银包铜粉及聚合物导体浆料制备与性能研究

【作者】 朱晓云；

【导师】 杨显万；

【作者基本信息】 昆明理工大学 ， 有色金属冶金， 2011， 博士

【摘要】 电子浆料制备技术中,导电相金属粉末的制备是关键。对于导体浆料而言,导电相大多以铂、钯、金和银等贵金属粉末为主,其中以银导体浆料应用最为广泛。近年来,由于贵金属价格的飙升,浆料成本增加；加之银迁移是银浆料自身存在的缺陷,不能满足高性能电子元器件的要求。因此降低成本、寻找性能优良的新型导电粉体、以贱金属代替贵金属制备电子浆料已成为发展的趋势,在此背景下提出了本课题的研究。本文采用发明专利技术置换-还原法制备银包铜粉,对镀银过程的热力学进行了分析和计算；优化了镀银工艺及银镀层结构；采用银包铜粉作导电相,制备了聚合物银包铜粉导体浆料；研究了银包铜粉浆料的性能,探讨了银包铜粉浆料的抗银迁移性能；并以本文研究技术实现了产业化。本文获得的主要结果如下：1、通过对Cu-Ag-NH3-H20系电位-pH图分析和计算及镀银过程热力学分析,为制备银包铜粉提供了理论依据。(1)在有NH3存在的溶液中,Cu和Ag氧化物稳定区缩小,溶液中Cu和Ag的水溶物的稳定区域大大扩宽,提高了溶液的稳定性,所以制备银包铜粉在含NH3的水溶液中为好。(2)在氨水溶液中,铜、银的电位差增大,反应的热力学趋势增加,在碱性条件下更有利于氧化还原反应进行。(3)在置换-还原反应中,必须加入还原剂,才能得到具有一定厚度的银镀层的银包铜粉。2、采用发明专利技术置换-还原法制备银包铜粉。通过对片状铜粉在水溶液中的分散性、镀银液组成和工艺条件对银包铜粉包覆效果和性能影响的研究,对银包铜粉的外观颜色、松装密度、压实电阻、表面形貌进行表征,优化的银包铜粉镀液组成和工艺条件是：AgNO3：2.4～14.2g/L,氨水：0.8 g/L,甲醛：1～3g/L,水合肼：1～4 g/L,复合分散剂：1.0 g/L,PH值：11,镀液温度：60℃,固液比为1：15～1：20,搅拌速度：1000r/min,银包铜粉的干燥：50℃,30min。3、采用银包铜粉较佳镀液组成及工艺条件,制备了不同银含量的银包铜粉,以外观颜色、压实电阻、表面形貌、比表面积和抗氧化性为表征,研究了镀银前后银包铜粉性能的变化规律,获得以下结论。(1)银包铜粉的形状、松装密度、振实密度主要由原料铜粉的性能所决定,银镀层对上述性能影响不大。(2)银镀层对银包铜粉的粒度分布有一定影响,片状银包铜粉的粒度D50随着银含量的增加而降低,当银含量大于20%后,D50开始变大。(3)银镀层对银包铜粉的压实电阻影响较大,压实电阻都随包覆银含量的增加而降低；当包覆银含量大于20%时,压实电阻的降低逐渐变慢并趋于稳定。(4)银镀层对银包铜粉的比表面积影响为：银包铜粉包覆银量低时,比表面积随着银含量增加而增加；包覆Ag含量大于5%后,比表面积随包覆银含量增加而减少。(5)银包铜粉在空气中放置,压实电阻都变大。从包覆银量上比较,低银含量比高银含量变化大。从时间上比较,前6天的变化较大,银包铜粉电阻变化率都大于了10%,银含量大于20%后银包铜粉电阻变化率小于10%；27天后,银包铜粉电阻变化率趋于稳定。(6)银包铜粉包覆银量不同,开始氧化温度不同。低银含量的开始氧化温度低于高银含量。(7)银包铜粉的镀层通过XRD分析为金属银和铜,没有氧化物及其它元素存在。(8)提出了抗氧化银镀层理想沉积方式是：银以片状形式沉积在铜粉表面,片与片之间相互搭结,致密无孔隙,把片状铜粉完全包覆并与外界隔离。(9)采用湿法球磨处理银包铜粉,在相同银含量下,经过球磨后的银包铜粉银对基体铜粉的包覆面积增大,银镀层与铜粉的结合更紧密,球磨后银包铜粉抗氧化能力提高。4、采用银包铜粉作导电相,通过对不同有机载体及不同配比组成的浆料的粘度、触变性、附着力、方阻、抗折强度、抗氧化性进行对比分析,优化获得了有机载体、聚合物银包铜粉浆料较佳配方,检测了其性能,得到以下结果：(1)有机载体优化体系是聚酯和聚丙烯酸酯按重量比1：1；乙二醇乙醚酯为溶剂,聚合物含量为lOwt%配制的有机载体。(2)聚合物银包铜粉浆料较佳配方是：银包铜粉(银含量30%)导电相含量55%,有机载体含量45%。(3)银浆中导电相银含量为50%～55%之间浆料的印刷性能较好,银包铜粉浆料中导电相银包铜粉的含量在55%～60%之间浆料的印刷性能较好；(4)在各自较佳配方下制备得到的浆料性能是：银浆料方阻是12.8mΩ/□、对折电阻变化率4%、附着力合格、稳定性良好；银包铜粉浆料方阻是14.6mΩ/□、对折电阻变化率5.5%、附着力合格、稳定性好。5、采用银浆料和银包铜粉浆料制备实验电极,通过水滴法实验比较观察不同的导电相、含量、图案形状,线间距等的银迁移现象；对实验电极进行塔菲尔曲线、交流阻抗曲线测试；研究了不同银含量银包铜粉浆料电极银迁移性能,得到以下结论：(1)水滴实验中迁移现象的主要特征是施加外电压后,处于水溶液中的电极会发生离子迁移；树枝状沉积物总是在阴极上产生,并向阳极生长；树枝状沉积物并不是一通电就开始生长的,不同导电相、不同形状电极、不同外加电压都会影响迁移速度；整个迁移过程中,都伴随着絮状沉淀物的生产。(2)银浆料电极和银包铜粉浆料电极塔菲尔曲线、交流阻抗曲线测试结果表明：银包铜浆料电极比银浆料电极的自腐蚀电位向正方向移动,自腐蚀电流更低,耐腐蚀性好,电极的溶解较慢；银包铜浆料电极在该电解质溶液中的电化学稳定性比银浆料电极好；银浆料电极更容易腐蚀,银包铜浆料电极的耐腐蚀性优于银浆料电极,银包铜浆料电极的溶解比银浆料电极慢。(3)银包铜粉的抗迁移机理是：铜的存在抑制了银包铜粉阳极中银的溶解,银离子浓度降低,使其在阴极上沉降速度和枝晶生长变慢,提高了其抗迁移能力。(4)用银包铜粉制备的浆料抗银迁移性能比银浆料强得多；研究发现银包铜粉浆料的抗银迁移性能不是随银包铜粉中银含量的增加而增强,而是存在一个合适的含银范围,银包铜粉含银量为25%左右时,其银包铜粉浆料抗银迁移性能最好。(5)首次揭示了银包铜粉的抗银迁移能力与镀银层结构的关系。银包铜粉镀层结构为网状时抗银迁移能力比致密形结构更好。6、以本文研发的银包铜粉及银包铜粉浆料技术成果,依托昆明理工恒达科技有限公司实现了产业化。在昆明高新开发区建立了产业化示范基地,建成了年产400吨银包铜粉、2吨银包铜粉浆料和100吨银包铜粉电磁屏蔽涂料生产线。2006年～2008年间累计新增产值6300万元；申报专利4项；制定企业标准2项；发表论文6篇。该技术成果于2009年获中国有色金属工业科学技术一等奖：云南省科技发明二等奖；取得了较好的经济和社会效益。更多还原

【Abstract】 To manufacture electronic paste, manufacturing of conductive metal powder is the key technology. For conductive paste, the conductive phase is mainly made up of powder from precious metals such as platinum, palladium, gold and silver and silver-based conductive paste is most widely used among these. In recent years, due to the sharp rise of the prices of precious metals, the cost for electronic paste increases. In addition, silver migration is the inherent drawback of silver-based paste and hence cannot meet the requirements of high performance electronic components. Therefore, reducing the cost, searching for new conductive powder with excellent properties and using less expensive metals in place of precious ones to manufacture electronic paste have become the major development trends for electronic paste. In this context, the research topic for this thesis has been proposed.In this study an invented and patented replacement-reduction method is used to prepare silver-coated copper powder and the thermodynamics of the silver-coating process is analysed. The silver-coating process and silver-coating layer structure are optimised. Using silver-coated copper powder as the conductive phase, polymer silver-coated copper powder conductive paste is prepared. Properties of silver-coated copper powder paste are analysed and for the first time a study is made with respect to the properties of silver-coated copper powder paste against silver migration. With the work presented in this thesis the technology is commercialised.The major findings of the research are as follows:1. Through analysis of the E-pH charts for Cu-Ag-NH3-H2O series and calculations and thermodynamics analysis of the silver-coating process, a theoretical base for manufacturing silver-coated copper powder is provided.(1) In a solution containing NH3, the stability regions for Cu and Ag oxidants are reduced. The stability regions for the water dissolvables of Cu and Ag in the solution are greatly broadened and the stability of the solution is enhanced. Therefore it is advantageous to prepare silver-coated copper powder in water solutions containing NH3.(2) In ammoniac solutions the potential differences of copper and silver increase; the thermodynamics trend of the reaction increases and the alkaline condition is more favourable for the oxidation-reduction reaction to proceed.(3) For replacement and reduction reactions, reductants must be added so that silver-coated copper powder with a silver layer of a certain thickness can be obtained.2. Silver-coated copper powder is prepared using the invented and patented replacement-reduction method. The dispersion of flake copper powder in water solution, the effects of composition of the coating fluid and of processing conditions on the coverage of silver-coated copper powder and the properties are studied. Characterisation is made of the colour, apparent density, compact resistance and surface morphology for silver-coated copper powder. Optimal coating liquid composition and process conditions when manufacturing silver coated copper powder are obtained, i.e., AgNO3:2.4-14.2g/L, ammonia solution:0.8g/L, formaldehyde:1-3g/L, hydrazine hydrate:1-4g/L, composite dispersing agent:1.0g/L, PH value:11, coating liquid temperature:60℃, solid to liquid ratio:1:15-1:20, stirring speed:1000 rpm, drying of silver coated copper powder:50℃for a time period of 30 minutes.3. Using the optimal silver-coated copper powder composition and processing conditions, silver-coated powders of different morphology and contents are prepared. By characterising the colour, compact resistance, surface morphology, ratio surface and anti-oxidation, the changes in properties of silver-coated copper powder before and after silver-coating are studied and the following results are obtained.(1) The shape of silver coated copper powder, apparent density and tap density are mainly dependent on the properties of the copper powder as raw material while the silver coating layer does not have a significant impact on these properties.(2) The silver coating layer has some impact on the distribution of the size for the silver coated copper powder. Size D50 of flake shaped silver coated copper powder decreases with the increase of the silver content. When the silver content exceeds 20%, its D50 starts to increase.(3) Silver coat layer has large impact on the compact resistance of silver-coated copper powder and compact resistance of silver-coated copper powder will decrease with the increase of silver contents. When the silver content exceeds 20%, the compact resistance decreases slowly and tends to be stable.(4) Silver coat layer has the following impacts on the ratio surface of silver-coated copper powder:when the silver content is low in silver-coated copper powder, the ratio surface for flake silver-coated copper powder increases with increasing silver content. When Ag content exceeds 5%, the ratio surface of silver-coated copper powder decreases with the increase of the coating silver content.(5) Being left in the air, compact resistance of silver coated copper powder will increase. Regarding the silver content, with low silver content, the changes are greater than with high silver content. Considering the exposure time, the change is larger during the first 6 days and the rate of change in compact resistance for silver-coated copper powder is all greater than 10%. When silver content exceeds 20%, the rate of change in compact resistance for silver-coated copper powder is less than 10%. After 27 days, the rate of change in compact resistance for silver-coated copper powder tends to be stable.(6) Oxidation starts at different temperatures for silver-coated copper powder with different silver contents. The one with low silver content starts the oxidation at a high temperature.(7) The coated layer on silver-coated copper powder is found by XRD analysis to be metal silver and copper and there exist no other oxidants or elements.(8) The ideal sedimentation structure of silver coating layer for oxidation resistance is characterised by:flake-shaped silver is sedimented on the copper surface such that the flakes are joined and rest on each other at the ends. This way, a seamless and tight layer will cover completely the copper powder and isolate it from the surrounding.(9) A ball mill with wet process is used to treat the silver coated copper powder. With the same silver content, for silver coated copper powder treated by a ball mill, the area of the base copper powder covered by silver increases. At the same time, the bounding between the silver coating layer and the copper powder will get stronger. The silver coated copper powder will also become more antioxidant with the use of a ball mill.4. Using silver-coated copper powder as the conductive phase, comparative studies are carried out, with respect to viscosity, thixotropy, adhesion, square resistance, rupture strength and oxidation resistance, on the paste with different organic carriers and formulas.The following results are obtained:(1) The optimal series of organic carrier is the one with polymer being made up of polyester and polyacrylate following a weight ratio 1:1; with glycol ether ester as the solvent and with polymer content of 1 Owt%;(2) The optimal formula for the polymer silver-coated copper powder paste is:a conductive phase content of 55% for silver coated copper powder (silver content 30%) and a content of 45% for the organic carrier.(3) The printing properties are better for a silver paste with conductive phase content of 50-55% while for silver-coated copper powder paste, the better printing properties are obtained with a silver content of 55-60%.(4) Preparing the pastes using respective optimal formulas, the results are respectively: for silver paste, the square resistance is 12.8mΩ/□, rate of crease resistance 4%, adhesion requirement met, and good stability for silver paste; for silver-coated copper powder paste, 14.6mΩ/□, rate of crease resistance 5.5%, adhesion requirement met, and excellent stability.5. Using silver paste and silver-coated copper powder paste to prepare experiment electrodes, water drop method is used to observe and compare silver migration for different conductive phases, contents, geometric shapes and distances. Measurements are made on the experiment electrodes with respect to Tafel curves and DC impedance curves. Electrode silver migration with different silver contents in silver-coated copper powder paste is studied. All these lead to the conclusions:(1) The main characteristic of the migration phenomenon in water drop experiment is when external voltage is applied, ion migration will occur on electrode in the electrolyte solution. Tree-shaped sediment always emerges on the cathode and will grow towards anode. Such sediment will not start to appear once the voltage is applied as different conductive phases, different shapes of the electrodes, different voltages applied will all affect the migration speed. During the migration process flocks of sediment will generally be generated.(2) Through measurements and drawing Tafel curves and DC impedance curves for electrodes using silver paste and silver-coated copper powder paste, it is shown that the self-corrosion potential for silver-coated copper powder paste moves in a more positive direction than that of silver paste. The former has lower self-corrosion current and good corrosion resistance and slow dissolution of electrodes. Electrodes of silver-coated copper powder paste have more favourable electrochemical stability in the electrolyte solution than electrodes of silver paste. Electrodes of silver paste are more prone to corrosion and the anti-corrosiveness of electrodes of silver-coated copper powder paste is superior to that of silver paste as well. In addition, the dissolution of electrode of silver-coated copper powder paste is slower than that of silver paste.(3) The mechanism of anti-migration for silver coated copper powder is studied. The results show that the existence of copper suppresses the dissolution of the silver on the anode in silver coated copper powder and the concentration of silver ion in the electrolyte decreases. This causes the sedimentation speed on cathode to be lower and the dendrite growth to get slower and thus enhances the ability against silver migration.(4) Paste made by silver-coated copper powder is much stronger for resistance against silver migration than silver paste. The study shows such a resistance with silver-coated copper powder paste does not increase with the increase of silver content; rather, there exists an appropriate range of silver content. When the silver content is around 25% in silver-coated copper powder, the paste has the maximal resistance against silver migration.(5) For the first time, the relationship between the silver migration resistance and the coating layer structure for silver-coated copper powder is revealed. It is concluded that the most ideal coating layer structure for silver-coated copper powder is net-shaped, which is better than compact structure.6. With the achievements made through this work for silver-coated copper powder and paste, commercialization is carried out through Kunming Hendera Science and Technology Ltd., Co. A commercialisation demonstration base is established in Kunming High Tech Development Park. A production line with capability of annually producing 400 tonnes of silver-coated copper powder,2 tonnes of silver-coated copper powder paste and 100 tonnes of electromagnetic insulation paint of silver-coated copper powder is built. During 2006-2008, an accumulated production of RMB 63 million has been made.4 patents are applied and approved and 2 corporate standards are issued.6 papers are published. The achievement won first prize in China Non-ferrous Metal Industry Science and Technology award in 2009 and second prize in Yunnan Province’s Science and Technology Innovation award. A great benefit has been gained for the economy and social life.更多还原