高温老化期间引线键合空洞形成探讨

Study of Wire-bond Void Formation During High Temperature Aging

在金-铝金属间化合物相中形成的空洞,降低了把金丝与焊盘键合的长期可靠性。文中通过一系列微结构研究来评定引线键合中空洞的形成。把形成的空洞分为初始、环形和极小三种类型。形成初始空洞的主要原因是探测标记和铝焊盘污染,初始空洞阻碍合金扩散并使金属间化合物生长减缓。环形空洞是由热超声引线键合的超声挤榨作用造成的,这些压焊缝隙可能导致会腐蚀并降低引线键合的一类卤化物的形成。极小的空洞是在Au4Al相阶段形成的。由于不同Au4Al相形成的反应,或与金球表层上晶粒界面影响的关系,在这些空洞中会出现两种Au4Al相的纹理。

Voids formed in Au-A1 intermetallic phases degrade the long-term reliability of gold wire bonds to aluminium pads. In this study, a series of microstructural studies were performed to evaluate void formation in wire bonds. Voids are classified as initial, annular or minute. Probe marks and A1 pad contamination are the main causes of initial voids that block alloy diffusion and slow down intermetallic growth. Annular voids are caused by the ultrasonic squeeze effect of thermo sonic wire bonding. These bonding gaps may become pathways for halide species that corrode and degrade wire bonds. Minute voids are formed during the Au4A1 phase. The two Au4A1 phase textures in three voids may be due to different Au4A1 phase formation reactions or be related to grain boundary effects on the surface layer of the Au ball.