Introduction to Fine Copper Wire Development

Investigation of growth behavior of Al–Cu intermetallic compounds in Cu wire bonding

“…Further studies identified that Al 2 Cu is the first nucleus at the bond interface [17,33], and Premkumar et al [17] claimed that this nucleus becomes Al 4 Cu 9 or AlCu as the purity of Cu wire increases. Analyses of thermally annealed samples indicated that from Al to Cu there are sequentially AlCu, Al 4 Cu 9 , and Al 2 Cu 3 [27], Al 2 Cu and AlCu [29], or Al 2 Cu, AlCu, and Al 4 Cu 9 [30] IMC layers.The h-Al 2 Cu, crystallized in tetragonal symmetry within space group I4/mcm, is the most widely studied in the phase precipitation sequence of the Al-Cu alloy system [40]. Each Cu atom in Al 2 Cu is surrounded by eight Al atoms situated at the corners of an Archimedean square antiprism, and has two Cu atoms at a distance of c/2, forming linear chains.…”

“…On account of the soaring price of Au in recent years, enormous efforts have been devoted in the electronic packaging industry to replacing Au by Cu wire. However, technical issues such as the need and control of forming gas during FAB formation [2][3][4][5][6][7][8][9][10][11][12][13], underpad damage caused by the much stiffer FAB [2,[13][14][15], Al pad splash that may lead to short circuit in fine-pitch applications as well as degraded reliability [2,13,16,17], slow AlCu intermetallic compound (IMC) formation and growth [3,[18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34], and long-term reliability under humid environments [7,10,18,22,28,35,36] have been considered as significant technical challenges for Cu wire bonding.…”

Failure analysis for Copper Wire Bonding process from machine perspective

“…The ball fonnation of copper wire must take place under a sllield gas in tile electronic flame off (EFO) area in order to retard oxidation and insure uniform ball fonnation [9]. ].…”