【作者】 白鹏飞；

【导师】 张化宇； 张璟；

【作者基本信息】 哈尔滨工业大学 ， 材料加工工程， 2008， 硕士

【摘要】 现代微连接中无铅钎料的使用符合人类的环保及生态需求,是未来电子组装业的必然趋势。而电子产品中的无铅焊点在生产和使用中经常处于腐蚀环境中,所导致的腐蚀会改变其机械性能、电性能,从而引发故障,所以腐蚀问题不容忽视。本课题以硬盘磁头中无铅微焊点为对象,研究它在水环境下的腐蚀特性。本文根据焊点所处的外界环境以及钎料Sn3.0Ag0.5Cu的自身特点,研究影响焊点腐蚀的内外部因素,并提出针对性的防腐措施。本文的研究内容主要包括以下几个方面:(1)腐蚀产物为电化学腐蚀产生的锡的氧化物,而腐蚀产物形貌差异的主要原因是腐蚀环境中溶质的溶液过饱和度不同。(2)腐蚀过程本身和腐蚀产物都对硬盘可靠性有较大影响。分别对腐蚀过程和腐蚀产物对硬盘可靠性造成的影响进行研究。(3)溶液中腐蚀性离子的含量及浓度对焊点腐蚀有较大影响。而影响焊点腐蚀的腐蚀性离子主要来源于承载磁头的折片。焊接前对折片清洗,可以有效的降低焊点的腐蚀率。(4)锡离子作为腐蚀与结晶的一个中间产物,在腐蚀过程中起着重要的作用。溶液中的锡离子为腐蚀产物的结晶提供溶液过饱和度和质量运输所需的浓度梯度。同时锡离子浓度可作为一种评价腐蚀程度的标准。(5)焊点表面氧化膜厚度是影响腐蚀的一个最主要的内部因素。在一定范围内,氧化膜越厚,焊点表面的电导性就越差,对焊点的保护越好,电化学腐蚀就不容易发生。利用锈蚀反应原理,提高焊接能量,降低氮气保护的压力,可以有效的增加焊点表面膜的厚度,降低焊点的腐蚀率。通过上述研究得出了腐蚀对硬盘可靠性造成的影响,揭示了在水相环境下影响无铅焊点腐蚀的内外部因素,同时对不同焊点腐蚀出现较大差异性的原因进行了解释。在此基础上,结合实际生产,制定出切实可行的防腐措施,提高了硬盘的可靠性,对实际生产具有显著意义。更多还原

【Abstract】 The lead-free solder used in the modern microjoining accords with the human environmental protection and ecological need, so it is the necessary trend of the future electronic assembly. While the lead-free solder joints of electronic products are usually applied in the corrosive environment during the process of production and usage. The corrosion can’t be ignored, because mechanical property and electrical property could be affected, which finally result in electrical failure. Based on the lead-free solder joints of the hard disk head, this work mainly focuses on its corrosion character in the aqua environment during the process of cleaning. This paper analyses the intrinsic and extrinsic factors resulting in the solder joints’corrosion, studies the external environment of solder joints and the character of Sn3.0Ag0.5Cu solder itself. Based on this study result, some anti-corrosive measures for corrosion are raised.The main contents of this paper include:(1)The corrosion product is validated to be the oxide of tin and generate in the electrochemical corrosion process. The reason why corrosion products have different shape is the corrosion environments having different supersaturation of the solution.(2)The corrosion process and corrosion product all show serious effect on the reliability of hard disk. The effect on the hard disk caused by corrosion process and product respectively are studied.(3)The content and concentration of corrosive ion in solution have serious effect on solder joints corrosion, and they are mainly from the suspension. The solder joint’s corrosive ratio will become low if the suspension is cleaned before jointing.(4)As the intermediate between corrosion and crystal, the tin ion concentration in the solution is very important for corrosion process. It supplies the supersaturation of the solution for crystal and concentration grads for‘mass transport’. The tin ion concentration in the solution can be used as an effective criterion of corrosion degree.(5)The thickness of oxide-film on the surface of solder joint is a main inner factor for corrosion. In a certain range thicker oxide-film on solder joint shows worse electric property and better protection, and the electrochemical corrosion is more difficult. Base on the theory of rust reaction, the solder joint’s surface film becomes thicker by increasing jointing energy and decreasing the pressure of protection N2. That can decrease the solder joint’s corrosion ratio.The above studies obtains the corrosion effect on hard disk reliability; reveals intrinsic and extrinsic factors that affect the corrosion of lead-free solder joints in the aqua environment; explains the obvious different corrosion degree among different solder joint. In the end, some feasible anti-corrosive measures are put forward, which will improve the reliability of hard disk, and it has significant meaning to the practical production.更多还原