface structure and crystal orientation of pulse plating layer improves the wear resistance.However,compared with hard gold,pulsed electroplating Pt as the surface layer still has the risk of wear failure,mainly for the wear test after the coating cracks,the bottom base metal Cu migration to the surface layer.An environmentally friendly preparation technology of high-performance CoNiWReP high-entropy alloy coating and aqueous solution pulse electroplating was developed.CoNiWReP high-entropy alloy coating was successfully prepared from aqueous solution system for the first time.The formula and process conditions of electroplating solution were optimized.The content of each element of CoNiWReP alloy obtained by pulse electroplating in the range of 5%～35%conforms to the definition of high-entropy alloy,which can play a sacrificial anode cathodic protection role on copper substrate,and the protection efficiency is as high as 73.8%.The test of composite coating shows that the ’AuCo/CoNiWReP/Ni’three-layer structure coating containing higher than 0.1 μm high entropy alloy coating can significantly improve the resistance to nitric acid corrosion of traditional hard gold AuCo/Ni system under the condition of low gold thickness on the surface.Based on the characteristics of the above four coatings,two new types of lowcost,high-performance electrical contact coating systems and complete sets of electroplating technologies for connectors were designed and successfully constructed:First,a low-cost electrolytic corrosion-resistant composite coating suitable for cathode contact terminals is AuCu/Pt/Ni composite coating.The precious metal cost is 30%lower than that of hard gold AuCo/Ni composite coating,and the performance is much higher than that of traditional hard gold AuCo/Ni composite coating,especially the electrolytic corrosion resistance is more than 30 times higher than that of traditional hard gold AuCo/Ni composite coating;the second is a low-cost electrochemical corrosion-resistant composite coating suitable for non-cathode contact terminals.It is a PdNi/HEA/Ni composite coating.The precious metal cost is 35%lower than that of hard gold AuCo/Ni composite coating.The performance is much higher than the traditional hard gold AuCo/Ni composite coating,and the process does not contain cyanide.It is an environmentally friendly manufacturing technology.It is revealed that the electrolytic corrosion failure mechanism of the precious metal composite coating is that the anode corrosion and pore corrosion of the precious metal make the coating peel off.while the AuCu/Pt/Ni composite coating has high electrolytic corrosion resistance because:1)The Pt coating material itself is corroded slowly under the condition of anode electrolysis,and 2)AuCu electrodeposition is easier to fill the pores in the Pt coating.更多还原