钯催化亚硫酸体系镀金工艺与性能的研究

发布时间：2018-05-26 19:13

本文选题：亚硫酸体系镀金 + 黑盘　；参考：《哈尔滨工业大学》2016年博士论文

【摘要】：印制电路板(PCB)终饰工艺是其制造流程中最后的表面处理步骤,不仅为线路表面提供保护层,更是保证印刷电路板在装配和使用中能够有效连接的关键技术。本文以PCB终饰工艺为研究背景,针对化学镀镍/置换镀金(ENIG)工艺存在的缺陷,开发钯催化化学镀金方法,并将该工艺用于PCB终饰,作为化学镀镍/化学镀钯/置换镀金(ENEPIG)工艺的组成部分。传统的ENIG工艺过程中,金的沉积是通过镍金置换反应来进行,由于Ni-P表面的胞状结构以及氰根离子的渗透作用,使表面电荷分布不均匀,在置换反应过程中造成局部位置的严重腐蚀。这种出现Ni-P层过腐蚀的ENIG镀层在焊接过程中容易出现“黑盘”问题。本研究以亚硫酸体系镀金溶液在ENIG工艺中的应用为切入点,通过镀液稳定性和镀层均匀性的表征,对配位剂组成和工艺条件进行了优化。优化后的镀液稳定,在Ni-P表面施镀10 min,所得镀层厚度为0.05μm,相对标准偏差(RSD)值小于10%,镀层表面粗糙度为20.8 nm。通过对金层在Ni-P表面的沉积过程及镀层形貌的表征和分析,建立金层在Ni-P表面的生长模型,发现亚硫酸体系镀金液在Ni-P表面镀金过程依然是置换反应,无“基体催化”效果,不能够解决PCB“黑盘”问题。此外,在使用亚硫酸-硫代硫酸盐的体系在Ni-P表面镀金过程中,发现镀层中有杂质S存在。通过实验证明了S杂质主要存在于Ni-P表面,在镀金过程中随着Au层厚度的增加,S杂质含量逐渐降低。在上述研究的基础上,通过在ENIG工艺中加入钯层解决Ni-P腐蚀问题。首先对置换镀钯、次磷酸镀钯以及甲酸镀钯的工艺过程及镀层形貌进行表征,发现这几种常用镀钯工艺存在不同的缺陷:置换镀层存在孔隙、次磷酸钠镀钯层以胞状结构存在、甲酸镀钯层由晶体颗粒组成,这几种镀钯层并不适合作为Ni-P表面的阻挡层。另外,使用甲酸盐作为还原剂在Ni-P表面镀钯的过程是“两段式”反应,通过实验证明了这个过程中首先进行的是Ni和Pd2+的置换反应,然后在Pd上进行自催化沉积过程。本文在明确了镀钯层形貌与组成之间的关系后,设计制备以Na H2PO2和HCOONa复配的双还原剂新型镀钯技术,获得通过调整Na H2PO2的量来控制Pd-P层中磷含量的方法。工艺优化后制备镀层磷含量能够低于1 wt%,经过SEM和AFM测试,证实了该工艺得到的低磷Pd-P镀层具有平整光洁的表面。在Ni-P表面镀覆了低磷Pd-P层之后,其“胞状”结构被掩盖,镀层耐蚀性能显著提高。在制备合适的Pd-P镀层之后,将亚硫酸镀金体系用于Pd-P镀层表面镀金,组成整个ENEPIG工艺过程。通过对反应过程电位变化、镀液金属离子浓度变化以及镀层生长速率的测试分析,证明了金在Pd-P镀层表面的沉积反应类型为基体催化化学镀金,无钯金置换反应发生。在镀覆了薄层Pd-P的Ni-P表面,金的沉积反应包括镍金置换沉积和基体催化化学沉积。提高Pd-P层厚度能够降低置换反应比例,当镀覆Pd-P层厚度为0.1μm时,镀金过程对Ni-P的置换比例为34.2%。在Ni-P层和金层中间加入Pd-P层,能够抑制“黑盘”产生的原因包括:减少了沉积金层过程中镀金液对Ni的置换侵蚀;对Ni-P“胞状”结构之间的缝隙进行覆盖填充,使其在沉积Au层过程中不发生严重的局部腐蚀;使ENEPIG工艺表面无富磷层、无S杂质,有利于提高焊接牢度。最后对ENEPIG镀层耐蚀性、可焊性及焊接牢度进行表征,验证了本文研制的ENEPIG工艺具有良好的实用性。
[Abstract]:The finishing process of printed circuit board (PCB) is the last surface treatment step in its manufacturing process. It not only provides protection layer for the line surface, but also the key technology to ensure the effective connection of printed circuit board in assembly and use. In this paper, the defects of electroless nickel / replacement gold plating (ENIG) process are introduced with the research background of the PCB finishing process. The method of palladium catalyzed chemical gold plating was developed and used in PCB finishing as part of the electroless nickel plating / electroless palladium / replacement gold plating (ENEPIG) process. In the traditional process of ENIG, gold deposition was carried out through the nickel gold replacement reaction. The surface charge of the Ni-P surface and the penetration of cyanogen ions made the surface charge. The distribution is not uniform and the local position is seriously corroded during the replacement process. The Ni-P layer of ENIG coating is prone to "black disk" problem during the welding process. This study is based on the application of gold plating solution in the sulfite system in the ENIG process as the breakthrough point, by the stability of the plating bath and the characterization of the uniformity of the coating, the coordination of the coordination of the plating solution to the coordination of the plating solution is made. The composition and technological conditions were optimized. The optimized plating bath was stable and 10 min was plated on the Ni-P surface. The thickness of the coating was 0.05 mu m, the relative standard deviation (RSD) value was less than 10%, the surface roughness of the coating was 20.8 nm., and the growth of gold layer on the Ni-P surface was established by the deposition process of gold layer on the surface of Ni-P and the analysis of the appearance of the coating. It is found that the gold plating process in the sulfite system is still a replacement reaction on the Ni-P surface, without the "matrix catalysis" effect and can not solve the PCB "black disk" problem. In addition, the presence of impurity S in the coating is found in the gold plating process on the Ni-P surface using sulfite thiosulfate system. It is proved by experiments that the S impurity is mainly stored. In the Ni-P surface, the content of S impurities gradually decreases with the increase of the thickness of the Au layer during the gold plating process. On the basis of the above study, the palladium layer is added to the Ni-P corrosion problem by adding the palladium layer in the ENIG process. First, the process of replacement palladium plating, palladium plating and palladium plating of the formic acid are characterized, and these commonly used palladium plating are found. There are different defects in the process: the replacement coating has a pore, the palladium layer of sodium hypophosphite is in a cellular structure, the palladium coating of the formic acid is composed of crystal particles. These palladium plating layers are not suitable to be used as the barrier layer on the surface of Ni-P. In addition, the process of using formate as a reductant on Ni-P surface is a "two stage" reaction, through experimental evidence. It is clear that the first process is the replacement reaction of Ni and Pd2+, and then the process of autocatalytic deposition on Pd. After making clear the relationship between the morphology and composition of the palladium plating layer, a new palladium plating technology was designed to prepare a double reductant with Na H2PO2 and HCOONa, and the amount of Na H2PO2 was adjusted to control the phosphorus content in the Pd-P layer. The phosphorus content of the deposited coating can be less than 1 wt% after the process optimization. After SEM and AFM tests, it is proved that the low phosphorus Pd-P coating obtained by this process has a smooth and smooth surface. After coating the low phosphorus Pd-P layer on the Ni-P surface, the "cell" structure is covered up and the corrosion resistance of the coating can be significantly improved. After the preparation of the suitable Pd-P coating, the coating will be prepared. The gold plating system of sulfite is used for gold plating on the surface of Pd-P coating to form the whole process of ENEPIG process. By analyzing the change of the potential of the reaction process, the change of metal ion concentration and the growth rate of the coating, it is proved that the type of deposition reaction of gold on the surface of the Pd-P coating is the matrix plating chemical gold plating, no palladium replacement reaction occurred. On the Ni-P surface of the thin layer of Pd-P, the deposition reaction of gold includes nickel gold replacement deposition and matrix catalytic chemical deposition. Increasing the thickness of Pd-P layer can reduce the proportion of replacement reaction. When the thickness of the coating Pd-P layer is 0.1 u m, the replacement proportion of the gold plating process to Ni-P is 34.2%. in the Ni-P layer and the gold layer, which can inhibit the "black disk" production. The reasons include: reducing the replacement erosion of gold plating solution to Ni during the deposition of gold deposits, covering and filling the cracks between the Ni-P "cell" structures so that they do not have serious local corrosion during the deposition of the Au layer, so that the surface of the ENEPIG process has no phosphorous rich layer, no S impurities, and it is beneficial to improve the fastness of the welding. Finally, the corrosion resistance of the ENEPIG coating is improved. Characterization of weldability and welding fastness proves that the ENEPIG process developed in this paper has good practicability.
【学位授予单位】：哈尔滨工业大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TB306;TN41

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