【作者】 张炜； 成旦红； 郁祖湛； Werner Jillek；

【Author】 Zhang wei~1 Cheng Danhong~2 Yu Zuzhan~3 Werner Jillek~4 1.Dept.of Chemistry of College of Science of Shanghai University,Shanghai 200444; 2.Dept.of Students of China Executive Leadership Academy Pudong,Shanghai 201204; 3.Dept.of Chemistry of Fudan University,Shanghai 200433; 4.Dept.of EFI of Georg-Simon-Ohm-Fachhochschule,Nürnberg 90489,Germang)

【机构】 上海大学理学院化学系； 中国浦东干部学院培训部； 复旦大学化学系； 乔治西蒙欧姆应用科技大学电子机械信息系；

【摘要】 随着印制电路板上电子器件集成密度的不断提高,焊点除了由于散热不好引起的热疲劳等问题外,焊点之间发生的电化学迁移问题越来越为人们所关注,已经成为电子封装领域的一个重大课题.本文通过恒定电压条件下的水滴实验,对 PCB 上 Sn95.5Ag4Cu0.5钎料焊点的电化学迁移行为进行了原位观察和研究.结果表明,树枝状的金属沉积物总是在阴极上生成,其形成需要经过一个孕育期,树枝状沉积物一旦形成,就会迅速地生长到阳极上,造成短路失效;钎料焊点间距的减少和外加电压的增加都会使得电化学迁移造成的短路失效时间显著缩短; 外加电压低于1.3V 时不发生电化学迁移短路失效;当钎料不能完全包裹焊盘或者焊盘局部位置上钎料的厚度很薄时,发生电化学迁移的金属除了来自钎料焊点,还会来自 Cu 焊盘;钎料中的 Ag 不发生迁移.更多还原

【Abstract】 A board with a high density of components generates much more heat during operation resulting in more severe thermal fatigue of the solder joints.Another one important problem arising from boards with greater mounting density was electrochemical migration(ECM)between two narrowly arranged solder joints,which has been recognized as one of the most serious problems connected to electronics packaging.Electrochemical migration tests on SnAgCu solder joints were conducted by applying constant voltage with a DC power supply.Distilled water was used as the test environment.A period of incubation was necessary for the formation of dendrites on the cathode solder joints.Then the dendrite would grow fast towards the anode solder joint,resulting in a shortcut.Time to short would decrease rapidly with the increase of applied voltage and the decrease of the distance between the two solder joint specimens.A critical short voltage to initiate ECM seemed to exist.ECM did not occur below 1.3V.The solder joint was not the only source for migrating metal elements.The Cu pad might be another source when the solder could not cover all the surface of the pad very well.Ag seemed to be immune to ECM.更多还原